package stream

import (
	"fmt"
	"io"
	"sync"
	"testing"
	"time"

	"github.com/rs/zerolog"
	"github.com/stretchr/testify/require"
)

func TestPipeBidirectionalFinishBothSides(t *testing.T) {
	fun := func(upstream, downstream *mockedStream) {
		downstream.closeReader()
		upstream.closeReader()
	}

	testPipeBidirectionalUnblocking(t, fun, time.Millisecond*200, false)
}

func TestPipeBidirectionalFinishOneSideTimeout(t *testing.T) {
	fun := func(upstream, downstream *mockedStream) {
		downstream.closeReader()
	}

	testPipeBidirectionalUnblocking(t, fun, time.Millisecond*200, true)
}

func TestPipeBidirectionalClosingWriteBothSidesAlsoExists(t *testing.T) {
	fun := func(upstream, downstream *mockedStream) {
		_ = downstream.CloseWrite()
		_ = upstream.CloseWrite()

		downstream.writeToReader("abc")
		upstream.writeToReader("abc")
	}

	testPipeBidirectionalUnblocking(t, fun, time.Millisecond*200, false)
}

func TestPipeBidirectionalClosingWriteSingleSideAlsoExists(t *testing.T) {
	fun := func(upstream, downstream *mockedStream) {
		_ = downstream.CloseWrite()

		downstream.writeToReader("abc")
		upstream.writeToReader("abc")
	}

	testPipeBidirectionalUnblocking(t, fun, time.Millisecond*200, true)
}

// TestPipeBidirectionalReturnsWhenBothSidesFinish verifies that
// PipeBidirectional returns as soon as both stream directions finish, without
// waiting for the full timeout grace period to expire. This guards against a
// regression where the second-stream wait would block for the whole timeout
// even when the result is already available.
func TestPipeBidirectionalReturnsWhenBothSidesFinish(t *testing.T) {
	t.Parallel()

	const (
		timeout     = time.Second * 5
		maxWallTime = time.Millisecond * 500
	)

	logger := zerolog.Nop()
	downstream := newMockedStream()
	upstream := newMockedStream()

	resultCh := make(chan error, 1)
	go func() {
		resultCh <- PipeBidirectional(downstream, upstream, timeout, &logger)
	}()

	// Close both reader sides so both stream directions reach EOF promptly.
	downstream.closeReader()
	upstream.closeReader()

	start := time.Now()
	select {
	case err := <-resultCh:
		elapsed := time.Since(start)
		require.NoError(t, err)
		require.Less(t, elapsed, maxWallTime,
			"PipeBidirectional should return as soon as both streams finish, not after the full %s timeout (took %s)",
			timeout, elapsed,
		)
	case <-time.After(timeout):
		require.Fail(t, "PipeBidirectional did not return before the timeout expired")
	}
}

func testPipeBidirectionalUnblocking(t *testing.T, afterFun func(*mockedStream, *mockedStream), timeout time.Duration, expectTimeout bool) {
	logger := zerolog.Nop()

	downstream := newMockedStream()
	upstream := newMockedStream()

	resultCh := make(chan error)
	go func() {
		resultCh <- PipeBidirectional(downstream, upstream, timeout, &logger)
	}()

	afterFun(upstream, downstream)

	select {
	case err := <-resultCh:
		if expectTimeout {
			require.Error(t, err)
		} else {
			require.NoError(t, err)
		}

	case <-time.After(timeout * 2):
		require.Fail(t, "test timeout")
	}
}

func newMockedStream() *mockedStream {
	return &mockedStream{
		readCh:  make(chan *string),
		writeCh: make(chan struct{}),
	}
}

type mockedStream struct {
	readCh  chan *string
	writeCh chan struct{}

	writeCloseOnce sync.Once
}

func (m *mockedStream) Read(p []byte) (n int, err error) {
	result := <-m.readCh
	if result == nil {
		return 0, io.EOF
	}

	return len(*result), nil
}

func (m *mockedStream) Write(p []byte) (n int, err error) {
	<-m.writeCh

	return 0, fmt.Errorf("closed")
}

func (m *mockedStream) CloseWrite() error {
	m.writeCloseOnce.Do(func() {
		close(m.writeCh)
	})

	return nil
}

func (m *mockedStream) closeReader() {
	close(m.readCh)
}
func (m *mockedStream) writeToReader(content string) {
	m.readCh <- &content
}