package stream

import (
	"io"
	"sync"

	"golang.org/x/net/context"

	"github.com/Sirupsen/logrus"
	"github.com/docker/docker/pkg/promise"
)

var defaultEscapeSequence = []byte{16, 17} // ctrl-p, ctrl-q

// DetachError is special error which returned in case of container detach.
type DetachError struct{}

func (DetachError) Error() string {
	return "detached from container"
}

// AttachConfig is the config struct used to attach a client to a stream's stdio
type AttachConfig struct {
	// Tells the attach copier that the stream's stdin is a TTY and to look for
	// escape sequences in stdin to detach from the stream.
	// When true the escape sequence is not passed to the underlying stream
	TTY bool
	// Specifies the detach keys the client will be using
	// Only useful when `TTY` is true
	DetachKeys []byte

	// CloseStdin signals that once done, stdin for the attached stream should be closed
	// For example, this would close the attached container's stdin.
	CloseStdin bool

	// Provide client streams to wire up to
	Stdin          io.ReadCloser
	Stdout, Stderr io.Writer
}

// Attach attaches the stream config to the streams specified in
// the AttachOptions
func (c *Config) Attach(ctx context.Context, cfg *AttachConfig) chan error {
	var (
		cStdout, cStderr io.ReadCloser
		cStdin           io.WriteCloser
		wg               sync.WaitGroup
		errors           = make(chan error, 3)
	)

	if cfg.Stdin != nil {
		cStdin = c.StdinPipe()
		wg.Add(1)
	}

	if cfg.Stdout != nil {
		cStdout = c.StdoutPipe()
		wg.Add(1)
	}

	if cfg.Stderr != nil {
		cStderr = c.StderrPipe()
		wg.Add(1)
	}

	// Connect stdin of container to the attach stdin stream.
	go func() {
		if cfg.Stdin == nil {
			return
		}
		logrus.Debug("attach: stdin: begin")

		var err error
		if cfg.TTY {
			_, err = copyEscapable(cStdin, cfg.Stdin, cfg.DetachKeys)
		} else {
			_, err = io.Copy(cStdin, cfg.Stdin)
		}
		if err == io.ErrClosedPipe {
			err = nil
		}
		if err != nil {
			logrus.Errorf("attach: stdin: %s", err)
			errors <- err
		}
		if cfg.CloseStdin && !cfg.TTY {
			cStdin.Close()
		} else {
			// No matter what, when stdin is closed (io.Copy unblock), close stdout and stderr
			if cStdout != nil {
				cStdout.Close()
			}
			if cStderr != nil {
				cStderr.Close()
			}
		}
		logrus.Debug("attach: stdin: end")
		wg.Done()
	}()

	attachStream := func(name string, stream io.Writer, streamPipe io.ReadCloser) {
		if stream == nil {
			return
		}

		logrus.Debugf("attach: %s: begin", name)
		_, err := io.Copy(stream, streamPipe)
		if err == io.ErrClosedPipe {
			err = nil
		}
		if err != nil {
			logrus.Errorf("attach: %s: %v", name, err)
			errors <- err
		}
		// Make sure stdin gets closed
		if cfg.Stdin != nil {
			cfg.Stdin.Close()
		}
		streamPipe.Close()
		logrus.Debugf("attach: %s: end", name)
		wg.Done()
	}

	go attachStream("stdout", cfg.Stdout, cStdout)
	go attachStream("stderr", cfg.Stderr, cStderr)

	return promise.Go(func() error {
		done := make(chan struct{})
		go func() {
			wg.Wait()
			close(done)
		}()
		select {
		case <-done:
		case <-ctx.Done():
			// close all pipes
			if cStdin != nil {
				cStdin.Close()
			}
			if cStdout != nil {
				cStdout.Close()
			}
			if cStderr != nil {
				cStderr.Close()
			}
			<-done
		}
		close(errors)
		for err := range errors {
			if err != nil {
				return err
			}
		}
		return nil
	})
}

// ttyProxy is used only for attaches with a TTY. It is used to proxy
// stdin keypresses from the underlying reader and look for the passed in
// escape key sequence to signal a detach.
type ttyProxy struct {
	escapeKeys   []byte
	escapeKeyPos int
	r            io.Reader
}

func (r *ttyProxy) Read(buf []byte) (int, error) {
	nr, err := r.r.Read(buf)

	preserve := func() {
		// this preserves the original key presses in the passed in buffer
		nr += r.escapeKeyPos
		preserve := make([]byte, 0, r.escapeKeyPos+len(buf))
		preserve = append(preserve, r.escapeKeys[:r.escapeKeyPos]...)
		preserve = append(preserve, buf...)
		r.escapeKeyPos = 0
		copy(buf[0:nr], preserve)
	}

	if nr != 1 || err != nil {
		if r.escapeKeyPos > 0 {
			preserve()
		}
		return nr, err
	}

	if buf[0] != r.escapeKeys[r.escapeKeyPos] {
		if r.escapeKeyPos > 0 {
			preserve()
		}
		return nr, nil
	}

	if r.escapeKeyPos == len(r.escapeKeys)-1 {
		return 0, DetachError{}
	}

	// Looks like we've got an escape key, but we need to match again on the next
	// read.
	// Store the current escape key we found so we can look for the next one on
	// the next read.
	// Since this is an escape key, make sure we don't let the caller read it
	// If later on we find that this is not the escape sequence, we'll add the
	// keys back
	r.escapeKeyPos++
	return nr - r.escapeKeyPos, nil
}

func copyEscapable(dst io.Writer, src io.ReadCloser, keys []byte) (written int64, err error) {
	if len(keys) == 0 {
		keys = defaultEscapeSequence
	}
	pr := &ttyProxy{escapeKeys: keys, r: src}
	defer src.Close()

	return io.Copy(dst, pr)
}