# -*- encoding: binary -*-
# Copyright (C) 2013, Eric Wong <normalperson@yhbt.net> and all contributors
# License: GPLv2 or later (https://www.gnu.org/licenses/gpl-2.0.txt)
class ExecCgi
  class MyIO < Kgio::Pipe
    attr_writer :my_pid
    attr_writer :body_tip
    attr_writer :chunked

    def each
      buf = @body_tip || ""
      if buf.size > 0
        buf = "#{buf.size.to_s(16)}\r\n#{buf}\r\n" if @chunked
        yield buf
      end
      while tmp = kgio_read(8192, buf)
        tmp = "#{tmp.size.to_s(16)}\r\n#{tmp}\r\n" if @chunked
        yield tmp
      end
      yield("0\r\n\r\n") if @chunked
      self
    end

    def close
      super
      if defined?(@my_pid) && @my_pid
        begin
          Process.waitpid(@my_pid)
        rescue Errno::ECHILD
        end
      end
      nil
    end
  end

  PASS_VARS = %w(
    CONTENT_LENGTH
    CONTENT_TYPE
    GATEWAY_INTERFACE
    AUTH_TYPE
    PATH_INFO
    PATH_TRANSLATED
    QUERY_STRING
    REMOTE_ADDR
    REMOTE_HOST
    REMOTE_IDENT
    REMOTE_USER
    REQUEST_METHOD
    SERVER_NAME
    SERVER_PORT
    SERVER_PROTOCOL
    SERVER_SOFTWARE
  ).map(&:freeze)  # frozen strings are faster for Hash assignments

  def initialize(*args)
    @args = args
    first = args[0] or
      raise ArgumentError, "need path to executable"
    first[0] == ?/ or args[0] = ::File.expand_path(first)
    File.executable?(args[0]) or
      raise ArgumentError, "#{args[0]} is not executable"
  end

  # Calls the app
  def call(env)
    cgi_env = { "SCRIPT_NAME" => @args[0], "GATEWAY_INTERFACE" => "CGI/1.1" }
    PASS_VARS.each { |key| val = env[key] and cgi_env[key] = val }
    env.each { |key,val| cgi_env[key] = val if key =~ /\AHTTP_/ }
    pipe = MyIO.pipe
    pipe[0].my_pid = Process.spawn(cgi_env, *@args,
                                   out: pipe[1], close_others: true)
    pipe[1].close
    pipe = pipe[0]

    if head = pipe.kgio_read(8192)
      until head =~ /\r?\n\r?\n/
        tmp = pipe.kgio_read(8192) or break
        head << tmp
      end
      head, body = head.split(/\r?\n\r?\n/)
      pipe.body_tip = body
      pipe.chunked = false

      headers = Rack::Utils::HeaderHash.new
      prev = nil
      head.split(/\r?\n/).each do |line|
        case line
        when /^([A-Za-z0-9-]+):\s*(.*)$/ then headers[prev = $1] = $2
        when /^[ \t]/ then headers[prev] << "\n#{line}" if prev
        end
      end
      status = headers.delete("Status") || 200
      unless headers.include?("Content-Length") ||
             headers.include?("Transfer-Encoding")
        case env['HTTP_VERSION']
        when 'HTTP/1.0', nil
          # server will drop connection anyways
        else
          headers["Transfer-Encoding"] = "chunked"
          pipe.chunked = true
        end
      end
      [ status, headers, pipe ]
    else
      [ 500, { "Content-Length" => "0", "Content-Type" => "text/plain" }, [] ]
    end
  end
end