module Utils from "./utils";
import Exception from "./exception";
import { COMPILER_REVISION, REVISION_CHANGES, createFrame } from "./base";

export function checkRevision(compilerInfo) {
  var compilerRevision = compilerInfo && compilerInfo[0] || 1,
      currentRevision = COMPILER_REVISION;

  if (compilerRevision !== currentRevision) {
    if (compilerRevision < currentRevision) {
      var runtimeVersions = REVISION_CHANGES[currentRevision],
          compilerVersions = REVISION_CHANGES[compilerRevision];
      throw new Exception("Template was precompiled with an older version of Handlebars than the current runtime. "+
            "Please update your precompiler to a newer version ("+runtimeVersions+") or downgrade your runtime to an older version ("+compilerVersions+").");
    } else {
      // Use the embedded version info since the runtime doesn't know about this revision yet
      throw new Exception("Template was precompiled with a newer version of Handlebars than the current runtime. "+
            "Please update your runtime to a newer version ("+compilerInfo[1]+").");
    }
  }
}

// TODO: Remove this line and break up compilePartial

export function template(templateSpec, env) {
  /* istanbul ignore next */
  if (!env) {
    throw new Exception("No environment passed to template");
  }
  if (!templateSpec || !templateSpec.main) {
    throw new Exception('Unknown template object: ' + typeof templateSpec);
  }

  // Note: Using env.VM references rather than local var references throughout this section to allow
  // for external users to override these as psuedo-supported APIs.
  env.VM.checkRevision(templateSpec.compiler);

  var invokePartialWrapper = function(partial, indent, name, context, hash, helpers, partials, data, depths) {
    if (hash) {
      context = Utils.extend({}, context, hash);
    }

    var result = env.VM.invokePartial.call(this, partial, name, context, helpers, partials, data, depths);

    if (result == null && env.compile) {
      var options = { helpers: helpers, partials: partials, data: data, depths: depths };
      partials[name] = env.compile(partial, { data: data !== undefined, compat: templateSpec.compat }, env);
      result = partials[name](context, options);
    }
    if (result != null) {
      if (indent) {
        var lines = result.split('\n');
        for (var i = 0, l = lines.length; i < l; i++) {
          if (!lines[i] && i + 1 === l) {
            break;
          }

          lines[i] = indent + lines[i];
        }
        result = lines.join('\n');
      }
      return result;
    } else {
      throw new Exception("The partial " + name + " could not be compiled when running in runtime-only mode");
    }
  };

  // Just add water
  var container = {
    lookup: function(depths, name) {
      var len = depths.length;
      for (var i = 0; i < len; i++) {
        if (depths[i] && depths[i][name] != null) {
          return depths[i][name];
        }
      }
    },
    lambda: function(current, context) {
      return typeof current === 'function' ? current.call(context) : current;
    },

    escapeExpression: Utils.escapeExpression,
    invokePartial: invokePartialWrapper,

    fn: function(i) {
      return templateSpec[i];
    },

    programs: [],
    program: function(i, data, depths) {
      var programWrapper = this.programs[i],
          fn = this.fn(i);
      if (data || depths) {
        programWrapper = program(this, i, fn, data, depths);
      } else if (!programWrapper) {
        programWrapper = this.programs[i] = program(this, i, fn);
      }
      return programWrapper;
    },

    data: function(data, depth) {
      while (data && depth--) {
        data = data._parent;
      }
      return data;
    },
    merge: function(param, common) {
      var ret = param || common;

      if (param && common && (param !== common)) {
        ret = Utils.extend({}, common, param);
      }

      return ret;
    },

    noop: env.VM.noop,
    compilerInfo: templateSpec.compiler
  };

  var ret = function(context, options) {
    options = options || {};
    var data = options.data;

    ret._setup(options);
    if (!options.partial && templateSpec.useData) {
      data = initData(context, data);
    }
    var depths;
    if (templateSpec.useDepths) {
      depths = options.depths ? [context].concat(options.depths) : [context];
    }

    return templateSpec.main.call(container, context, container.helpers, container.partials, data, depths);
  };
  ret.isTop = true;

  ret._setup = function(options) {
    if (!options.partial) {
      container.helpers = container.merge(options.helpers, env.helpers);

      if (templateSpec.usePartial) {
        container.partials = container.merge(options.partials, env.partials);
      }
    } else {
      container.helpers = options.helpers;
      container.partials = options.partials;
    }
  };

  ret._child = function(i, data, depths) {
    if (templateSpec.useDepths && !depths) {
      throw new Exception('must pass parent depths');
    }

    return program(container, i, templateSpec[i], data, depths);
  };
  return ret;
}

export function program(container, i, fn, data, depths) {
  var prog = function(context, options) {
    options = options || {};

    return fn.call(container, context, container.helpers, container.partials, options.data || data, depths && [context].concat(depths));
  };
  prog.program = i;
  prog.depth = depths ? depths.length : 0;
  return prog;
}

export function invokePartial(partial, name, context, helpers, partials, data, depths) {
  var options = { partial: true, helpers: helpers, partials: partials, data: data, depths: depths };

  if(partial === undefined) {
    throw new Exception("The partial " + name + " could not be found");
  } else if(partial instanceof Function) {
    return partial(context, options);
  }
}

export function noop() { return ""; }

function initData(context, data) {
  if (!data || !('root' in data)) {
    data = data ? createFrame(data) : {};
    data.root = context;
  }
  return data;
}