#--
# rbmh/pager.rb : rbmhshow 0.4.2
#
# Copyright (C) 2004--2005  Merlin Hughes  <ruby AT merlin DOT org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
#++
# Managed less pager

require 'tempfile'
require 'merlin/let'
require 'rbmh/command'

module RBMH
  class Pager
    def initialize(context)
      @context = context
      @commands = {0 => [RBMH::Command.lookup("exit", "0", context)]}
      # @less_file @less_prompt @temp_file @exit_code
      profile_init
    end

    # TODO: handle name=nil, handle prompt code ?f___:___.
    def page(io, message)
      @message = message
      dispname = message.display_name.gsub(/\./, '\\.') # other chars too
      prompt = @less_prompt.gsub(/(^|[^\\])%f/, dispname)
      less_env = "-RmPm#{prompt}$PM#{prompt}$k#{@less_file}$#{ENV['LESS']}"
      ENV.let([ 'LESS', less_env ]) {
        STDIN.let(io) {
          system "less -"
        }
      }
      @exit_code = $?.exitstatus
      raise RBMH::Exception, "unknown less exit code - #{less_exit_code}" unless @commands.has_key?(@exit_code)
    end

    def execute_exit_commands(message)
      catch :show do
        @commands[@exit_code].each { |command|
          command.execute(message)
        }
        return false
      end
      return true
    end

    private

    def profile_init
      profile = @context.profile

      # I do this in two loops so I can sort the keys, to protect
      # against the hash ordering changing between invocations
      actions = {}
      profile.each(ProfileLessKeyRE) { |key, value|
        raise RBMH::Exception, "invalid commands - #{value}" unless value =~ CommandsRE
        commands = value.scan(CommandRE)
        commands.collect! { |command, parameter|
          RBMH::Command.lookup(command, parameter, @context)
        }
        actions[key] = commands
      }
      exit = "@"
      exits = {}
      actions.sort.each { |key, commands|
        exit[0] += 1
        exits[key] = exit.dup
        @commands[exit[0]] = commands
      }

      file = profile[ProfileLessFile]
      if file.nil?
        @temp_file = Tempfile.new("rbmh-less")
        @temp_file.close
        @less_file = @temp_file.path
        lesskeys(exits)
      else
        @less_file = File.expand_path(file)
        if (not FileTest.exists?(@less_file)) or
           (profile.mtime > File.stat(@less_file).mtime)
          STDERR.puts "rbmh: updating #{@less_file}"
          lesskeys(exits)
        end
      end

      prompt = profile[ProfileLessPrompt]
      @less_prompt = prompt || LessPrompt
    end

    # things will go badly wrong if you change .mh_profile and
    # its mtime precedes .rbmh_less' because the exit codes will
    # no longer line up
    def lesskeys(exits)
      IO.popen("lesskey -o #{@less_file} -", "w") { | lesskey |
        exits.each { | key, exit |
          lesskey.puts "#{key} quit #{exit}"
        }
      }
      exit 1 if $?.exitstatus != 0
    end

    ProfileLessFile = 'rbmh-less-file'
    ProfileLessPrompt = 'rbmh-less-prompt'
    ProfileLessKeyRE = /^rbmh-less-key-(\S+)$/
    LessPrompt = '%f ?ltlines %lt-%lb?L/%L. : byte % bB?s/%s. .?e(END):?pB%pB\%..%t'
    # TODO: optional parens, as ruby.. can't express it elegantly
    ParameterRE = /(?:\((?>\s*)((?:[^\\)]|\\.)*(?:[^ \\)]|\\.))?\s*\))?/ # $1: parameter
    CommandRE = /\s*(\w+)\s*#{ParameterRE.source}\s*/ # $1: command, $2: parameter
    CommandsRE = /^#{CommandRE.source}(;#{CommandRE.source})*$/
  end # class Pager
end # module RBMH