// SPDX-License-Identifier: Apache-2.0
//
// Copyright The Prometheus 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 log

import (
	"bytes"
	"io"
	"sync"
)

const defaultNonBlockingWriterBufferSize = 1024

type nonBlockingWriter struct {
	writer     io.Writer
	queue      chan []byte
	workerDone chan struct{}
	mu         sync.RWMutex
	closed     bool
}

func newNonBlockingWriter(writer io.Writer, queueSize int) *nonBlockingWriter {
	if queueSize <= 0 {
		queueSize = defaultNonBlockingWriterBufferSize
	}

	w := &nonBlockingWriter{
		writer:     writer,
		queue:      make(chan []byte, queueSize),
		workerDone: make(chan struct{}),
	}

	go func() {
		defer close(w.workerDone)

		for p := range w.queue {
			_, _ = w.writer.Write(p)
		}
	}()

	return w
}

func (w *nonBlockingWriter) Write(p []byte) (int, error) {
	msg := bytes.Clone(p)

	w.mu.RLock()
	defer w.mu.RUnlock()

	if w.closed {
		return 0, io.ErrClosedPipe
	}

	select {
	case w.queue <- msg:
	default:
	}

	return len(p), nil
}

func (w *nonBlockingWriter) Close() error {
	w.mu.Lock()
	if !w.closed {
		w.closed = true
		close(w.queue)
	}
	w.mu.Unlock()

	<-w.workerDone

	return nil
}