/***********************************************************************

  A JavaScript tokenizer / parser / beautifier / compressor.

  This version is suitable for Node.js.  With minimal changes (the
  exports stuff) it should work on any JS platform.

  This file implements some AST processors.  They work on data built
  by parse-js.

  Exported functions:

    - ast_mangle(ast, include_toplevel) -- mangles the
      variable/function names in the AST.  Returns an AST.  Pass true
      as second argument to mangle toplevel names too.

    - ast_squeeze(ast) -- employs various optimizations to make the
      final generated code even smaller.  Returns an AST.

    - gen_code(ast, beautify) -- generates JS code from the AST.  Pass
      true (or an object, see the code for some options) as second
      argument to get "pretty" (indented) code.

  -------------------------------- (C) ---------------------------------

                           Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

  Distributed under a ZLIB license:

    Copyright 2010 (c) Mihai Bazon <mihai.bazon@gmail.com>

    This software is provided 'as-is', without any express or implied
    warranty. In no event will the authors be held liable for any
    damages arising from the use of this software.

    Permission is granted to anyone to use this software for any
    purpose, including commercial applications, and to alter it and
    redistribute it freely, subject to the following restrictions:

    1. The origin of this software must not be misrepresented; you must
       not claim that you wrote the original software. If you use this
       software in a product, an acknowledgment in the product
       documentation would be appreciated but is not required.

    2. Altered source versions must be plainly marked as such, and must
       not be misrepresented as being the original software.

    3. This notice may not be removed or altered from any source
       distribution.

 ***********************************************************************/

var jsp = require("./parse-js"),
    slice = jsp.slice,
    member = jsp.member,
    PRECEDENCE = jsp.PRECEDENCE,
    OPERATORS = jsp.OPERATORS;

var sys = require(/^v0\.[012]/.test(process.version) ? "sys" : "util");

/* -----[ helper for AST traversal ]----- */

function ast_walker(ast) {
        function _vardefs(defs) {
                return defs.map(function(def){
                        var a = [ def[0] ];
                        if (def.length > 1)
                                a[1] = walk(def[1]);
                        return a;
                });
        };
        var walkers = {
                "string": function(str) {
                        return [ "string", str ];
                },
                "num": function(num) {
                        return [ "num", num ];
                },
                "name": function(name) {
                        return [ "name", name ];
                },
                "toplevel": function(statements) {
                        return [ "toplevel", statements.map(walk) ];
                },
                "block": function(statements) {
                        var out = [ "block" ];
                        if (statements != null)
                                out.push(statements.map(walk));
                        return out;
                },
                "var": function(defs) {
                        return [ "var", _vardefs(defs) ];
                },
                "const": function(defs) {
                        return [ "const", _vardefs(defs) ];
                },
                "try": function(t, c, f) {
                        return [
                                "try",
                                t.map(walk),
                                c != null ? [ c[0], c[1].map(walk) ] : null,
                                f != null ? f.map(walk) : null
                        ];
                },
                "throw": function(expr) {
                        return [ "throw", walk(expr) ];
                },
                "new": function(ctor, args) {
                        return [ "new", walk(ctor), args.map(walk) ];
                },
                "switch": function(expr, body) {
                        return [ "switch", walk(expr), body.map(function(branch){
                                return [ branch[0] ? walk(branch[0]) : null,
                                         branch[1].map(walk) ];
                        }) ];
                },
                "break": function(label) {
                        return [ "break", label ];
                },
                "continue": function(label) {
                        return [ "continue", label ];
                },
                "conditional": function(cond, t, e) {
                        return [ "conditional", walk(cond), walk(t), walk(e) ];
                },
                "assign": function(op, lvalue, rvalue) {
                        return [ "assign", op, walk(lvalue), walk(rvalue) ];
                },
                "dot": function(expr) {
                        return [ "dot", walk(expr) ].concat(slice(arguments, 1));
                },
                "call": function(expr, args) {
                        return [ "call", walk(expr), args.map(walk) ];
                },
                "function": function(name, args, body) {
                        return [ "function", name, args.slice(), body.map(walk) ];
                },
                "defun": function(name, args, body) {
                        return [ "defun", name, args.slice(), body.map(walk) ];
                },
                "if": function(conditional, t, e) {
                        return [ "if", walk(conditional), walk(t), walk(e) ];
                },
                "for": function(init, cond, step, block) {
                        return [ "for", walk(init), walk(cond), walk(step), walk(block) ];
                },
                "for-in": function(has_var, key, hash, block) {
                        return [ "for-in", has_var, key, walk(hash), walk(block) ];
                },
                "while": function(cond, block) {
                        return [ "while", walk(cond), walk(block) ];
                },
                "do": function(cond, block) {
                        return [ "do", walk(cond), walk(block) ];
                },
                "return": function(expr) {
                        return [ "return", walk(expr) ];
                },
                "binary": function(op, left, right) {
                        return [ "binary", op, walk(left), walk(right) ];
                },
                "unary-prefix": function(op, expr) {
                        return [ "unary-prefix", op, walk(expr) ];
                },
                "unary-postfix": function(op, expr) {
                        return [ "unary-postfix", op, walk(expr) ];
                },
                "sub": function(expr, subscript) {
                        return [ "sub", walk(expr), walk(subscript) ];
                },
                "object": function(props) {
                        return [ "object", props.map(function(p){
                                return [ p[0], walk(p[1]) ];
                        }) ];
                },
                "regexp": function(rx, mods) {
                        return [ "regexp", rx, mods ];
                },
                "array": function(elements) {
                        return [ "array", elements.map(walk) ];
                },
                "stat": function(stat) {
                        return [ "stat", walk(stat) ];
                },
                "seq": function() {
                        return [ "seq" ].concat(slice(arguments).map(walk));
                },
                "label": function(name, block) {
                        return [ "label", name, walk(block) ];
                },
                "with": function(expr, block) {
                        return [ "with", walk(expr), walk(block) ];
                },
                "atom": function(name) {
                        return [ "atom", name ];
                }
        };

        var user = {};
        var stack = [];
        function walk(ast) {
                if (ast == null)
                        return null;
                try {
                        stack.push(ast);
                        var type = ast[0];
                        var gen = user[type];
                        if (gen) {
                                var ret = gen.apply(ast, ast.slice(1));
                                if (ret != null)
                                        return ret;
                        }
                        gen = walkers[type];
                        return gen.apply(ast, ast.slice(1));
                } finally {
                        stack.pop();
                }
        };

        function with_walkers(walkers, cont){
                var save = {}, i;
                for (i in walkers) if (HOP(walkers, i)) {
                        save[i] = user[i];
                        user[i] = walkers[i];
                }
                try { return cont(); }
                finally {
                        for (i in save) if (HOP(save, i)) {
                                if (!save[i]) delete user[i];
                                else user[i] = save[i];
                        }
                }
        };

        return {
                walk: walk,
                with_walkers: with_walkers,
                parent: function() {
                        return stack[stack.length - 2]; // last one is current node
                },
                stack: function() {
                        return stack;
                }
        };
};

/* -----[ Scope and mangling ]----- */

function Scope(parent) {
        this.names = {};        // names defined in this scope
        this.mangled = {};      // mangled names (orig.name => mangled)
        this.rev_mangled = {};  // reverse lookup (mangled => orig.name)
        this.cname = -1;        // current mangled name
        this.refs = {};         // names referenced from this scope
        this.uses_with = false; // will become TRUE if eval() is detected in this or any subscopes
        this.uses_eval = false; // will become TRUE if with() is detected in this or any subscopes
        this.parent = parent;   // parent scope
        this.children = [];     // sub-scopes
        if (parent) {
                this.level = parent.level + 1;
                parent.children.push(this);
        } else {
                this.level = 0;
        }
};

var base54 = (function(){
        var DIGITS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_";
        return function(num) {
                var ret = "";
                do {
                        ret = DIGITS.charAt(num % 54) + ret;
                        num = Math.floor(num / 54);
                } while (num > 0);
                return ret;
        };
})();

Scope.prototype = {
        has: function(name) {
                for (var s = this; s; s = s.parent)
                        if (HOP(s.names, name))
                                return s;
        },
        has_mangled: function(mname) {
                for (var s = this; s; s = s.parent)
                        if (HOP(s.rev_mangled, mname))
                                return s;
        },
        toJSON: function() {
                return {
                        names: this.names,
                        uses_eval: this.uses_eval,
                        uses_with: this.uses_with
                };
        },

        next_mangled: function() {
                // we must be careful that the new mangled name:
                //
                // 1. doesn't shadow a mangled name from a parent
                //    scope, unless we don't reference the original
                //    name from this scope OR from any sub-scopes!
                //    This will get slow.
                //
                // 2. doesn't shadow an original name from a parent
                //    scope, in the event that the name is not mangled
                //    in the parent scope and we reference that name
                //    here OR IN ANY SUBSCOPES!
                //
                // 3. doesn't shadow a name that is referenced but not
                //    defined (possibly global defined elsewhere).
                for (;;) {
                        var m = base54(++this.cname), prior;

                        // case 1.
                        prior = this.has_mangled(m);
                        if (prior && this.refs[prior.rev_mangled[m]] === prior)
                                continue;

                        // case 2.
                        prior = this.has(m);
                        if (prior && prior !== this && this.refs[m] === prior && !prior.has_mangled(m))
                                continue;

                        // case 3.
                        if (HOP(this.refs, m) && this.refs[m] == null)
                                continue;

                        // I got "do" once. :-/
                        if (!is_identifier(m))
                                continue;

                        return m;
                }
        },
        get_mangled: function(name, newMangle) {
                if (this.uses_eval || this.uses_with) return name; // no mangle if eval or with is in use
                var s = this.has(name);
                if (!s) return name; // not in visible scope, no mangle
                if (HOP(s.mangled, name)) return s.mangled[name]; // already mangled in this scope
                if (!newMangle) return name;                      // not found and no mangling requested

                var m = s.next_mangled();
                s.rev_mangled[m] = name;
                return s.mangled[name] = m;
        },
        define: function(name) {
                if (name != null)
                        return this.names[name] = name;
        }
};

function ast_add_scope(ast) {

        var current_scope = null;
        var w = ast_walker(), walk = w.walk;
        var having_eval = [];

        function with_new_scope(cont) {
                current_scope = new Scope(current_scope);
                try {
                        var ret = current_scope.body = cont();
                        ret.scope = current_scope;
                        return ret;
                }
                finally {
                        current_scope = current_scope.parent;
                }
        };

        function define(name) {
                return current_scope.define(name);
        };

        function reference(name) {
                current_scope.refs[name] = true;
        };

        function _lambda(name, args, body) {
                return [ this[0], define(name), args, with_new_scope(function(){
                        args.map(define);
                        return body.map(walk);
                })];
        };

        return with_new_scope(function(){
                // process AST
                var ret = w.with_walkers({
                        "function": _lambda,
                        "defun": _lambda,
                        "with": function(expr, block) {
                                for (var s = current_scope; s; s = s.parent)
                                        s.uses_with = true;
                        },
                        "var": function(defs) {
                                defs.map(function(d){ define(d[0]) });
                        },
                        "const": function(defs) {
                                defs.map(function(d){ define(d[0]) });
                        },
                        "try": function(t, c, f) {
                                if (c != null) return [
                                        "try",
                                        t.map(walk),
                                        [ define(c[0]), c[1].map(walk) ],
                                        f != null ? f.map(walk) : null
                                ];
                        },
                        "name": function(name) {
                                if (name == "eval")
                                        having_eval.push(current_scope);
                                reference(name);
                        },
                        "for-in": function(has_var, name) {
                                if (has_var) define(name);
                                else reference(name);
                        }
                }, function(){
                        return walk(ast);
                });

                // the reason why we need an additional pass here is
                // that names can be used prior to their definition.

                // scopes where eval was detected and their parents
                // are marked with uses_eval, unless they define the
                // "eval" name.
                having_eval.map(function(scope){
                        if (!scope.has("eval")) while (scope) {
                                scope.uses_eval = true;
                                scope = scope.parent;
                        }
                });

                // for referenced names it might be useful to know
                // their origin scope.  current_scope here is the
                // toplevel one.
                function fixrefs(scope, i) {
                        // do children first; order shouldn't matter
                        for (i = scope.children.length; --i >= 0;)
                                fixrefs(scope.children[i]);
                        for (i in scope.refs) if (HOP(scope.refs, i)) {
                                // find origin scope and propagate the reference to origin
                                for (var origin = scope.has(i), s = scope; s; s = s.parent) {
                                        s.refs[i] = origin;
                                        if (s === origin) break;
                                }
                        }
                };
                fixrefs(current_scope);

                return ret;
        });

};

/* -----[ mangle names ]----- */

function ast_mangle(ast, do_toplevel) {
        var w = ast_walker(), walk = w.walk, scope;

        function get_mangled(name, newMangle) {
                if (!do_toplevel && !scope.parent) return name; // don't mangle toplevel
                return scope.get_mangled(name, newMangle);
        };

        function _lambda(name, args, body) {
                if (name) name = get_mangled(name);
                body = with_scope(body.scope, function(){
                        args = args.map(function(name){ return get_mangled(name) });
                        return body.map(walk);
                });
                return [ this[0], name, args, body ];
        };

        function with_scope(s, cont) {
                var _scope = scope;
                scope = s;
                for (var i in s.names) if (HOP(s.names, i)) {
                        get_mangled(i, true);
                }
                try { var ret = cont(); ret.scope = s; return ret; }
                finally { scope = _scope; };
        };

        function _vardefs(defs) {
                return defs.map(function(d){
                        return [ get_mangled(d[0]), walk(d[1]) ];
                });
        };

        return w.with_walkers({
                "function": _lambda,
                "defun": _lambda,
                "var": function(defs) {
                        return [ "var", _vardefs(defs) ];
                },
                "const": function(defs) {
                        return [ "const", _vardefs(defs) ];
                },
                "name": function(name) {
                        return [ "name", get_mangled(name) ];
                },
                "try": function(t, c, f) {
                        return [ "try",
                                 t.map(walk),
                                 c != null ? [ get_mangled(c[0]), c[1].map(walk) ] : null,
                                 f != null ? f.map(walk) : null ];
                },
                "toplevel": function(body) {
                        return with_scope(this.scope, function(){
                                return [ "toplevel", body.map(walk) ];
                        });
                },
                "for-in": function(has_var, name, obj, stat) {
                        return [ "for-in", has_var, get_mangled(name), walk(obj), walk(stat) ];
                }
        }, function() {
                return walk(ast_add_scope(ast));
        });
};

/* -----[
   - compress foo["bar"] into foo.bar,
   - remove block brackets {} where possible
   - join consecutive var declarations
   - various optimizations for IFs:
     - if (cond) foo(); else bar();  ==>  cond?foo():bar();
     - if (cond) foo();  ==>  cond&&foo();
     - if (foo) return bar(); else return baz();  ==> return foo?bar():baz(); // also for throw
     - if (foo) return bar(); else something();  ==> {if(foo)return bar();something()}
   ]----- */

function warn(msg) {
        sys.debug(msg);
};

function best_of(ast1, ast2) {
        return gen_code(ast1).length > gen_code(ast2[0] == "stat" ? ast2[1] : ast2).length ? ast2 : ast1;
};

function last_stat(b) {
        if (b[0] == "block" && b[1] && b[1].length > 0)
                return b[1][b[1].length - 1];
        return b;
}

function aborts(t) {
        if (t) {
                t = last_stat(t);
                if (t[0] == "return" || t[0] == "break" || t[0] == "continue" || t[0] == "throw")
                        return true;
        }
};

function negate(c) {
        var not_c = [ "unary-prefix", "!", c ];
        switch (c[0]) {
            case "unary-prefix":
                return c[1] == "!" ? c[2] : c;
            case "atom":
                switch (c[1]) {
                    case "false": return [ "num", 0 ];
                    case "true": return [ "num", 1 ];
                }
                break;
            case "binary":
                var op = c[1], left = c[2], right = c[3];
                switch (op) {
                    case "<=": return [ "binary", ">", left, right ];
                    case "<": return [ "binary", ">=", left, right ];
                    case ">=": return [ "binary", "<", left, right ];
                    case ">": return [ "binary", "<=", left, right ];
                    case "==": return [ "binary", "!=", left, right ];
                    case "!=": return [ "binary", "==", left, right ];
                    case "===": return [ "binary", "!==", left, right ];
                    case "!==": return [ "binary", "===", left, right ];
                    case "&&": return best_of(not_c, [ "binary", "||", negate(left), negate(right) ]);
                    case "||": return best_of(not_c, [ "binary", "&&", negate(left), negate(right) ]);
                }
                break;
        }
        return not_c;
};

function make_conditional(c, t, e) {
        if (c[0] == "unary-prefix" && c[1] == "!") {
                return e ? [ "conditional", c[2], e, t ] : [ "binary", "||", c[2], t ];
        } else {
                return e ? [ "conditional", c, t, e ] : [ "binary", "&&", c, t ];
        }
};

function empty(b) {
        return !b || (b[0] == "block" && (!b[1] || b[1].length == 0));
};

function ast_squeeze(ast, options) {
        options = defaults(options, {
                make_seqs   : true,
                dead_code   : true,
                no_warnings : false,
                extra       : false
        });

        var w = ast_walker(), walk = w.walk;

        function is_constant(node) {
                return node[0] == "string" || node[0] == "num";
        };

        function find_first_execute(node) {
                if (!node)
                        return false;

                switch (node[0]) {
                        case "num":
                        case "string":
                        case "name":
                                return node;
                        case "call":
                        case "conditional":
                        case "for":
                        case "if":
                        case "new":
                        case "return":
                        case "stat":
                        case "switch":
                        case "throw":
                                return find_first_execute(node[1]);
                        case "binary":
                                return find_first_execute(node[2]);
                        case "assign":
                                if (node[1] === true)
                                        return find_first_execute(node[3]);
                                break;
                        case "var":
                                if (node[1][0].length > 1)
                                        return find_first_execute(node[1][0][1]);
                                break;
                }
                return null;
        }

        function find_assign_recursive(p, v) {
                if (p[0] == "assign" && p[1] != true || p[0] == "unary-prefix") {
                        if (p[2][0] == "name" && v[0] == "name" && p[2][1] == v[1])
                                return true;
                        return false;
                }

                if (p[0] != "assign" || p[1] !== true)
                        return false;

                if ((is_constant(p[3]) && p[3][0] == v[0] && p[3][1] == v[1]) ||
                    (p[3][0] == "name" && v[0] == "name" && p[3][1] == v[1]) ||
                    (p[2][0] == "name" && v[0] == "name" && p[2][1] == v[1]))
                        return true;

                return find_assign_recursive(p[3], v);
        };

        function rmblock(block) {
                if (block != null && block[0] == "block" && block[1] && block[1].length == 1)
                        block = block[1][0];
                return block;
        };

        function clone(obj) {
                if (obj && obj.constructor == Array)
                        return obj.map(clone);
                return obj;
        };

        function make_seq_to_statements(node) {
                if (node[0] != "seq") {
                        switch (node[0]) {
                                case "var":
                                case "const":
                                        return [ node ];
                                default:
                                        return [ [ "stat", node ] ];
                        }
                }

                var ret = [];
                for (var i = 1; i < node.length; i++)
                        ret.push.apply(ret, make_seq_to_statements(node[i]));

                return ret;
        };

        function _lambda(name, args, body) {
                return [ this[0], name, args, tighten(body.map(walk), "lambda") ];
        };

        // we get here for blocks that have been already transformed.
        // this function does a few things:
        // 1. discard useless blocks
        // 2. join consecutive var declarations
        // 3. remove obviously dead code
        // 4. transform consecutive statements using the comma operator
        // 5. if block_type == "lambda" and it detects constructs like if(foo) return ... - rewrite like if (!foo) { ... }
        function tighten(statements, block_type) {
                statements = statements.reduce(function(a, stat){
                        if (stat[0] == "block") {
                                if (stat[1]) {
                                        a.push.apply(a, stat[1]);
                                }
                        } else {
                                a.push(stat);
                        }
                        return a;
                }, []);

                if (options.extra) {
                        // Detightening things. We do this because then we can assume that the
                        // statements are structured in a specific way.
                        statements = (function(a, prev) {
                                statements.forEach(function(cur) {
                                        switch (cur[0]) {
                                            case "for":
                                                if (cur[1] != null) {
                                                        a.push.apply(a, make_seq_to_statements(cur[1]));
                                                        cur[1] = null;
                                                }
                                                a.push(cur);
                                                break;
                                            case "stat":
                                                var stats = make_seq_to_statements(cur[1]);
                                                stats.forEach(function(s) {
                                                        if (s[1][0] == "unary-postfix")
                                                                s[1][0] = "unary-prefix";
                                                });
                                                a.push.apply(a, stats);
                                                break;
                                            default:
                                                a.push(cur);
                                        }
                                });
                                return a;
                        })([]);

                        statements = (function(a, prev) {
                                statements.forEach(function(cur) {
                                        if (!(prev && prev[0] == "stat")) {
                                                a.push(cur);
                                                prev = cur;
                                                return;
                                        }

                                        var p = prev[1];
                                        var c = find_first_execute(cur);
                                        if (c && find_assign_recursive(p, c)) {
                                                var old_cur = clone(cur);
                                                c.splice(0, c.length);
                                                c.push.apply(c, p);
                                                var tmp_cur = best_of(cur, [ "toplevel", [ prev, old_cur ] ]);
                                                if (tmp_cur == cur) {
                                                        a[a.length -1] = cur;
                                                } else {
                                                        cur = old_cur;
                                                        a.push(cur);
                                                }
                                        } else {
                                                a.push(cur);
                                        }
                                        prev = cur;
                                });
                                return a;
                        })([]);
                }

                statements = (function(a, prev){
                        statements.forEach(function(cur){
                                if (prev && ((cur[0] == "var" && prev[0] == "var") ||
                                             (cur[0] == "const" && prev[0] == "const"))) {
                                        prev[1] = prev[1].concat(cur[1]);
                                } else {
                                        a.push(cur);
                                        prev = cur;
                                }
                        });
                        return a;
                })([]);

                if (options.dead_code) statements = (function(a, has_quit){
                        statements.forEach(function(st){
                                if (has_quit) {
                                        if (member(st[0], [ "function", "defun" , "var", "const" ])) {
                                                a.push(st);
                                        }
                                        else if (!options.no_warnings)
                                                warn("Removing unreachable code: " + gen_code(st, true));
                                }
                                else {
                                        a.push(st);
                                        if (member(st[0], [ "return", "throw", "break", "continue" ]))
                                                has_quit = true;
                                }
                        });
                        return a;
                })([]);

                if (options.make_seqs) statements = (function(a, prev) {
                        statements.forEach(function(cur){
                                if (prev && prev[0] == "stat" && cur[0] == "stat") {
                                        prev[1] = [ "seq", prev[1], cur[1] ];
                                } else {
                                        a.push(cur);
                                        prev = cur;
                                }
                        });
                        return a;
                })([]);

                if (options.extra) {
                        statements = (function(a, prev){
                                statements.forEach(function(cur){
                                        var replaced = false;
                                        if (prev && cur[0] == "for" && cur[1] == null && (prev[0] == "var" || prev[0] == "const" || prev[0] == "stat")) {
                                                cur[1] = prev;
                                                a[a.length - 1] = cur;
                                        } else {
                                                a.push(cur);
                                        }
                                        prev = cur;
                                });
                                return a;
                        })([]);
                }

                if (block_type == "lambda") statements = (function(i, a, stat){
                        while (i < statements.length) {
                                stat = statements[i++];
                                if (stat[0] == "if" && !stat[3]) {
                                        if (stat[2][0] == "return" && stat[2][1] == null) {
                                                a.push(make_if(negate(stat[1]), [ "block", statements.slice(i) ]));
                                                break;
                                        }
                                        var last = last_stat(stat[2]);
                                        if (last[0] == "return" && last[1] == null) {
                                                a.push(make_if(stat[1], [ "block", stat[2][1].slice(0, -1) ], [ "block", statements.slice(i) ]));
                                                break;
                                        }
                                }
                                a.push(stat);
                        }
                        return a;
                })(0, []);

                return statements;
        };

        function make_if(c, t, e) {
                c = walk(c);
                t = walk(t);
                e = walk(e);

                if (empty(t)) {
                        c = negate(c);
                        t = e;
                        e = null;
                } else if (empty(e)) {
                        e = null;
                } else {
                        // if we have both else and then, maybe it makes sense to switch them?
                        (function(){
                                var a = gen_code(c);
                                var n = negate(c);
                                var b = gen_code(n);
                                if (b.length < a.length) {
                                        var tmp = t;
                                        t = e;
                                        e = tmp;
                                        c = n;
                                }
                        })();
                }
                if (empty(e) && empty(t))
                        return [ "stat", c ];
                var ret = [ "if", c, t, e ];
                if (t[0] == "stat") {
                        if (e) {
                                if (e[0] == "stat") {
                                        ret = best_of(ret, [ "stat", make_conditional(c, t[1], e[1]) ]);
                                }
                        }
                        else {
                                ret = best_of(ret, [ "stat", make_conditional(c, t[1]) ]);
                        }
                }
                else if (e && t[0] == e[0] && (t[0] == "return" || t[0] == "throw")) {
                        ret = best_of(ret, [ t[0], make_conditional(c, t[1], e[1] ) ]);
                }
                else if (e && aborts(t)) {
                        ret = [ [ "if", c, t ] ];
                        if (e[0] == "block") {
                                if (e[1]) ret = ret.concat(e[1]);
                        }
                        else {
                                ret.push(e);
                        }
                        ret = walk([ "block", ret ]);
                }
                else if (t && aborts(e)) {
                        ret = [ [ "if", negate(c), e ] ];
                        if (t[0] == "block") {
                                if (t[1]) ret = ret.concat(t[1]);
                        } else {
                                ret.push(t);
                        }
                        ret = walk([ "block", ret ]);
                }
                return ret;
        };

        return w.with_walkers({
                "sub": function(expr, subscript) {
                        if (subscript[0] == "string") {
                                var name = subscript[1];
                                if (is_identifier(name)) {
                                        return [ "dot", walk(expr), name ];
                                }
                        }
                },
                "if": make_if,
                "toplevel": function(body) {
                        return [ "toplevel", tighten(body.map(walk)) ];
                },
                "switch": function(expr, body) {
                        var last = body.length - 1;
                        return [ "switch", walk(expr), body.map(function(branch, i){
                                var block = tighten(branch[1].map(walk));
                                if (i == last && block.length > 0) {
                                        var node = block[block.length - 1];
                                        if (node[0] == "break" && !node[1])
                                                block.pop();
                                }
                                return [ branch[0] ? walk(branch[0]) : null, block ];
                        }) ];
                },
                "function": _lambda,
                "defun": _lambda,
                "block": function(body) {
                        if (body) return rmblock([ "block", tighten(body.map(walk)) ]);
                },
                "binary": function(op, left, right) {
                        left = walk(left);
                        right = walk(right);
                        var best = [ "binary", op, left, right ];
                        if (is_constant(right)) {
                                if (is_constant(left)) {
                                        var val = null;
                                        switch (op) {
                                            case "+": val = left[1] + right[1]; break;
                                            case "*": val = left[1] * right[1]; break;
                                            case "/": val = left[1] / right[1]; break;
                                            case "-": val = left[1] - right[1]; break;
                                            case "<<": val = left[1] << right[1]; break;
                                            case ">>": val = left[1] >> right[1]; break;
                                            case ">>>": val = left[1] >>> right[1]; break;
                                        }
                                        if (val != null) {
                                                best = best_of(best, [ typeof val == "string" ? "string" : "num", val ]);
                                        }
                                } else if (left[0] == "binary" && left[1] == "+" && left[3][0] == "string") {
                                        best = best_of(best, [ "binary", "+", left[2], [ "string", left[3][1] + right[1] ] ]);
                                }
                        }
                        return best;
                },
                "conditional": function(c, t, e) {
                        return make_conditional(walk(c), walk(t), walk(e));
                },
                "try": function(t, c, f) {
                        return [
                                "try",
                                tighten(t.map(walk)),
                                c != null ? [ c[0], tighten(c[1].map(walk)) ] : null,
                                f != null ? tighten(f.map(walk)) : null
                        ];
                },
                "unary-prefix": function(op, cond) {
                        if (op == "!")
                                return best_of(this, negate(cond));
                },
                "call": function(expr, args) {
                        if (expr[0] == "dot" && expr[2] == "toString" && args.length == 0) {
                                // foo.toString()  ==>  foo+""
                                return [ "binary", "+", expr[1], [ "string", "" ]];
                        }
                }
        }, function() {
                return walk(ast);
        });

};

/* -----[ re-generate code from the AST ]----- */

var DOT_CALL_NO_PARENS = jsp.array_to_hash([
        "name",
        "array",
        "string",
        "dot",
        "sub",
        "call",
        "regexp"
]);

function gen_code(ast, beautify) {
        if (beautify) beautify = defaults(beautify, {
                indent_start : 0,
                indent_level : 4,
                quote_keys   : false,
                space_colon  : false
        });
        var indentation = 0,
            newline = beautify ? "\n" : "",
            space = beautify ? " " : "";

        function indent(line) {
                if (line == null)
                        line = "";
                if (beautify)
                        line = repeat_string(" ", beautify.indent_start + indentation * beautify.indent_level) + line;
                return line;
        };

        function with_indent(cont, incr) {
                if (incr == null) incr = 1;
                indentation += incr;
                try { return cont.apply(null, slice(arguments, 1)); }
                finally { indentation -= incr; }
        };

        function add_spaces(a) {
                if (beautify)
                        return a.join(" ");
                var b = [];
                for (var i = 0; i < a.length; ++i) {
                        var next = a[i + 1];
                        b.push(a[i]);
                        if (next &&
                            ((/[a-z0-9_\x24]$/i.test(a[i].toString()) && /^[a-z0-9_\x24]/i.test(next.toString())) ||
                             (/[\+\-]$/.test(a[i].toString()) && /^[\+\-]/.test(next.toString())))) {
                                b.push(" ");
                        }
                }
                return b.join("");
        };

        function add_commas(a) {
                return a.join("," + space);
        };

        function parenthesize(expr) {
                var gen = make(expr);
                for (var i = 1; i < arguments.length; ++i) {
                        var el = arguments[i];
                        if ((el instanceof Function && el(expr)) || expr[0] == el)
                                return "(" + gen + ")";
                }
                return gen;
        };

        function best_of(a) {
                if (a.length == 1) {
                        return a[0];
                }
                if (a.length == 2) {
                        var b = a[1];
                        a = a[0];
                        return a.length <= b.length ? a : b;
                }
                return best_of([ a[0], best_of(a.slice(1)) ]);
        };

        function needs_parens(expr) {
                if (expr[0] == "function") {
                        // dot/call on a literal function requires the
                        // function literal itself to be parenthesized
                        // only if it's the first "thing" in a
                        // statement.  This means that the parent is
                        // "stat", but it could also be a "seq" and
                        // we're the first in this "seq" and the
                        // parent is "stat", and so on.  Messy stuff,
                        // but it worths the trouble.
                        var a = slice($stack), self = a.pop(), p = a.pop();
                        while (true) {
                                if (p[0] == "stat") return true;
                                if ((p[0] == "seq" && p[1] === self) ||
                                    (p[0] == "call" && p[1] === self) ||
                                    (p[0] == "binary" && p[2] === self)) {
                                        self = p;
                                        p = a.pop();
                                } else {
                                        return false;
                                }
                        }
                }
                return !HOP(DOT_CALL_NO_PARENS, expr[0]);
        };

        function make_num(num) {
                var str = num.toString(10), a = [ str.replace(/^0\./, ".") ], m;
                if (Math.floor(num) === num) {
                        a.push("0x" + num.toString(16).toLowerCase(), // probably pointless
                               "0" + num.toString(8)); // same.
                        if ((m = /^(.*?)(0+)$/.exec(num))) {
                                a.push(m[1] + "e" + m[2].length);
                        }
                } else if ((m = /^0?\.(0+)(.*)$/.exec(num))) {
                        a.push(m[2] + "e-" + (m[1].length + 1),
                               str.substr(str.indexOf(".")));
                }
                return best_of(a);
        };

        var generators = {
                "string": make_string,
                "num": make_num,
                "name": make_name,
                "toplevel": function(statements) {
                        return make_block_statements(statements)
                                .join(newline + newline);
                },
                "block": make_block,
                "var": function(defs) {
                        return "var " + add_commas(defs.map(make_1vardef)) + ";";
                },
                "const": function(defs) {
                        return "const " + add_commas(defs.map(make_1vardef)) + ";";
                },
                "try": function(tr, ca, fi) {
                        var out = [ "try", make_block(tr) ];
                        if (ca) out.push("catch", "(" + ca[0] + ")", make_block(ca[1]));
                        if (fi) out.push("finally", make_block(fi));
                        return add_spaces(out);
                },
                "throw": function(expr) {
                        return add_spaces([ "throw", make(expr) ]) + ";";
                },
                "new": function(ctor, args) {
                        args = args.length > 0 ? "(" + add_commas(args.map(make)) + ")" : "";
                        return add_spaces([ "new", parenthesize(ctor, "seq", "binary", "conditional", "assign", function(expr){
                                var w = ast_walker(), has_call = {};
                                try {
                                        w.with_walkers({
                                                "call": function() { throw has_call },
                                                "function": function() { return this }
                                        }, function(){
                                                w.walk(expr);
                                        });
                                } catch(ex) {
                                        if (ex === has_call)
                                                return true;
                                        throw ex;
                                }
                        }) + args ]);
                },
                "switch": function(expr, body) {
                        return add_spaces([ "switch", "(" + make(expr) + ")", make_switch_block(body) ]);
                },
                "break": function(label) {
                        var out = "break";
                        if (label != null)
                                out += " " + make_name(label);
                        return out + ";";
                },
                "continue": function(label) {
                        var out = "continue";
                        if (label != null)
                                out += " " + make_name(label);
                        return out + ";";
                },
                "conditional": function(co, th, el) {
                        return add_spaces([ parenthesize(co, "assign", "seq", "conditional"), "?",
                                            parenthesize(th, "seq"), ":",
                                            parenthesize(el, "seq") ]);
                },
                "assign": function(op, lvalue, rvalue) {
                        if (op && op !== true) op += "=";
                        else op = "=";
                        return add_spaces([ make(lvalue), op, parenthesize(rvalue, "seq") ]);
                },
                "dot": function(expr) {
                        var out = make(expr), i = 1;
                        if (needs_parens(expr))
                                out = "(" + out + ")";
                        while (i < arguments.length)
                                out += "." + make_name(arguments[i++]);
                        return out;
                },
                "call": function(func, args) {
                        var f = make(func);
                        if (needs_parens(func))
                                f = "(" + f + ")";
                        return f + "(" + add_commas(args.map(make)) + ")";
                },
                "function": make_function,
                "defun": make_function,
                "if": function(co, th, el) {
                        var out = [ "if", "(" + make(co) + ")", el ? make_then(th) : make(th) ];
                        if (el) {
                                out.push("else", make(el));
                        }
                        return add_spaces(out);
                },
                "for": function(init, cond, step, block) {
                        var out = [ "for" ];
                        init = (init != null ? make(init) : "").replace(/;*\s*$/, ";" + space);
                        cond = (cond != null ? make(cond) : "").replace(/;*\s*$/, ";" + space);
                        step = (step != null ? make(step) : "").replace(/;*\s*$/, "");
                        var args = init + cond + step;
                        if (args == "; ; ") args = ";;";
                        out.push("(" + args + ")", make(block));
                        return add_spaces(out);
                },
                "for-in": function(has_var, key, hash, block) {
                        var out = add_spaces([ "for", "(" ]);
                        if (has_var)
                                out += "var ";
                        out += add_spaces([ make_name(key) + " in " + make(hash) + ")", make(block) ]);
                        return out;
                },
                "while": function(condition, block) {
                        return add_spaces([ "while", "(" + make(condition) + ")", make(block) ]);
                },
                "do": function(condition, block) {
                        return add_spaces([ "do", make(block), "while", "(" + make(condition) + ")" ]) + ";";
                },
                "return": function(expr) {
                        var out = [ "return" ];
                        if (expr != null) out.push(make(expr));
                        return add_spaces(out) + ";";
                },
                "binary": function(operator, lvalue, rvalue) {
                        var left = make(lvalue), right = make(rvalue);
                        // XXX: I'm pretty sure other cases will bite here.
                        //      we need to be smarter.
                        //      adding parens all the time is the safest bet.
                        if (member(lvalue[0], [ "assign", "conditional", "seq" ]) ||
                            lvalue[0] == "binary" && PRECEDENCE[operator] > PRECEDENCE[lvalue[1]]) {
                                left = "(" + left + ")";
                        }
                        if (member(rvalue[0], [ "assign", "conditional", "seq" ]) ||
                            rvalue[0] == "binary" && PRECEDENCE[operator] >= PRECEDENCE[rvalue[1]]) {
                                right = "(" + right + ")";
                        }
                        return add_spaces([ left, operator, right ]);
                },
                "unary-prefix": function(operator, expr) {
                        var val = make(expr);
                        if (!(expr[0] == "num" || (expr[0] == "unary-prefix" && !HOP(OPERATORS, operator + expr[1])) || !needs_parens(expr)))
                                val = "(" + val + ")";
                        return operator + (jsp.is_alphanumeric_char(operator.charAt(0)) ? " " : "") + val;
                },
                "unary-postfix": function(operator, expr) {
                        var val = make(expr);
                        if (!(expr[0] == "num" || (expr[0] == "unary-postfix" && !HOP(OPERATORS, operator + expr[1])) || !needs_parens(expr)))
                                val = "(" + val + ")";
                        return val + operator;
                },
                "sub": function(expr, subscript) {
                        var hash = make(expr);
                        if (needs_parens(expr))
                                hash = "(" + hash + ")";
                        return hash + "[" + make(subscript) + "]";
                },
                "object": function(props) {
                        if (props.length == 0)
                                return "{}";
                        return "{" + newline + with_indent(function(){
                                return props.map(function(p){
                                        var key = p[0], val = make(p[1]);
                                        if (beautify && beautify.quote_keys) {
                                                key = make_string(key);
                                        } else if (typeof key == "number" || !beautify && +key + "" == key) {
                                                key = make_num(+key);
                                        } else if (!is_identifier(key)) {
                                                key = make_string(key);
                                        }
                                        return indent(add_spaces(beautify && beautify.space_colon
                                                                 ? [ key, ":", val ]
                                                                 : [ key + ":", val ]));
                                }).join("," + newline);
                        }) + newline + indent("}");
                },
                "regexp": function(rx, mods) {
                        return "/" + rx + "/" + mods;
                },
                "array": function(elements) {
                        if (elements.length == 0) return "[]";
                        return add_spaces([ "[", add_commas(elements.map(make)), "]" ]);
                },
                "stat": function(stmt) {
                        return make(stmt).replace(/;*\s*$/, ";");
                },
                "seq": function() {
                        return add_commas(slice(arguments).map(make));
                },
                "label": function(name, block) {
                        return add_spaces([ make_name(name), ":", make(block) ]);
                },
                "with": function(expr, block) {
                        return add_spaces([ "with", "(" + make(expr) + ")", make(block) ]);
                },
                "atom": function(name) {
                        return make_name(name);
                },
                "comment1": function(text) {
                        return "//" + text + "\n";
                },
                "comment2": function(text) {
                        return "/*" + text + "*/";
                }
        };

        // The squeezer replaces "block"-s that contain only a single
        // statement with the statement itself; technically, the AST
        // is correct, but this can create problems when we output an
        // IF having an ELSE clause where the THEN clause ends in an
        // IF *without* an ELSE block (then the outer ELSE would refer
        // to the inner IF).  This function checks for this case and
        // adds the block brackets if needed.
        function make_then(th) {
                var b = th;
                while (true) {
                        var type = b[0];
                        if (type == "if") {
                                if (!b[3])
                                        // no else, we must add the block
                                        return make([ "block", [ th ]]);
                                b = b[3];
                        }
                        else if (type == "while" || type == "do") b = b[2];
                        else if (type == "for" || type == "for-in") b = b[4];
                        else break;
                }
                return make(th);
        };

        function make_function(name, args, body) {
                var out = "function";
                if (name) {
                        out += " " + make_name(name);
                }
                out += "(" + add_commas(args.map(make_name)) + ")";
                return add_spaces([ out, make_block(body) ]);
        };

        function make_string(str) {
                // return '"' +
                //         str.replace(/\x5c/g, "\\\\")
                //         .replace(/\r?\n/g, "\\n")
                //         .replace(/\t/g, "\\t")
                //         .replace(/\r/g, "\\r")
                //         .replace(/\f/g, "\\f")
                //         .replace(/[\b]/g, "\\b")
                //         .replace(/\x22/g, "\\\"")
                //         .replace(/[\x00-\x1f]|[\x80-\xff]/g, function(c){
                //                 var hex = c.charCodeAt(0).toString(16);
                //                 if (hex.length < 2)
                //                         hex = "0" + hex;
                //                 return "\\x" + hex;
                //         })
                //         + '"';
                return JSON.stringify(str); // STILL cheating.
        };

        function make_name(name) {
                switch (name) {
                    case "true": return beautify ? "true" : "!0";
                    case "false": return beautify ? "false" : "!1";
                }
                return name.toString();
        };

        function make_block_statements(statements) {
                for (var a = [], last = statements.length - 1, i = 0; i <= last; ++i) {
                        var stat = statements[i];
                        var code = make(stat);
                        if (code != ";") {
                                if (!beautify && i == last)
                                        code = code.replace(/;+\s*$/, "");
                                a.push(code);
                        }
                }
                return a.map(indent);
        };

        function make_switch_block(body) {
                var n = body.length;
                if (n == 0) return "{}";
                return "{" + newline + body.map(function(branch, i){
                        var has_body = branch[1].length > 0, code = with_indent(function(){
                                return indent(branch[0]
                                              ? add_spaces([ "case", make(branch[0]) + ":" ])
                                              : "default:");
                        }, 0.5) + (has_body ? newline + with_indent(function(){
                                return make_block_statements(branch[1]).join(newline);
                        }) : "");
                        if (!beautify && has_body && i < n - 1)
                                code += ";";
                        return code;
                }).join(newline) + newline + indent("}");
        };

        function make_block(statements) {
                if (!statements) return ";";
                if (statements.length == 0) return "{}";
                return "{" + newline + with_indent(function(){
                        return make_block_statements(statements).join(newline);
                }) + newline + indent("}");
        };

        function make_1vardef(def) {
                var name = def[0], val = def[1];
                if (val != null)
                        name = add_spaces([ name, "=", make(val) ]);
                return name;
        };

        var $stack = [];

        function make(node) {
                var type = node[0];
                var gen = generators[type];
                if (!gen)
                        throw new Error("Can't find generator for \"" + type + "\"");
                $stack.push(node);
                var ret = gen.apply(type, node.slice(1));
                $stack.pop();
                return ret;
        };

        return make(ast);
};

/* -----[ Utilities ]----- */

function repeat_string(str, i) {
        if (i <= 0) return "";
        if (i == 1) return str;
        var d = repeat_string(str, i >> 1);
        d += d;
        if (i & 1) d += str;
        return d;
};

function defaults(args, defs) {
        var ret = {};
        if (args === true)
                args = {};
        for (var i in defs) if (HOP(defs, i)) {
                ret[i] = (args && HOP(args, i)) ? args[i] : defs[i];
        }
        return ret;
};

function is_identifier(name) {
        return /^[a-z_$][a-z0-9_$]*$/i.test(name)
                && name != "this"
                && !HOP(jsp.KEYWORDS_ATOM, name)
                && !HOP(jsp.RESERVED_WORDS, name)
                && !HOP(jsp.KEYWORDS, name);
};

function HOP(obj, prop) {
        return Object.prototype.hasOwnProperty.call(obj, prop);
};

/* -----[ Exports ]----- */

exports.ast_walker = ast_walker;
exports.ast_mangle = ast_mangle;
exports.ast_squeeze = ast_squeeze;
exports.gen_code = gen_code;
exports.ast_add_scope = ast_add_scope;