/*
Copyright 2014 The Perkeep Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

/*
Package thumbnail generates image thumbnails from videos.

(*Service).Generate spawns an HTTP server listening on a local random
port to serve the video to an external program (see Thumbnailer interface).
The external program is expected to output the thumbnail image on its
standard output.

The default implementation uses ffmpeg.

See ServiceFromConfig for accepted configuration.
*/
package thumbnail // import "perkeep.org/internal/video/thumbnail"

import (
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"net/url"
	"time"

	"go4.org/jsonconfig"
	"perkeep.org/internal/netutil"
	"perkeep.org/pkg/blob"

	"go4.org/syncutil"
)

// A Service controls the generation of video thumbnails.
type Service struct {
	thumbnailer Thumbnailer
	// Timeout is the maximum duration for the thumbnailing subprocess execution.
	timeout time.Duration
	gate    *syncutil.Gate // of subprocesses.
}

// ServiceFromConfig builds a new Service from configuration.
// Example expected configuration object (all keys are optional) :
// {
//   // command defaults to FFmpegThumbnailer and $uri is replaced by
//   // the real value at runtime.
//   "command": ["/opt/local/bin/ffmpeg", "-i", "$uri", "pipe:1"],
//   // Maximun number of milliseconds for running the thumbnailing subprocess.
//   // A zero or negative timeout means no timeout.
//   "timeout": 2000,
//   // Maximum number of thumbnailing subprocess running at same time.
//   // A zero or negative maxProcs means no limit.
//   "maxProcs": 5
// }
func ServiceFromConfig(conf jsonconfig.Obj) (*Service, error) {
	th := thumbnailerFromConfig(conf)
	timeout := conf.OptionalInt("timeout", 5000)
	maxProc := conf.OptionalInt("maxProcs", 5)

	err := conf.Validate()
	if err != nil {
		return nil, err
	}

	return NewService(th, time.Millisecond*time.Duration(timeout), maxProc), nil
}

// NewService builds a new Service. Zero timeout or maxProcs means no limit.
func NewService(th Thumbnailer, timeout time.Duration, maxProcs int) *Service {

	var g *syncutil.Gate
	if maxProcs > 0 {
		g = syncutil.NewGate(maxProcs)
	}

	return &Service{
		thumbnailer: th,
		timeout:     timeout,
		gate:        g,
	}
}

var errTimeout = errors.New("timeout")

// Generate reads the video given by videoRef from src and writes its thumbnail image to w.
func (s *Service) Generate(videoRef blob.Ref, w io.Writer, src blob.Fetcher) error {

	if s.gate != nil {
		s.gate.Start()
		defer s.gate.Done()
	}

	ln, err := netutil.ListenOnLocalRandomPort()
	if err != nil {
		return err
	}
	defer ln.Close()

	videoUri := &url.URL{
		Scheme: "http",
		Host:   ln.Addr().String(),
		Path:   videoRef.String(),
	}

	cmdErrc := make(chan error, 1)
	cmd := buildCmd(s.thumbnailer, videoUri, w)
	cmdErrOut, err := cmd.StderrPipe()
	if err != nil {
		return err
	}
	if err := cmd.Start(); err != nil {
		return err
	}
	defer cmd.Process.Kill()
	go func() {
		out, err := ioutil.ReadAll(cmdErrOut)
		if err != nil {
			cmdErrc <- err
			return
		}
		cmd.Wait()
		if cmd.ProcessState.Success() {
			cmdErrc <- nil
			return
		}
		cmdErrc <- fmt.Errorf("thumbnail subprocess failed:\n%s", out)
	}()

	servErrc := make(chan error, 1)
	go func() {
		servErrc <- http.Serve(ln, createVideothumbnailHandler(videoRef, src))
	}()

	select {
	case err := <-cmdErrc:
		return err
	case err := <-servErrc:
		return err
	case <-s.timer():
		return errTimeout
	}
}

func (s *Service) timer() <-chan time.Time {
	if s.timeout <= 0 {
		return make(<-chan time.Time)
	}
	return time.After(s.timeout)
}