module Expressive
  class Scope
    def initialize(parent = {})
      @parent = parent
      @symbols = {}
    end

    def [](name)
      @symbols[name] || @parent[name]
    end

    def []=(name, value)
      @symbols[name] = value
    end

    def merge(scope)
      @symbols.merge!(scope)
    end

    def override_scope(scope)
      scope.merge!(@symbols)
      @symbols = scope
    end

    def retrieve_scope
      @symbols
    end

    def define(name, &block)
      self[name] =  Function.new(&block)
    end

    def syntax(name, &block)
      self[name] =  Syntax.new(&block)
    end
  end

  class Webhook

    def initialize(verb, url, params)
      @verb, @url, @params = verb, url, params
    end

    def execute
      self.send(@verb)
    end

    private

      def post
        RestClient.post(@url, @params)
      end

      def get
        RestClient.get(@url, {params: @params})
      end

      def put
        RestClient.put(@url, @params)
      end

  end

  class TopLevel < Scope

    def initialize
      super

      syntax('set') do |scope, cells|
        scope[cells.first.text_value] = cells[1].eval(scope)
      end

      syntax('post') do |scope, cells|
        perform_webhook(:post, scope, cells)
      end

      syntax('put') do |scope, cells|
        perform_webhook(:put, scope, cells)
      end

      syntax('get') do |scope, cells|
        perform_webhook(:get, scope, cells)
      end

      define('+') {|a,b| a.to_f + b.to_f }
      define('-') {|a,b| a.to_f - b.to_f }
      define('*') {|a,b| a.to_f * b.to_f }
      define('/') {|a,b| a.to_f / b.to_f }
      define('=') {|a,b| a == b }
      define('>') {|a,b| a.to_f > b.to_f }
      define('<') {|a,b| a.to_f < b.to_f }
      define('>=') {|a,b| a.to_f >= b.to_f }
      define('<=') {|a,b| a.to_f <= b.to_f }
      define('and') {|a,b| !!a && !!b }
      define('or') {|a,b| !!a || !!b }
      define('sum') { |*args| args.flatten.map(&:to_f).reduce(:+) }
      define('if') { |*args| args.compact!; args[0] ? args[1] : args[2] }
    end

    def to_hash
      h = self.retrieve_scope.dup
      h.delete_if{|k, v| v.kind_of?(Expressive::Function)}
    end

    private

    #(post "http://example.com" name age other)
    #(get "http://example.com" "*")

    def perform_webhook(verb, scope, cells)
      url = cells.shift.text_value.gsub('"', '')
      params = create_webhook_parameters(scope, cells)
      begin
        response = Webhook.new(verb, url, params).execute
        scope = scope.merge(response) if response.is_a?(Hash)
      rescue RestClient::Exception => e
        scope['_errors'] = e.message
      end
      scope
    end

    def create_webhook_parameters(scope, cells)
      if cells.first && cells.first.text_value.gsub('"', '') == '*'
        scope.to_hash
      else
        cells.inject({}) do |params, key|
          params[key.text_value] = scope[key.text_value]
          params
        end
      end
    end
  end
end