package httpserver

import (
	"errors"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/krow/krow-backend/go-api/internal/auth"
	"github.com/krow/krow-backend/go-api/internal/authctx"
	"github.com/krow/krow-backend/go-api/internal/domain"
	"github.com/krow/krow-backend/go-api/internal/orgctx"
)

// The authentication surface: sign in, sign out, and the middleware that turns
// a cookie into an identity.
//
// The shape of the whole thing is one sentence: the browser holds an opaque
// random string it cannot read, the database holds SHA-256 of that string, and
// every protected request is a lookup from one to the other. No claim travels
// in the request. There is no token in a JSON body, no user id in a query
// string, no organization in a header — those are all things a client can
// write, and a client writing its own identity is the bug this replaces.

// sessionCookieName is the cookie the browser holds.
//
// The "__Host-" prefix would be stronger — browsers enforce Secure, Path=/ and
// no Domain on it — but it also *requires* Secure, which cannot be set over
// plain HTTP on localhost. A cookie name that only works in production is worse
// than a plain one that works everywhere, so the hardening is done by the
// attributes below instead, where it can be conditional.
const sessionCookieName = "krow_session"

/* ── Cookie ─────────────────────────────────────────────────────────────── */

// secureCookies reports whether Secure may be set.
//
// Secure means "only ever send this over HTTPS". Setting it in development
// would mean the browser silently declines to send the cookie back to
// http://localhost, and the symptom is an endless loop of successful logins
// that never authenticate anything.
func (s *Server) secureCookies() bool { return s.cfg.AppEnv != "development" }

// setSessionCookie writes the raw token to the browser.
//
// This is the only place the raw token is written to a response, and it goes
// into a Set-Cookie header rather than a body: HttpOnly means no script on the
// page can read it, which is what makes an XSS bug stop short of session theft.
//
// maxAge matches the session's own lifetime so the browser drops the cookie at
// roughly the moment the server would refuse it. The server is still the
// authority — a cookie the browser keeps too long is simply rejected — but a
// cookie that expires with its session keeps the two honest.
func (s *Server) setSessionCookie(w http.ResponseWriter, token string, lifetime time.Duration) {
	http.SetCookie(w, &http.Cookie{
		Name:  sessionCookieName,
		Value: token,
		Path:  "/",
		// HttpOnly: script cannot read it.
		HttpOnly: true,
		// Lax, not Strict and not None. Strict would drop the cookie on any
		// cross-site navigation, so following a link into the app would land on
		// a login page despite a live session. None would require Secure and
		// would send the cookie on cross-site POSTs, which is the CSRF hole Lax
		// exists to close.
		SameSite: http.SameSiteLaxMode,
		Secure:   s.secureCookies(),
		MaxAge:   int(lifetime.Seconds()),
	})
}

// clearSessionCookie expires the cookie in the browser.
//
// The attributes must match the ones it was set with — a cookie is identified
// by name, domain and path, so clearing it with a different Path leaves the
// original in place and the browser keeps sending a token the server has
// already deleted.
func (s *Server) clearSessionCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{
		Name:     sessionCookieName,
		Value:    "",
		Path:     "/",
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		Secure:   s.secureCookies(),
		MaxAge:   -1,
	})
}

// sessionToken reads the raw token out of the request, if there is one.
func sessionToken(r *http.Request) string {
	c, err := r.Cookie(sessionCookieName)
	if err != nil || c == nil {
		return ""
	}
	return strings.TrimSpace(c.Value)
}

/* ── Routes ─────────────────────────────────────────────────────────────── */

func (s *Server) routeAuth(mux *http.ServeMux) int {
	mux.HandleFunc("POST /api/v1/auth/login", s.handleLogin)
	mux.HandleFunc("POST /api/v1/auth/logout", s.handleLogout)
	return 2
}

// loginRequest is the body of POST /api/v1/auth/login.
type loginRequest struct {
	Email      string `json:"email"`
	Password   string `json:"password"`
	RememberMe bool   `json:"remember_me"`
}

// handleLogin verifies a password and issues a session.
//
// The order of operations is deliberate:
//
//  1. Parse and validate the *shape* of the request. A missing field is a
//     malformed request, not a failed login, and saying so reveals nothing.
//  2. Check the rate limit, before any expensive work. Refusing early is the
//     point — an attacker must not be able to make the server hash for them.
//  3. Verify the credentials, which takes the same measurable time whether the
//     email exists or not (see auth.Credentials).
//  4. Issue the session and set the cookie.
//
// Every failure in step 3 produces one identical response. The reason goes to
// the log, at warn, with the email — which is already in the request — and
// never the password.
func (s *Server) handleLogin(w http.ResponseWriter, r *http.Request) {
	var req loginRequest
	if err := decodeInto(r, &req); err != nil {
		writeError(w, s.log, err)
		return
	}

	email := strings.TrimSpace(req.Email)
	details := map[string]string{}
	if email == "" {
		details["email"] = "an email address is required"
	}
	if req.Password == "" {
		details["password"] = "a password is required"
	}
	if len(details) > 0 {
		writeError(w, s.log, domain.Validation("email and password are required", details))
		return
	}

	// Two budgets, both consulted, both counted. The per-email budget stops one
	// account being ground down from many addresses; the per-address budget,
	// which is wider, stops one host working through many accounts. They are
	// separate limiters because they are deliberately different sizes — see the
	// note on Server.
	addr := clientAddr(r)
	emailKey := strings.ToLower(email)
	for _, check := range []struct {
		limiter *attemptLimiter
		key     string
		scope   string
	}{
		{s.loginByEmail, emailKey, "email"},
		{s.loginByAddr, addr, "address"},
	} {
		if ok, retryAfter := check.limiter.Allow(check.key); !ok {
			w.Header().Set("Retry-After", retryAfterSeconds(retryAfter))
			s.log.Warn("login rate limited", "scope", check.scope,
				"email", email, "addr", addr,
				"retry_after_seconds", retryAfterSeconds(retryAfter))
			writeError(w, s.log, domain.RateLimited(
				"too many sign-in attempts; wait a few minutes and try again"))
			return
		}
	}

	user, reason, err := s.credentials.Verify(r.Context(), email, req.Password)
	if errors.Is(err, auth.ErrInvalidCredentials) {
		s.loginByEmail.Fail(emailKey)
		s.loginByAddr.Fail(addr)
		// The reason is the whole value of this line and must never leave it.
		s.log.Warn("login failed", "email", email, "addr", addr, "reason", string(reason))
		writeError(w, s.log, domain.Unauthenticated())
		return
	}
	if err != nil {
		// The database is down, or a stored hash is unreadable. The caller's
		// credentials were never judged, so this is a 500 and not a 401.
		writeError(w, s.log, domain.Internal(err))
		return
	}

	token, sess, err := s.sessions.Issue(r.Context(), user.ID, req.RememberMe)
	if err != nil {
		writeError(w, s.log, domain.Internal(err))
		return
	}

	// A correct password clears the email's penalty, so two typos followed by a
	// success leave nothing behind. The address counter is left alone: one
	// correct login should not wipe the budget for every other account being
	// tried from the same host.
	s.loginByEmail.Reset(emailKey)

	s.setSessionCookie(w, token, time.Until(sess.ExpiresAt))

	// Best effort, deliberately after the session exists: a failure to stamp
	// last_login_at is a lost diagnostic, not a reason to refuse a sign-in that
	// has already succeeded.
	if err := s.users.MarkLoggedIn(r.Context(), user.ID, s.now()); err != nil {
		s.log.Warn("could not record last_login_at", "user_id", user.ID, "error", err)
	}

	s.log.Info("login", "user_id", user.ID, "email", user.Email,
		"remember_me", req.RememberMe, "session_id", sess.ID,
		"expires_at", sess.ExpiresAt, "absolute_expires_at", sess.AbsoluteExpiresAt)

	// The body is the user, in exactly the shape GET /me returns, so the
	// frontend can render the signed-in state without a second round trip.
	//
	// The token is NOT here and must never be. It went out in a Set-Cookie
	// header the page cannot read; putting it in the body would hand it to
	// every script on the page and undo HttpOnly entirely.
	record, err := s.userRecord(r.Context(), s.db.Pool, user.ID)
	if err != nil {
		writeError(w, s.log, err)
		return
	}
	writeRecord(w, http.StatusOK, record)
}

// handleLogout revokes the session behind the cookie and clears the cookie.
//
// Idempotent by construction: no cookie, an unknown token and a live session
// all end the same way — the cookie is cleared and the answer is 200. Logging
// out is a request to not be signed in, and the caller is not signed in
// afterwards in every one of those cases.
//
// It is deliberately public. Requiring a valid session to log out means a user
// whose session has already expired gets a 401 from the one action that would
// have tidied up their stale cookie.
func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
	if token := sessionToken(r); token != "" {
		if err := s.sessions.Revoke(r.Context(), token); err != nil {
			// Revoke already treats "no such session" as success, so this is a
			// real failure — the database, most likely. Clearing the cookie is
			// still the right thing to do, and reporting a 500 for a logout
			// would leave the caller signed in with no way to fix it.
			s.log.Error("could not revoke session on logout", "error", err)
		}
	}
	s.clearSessionCookie(w)
	writeJSON(w, http.StatusOK, envelope{Data: map[string]any{"status": "signed_out"}})
}

/* ── Middleware ─────────────────────────────────────────────────────────── */

// publicPaths are the only endpoints reachable without a session.
//
// An allowlist rather than a list of protected prefixes, so the failure mode of
// forgetting to update it is a route that refuses everyone — not one that
// serves everyone. A new endpoint is private until someone deliberately says
// otherwise, which is the direction a mistake should fall in.
var publicPaths = map[string]bool{
	"/health":             true,
	"/api/v1/auth/login":  true,
	"/api/v1/auth/logout": true,
}

// authenticate resolves the session cookie into an identity, or refuses.
//
// This replaces devOrgMiddleware, which put a fixed organization on every
// request with no credential behind it. The seam is the same one that comment
// promised: everything downstream still reads the organization from
// orgctx, and not one service or repository changed.
//
// What the request cannot influence: nothing here reads the body, the query
// string or any header other than Cookie. The user id, the organization and the
// role are all read from the sessions and users tables, keyed by a token the
// client cannot forge without already holding it.
func (s *Server) authenticate(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if publicPaths[r.URL.Path] {
			next.ServeHTTP(w, r)
			return
		}

		token := sessionToken(r)
		if token == "" {
			writeError(w, s.log, domain.Unauthenticated())
			return
		}

		sess, err := s.sessions.Authenticate(r.Context(), token)
		if err != nil {
			// Not found and expired are logged apart and answered identically.
			// Clearing the cookie stops the browser re-sending a token that
			// will never work again.
			s.log.Debug("session rejected", "reason", sessionRejection(err), "path", r.URL.Path)
			if errors.Is(err, auth.ErrSessionNotFound) || errors.Is(err, auth.ErrSessionExpired) ||
				errors.Is(err, auth.ErrEmptyToken) {
				s.clearSessionCookie(w)
				writeError(w, s.log, domain.Unauthenticated())
				return
			}
			writeError(w, s.log, domain.Internal(err))
			return
		}

		// The user is re-read on every request rather than cached in the
		// session row, so suspending an account takes effect on the account's
		// next request instead of whenever its session happens to lapse.
		user, err := s.users.FindByID(r.Context(), sess.UserID)
		if err != nil {
			if errors.Is(err, auth.ErrUserNotFound) {
				// The FK cascades, so this should be unreachable. If it happens
				// the session is orphaned and worth destroying.
				s.log.Warn("session references a missing user", "session_id", sess.ID)
				_ = s.sessions.RevokeID(r.Context(), sess.ID)
				s.clearSessionCookie(w)
				writeError(w, s.log, domain.Unauthenticated())
				return
			}
			writeError(w, s.log, domain.Internal(err))
			return
		}
		if !user.IsActive() {
			// Suspension revokes on contact. Leaving the session alive would
			// mean a suspended account keeps a working cookie for up to thirty
			// days, refused one request at a time.
			s.log.Warn("session for an inactive user revoked",
				"user_id", user.ID, "status", user.Status)
			_ = s.sessions.RevokeID(r.Context(), sess.ID)
			s.clearSessionCookie(w)
			writeError(w, s.log, domain.Unauthenticated())
			return
		}

		id := authctx.Identity{
			UserID: user.ID, OrgID: user.OrgID, Email: user.Email,
			FullName: user.FullName, Role: user.Role, AccountType: user.AccountType,
			Status: user.Status, SessionID: sess.ID, ExpiresAt: sess.ExpiresAt,
		}
		ctx := authctx.With(r.Context(), id)
		// The organization comes from the user's row, never from the request.
		// Every service and repository already takes it as a parameter, so this
		// one line is the whole of the tenancy change.
		ctx = orgctx.With(ctx, user.OrgID)
		next.ServeHTTP(w, r.WithContext(ctx))
	})
}

// sessionRejection names why a session was refused, for the log only.
func sessionRejection(err error) string {
	switch {
	case errors.Is(err, auth.ErrSessionNotFound):
		return "not_found"
	case errors.Is(err, auth.ErrSessionExpired):
		return "expired"
	case errors.Is(err, auth.ErrEmptyToken):
		return "empty_token"
	default:
		return "error"
	}
}

// retryAfterSeconds renders a duration for the Retry-After header, rounded up
// and never below one second — "Retry-After: 0" invites an immediate retry.
func retryAfterSeconds(d time.Duration) string {
	secs := int(d.Round(time.Second) / time.Second)
	if secs < 1 {
		secs = 1
	}
	return strconv.Itoa(secs)
}