# -*- encoding: utf-8 -*-
require 'etc'
require "shellwords"

module Bluepill
  # This class represents the system that bluepill is running on.. It's mainly used to memoize
  # results of running ps auxx etc so that every watch in the every process will not result in a fork
  module System
    APPEND_MODE = "a"
    extend self

    # The position of each field in ps output
    IDX_MAP = {
      :pid => 0,
      :ppid => 1,
      :pcpu => 2,
      :rss => 3
    }

    def pid_alive?(pid)
      begin
        ::Process.kill(0, pid)
        true
      rescue Errno::ESRCH
        false
      end
    end

    def cpu_usage(pid)
      ps_axu[pid] && ps_axu[pid][IDX_MAP[:pcpu]].to_f
    end

    def memory_usage(pid)
      ps_axu[pid] && ps_axu[pid][IDX_MAP[:rss]].to_f
    end

    def get_children(parent_pid)
      child_pids = Array.new
      ps_axu.each_pair do |pid, chunks|
        child_pids << chunks[IDX_MAP[:pid]].to_i if chunks[IDX_MAP[:ppid]].to_i == parent_pid.to_i
      end
      child_pids
    end

    # Returns the pid of the child that executes the cmd
    def daemonize(cmd, options = {})
      rd, wr = IO.pipe

      if child = Daemonize.safefork
        # we do not wanna create zombies, so detach ourselves from the child exit status
        ::Process.detach(child)

        # parent
        wr.close

        daemon_id = rd.read.to_i
        rd.close

        return daemon_id if daemon_id > 0

      else
        # child
        rd.close

        drop_privileges(options[:uid], options[:gid], options[:supplementary_groups])

        # if we cannot write the pid file as the provided user, err out
        exit unless can_write_pid_file(options[:pid_file], options[:logger])

        to_daemonize = lambda do
          # Setting end PWD env emulates bash behavior when dealing with symlinks
          Dir.chdir(ENV["PWD"] = options[:working_dir]) if options[:working_dir]
          options[:environment].each { |key, value| ENV[key.to_s] = value.to_s } if options[:environment]

          redirect_io(*options.values_at(:stdin, :stdout, :stderr))

          ::Kernel.exec(*Shellwords.shellwords(cmd))
          exit
        end

        daemon_id = Daemonize.call_as_daemon(to_daemonize, nil, cmd)

        File.open(options[:pid_file], "w") {|f| f.write(daemon_id)}

        wr.write daemon_id
        wr.close

        exit
      end
    end

    # Returns the stdout, stderr and exit code of the cmd
    def execute_blocking(cmd, options = {})
      rd, wr = IO.pipe

      if child = Daemonize.safefork
        # parent
        wr.close

        cmd_status = rd.read
        rd.close

        ::Process.waitpid(child)

        cmd_status.strip != '' ? Marshal.load(cmd_status) : {:exit_code => 0, :stdout => '', :stderr => ''}
      else
        # child
        rd.close

        # create a child in which we can override the stdin, stdout and stderr
        cmd_out_read, cmd_out_write = IO.pipe
        cmd_err_read, cmd_err_write = IO.pipe

        pid = fork {
          # grandchild
          drop_privileges(options[:uid], options[:gid], options[:supplementary_groups])

          Dir.chdir(ENV["PWD"] = options[:working_dir]) if options[:working_dir]
          options[:environment].each { |key, value| ENV[key.to_s] = value.to_s } if options[:environment]

          # close unused fds so ancestors wont hang. This line is the only reason we are not
          # using something like popen3. If this fd is not closed, the .read call on the parent
          # will never return because "wr" would still be open in the "exec"-ed cmd
          wr.close

          # we do not care about stdin of cmd
          STDIN.reopen("/dev/null")

          # point stdout of cmd to somewhere we can read
          cmd_out_read.close
          STDOUT.reopen(cmd_out_write)
          cmd_out_write.close

          # same thing for stderr
          cmd_err_read.close
          STDERR.reopen(cmd_err_write)
          cmd_err_write.close

          # finally, replace grandchild with cmd
          ::Kernel.exec(*Shellwords.shellwords(cmd))
        }

        # we do not use these ends of the pipes in the child
        cmd_out_write.close
        cmd_err_write.close

        # wait for the cmd to finish executing and acknowledge it's death
        ::Process.waitpid(pid)

        # collect stdout, stderr and exitcode
        result = {
          :stdout => cmd_out_read.read,
          :stderr => cmd_err_read.read,
          :exit_code => $?.exitstatus
        }

        # We're done with these ends of the pipes as well
        cmd_out_read.close
        cmd_err_read.close

        # Time to tell the parent about what went down
        wr.write Marshal.dump(result)
        wr.close

        exit
      end
    end

    def store
      @store ||= Hash.new
    end

    def reset_data
      store.clear unless store.empty?
    end

    def ps_axu
      # TODO: need a mutex here
      store[:ps_axu] ||= begin
        # BSD style ps invocation
        lines = `ps axo pid,ppid,pcpu,rss`.split("\n")

        lines.inject(Hash.new) do |mem, line|
          chunks = line.split(/\s+/)
          chunks.delete_if {|c| c.strip.empty? }
          pid = chunks[IDX_MAP[:pid]].strip.to_i
          mem[pid] = chunks
          mem
        end
      end
    end

    # be sure to call this from a fork otherwise it will modify the attributes
    # of the bluepill daemon
    def drop_privileges(uid, gid, supplementary_groups)
      if ::Process::Sys.geteuid == 0
        uid_num = Etc.getpwnam(uid).uid if uid
        gid_num = Etc.getgrnam(gid).gid if gid

        group_nums = supplementary_groups.map do |group|
          Etc.getgrnam(group).gid
        end

        ::Process.groups = [gid_num] if gid
        ::Process.groups |= group_nums unless group_nums.empty?
        ::Process::Sys.setgid(gid_num) if gid
        ::Process::Sys.setuid(uid_num) if uid
      end
    end

    def can_write_pid_file(pid_file, logger)
      FileUtils.touch(pid_file)
      File.unlink(pid_file)
      return true

    rescue Exception => e
      logger.warning "%s - %s" % [e.class.name, e.message]
      e.backtrace.each {|l| logger.warning l}
      return false
    end

    def redirect_io(io_in, io_out, io_err)
      $stdin.reopen(io_in) if io_in

      if !io_out.nil? && !io_err.nil? && io_out == io_err
        $stdout.reopen(io_out, APPEND_MODE)
        $stderr.reopen($stdout)

      else
        $stdout.reopen(io_out, APPEND_MODE) if io_out
        $stderr.reopen(io_err, APPEND_MODE) if io_err
      end
    end
  end
end