// 账户相关的公开端点：第三方身份绑定、passkey 登录。
//
// 绑定复用登录的 OAuth 跳转，只在发起时多打一个一次性 cookie 表明意图；
// 回调拿到身份后统一走 afterIdentity 分流，免得三个 provider 各写一遍判断。
//
// 分流规则（顺序即优先级）：
//  1. 带绑定意图 + 当前是有效管理员会话 → 把该外部身份绑到站主账号，回账户页
//  2. 该外部身份已绑到某账号 → 站主发后台会话，读者发读者会话
//  3. 谁都不认识 → 按老路建/更新读者档案，发读者会话
//
// 第 1 步必须校验管理员会话：否则任何人都能跑一遍自己的 OAuth 流程，
// 把身份塞进别人的账号上。
package api

import (
	"encoding/json"
	"errors"
	"log"
	"net/http"
	"net/url"
	"strings"

	"oneblog/internal/auth"
	"oneblog/internal/httpx"
	"oneblog/internal/model"
	"oneblog/internal/ratelimit"
	"oneblog/internal/store"
)

const oauthBindCook = "one_oauth_bind"

// startOAuth 备好 state（防 CSRF）与回跳地址，然后跳到 provider 授权页。
// authorize 拿到 state 拼出最终授权 URL —— state 必须在这里生成，
// 又要出现在 URL 里，所以用回调而不是先算好传进来。
func (a *API) startOAuth(w http.ResponseWriter, r *http.Request, authorize func(state string) string) {
	state := randHex(16)
	http.SetCookie(w, &http.Cookie{Name: oauthStateCook, Value: state, Path: "/",
		HttpOnly: true, MaxAge: 600})
	// 记下发起登录的前台 origin：开发时前端 :3000、后端 :8080 分离，
	// 回调只有靠它才知道该跳回哪儿。
	if ref := r.Referer(); ref != "" {
		if u, err := url.Parse(ref); err == nil && u.Scheme != "" && u.Host != "" {
			http.SetCookie(w, &http.Cookie{Name: oauthBackCook,
				Value: u.Scheme + "://" + u.Host, Path: "/", HttpOnly: true, MaxAge: 600})
		}
	}
	http.Redirect(w, r, authorize(state), http.StatusFound)
}

// beginBind 发起绑定。只有已登录的后台管理员能发起，且平台必须已配置。
func (a *API) beginBind(w http.ResponseWriter, r *http.Request) {
	provider := strings.Trim(strings.TrimPrefix(r.URL.Path, "/api/auth/"), "/")
	provider = strings.TrimSuffix(provider, "/bind")
	if !a.adminSessionValid(r) {
		httpx.Unauthorized(w)
		return
	}
	setBindCookie(w)
	switch provider {
	case "github":
		if !a.GH.Enabled() {
			clearBindCookie(w)
			httpx.NotFound(w)
			return
		}
		a.startOAuth(w, r, func(state string) string {
			return a.GH.LoginURL(a.Cfg.SiteURL+"/api/auth/callback/github", state)
		})
	case "google":
		if !a.GG.Enabled() {
			clearBindCookie(w)
			httpx.NotFound(w)
			return
		}
		a.startOAuth(w, r, func(state string) string {
			return a.GG.LoginURL(a.Cfg.SiteURL+"/api/auth/callback/google", state)
		})
	default:
		clearBindCookie(w)
		httpx.NotFound(w)
	}
}

func setBindCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{Name: oauthBindCook, Value: "1", Path: "/",
		HttpOnly: true, MaxAge: 600, SameSite: http.SameSiteLaxMode})
}

func clearBindCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{Name: oauthBindCook, Value: "", Path: "/", MaxAge: -1})
}

func bindRequested(r *http.Request) bool {
	ck, err := r.Cookie(oauthBindCook)
	return err == nil && ck.Value == "1"
}

// adminSessionValid 判断当前请求带的是不是有效后台会话。
// 公开 API 只依赖注入的接口（不 import admin 包，免得两个 API 互相引用成环）。
func (a *API) adminSessionValid(r *http.Request) bool {
	if a.AdminSessions == nil {
		return false
	}
	ck, err := r.Cookie(adminCookieName)
	if err != nil || ck.Value == "" {
		return false
	}
	_, verr := a.AdminSessions.Verify(ck.Value)
	return verr == nil
}

const adminCookieName = "one_session"

// afterIdentity 见文件头的分流规则。返回空串表示响应已写好，调用方直接 return。
func (a *API) afterIdentity(w http.ResponseWriter, r *http.Request, provider, externUID, display string, persona model.Reader) string {
	defer clearBindCookie(w) // 意图用完即清，免得下次普通登录误判成绑定
	if externUID == "" {
		// provider 没给稳定 id：宁可退回老流程按 handle 认人，也不建一条
		// 空 extern_uid 的绑定 —— 空值会和别人的空值撞唯一键。
		return a.issueReaderLogin(w, r, persona)
	}

	if bindRequested(r) {
		owner, err := a.Store.EnsureOwner(a.Cfg.AdminUser)
		if err != nil {
			httpx.ServerError(w, err)
			return ""
		}
		if err := a.Store.BindIdentity(owner.ID, provider, externUID, display); err != nil {
			if errors.Is(err, store.ErrConflict) {
				httpx.Error(w, http.StatusConflict, "该账号已绑定到其他用户")
				return ""
			}
			httpx.ServerError(w, err)
			return ""
		}
		http.Redirect(w, r, strings.TrimRight(a.Cfg.SiteURL, "/")+"/admin/account?bound="+url.QueryEscape(provider), http.StatusFound)
		return ""
	}

	// 已绑定的身份优先于新建档案：站主用绑定的 GitHub 登录要拿到后台会话
	u, err := a.Store.GetUserByIdentity(provider, externUID)
	switch {
	case err == nil && u.Role == model.RoleOwner:
		a.issueAdminSession(w, r)
		return ""
	case err == nil:
		return a.issueReaderSession(w, r, u.ID)
	case !errors.Is(err, store.ErrNotFound):
		httpx.ServerError(w, err)
		return ""
	}
	return a.issueReaderLogin(w, r, persona)
}

func (a *API) issueReaderLogin(w http.ResponseWriter, r *http.Request, persona model.Reader) string {
	reader, err := a.Store.UpsertReader(persona)
	if err != nil {
		httpx.ServerError(w, err)
		return ""
	}
	return a.issueReaderSession(w, r, reader.ID)
}

func (a *API) issueReaderSession(w http.ResponseWriter, r *http.Request, readerID int64) string {
	token, _ := a.ReaderSessions.Issue(readerID)
	http.SetCookie(w, &http.Cookie{Name: auth.ReaderCookie, Value: token, Path: "/",
		HttpOnly: true, SameSite: http.SameSiteLaxMode, MaxAge: a.ReaderSessions.TTL()})
	return a.loginBack(w, r)
}

// loginBack 决定登录完跳回哪儿：优先回发起登录的前台 origin
// （开发时前端 :3000、后端 :8080 分离，只有它才不会跳错站），
// 没有记录（直接敲 URL 进来的）就回站点根。
func (a *API) loginBack(w http.ResponseWriter, r *http.Request) string {
	back := a.Cfg.SiteURL
	if ck, err := r.Cookie(oauthBackCook); err == nil && ck.Value != "" {
		if u, err := url.Parse(ck.Value); err == nil && (u.Scheme == "http" || u.Scheme == "https") && u.Host != "" && u.Path == "" {
			back = u.Scheme + "://" + u.Host
		}
	}
	http.SetCookie(w, &http.Cookie{Name: oauthBackCook, Value: "", Path: "/", MaxAge: -1})
	return back
}

// issueAdminSession 让已绑定的第三方身份直接换发后台会话 —— 「绑定即提权」
// 的落点。Secure / SameSite 与密码登录发的 cookie 完全一致，否则 HTTPS 下
// 浏览器会把它当不安全 cookie 丢掉。
func (a *API) issueAdminSession(w http.ResponseWriter, r *http.Request) {
	token, exp := a.AdminSessions.Issue(a.Cfg.AdminUser)
	http.SetCookie(w, &http.Cookie{
		Name: adminCookieName, Value: token, Path: "/", HttpOnly: true,
		Secure: isTLS(r), SameSite: http.SameSiteLaxMode,
		Expires: exp, MaxAge: a.AdminSessions.TTL(),
	})
}

// isTLS 判断最终用户看到的是不是 HTTPS（含反代 X-Forwarded-Proto）。
// admin 包有一份同名私有函数：两边各自独立，不为三行代码造共享包。
func isTLS(r *http.Request) bool {
	if r.TLS != nil {
		return true
	}
	return r.Header.Get("X-Forwarded-Proto") == "https"
}

// ---------- passkey 登录（公开） ----------

// passkeyBegin 发起一次发现式登录：不预先要用户名，凭据自己带出身份。
func (a *API) passkeyBegin(w http.ResponseWriter, r *http.Request) {
	if a.Passkeys == nil {
		httpx.NotFound(w)
		return
	}
	if a.passkeyFails.Blocked(ratelimit.SourceKey(r)) {
		httpx.Error(w, http.StatusTooManyRequests, "尝试次数过多，请稍后再试")
		return
	}
	options, token, err := a.Passkeys.BeginLogin()
	if err != nil {
		httpx.ServerError(w, err)
		return
	}
	httpx.OK(w, map[string]any{"options": options, "token": token})
}

// passkeyFinish 校验断言。命中站主发后台会话，命中读者发读者会话。
func (a *API) passkeyFinish(w http.ResponseWriter, r *http.Request) {
	if a.Passkeys == nil {
		httpx.NotFound(w)
		return
	}
	var in struct {
		Token      string          `json:"token"`
		Credential json.RawMessage `json:"credential"`
	}
	if err := httpx.Decode(r, &in); err != nil || in.Token == "" || len(in.Credential) == 0 {
		httpx.BadRequest(w, "token 与 credential 都要传")
		return
	}
	ip := ratelimit.SourceKey(r)
	if a.passkeyFails.Blocked(ip) {
		httpx.Error(w, http.StatusTooManyRequests, "尝试次数过多，请稍后再试")
		return
	}
	res, err := a.Passkeys.FinishLogin(in.Token, in.Credential, func(credID string) (model.Passkey, error) {
		return a.Store.GetPasskeyByCredentialID(credID)
	})
	if err != nil {
		a.passkeyFails.Add(ip)
		httpx.Error(w, http.StatusUnauthorized, "passkey 校验失败")
		return
	}
	pk, err := a.Store.GetPasskeyByCredentialID(res.CredentialID)
	if err != nil {
		a.passkeyFails.Add(ip)
		httpx.Unauthorized(w)
		return
	}
	if err := a.Store.TouchPasskey(pk.ID, res.SignCount); err != nil {
		// 计数回写失败不该挡住已验签成功的登录，但要留痕：
		// 丢了计数就等于丢了克隆检测能力。
		log.Printf("passkey: 回写签名计数失败 (id=%d): %v", pk.ID, err)
	}
	if res.CloneWarning {
		log.Printf("passkey: 凭据 %q 签名计数回退，可能被克隆或多设备同步", pk.Name)
	}
	u, err := a.Store.GetReader(pk.UserID)
	if err != nil {
		httpx.Unauthorized(w)
		return
	}
	if u.Role == model.RoleOwner {
		a.issueAdminSession(w, r)
		httpx.OK(w, map[string]any{"ok": true, "role": u.Role})
		return
	}
	a.issueReaderSession(w, r, u.ID)
	httpx.OK(w, map[string]any{"ok": true, "role": u.Role})
}