require "active_support/core_ext/module/attribute_accessors"
require "rack/utils"

module ActionDispatch
  class ExceptionWrapper
    cattr_accessor :rescue_responses, default: Hash.new(:internal_server_error).merge!(
      "ActionController::RoutingError"               => :not_found,
      "AbstractController::ActionNotFound"           => :not_found,
      "ActionController::MethodNotAllowed"           => :method_not_allowed,
      "ActionController::UnknownHttpMethod"          => :method_not_allowed,
      "ActionController::NotImplemented"             => :not_implemented,
      "ActionController::UnknownFormat"              => :not_acceptable,
      "ActionController::InvalidAuthenticityToken"   => :unprocessable_entity,
      "ActionController::InvalidCrossOriginRequest"  => :unprocessable_entity,
      "ActionDispatch::Http::Parameters::ParseError" => :bad_request,
      "ActionController::BadRequest"                 => :bad_request,
      "ActionController::ParameterMissing"           => :bad_request,
      "Rack::QueryParser::ParameterTypeError"        => :bad_request,
      "Rack::QueryParser::InvalidParameterError"     => :bad_request
    )

    cattr_accessor :rescue_templates, default: Hash.new("diagnostics").merge!(
      "ActionView::MissingTemplate"         => "missing_template",
      "ActionController::RoutingError"      => "routing_error",
      "AbstractController::ActionNotFound"  => "unknown_action",
      "ActionView::Template::Error"         => "template_error"
    )

    attr_reader :backtrace_cleaner, :exception, :line_number, :file

    def initialize(backtrace_cleaner, exception)
      @backtrace_cleaner = backtrace_cleaner
      @exception = original_exception(exception)

      expand_backtrace if exception.is_a?(SyntaxError) || exception.cause.is_a?(SyntaxError)
    end

    def rescue_template
      @@rescue_templates[@exception.class.name]
    end

    def status_code
      self.class.status_code_for_exception(@exception.class.name)
    end

    def application_trace
      clean_backtrace(:silent)
    end

    def framework_trace
      clean_backtrace(:noise)
    end

    def full_trace
      clean_backtrace(:all)
    end

    def traces
      application_trace_with_ids = []
      framework_trace_with_ids = []
      full_trace_with_ids = []

      full_trace.each_with_index do |trace, idx|
        trace_with_id = { id: idx, trace: trace }

        if application_trace.include?(trace)
          application_trace_with_ids << trace_with_id
        else
          framework_trace_with_ids << trace_with_id
        end

        full_trace_with_ids << trace_with_id
      end

      {
        "Application Trace" => application_trace_with_ids,
        "Framework Trace" => framework_trace_with_ids,
        "Full Trace" => full_trace_with_ids
      }
    end

    def self.status_code_for_exception(class_name)
      Rack::Utils.status_code(@@rescue_responses[class_name])
    end

    def source_extracts
      backtrace.map do |trace|
        file, line_number = extract_file_and_line_number(trace)

        {
          code: source_fragment(file, line_number),
          line_number: line_number
        }
      end
    end

    private

      def backtrace
        Array(@exception.backtrace)
      end

      def original_exception(exception)
        if @@rescue_responses.has_key?(exception.cause.class.name)
          exception.cause
        else
          exception
        end
      end

      def clean_backtrace(*args)
        if backtrace_cleaner
          backtrace_cleaner.clean(backtrace, *args)
        else
          backtrace
        end
      end

      def source_fragment(path, line)
        return unless Rails.respond_to?(:root) && Rails.root
        full_path = Rails.root.join(path)
        if File.exist?(full_path)
          File.open(full_path, "r") do |file|
            start = [line - 3, 0].max
            lines = file.each_line.drop(start).take(6)
            Hash[*(start + 1..(lines.count + start)).zip(lines).flatten]
          end
        end
      end

      def extract_file_and_line_number(trace)
        # Split by the first colon followed by some digits, which works for both
        # Windows and Unix path styles.
        file, line = trace.match(/^(.+?):(\d+).*$/, &:captures) || trace
        [file, line.to_i]
      end

      def expand_backtrace
        @exception.backtrace.unshift(
          @exception.to_s.split("\n")
        ).flatten!
      end
  end
end