package tests

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"runtime"
	"strings"
	"sync"
	"sync/atomic"
	"testing"
	"time"

	"github.com/olekukonko/ll/lh"
	"github.com/olekukonko/ll/lx"
)

// errorWriter is an io.Writer that always returns an error.
type errorWriter struct {
	err error
}

func (w *errorWriter) Write(p []byte) (n int, err error) { return 0, w.err }

// safeBuffer wraps bytes.Buffer with a mutex so tests can safely read while
// background goroutines are writing.
type safeBuffer struct {
	mu sync.Mutex
	b  bytes.Buffer
}

func (s *safeBuffer) Write(p []byte) (int, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.b.Write(p)
}

func (s *safeBuffer) String() string {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.b.String()
}

// blockingWriter is an io.Writer whose Write blocks until the gate channel is
// closed.  It is used to freeze the Buffered worker goroutine inside a flush
// so that the entries channel stays full and overflow can be reliably triggered.
type blockingWriter struct {
	gate chan struct{} // close to unblock all pending Write calls
	buf  safeBuffer
}

func (w *blockingWriter) Write(p []byte) (int, error) {
	<-w.gate // block until released
	return w.buf.Write(p)
}

// waitUntil polls until condition is true or timeout elapses.
// Helps avoid brittle sleeps while not requiring internal acks from the handler.
func waitUntil(timeout time.Duration, cond func() bool) bool {
	deadline := time.Now().Add(timeout)
	for time.Now().Before(deadline) {
		if cond() {
			return true
		}
		time.Sleep(5 * time.Millisecond)
	}
	return cond()
}

func TestBufferedHandler(t *testing.T) {
	t.Run("BasicFunctionality", func(t *testing.T) {
		buf := &safeBuffer{}
		textHandler := lh.NewTextHandler(buf)
		handler := lh.NewBuffered(textHandler,
			lh.WithBatchSize(2),
			lh.WithFlushInterval(100*time.Millisecond),
			lh.WithErrorOutput(io.Discard),
		)

		_ = handler.Handle(&lx.Entry{Message: "test1"})
		_ = handler.Handle(&lx.Entry{Message: "test2"})

		// Give the worker some time to flush (interval-based or batch-based).
		ok := waitUntil(500*time.Millisecond, func() bool {
			out := buf.String()
			return strings.Contains(out, "test1") && strings.Contains(out, "test2")
		})

		_ = handler.Close()

		output := buf.String()
		if !ok {
			t.Fatalf("Expected both messages in output, got: %q", output)
		}
	})

	t.Run("PeriodicFlushing", func(t *testing.T) {
		buf := &safeBuffer{}
		textHandler := lh.NewTextHandler(buf)
		handler := lh.NewBuffered(textHandler,
			lh.WithBatchSize(100),
			lh.WithFlushInterval(50*time.Millisecond),
			lh.WithErrorOutput(io.Discard),
		)

		_ = handler.Handle(&lx.Entry{Message: "test"})

		ok := waitUntil(500*time.Millisecond, func() bool {
			return strings.Contains(buf.String(), "test")
		})

		_ = handler.Close()

		if !ok {
			t.Fatalf("Expected message to be flushed after interval, got: %q", buf.String())
		}
	})

	// OverflowHandling verifies that Handle returns an error when the internal
	// channel is full.
	//
	// The race: the worker goroutine drains entries from the channel into its
	// local batch slice one-by-one.  Each read frees a channel slot, so a
	// naive "fill then probe" loop races with the worker and the channel may
	// never actually be full when the probe fires.
	//
	// Fix: use a blockingWriter whose Write blocks on a gate channel.  We send
	// one entry and trigger a flush so the worker enters TextHandler.Write and
	// blocks there.  While blocked it cannot read further entries from the
	// channel, so we can fill it to capacity and reliably trigger overflow.
	t.Run("OverflowHandling", func(t *testing.T) {
		gate := make(chan struct{})
		bw := &blockingWriter{gate: gate}
		textHandler := lh.NewTextHandler(bw)

		var overflowCalled atomic.Bool
		handler := lh.NewBuffered(textHandler,
			lh.WithBatchSize(2),
			lh.WithMaxBuffer(2),
			lh.WithOverflowHandler(func(int) { overflowCalled.Store(true) }),
			lh.WithErrorOutput(io.Discard),
		)
		defer handler.Close()

		maxBuffer := handler.Config().MaxBuffer // actual capacity (= 2 here)

		// Seed one entry and flush so the worker enters blockingWriter.Write
		// and blocks on the gate.
		_ = handler.Handle(&lx.Entry{Message: "seed"})
		handler.Flush()

		// Give the worker time to reach blockingWriter.Write and block.
		time.Sleep(20 * time.Millisecond)

		// Fill the channel to capacity.  The worker is frozen so no slots are
		// freed between iterations.
		for i := 0; i < maxBuffer; i++ {
			if err := handler.Handle(&lx.Entry{Message: fmt.Sprintf("fill%d", i)}); err != nil {
				close(gate)
				t.Fatalf("unexpected error filling slot %d: %v", i, err)
			}
		}

		// Channel is now full — the next Handle must overflow.
		err := handler.Handle(&lx.Entry{Message: "overflow"})

		// Unblock the worker so deferred Close() can drain and finish cleanly.
		close(gate)

		if err == nil {
			t.Fatal("Expected error on overflow")
		}
		if !overflowCalled.Load() {
			t.Fatal("Expected overflow handler to be called")
		}
	})

	t.Run("ExplicitFlush", func(t *testing.T) {
		buf := &safeBuffer{}
		textHandler := lh.NewTextHandler(buf)
		handler := lh.NewBuffered(textHandler, lh.WithBatchSize(100), lh.WithErrorOutput(io.Discard))
		defer handler.Close()

		_ = handler.Handle(&lx.Entry{Message: "test"})
		handler.Flush()

		ok := waitUntil(500*time.Millisecond, func() bool {
			return strings.Contains(buf.String(), "test")
		})

		if !ok {
			t.Fatalf("Expected message to be flushed after explicit flush, got: %q", buf.String())
		}
	})

	t.Run("ShutdownDrainsBuffer", func(t *testing.T) {
		buf := &safeBuffer{}
		textHandler := lh.NewTextHandler(buf)
		handler := lh.NewBuffered(textHandler, lh.WithBatchSize(100), lh.WithErrorOutput(io.Discard))

		_ = handler.Handle(&lx.Entry{Message: "test"})
		_ = handler.Close()

		if !strings.Contains(buf.String(), "test") {
			t.Fatalf("Expected message to be flushed on shutdown, got: %q", buf.String())
		}
	})

	t.Run("ConcurrentAccess", func(t *testing.T) {
		buf := &safeBuffer{}
		textHandler := lh.NewTextHandler(buf)
		handler := lh.NewBuffered(textHandler,
			lh.WithBatchSize(100),
			lh.WithFlushInterval(10*time.Millisecond),
			lh.WithMaxBuffer(2000),
			lh.WithErrorOutput(io.Discard),
		)

		var wg sync.WaitGroup
		for i := 0; i < 100; i++ {
			wg.Add(1)
			go func(i int) {
				defer wg.Done()
				_ = handler.Handle(&lx.Entry{Message: fmt.Sprintf("test%d", i)})
			}(i)
		}
		wg.Wait()

		handler.Flush()
		_ = handler.Close() // Stop worker; should drain/flush remaining.

		output := buf.String()
		for i := 0; i < 100; i++ {
			if !strings.Contains(output, fmt.Sprintf("test%d", i)) {
				t.Fatalf("Missing message test%d in output", i)
			}
		}
	})

	t.Run("ErrorHandling", func(t *testing.T) {
		errWriter := &errorWriter{err: errors.New("write error")}
		textHandler := lh.NewTextHandler(errWriter)
		handler := lh.NewBuffered(textHandler, lh.WithBatchSize(1), lh.WithErrorOutput(io.Discard))
		defer handler.Close()

		// Buffered handler should accept the entry; write error occurs during flush.
		if err := handler.Handle(&lx.Entry{Message: "test"}); err != nil {
			t.Fatalf("Unexpected error on Handle: %v", err)
		}

		handler.Flush()
		// Inactive assertion here; this test is to ensure it doesn't race/panic.
		_ = waitUntil(300*time.Millisecond, func() bool { return true })
	})

	t.Run("Finalizer", func(t *testing.T) {
		buf := &safeBuffer{}
		textHandler := lh.NewTextHandler(buf)
		handler := lh.NewBuffered(textHandler, lh.WithBatchSize(100), lh.WithErrorOutput(io.Discard))

		_ = handler.Handle(&lx.Entry{Message: "test"})

		// Ensure our test isn't relying on GC timing; call Final directly.
		runtime.SetFinalizer(handler, nil)
		handler.Final() // Calls Close()

		if !strings.Contains(buf.String(), "test") {
			t.Fatalf("Expected message to be flushed by finalizer, got: %q", buf.String())
		}
	})
}

func TestBufferedHandlerOptions(t *testing.T) {
	t.Run("DefaultValues", func(t *testing.T) {
		textHandler := lh.NewTextHandler(&safeBuffer{})
		handler := lh.NewBuffered(textHandler, lh.WithErrorOutput(io.Discard))
		defer handler.Close()

		if handler.Config().BatchSize != 100 {
			t.Errorf("Expected default BatchSize=100, got %d", handler.Config().BatchSize)
		}
		if handler.Config().FlushInterval != 10*time.Second {
			t.Errorf("Expected default FlushInterval=10s, got %v", handler.Config().FlushInterval)
		}
		if handler.Config().MaxBuffer != 1000 {
			t.Errorf("Expected default MaxBuffer=1000, got %d", handler.Config().MaxBuffer)
		}
	})

	t.Run("CustomOptions", func(t *testing.T) {
		textHandler := lh.NewTextHandler(&safeBuffer{})

		var called atomic.Bool
		handler := lh.NewBuffered(textHandler,
			lh.WithBatchSize(50),
			lh.WithFlushInterval(5*time.Second),
			lh.WithMaxBuffer(500),
			lh.WithOverflowHandler(func(int) { called.Store(true) }),
			lh.WithErrorOutput(io.Discard),
		)
		defer handler.Close()

		if handler.Config().BatchSize != 50 {
			t.Errorf("Expected BatchSize=50, got %d", handler.Config().BatchSize)
		}
		if handler.Config().FlushInterval != 5*time.Second {
			t.Errorf("Expected FlushInterval=5s, got %v", handler.Config().FlushInterval)
		}
		if handler.Config().MaxBuffer != 500 {
			t.Errorf("Expected MaxBuffer=500, got %d", handler.Config().MaxBuffer)
		}

		handler.Config().OnOverflow(1)
		if !called.Load() {
			t.Error("Expected overflow handler to be called")
		}
	})
}

func TestBufferedHandlerEdgeCases(t *testing.T) {
	t.Run("ZeroBatchSize", func(t *testing.T) {
		textHandler := lh.NewTextHandler(&safeBuffer{})
		handler := lh.NewBuffered(textHandler, lh.WithBatchSize(0), lh.WithErrorOutput(io.Discard))
		defer handler.Close()

		if handler.Config().BatchSize != 1 {
			t.Errorf("Expected BatchSize to be adjusted to 1, got %d", handler.Config().BatchSize)
		}
	})

	t.Run("NegativeFlushInterval", func(t *testing.T) {
		textHandler := lh.NewTextHandler(&safeBuffer{})
		handler := lh.NewBuffered(textHandler, lh.WithFlushInterval(-1*time.Second))
		defer handler.Close()

		if handler.Config().FlushInterval != 10*time.Second {
			t.Errorf("Expected FlushInterval to be adjusted to 10s, got %v", handler.Config().FlushInterval)
		}
	})

	t.Run("SmallMaxBuffer", func(t *testing.T) {
		textHandler := lh.NewTextHandler(&safeBuffer{})
		handler := lh.NewBuffered(textHandler,
			lh.WithBatchSize(10),
			lh.WithMaxBuffer(5),
			lh.WithErrorOutput(io.Discard),
		)
		defer handler.Close()

		if handler.Config().MaxBuffer < handler.Config().BatchSize {
			t.Errorf("Expected MaxBuffer >= BatchSize, got %d < %d",
				handler.Config().MaxBuffer, handler.Config().BatchSize)
		}
	})
}

func TestBufferedHandlerIntegration(t *testing.T) {
	t.Run("WithTextHandler", func(t *testing.T) {
		buf := &safeBuffer{}
		textHandler := lh.NewTextHandler(buf)
		handler := lh.NewBuffered(textHandler,
			lh.WithBatchSize(2),
			lh.WithFlushInterval(50*time.Millisecond),
			lh.WithErrorOutput(io.Discard),
		)

		_ = handler.Handle(&lx.Entry{Message: "message1"})
		_ = handler.Handle(&lx.Entry{Message: "message2"})

		ok := waitUntil(500*time.Millisecond, func() bool {
			out := buf.String()
			return strings.Contains(out, "message1") && strings.Contains(out, "message2")
		})

		_ = handler.Close()

		if !ok {
			t.Fatalf("Expected both messages in output, got: %q", buf.String())
		}
	})

	t.Run("WithJSONHandler", func(t *testing.T) {
		buf := &safeBuffer{}
		jsonHandler := lh.NewJSONHandler(buf)
		handler := lh.NewBuffered(jsonHandler, lh.WithBatchSize(2))

		_ = handler.Handle(&lx.Entry{Message: "message1"})
		_ = handler.Handle(&lx.Entry{Message: "message2"})
		handler.Flush()

		_ = handler.Close() // Ensure no concurrent writes during decode.

		dec := json.NewDecoder(strings.NewReader(buf.String()))
		count := 0
		for dec.More() {
			var obj map[string]interface{}
			if err := dec.Decode(&obj); err != nil {
				t.Fatalf("Failed to decode JSON: %v", err)
			}
			count++
		}
		if count != 2 {
			t.Fatalf("Expected 2 JSON objects, got %d", count)
		}
	})
}

// Ensure the os import is used (kept for parity with original file).
var _ = os.Stderr