package httpapi

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/base64"
	"encoding/json"
	"errors"
	"log/slog"
	"net"
	"net/http"
	"net/url"
	"strings"
	"time"

	"commilitia.net/cdrop/internal/db"
	"commilitia.net/cdrop/internal/jwtauth"
)

// Scan-login (QR), AUTH.md §4. A new device shows a QR; an already-logged-in
// phone scans and approves it into the user's account as a restricted guest
// session. Three secrets are kept apart so the QR — which can be photographed —
// only lets someone *request* approval, never collect the session:
//
//   - request_id   : public handle, in the QR.
//   - approval_code : in the QR; binds the authed approver to this request.
//   - poll_secret  : returned ONCE to the new device, never in the QR; only its
//     SHA-256 is stored. The session is delivered solely on the connection that
//     proves the plaintext, so a QR photographer (no poll_secret, not logged in)
//     fails twice.
//
// The session row is created when the new device collects it (handleQRStatus),
// not at approve time, so the cookie secret is generated on and returned to the
// new device's own TLS connection and never travels through the phone.

// qrStatusPollWindow caps how long one status long-poll blocks before returning
// "pending" for the client to re-poll. var (not const) so tests can shrink it.
var qrStatusPollWindow = 25 * time.Second

type qrStartReq struct {
	DeviceName string `json:"device_name"`
	DeviceType string `json:"device_type"`
}

type qrStartResp struct {
	RequestID  string `json:"request_id"`
	PollSecret string `json:"poll_secret"`
	QRPayload  string `json:"qr_payload"`
	ExpiresAt  int64  `json:"expires_at"`
}

type qrStatusResp struct {
	Status      string    `json:"status"` // pending | approved | denied | expired
	AccessToken string    `json:"access_token,omitempty"`
	ExpiresIn   int       `json:"expires_in,omitempty"`
	User        *userResp `json:"user,omitempty"`
	DeviceName  string    `json:"device_name,omitempty"`
}

type qrRequestResp struct {
	DeviceName string `json:"device_name"`
	DeviceType string `json:"device_type"`
	RequestIP  string `json:"request_ip"`
	ExpiresAt  int64  `json:"expires_at"`
	Status     string `json:"status"`
	// StepUp tells the approver UI a fresh re-auth is required before approving.
	StepUp bool `json:"step_up"`
}

type qrApproveReq struct {
	RequestID    string `json:"request_id"`
	ApprovalCode string `json:"approval_code"`
	Scope        string `json:"scope"`   // full | guest (this milestone always guest)
	Persist      string `json:"persist"` // once | persist
	// Step-up (when CDROP_STEP_UP_ENABLED): a fresh prompt=login PKCE code+verifier
	// the backend exchanges and checks for a recent auth_time (AUTH.md §6).
	StepUpCode     string `json:"step_up_code"`
	StepUpVerifier string `json:"step_up_verifier"`
}

type qrDenyReq struct {
	RequestID    string `json:"request_id"`
	ApprovalCode string `json:"approval_code"`
}

// handleQRStart (public, rate-limited) opens a scan-login request for a new
// device and returns the QR payload plus the device-private poll secret.
func (s *Server) handleQRStart(w http.ResponseWriter, r *http.Request) {
	if !s.cfg.QRLoginOn() {
		writeJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "scan login disabled"})
		return
	}
	var req qrStartReq
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 4096)).Decode(&req); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid json"})
		return
	}
	deviceName := jwtauth.SanitizeDeviceName(req.DeviceName)
	if deviceName == "" {
		deviceName = "New device"
	}

	requestID, err1 := randB64(16)
	approvalCode, err2 := randB64(9)
	pollSecret, err3 := randB64(32)
	if err := errors.Join(err1, err2, err3); err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "id gen"})
		return
	}

	now := time.Now()
	expires := now.Add(time.Duration(s.cfg.QRRequestTTLSeconds) * time.Second)
	if err := s.queries.CreateLoginRequest(r.Context(), db.CreateLoginRequestParams{
		ID:            requestID,
		PollSecret:    sessionID(pollSecret), // store only the hash
		ApprovalCode:  approvalCode,
		NewDeviceName: deviceName,
		NewDeviceType: qrDeviceType(req.DeviceType),
		UserAgent:     truncate(r.UserAgent(), 256),
		RequestIp:     clientIP(r),
		CreatedAt:     now.Unix(),
		ExpiresAt:     expires.Unix(),
	}); err != nil {
		slog.Error("create login request failed", "err", err)
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "db"})
		return
	}

	writeJSON(w, http.StatusOK, qrStartResp{
		RequestID:  requestID,
		PollSecret: pollSecret,
		QRPayload:  s.qrPayload(r, requestID, approvalCode),
		ExpiresAt:  expires.Unix(),
	})
}

// handleQRStatus (public, rate-limited) is the new device's long-poll. It proves
// the poll_secret, then reports pending until the request is approved/denied/
// expired. On approval it creates the session, sets the cookie on THIS response,
// mints the first access token, and marks the request consumed (single use).
func (s *Server) handleQRStatus(w http.ResponseWriter, r *http.Request) {
	if !s.cfg.QRLoginOn() {
		writeJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "scan login disabled"})
		return
	}
	requestID := r.URL.Query().Get("request_id")
	pollSecret := r.Header.Get("X-Poll-Secret")
	if requestID == "" || pollSecret == "" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "missing request_id or poll secret"})
		return
	}
	pollHash := sessionID(pollSecret)

	deadline := time.Now().Add(qrStatusPollWindow)
	for {
		req, err := s.queries.GetLoginRequest(r.Context(), requestID)
		if err != nil {
			// Unknown / reaped → treat as expired without leaking existence.
			writeJSON(w, http.StatusOK, qrStatusResp{Status: "expired"})
			return
		}
		if subtle.ConstantTimeCompare([]byte(req.PollSecret), []byte(pollHash)) != 1 {
			writeJSON(w, http.StatusForbidden, map[string]string{"error": "bad poll secret"})
			return
		}
		if req.ExpiresAt < time.Now().Unix() {
			writeJSON(w, http.StatusOK, qrStatusResp{Status: "expired"})
			return
		}
		switch req.Status {
		case "approved":
			s.collectQRSession(w, r, req)
			return
		case "denied":
			writeJSON(w, http.StatusOK, qrStatusResp{Status: "denied"})
			return
		case "consumed":
			writeJSON(w, http.StatusOK, qrStatusResp{Status: "expired"})
			return
		default: // pending
			if time.Now().After(deadline) {
				writeJSON(w, http.StatusOK, qrStatusResp{Status: "pending"})
				return
			}
			select {
			case <-r.Context().Done():
				return
			case <-time.After(time.Second):
			}
		}
	}
}

// collectQRSession turns an approved request into a live session for the new
// device. ConsumeLoginRequest is the single-use guard: only the poll that flips
// approved→consumed proceeds, so a duplicated/raced poll can't mint a second
// session.
func (s *Server) collectQRSession(w http.ResponseWriter, r *http.Request, req db.LoginRequest) {
	n, err := s.queries.ConsumeLoginRequest(r.Context(), req.ID)
	if err != nil {
		slog.Error("consume login request failed", "err", err)
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "db"})
		return
	}
	if n == 0 {
		// Lost the race to another poll; the winner already has the session.
		writeJSON(w, http.StatusOK, qrStatusResp{Status: "expired"})
		return
	}

	raw, id, err := newSessionToken()
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "id gen"})
		return
	}
	scope := req.GrantScope
	if scope != "full" {
		scope = "guest"
	}
	// Persistent borrows slide their window (kind self); one-time borrows are kind
	// guest with a fixed short expiry that refresh never extends (AUTH.md §3.1).
	now := time.Now()
	kind := "guest"
	exp := now.Add(time.Duration(s.cfg.QRGuestTTLSeconds) * time.Second)
	if req.GrantPersist == "persist" {
		kind = "self"
		exp = now.Add(time.Duration(s.cfg.QRPersistTTLHours) * time.Hour)
	}
	if err := s.queries.CreateSelfSession(r.Context(), db.CreateSelfSessionParams{
		ID:         id,
		UserID:     req.ApproverUserID,
		DeviceName: req.NewDeviceName,
		UserAgent:  req.UserAgent,
		Kind:       kind,
		Scope:      scope,
		GrantedBy:  "qr",
		CreatedAt:  now.Unix(),
		LastUsedAt: now.Unix(),
		ExpiresAt:  exp.Unix(),
	}); err != nil {
		slog.Error("create self session failed", "err", err)
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "db"})
		return
	}

	token, expiresIn, err := s.mintSessionToken(req.ApproverUserID, id, scope)
	if err != nil {
		slog.Error("mint session token failed", "err", err)
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "mint failed"})
		return
	}
	setSessionCookie(w, raw)

	user := userResp{ID: req.ApproverUserID, Name: req.ApproverUserID}
	if acct, err := s.queries.GetAccount(r.Context(), req.ApproverUserID); err == nil {
		if acct.DisplayName != "" {
			user.Name = acct.DisplayName
		}
		user.Avatar = acct.AvatarUrl
	}
	writeJSON(w, http.StatusOK, qrStatusResp{
		Status:      "approved",
		AccessToken: token,
		ExpiresIn:   expiresIn,
		User:        &user,
		DeviceName:  req.NewDeviceName,
	})
}

// handleQRRequest (full session) lets the approver see what they are about to
// authorise. The approval_code (from the QR) gates the lookup, so only someone
// who scanned the code can read the request's device info.
func (s *Server) handleQRRequest(w http.ResponseWriter, r *http.Request) {
	if !s.cfg.QRLoginOn() {
		writeJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "scan login disabled"})
		return
	}
	req, ok := s.lookupQRRequest(w, r, r.URL.Query().Get("request_id"), r.URL.Query().Get("code"))
	if !ok {
		return
	}
	writeJSON(w, http.StatusOK, qrRequestResp{
		DeviceName: req.NewDeviceName,
		DeviceType: req.NewDeviceType,
		RequestIP:  req.RequestIp,
		ExpiresAt:  req.ExpiresAt,
		Status:     req.Status,
		StepUp:     s.cfg.StepUpEnabled,
	})
}

// handleQRApprove (full session) binds the request to the caller and records the
// granted scope/persistence. The new device's poll then collects the session.
func (s *Server) handleQRApprove(w http.ResponseWriter, r *http.Request) {
	if !s.cfg.QRLoginOn() {
		writeJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "scan login disabled"})
		return
	}
	var body qrApproveReq
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 4096)).Decode(&body); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid json"})
		return
	}
	req, ok := s.lookupQRRequest(w, r, body.RequestID, body.ApprovalCode)
	if !ok {
		return
	}
	claims, _ := jwtauth.ClaimsFromContext(r.Context())

	// Step-up: approving a new device into your account is sensitive. When enabled,
	// require a fresh prompt=login re-auth (the provider's 2FA, if configured, is
	// enforced during that exchange) within the freshness window (AUTH.md §6).
	if s.cfg.StepUpEnabled && !s.verifyStepUp(r, claims.UserID, body.StepUpCode, body.StepUpVerifier) {
		writeJSON(w, http.StatusForbidden, map[string]string{"error": "step_up_required"})
		return
	}

	scope := "guest" // this milestone grants restricted guest sessions only
	if body.Scope == "full" {
		scope = "full"
	}
	persist := "once"
	if body.Persist == "persist" {
		persist = "persist"
	}
	now := time.Now()
	n, err := s.queries.ApproveLoginRequest(r.Context(), db.ApproveLoginRequestParams{
		ApproverUserID: claims.UserID,
		GrantScope:     scope,
		GrantPersist:   persist,
		ApprovedAt:     ptrInt64(now.Unix()),
		ID:             req.ID,
	})
	if err != nil {
		slog.Error("approve login request failed", "err", err)
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "db"})
		return
	}
	if n == 0 {
		// Raced to denied/consumed/expired between lookup and update.
		writeJSON(w, http.StatusConflict, map[string]string{"error": "request no longer pending"})
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// handleQRDeny (full session) rejects a pending request.
func (s *Server) handleQRDeny(w http.ResponseWriter, r *http.Request) {
	if !s.cfg.QRLoginOn() {
		writeJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "scan login disabled"})
		return
	}
	var body qrDenyReq
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 4096)).Decode(&body); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid json"})
		return
	}
	req, ok := s.lookupQRRequest(w, r, body.RequestID, body.ApprovalCode)
	if !ok {
		return
	}
	if _, err := s.queries.DenyLoginRequest(r.Context(), req.ID); err != nil {
		slog.Error("deny login request failed", "err", err)
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "db"})
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// verifyStepUp exchanges a fresh prompt=login authorization code and confirms it
// proves a recent interactive re-authentication by the same user: the id_token's
// signature validates (JWKS), its sub matches the caller, and its auth_time is
// within StepUpMaxAgeSeconds. Any failure → false (the caller answers 403). The
// code is single-use at the IdP, so it can't be replayed (AUTH.md §6).
func (s *Server) verifyStepUp(r *http.Request, userID, code, verifier string) bool {
	if code == "" || verifier == "" || s.cfg.OIDCTokenURL == "" {
		return false
	}
	form := url.Values{}
	form.Set("grant_type", "authorization_code")
	form.Set("code", code)
	form.Set("code_verifier", verifier)
	form.Set("client_id", s.cfg.OIDCClientID)
	form.Set("redirect_uri", s.cfg.OIDCRedirectURI)
	if s.cfg.OIDCClientSecret != "" {
		form.Set("client_secret", s.cfg.OIDCClientSecret)
	}
	tr, err := postOIDCToken(r.Context(), s.cfg.OIDCTokenURL, form)
	if err != nil {
		slog.Warn("step-up exchange failed", "err", err)
		return false
	}
	if tr.IDToken == "" {
		return false
	}
	sub, authTime, err := s.auth.VerifyIDToken(r.Context(), tr.IDToken)
	if err != nil {
		slog.Warn("step-up id_token invalid", "err", err)
		return false
	}
	if sub != userID {
		return false
	}
	maxAge := int64(s.cfg.StepUpMaxAgeSeconds)
	if maxAge <= 0 {
		maxAge = 300
	}
	return time.Now().Unix()-authTime <= maxAge
}

// lookupQRRequest fetches a request and verifies the approval_code in constant
// time. It writes the error response itself and returns ok=false on any failure
// (missing args, unknown request, bad code, expired), so callers just early-return.
func (s *Server) lookupQRRequest(w http.ResponseWriter, r *http.Request, requestID, code string) (db.LoginRequest, bool) {
	if requestID == "" || code == "" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "missing request_id or code"})
		return db.LoginRequest{}, false
	}
	req, err := s.queries.GetLoginRequest(r.Context(), requestID)
	if err != nil {
		writeJSON(w, http.StatusNotFound, map[string]string{"error": "request not found"})
		return db.LoginRequest{}, false
	}
	if subtle.ConstantTimeCompare([]byte(req.ApprovalCode), []byte(code)) != 1 {
		writeJSON(w, http.StatusForbidden, map[string]string{"error": "bad approval code"})
		return db.LoginRequest{}, false
	}
	if req.ExpiresAt < time.Now().Unix() {
		writeJSON(w, http.StatusGone, map[string]string{"error": "request expired"})
		return db.LoginRequest{}, false
	}
	return req, true
}

// qrPayload builds the URL encoded into the QR: the approver opens it on their
// phone. Prefers the configured site origin; falls back to the request's own
// scheme/host for dev.
func (s *Server) qrPayload(r *http.Request, requestID, approvalCode string) string {
	origin := s.siteOrigin
	if origin == "" {
		scheme := "https"
		if r.TLS == nil && r.Header.Get("X-Forwarded-Proto") == "" {
			scheme = "http"
		}
		origin = scheme + "://" + r.Host
	}
	return origin + "/link?r=" + requestID + "&c=" + approvalCode
}

func qrDeviceType(raw string) string {
	switch t := strings.ToLower(strings.TrimSpace(raw)); t {
	case "macos", "windows", "linux", "ios", "browser":
		return t
	default:
		return "browser"
	}
}

func clientIP(r *http.Request) string {
	if host, _, err := net.SplitHostPort(r.RemoteAddr); err == nil {
		return host
	}
	return r.RemoteAddr
}

func ptrInt64(v int64) *int64 { return &v }

func randB64(n int) (string, error) {
	b := make([]byte, n)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return base64.RawURLEncoding.EncodeToString(b), nil
}