# frozen_string_literal: true

module Jsrb
  # Base is a centralized class for Jsrb template.
  # `jsrb`, accessed from views (i.e. `*.js.jsrb` files), is an instance of Jsrb::Base.
  #
  # Jsrb::Base provides some utilities to push statements,
  # construct expressions and generate the final JavaScript code,
  # with preserving a statement context to build the abstract syntax tree.
  class Base
    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 a VariableDeclaration to the current context
    # and returns an access to created identifier.
    #
    # @param optional [Symbol] name a name of identifier, autogenerated if not specified.
    # @yield optional block for initializer
    # @yieldreturn an initializer expression (optional)
    # @return [Jsrb::ExprChain] the expression that represents constructed new identifier
    def var!(id = nil)
      id ||= @context.gen_var_name!
      if block_given?
        raw_expr = yield
        val = raw_expr.is_a?(ExprChain) ? raw_expr : expr(@context.ruby_to_js_ast(raw_expr))
        val.as_variable_declaration!(id)
      else
        expr.as_variable_declaration!(id)
      end
      expr.member!(id)
    end

    #
    # Constructs a new conditional chain that **pushes an IfStatement** to the current context
    # after the chain ended.
    #
    # @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 **returns a conditional expression** after the chain ended.
    #
    # @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 optional [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 you
      # rewrite in Ruby*.
      #
      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