package dev

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"sync/atomic"
	"syscall"
	"testing"
	"time"
)

func TestWatchRebuildsOnSourceEdit(t *testing.T) {
	dir := t.TempDir()
	writeWatchApp(t, dir)

	var out bytes.Buffer
	var builds atomic.Int32
	var starts atomic.Int32

	ctx, cancel := context.WithCancel(t.Context())
	defer cancel()

	opts := Options{
		Debounce: 40 * time.Millisecond,
		Build: func(ctx context.Context, appDir string, w io.Writer) error {
			builds.Add(1)
			fmt.Fprintln(w, "built hello in 1ms")
			return nil
		},
		Start: func(ctx context.Context, binPath string, stdout, stderr io.Writer) (*exec.Cmd, error) {
			starts.Add(1)
			cmd := exec.Command("sleep", "30")
			if err := cmd.Start(); err != nil {
				return nil, err
			}
			return cmd, nil
		},
	}

	done := make(chan error, 1)
	go func() { done <- watch(ctx, dir, &out, opts) }()

	waitUntil(t, "initial start", func() bool { return starts.Load() == 1 })
	if builds.Load() != 1 {
		t.Fatalf("initial builds = %d", builds.Load())
	}

	if err := os.WriteFile(filepath.Join(dir, "plugin.go"), []byte("package p\n// edited\n"), 0o644); err != nil {
		t.Fatal(err)
	}
	waitUntil(t, "restart after edit", func() bool { return starts.Load() == 2 })
	if builds.Load() != 2 {
		t.Fatalf("builds after edit = %d", builds.Load())
	}

	if err := os.WriteFile(filepath.Join(dir, "plugins.gen.go"), []byte("package main\n// generated\n"), 0o644); err != nil {
		t.Fatal(err)
	}
	if err := os.WriteFile(filepath.Join(dir, "main.go"), []byte("package main\n// generated\n"), 0o644); err != nil {
		t.Fatal(err)
	}
	time.Sleep(200 * time.Millisecond)
	if starts.Load() != 2 || builds.Load() != 2 {
		t.Fatalf("generated files triggered rebuild starts=%d builds=%d", starts.Load(), builds.Load())
	}

	got := out.String()
	if strings.Count(got, "rebuild:") != 2 {
		t.Fatalf("want 2 rebuild latency lines, got %q", got)
	}

	cancel()
	select {
	case err := <-done:
		if err != nil && err != context.Canceled {
			t.Fatalf("watch exit: %v", err)
		}
	case <-time.After(3 * time.Second):
		t.Fatal("watch did not exit on cancel")
	}
}

func TestWatchKeepsChildOnBuildFailure(t *testing.T) {
	dir := t.TempDir()
	writeWatchApp(t, dir)

	var out bytes.Buffer
	var builds atomic.Int32
	var starts atomic.Int32
	var pid atomic.Int32

	ctx, cancel := context.WithCancel(t.Context())
	defer cancel()

	opts := Options{
		Debounce: 40 * time.Millisecond,
		Build: func(ctx context.Context, appDir string, w io.Writer) error {
			n := builds.Add(1)
			if n >= 2 {
				return fmt.Errorf("compile failed")
			}
			return nil
		},
		Start: func(ctx context.Context, binPath string, stdout, stderr io.Writer) (*exec.Cmd, error) {
			starts.Add(1)
			cmd := exec.Command("sleep", "30")
			if err := cmd.Start(); err != nil {
				return nil, err
			}
			pid.Store(int32(cmd.Process.Pid))
			return cmd, nil
		},
	}

	done := make(chan error, 1)
	go func() { done <- watch(ctx, dir, &out, opts) }()
	waitUntil(t, "initial start", func() bool { return starts.Load() == 1 })

	if err := os.WriteFile(filepath.Join(dir, "plugin.go"), []byte("package p\n// bad\n"), 0o644); err != nil {
		t.Fatal(err)
	}
	waitUntil(t, "failed rebuild", func() bool { return builds.Load() >= 2 })
	time.Sleep(80 * time.Millisecond)
	if starts.Load() != 1 {
		t.Fatalf("build failure restarted child: starts=%d", starts.Load())
	}
	if !strings.Contains(out.String(), "compile failed") {
		t.Fatalf("missing build error: %s", out.String())
	}
	proc, err := os.FindProcess(int(pid.Load()))
	if err != nil {
		t.Fatal(err)
	}
	if err := proc.Signal(syscall.Signal(0)); err != nil {
		t.Fatalf("child was reaped after failed build: %v", err)
	}

	cancel()
	select {
	case <-done:
	case <-time.After(3 * time.Second):
		t.Fatal("watch did not exit")
	}
	deadline := time.Now().Add(2 * time.Second)
	for time.Now().Before(deadline) {
		if err := proc.Signal(syscall.Signal(0)); err != nil {
			return
		}
		time.Sleep(20 * time.Millisecond)
	}
	t.Fatal("child still running after cancel")
}

func writeWatchApp(t *testing.T, dir string) {
	t.Helper()
	write(t, filepath.Join(dir, "summer.yaml"), "module: example.com/app\nbinary: hello\nplugins:\n  - id: a.b\n    module: example.com/app/plugins/demo\n")
	write(t, filepath.Join(dir, "plugin.go"), "package p\n")
	write(t, filepath.Join(dir, "main.go"), "package main\n")
	write(t, filepath.Join(dir, "plugins.gen.go"), "package main\n")
}

func write(t *testing.T, path, body string) {
	t.Helper()
	if err := os.WriteFile(path, []byte(body), 0o644); err != nil {
		t.Fatal(err)
	}
}

func waitUntil(t *testing.T, name string, ok func() bool) {
	t.Helper()
	deadline := time.Now().Add(3 * time.Second)
	for time.Now().Before(deadline) {
		if ok() {
			return
		}
		time.Sleep(15 * time.Millisecond)
	}
	t.Fatalf("timed out waiting for %s", name)
}