require 'tempfile'
require 'fileutils'
require 'readline'
require 'pathname'

module AviGlitch
  # Base is the object that provides interfaces mainly used.
  # To glitch, and save file. The instance returned through AviGlitch#open.
  #
  class Base
    SAFE_FRAMES_COUNT = 150000 # :nodoc:

    # AviGlitch::Frames object generated from the +file+.
    attr_reader :frames
    # The input file (copied tempfile).
    attr_reader :file

    ##
    # Create a new instance of AviGlitch::Base, open the file and 
    # make it ready to manipulate.
    # It requires +path+ as Pathname.
    def initialize path
      File.open(path) do |f|
        # copy as tempfile
        @file = Tempfile.open 'aviglitch'
        f.rewind
        while d = f.read(1024) do
          @file.print d
        end
      end

      unless AviGlitch::Base.surely_formatted? @file
        raise 'Unsupported file passed.'
      end
      unless safe_frames_count? @file
        close
        exit
      end
      @frames = Frames.new @file
      # I believe Ruby's GC to close and remove the Tempfile..
    end

    ##
    # Output the glitched file to +path+, and close the file.
    def output path
      FileUtils.cp @file.path, path
      close
    end

    ##
    # An explicit file close.
    def close
      @file.close!
    end

    ##
    # Glitch each frame data.
    # It is a convent method to iterate each frame.
    #
    # The argument +target+ takes symbols listed below:
    # [<tt>:keyframe</tt> or <tt>:iframe</tt>]   select video key frames (aka I-frame)
    # [<tt>:deltaframe</tt> or <tt>:pframe</tt>] select video delta frames (difference frames)
    # [<tt>:videoframe</tt>] select both of keyframe and deltaframe
    # [<tt>:audioframe</tt>] select audio frames
    # [<tt>:all</tt>]        select all frames
    #
    # It also requires a block. In the block, you take the frame data
    # as a String parameter.
    # To modify the data, simply return a modified data.
    def glitch target = :all, &block  # :yield: data
      frames.each do |frame|
        if valid_target? target, frame
          frame.data = yield frame.data
        end
      end
    end

    ##
    # Do glitch with index.
    def glitch_with_index target = :all, &block  # :yield: data, index
      i = 0
      frames.each do |frame|
        if valid_target? target, frame
          frame.data = yield(frame.data, i)
          i += 1
        end
      end
    end

    alias :write :output

    def valid_target? target, frame # :nodoc:
      return true if target == :all
      begin
        frame.send "is_#{target.to_s}?"
      rescue
        false
      end
    end

    def safe_frames_count? io # :nodoc:
      r = true
      io.pos = 12
      while io.read(4) != 'idx1' do
        s = io.read(4).unpack('V').first
        io.pos += s
      end
      s = io.read(4).unpack('V').first
      fc = s / 16
      if fc >= SAFE_FRAMES_COUNT
        trap(:INT) do
          close
          exit
        end
        m = ["WARNING: The passed file has too many frames (#{fc}).\n",
          "It may use a large memory to process. ",
            "We recommend to chop the movie to smaller chunks before you glitch.\n",
            "Do you want to continue anyway? [yN] "].join('')
          a = Readline.readline m
          r = a == 'y'
      end
      r
    end

    private_instance_methods [:valid_target?, :is_safe_frames_count?]

    class << self
      ##
      # Check if the +file+ is a correctly formetted AVI file.
      # +file+ can be String or Pathname or IO.
      def surely_formatted? file, debug = false
        answer = true
        is_io = file.respond_to?(:seek)  # Probably IO.
        file = File.open(file) unless is_io
        begin
          file.seek 0, IO::SEEK_END
          eof = file.pos
          file.rewind
          unless file.read(4) == 'RIFF'
            answer = false
            warn 'RIFF sign is not found' if debug
          end
          len = file.read(4).unpack('V').first
          unless file.read(4) == 'AVI '
            answer = false
            warn 'AVI sign is not found' if debug
          end
          while file.read(4) =~ /^(?:LIST|JUNK)$/ do
            s = file.read(4).unpack('V').first
            file.pos += s
          end
          file.pos -= 4
          # we require idx1
          unless file.read(4) == 'idx1'
            answer = false
            warn 'idx1 is not found' if debug
          end
          s = file.read(4).unpack('V').first
          file.pos += s
        rescue => err
          warn err.message if debug
          answer = false
        ensure
          file.close unless is_io
        end
        answer
      end
    end
  end
end