package oss

import "io"

// ProgressEventType defines transfer progress event type
type ProgressEventType int

const (
	// TransferStartedEvent transfer started, set TotalBytes
	TransferStartedEvent ProgressEventType = 1 + iota
	// TransferDataEvent transfer data, set ConsumedBytes anmd TotalBytes
	TransferDataEvent
	// TransferCompletedEvent transfer completed
	TransferCompletedEvent
	// TransferFailedEvent transfer encounters an error
	TransferFailedEvent
)

// ProgressEvent defines progress event
type ProgressEvent struct {
	ConsumedBytes int64
	TotalBytes    int64
	EventType     ProgressEventType
}

// ProgressListener listens progress change
type ProgressListener interface {
	ProgressChanged(event *ProgressEvent)
}

// -------------------- Private --------------------

func newProgressEvent(eventType ProgressEventType, consumed, total int64) *ProgressEvent {
	return &ProgressEvent{
		ConsumedBytes: consumed,
		TotalBytes:    total,
		EventType:     eventType}
}

// publishProgress
func publishProgress(listener ProgressListener, event *ProgressEvent) {
	if listener != nil && event != nil {
		listener.ProgressChanged(event)
	}
}

type readerTracker struct {
	completedBytes int64
}

type teeReader struct {
	reader        io.Reader
	writer        io.Writer
	listener      ProgressListener
	consumedBytes int64
	totalBytes    int64
	tracker       *readerTracker
}

// TeeReader returns a Reader that writes to w what it reads from r.
// All reads from r performed through it are matched with
// corresponding writes to w.  There is no internal buffering -
// the write must complete before the read completes.
// Any error encountered while writing is reported as a read error.
func TeeReader(reader io.Reader, writer io.Writer, totalBytes int64, listener ProgressListener, tracker *readerTracker) io.Reader {
	return &teeReader{
		reader:        reader,
		writer:        writer,
		listener:      listener,
		consumedBytes: 0,
		totalBytes:    totalBytes,
		tracker:       tracker,
	}
}

func (t *teeReader) Read(p []byte) (n int, err error) {
	n, err = t.reader.Read(p)

	// Read encountered error
	if err != nil && err != io.EOF {
		event := newProgressEvent(TransferFailedEvent, t.consumedBytes, t.totalBytes)
		publishProgress(t.listener, event)
	}

	if n > 0 {
		t.consumedBytes += int64(n)
		// CRC
		if t.writer != nil {
			if n, err := t.writer.Write(p[:n]); err != nil {
				return n, err
			}
		}
		// Progress
		if t.listener != nil {
			event := newProgressEvent(TransferDataEvent, t.consumedBytes, t.totalBytes)
			publishProgress(t.listener, event)
		}
		// Track
		if t.tracker != nil {
			t.tracker.completedBytes = t.consumedBytes
		}
	}

	return
}