package browser

import (
	"fmt"
	"os"
	"path/filepath"
	"testing"
	"time"
)

// --- Fixture setup ---

type testEntry struct {
	name  string
	isDir bool
	size  int64
}

func setupTestDir(t *testing.T, entries []testEntry) string {
	t.Helper()
	dir := t.TempDir()

	for _, e := range entries {
		path := filepath.Join(dir, e.name)
		if e.isDir {
			err := os.Mkdir(path, 0755)
			if err != nil {
				t.Fatalf("failed to create dir %s: %v", e.name, err)
			}
		} else {
			err := os.WriteFile(path, make([]byte, e.size), 0644)
			if err != nil {
				t.Fatalf("failed to create file %s: %v", e.name, err)
			}
		}
	}
	return dir
}

// --- Test: Build Index - Empty Dir ---

func TestBuildIndex_EmptyDir(t *testing.T) {
	dir := setupTestDir(t, nil)

	idx, err := buildIndex(dir)
	if err != nil {
		t.Fatalf("buildIndex(empty) returned error: %v", err)
	}
	if idx.EntryCount != 0 {
		t.Errorf("expected EntryCount=0, got %d", idx.EntryCount)
	}
	if len(idx.Entries) != 0 {
		t.Errorf("expected 0 entries, got %d", len(idx.Entries))
	}
}

// --- Test: Build Index - Unsorted (raw metadata) ---
// Per design: index stores raw metadata; sorting happens at page-load time.

func TestBuildIndex_UnsortedRawMetadata(t *testing.T) {
	dir := setupTestDir(t, []testEntry{
		{name: "Zebra.txt", size: 100},
		{name: "apple.txt", size: 200},
		{name: "Banana.txt", size: 300},
		{name: "cherry.txt", size: 400},
	})

	idx, err := buildIndex(dir)
	if err != nil {
		t.Fatalf("buildIndex returned error: %v", err)
	}

	// Index should contain all entries (order not guaranteed - raw metadata)
	if len(idx.Entries) != 4 {
		t.Fatalf("expected 4 entries, got %d", len(idx.Entries))
	}

	// Verify all entries are present (regardless of order)
	names := make(map[string]bool)
	for _, e := range idx.Entries {
		names[e.Name] = true
	}
	for _, want := range []string{"Zebra.txt", "apple.txt", "Banana.txt", "cherry.txt"} {
		if !names[want] {
			t.Errorf("expected entry %q not found in index", want)
		}
	}
}

// --- Test: Build Index - Dirs and Files Both Present ---
// Per design: index stores raw metadata; dir/file ordering happens at page-load time.

func TestBuildIndex_DirsAndFilesPresent(t *testing.T) {
	dir := setupTestDir(t, []testEntry{
		{name: "file.txt", size: 100},
		{name: "adir", isDir: true},
		{name: "another.txt", size: 200},
		{name: "bdir", isDir: true},
	})

	idx, err := buildIndex(dir)
	if err != nil {
		t.Fatalf("buildIndex returned error: %v", err)
	}

	// Both dirs and files should be present
	var gotDirs, gotFiles int
	for _, e := range idx.Entries {
		if e.IsDir {
			gotDirs++
		} else {
			gotFiles++
		}
	}
	if gotDirs != 2 {
		t.Errorf("expected 2 directories, got %d", gotDirs)
	}
	if gotFiles != 2 {
		t.Errorf("expected 2 files, got %d", gotFiles)
	}
}

// --- Test: Build Index - Cache Written ---

func TestBuildIndex_CacheWritten(t *testing.T) {
	dir := setupTestDir(t, []testEntry{
		{name: "test.txt", size: 100},
	})

	_, err := buildIndex(dir)
	if err != nil {
		t.Fatalf("buildIndex returned error: %v", err)
	}

	// Verify cache file exists
	cachePath := getCachePath(dir)
	if _, err := os.Stat(cachePath); os.IsNotExist(err) {
		t.Errorf("expected cache file at %s, but it does not exist", cachePath)
	}
}

// --- Test: Build Index - Cache Invalidated On Mtime Change ---

func TestBuildIndex_CacheInvalidatedOnMtimeChange(t *testing.T) {
	dir := setupTestDir(t, []testEntry{
		{name: "test.txt", size: 100},
	})

	// First build
	idx1, err := buildIndex(dir)
	if err != nil {
		t.Fatalf("first buildIndex returned error: %v", err)
	}

	// Modify directory (add a file)
	newFile := filepath.Join(dir, "newfile.txt")
	if err := os.WriteFile(newFile, []byte("new"), 0644); err != nil {
		t.Fatalf("failed to create new file: %v", err)
	}

	// Second build should detect change and rebuild
	idx2, err := buildIndex(dir)
	if err != nil {
		t.Fatalf("second buildIndex returned error: %v", err)
	}

	if idx2.EntryCount <= idx1.EntryCount {
		t.Errorf("expected entry count to increase after adding file; before=%d, after=%d",
			idx1.EntryCount, idx2.EntryCount)
	}
}

// --- Test: Build Index - Cache Reused When Unchanged ---

func TestBuildIndex_CacheReusedWhenUnchanged(t *testing.T) {
	dir := setupTestDir(t, []testEntry{
		{name: "test.txt", size: 100},
	})

	// First build
	idx1, err := buildIndex(dir)
	if err != nil {
		t.Fatalf("first buildIndex returned error: %v", err)
	}

	// Second build (no changes)
	idx2, err := buildIndex(dir)
	if err != nil {
		t.Fatalf("second buildIndex returned error: %v", err)
	}

	if idx1.EntryCount != idx2.EntryCount {
		t.Errorf("expected same entry count; first=%d, second=%d",
			idx1.EntryCount, idx2.EntryCount)
	}
}

// --- Test: Build Index - Large Directory ---

func TestBuildIndex_LargeDirectory(t *testing.T) {
	const count = 10000
	entries := make([]testEntry, count)
	for i := 0; i < count; i++ {
		entries[i] = testEntry{
			name: fmt.Sprintf("file_%05d.txt", i),
			size: int64(i * 10),
		}
	}
	dir := setupTestDir(t, entries)

	start := time.Now()
	idx, err := buildIndex(dir)
	elapsed := time.Since(start)

	if err != nil {
		t.Fatalf("buildIndex returned error: %v", err)
	}
	if idx.EntryCount != count {
		t.Errorf("expected %d entries, got %d", count, idx.EntryCount)
	}

	// Time budget: 5 seconds for 10k entries
	if elapsed > 5*time.Second {
		t.Errorf("buildIndex took %v, expected < 5s", elapsed)
	}
}