package api

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

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

// messageHandler is the host-facing surface for Tier 2 Block F:
// scheduled reminders + custom broadcasts. Editor+ for writes; viewer+
// for reads via the existing requireRole gate.
type messageHandler struct {
	logger   *slog.Logger
	events   *storage.EventRepo
	collabs  *storage.CollaboratorRepo
	repo     *storage.MessageRepo
}

// --- response shapes ---

// messageView wraps the persisted row with a delivery summary. We don't
// inline the per-recipient rows here — the host expands a single message
// to drill into those — but the "X of Y delivered" rollup is useful in
// the list view.
type messageView struct {
	*domain.ScheduledMessage
	DeliveryStats storage.DeliveryStats `json:"delivery_stats"`
}

type listMessagesResponse struct {
	Messages []messageView `json:"messages"`
}

// GET /events/{id}/messages — viewer+.
func (h *messageHandler) 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 _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleViewer); !ok {
		return
	}
	msgs, err := h.repo.ListByEvent(r.Context(), eventID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to list messages")
		return
	}
	views := make([]messageView, 0, len(msgs))
	for i := range msgs {
		stats, _ := h.repo.DeliveryStats(r.Context(), msgs[i].ID)
		views = append(views, messageView{
			ScheduledMessage: &msgs[i],
			DeliveryStats:    stats,
		})
	}
	writeJSON(w, http.StatusOK, listMessagesResponse{Messages: views})
}

// composeMessageRequest is what the Communications tab POSTs / PATCHes.
// SendAt is optional on create — omit it together with status="draft" to
// save a draft, or set it for scheduling. Channel defaults to email.
type composeMessageRequest struct {
	SendAt   *time.Time              `json:"send_at"`
	Audience domain.MessageAudience  `json:"audience"`
	Channel  domain.MessageChannel   `json:"channel"`
	Subject  string                  `json:"subject"`
	Body     string                  `json:"body"`
	Draft    bool                    `json:"draft"`
}

// recipientCountResponse is what the live "X guests will receive this"
// preview chip on the compose form fetches when the audience picker
// changes.
type recipientCountResponse struct {
	Count int `json:"count"`
}

// GET /events/{id}/messages/recipient-count?audience=... — viewer+. Lets
// the compose form show a live count without needing to load the full
// guest list client-side.
func (h *messageHandler) recipientCount(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.RoleViewer); !ok {
		return
	}
	audience := domain.MessageAudience(r.URL.Query().Get("audience"))
	if !audience.Valid() {
		writeError(w, http.StatusBadRequest, "audience must be one of: all|attending|pending|declined|maybe")
		return
	}
	n, err := h.repo.CountRecipients(r.Context(), eventID, audience)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to count recipients")
		return
	}
	writeJSON(w, http.StatusOK, recipientCountResponse{Count: n})
}

// POST /events/{id}/messages — editor+.
//
// The host can save a draft (Draft=true, SendAt nil → status=draft) or
// schedule for later (SendAt set → status=scheduled). Send-immediately is
// just "schedule for now"; we expose a separate send-now route for the
// "send this draft right now" affordance below.
func (h *messageHandler) create(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
	}
	var req composeMessageRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	if !req.Audience.Valid() {
		writeError(w, http.StatusBadRequest, "audience required (all|attending|pending|declined|maybe)")
		return
	}
	if req.Channel == "" {
		req.Channel = domain.ChannelEmail
	}
	if !req.Channel.Valid() {
		writeError(w, http.StatusBadRequest, "channel must be one of: email|sms|both")
		return
	}
	if req.Body == "" {
		writeError(w, http.StatusBadRequest, "body is required")
		return
	}

	// Pick the status from send_at + draft flag.
	status := domain.StatusScheduled
	sendAt := time.Now().UTC()
	if req.Draft || req.SendAt == nil {
		if req.Draft {
			status = domain.StatusDraft
		} else {
			// No send_at given and not flagged as draft: send now.
			status = domain.StatusScheduled
		}
	} else {
		sendAt = req.SendAt.UTC()
	}

	subj := req.Subject
	var subjPtr *string
	if subj != "" {
		subjPtr = &subj
	}

	m, err := h.repo.Create(r.Context(), storage.CreateMessageParams{
		EventID:   eventID,
		SendAt:    sendAt,
		Audience:  req.Audience,
		Channel:   req.Channel,
		Subject:   subjPtr,
		Body:      req.Body,
		Status:    status,
		CreatedBy: &hostID,
	})
	if err != nil {
		h.logger.Error("create message", "err", err)
		writeError(w, http.StatusInternalServerError, "failed to create message")
		return
	}
	writeJSON(w, http.StatusCreated, m)
}

// PATCH /events/{id}/messages/{message_id} — editor+. Only legal while
// the message is still draft or scheduled (the storage layer enforces
// this with a row lock).
func (h *messageHandler) update(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
	}
	msgID, ok := parseIDParam(w, r, "message_id")
	if !ok {
		return
	}
	var req composeMessageRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}

	params := storage.UpdateMessageParams{}
	if req.SendAt != nil {
		t := req.SendAt.UTC()
		params.SendAt = &t
	}
	if req.Audience != "" {
		if !req.Audience.Valid() {
			writeError(w, http.StatusBadRequest, "invalid audience")
			return
		}
		params.Audience = &req.Audience
	}
	if req.Channel != "" {
		if !req.Channel.Valid() {
			writeError(w, http.StatusBadRequest, "invalid channel")
			return
		}
		params.Channel = &req.Channel
	}
	if req.Subject != "" {
		params.Subject = &req.Subject
	}
	if req.Body != "" {
		params.Body = &req.Body
	}

	m, err := h.repo.Update(r.Context(), eventID, msgID, params)
	if err != nil {
		switch {
		case errors.Is(err, domain.ErrMessageNotFound):
			writeError(w, http.StatusNotFound, "message not found")
		case errors.Is(err, domain.ErrMessageNotEditable):
			writeError(w, http.StatusConflict, "message can only be edited while scheduled or draft")
		default:
			h.logger.Error("update message", "err", err)
			writeError(w, http.StatusInternalServerError, "failed to update message")
		}
		return
	}
	writeJSON(w, http.StatusOK, m)
}

// POST /events/{id}/messages/{message_id}/send-now — editor+.
// Promotes a draft or future-scheduled message to send_at=now, so the
// next scheduler poll picks it up.
func (h *messageHandler) sendNow(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
	}
	msgID, ok := parseIDParam(w, r, "message_id")
	if !ok {
		return
	}
	if err := h.repo.PromoteToScheduled(r.Context(), eventID, msgID); err != nil {
		if errors.Is(err, domain.ErrMessageNotEditable) {
			writeError(w, http.StatusConflict, "message has already been sent or cancelled")
			return
		}
		writeError(w, http.StatusInternalServerError, "failed to schedule send")
		return
	}
	w.WriteHeader(http.StatusAccepted)
}

// DELETE /events/{id}/messages/{message_id} — editor+. Cancels a
// scheduled / draft message. Sent or sending messages can't be deleted.
func (h *messageHandler) cancel(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
	}
	msgID, ok := parseIDParam(w, r, "message_id")
	if !ok {
		return
	}
	if err := h.repo.Cancel(r.Context(), eventID, msgID); err != nil {
		if errors.Is(err, domain.ErrMessageNotEditable) {
			writeError(w, http.StatusConflict, "message has already been sent")
			return
		}
		writeError(w, http.StatusInternalServerError, "failed to cancel message")
		return
	}
	w.WriteHeader(http.StatusNoContent)
}