// Package handlers implements HTTP handlers for NextReceipt, providing
// passwordless email OTP authentication and purchase management.
package handlers

import (
	"database/sql"
	"fmt"
	"html/template"
	"log"
	"net/http"
	"os"
	"strings"
	"sync"
	"time"

	"github.com/cclohmar/NextReceipt/internal/auth"
	"github.com/cclohmar/NextReceipt/internal/database"
	"github.com/cclohmar/NextReceipt/internal/email"
	"github.com/cclohmar/NextReceipt/internal/utils"
)

// ---------------------------------------------------------------------------
// AuthHandler
// ---------------------------------------------------------------------------

// AuthHandler handles passwordless email OTP authentication endpoints.
type AuthHandler struct {
	DB             *sql.DB
	Sessions       *auth.SessionStore
	FailureTracker *auth.FailureTracker
	EmailSender    *email.Sender

	otpMu sync.Mutex // prevents OTP reuse via race conditions
}

// ---------------------------------------------------------------------------
// Handlers
// ---------------------------------------------------------------------------

// LandingPage renders the landing page with the email input form for OTP login.
func (h *AuthHandler) LandingPage(w http.ResponseWriter, r *http.Request) {
	// If the user already has a valid session, redirect to the dashboard.
	if cookie, err := r.Cookie("session_token"); err == nil && cookie.Value != "" {
		if _, ok := h.Sessions.Get(cookie.Value); ok {
			w.Header().Set("HX-Redirect", "/dashboard")
			w.WriteHeader(http.StatusOK)
			return
		}
	}

	tmpl := getTemplate("index.html")
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := tmpl.Execute(w, nil); err != nil {
		log.Printf("ERROR [%s] handlers: LandingPage execute template: %v", time.Now().Format(time.RFC3339), err)
	}
}

// RequestOTP handles OTP generation and email delivery.
func (h *AuthHandler) RequestOTP(w http.ResponseWriter, r *http.Request) {
	emailAddr := strings.TrimSpace(r.FormValue("email"))
	if emailAddr == "" {
		renderError(w, "Email is required.")
		return
	}

	// Rate-limit check: 3 failed attempts trigger a 1-minute lockout.
	if h.FailureTracker.IsLockedOut(emailAddr) {
		renderError(w, "Too many attempts. Please wait 1 minute before trying again.")
		return
	}

	// Retrieve or create the user.
	user, err := database.GetUserByEmail(h.DB, emailAddr)
	if err != nil {
		log.Printf("ERROR [%s] handlers: RequestOTP GetUserByEmail(%s): %v", time.Now().Format(time.RFC3339), emailAddr, err)
		renderError(w, "An error occurred. Please try again.")
		return
	}
	if user == nil {
		userID := utils.NewUUID()
		if err := database.CreateUser(h.DB, userID, emailAddr); err != nil {
			log.Printf("ERROR [%s] handlers: RequestOTP CreateUser(%s): %v", time.Now().Format(time.RFC3339), emailAddr, err)
			renderError(w, "An error occurred. Please try again.")
			return
		}
		user = &database.User{ID: userID, Email: emailAddr}
	}

	// Generate a cryptographically secure 6-digit OTP.
	code, err := auth.GenerateOTP()
	if err != nil {
		log.Printf("ERROR [%s] handlers: RequestOTP GenerateOTP: %v", time.Now().Format(time.RFC3339), err)
		renderError(w, "An error occurred. Please try again.")
		return
	}

	// Persist the OTP with a 5-minute expiry.
	expiresAt := time.Now().Add(5 * time.Minute)
	if err := database.SaveOTP(h.DB, emailAddr, code, expiresAt.Format(time.RFC3339)); err != nil {
		log.Printf("ERROR [%s] handlers: RequestOTP SaveOTP(%s): %v", time.Now().Format(time.RFC3339), emailAddr, err)
		renderError(w, "An error occurred. Please try again.")
		return
	}

	// Deliver OTP via email. Log the error but do not fail the request.
	if h.EmailSender != nil {
		if err := h.EmailSender.SendOTP(emailAddr, code); err != nil {
			log.Printf("ERROR [%s] handlers: RequestOTP SendOTP(%s): %v", time.Now().Format(time.RFC3339), emailAddr, err)
		}
	} else {
		log.Printf("WARN  [%s] handlers: RequestOTP(%s): SMTP not configured — OTP code %s not delivered via email",
			time.Now().Format(time.RFC3339), emailAddr, code)
	}

	// Render the OTP verification form as an HTMX fragment.
	renderOTPForm(w, emailAddr, "")
}

// VerifyOTP handles OTP code verification and session creation.
func (h *AuthHandler) VerifyOTP(w http.ResponseWriter, r *http.Request) {
	emailAddr := strings.TrimSpace(r.FormValue("email"))
	otpCode := collectOTP(r)

	if emailAddr == "" || otpCode == "" {
		renderOTPForm(w, emailAddr, "Email and OTP code are required.")
		return
	}

	// Fetch the stored OTP record.
	stored, err := database.GetOTP(h.DB, emailAddr)
	if err != nil {
		log.Printf("ERROR [%s] handlers: VerifyOTP GetOTP(%s): %v", time.Now().Format(time.RFC3339), emailAddr, err)
		renderOTPForm(w, emailAddr, "An error occurred. Please try again.")
		return
	}
	if stored == nil {
		renderOTPForm(w, emailAddr, "No OTP found for this email. Please request a new code.")
		return
	}

	// Parse the stored expiry timestamp.
	expiresAt, err := time.Parse(time.RFC3339, stored.ExpiresAt)
	if err != nil {
		log.Printf("ERROR [%s] handlers: VerifyOTP parse expiry(%s): %v", time.Now().Format(time.RFC3339), stored.ExpiresAt, err)
		renderOTPForm(w, emailAddr, "An error occurred. Please try again.")
		return
	}

	// Validate + delete OTP atomically to prevent race-condition reuse.
	h.otpMu.Lock()
	if !auth.ValidateOTP(otpCode, stored.OTPCode, expiresAt) {
		h.otpMu.Unlock()
		h.FailureTracker.RecordFailure(emailAddr)
		renderOTPForm(w, emailAddr, "Invalid or expired OTP code. Please try again.")
		return
	}

	// Successful verification: delete OTP immediately.
	h.FailureTracker.Reset(emailAddr)
	if err := database.DeleteOTP(h.DB, emailAddr); err != nil {
		log.Printf("ERROR [%s] handlers: VerifyOTP DeleteOTP(%s): %v", time.Now().Format(time.RFC3339), emailAddr, err)
	}
	h.otpMu.Unlock()

	// Retrieve the user record to obtain the user ID.
	user, err := database.GetUserByEmail(h.DB, emailAddr)
	if err != nil || user == nil {
		log.Printf("ERROR [%s] handlers: VerifyOTP GetUserByEmail(%s): err=%v", time.Now().Format(time.RFC3339), emailAddr, err)
		renderOTPForm(w, emailAddr, "An error occurred. Please try again.")
		return
	}

	// Generate an in-memory session token.
	token, err := h.Sessions.Generate(user.ID)
	if err != nil {
		log.Printf("ERROR [%s] handlers: VerifyOTP Session Generate(%s): %v", time.Now().Format(time.RFC3339), user.ID, err)
		renderOTPForm(w, emailAddr, "An error occurred. Please try again.")
		return
	}

	// Set the session cookie (HttpOnly, SameSite=Lax, Secure, 24h).
	secure := strings.HasPrefix(os.Getenv("BASE_URL"), "https://")
	http.SetCookie(w, &http.Cookie{
		Name:     "session_token",
		Value:    token,
		Path:     "/",
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		Secure:   secure,
		Expires:  time.Now().Add(24 * time.Hour),
	})

	// Always redirect to dashboard (no onboarding step needed).
	w.Header().Set("HX-Redirect", "/dashboard")
	w.WriteHeader(http.StatusOK)
}

// ---------------------------------------------------------------------------
// Middleware
// ---------------------------------------------------------------------------

// RequireAuth is HTTP middleware that validates the session cookie on protected
// routes. If the session is invalid or expired it redirects to the landing page.
func (h *AuthHandler) RequireAuth(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		cookie, err := r.Cookie("session_token")
		if err != nil {
			w.Header().Set("HX-Redirect", "/")
			w.WriteHeader(http.StatusUnauthorized)
			return
		}

		userID, ok := h.Sessions.Get(cookie.Value)
		if !ok {
			w.Header().Set("HX-Redirect", "/")
			w.WriteHeader(http.StatusUnauthorized)
			return
		}

		r.Header.Set("X-User-ID", userID)
		next.ServeHTTP(w, r)
	})
}

// getUserID returns the authenticated user ID from the request.
func getUserID(r *http.Request) string {
	return r.Header.Get("X-User-ID")
}

// ---------------------------------------------------------------------------
// Logout
// ---------------------------------------------------------------------------

// Logout clears the session cookie and invalidates the server-side session.
func (h *AuthHandler) Logout(w http.ResponseWriter, r *http.Request) {
	if cookie, err := r.Cookie("session_token"); err == nil && cookie.Value != "" {
		h.Sessions.Delete(cookie.Value)
	}
	http.SetCookie(w, &http.Cookie{
		Name:     "session_token",
		Value:    "",
		Path:     "/",
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		MaxAge:   -1,
	})
	w.Header().Set("HX-Redirect", "/")
	w.WriteHeader(http.StatusOK)
}

// ---------------------------------------------------------------------------
// Internal helpers
// ---------------------------------------------------------------------------

// renderError writes an HTMX-compatible HTML error fragment to the response.
func renderError(w http.ResponseWriter, message string) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	fmt.Fprintf(w, `<div class="error-message" style="color: #fca5a5; margin-bottom: 1rem;">%s</div>`, template.HTMLEscapeString(message))
}

// renderOTPForm writes the OTP verification form partial as an HTMX fragment.
func renderOTPForm(w http.ResponseWriter, email string, errMsg string) {
	tmpl := getTemplate("otp_form")
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := tmpl.Execute(w, map[string]string{"Email": email, "Error": errMsg}); err != nil {
		log.Printf("ERROR [%s] handlers: renderOTPForm execute: %v", time.Now().Format(time.RFC3339), err)
	}
}

// collectOTP reads the 6-digit OTP code from the form value.
func collectOTP(r *http.Request) string {
	code := r.FormValue("otp_code")
	code = strings.Map(func(r rune) rune {
		if r >= '0' && r <= '9' {
			return r
		}
		return -1
	}, code)
	if len(code) != 6 {
		return ""
	}
	return code
}