package exec

import (
	"crypto/md5"
	"encoding/hex"
	"errors"
	"fmt"
	"net/url"
	"os"
	"os/exec"
	"strings"
	"sync"
	"time"

	"github.com/AlexxIT/go2rtc/internal/app"
	"github.com/AlexxIT/go2rtc/internal/rtsp"
	"github.com/AlexxIT/go2rtc/internal/streams"
	"github.com/AlexxIT/go2rtc/pkg/core"
	"github.com/AlexxIT/go2rtc/pkg/magic"
	pkg "github.com/AlexxIT/go2rtc/pkg/rtsp"
	"github.com/AlexxIT/go2rtc/pkg/shell"
	"github.com/AlexxIT/go2rtc/pkg/stdin"
	"github.com/rs/zerolog"
)

func Init() {
	rtsp.HandleFunc(func(conn *pkg.Conn) bool {
		waitersMu.Lock()
		waiter := waiters[conn.URL.Path]
		waitersMu.Unlock()

		if waiter == nil {
			return false
		}

		// unblocking write to channel
		select {
		case waiter <- conn:
			return true
		default:
			return false
		}
	})

	streams.HandleFunc("exec", execHandle)

	log = app.GetLogger("exec")
}

func execHandle(rawURL string) (core.Producer, error) {
	var path string
	var query url.Values

	// RTSP flow should have `{output}` inside URL
	// pipe flow may have `#{params}` inside URL
	if i := strings.Index(rawURL, "{output}"); i > 0 {
		if rtsp.Port == "" {
			return nil, errors.New("exec: rtsp module disabled")
		}

		sum := md5.Sum([]byte(rawURL))
		path = "/" + hex.EncodeToString(sum[:])
		rawURL = rawURL[:i] + "rtsp://127.0.0.1:" + rtsp.Port + path + rawURL[i+8:]
	} else if i = strings.IndexByte(rawURL, '#'); i > 0 {
		query = streams.ParseQuery(rawURL[i+1:])
		rawURL = rawURL[:i]
	}

	args := shell.QuoteSplit(rawURL[5:]) // remove `exec:`
	cmd := exec.Command(args[0], args[1:]...)
	cmd.Stderr = &logWriter{
		buf:   make([]byte, 512),
		debug: log.Debug().Enabled(),
	}

	if path == "" {
		return handlePipe(rawURL, cmd, query)
	}

	return handleRTSP(rawURL, cmd, path)
}

func handlePipe(_ string, cmd *exec.Cmd, query url.Values) (core.Producer, error) {
	if query.Get("backchannel") == "1" {
		return stdin.NewClient(cmd)
	}

	r, err := PipeCloser(cmd, query)
	if err != nil {
		return nil, err
	}

	log.Debug().Strs("args", cmd.Args).Msg("[exec] run pipe")

	ts := time.Now()

	if err = cmd.Start(); err != nil {
		return nil, err
	}

	prod, err := magic.Open(r)
	if err != nil {
		_ = r.Close()
	}

	log.Debug().Stringer("launch", time.Since(ts)).Msg("[exec] run pipe")

	return prod, fmt.Errorf("exec/pipe: %w\n%s", err, cmd.Stderr)
}

func handleRTSP(url string, cmd *exec.Cmd, path string) (core.Producer, error) {
	if log.Trace().Enabled() {
		cmd.Stdout = os.Stdout
	}

	waiter := make(chan *pkg.Conn, 1)

	waitersMu.Lock()
	waiters[path] = waiter
	waitersMu.Unlock()

	defer func() {
		waitersMu.Lock()
		delete(waiters, path)
		waitersMu.Unlock()
	}()

	log.Debug().Strs("args", cmd.Args).Msg("[exec] run rtsp")

	ts := time.Now()

	if err := cmd.Start(); err != nil {
		log.Error().Err(err).Str("url", url).Msg("[exec]")
		return nil, err
	}

	done := make(chan error, 1)
	go func() {
		done <- cmd.Wait()
	}()

	select {
	case <-time.After(time.Second * 60):
		_ = cmd.Process.Kill()
		log.Error().Str("url", url).Msg("[exec] timeout")
		return nil, errors.New("exec: timeout")
	case <-done:
		// limit message size
		return nil, fmt.Errorf("exec/rtsp\n%s", cmd.Stderr)
	case prod := <-waiter:
		log.Debug().Stringer("launch", time.Since(ts)).Msg("[exec] run rtsp")
		prod.OnClose = func() error {
			log.Debug().Msgf("[exec] kill rtsp")
			return errors.Join(cmd.Process.Kill(), cmd.Wait())
		}
		return prod, nil
	}
}

// internal

var (
	log       zerolog.Logger
	waiters   = make(map[string]chan *pkg.Conn)
	waitersMu sync.Mutex
)

type logWriter struct {
	buf   []byte
	debug bool
	n     int
}

func (l *logWriter) String() string {
	if l.n == len(l.buf) {
		return string(l.buf) + "..."
	}
	return string(l.buf[:l.n])
}

func (l *logWriter) Write(p []byte) (n int, err error) {
	if l.n < cap(l.buf) {
		l.n += copy(l.buf[l.n:], p)
	}
	n = len(p)
	if l.debug {
		if p = trimSpace(p); p != nil {
			log.Debug().Msgf("[exec] %s", p)
		}
	}
	return
}

func trimSpace(b []byte) []byte {
	start := 0
	stop := len(b)
	for ; start < stop; start++ {
		if b[start] >= ' ' {
			break // trim all ASCII before 0x20
		}
	}
	for ; ; stop-- {
		if stop == start {
			return nil // skip empty output
		}
		if b[stop-1] > ' ' {
			break // trim all ASCII before 0x21
		}
	}
	return b[start:stop]
}