package stario

import (
	"bytes"
	"errors"
	"io"
	"os"
	"testing"
)

type chunkedReader struct {
	data []byte
	max  int
}

func (reader *chunkedReader) Read(p []byte) (int, error) {
	if len(reader.data) == 0 {
		return 0, io.EOF
	}
	if reader.max > 0 && len(p) > reader.max {
		p = p[:reader.max]
	}
	n := copy(p, reader.data)
	reader.data = reader.data[n:]
	return n, nil
}

type trackingReader struct {
	data         []byte
	maxRequested int
}

func (reader *trackingReader) Read(p []byte) (int, error) {
	if len(p) > reader.maxRequested {
		reader.maxRequested = len(p)
	}
	if len(reader.data) == 0 {
		return 0, io.EOF
	}
	n := copy(p, reader.data)
	reader.data = reader.data[n:]
	return n, nil
}

type stagedReaderStep struct {
	data []byte
	err  error
}

type stagedReader struct {
	steps []stagedReaderStep
	index int
}

func (reader *stagedReader) Read(p []byte) (int, error) {
	if reader.index >= len(reader.steps) {
		return 0, io.EOF
	}
	step := &reader.steps[reader.index]
	n := copy(p, step.data)
	step.data = step.data[n:]
	if len(step.data) == 0 {
		err := step.err
		reader.index++
		return n, err
	}
	return n, nil
}

func TestFrameWriterReaderRoundTrip(t *testing.T) {
	var wire bytes.Buffer
	writer := NewFrameWriter(&wire, nil)
	if err := writer.WriteFrame([]byte("one")); err != nil {
		t.Fatalf("WriteFrame failed: %v", err)
	}
	if err := writer.WriteFramesBuffers([][]byte{[]byte("two"), []byte("three")}...); err != nil {
		t.Fatalf("WriteFramesBuffers failed: %v", err)
	}

	reader := NewFrameReader(bytes.NewReader(wire.Bytes()), nil)
	cases := []string{"one", "two", "three"}
	for _, want := range cases {
		got, err := reader.Next()
		if err != nil {
			t.Fatalf("Next returned error: %v", err)
		}
		if string(got) != want {
			t.Fatalf("unexpected frame: got %q want %q", got, want)
		}
	}
	if _, err := reader.Next(); !errors.Is(err, io.EOF) {
		t.Fatalf("expected EOF after draining frames, got %v", err)
	}
}

func TestFrameReaderHandlesPartialTransportReads(t *testing.T) {
	var wire bytes.Buffer
	writer := NewFrameWriter(&wire, nil)
	if err := writer.WriteFrame([]byte("hello")); err != nil {
		t.Fatalf("WriteFrame failed: %v", err)
	}

	reader := NewFrameReader(&chunkedReader{data: wire.Bytes(), max: 3}, nil)
	reader.SetReadBufferSize(3)
	got, err := reader.Next()
	if err != nil {
		t.Fatalf("Next returned error: %v", err)
	}
	if string(got) != "hello" {
		t.Fatalf("unexpected frame: %q", got)
	}
}

func TestFrameReaderSetReadBufferSizeLimitsUnderlyingReadSize(t *testing.T) {
	var wire bytes.Buffer
	writer := NewFrameWriter(&wire, nil)
	if err := writer.WriteFrame([]byte("hello")); err != nil {
		t.Fatalf("WriteFrame failed: %v", err)
	}

	source := &trackingReader{data: wire.Bytes()}
	reader := NewFrameReader(source, nil)
	reader.SetReadBufferSize(3)

	got, err := reader.Next()
	if err != nil {
		t.Fatalf("Next returned error: %v", err)
	}
	if string(got) != "hello" {
		t.Fatalf("unexpected frame: %q", got)
	}
	if got, want := source.maxRequested, 3; got != want {
		t.Fatalf("max requested read size = %d, want %d", got, want)
	}
}

func TestFrameReaderNextPooledAndNextView(t *testing.T) {
	queue := NewQueue()
	wire := append(queue.BuildMessage([]byte("alpha")), queue.BuildMessage([]byte("beta"))...)
	reader := NewFrameReader(bytes.NewReader(wire), queue)

	first, release, err := reader.NextPooled()
	if err != nil {
		t.Fatalf("NextPooled returned error: %v", err)
	}
	if string(first) != "alpha" {
		t.Fatalf("unexpected pooled frame: %q", first)
	}
	if release == nil {
		t.Fatal("NextPooled should return a release func")
	}
	release()

	var second string
	if err := reader.NextView(func(view FrameView) error {
		second = string(view.Payload)
		return nil
	}); err != nil {
		t.Fatalf("NextView returned error: %v", err)
	}
	if second != "beta" {
		t.Fatalf("unexpected view frame: %q", second)
	}
}

func TestFrameReaderPreservesPartialFrameAcrossDeadline(t *testing.T) {
	queue := NewQueue()
	frame := queue.BuildMessage([]byte("hello"))
	reader := NewFrameReader(&stagedReader{
		steps: []stagedReaderStep{
			{data: append([]byte(nil), frame[:5]...), err: os.ErrDeadlineExceeded},
			{data: append([]byte(nil), frame[5:]...), err: nil},
		},
	}, queue)

	if _, _, err := reader.NextPooled(); !errors.Is(err, os.ErrDeadlineExceeded) {
		t.Fatalf("expected deadline exceeded on partial frame, got %v", err)
	}
	got, release, err := reader.NextPooled()
	if err != nil {
		t.Fatalf("NextPooled after deadline returned error: %v", err)
	}
	if string(got) != "hello" {
		t.Fatalf("unexpected frame after deadline: %q", got)
	}
	if release != nil {
		release()
	}
}

func TestFrameWriterNilWriterFails(t *testing.T) {
	writer := NewFrameWriter(nil, nil)
	if err := writer.WriteFrame([]byte("hello")); !errors.Is(err, io.ErrClosedPipe) {
		t.Fatalf("expected io.ErrClosedPipe, got %v", err)
	}
}

func TestFrameReaderTruncatedFrameReturnsUnexpectedEOF(t *testing.T) {
	queue := NewQueue()
	frame := queue.BuildMessage([]byte("hello"))
	reader := NewFrameReader(bytes.NewReader(frame[:len(frame)-1]), nil)

	if _, err := reader.Next(); !errors.Is(err, io.ErrUnexpectedEOF) {
		t.Fatalf("expected io.ErrUnexpectedEOF, got %v", err)
	}
}

func TestFrameReaderReturnsUnexpectedEOFAfterPendingFrames(t *testing.T) {
	queue := NewQueue()
	first := queue.BuildMessage([]byte("one"))
	second := queue.BuildMessage([]byte("two"))
	wire := append(append([]byte{}, first...), second[:len(second)-1]...)
	reader := NewFrameReader(bytes.NewReader(wire), nil)

	got, err := reader.Next()
	if err != nil {
		t.Fatalf("unexpected error on first frame: %v", err)
	}
	if string(got) != "one" {
		t.Fatalf("unexpected first frame: %q", got)
	}
	if _, err := reader.Next(); !errors.Is(err, io.ErrUnexpectedEOF) {
		t.Fatalf("expected io.ErrUnexpectedEOF after draining pending frame, got %v", err)
	}
}