package api

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"time"

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

type rsvpPublisher interface {
	PublishRSVPConfirmed(ctx context.Context, evt natspub.RSVPConfirmed) error
}

type fraudScorer interface {
	Score(ctx context.Context, in fraud.ScoreInput) fraud.Decision
}

type rsvpHandler struct {
	logger     *slog.Logger
	guests     *storage.GuestRepo
	tokens     *storage.TokenRepo
	events     *storage.EventRepo
	rsvps      *storage.RSVPRepo
	accessLogs *storage.AccessLogRepo
	scorer     fraudScorer
	pub        rsvpPublisher
}

type submitRSVPRequest struct {
	Response     string         `json:"response"`
	PlusOnes     int            `json:"plus_ones"`
	DietaryNotes *string        `json:"dietary_notes"`
	Fingerprint  map[string]any `json:"fingerprint"`
}

type submitRSVPResponse struct {
	RSVP      *domain.RSVP   `json:"rsvp"`
	Decision  fraud.Decision `json:"fraud"`
	Blocked   bool           `json:"blocked"`
}

// POST /rsvp/{token} — synchronous fraud check + RSVP recording.
func (h *rsvpHandler) submit(w http.ResponseWriter, r *http.Request) {
	raw := r.PathValue("token")
	if err := auth.ValidateFormat(raw); err != nil {
		writeError(w, http.StatusBadRequest, "malformed token")
		return
	}

	tk, err := h.tokens.GetByHash(r.Context(), auth.HashToken(raw))
	if err != nil {
		if errors.Is(err, domain.ErrTokenNotFound) {
			writeError(w, http.StatusNotFound, "token not found")
			return
		}
		writeError(w, http.StatusInternalServerError, "failed to load token")
		return
	}
	if err := tk.IsValid(time.Now().UTC()); err != nil {
		writeError(w, http.StatusGone, err.Error())
		return
	}

	var req submitRSVPRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	resp := domain.RSVPResponse(req.Response)
	if !resp.Valid() {
		writeError(w, http.StatusBadRequest, "response must be attending|declined|maybe")
		return
	}
	if req.PlusOnes < 0 {
		writeError(w, http.StatusBadRequest, "plus_ones must be >= 0")
		return
	}

	guest, err := h.guests.Get(r.Context(), tk.GuestID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to load guest")
		return
	}
	if req.PlusOnes > guest.PlusOnes {
		writeError(w, http.StatusBadRequest,
			fmt.Sprintf("you may bring up to %d plus-one(s)", guest.PlusOnes))
		return
	}
	event, err := h.events.Get(r.Context(), guest.EventID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to load event")
		return
	}

	fingerprint := mergeFingerprint(req.Fingerprint, collectFingerprint(r))
	ip := clientIP(r)

	accessLogID, err := h.accessLogs.Create(r.Context(), storage.CreateAccessLogParams{
		GuestID:     guest.ID,
		TokenID:     tk.ID,
		Fingerprint: fingerprint,
		IPAddress:   ip,
	})
	if err != nil {
		h.logger.Error("create access log", "err", err)
	}

	decision := h.scorer.Score(r.Context(), fraud.ScoreInput{
		EventID:     event.ID,
		GuestID:     guest.ID,
		TokenID:     tk.ID,
		AccessLogID: accessLogID,
		Fingerprint: stringifyFingerprint(fingerprint),
		IPAddress:   ip,
		UserAgent:   r.UserAgent(),
		Referrer:    r.Referer(),
	})

	if fraud.IsBlock(decision) {
		writeJSON(w, http.StatusForbidden, submitRSVPResponse{
			Decision: decision,
			Blocked:  true,
		})
		return
	}

	score := decision.Score
	rsvp, err := h.rsvps.Create(r.Context(), storage.CreateRSVPParams{
		GuestID:           guest.ID,
		Response:          resp,
		PlusOnes:          req.PlusOnes,
		DietaryNotes:      req.DietaryNotes,
		DeviceFingerprint: fingerprint,
		IPAddress:         ip,
		RiskScore:         &score,
	})
	if err != nil {
		if errors.Is(err, domain.ErrRSVPAlreadySubmitted) {
			writeError(w, http.StatusConflict, "rsvp already submitted for this guest")
			return
		}
		h.logger.Error("create rsvp", "err", err, "guest_id", guest.ID)
		writeError(w, http.StatusInternalServerError, "failed to record rsvp")
		return
	}

	if err := h.tokens.MarkUsed(r.Context(), tk.ID); err != nil {
		h.logger.Warn("mark token used", "err", err, "token_id", tk.ID)
	}

	go func(evt natspub.RSVPConfirmed) {
		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		if err := h.pub.PublishRSVPConfirmed(ctx, evt); err != nil {
			h.logger.Error("publish rsvp.confirmed", "err", err, "rsvp_id", evt.RSVPID)
		}
	}(natspub.RSVPConfirmed{
		EventID:     event.ID,
		GuestID:     guest.ID,
		RSVPID:      rsvp.ID,
		Response:    string(rsvp.Response),
		PlusOnes:    rsvp.PlusOnes,
		RiskScore:   &score,
		SubmittedAt: rsvp.SubmittedAt,
	})

	writeJSON(w, http.StatusCreated, submitRSVPResponse{
		RSVP:     rsvp,
		Decision: decision,
		Blocked:  false,
	})
}

func mergeFingerprint(client map[string]any, server map[string]any) map[string]any {
	out := make(map[string]any, len(server)+len(client))
	for k, v := range server {
		out[k] = v
	}
	for k, v := range client {
		out["client_"+k] = v
	}
	return out
}

func stringifyFingerprint(fp map[string]any) map[string]string {
	if fp == nil {
		return nil
	}
	out := make(map[string]string, len(fp))
	for k, v := range fp {
		switch tv := v.(type) {
		case string:
			out[k] = tv
		default:
			b, _ := json.Marshal(tv)
			out[k] = string(b)
		}
	}
	return out
}