package api

import (
	"context"
	"encoding/base64"
	"encoding/json"
	"errors"
	"log/slog"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/skip2/go-qrcode"

	"github.com/alchemistkay/guestguard/internal/auth"
	"github.com/alchemistkay/guestguard/internal/domain"
	"github.com/alchemistkay/guestguard/internal/flags"
	"github.com/alchemistkay/guestguard/internal/storage"
)

// checkInHandler is the host-facing surface for Tier 2 Block H: scan QR
// codes at the door, record arrivals, register walk-ins, drive the
// live arrivals counter on the dashboard.
type checkInHandler struct {
	logger        *slog.Logger
	events        *storage.EventRepo
	guests        *storage.GuestRepo
	collabs       *storage.CollaboratorRepo
	repo          *storage.CheckInRepo
	qrSigner      *auth.CheckInQRSigner
	scannerSigner *auth.ScannerJWTSigner
	publicBaseURL string
	hub           *Hub
	enforcer      *tierEnforcer
	flags         *flags.Store
}

// --- preview a check-in (POST /events/{id}/check-in/preview) ---
//
// The scanner submits the decoded QR string; we validate the JWT and
// return the guest plus what we already know about them — name,
// expected party size, and whether they've already been recorded.
// No DB writes. The frontend uses this to render the
// "Just them / +1 / +2 / Other" confirmation step before committing
// the check-in, matching how Eventbrite / Lu.ma scanners handle
// plus-ones at the door.

type previewCheckInRequest struct {
	QRPayload string `json:"qr_payload"`
}

type previewCheckInResponse struct {
	Guest             *domain.Guest   `json:"guest"`
	ExpectedPartySize int             `json:"expected_party_size"`
	AlreadyCheckedIn  bool            `json:"already_checked_in"`
	ExistingCheckIn   *domain.CheckIn `json:"existing_check_in,omitempty"`
}

func (h *checkInHandler) preview(w http.ResponseWriter, r *http.Request) {
	hostID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	eventID, ok := parseIDParam(w, r, "id")
	if !ok {
		return
	}
	if !requireScannerEventMatch(w, r, eventID) {
		return
	}
	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleEditor); !ok {
		return
	}

	var req previewCheckInRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	req.QRPayload = strings.TrimSpace(req.QRPayload)
	if req.QRPayload == "" {
		writeError(w, http.StatusBadRequest, "qr_payload is required")
		return
	}

	claims, status, msg := h.parseCheckInQR(r.Context(), req.QRPayload, eventID)
	if status != 0 {
		writeError(w, status, msg)
		return
	}

	guest, gerr := h.guests.Get(r.Context(), claims.GuestID)
	if gerr != nil || guest == nil {
		writeError(w, http.StatusNotFound, "guest not found")
		return
	}
	// arrival_count counts the guest plus their plus-ones; the door
	// volunteer most often presses the matching number, so this is what
	// drives the default-highlight in the UI.
	expected := guest.PlusOnes + 1

	existing, _ := h.repo.GetByGuest(r.Context(), guest.ID)
	resp := previewCheckInResponse{
		Guest:             guest,
		ExpectedPartySize: expected,
		AlreadyCheckedIn:  existing != nil,
		ExistingCheckIn:   existing,
	}
	writeJSON(w, http.StatusOK, resp)
}

// parseCheckInQR centralises the JWT validation + event-binding +
// guest-belongs-to-event checks that both preview and record need.
// Returns (claims, 0, "") on success or (nil, statusCode, message) on
// the recoverable error paths so the caller writes a single response.
func (h *checkInHandler) parseCheckInQR(ctx context.Context, payload string, eventID uuid.UUID) (*auth.CheckInQR, int, string) {
	claims, err := h.qrSigner.Parse(payload)
	if err != nil {
		if errors.Is(err, auth.ErrExpiredJWT) {
			return nil, http.StatusGone, "this QR has expired"
		}
		return nil, http.StatusBadRequest, "invalid QR"
	}
	if claims.EventID != eventID {
		return nil, http.StatusBadRequest, "this QR belongs to a different event"
	}
	belongs, err := h.repo.GuestBelongsToEvent(ctx, claims.GuestID, eventID)
	if err != nil {
		return nil, http.StatusInternalServerError, "failed to verify guest"
	}
	if !belongs {
		return nil, http.StatusNotFound, "guest is no longer on this event"
	}
	return claims, 0, ""
}

// --- record a check-in (QR-scanner POST) ---

type recordCheckInRequest struct {
	QRPayload    string `json:"qr_payload"`
	ArrivalCount int    `json:"arrival_count"`
	Notes        string `json:"notes"`
}

type recordCheckInResponse struct {
	CheckIn domain.CheckIn       `json:"check_in"`
	Guest   *domain.Guest        `json:"guest"`
	Summary domain.CheckInSummary `json:"summary"`
}

// POST /events/{id}/check-in — editor+. The scanner UI submits the
// decoded QR payload plus how many people in the party actually walked
// in. Duplicate scans surface as 409 with a friendly "already in"
// message; that's how the scanner UI knows to flash orange instead of
// green.
func (h *checkInHandler) record(w http.ResponseWriter, r *http.Request) {
	hostID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	eventID, ok := parseIDParam(w, r, "id")
	if !ok {
		return
	}
	if !requireScannerEventMatch(w, r, eventID) {
		return
	}
	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleEditor); !ok {
		return
	}

	var req recordCheckInRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	req.QRPayload = strings.TrimSpace(req.QRPayload)
	if req.QRPayload == "" {
		writeError(w, http.StatusBadRequest, "qr_payload is required")
		return
	}

	claims, status, msg := h.parseCheckInQR(r.Context(), req.QRPayload, eventID)
	if status != 0 {
		writeError(w, status, msg)
		return
	}

	ci, err := h.repo.Record(r.Context(), storage.RecordCheckInParams{
		GuestID:      claims.GuestID,
		CheckedInBy:  hostID,
		ArrivalCount: req.ArrivalCount,
		Notes:        req.Notes,
		WalkIn:       false,
	})
	if err != nil {
		if errors.Is(err, domain.ErrAlreadyCheckedIn) {
			writeError(w, http.StatusConflict, "this guest is already checked in")
			return
		}
		h.logger.Error("record check-in", "err", err)
		writeError(w, http.StatusInternalServerError, "failed to record check-in")
		return
	}

	guest, _ := h.guests.Get(r.Context(), claims.GuestID)
	summary, _ := h.repo.Summary(r.Context(), eventID)

	// Broadcast to the live arrivals dashboard.
	h.broadcast(eventID, "check_in.recorded", map[string]any{
		"check_in":          ci,
		"guest_id":          ci.GuestID,
		"guest_name":        nameOf(guest),
		"arrived_headcount": summary.ArrivedHeadcount,
		"expected_headcount": summary.ExpectedHeadcount,
		"guests_checked_in": summary.GuestsCheckedIn,
	})

	writeJSON(w, http.StatusOK, recordCheckInResponse{
		CheckIn: *ci,
		Guest:   guest,
		Summary: summary,
	})
}

// --- walk-ins ---

type walkInRequest struct {
	Name         string `json:"name"`
	Email        string `json:"email"`
	Phone        string `json:"phone"`
	ArrivalCount int    `json:"arrival_count"`
	Notes        string `json:"notes"`
}

// POST /events/{id}/walk-ins — editor+. Creates the guest + check-in
// row in one logical operation so the door volunteer doesn't have to
// fumble between two screens for a party-crasher who was meant to be
// invited.
func (h *checkInHandler) walkIn(w http.ResponseWriter, r *http.Request) {
	hostID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	eventID, ok := parseIDParam(w, r, "id")
	if !ok {
		return
	}
	if !requireScannerEventMatch(w, r, eventID) {
		return
	}
	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleEditor); !ok {
		return
	}

	var req walkInRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	req.Name = strings.TrimSpace(req.Name)
	if req.Name == "" {
		writeError(w, http.StatusBadRequest, "name is required")
		return
	}
	if req.ArrivalCount <= 0 {
		req.ArrivalCount = 1
	}

	emailPtr := optStr(req.Email)
	phonePtr := optStr(req.Phone)
	guest, err := h.guests.Create(r.Context(), storage.CreateGuestParams{
		EventID:  eventID,
		Name:     req.Name,
		Email:    emailPtr,
		Phone:    phonePtr,
		PlusOnes: req.ArrivalCount - 1,
	})
	if err != nil {
		h.logger.Error("create walk-in guest", "err", err)
		writeError(w, http.StatusInternalServerError, "failed to create guest")
		return
	}

	ci, err := h.repo.Record(r.Context(), storage.RecordCheckInParams{
		GuestID:      guest.ID,
		CheckedInBy:  hostID,
		ArrivalCount: req.ArrivalCount,
		Notes:        req.Notes,
		WalkIn:       true,
	})
	if err != nil {
		h.logger.Error("record walk-in check-in", "err", err)
		writeError(w, http.StatusInternalServerError, "failed to record check-in")
		return
	}

	summary, _ := h.repo.Summary(r.Context(), eventID)
	h.broadcast(eventID, "check_in.recorded", map[string]any{
		"check_in":           ci,
		"guest_id":           ci.GuestID,
		"guest_name":         guest.Name,
		"walk_in":            true,
		"arrived_headcount":  summary.ArrivedHeadcount,
		"expected_headcount": summary.ExpectedHeadcount,
		"guests_checked_in":  summary.GuestsCheckedIn,
	})

	writeJSON(w, http.StatusCreated, recordCheckInResponse{
		CheckIn: *ci,
		Guest:   guest,
		Summary: summary,
	})
}

// --- list + summary ---

// GET /events/{id}/check-ins — viewer+.
func (h *checkInHandler) list(w http.ResponseWriter, r *http.Request) {
	hostID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	eventID, ok := parseIDParam(w, r, "id")
	if !ok {
		return
	}
	if !requireScannerEventMatch(w, r, eventID) {
		return
	}
	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleViewer); !ok {
		return
	}
	rows, err := h.repo.ListByEvent(r.Context(), eventID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to list check-ins")
		return
	}
	summary, _ := h.repo.Summary(r.Context(), eventID)
	writeJSON(w, http.StatusOK, map[string]any{
		"check_ins": rows,
		"summary":   summary,
	})
}

// --- helpers ---

func (h *checkInHandler) broadcast(eventID uuid.UUID, evtType string, payload any) {
	if h.hub == nil {
		return
	}
	body, err := json.Marshal(payload)
	if err != nil {
		h.logger.Warn("marshal check-in ws event", "err", err)
		return
	}
	h.hub.Broadcast(WSEvent{
		Type:    evtType,
		EventID: eventID,
		Payload: body,
	})
}

func optStr(s string) *string {
	t := strings.TrimSpace(s)
	if t == "" {
		return nil
	}
	return &t
}

func nameOf(g *domain.Guest) string {
	if g == nil {
		return ""
	}
	return g.Name
}

// --- scanner magic-link (POST /events/{id}/scanner-ticket) ---

type scannerTicketResponse struct {
	Token     string    `json:"token"`
	URL       string    `json:"url"`
	QRImage   string    `json:"qr_image"` // data: URL PNG
	ExpiresAt time.Time `json:"expires_at"`
}

// issueScannerTicket mints a short-lived, event-scoped JWT that a host
// can render into a QR code on their desktop event-detail page. The
// door volunteer scans that QR with their phone camera, the scanner
// page reads ?token=<jwt> out of the URL, and uses it as a Bearer for
// the three check-in endpoints — no separate phone login required.
//
// Editor+ on the event. Rate-limited at the route level. Tickets last
// four hours by default (see NewScannerJWTSigner), long enough for a
// full event without the host having to re-mint mid-night.
func (h *checkInHandler) issueScannerTicket(w http.ResponseWriter, r *http.Request) {
	hostID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	eventID, ok := parseIDParam(w, r, "id")
	if !ok {
		return
	}
	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleEditor); !ok {
		return
	}
	// Kill switch — ops can disable scanner ticket minting without a
	// redeploy if the magic-link UX needs to be pulled back.
	if !h.flags.Enabled("checkin_pwa", hostID) {
		writeError(w, http.StatusServiceUnavailable, "the scanner is temporarily disabled")
		return
	}
	// The day-of scanner is a Pro+ feature. Free-tier hosts can still
	// see arrivals (the headline widget on the overview reads
	// /check-ins which is viewer+) but minting a magic link for a
	// volunteer's phone is an upsell lever.
	if !h.enforcer.allowFeature(w, r, hostID, "scanner",
		"The day-of check-in scanner is a Pro feature.") {
		return
	}
	if h.scannerSigner == nil {
		writeError(w, http.StatusServiceUnavailable, "scanner tickets are not configured")
		return
	}

	tok, exp, err := h.scannerSigner.Issue(hostID, eventID, time.Now())
	if err != nil {
		h.logger.Error("issue scanner ticket", "err", err, "event_id", eventID)
		writeError(w, http.StatusInternalServerError, "failed to issue ticket")
		return
	}

	// publicBaseURL is the front-of-house origin (e.g. https://guestguard.k4scloud.com).
	// We embed the event id as well as the token so the scanner page can
	// load the right event metadata before any check-in roundtrip.
	base := strings.TrimRight(h.publicBaseURL, "/")
	if base == "" {
		base = ""
	}
	scannerURL := base + "/scanner?token=" + url.QueryEscape(tok) + "&event=" + url.QueryEscape(eventID.String())

	qrImage, err := renderQRPNG(scannerURL)
	if err != nil {
		h.logger.Error("render scanner QR", "err", err)
		writeError(w, http.StatusInternalServerError, "failed to render QR")
		return
	}

	writeJSON(w, http.StatusOK, scannerTicketResponse{
		Token:     tok,
		URL:       scannerURL,
		QRImage:   qrImage,
		ExpiresAt: exp,
	})
}

// renderQRPNG converts a JWT-shaped string into a base64-encoded PNG
// data URL the frontend can drop straight into an <img src>. Used by
// the access response so a successful RSVP comes back with the guest's
// scannable code already rendered.
func renderQRPNG(payload string) (string, error) {
	png, err := qrcode.Encode(payload, qrcode.Medium, 320)
	if err != nil {
		return "", err
	}
	return "data:image/png;base64," + base64.StdEncoding.EncodeToString(png), nil
}