package main

import (
	"context"
	"encoding/json"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"golang.org/x/crypto/bcrypt"
)

// Website-serving layer: static frontend + login/logout, porting main.py so the
// unchanged frontend loads on the Go tracker. Cookie issuing/verifying is in
// auth.go; this file is the handlers + the static file server.

// A fixed bcrypt hash used to keep the no-such-user path constant-time, matching
// Python's _DUMMY_HASH. (Hash of an arbitrary constant; never matches input.)
var dummyBcryptHash = []byte("$2a$12$C6UzMDM.H6dfI/f/IKcEeO3Jj6Q1jK7Z1qkq9b2yY6m4eW7N0pZ2K")

type loginLimiter struct {
	mu   sync.Mutex
	last map[string]time.Time
}

func newLoginLimiter() *loginLimiter { return &loginLimiter{last: map[string]time.Time{}} }

// allow returns false if this IP attempted within the 5s cooldown (main.py).
func (l *loginLimiter) allow(ip string) bool {
	l.mu.Lock()
	defer l.mu.Unlock()
	now := time.Now()
	if t, ok := l.last[ip]; ok && now.Sub(t) < 5*time.Second {
		return false
	}
	l.last[ip] = now
	return true
}

// GET /login — serve the login page (main.py:login_page).
func (s *Server) handleLoginGet(w http.ResponseWriter, r *http.Request) {
	s.serveStaticFile(w, r, "login.html")
}

// POST /login — authenticate and set the session cookie (main.py:login).
func (s *Server) handleLoginPost(w http.ResponseWriter, r *http.Request) {
	ip := clientIP(r)
	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
		ip = strings.TrimSpace(strings.Split(xff, ",")[0])
	}
	if !s.loginLimiter.allow(ip) {
		writeJSON(w, http.StatusTooManyRequests, map[string]any{"detail": "Too many login attempts. Try again in a few seconds."})
		return
	}
	var body struct {
		Username string `json:"username"`
		Password string `json:"password"`
	}
	if json.NewDecoder(http.MaxBytesReader(w, r.Body, 1<<20)).Decode(&body) != nil {
		writeJSON(w, http.StatusBadRequest, map[string]any{"detail": "Invalid request body"})
		return
	}
	username := strings.ToLower(strings.TrimSpace(body.Username))
	if username == "" || body.Password == "" {
		writeJSON(w, http.StatusBadRequest, map[string]any{"detail": "Username and password required"})
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), 10*time.Second)
	defer cancel()
	var dbUser, hash string
	var isAdmin bool
	err := s.pool.QueryRow(ctx,
		"SELECT username, password_hash, is_admin FROM users WHERE LOWER(username) = $1", username,
	).Scan(&dbUser, &hash, &isAdmin)
	// Constant-time: always run bcrypt, even when the user doesn't exist.
	pwOK := false
	if err == nil {
		pwOK = bcrypt.CompareHashAndPassword([]byte(hash), []byte(body.Password)) == nil
	} else {
		_ = bcrypt.CompareHashAndPassword(dummyBcryptHash, []byte(body.Password))
	}
	if !pwOK {
		writeJSON(w, http.StatusUnauthorized, map[string]any{"detail": "Invalid username or password"})
		return
	}

	token := issueSessionCookie(s.secretKey, sessionUser{Username: dbUser, IsAdmin: isAdmin})
	http.SetCookie(w, &http.Cookie{
		Name: "session", Value: token, Path: "/", MaxAge: sessionMaxAge,
		HttpOnly: true, Secure: true, SameSite: http.SameSiteLaxMode,
	})
	writeJSON(w, http.StatusOK, map[string]any{"ok": true, "username": dbUser, "is_admin": isAdmin})
}

// GET /logout — clear the cookie and redirect to /login (main.py:logout).
func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
	http.SetCookie(w, &http.Cookie{Name: "session", Value: "", Path: "/", MaxAge: -1})
	http.Redirect(w, r, "/login", http.StatusFound)
}

// GET /icons/{filename} — serve an icon file (main.py:serve_icon).
func (s *Server) handleIcon(w http.ResponseWriter, r *http.Request) {
	name := r.PathValue("filename")
	if name == "" || strings.ContainsAny(name, "/\\") || strings.Contains(name, "..") {
		http.NotFound(w, r)
		return
	}
	s.serveStaticFile(w, r, filepath.Join("icons", name))
}

// handleStatic is the catch-all GET handler: serves files from staticDir, falls
// back to index.html for SPA routes (React client-side routing). Registered last
// so the specific API routes take precedence.
func (s *Server) handleStatic(w http.ResponseWriter, r *http.Request) {
	upath := path.Clean("/" + r.URL.Path)
	full := filepath.Join(s.staticDir, filepath.FromSlash(upath))
	// Guard against path traversal escaping staticDir.
	if rel, err := filepath.Rel(s.staticDir, full); err != nil || strings.HasPrefix(rel, "..") {
		http.NotFound(w, r)
		return
	}
	if info, err := os.Stat(full); err == nil {
		if info.IsDir() {
			if idx := filepath.Join(full, "index.html"); fileExists(idx) {
				http.ServeFile(w, r, idx)
				return
			}
		} else {
			http.ServeFile(w, r, full)
			return
		}
	}
	// SPA fallback — serve the app shell for unknown (client-routed) paths.
	http.ServeFile(w, r, filepath.Join(s.staticDir, "index.html"))
}

func (s *Server) serveStaticFile(w http.ResponseWriter, r *http.Request, rel string) {
	full := filepath.Join(s.staticDir, filepath.FromSlash(rel))
	if !fileExists(full) {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	http.ServeFile(w, r, full)
}

func fileExists(p string) bool {
	info, err := os.Stat(p)
	return err == nil && !info.IsDir()
}

// runIssueCookieCLI prints a session token for cross-checking itsdangerous
// cookie interop with the Python service.
func runIssueCookieCLI() {
	if len(os.Args) < 5 {
		os.Stderr.WriteString("usage: tracker-go issue-cookie <username> <is_admin:true|false> <secret_key>\n")
		os.Exit(2)
	}
	os.Stdout.WriteString(issueSessionCookie(os.Args[4], sessionUser{Username: os.Args[2], IsAdmin: os.Args[3] == "true"}))
}