/*
 * @Author: Vincent Young
 * @Date: 2024-09-16 11:59:24
 * @LastEditors: Vincent Yang
 * @LastEditTime: 2026-08-04 00:00:00
 * @FilePath: /DLX/translate/translate.go
 * @Telegram: https://t.me/missuo
 * @GitHub: https://github.com/missuo
 *
 * Copyright © 2024 by Vincent, All Rights Reserved.
 */

package translate

import (
	"compress/flate"
	"compress/gzip"
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/http/cookiejar"
	"net/url"
	"sort"
	"strings"
	"sync"
	"time"
	"unicode/utf8"

	"github.com/andybalholm/brotli"
	"github.com/imroc/req/v3"
	"github.com/tidwall/gjson"
)

// DeepL's interactive clients (web, Chrome extension, and the official iOS
// app) all share the same stateless "oneshot" translate endpoint. The
// legacy LMT_handle_texts backend on www2.deepl.com rate-limits anonymous
// traffic hard; oneshot lives on a separate pool and accepts the literal
// header `Authorization: None` for free requests.
//
// Request shape below is reverse-engineered from DeepL iOS 26.42
// (build 5443737, bundle com.linguee.DeepLMobileTranslator):
//   - Free URL   → https://oneshot-free.www.deepl.com/v1/translate
//   - Pro URL    → https://oneshot-pro.www.deepl.com/v1/translate
//                  (iOS also constructs https://oneshot. + .pro.deepl.com/v1/translate)
//   - Body       → OneShotTranslator + ItaClient.AppInformation
//   - Headers    → ClientInfos.appHeaders (x-app-*) + Authorization
//   - usage_type → ItaClient.OneShotUsageType.translate
const (
	oneshotFreeEndpoint = "https://oneshot-free.www.deepl.com/v1/translate"
	oneshotProEndpoint  = "https://oneshot-pro.www.deepl.com/v1/translate"

	// Pinned to DeepL iOS IPA (Info.plist CFBundleShortVersionString /
	// CFBundleVersion). Keep app_information in lockstep with the TLS
	// fingerprint and User-Agent so the request tells one consistent story.
	iosAppVersion = "26.42"
	iosAppBuild   = "5443737"
	iosBundleID   = "com.linguee.DeepLMobileTranslator"
	// Stable OS version reported in app_information + x-app-os-version.
	// HelloIOS_Auto does not pin a specific iOS minor; 18.5 is a current
	// shipping major that matches MinimumOSVersion 17.0+ of the IPA.
	iosOSVersion = "18.5"

	// oneshot enforces a 1500-character hard cap on the total length of
	// the `text` array for anonymous traffic (same limit the Chrome
	// extension documents as G.notLoggedIn). Bail early to spare the
	// upstream and give the caller a faster error.
	maxFreeTextLength = 1500

	// oneshotTimeout caps how long we wait on a single translate request.
	oneshotTimeout = 20 * time.Second

	// warmupTimeout caps the initial GET to www.deepl.com that seeds the
	// cookie jar. Cookies are best-effort; skip a slow warmup rather than
	// block the first translation.
	warmupTimeout = 5 * time.Second
)

// instanceID mirrors the UUID the iOS app persists for analytics /
// app_information.instance_id and x-app-instance-id: stable for the life
// of the process, reused on every request. Rotating per-request is a
// stronger bot signal than reusing one.
var instanceID = newInstanceID()

// sessionID is sent as x-app-session-id (ClientInfos.appHeaders). Stable
// for the process lifetime, independent of instanceID.
var sessionID = newInstanceID()

// A real iOS URLSession inherits whatever cookies the app has on
// .deepl.com. A cold visit to www.deepl.com sets userCountry=<iso2> and
// verifiedBot=false. Share a process-wide jar so every oneshot POST
// carries whatever the warmup GET picked up.
var (
	cookieJar     http.CookieJar
	cookieJarOnce sync.Once
	cookieWarmer  sync.Once
)

// oneshotClients caches one req.Client per proxy URL so all translate
// calls share the underlying TCP / TLS / HTTP/2 connection pool.
var oneshotClients sync.Map // map[string]*req.Client

func sharedCookieJar() http.CookieJar {
	cookieJarOnce.Do(func() {
		j, _ := cookiejar.New(nil)
		cookieJar = j
	})
	return cookieJar
}

// warmCookies primes the shared jar by GETting www.deepl.com once.
// The Set-Cookie response lands on .deepl.com (eTLD+1 of oneshot-free),
// so subsequent POSTs carry those cookies automatically.
func warmCookies(client *req.Client) {
	cookieWarmer.Do(func() {
		ctx, cancel := context.WithTimeout(context.Background(), warmupTimeout)
		defer cancel()
		_, _ = client.R().SetContext(ctx).Get("https://www.deepl.com/translator")
	})
}

func newInstanceID() string {
	b := make([]byte, 16)
	if _, err := rand.Read(b); err != nil {
		return "00000000-0000-4000-8000-000000000000"
	}
	b[6] = (b[6] & 0x0f) | 0x40 // RFC 4122 v4
	b[8] = (b[8] & 0x3f) | 0x80
	s := hex.EncodeToString(b)
	return fmt.Sprintf("%s-%s-%s-%s-%s", s[0:8], s[8:12], s[12:16], s[16:20], s[20:32])
}

// Language code tables mirror ItaClient.OutputLanguage / InputLanguage
// (regional cases enUs, enGb, frCa, deCh, ptPt, ptBr, es419, zhHant, …)
// plus the full target-capable set the oneshot endpoint accepts.
//
// Keys are the uppercase forms callers pass; values are the lowercase
// BCP-47-ish forms oneshot expects ("de", "en-US", "zh-Hans", ...).
//
// EN and PT are intentionally absent as bare target codes — DeepL
// deprecated them in favour of EN-US/EN-GB and PT-BR/PT-PT. We accept
// EN/PT as a backward-compat convenience and resolve them to the
// regional default (en-US, pt-BR).
var targetLangMap = map[string]string{
	"AR": "ar", "BG": "bg", "CS": "cs", "DA": "da", "DE": "de", "DE-CH": "de-CH",
	"EL": "el",
	"EN-GB": "en-GB", "EN-US": "en-US",
	"ES": "es", "ES-419": "es-419", "ET": "et", "FI": "fi", "FR": "fr", "FR-CA": "fr-CA",
	"HE": "he", "HU": "hu", "ID": "id", "IT": "it", "JA": "ja", "KO": "ko",
	"LT": "lt", "LV": "lv", "NB": "nb", "NL": "nl", "PL": "pl",
	"PT-BR": "pt-BR", "PT-PT": "pt-PT",
	"RO": "ro", "RU": "ru", "SK": "sk", "SL": "sl", "SV": "sv",
	"TR": "tr", "UK": "uk", "VI": "vi",
	"ZH": "zh-Hans", "ZH-HANS": "zh-Hans", "ZH-HANT": "zh-Hant",
	// Convenience aliases for legacy callers.
	"EN": "en-US",
	"PT": "pt-BR",
}

// sourceLangMap is what the API accepts as `source_lang`. It is a
// superset of targetLangMap: EN and PT are first-class source codes
// mapping to the generic "en"/"pt".
var sourceLangMap = func() map[string]string {
	m := make(map[string]string, len(targetLangMap)+2)
	for k, v := range targetLangMap {
		m[k] = v
	}
	m["EN"] = "en"
	m["PT"] = "pt"
	return m
}()

// resolveTargetLang validates and normalizes a user-supplied target
// language code. Returns "" and a non-nil error if the code is empty,
// "auto", or otherwise not in the supported set.
func resolveTargetLang(code string) (string, error) {
	if code == "" {
		return "", fmt.Errorf("target_lang is required")
	}
	if strings.EqualFold(code, "auto") {
		return "", fmt.Errorf("target_lang cannot be \"auto\"; pick one of: %s", supportedTargetLangsList())
	}
	if v, ok := targetLangMap[strings.ToUpper(code)]; ok {
		return v, nil
	}
	return "", fmt.Errorf("unsupported target_lang %q; valid codes: %s", code, supportedTargetLangsList())
}

// resolveSourceLang validates and normalizes a user-supplied source
// language code. An empty string or "auto" is allowed and returns
// ("", nil) so the caller omits source_lang and lets the server
// autodetect.
func resolveSourceLang(code string) (string, error) {
	if code == "" || strings.EqualFold(code, "auto") {
		return "", nil
	}
	if v, ok := sourceLangMap[strings.ToUpper(code)]; ok {
		return v, nil
	}
	return "", fmt.Errorf("unsupported source_lang %q; valid codes: %s (or \"auto\")", code, supportedSourceLangsList())
}

// supportedTargetLangsList / supportedSourceLangsList return a sorted,
// comma-separated rendering of the supported codes for use in error
// messages. Cached at first call.
var (
	targetLangsListOnce sync.Once
	targetLangsList     string
	sourceLangsListOnce sync.Once
	sourceLangsList     string
)

func supportedTargetLangsList() string {
	targetLangsListOnce.Do(func() {
		targetLangsList = sortedKeys(targetLangMap)
	})
	return targetLangsList
}

func supportedSourceLangsList() string {
	sourceLangsListOnce.Do(func() {
		sourceLangsList = sortedKeys(sourceLangMap)
	})
	return sourceLangsList
}

func sortedKeys(m map[string]string) string {
	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	return strings.Join(keys, ", ")
}

// appInformation matches ItaClient.AppInformation (os, os_version,
// app_version, app_build, instance_id) as serialized by the iOS client.
type appInformation struct {
	OS         string `json:"os"`
	OSVersion  string `json:"os_version"`
	AppVersion string `json:"app_version"`
	AppBuild   string `json:"app_build"`
	InstanceID string `json:"instance_id"`
}

// oneshotRequest mirrors the body assembled by the iOS OneShotTranslator
// / ItaClient oneshot path. Field order matches the app's serialization
// so the JSON is byte-stable (encoding/json honours struct field order).
type oneshotRequest struct {
	Text           []string       `json:"text"`
	TargetLang     string         `json:"target_lang"`
	SourceLang     string         `json:"source_lang,omitempty"`
	UsageType      string         `json:"usage_type"`
	AppInformation appInformation `json:"app_information"`
}

// getOneshotClient returns a process-wide cached client for the given
// proxy URL, creating it on first use. Sharing the client across
// requests keeps the TLS / HTTP/2 connection in the pool.
func getOneshotClient(proxyURL string) (*req.Client, error) {
	if c, ok := oneshotClients.Load(proxyURL); ok {
		return c.(*req.Client), nil
	}
	c, err := newOneshotClient(proxyURL)
	if err != nil {
		return nil, err
	}
	if actual, loaded := oneshotClients.LoadOrStore(proxyURL, c); loaded {
		return actual.(*req.Client), nil
	}
	go warmCookies(c)
	return c, nil
}

func newOneshotClient(proxyURL string) (*req.Client, error) {
	// iOS TLS ClientHello via utls HelloIOS_Auto. Headers are set per
	// request in callOneshot to match ClientInfos.appHeaders rather than
	// a browser navigation profile.
	client := req.C().
		SetTLSFingerprintIOS().
		SetCookieJar(sharedCookieJar()).
		SetTimeout(oneshotTimeout).
		SetUserAgent(iosUserAgent()).
		SetCommonHeader("Accept-Encoding", "gzip, deflate, br").
		SetCommonHeader("Accept", "*/*").
		SetCommonHeader("Accept-Language", "en-US,en;q=0.9")

	if proxyURL != "" {
		u, err := url.Parse(proxyURL)
		if err != nil {
			return nil, err
		}
		client.SetProxyURL(u.String())
	}
	return client, nil
}

// iosUserAgent approximates the CFNetwork-style UA the DeepL iOS app
// advertises via ClientInfos.userAgent.
func iosUserAgent() string {
	return fmt.Sprintf(
		"DeepL/%s (%s; build:%s; iOS %s)",
		iosAppVersion, iosBundleID, iosAppBuild, iosOSVersion,
	)
}

// callOneshot POSTs to the oneshot endpoint and returns the parsed JSON.
// For anonymous traffic bearerToken is empty and we send the literal
// header `Authorization: None` — matching ItaClient.LoginNone. Omitting
// that header puts the request on a different server-side auth branch.
func callOneshot(endpoint string, body []byte, bearerToken, proxyURL string) (gjson.Result, int, error) {
	client, err := getOneshotClient(proxyURL)
	if err != nil {
		return gjson.Result{}, 0, err
	}

	authValue := "None"
	if bearerToken != "" {
		authValue = "Bearer " + bearerToken
	}

	resp, err := client.R().
		DisableAutoReadResponse().
		SetHeader("Content-Type", "application/json").
		SetHeader("Authorization", authValue).
		// ClientInfos.appHeaders from DeepL iOS (Util/ClientInfos.swift).
		SetHeader("x-app-os-version", iosOSVersion).
		SetHeader("x-app-instance-id", instanceID).
		SetHeader("x-app-session-id", sessionID).
		SetBodyBytes(body). // pins Content-Length; an io.Reader would
		// force Transfer-Encoding: chunked, which URLSession JSON bodies
		// never emit.
		Post(endpoint)
	if err != nil {
		return gjson.Result{}, 0, err
	}
	defer resp.Body.Close()

	// Once we set Accept-Encoding ourselves, Go's HTTP stack stops
	// transparently decompressing, so handle gzip/deflate/br by hand.
	var reader io.Reader = resp.Body
	switch strings.ToLower(resp.Header.Get("Content-Encoding")) {
	case "gzip":
		gr, err := gzip.NewReader(resp.Body)
		if err != nil {
			return gjson.Result{}, resp.StatusCode, fmt.Errorf("gzip reader: %w", err)
		}
		defer gr.Close()
		reader = gr
	case "deflate":
		reader = flate.NewReader(resp.Body)
	case "br":
		reader = brotli.NewReader(resp.Body)
	}
	raw, err := io.ReadAll(reader)
	if err != nil {
		return gjson.Result{}, resp.StatusCode, fmt.Errorf("read response body: %w", err)
	}
	return gjson.ParseBytes(raw), resp.StatusCode, nil
}

// TranslateByDLX performs translation via the DeepL oneshot endpoint.
// Passing dlSession switches to the Pro endpoint; the value is sent
// verbatim as the Bearer token (i.e. it must be an OAuth access token,
// not the legacy dl_session cookie).
func TranslateByDLX(sourceLang, targetLang, text string, tagHandling string, proxyURL string, dlSession string) (DLXTranslationResult, error) {
	if text == "" {
		return DLXTranslationResult{
			Code:    http.StatusNotFound,
			Message: "No text to translate",
		}, nil
	}

	resolvedTarget, err := resolveTargetLang(targetLang)
	if err != nil {
		return DLXTranslationResult{
			Code:    http.StatusBadRequest,
			Message: err.Error(),
		}, nil
	}
	resolvedSource, err := resolveSourceLang(sourceLang)
	if err != nil {
		return DLXTranslationResult{
			Code:    http.StatusBadRequest,
			Message: err.Error(),
		}, nil
	}

	if n := utf8.RuneCountInString(text); n > maxFreeTextLength {
		return DLXTranslationResult{
			Code:    http.StatusRequestEntityTooLarge,
			Message: fmt.Sprintf("text exceeds maximum length: %d characters (anonymous oneshot limit is %d)", n, maxFreeTextLength),
		}, nil
	}

	// tagHandling is accepted by the public DLX API for compatibility
	// but oneshot does not expose html/xml tag handling the way the
	// official v2 API does — ignored upstream.
	_ = tagHandling

	reqStruct := oneshotRequest{
		Text:       []string{text},
		TargetLang: resolvedTarget,
		SourceLang: resolvedSource, // empty = autodetect; omitempty drops the field
		// ItaClient.OneShotUsageType.translate (also: ocr, voiceforconversations)
		UsageType: "translate",
		AppInformation: appInformation{
			OS:         "iOS",
			OSVersion:  iosOSVersion,
			AppVersion: iosAppVersion,
			AppBuild:   iosAppBuild,
			InstanceID: instanceID,
		},
	}
	bodyBytes, _ := json.Marshal(reqStruct)

	endpoint := oneshotFreeEndpoint
	if dlSession != "" {
		endpoint = oneshotProEndpoint
	}

	id := time.Now().UnixMilli()
	result, status, err := callOneshot(endpoint, bodyBytes, dlSession, proxyURL)
	if err != nil {
		// Map upstream timeouts to 504 so callers can distinguish "DeepL
		// took too long" from other 503 failure modes (DNS, TLS, etc.).
		var ue *url.Error
		if errors.Is(err, context.DeadlineExceeded) || (errors.As(err, &ue) && ue.Timeout()) {
			return DLXTranslationResult{
				ID:      id,
				Code:    http.StatusGatewayTimeout,
				Message: fmt.Sprintf("upstream DeepL request timed out after %s", oneshotTimeout),
			}, nil
		}
		return DLXTranslationResult{
			ID:      id,
			Code:    http.StatusServiceUnavailable,
			Message: err.Error(),
		}, nil
	}

	switch status {
	case http.StatusOK:
		// fall through to body parsing
	case http.StatusTooManyRequests:
		return DLXTranslationResult{
			ID:      id,
			Code:    http.StatusTooManyRequests,
			Message: "too many requests, your IP has been blocked by DeepL temporarily, please don't request it frequently in a short time",
		}, nil
	case http.StatusForbidden:
		// iOS surfaces this as OneShot: Forbidden / AuthenticationFailed /
		// OutdatedClient / UserBlocked depending on body; collapse to 403.
		msg := result.Get("title").String()
		if msg == "" {
			msg = result.Get("message").String()
		}
		if msg == "" {
			msg = "request forbidden by DeepL (auth failed, outdated client, or blocked)"
		}
		return DLXTranslationResult{
			ID:      id,
			Code:    http.StatusForbidden,
			Message: msg,
		}, nil
	default:
		return DLXTranslationResult{
			ID:      id,
			Code:    http.StatusServiceUnavailable,
			Message: fmt.Sprintf("request failed with status code: %d", status),
		}, nil
	}

	translations := result.Get("translations").Array()
	if len(translations) == 0 {
		return DLXTranslationResult{
			ID:      id,
			Code:    http.StatusServiceUnavailable,
			Message: "Translation failed",
		}, nil
	}

	mainText := translations[0].Get("text").String()
	if mainText == "" {
		return DLXTranslationResult{
			ID:      id,
			Code:    http.StatusServiceUnavailable,
			Message: "Translation failed",
		}, nil
	}

	if detected := translations[0].Get("detected_source_language").String(); detected != "" {
		sourceLang = strings.ToUpper(detected)
	}

	return DLXTranslationResult{
		Code:         http.StatusOK,
		ID:           id,
		Data:         mainText,
		Alternatives: nil, // oneshot does not return alternatives
		SourceLang:   sourceLang,
		TargetLang:   targetLang,
		Method:       map[bool]string{true: "Pro", false: "Free"}[dlSession != ""],
	}, nil
}