package apt

import (
	"bytes"
	"compress/gzip"
	"os"
	"path/filepath"
	"strings"
	"testing"
)

var testCfg = Config{
	Suite:         "bookworm",
	Components:    []string{"main"},
	Architectures: []string{"amd64"},
}

// buildPackagesGz creates a gzipped Packages file from a list of stanzas.
func buildPackagesGz(t *testing.T, stanzas []string) []byte {
	t.Helper()
	plain := []byte(strings.Join(stanzas, "\n\n") + "\n")

	var buf bytes.Buffer
	gzw := gzip.NewWriter(&buf)
	gzw.Write(plain)
	gzw.Close()
	return buf.Bytes()
}

func makeStanza(pkg, version, filename, sha256 string, size int) string {
	return strings.Join([]string{
		"Package: " + pkg,
		"Version: " + version,
		"Architecture: amd64",
		"Filename: " + filename,
		"SHA256: " + sha256,
		"Size: " + itoa(size),
	}, "\n")
}

func itoa(n int) string {
	if n == 0 {
		return "0"
	}
	buf := make([]byte, 0, 10)
	for n > 0 {
		buf = append([]byte{byte('0' + n%10)}, buf...)
		n /= 10
	}
	return string(buf)
}

// setupAptRepo creates the directory structure and writes the upstream
// Packages.gz for component/arch. It creates the given deb files on disk.
func setupAptRepo(t *testing.T, stanzas []string, presentOnDisk []string) string {
	t.Helper()
	dir := t.TempDir()

	binDir := filepath.Join(dir, "dists", testCfg.Suite, "main", "binary-amd64")
	os.MkdirAll(binDir, 0o755)
	os.MkdirAll(filepath.Join(dir, "pool"), 0o755)

	// Write upstream Packages.gz.
	gzData := buildPackagesGz(t, stanzas)
	if err := os.WriteFile(filepath.Join(binDir, upstreamPackagesGz), gzData, 0o644); err != nil {
		t.Fatalf("write upstream Packages.gz: %v", err)
	}

	// Create selected deb files on disk.
	for _, filename := range presentOnDisk {
		dest := filepath.Join(dir, filepath.FromSlash(filename))
		os.MkdirAll(filepath.Dir(dest), 0o755)
		if err := os.WriteFile(dest, []byte("fake-deb"), 0o644); err != nil {
			t.Fatalf("write deb %s: %v", filename, err)
		}
	}

	return dir
}

// readLocalPackages reads and parses the local Packages file (plain text).
func readLocalPackages(t *testing.T, dir string) []DebPackage {
	t.Helper()
	path := filepath.Join(dir, "dists", testCfg.Suite, "main", "binary-amd64", "Packages")
	data, err := os.ReadFile(path)
	if err != nil {
		t.Fatalf("read Packages: %v", err)
	}
	pkgs, err := ParsePackages(data)
	if err != nil {
		t.Fatalf("parse Packages: %v", err)
	}
	return pkgs
}

// --- InitEmptyRepo ---

func TestInitEmptyRepo_createsStructure(t *testing.T) {
	dir := t.TempDir()
	if err := InitEmptyRepo(dir, testCfg); err != nil {
		t.Fatalf("InitEmptyRepo: %v", err)
	}

	for _, path := range []string{
		filepath.Join(dir, "pool"),
		filepath.Join(dir, "dists", testCfg.Suite),
		filepath.Join(dir, "dists", testCfg.Suite, "main", "binary-amd64"),
		filepath.Join(dir, "dists", testCfg.Suite, "Release"),
	} {
		if _, err := os.Stat(path); err != nil {
			t.Errorf("expected %s to exist: %v", path, err)
		}
	}
}

func TestInitEmptyRepo_releaseIsParseable(t *testing.T) {
	dir := t.TempDir()
	InitEmptyRepo(dir, testCfg)

	data, _ := os.ReadFile(filepath.Join(dir, "dists", testCfg.Suite, "Release"))
	rf, err := ParseRelease(data)
	if err != nil {
		t.Fatalf("ParseRelease on generated file: %v", err)
	}
	if rf.Suite != testCfg.Suite {
		t.Errorf("Suite: got %q, want %q", rf.Suite, testCfg.Suite)
	}
}

func TestInitEmptyRepo_idempotent(t *testing.T) {
	dir := t.TempDir()
	InitEmptyRepo(dir, testCfg)

	releaseBefore, _ := os.ReadFile(filepath.Join(dir, "dists", testCfg.Suite, "Release"))
	InitEmptyRepo(dir, testCfg) // second call
	releaseAfter, _ := os.ReadFile(filepath.Join(dir, "dists", testCfg.Suite, "Release"))

	if !bytes.Equal(releaseBefore, releaseAfter) {
		t.Error("second InitEmptyRepo modified Release file")
	}
}

// --- RegenerateMetadata ---

func TestRegenerateMetadata_keepsOnlyPresentFiles(t *testing.T) {
	stanzas := []string{
		makeStanza("curl", "7.88", "pool/main/c/curl/curl_7.88_amd64.deb", "aaa", 100),
		makeStanza("wget", "1.21", "pool/main/w/wget/wget_1.21_amd64.deb", "bbb", 200),
		makeStanza("vim", "9.0", "pool/main/v/vim/vim_9.0_amd64.deb", "ccc", 300),
	}
	// Only curl and vim are present.
	present := []string{
		"pool/main/c/curl/curl_7.88_amd64.deb",
		"pool/main/v/vim/vim_9.0_amd64.deb",
	}
	dir := setupAptRepo(t, stanzas, present)

	if err := RegenerateMetadata(dir, testCfg); err != nil {
		t.Fatalf("RegenerateMetadata: %v", err)
	}

	pkgs := readLocalPackages(t, dir)
	if len(pkgs) != 2 {
		t.Fatalf("expected 2 packages, got %d", len(pkgs))
	}
	names := map[string]bool{pkgs[0].Package: true, pkgs[1].Package: true}
	if !names["curl"] {
		t.Error("expected curl in output")
	}
	if !names["vim"] {
		t.Error("expected vim in output")
	}
	if names["wget"] {
		t.Error("wget should be filtered out (not on disk)")
	}
}

func TestRegenerateMetadata_allAbsent(t *testing.T) {
	stanzas := []string{
		makeStanza("curl", "7.88", "pool/main/c/curl/curl_7.88_amd64.deb", "aaa", 100),
	}
	dir := setupAptRepo(t, stanzas, nil) // nothing on disk

	if err := RegenerateMetadata(dir, testCfg); err != nil {
		t.Fatalf("RegenerateMetadata: %v", err)
	}

	pkgs := readLocalPackages(t, dir)
	if len(pkgs) != 0 {
		t.Errorf("expected 0 packages, got %d", len(pkgs))
	}
}

func TestRegenerateMetadata_writesRelease(t *testing.T) {
	stanzas := []string{
		makeStanza("curl", "7.88", "pool/main/c/curl/curl_7.88_amd64.deb", "aaa", 100),
	}
	dir := setupAptRepo(t, stanzas, []string{"pool/main/c/curl/curl_7.88_amd64.deb"})

	if err := RegenerateMetadata(dir, testCfg); err != nil {
		t.Fatalf("RegenerateMetadata: %v", err)
	}

	releasePath := filepath.Join(dir, "dists", testCfg.Suite, "Release")
	data, err := os.ReadFile(releasePath)
	if err != nil {
		t.Fatalf("Release not written: %v", err)
	}

	rf, err := ParseRelease(data)
	if err != nil {
		t.Fatalf("ParseRelease: %v", err)
	}
	if rf.Suite != testCfg.Suite {
		t.Errorf("Suite: got %q, want %q", rf.Suite, testCfg.Suite)
	}
	// Release must reference both Packages and Packages.gz.
	paths := map[string]bool{}
	for _, e := range rf.SHA256 {
		paths[e.Path] = true
	}
	if !paths["main/binary-amd64/Packages"] {
		t.Error("Release missing main/binary-amd64/Packages entry")
	}
	if !paths["main/binary-amd64/Packages.gz"] {
		t.Error("Release missing main/binary-amd64/Packages.gz entry")
	}
}

func TestRegenerateMetadata_writesPackagesGz(t *testing.T) {
	stanzas := []string{
		makeStanza("curl", "7.88", "pool/main/c/curl/curl_7.88_amd64.deb", "aaa", 100),
	}
	dir := setupAptRepo(t, stanzas, []string{"pool/main/c/curl/curl_7.88_amd64.deb"})

	RegenerateMetadata(dir, testCfg)

	gzPath := filepath.Join(dir, "dists", testCfg.Suite, "main", "binary-amd64", "Packages.gz")
	if _, err := os.Stat(gzPath); err != nil {
		t.Errorf("Packages.gz not written: %v", err)
	}
}

func TestRegenerateMetadata_noUpstream_skips(t *testing.T) {
	// No .upstream-Packages.gz — should return nil (skip silently).
	dir := t.TempDir()
	os.MkdirAll(filepath.Join(dir, "dists", testCfg.Suite, "main", "binary-amd64"), 0o755)

	if err := RegenerateMetadata(dir, testCfg); err != nil {
		t.Errorf("expected no error when upstream missing, got: %v", err)
	}
}

func TestRegenerateMetadata_alwaysFiltersFromUpstream(t *testing.T) {
	// Two successive regens must always start from the upstream list.
	stanzas := []string{
		makeStanza("curl", "7.88", "pool/main/c/curl/curl_7.88_amd64.deb", "aaa", 100),
		makeStanza("wget", "1.21", "pool/main/w/wget/wget_1.21_amd64.deb", "bbb", 200),
	}
	dir := setupAptRepo(t, stanzas, []string{"pool/main/c/curl/curl_7.88_amd64.deb"})

	// First regen: only curl.
	RegenerateMetadata(dir, testCfg)
	if len(readLocalPackages(t, dir)) != 1 {
		t.Fatal("first regen: expected 1 package")
	}

	// Add wget, regen again.
	dest := filepath.Join(dir, "pool/main/w/wget/wget_1.21_amd64.deb")
	os.MkdirAll(filepath.Dir(dest), 0o755)
	os.WriteFile(dest, []byte("fake"), 0o644)

	RegenerateMetadata(dir, testCfg)
	pkgs := readLocalPackages(t, dir)
	if len(pkgs) != 2 {
		t.Fatalf("second regen: expected 2 packages, got %d", len(pkgs))
	}
}