package app

import (
	"crypto/hmac"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"net/http"
	"strconv"
	"strings"
	"time"
)

const (
	adminSessionCookieName = "sub2api_crm_admin_session"
	defaultAdminUsername   = "admin"
	defaultAdminSessionTTL = 12 * time.Hour
)

type AdminAuthConfig struct {
	Token      string
	Username   string
	Password   string
	SessionTTL time.Duration
	Now        func() time.Time
}

type adminLoginRequest struct {
	Username string `json:"username"`
	Password string `json:"password"`
}

type adminSessionInfo struct {
	Username  string
	ExpiresAt time.Time
}

func (c AdminAuthConfig) normalized() AdminAuthConfig {
	c.Token = strings.TrimSpace(c.Token)
	c.Username = strings.TrimSpace(c.Username)
	c.Password = strings.TrimSpace(c.Password)
	if c.Username == "" {
		c.Username = defaultAdminUsername
	}
	if c.Password == "" {
		c.Password = c.Token
	}
	if c.SessionTTL <= 0 {
		c.SessionTTL = defaultAdminSessionTTL
	}
	if c.Now == nil {
		c.Now = time.Now
	}
	return c
}

func (c AdminAuthConfig) loginEnabled() bool {
	cfg := c.normalized()
	return cfg.Token != "" && cfg.Password != ""
}

func (c AdminAuthConfig) now() time.Time {
	return c.normalized().Now()
}

func (c AdminAuthConfig) sessionCookie(r *http.Request) (*http.Cookie, *adminSessionInfo, bool) {
	cfg := c.normalized()
	cookie, err := r.Cookie(adminSessionCookieName)
	if err != nil || cookie == nil || strings.TrimSpace(cookie.Value) == "" {
		return nil, nil, false
	}

	info, ok := verifyAdminSessionValue(cfg.Token, cookie.Value, cfg.now())
	if !ok {
		return cookie, nil, false
	}
	return cookie, info, true
}

func (c AdminAuthConfig) requestAuthorized(r *http.Request) bool {
	cfg := c.normalized()
	if secureCompare(bearerToken(r), cfg.Token) {
		return true
	}
	_, _, ok := cfg.sessionCookie(r)
	return ok
}

func secureCompare(left, right string) bool {
	if left == "" || right == "" {
		return false
	}
	return subtle.ConstantTimeCompare([]byte(left), []byte(right)) == 1
}

func signAdminSessionValue(secret, username string, expiresAt time.Time) string {
	payload := strings.TrimSpace(username) + "|" + strconv.FormatInt(expiresAt.Unix(), 10)
	mac := hmac.New(sha256.New, []byte(secret))
	_, _ = mac.Write([]byte(payload))
	signature := base64.RawURLEncoding.EncodeToString(mac.Sum(nil))
	return base64.RawURLEncoding.EncodeToString([]byte(payload)) + "." + signature
}

func verifyAdminSessionValue(secret, raw string, now time.Time) (*adminSessionInfo, bool) {
	if strings.TrimSpace(secret) == "" || strings.TrimSpace(raw) == "" {
		return nil, false
	}
	parts := strings.Split(raw, ".")
	if len(parts) != 2 {
		return nil, false
	}
	payloadBytes, err := base64.RawURLEncoding.DecodeString(parts[0])
	if err != nil {
		return nil, false
	}
	payload := string(payloadBytes)
	mac := hmac.New(sha256.New, []byte(secret))
	_, _ = mac.Write([]byte(payload))
	expectedSignature := mac.Sum(nil)
	signatureBytes, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return nil, false
	}
	if subtle.ConstantTimeCompare(signatureBytes, expectedSignature) != 1 {
		return nil, false
	}

	fields := strings.Split(payload, "|")
	if len(fields) != 2 {
		return nil, false
	}
	username := strings.TrimSpace(fields[0])
	if username == "" {
		return nil, false
	}
	unixSeconds, err := strconv.ParseInt(fields[1], 10, 64)
	if err != nil {
		return nil, false
	}
	expiresAt := time.Unix(unixSeconds, 0)
	if !expiresAt.After(now) {
		return nil, false
	}
	return &adminSessionInfo{Username: username, ExpiresAt: expiresAt}, true
}

func issueAdminSessionCookie(w http.ResponseWriter, r *http.Request, cfg AdminAuthConfig, username string) *adminSessionInfo {
	cfg = cfg.normalized()
	expiresAt := cfg.now().Add(cfg.SessionTTL)
	http.SetCookie(w, &http.Cookie{
		Name:     adminSessionCookieName,
		Value:    signAdminSessionValue(cfg.Token, username, expiresAt),
		Path:     "/",
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		Secure:   requestUsesHTTPS(r),
		Expires:  expiresAt,
		MaxAge:   int(cfg.SessionTTL.Seconds()),
	})
	return &adminSessionInfo{Username: username, ExpiresAt: expiresAt}
}

func clearAdminSessionCookie(w http.ResponseWriter, r *http.Request) {
	http.SetCookie(w, &http.Cookie{
		Name:     adminSessionCookieName,
		Value:    "",
		Path:     "/",
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		Secure:   requestUsesHTTPS(r),
		Expires:  time.Unix(0, 0),
		MaxAge:   -1,
	})
}

func requestUsesHTTPS(r *http.Request) bool {
	if r != nil && r.TLS != nil {
		return true
	}
	return strings.EqualFold(strings.TrimSpace(r.Header.Get("X-Forwarded-Proto")), "https")
}

func handleAdminSessionState(w http.ResponseWriter, r *http.Request, cfg AdminAuthConfig) {
	cfg = cfg.normalized()
	payload := map[string]any{
		"authenticated": false,
		"login_enabled": cfg.loginEnabled(),
		"username":      cfg.Username,
	}
	if _, session, ok := cfg.sessionCookie(r); ok {
		payload["authenticated"] = true
		payload["username"] = session.Username
		payload["expires_at"] = session.ExpiresAt.Format(time.RFC3339)
	}
	writeJSON(w, http.StatusOK, payload)
}

func handleAdminSessionLogin(w http.ResponseWriter, r *http.Request, cfg AdminAuthConfig) {
	cfg = cfg.normalized()
	if cfg.Token == "" {
		writeHTTPError(w, &httpError{StatusCode: http.StatusInternalServerError, Code: "server_misconfigured", Message: "admin token is not configured"})
		return
	}
	if !cfg.loginEnabled() {
		writeHTTPError(w, &httpError{StatusCode: http.StatusServiceUnavailable, Code: "login_disabled", Message: "admin login is not enabled"})
		return
	}
	var req adminLoginRequest
	if err := decodeJSON(r, &req); err != nil {
		writeHTTPError(w, err)
		return
	}
	if strings.TrimSpace(req.Username) == "" || strings.TrimSpace(req.Password) == "" {
		writeHTTPError(w, &httpError{StatusCode: http.StatusBadRequest, Code: "bad_request", Message: "username and password are required"})
		return
	}
	if !secureCompare(strings.TrimSpace(req.Username), cfg.Username) || !secureCompare(strings.TrimSpace(req.Password), cfg.Password) {
		writeHTTPError(w, &httpError{StatusCode: http.StatusUnauthorized, Code: "unauthorized", Message: "invalid admin credentials"})
		return
	}
	session := issueAdminSessionCookie(w, r, cfg, cfg.Username)
	writeJSON(w, http.StatusOK, map[string]any{
		"authenticated": true,
		"username":      session.Username,
		"expires_at":    session.ExpiresAt.Format(time.RFC3339),
	})
}

func handleAdminSessionLogout(w http.ResponseWriter, r *http.Request) {
	clearAdminSessionCookie(w, r)
	w.WriteHeader(http.StatusNoContent)
}

func requireAdminAccess(cfg AdminAuthConfig, next http.Handler) http.Handler {
	cfg = cfg.normalized()
	if cfg.Token == "" {
		return http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
			writeHTTPError(w, &httpError{StatusCode: http.StatusInternalServerError, Code: "server_misconfigured", Message: "admin token is not configured"})
		})
	}
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !cfg.requestAuthorized(r) {
			writeHTTPError(w, &httpError{StatusCode: http.StatusUnauthorized, Code: "unauthorized", Message: "missing or invalid admin credentials"})
			return
		}
		next.ServeHTTP(w, r)
	})
}

func adminSessionDebugValue(secret, username string, expiresAt time.Time) string {
	return hex.EncodeToString([]byte(signAdminSessionValue(secret, username, expiresAt)))
}

func adminSessionPayload(raw string) map[string]any {
	payload := map[string]any{"raw": raw}
	parts := strings.Split(raw, ".")
	if len(parts) != 2 {
		return payload
	}
	body, err := base64.RawURLEncoding.DecodeString(parts[0])
	if err != nil {
		return payload
	}
	fields := strings.Split(string(body), "|")
	payload["payload"] = string(body)
	if len(fields) == 2 {
		payload["username"] = fields[0]
		payload["expires_unix"] = fields[1]
	}
	return payload
}

func marshalAdminSessionPayload(raw string) string {
	body, _ := json.Marshal(adminSessionPayload(raw))
	return string(body)
}