package app

import (
	"archive/zip"
	"bytes"
	"io"
	"os"
	"path/filepath"
	"sort"
	"testing"
	"time"
)

func writeTestFile(t *testing.T, path string, content string, mtime time.Time) {
	t.Helper()
	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
		t.Fatalf("mkdir: %v", err)
	}
	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
		t.Fatalf("write: %v", err)
	}
	if err := os.Chtimes(path, mtime, mtime); err != nil {
		t.Fatalf("chtimes: %v", err)
	}
}

func readZipEntries(t *testing.T, path string) map[string]string {
	t.Helper()
	r, err := zip.OpenReader(path)
	if err != nil {
		t.Fatalf("open zip %s: %v", path, err)
	}
	defer r.Close()
	out := map[string]string{}
	for _, f := range r.File {
		rc, err := f.Open()
		if err != nil {
			t.Fatalf("open entry %s: %v", f.Name, err)
		}
		data, err := io.ReadAll(rc)
		rc.Close()
		if err != nil {
			t.Fatalf("read entry %s: %v", f.Name, err)
		}
		out[f.Name] = string(data)
	}
	return out
}

func TestBuildZipArchiveRoundTrip(t *testing.T) {
	root := t.TempDir()
	mtime := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
	writeTestFile(t, filepath.Join(root, "a.txt"), "hello", mtime)
	writeTestFile(t, filepath.Join(root, "sub", "b.txt"), "world", mtime)

	dest := filepath.Join(t.TempDir(), "out.zip")
	if err := buildZipArchive(root, dest); err != nil {
		t.Fatalf("buildZipArchive: %v", err)
	}

	entries := readZipEntries(t, dest)
	if entries["a.txt"] != "hello" || entries["sub/b.txt"] != "world" {
		t.Fatalf("entries=%+v", entries)
	}
}

func TestBuildZipArchiveDeterministicWhenUnchanged(t *testing.T) {
	root := t.TempDir()
	mtime := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
	writeTestFile(t, filepath.Join(root, "a.txt"), "hello", mtime)
	writeTestFile(t, filepath.Join(root, "b.txt"), "world", mtime)

	dir := t.TempDir()
	p1 := filepath.Join(dir, "one.zip")
	p2 := filepath.Join(dir, "two.zip")
	if err := buildZipArchive(root, p1); err != nil {
		t.Fatalf("build 1: %v", err)
	}
	if err := buildZipArchive(root, p2); err != nil {
		t.Fatalf("build 2: %v", err)
	}
	b1, _ := os.ReadFile(p1)
	b2, _ := os.ReadFile(p2)
	if !bytes.Equal(b1, b2) {
		t.Fatalf("two builds of an unchanged tree produced different bytes (len %d vs %d)", len(b1), len(b2))
	}
}

func TestPatchArchiveOnTargetIncrementalAndValid(t *testing.T) {
	root := t.TempDir()
	mtime := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
	writeTestFile(t, filepath.Join(root, "static.txt"), "does not change", mtime)
	writeTestFile(t, filepath.Join(root, "growing.txt"), "cycle-1 line\n", mtime)

	work := t.TempDir()
	cachedPath := filepath.Join(work, "cache.zip")
	newPath := filepath.Join(work, "new.zip")
	targetPath := filepath.Join(work, "target.zip")

	// Cycle 1: cold start, no cache, no target yet.
	if err := buildZipArchive(root, newPath); err != nil {
		t.Fatalf("build cycle1: %v", err)
	}
	if err := patchArchiveOnTarget(targetPath, newPath, cachedPath); err != nil {
		t.Fatalf("patch cycle1: %v", err)
	}
	if err := os.Rename(newPath, cachedPath); err != nil {
		t.Fatalf("rename cycle1: %v", err)
	}

	want1, _ := os.ReadFile(cachedPath)
	got1, _ := os.ReadFile(targetPath)
	if !bytes.Equal(want1, got1) {
		t.Fatalf("cycle1: target does not match freshly built zip")
	}
	entries1 := readZipEntries(t, targetPath)
	if entries1["static.txt"] != "does not change" || entries1["growing.txt"] != "cycle-1 line\n" {
		t.Fatalf("cycle1 entries=%+v", entries1)
	}

	// Cycle 2: only growing.txt changes (as it would with an appended log).
	writeTestFile(t, filepath.Join(root, "growing.txt"), "cycle-1 line\ncycle-2 line\n", mtime.Add(time.Minute))

	if err := buildZipArchive(root, newPath); err != nil {
		t.Fatalf("build cycle2: %v", err)
	}
	prefixLen, err := commonPrefixLen(cachedPath, newPath)
	if err != nil {
		t.Fatalf("commonPrefixLen: %v", err)
	}
	newInfo, _ := os.Stat(newPath)
	if prefixLen <= 0 {
		t.Fatalf("expected a nonzero unchanged prefix (static.txt entry should be identical), got %d", prefixLen)
	}
	if prefixLen >= newInfo.Size() {
		t.Fatalf("expected the changed growing.txt entry to make the archives diverge before EOF, prefixLen=%d size=%d", prefixLen, newInfo.Size())
	}

	if err := patchArchiveOnTarget(targetPath, newPath, cachedPath); err != nil {
		t.Fatalf("patch cycle2: %v", err)
	}
	if err := os.Rename(newPath, cachedPath); err != nil {
		t.Fatalf("rename cycle2: %v", err)
	}

	want2, _ := os.ReadFile(cachedPath)
	got2, _ := os.ReadFile(targetPath)
	if !bytes.Equal(want2, got2) {
		t.Fatalf("cycle2: target does not match freshly built zip after incremental patch")
	}
	entries2 := readZipEntries(t, targetPath)
	if entries2["growing.txt"] != "cycle-1 line\ncycle-2 line\n" {
		t.Fatalf("cycle2 growing.txt=%q", entries2["growing.txt"])
	}
	if entries2["static.txt"] != "does not change" {
		t.Fatalf("cycle2 static.txt=%q", entries2["static.txt"])
	}
}

func TestPatchArchiveOnTargetFallsBackOnDrift(t *testing.T) {
	root := t.TempDir()
	mtime := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
	writeTestFile(t, filepath.Join(root, "a.txt"), "hello", mtime)

	work := t.TempDir()
	cachedPath := filepath.Join(work, "cache.zip")
	newPath := filepath.Join(work, "new.zip")
	targetPath := filepath.Join(work, "target.zip")

	if err := buildZipArchive(root, newPath); err != nil {
		t.Fatalf("build: %v", err)
	}
	if err := patchArchiveOnTarget(targetPath, newPath, cachedPath); err != nil {
		t.Fatalf("patch: %v", err)
	}
	if err := os.Rename(newPath, cachedPath); err != nil {
		t.Fatalf("rename: %v", err)
	}

	// Simulate drift: something external truncated/replaced the target file
	// so its size no longer matches what our local cache expects.
	if err := os.WriteFile(targetPath, []byte("garbage"), 0644); err != nil {
		t.Fatalf("simulate drift: %v", err)
	}

	writeTestFile(t, filepath.Join(root, "a.txt"), "hello again", mtime.Add(time.Minute))
	if err := buildZipArchive(root, newPath); err != nil {
		t.Fatalf("build2: %v", err)
	}
	if err := patchArchiveOnTarget(targetPath, newPath, cachedPath); err != nil {
		t.Fatalf("patch2: %v", err)
	}

	want, _ := os.ReadFile(newPath)
	got, _ := os.ReadFile(targetPath)
	if !bytes.Equal(want, got) {
		t.Fatalf("expected drift to trigger a full rewrite, target still corrupt/stale")
	}
	entries := readZipEntries(t, targetPath)
	if entries["a.txt"] != "hello again" {
		t.Fatalf("entries=%+v", entries)
	}
}

func TestCommonPrefixLenSortedIndependent(t *testing.T) {
	// Sanity check that WalkDir's lexical ordering means entry order in the
	// zip doesn't depend on directory-read order — build twice from the same
	// tree and expect the entry name list to already come out sorted.
	root := t.TempDir()
	mtime := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
	names := []string{"z.txt", "a.txt", "m/one.txt", "m/two.txt"}
	for _, n := range names {
		writeTestFile(t, filepath.Join(root, n), n, mtime)
	}
	dest := filepath.Join(t.TempDir(), "out.zip")
	if err := buildZipArchive(root, dest); err != nil {
		t.Fatalf("build: %v", err)
	}
	r, err := zip.OpenReader(dest)
	if err != nil {
		t.Fatalf("open: %v", err)
	}
	defer r.Close()
	var got []string
	for _, f := range r.File {
		got = append(got, f.Name)
	}
	sorted := append([]string(nil), got...)
	sort.Strings(sorted)
	for i := range got {
		if got[i] != sorted[i] {
			t.Fatalf("entries not in lexical order: %v", got)
		}
	}
}