package auth

import (
	"context"
	"database/sql"
	"log/slog"
	"net"
	"net/http"
	"strings"
	"sync"
	"time"

	"github.com/mithral/vellum/internal/httpx"
)

// contextKey is unexported so no other package can collide with our context values.
type contextKey string

const (
	userContextKey    contextKey = "auth.user"
	sessionContextKey contextKey = "auth.session"
)

// defaultTouchEvery throttles last_seen writes. last_seen exists for session
// listing and expiry hygiene, not security, so minute granularity is plenty and
// a write per request is not worth the contention it causes on SQLite's single
// write lock — especially for media playback, where one seek fires several
// Range requests that would otherwise each take the write lock.
const defaultTouchEvery = 5 * time.Minute

// Authenticator loads sessions from cookies and enforces access.
type Authenticator struct {
	DB         *sql.DB
	CookieName string
	CookieTTL  time.Duration
	Secure     bool
	Log        *slog.Logger
	// TrustedProxies are the networks allowed to name the real client in
	// X-Forwarded-For. Empty means trust nobody. Set from cfg.TrustedProxies.
	TrustedProxies []*net.IPNet

	// limiter throttles password attempts. It lives here rather than on any one
	// handler so that every surface which checks a password — the web login,
	// the Jellyfin login, Subsonic's per-request auth — spends one budget, and
	// an attacker cannot multiply it by guessing through a different surface.
	limiter *loginLimiter

	// touchEvery is the minimum age of a session's last_seen before Middleware
	// will write it again. A zero value means "touch on every request" (the
	// pre-throttling behaviour), which is a safe fallback for hand-built values.
	touchEvery time.Duration
}

// NewAuthenticator builds an Authenticator with sane cookie defaults.
func NewAuthenticator(db *sql.DB, cookieName string, ttl time.Duration, secure bool, log *slog.Logger) *Authenticator {
	if cookieName == "" {
		cookieName = "vellum_session"
	}
	return &Authenticator{
		DB:         db,
		CookieName: cookieName,
		CookieTTL:  ttl,
		Secure:     secure,
		Log:        log,
		limiter:    newLoginLimiter(10, 5*time.Minute),
		touchEvery: defaultTouchEvery,
	}
}

// Middleware attaches the current user to the request context when a valid
// session cookie is present. It never rejects a request: enforcement is the
// job of RequireAuth, so public routes can also see the caller.
func (a *Authenticator) Middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		ctx := r.Context()

		if token, err := a.TokenFromRequest(r); err == nil {
			if sess, err := SessionByToken(ctx, a.DB, token); err == nil {
				if u, err := GetUserByID(ctx, a.DB, sess.UserID); err == nil {
					ctx = context.WithValue(ctx, userContextKey, u)
					ctx = context.WithValue(ctx, sessionContextKey, sess)
					// Throttle the last_seen write. It is for session listing
					// and expiry hygiene, not security, so minute granularity
					// is plenty; a write on every request would take SQLite's
					// single write lock each time, and a media seek alone can
					// issue several Range requests. The decision is made from
					// the LastSeen we already loaded via SessionByToken, so no
					// extra query is added.
					if time.Since(sess.LastSeen) >= a.touchEvery {
						// Best-effort; must not fail the request.
						if err := TouchSession(ctx, a.DB, sess.ID); err != nil {
							a.Log.Warn("touch session", "err", err)
						}
					}
					r = r.WithContext(ctx)
				} else if a.Log != nil {
					a.Log.Warn("session references missing user", "user_id", sess.UserID)
				}
			} else if err != ErrNoSession && a.Log != nil {
				a.Log.Warn("load session", "err", err)
			}
		}
		next.ServeHTTP(w, r)
	})
}

// RequireAuth rejects unauthenticated requests with 401.
func (a *Authenticator) RequireAuth(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if _, ok := CurrentUser(r.Context()); !ok {
			httpx.WriteError(w, http.StatusUnauthorized, "authentication required")
			return
		}
		next.ServeHTTP(w, r)
	})
}

// RequireAdmin rejects authenticated non-admins with 403.
func (a *Authenticator) RequireAdmin(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		u, ok := CurrentUser(r.Context())
		if !ok {
			httpx.WriteError(w, http.StatusUnauthorized, "authentication required")
			return
		}
		if !u.IsAdmin {
			httpx.WriteError(w, http.StatusForbidden, "administrator access required")
			return
		}
		next.ServeHTTP(w, r)
	})
}

// Require calls fn with the current user, or 401s if there is none.
func (a *Authenticator) Require(fn func(http.ResponseWriter, *http.Request, User)) http.Handler {
	return a.RequireAuth(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		u, _ := CurrentUser(r.Context())
		fn(w, r, u)
	}))
}

// CurrentUser returns the authenticated user, if any.
func CurrentUser(ctx context.Context) (User, bool) {
	u, ok := ctx.Value(userContextKey).(User)
	return u, ok
}

// CurrentSession returns the session backing the authenticated user, if any.
func CurrentSession(ctx context.Context) (Session, bool) {
	s, ok := ctx.Value(sessionContextKey).(Session)
	return s, ok
}

// ── cookies ────────────────────────────────────────────────────────────

// SetSessionCookie issues the session cookie. HttpOnly and SameSite=Lax are
// always on; Secure follows configuration (it must be off for plain-HTTP dev).
func (a *Authenticator) SetSessionCookie(w http.ResponseWriter, token string, expires time.Time) {
	http.SetCookie(w, &http.Cookie{
		Name:     a.CookieName,
		Value:    token,
		Path:     "/",
		Expires:  expires,
		MaxAge:   int(time.Until(expires).Seconds()),
		HttpOnly: true,
		Secure:   a.Secure,
		SameSite: http.SameSiteLaxMode,
	})
}

// ClearSessionCookie removes the session cookie.
func (a *Authenticator) ClearSessionCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{
		Name:     a.CookieName,
		Value:    "",
		Path:     "/",
		MaxAge:   -1,
		HttpOnly: true,
		Secure:   a.Secure,
		SameSite: http.SameSiteLaxMode,
	})
}

// TokenFromRequest reads the session token from the cookie, or the
// Authorization: Bearer header for non-browser clients (native apps, CLIs).
func (a *Authenticator) TokenFromRequest(r *http.Request) (string, error) {
	if c, err := r.Cookie(a.CookieName); err == nil && c.Value != "" {
		return c.Value, nil
	}
	if h := r.Header.Get("Authorization"); len(h) > 7 && h[:7] == "Bearer " {
		return h[7:], nil
	}
	return "", ErrNoSession
}

// ClientIP extracts a best-effort client address for logging and rate limiting.
//
// Behind a reverse proxy every request arrives from the proxy, so RemoteAddr
// alone keys the login limiter identically for every client on the internet:
// one attacker locks out a username for everyone, and sessions.ip records the
// proxy. X-Forwarded-For fixes that, but only for a peer we already trust —
// from an untrusted peer that header is attacker-controlled, so it is ignored
// outright and the connection's own address is used, as before.
//
// With a trusted peer the chain is walked right-to-left and the first address
// that is not itself a trusted proxy wins: everything to its right is a hop we
// control, and everything to its left was appended by a client we do not. If
// every hop is trusted the leftmost entry is the best available answer.
func (a *Authenticator) ClientIP(r *http.Request) string {
	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		host = r.RemoteAddr
	}
	if !a.trusts(host) {
		return host
	}
	chain := r.Header.Get("X-Forwarded-For")
	if chain == "" {
		return host
	}
	hops := strings.Split(chain, ",")
	for i := len(hops) - 1; i >= 0; i-- {
		if hop := strings.TrimSpace(hops[i]); !a.trusts(hop) {
			return hop
		}
	}
	return strings.TrimSpace(hops[0])
}

// trusts reports whether ip falls inside one of the configured proxy networks.
func (a *Authenticator) trusts(ip string) bool {
	parsed := net.ParseIP(ip)
	if parsed == nil {
		return false
	}
	for _, n := range a.TrustedProxies {
		if n.Contains(parsed) {
			return true
		}
	}
	return false
}

// ── login rate limiting ─────────────────────────────────────────────────

// AllowLogin records a password attempt and reports whether it is still within
// budget. Call it before checking a password, on every surface that checks one.
func (a *Authenticator) AllowLogin(ip, username string) bool {
	return a.limiter.allow(loginKey(ip, username))
}

// ResetLogin clears the window after a successful login, so a user who fumbled
// a few guesses is not left locked out of their own account.
func (a *Authenticator) ResetLogin(ip, username string) {
	a.limiter.reset(loginKey(ip, username))
}

// loginKey builds the limiter key. It lives here so the web login, Jellyfin and
// Subsonic all count one thing as one attempt.
func loginKey(ip, username string) string { return ip + "|" + username }

// loginLimiter is a fixed-window counter keyed by "ip|username".
//
// In-memory is the right scope for a single-process server: it cannot be
// bypassed by restarting a client, and there is no second process to share it
// with. Persisting failed-login counts would be overkill for a LAN server.
type loginLimiter struct {
	mu     sync.Mutex
	hits   map[string]*hitWindow
	max    int
	window time.Duration
}

type hitWindow struct {
	count int
	reset time.Time
}

func newLoginLimiter(max int, window time.Duration) *loginLimiter {
	return &loginLimiter{hits: make(map[string]*hitWindow), max: max, window: window}
}

func (l *loginLimiter) allow(key string) bool {
	l.mu.Lock()
	defer l.mu.Unlock()

	now := time.Now()
	h, ok := l.hits[key]
	if !ok || now.After(h.reset) {
		l.hits[key] = &hitWindow{count: 1, reset: now.Add(l.window)}
		l.pruneLocked(now)
		return true
	}
	h.count++
	return h.count <= l.max
}

func (l *loginLimiter) reset(key string) {
	l.mu.Lock()
	defer l.mu.Unlock()
	delete(l.hits, key)
}

// pruneLocked drops expired windows so the map cannot grow without bound.
func (l *loginLimiter) pruneLocked(now time.Time) {
	if len(l.hits) < 1000 {
		return
	}
	for k, h := range l.hits {
		if now.After(h.reset) {
			delete(l.hits, k)
		}
	}
}