package handlers

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/hex"
	"fmt"
	"log"
	"net/http"
	"time"

	"mail_go/config"
	"mail_go/internal/auth"
	"mail_go/internal/db"
	"mail_go/internal/store"

	"github.com/gin-contrib/sessions"
	"github.com/gin-gonic/gin"
)

// AuthHandler handles authentication-related routes (login, logout, LDAP, OAuth2).
type AuthHandler struct {
	stores  *store.Stores
	authCfg config.AuthConfig
	banCfg  config.BanConfig
}

// NewAuthHandler creates a new AuthHandler with the given stores, auth config, and ban config.
func NewAuthHandler(stores *store.Stores, authCfg config.AuthConfig, banCfg config.BanConfig) *AuthHandler {
	return &AuthHandler{stores: stores, authCfg: authCfg, banCfg: banCfg}
}

// ShowLogin renders the login page.
func (h *AuthHandler) ShowLogin(c *gin.Context) {
	// If already logged in, redirect to inbox
	session := sessions.Default(c)
	if session.Get("userID") != nil {
		c.Redirect(302, "/inbox")
		return
	}
	c.HTML(200, "login", gin.H{
		"error":          "",
		"oauth2Enabled":  h.authCfg.OAuth2Enabled,
		"ldapEnabled":    h.authCfg.LDAPEnabled,
		"oauth2Provider": h.authCfg.OAuth2Provider,
	})
}

// DoLogin processes the login form submission.
// It authenticates the user with email and password, sets session data
// on success, or re-renders the login page with an error on failure.
func (h *AuthHandler) DoLogin(c *gin.Context) {
	ip := c.ClientIP()

	// Check if IP is banned
	banned, entry := h.stores.Bans.IsBanned(ip)
	if banned {
		c.HTML(http.StatusForbidden, "banned", gin.H{"entry": entry})
		return
	}

	email := c.PostForm("email")
	password := c.PostForm("password")

	if email == "" || password == "" {
		c.HTML(200, "login", gin.H{
			"error":          "请输入邮箱和密码",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	user, err := h.stores.Users.Authenticate(email, password)
	if err != nil {
		failCount, _ := h.stores.Bans.IncrementFail(ip)

		if failCount >= h.banCfg.MaxFailAttempts {
			banDuration := time.Duration(h.banCfg.BanDurationMin) * time.Minute
			banEntry := &db.BanEntry{
				IPAddress: ip,
				Reason:    fmt.Sprintf("登录失败次数过多 (%d次)", failCount),
				FailCount: failCount,
				ExpiresAt: time.Now().Add(banDuration),
			}
			h.stores.Bans.Create(banEntry)

			c.HTML(http.StatusForbidden, "banned", gin.H{"entry": banEntry})
			return
		}

		remaining := h.banCfg.MaxFailAttempts - failCount
		c.HTML(200, "login", gin.H{
			"error":          fmt.Sprintf("用户名或密码错误，还剩 %d 次尝试机会", remaining),
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	// Login successful: reset fail count
	h.stores.Bans.ResetFail(ip)

	// Set session values（先清空旧会话状态，防止残留值；记录登录时间
	// 供中间件做绝对过期与滑动续期）
	session := sessions.Default(c)
	session.Clear()
	session.Set("userID", user.ID)
	session.Set("userEmail", user.Username+"@"+user.Domain.Name)
	session.Set("isAdmin", user.IsAdmin)
	session.Set("loginAt", time.Now().Unix())
	if err := session.Save(); err != nil {
		c.HTML(200, "login", gin.H{
			"error":          "会话保存失败，请重试",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	c.Redirect(302, "/inbox")
}

// LDAPLogin handles LDAP authentication form submission.
func (h *AuthHandler) LDAPLogin(c *gin.Context) {
	ip := c.ClientIP()

	// Check if IP is banned
	banned, entry := h.stores.Bans.IsBanned(ip)
	if banned {
		c.HTML(http.StatusForbidden, "banned", gin.H{"entry": entry})
		return
	}

	username := c.PostForm("username")
	password := c.PostForm("password")

	if username == "" || password == "" {
		c.HTML(200, "login", gin.H{
			"error":          "请输入LDAP用户名和密码",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	provider := auth.NewLDAPProvider(h.authCfg)
	email, err := provider.Authenticate(map[string]string{
		"username": username,
		"password": password,
	})
	if err != nil {
		log.Printf("LDAP 认证失败: %v", err)

		failCount, _ := h.stores.Bans.IncrementFail(ip)
		if failCount >= h.banCfg.MaxFailAttempts {
			banDuration := time.Duration(h.banCfg.BanDurationMin) * time.Minute
			banEntry := &db.BanEntry{
				IPAddress: ip,
				Reason:    fmt.Sprintf("登录失败次数过多 (%d次)", failCount),
				FailCount: failCount,
				ExpiresAt: time.Now().Add(banDuration),
			}
			h.stores.Bans.Create(banEntry)

			c.HTML(http.StatusForbidden, "banned", gin.H{"entry": banEntry})
			return
		}

		remaining := h.banCfg.MaxFailAttempts - failCount
		c.HTML(200, "login", gin.H{
			"error":          fmt.Sprintf("LDAP 认证失败，还剩 %d 次尝试机会", remaining),
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	// Look up or auto-create user by email
	user, err := h.stores.Users.GetByEmail(email)
	if err != nil {
		c.HTML(200, "login", gin.H{
			"error":          "LDAP 账号未接入本系统，请联系管理员",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	if !user.IsActive {
		c.HTML(200, "login", gin.H{
			"error":          "用户已被禁用",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	// Login successful: reset fail count
	h.stores.Bans.ResetFail(ip)

	// Set session values（先清空旧会话状态，防止残留值；记录登录时间
	// 供中间件做绝对过期与滑动续期）
	session := sessions.Default(c)
	session.Clear()
	session.Set("userID", user.ID)
	session.Set("userEmail", user.Username+"@"+user.Domain.Name)
	session.Set("isAdmin", user.IsAdmin)
	session.Set("loginAt", time.Now().Unix())
	if err := session.Save(); err != nil {
		c.HTML(200, "login", gin.H{
			"error":          "会话保存失败，请重试",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	c.Redirect(302, "/inbox")
}

// OAuth2 state cookie 配置。state 用于防止登录 CSRF / 授权码注入：
// 发起授权时下发随机值，回调时必须原样带回。
//
// 注意 state 不能放进主会话 cookie：主会话是 SameSite=Strict，
// OAuth2 回调是从 IdP 发起的跨站顶级导航，浏览器不会携带 Strict
// cookie，因此使用独立的短期 SameSite=Lax cookie。
const (
	oauth2StateCookie  = "mail_go_oauth2_state"
	oauth2StateMaxAge  = 600 // 秒，10 分钟内完成授权流程
	oauth2StateRandLen = 16  // 随机字节数（hex 编码后 32 字符）
)

// randomOAuth2State generates a hex-encoded cryptographically random state.
func randomOAuth2State() (string, error) {
	buf := make([]byte, oauth2StateRandLen)
	if _, err := rand.Read(buf); err != nil {
		return "", fmt.Errorf("生成 OAuth2 state 失败: %w", err)
	}
	return hex.EncodeToString(buf), nil
}

// oauth2LoginVars 是登录模板所需的公共变量。
func (h *AuthHandler) oauth2LoginVars() gin.H {
	return gin.H{
		"oauth2Enabled":  h.authCfg.OAuth2Enabled,
		"ldapEnabled":    h.authCfg.LDAPEnabled,
		"oauth2Provider": h.authCfg.OAuth2Provider,
	}
}

// OAuth2Start redirects to the OAuth2 provider's authorization page.
func (h *AuthHandler) OAuth2Start(c *gin.Context) {
	if !h.authCfg.OAuth2Enabled {
		c.String(http.StatusBadRequest, "OAuth2 未启用")
		return
	}

	provider := auth.NewOAuth2Provider(h.authCfg)
	state, err := randomOAuth2State()
	if err != nil {
		log.Printf("生成 OAuth2 state 失败: %v", err)
		c.String(http.StatusInternalServerError, "OAuth2 登录暂不可用，请稍后重试")
		return
	}
	c.SetCookie(oauth2StateCookie, state, oauth2StateMaxAge, "/auth/oauth2", "", true, true)
	c.Redirect(http.StatusFound, provider.GetAuthURL(state))
}

// OAuth2Callback handles the OAuth2 provider's callback after user authorization.
func (h *AuthHandler) OAuth2Callback(c *gin.Context) {
	if !h.authCfg.OAuth2Enabled {
		c.String(http.StatusBadRequest, "OAuth2 未启用")
		return
	}

	// 校验 state：必须与发起授权时下发的随机值一致（常量时间比较）。
	// 缺失或不匹配视为登录 CSRF / 授权码注入，直接拒绝。
	cookieState, cookieErr := c.Cookie(oauth2StateCookie)
	reqState := c.Query("state")
	if cookieErr != nil || reqState == "" ||
		subtle.ConstantTimeCompare([]byte(cookieState), []byte(reqState)) != 1 {
		c.HTML(http.StatusForbidden, "login", func() gin.H {
			v := h.oauth2LoginVars()
			v["error"] = "OAuth2 state 校验失败，请重新发起登录"
			return v
		}())
		return
	}
	// state 一次性使用：无论后续成败都立即失效
	c.SetCookie(oauth2StateCookie, "", -1, "/auth/oauth2", "", true, true)

	code := c.Query("code")
	if code == "" {
		c.HTML(200, "login", gin.H{
			"error":          "OAuth2 授权码缺失",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	provider := auth.NewOAuth2Provider(h.authCfg)
	email, err := provider.HandleCallback(code)
	if err != nil {
		log.Printf("OAuth2 回调失败: %v", err)
		c.HTML(200, "login", gin.H{
			"error":          "OAuth2 认证失败，请重试或联系管理员",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	// Look up user by email
	user, err := h.stores.Users.GetByEmail(email)
	if err != nil {
		c.HTML(200, "login", gin.H{
			"error":          "OAuth2 账号未接入本系统，请联系管理员",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	if !user.IsActive {
		c.HTML(200, "login", gin.H{
			"error":          "用户已被禁用",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	// Set session values（先清空旧会话状态，防止残留值；记录登录时间
	// 供中间件做绝对过期与滑动续期）
	session := sessions.Default(c)
	session.Clear()
	session.Set("userID", user.ID)
	session.Set("userEmail", user.Username+"@"+user.Domain.Name)
	session.Set("isAdmin", user.IsAdmin)
	session.Set("loginAt", time.Now().Unix())
	if err := session.Save(); err != nil {
		c.HTML(200, "login", gin.H{
			"error":          "会话保存失败，请重试",
			"oauth2Enabled":  h.authCfg.OAuth2Enabled,
			"ldapEnabled":    h.authCfg.LDAPEnabled,
			"oauth2Provider": h.authCfg.OAuth2Provider,
		})
		return
	}

	c.Redirect(302, "/inbox")
}

// DoLogout clears the session and redirects to the login page.
func (h *AuthHandler) DoLogout(c *gin.Context) {
	session := sessions.Default(c)
	session.Clear()
	session.Save()
	c.Redirect(302, "/login")
}