# frozen_string_literal: true

module Jsrb
  # `Jsrb::Base` is a centralized class for Jsrb template.
  # `js`, accessed from views (i.e. `*.jsrb` files), is an instance of Jsrb::Base.
  #
  # `Jsrb::Base` provides the interface for pushing statements,
  # constructing expressions and generating JavaScript outputs
  # with handling an internal statement context properly.
  class Base
    # @private
    def initialize
      @context = JSStatementContext.new
    end

    #
    # Generates executable JavaScript code from current context.
    #
    # @return [String] generated executable JavaScript code
    def generate_code
      generator = self.class.code_generator_class.new
      generator.call type: 'Program',
                     sourceType: 'script',
                     body: @context.stacks.first
    end

    #
    # **Pushes** an ExpressionStatement to the current context
    #
    # @example
    #   js.do!(js.expr[:x].set(100))
    #   # =>
    #   #   x = 100;
    # @param [Jsrb::ExprChain] expr target expression.
    # @return [nil]
    def do!(expr)
      ast = expr.object
      raise ArgumentError, 'Expression is empty' unless ast

      @context.push(
        type: 'ExpressionStatement',
        expression: ast
      )
    end

    #
    # **Pushes** an assignment statement `lhs = rhs;`.
    # This is a short hand of `js.do! lhs_expr.set(rhs_expr)`
    #
    # @example
    #   a = js.var! :a
    #   js.set!(a, 'dog')
    #   # =>
    #   #   var a;
    #   #   a = 'dog';
    #
    #   # directly pass a symbol of identifier name
    #   js.set!(:x, 100)
    #   # =>
    #   #   x = 100;
    # @param [Jsrb::ExprChain, String, Symbol] expr target expression.
    # @return [nil]
    def set!(lhs, rhs)
      lhs_expr = lhs.is_a?(ExprChain) ? lhs : expr(lhs)
      do! lhs_expr.set(rhs)
    end

    #
    # **Pushes** a VariableDeclaration to the current context
    # and returns an access to the created identifier.
    # @example
    #   name = js.var!(:name) { 'foo' }
    #   # var name = 'foo';
    #
    #   ary = js.var! :ary
    #   # var ary;
    #
    #   obj = js.var! :obj
    #   # var obj;
    #
    #   result = js.var!
    #   # var _v1; //<- auto generate variable name
    # @param [Symbol] name a name of identifier, autogenerated if not given
    # @yield optional block for initializer
    # @yieldreturn an initializer expression
    # @return [Jsrb::ExprChain] the expression which represents a newly created identifier
    def var!(id = nil)
      id ||= @context.gen_var_name!
      val_ast =
        if block_given?
          raw_expr = yield
          raw_expr.is_a?(ExprChain) ? raw_expr.unwrap : @context.ruby_to_js_ast(raw_expr)
        end
      if val_ast
        @context.push(
          type: 'VariableDeclaration',
          declarations: [{
            type: 'VariableDeclarator',
            id: {
              type: 'Identifier',
              name: id.to_s
            },
            init: val_ast
          }],
          kind: 'var'
        )
      else
        @context.push(
          type: 'VariableDeclaration',
          declarations: [{
            type: 'VariableDeclarator',
            id: {
              type: 'Identifier',
              name: id.to_s
            }
          }],
          kind: 'var'
        )
      end
      expr[id]
    end

    #
    # **Starts** a new conditional chain that pushes an IfStatement
    # to the current context at end.
    #
    # @example
    #   js.if!(expr1) {
    #     # ..
    #   }.elsif(expr2) {
    #     # ..
    #   }.else {
    #     # ..
    #   }
    #   # =>
    #   #   // The actual output will have certain immediate functions
    #   #   // that preserve variable scope for each case.
    #   #   if (..expr1..) {
    #   #     // ..
    #   #   } else if (..expr2..) {
    #   #     // ..
    #   #   } else {
    #   #     // ..
    #   #   }
    #
    #   # If you don't have else clause, close with `#end`.
    #   js.if!(expr1) {
    #     # ..
    #   }.elsif(expr2) {
    #     # ..
    #   }.end
    #   # =>
    #   #   if (..expr1..) {
    #   #     // ..
    #   #   } else if (..expr2..) {
    #   #     // ..
    #   #   }
    # @param [Jsrb::ExprChain, convertible ruby values] cond_expr an expression for the test
    # @yield new context block for the consequent case
    # @return [Jsrb::CondChain] condition chainable instance
    def if!(cond_expr, &block)
      CondChain.new(@context, false).elsif(cond_expr, &block)
    end

    #
    # **Constructs** a new conditional chain that
    # represents a conditional expression at end.
    #
    # @example
    #   result = var!
    #   js.do! result, js.if(expr1) {
    #     result_expr1
    #   }.elsif(expr2) {
    #     result_expr2
    #   }.else {
    #     result_expr3
    #   }
    #   # =>
    #   #   // The actual output will have certain immediate functions
    #   #   // that preserve variable scope for each case.
    #   #   var _v1;
    #   #   _v1 = (function() {
    #   #     if (..expr1..) {
    #   #       return ..result_expr1..;
    #   #     } else if (..expr2..) {
    #   #       return ..result_expr2..;
    #   #     } else {
    #   #       return ..result_expr3..;
    #   #     }
    #   #   })()
    # @param [Jsrb::ExprChain, convertible ruby values] cond_expr an expression for the test
    # @yield new context block for the consequent case
    # @return [Jsrb::CondChain] condition chainable instance
    def if(cond_expr, &block)
      CondChain.new(@context, true).elsif(cond_expr, &block)
    end

    #
    # **Constructs** a new expression chain with a given JavaScript AST node.
    #
    # @param [convertible ruby values] object represents JavaScript expression AST node
    # @return [Jsrb::ExprChain] chainable instance
    def expr(object = nil)
      @context.new_expression(object)
    end

    class << self
      #
      # Shows JavaScript generator class name, `'Jsrb::NotFastGenerator'` by default.
      #
      # ### **Help wanted!**
      #
      # *Jsrb::NotFastGenerator uses ExecJS and escodegen to generate JavaScript.
      # It could be more efficient and get better error messages if we
      # implement it in Ruby*.
      #
      # @return [String] class name of a code generator
      def code_generator
        @code_generator || 'Jsrb::NotFastGenerator'
      end

      attr_writer :code_generator

      # @private
      def code_generator_class
        @code_generator_class ||= Object.const_get(code_generator)
      end
    end
  end
end