package pwalk

import (
	"errors"
	"math/rand"
	"os"
	"path/filepath"
	"runtime"
	"sync/atomic"
	"testing"
	"time"
)

func TestWalk(t *testing.T) {
	var ac atomic.Uint32
	concurrency := runtime.NumCPU() * 2

	dir, total := prepareTestSet(t, 3, 2, 1)

	err := WalkN(dir,
		func(_ string, _ os.FileInfo, _ error) error {
			ac.Add(1)
			return nil
		},
		concurrency)
	if err != nil {
		t.Errorf("Walk failed: %v", err)
	}
	count := ac.Load()
	if count != total {
		t.Errorf("File count mismatch: found %d, expected %d", count, total)
	}

	t.Logf("concurrency: %d, files found: %d", concurrency, count)
}

func TestWalkTopLevelErrNotExistNotIgnored(t *testing.T) {
	if WalkN("non-existent-directory", cbEmpty, 8) == nil {
		t.Fatal("expected ErrNotExist, got nil")
	}
}

// https://github.com/opencontainers/selinux/issues/199
func TestWalkRaceWithRemoval(t *testing.T) {
	var ac atomic.Uint32
	concurrency := runtime.NumCPU() * 2
	// This test is still on a best-effort basis, meaning it can still pass
	// when there is a bug in the code, but the larger the test set is, the
	// higher the probability that this test fails (without a fix).
	//
	// With this set (4, 5, 6), and the fix commented out, it fails
	// 100 out of 100 runs on my machine.
	dir, total := prepareTestSet(t, 4, 5, 6)

	// Race walk with removal.
	go os.RemoveAll(dir)
	err := WalkN(dir,
		func(_ string, _ os.FileInfo, _ error) error {
			ac.Add(1)
			return nil
		},
		concurrency)
	count := int(ac.Load())
	t.Logf("found %d of %d files", count, total)
	if err != nil {
		t.Fatalf("expected nil, got %v", err)
	}
}

func TestWalkDirManyErrors(t *testing.T) {
	var ac atomic.Uint32

	dir, total := prepareTestSet(t, 3, 3, 2)

	maxFiles := total / 2
	e42 := errors.New("42")
	err := Walk(dir,
		func(_ string, _ os.FileInfo, _ error) error {
			if ac.Add(1) > maxFiles {
				return e42
			}
			return nil
		})
	count := ac.Load()
	t.Logf("found %d of %d files", count, total)

	if err == nil {
		t.Errorf("Walk succeeded, but error is expected")
		if count != total {
			t.Errorf("File count mismatch: found %d, expected %d", count, total)
		}
	}
}

func makeManyDirs(prefix string, levels, dirs, files int) (count uint32, err error) {
	for d := 0; d < dirs; d++ {
		var dir string
		dir, err = os.MkdirTemp(prefix, "d-")
		if err != nil {
			return count, err
		}
		count++
		for f := 0; f < files; f++ {
			var fi *os.File
			fi, err = os.CreateTemp(dir, "f-")
			if err != nil {
				return count, err
			}
			_ = fi.Close()
			count++
		}
		if levels == 0 {
			continue
		}
		var c uint32
		if c, err = makeManyDirs(dir, levels-1, dirs, files); err != nil {
			return count, err
		}
		count += c
	}

	return count, err
}

// prepareTestSet() creates a directory tree of shallow files,
// to be used for testing or benchmarking.
//
// Total dirs: dirs^levels + dirs^(levels-1) + ... + dirs^1
// Total files: total_dirs * files
func prepareTestSet(tb testing.TB, levels, dirs, files int) (dir string, total uint32) {
	tb.Helper()
	var err error

	dir = tb.TempDir()
	total, err = makeManyDirs(dir, levels, dirs, files)
	if err != nil {
		tb.Fatal(err)
	}
	total++ // this dir

	return dir, total
}

type walkerFunc func(root string, walkFn WalkFunc) error

func genWalkN(n int) walkerFunc {
	return func(root string, walkFn WalkFunc) error {
		return WalkN(root, walkFn, n)
	}
}

func BenchmarkWalk(b *testing.B) {
	const (
		levels = 5 // how deep
		dirs   = 3 // dirs on each levels
		files  = 8 // files on each levels
	)

	benchmarks := []struct {
		walk filepath.WalkFunc
		name string
	}{
		{name: "Empty", walk: cbEmpty},
		{name: "ReadFile", walk: cbReadFile},
		{name: "ChownChmod", walk: cbChownChmod},
		{name: "RandomSleep", walk: cbRandomSleep},
	}

	walkers := []struct {
		walker walkerFunc
		name   string
	}{
		{name: "filepath.Walk", walker: filepath.Walk},
		{name: "pwalk.Walk", walker: Walk},
		// test WalkN with various values of N
		{name: "pwalk.Walk1", walker: genWalkN(1)},
		{name: "pwalk.Walk2", walker: genWalkN(2)},
		{name: "pwalk.Walk4", walker: genWalkN(4)},
		{name: "pwalk.Walk8", walker: genWalkN(8)},
		{name: "pwalk.Walk16", walker: genWalkN(16)},
		{name: "pwalk.Walk32", walker: genWalkN(32)},
		{name: "pwalk.Walk64", walker: genWalkN(64)},
		{name: "pwalk.Walk128", walker: genWalkN(128)},
		{name: "pwalk.Walk256", walker: genWalkN(256)},
	}

	dir, total := prepareTestSet(b, levels, dirs, files)
	b.Logf("dataset: %d levels x %d dirs x %d files, total entries: %d", levels, dirs, files, total)

	for _, bm := range benchmarks {
		for _, w := range walkers {
			walker := w.walker
			walkFn := bm.walk
			// preheat
			if err := w.walker(dir, bm.walk); err != nil {
				b.Errorf("walk failed: %v", err)
			}
			// benchmark
			b.Run(bm.name+"/"+w.name, func(b *testing.B) {
				for i := 0; i < b.N; i++ {
					if err := walker(dir, walkFn); err != nil {
						b.Errorf("walk failed: %v", err)
					}
				}
			})
		}
	}
}

func cbEmpty(_ string, _ os.FileInfo, _ error) error {
	return nil
}

func cbChownChmod(path string, info os.FileInfo, _ error) error {
	_ = os.Chown(path, 0, 0)
	mode := os.FileMode(0o644)
	if info.Mode().IsDir() {
		mode = os.FileMode(0o755)
	}
	_ = os.Chmod(path, mode)

	return nil
}

func cbReadFile(path string, info os.FileInfo, _ error) error {
	var err error
	if info.Mode().IsRegular() {
		_, err = os.ReadFile(path)
	}
	return err
}

func cbRandomSleep(_ string, _ os.FileInfo, _ error) error {
	time.Sleep(time.Duration(rand.Intn(500)) * time.Microsecond) //nolint:gosec // ignore G404: Use of weak random number generator
	return nil
}
