// Package appupdate — раздача клиентов через сервер (docs/mobile.md#самообновление):
// сервер читает последний релиз Gitea своим токеном, кэширует ответ и файлы.
package appupdate

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"pipu/api/internal/api/gen"
	"pipu/api/internal/platform/apperr"
	"pipu/api/internal/platform/httpx"
)

// CodeUnavailable — обновления не настроены или релиза с клиентами нет.
const CodeUnavailable = "app.update_unavailable"

const cacheTTL = 10 * time.Minute

// keepClientReleases — сколько последних релизов с файлами отдаём на /download (как prune в CI).
const keepClientReleases = 8

var tagRe = regexp.MustCompile(`^v?(\d+)\.(\d+)\.(\d+)(?:-rc\.(\d+))?$`)

// VersionCode — versionCode по тегу; та же формула, что в scripts/version.mjs:
// MAJOR·1 000 000 + MINOR·10 000 + PATCH·100 + (99 для релиза | N для -rc.N).
func VersionCode(tag string) (string, int, error) {
	m := tagRe.FindStringSubmatch(strings.TrimSpace(tag))
	if m == nil {
		return "", 0, fmt.Errorf("appupdate: not a release tag: %q", tag)
	}
	n := func(s string) int { v, _ := strconv.Atoi(s); return v }
	major, minor, patch := n(m[1]), n(m[2]), n(m[3])
	if minor > 99 || patch > 99 {
		return "", 0, fmt.Errorf("appupdate: minor and patch must be <= 99: %q", tag)
	}
	rc, version := 99, fmt.Sprintf("%d.%d.%d", major, minor, patch)
	if m[4] != "" {
		rc = n(m[4])
		version += "-rc." + m[4]
	}
	return version, major*1_000_000 + minor*10_000 + patch*100 + rc, nil
}

// Config — доступ к Gitea и каталог кэша.
type Config struct {
	GiteaURL     string
	Repo         string // owner/name
	Token        string
	Dir          string // /updates
	MinSupported int
}

type asset struct {
	Name string `json:"name"`
	Size int64  `json:"size"`
	URL  string `json:"browser_download_url"`
}

type release struct {
	Tag         string    `json:"tag_name"`
	Body        string    `json:"body"`
	Draft       bool      `json:"draft"`
	PublishedAt time.Time `json:"published_at"`
	CreatedAt   time.Time `json:"created_at"`
	Assets      []asset   `json:"assets"`
}

type clientFile struct {
	Kind, Name, URL, ChecksumURL, SHA256 string
	Size                                 int64
}

// Latest — сведения о последней версии и файлах клиентов.
type Latest struct {
	Version     string
	VersionCode int
	Notes       string
	Files       map[string]clientFile
}

func (l *Latest) android() (clientFile, bool) {
	f, ok := l.Files["android"]
	return f, ok && f.SHA256 != ""
}

// Handler реализует app-часть gen.StrictServerInterface.
type Handler struct {
	cfg    Config
	client *http.Client
	log    *slog.Logger

	mu       sync.Mutex
	cached   *catalog
	cachedAt time.Time
	dl       sync.Mutex
}

type catalog struct {
	latest *Latest
	all    []*Latest
}

// NewHandler создаёт обработчик.
func NewHandler(cfg Config, log *slog.Logger) *Handler {
	return &Handler{cfg: cfg, client: &http.Client{Timeout: 10 * time.Minute}, log: log}
}

func (h *Handler) configured() bool {
	return h.cfg.GiteaURL != "" && h.cfg.Repo != "" &&
		!strings.Contains(h.cfg.GiteaURL, "example.") && !strings.HasPrefix(h.cfg.Repo, "owner/")
}

func (h *Handler) get(ctx context.Context, url string) (*http.Response, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, err
	}
	if h.cfg.Token != "" {
		req.Header.Set("Authorization", "token "+h.cfg.Token)
	}
	res, err := h.client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("gitea: %w", err)
	}
	if res.StatusCode != http.StatusOK {
		_ = res.Body.Close()
		return nil, fmt.Errorf("gitea: %s: status %d", url, res.StatusCode)
	}
	return res, nil
}

func classifyAsset(name string) string {
	n := strings.ToLower(name)
	if strings.HasSuffix(n, ".sha256") {
		return ""
	}
	switch {
	case strings.HasSuffix(n, ".apk"):
		return "android"
	case strings.HasSuffix(n, ".exe"), strings.HasSuffix(n, ".msi"):
		return "windows"
	case strings.HasSuffix(n, ".appimage"), strings.HasSuffix(n, ".deb"), strings.HasSuffix(n, ".rpm"):
		return "linux"
	case strings.HasSuffix(n, ".dmg"), strings.Contains(n, ".app.tar"):
		return "macos"
	default:
		return ""
	}
}

func assetRank(kind, name string) int {
	n := strings.ToLower(name)
	switch kind {
	case "windows":
		if strings.Contains(n, "setup") {
			return 2
		}
		return 1
	case "linux":
		switch {
		case strings.HasSuffix(n, ".deb"):
			return 3
		case strings.HasSuffix(n, ".rpm"):
			return 2
		default:
			return 1
		}
	default:
		return 1
	}
}

func pickClientFiles(assets []asset) map[string]clientFile {
	sums := map[string]string{}
	for _, a := range assets {
		if strings.HasSuffix(strings.ToLower(a.Name), ".sha256") {
			sums[strings.TrimSuffix(a.Name, ".sha256")] = a.URL
			sums[strings.TrimSuffix(a.Name, ".SHA256")] = a.URL
		}
	}
	out := map[string]clientFile{}
	for _, a := range assets {
		kind := classifyAsset(a.Name)
		if kind == "" {
			continue
		}
		cur, ok := out[kind]
		if ok && assetRank(kind, a.Name) <= assetRank(kind, cur.Name) {
			continue
		}
		out[kind] = clientFile{Kind: kind, Name: a.Name, URL: a.URL, Size: a.Size, ChecksumURL: sums[a.Name]}
	}
	return out
}

func (h *Handler) catalog(ctx context.Context) (*catalog, error) {
	if !h.configured() {
		return nil, apperr.NotFound(CodeUnavailable, "gitea is not configured")
	}
	h.mu.Lock()
	defer h.mu.Unlock()
	if h.cached != nil && time.Since(h.cachedAt) < cacheTTL {
		return h.cached, nil
	}
	ctx, cancel := context.WithTimeout(ctx, 15*time.Second)
	defer cancel()
	base := strings.TrimRight(h.cfg.GiteaURL, "/")
	repo := h.cfg.Repo
	rels, err := h.listReleases(ctx, base, repo)
	if err != nil {
		h.log.WarnContext(ctx, "app update: gitea unavailable", "err", err)
		if h.cached != nil {
			return h.cached, nil
		}
		return nil, apperr.NotFound(CodeUnavailable, "release is unavailable")
	}
	var all []*Latest
	for _, rel := range rels {
		if rel.Draft {
			continue
		}
		l := h.parseRelease(ctx, rel)
		if l == nil {
			continue
		}
		all = append(all, l)
		if len(all) >= keepClientReleases {
			break
		}
	}
	if len(all) == 0 {
		return nil, apperr.NotFound(CodeUnavailable, "release has no client builds")
	}
	cat := &catalog{latest: all[0], all: all}
	h.cached = cat
	h.cachedAt = time.Now()
	return cat, nil
}

func (h *Handler) listReleases(ctx context.Context, base, repo string) ([]release, error) {
	res, err := h.get(ctx, base+"/api/v1/repos/"+repo+"/releases?limit=20")
	if err == nil {
		var rels []release
		decErr := json.NewDecoder(res.Body).Decode(&rels)
		_ = res.Body.Close()
		if decErr != nil {
			return nil, fmt.Errorf("gitea: decode releases: %w", decErr)
		}
		sort.SliceStable(rels, func(i, j int) bool {
			ti, tj := rels[i].PublishedAt, rels[j].PublishedAt
			if ti.IsZero() {
				ti = rels[i].CreatedAt
			}
			if tj.IsZero() {
				tj = rels[j].CreatedAt
			}
			return ti.After(tj)
		})
		return rels, nil
	}
	res, err = h.get(ctx, base+"/api/v1/repos/"+repo+"/releases/latest")
	if err != nil {
		return nil, err
	}
	var rel release
	decErr := json.NewDecoder(res.Body).Decode(&rel)
	_ = res.Body.Close()
	if decErr != nil {
		return nil, fmt.Errorf("gitea: decode release: %w", decErr)
	}
	return []release{rel}, nil
}

func (h *Handler) parseRelease(ctx context.Context, rel release) *Latest {
	version, code, err := VersionCode(rel.Tag)
	if err != nil {
		return nil
	}
	files := pickClientFiles(rel.Assets)
	if len(files) == 0 {
		return nil
	}
	if apk, ok := files["android"]; ok {
		if apk.ChecksumURL == "" {
			delete(files, "android")
		} else if digest, err := h.readDigest(ctx, apk.ChecksumURL); err != nil {
			h.log.WarnContext(ctx, "app update: apk checksum unavailable", "err", err, "version", version)
			delete(files, "android")
		} else {
			apk.SHA256 = digest
			files["android"] = apk
		}
	}
	if len(files) == 0 {
		return nil
	}
	return &Latest{Version: version, VersionCode: code, Notes: rel.Body, Files: files}
}

func (h *Handler) latest(ctx context.Context) (*Latest, error) {
	cat, err := h.catalog(ctx)
	if err != nil {
		return nil, err
	}
	return cat.latest, nil
}

func (c *catalog) release(version string) *Latest {
	for _, l := range c.all {
		if l.Version == version {
			return l
		}
	}
	return nil
}

func (c *catalog) keepNames() map[string]struct{} {
	out := map[string]struct{}{}
	for _, l := range c.all {
		for _, f := range l.Files {
			out[f.Name] = struct{}{}
		}
	}
	return out
}

func (h *Handler) readDigest(ctx context.Context, url string) (string, error) {
	sres, err := h.get(ctx, url)
	if err != nil {
		return "", err
	}
	raw, err := io.ReadAll(io.LimitReader(sres.Body, 256))
	_ = sres.Body.Close()
	if err != nil {
		return "", err
	}
	digest := strings.ToLower(strings.Fields(string(raw) + " x")[0])
	if len(digest) != 64 {
		return "", fmt.Errorf("malformed checksum")
	}
	return digest, nil
}

func (h *Handler) fileURL(kind, version string) string {
	return "/api/v1/app/download/" + kind + "/" + version
}

// GetAppClients реализует gen.StrictServerInterface.
func (h *Handler) GetAppClients(ctx context.Context, _ gen.GetAppClientsRequestObject) (gen.GetAppClientsResponseObject, error) {
	cat, err := h.catalog(ctx)
	if err != nil {
		return nil, err
	}
	l := cat.latest
	order := []string{"windows", "macos", "linux", "android"}
	clients := make([]gen.AppClientFile, 0, len(order))
	for _, kind := range order {
		item, ok := h.clientWithOlder(cat, kind)
		if !ok {
			continue
		}
		clients = append(clients, item)
	}
	if len(clients) == 0 {
		return nil, apperr.NotFound(CodeUnavailable, "release has no client builds")
	}
	return gen.GetAppClients200JSONResponse{
		Version: l.Version, VersionCode: l.VersionCode, NotesMd: l.Notes, Clients: clients,
	}, nil
}

func (h *Handler) clientWithOlder(cat *catalog, kind string) (gen.AppClientFile, bool) {
	var head *Latest
	var file clientFile
	var older []gen.AppClientBuild
	for _, rel := range cat.all {
		f, ok := rel.Files[kind]
		if !ok {
			continue
		}
		if head == nil {
			head, file = rel, f
			continue
		}
		older = append(older, gen.AppClientBuild{
			Version:     rel.Version,
			Filename:    f.Name,
			Size:        f.Size,
			DownloadUrl: h.fileURL(kind, rel.Version),
			Sha256:      shaPtr(f.SHA256),
		})
	}
	if head == nil {
		return gen.AppClientFile{}, false
	}
	item := gen.AppClientFile{
		Client:      gen.AppClient(kind),
		Version:     &head.Version,
		Filename:    file.Name,
		Size:        file.Size,
		DownloadUrl: h.fileURL(kind, head.Version),
		Sha256:      shaPtr(file.SHA256),
	}
	if len(older) > 0 {
		item.Older = &older
	}
	return item, true
}

func shaPtr(s string) *string {
	if s == "" {
		return nil
	}
	return &s
}

// GetAndroidLatest реализует gen.StrictServerInterface.
func (h *Handler) GetAndroidLatest(ctx context.Context, _ gen.GetAndroidLatestRequestObject) (gen.GetAndroidLatestResponseObject, error) {
	l, err := h.latest(ctx)
	if err != nil {
		return nil, err
	}
	f, ok := l.android()
	if !ok {
		return nil, apperr.NotFound(CodeUnavailable, "release has no APK yet")
	}
	return gen.GetAndroidLatest200JSONResponse{
		Version: l.Version, VersionCode: l.VersionCode, NotesMd: l.Notes, Size: f.Size, Sha256: f.SHA256,
		DownloadUrl: "/api/v1/app/android/download/" + l.Version, MinSupported: h.cfg.MinSupported,
	}, nil
}

func (h *Handler) ensure(ctx context.Context, f clientFile) (string, error) {
	dst := filepath.Join(h.cfg.Dir, f.Name)
	if _, err := os.Stat(dst); err == nil {
		return dst, nil
	}
	h.dl.Lock()
	defer h.dl.Unlock()
	if _, err := os.Stat(dst); err == nil {
		return dst, nil
	}
	if err := os.MkdirAll(h.cfg.Dir, 0o755); err != nil {
		return "", err
	}
	res, err := h.get(ctx, f.URL)
	if err != nil {
		return "", err
	}
	defer func() { _ = res.Body.Close() }()
	tmp, err := os.CreateTemp(h.cfg.Dir, ".dl-*")
	if err != nil {
		return "", err
	}
	defer func() { _ = os.Remove(tmp.Name()) }()
	hash := sha256.New()
	if _, err := io.Copy(io.MultiWriter(tmp, hash), res.Body); err != nil {
		_ = tmp.Close()
		return "", fmt.Errorf("appupdate: download: %w", err)
	}
	if err := tmp.Close(); err != nil {
		return "", err
	}
	if f.SHA256 != "" {
		if got := hex.EncodeToString(hash.Sum(nil)); got != f.SHA256 {
			return "", fmt.Errorf("appupdate: checksum mismatch: %s != %s", got, f.SHA256)
		}
	}
	if err := os.Rename(tmp.Name(), dst); err != nil {
		return "", err
	}
	h.cleanup(f.Name)
	return dst, nil
}

func (h *Handler) cleanup(keepName string) {
	keep := map[string]struct{}{keepName: {}}
	h.mu.Lock()
	if h.cached != nil {
		for name := range h.cached.keepNames() {
			keep[name] = struct{}{}
		}
	}
	h.mu.Unlock()
	matches, _ := filepath.Glob(filepath.Join(h.cfg.Dir, "pipu-music-*"))
	for _, m := range matches {
		if _, ok := keep[filepath.Base(m)]; ok {
			continue
		}
		_ = os.Remove(m)
	}
}

func versionFromName(name string) string {
	m := regexp.MustCompile(`(\d+\.\d+\.\d+(?:-rc\.\d+)?)`).FindStringSubmatch(name)
	if m == nil {
		return ""
	}
	return m[1]
}

func (h *Handler) serveFile(ctx context.Context, l *Latest, kind string) (fileResponse, error) {
	f, ok := l.Files[kind]
	if !ok {
		return fileResponse{}, apperr.NotFound(CodeUnavailable, "client build is unavailable")
	}
	path, err := h.ensure(ctx, f)
	if err != nil {
		h.log.ErrorContext(ctx, "app update: download failed", "err", err, "client", kind)
		return fileResponse{}, apperr.New(http.StatusBadGateway, CodeUnavailable, "could not fetch the file")
	}
	return fileResponse{path: path, name: f.Name, req: httpx.RequestFrom(ctx)}, nil
}

// DownloadAndroidApk реализует gen.StrictServerInterface. Версия должна быть в каталоге (до 8 релизов).
func (h *Handler) DownloadAndroidApk(ctx context.Context, req gen.DownloadAndroidApkRequestObject) (gen.DownloadAndroidApkResponseObject, error) {
	cat, err := h.catalog(ctx)
	if err != nil {
		return nil, err
	}
	l := cat.release(req.Version)
	if l == nil {
		return nil, apperr.NotFound(CodeUnavailable, "this version is no longer available")
	}
	if _, ok := l.android(); !ok {
		return nil, apperr.NotFound(CodeUnavailable, "client build is unavailable")
	}
	return h.serveFile(ctx, l, "android")
}

// DownloadAppClient реализует gen.StrictServerInterface.
func (h *Handler) DownloadAppClient(ctx context.Context, req gen.DownloadAppClientRequestObject) (gen.DownloadAppClientResponseObject, error) {
	cat, err := h.catalog(ctx)
	if err != nil {
		return nil, err
	}
	l := cat.release(req.Version)
	if l == nil {
		return nil, apperr.NotFound(CodeUnavailable, "this version is no longer available")
	}
	return h.serveFile(ctx, l, string(req.Client))
}

type fileResponse struct {
	path string
	name string
	req  *http.Request
}

func (a fileResponse) VisitDownloadAndroidApkResponse(w http.ResponseWriter) error {
	return a.write(w)
}

func (a fileResponse) VisitDownloadAppClientResponse(w http.ResponseWriter) error {
	return a.write(w)
}

func (a fileResponse) write(w http.ResponseWriter) error {
	f, err := os.Open(a.path)
	if err != nil {
		return err
	}
	defer func() { _ = f.Close() }()
	info, err := f.Stat()
	if err != nil {
		return err
	}
	if a.req == nil {
		return errors.New("appupdate: request missing in context")
	}
	ctype := "application/octet-stream"
	if strings.HasSuffix(strings.ToLower(a.name), ".apk") {
		ctype = "application/vnd.android.package-archive"
	}
	w.Header().Set("Content-Type", ctype)
	w.Header().Set("Content-Disposition", `attachment; filename="`+a.name+`"`)
	http.ServeContent(w, a.req, a.name, info.ModTime(), f)
	return nil
}