class ScreenshotGenerator

# File lib/screenshot_generator.rb, line 5
def self.extract_frame(video, *args)
  new(video).extract_frame(*args)
end

# File lib/screenshot_generator.rb, line 9
def self.extract_multi(video, *args)
  new(video).extract_multi(*args)
end

# File lib/screenshot_generator.rb, line 13
def initialize(video, size: '640x400')
  @video = video
  @size = size
  raise ArgumentError, "Video does not exist" unless File.exist? @video
end

# File lib/screenshot_generator.rb, line 58
def self.ffmpeg
  @ffmpeg ||= `which ffmpeg`.chomp
end

# File lib/screenshot_generator.rb, line 21
def extract_frame(offset, path)
  raise ArgumentError, "File already exists" if File.exist? path
  offset = format_offset(offset)
  ffmpeg(
    "-loglevel", "error",
    "-ss", offset,
    "-i", video,
    "-frames:v", 1,
    "-s", size,
    path
  )
end

# File lib/screenshot_generator.rb, line 35
def extract_multi(dir, count)
  dir = Pathname.new(dir)
  0.upto(count) do |index|
    path = dir + "#{index}.jpg"
    segment_size = length / (count + 2)
    offset = (index + 1) * segment_size
    extract_frame(offset, path)
  end
end

# File lib/screenshot_generator.rb, line 45
def length
  @length ||= get_length
end

# File lib/screenshot_generator.rb, line 51
def ffmpeg(*args)
  options = [self.class.ffmpeg, *args].map(&:to_s)
  options.push(:err=>[:child, :out])
  IO.popen(options) {|io| return io.read }
  raise "ffmpeg comamnd #{options.inspect} failed" unless $?.success?
end

# File lib/screenshot_generator.rb, line 72
def format_offset(v)
  m, s = v.divmod(60)
  h, m = m.divmod(60)
  "%02i:%02i:%02i" % [h, m, s]
end

# File lib/screenshot_generator.rb, line 62
def get_length
  output = ffmpeg("-i", video, "-frames", 1)
  if output =~ /Duration:\s*([0-9:.]+)/
    h,m,s = $1.split(":").map(&:to_i)
    h*60^2 + m*60 + s
  else
    60
  end
end