package api

import (
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/jackc/pgx/v5/pgtype"

	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
	"git.fabledsword.com/bvandeusen/minstrel/internal/mailer"
	"git.fabledsword.com/bvandeusen/minstrel/internal/notifications"
)

// The notifications inbox (M489). Rows are written by internal/notifications;
// this surface lists them, counts the unread, marks them read, and holds each
// user's per-kind settings.

const (
	notificationsDefaultLimit = 30
	notificationsMaxLimit     = 100
)

// notificationResp is one inbox row, rendered server-side so every client
// says the same thing (notifications.Render).
type notificationResp struct {
	ID        string     `json:"id"`
	Kind      string     `json:"kind"`
	Title     string     `json:"title"`
	Body      string     `json:"body"`
	Link      string     `json:"link"`
	CreatedAt time.Time  `json:"created_at"`
	ReadAt    *time.Time `json:"read_at"`
}

type notificationsPageResp struct {
	Items       []notificationResp `json:"items"`
	UnreadCount int64              `json:"unread_count"`
	// NextBefore is the cursor for the next page, absent on the last one.
	NextBefore string `json:"next_before,omitempty"`
}

type unreadCountResp struct {
	UnreadCount int64 `json:"unread_count"`
}

// notificationSettingsResp is every kind the caller can receive, plus whether
// email can be delivered at all, so a client can say why before anyone tries.
type notificationSettingsResp struct {
	Kinds          []notifications.KindSetting `json:"kinds"`
	EmailAvailable bool                        `json:"email_available"`
	// EmailUnavailableReason is "no_address" or "smtp_not_configured" when
	// EmailAvailable is false.
	EmailUnavailableReason string `json:"email_unavailable_reason,omitempty"`
}

type notificationSettingsReq struct {
	Kinds []notifications.SettingChange `json:"kinds"`
}

// handleListMyNotifications implements GET /api/me/notifications?limit&before.
func (h *handlers) handleListMyNotifications(w http.ResponseWriter, r *http.Request) {
	user, ok := requireUser(w, r)
	if !ok {
		return
	}
	limit := notificationsDefaultLimit
	if raw := r.URL.Query().Get("limit"); raw != "" {
		n, err := strconv.Atoi(raw)
		if err != nil || n < 1 {
			writeErr(w, apierror.BadRequest("bad_limit", "limit must be a positive integer"))
			return
		}
		limit = min(n, notificationsMaxLimit)
	}
	params := dbq.ListNotificationsParams{UserID: user.ID, PageLimit: int32(limit)}
	if raw := r.URL.Query().Get("before"); raw != "" {
		at, id, ok := parseNotificationCursor(raw)
		if !ok {
			writeErr(w, apierror.BadRequest("bad_cursor", "before is not a cursor this server issued"))
			return
		}
		params.BeforeCreatedAt, params.BeforeID = at, id
	}

	q := dbq.New(h.pool)
	rows, err := q.ListNotifications(r.Context(), params)
	if err != nil {
		writeErrWithLog(w, h.logger, "notifications: list", apierror.Internal(err))
		return
	}
	unread, err := q.CountUnreadNotifications(r.Context(), user.ID)
	if err != nil {
		writeErrWithLog(w, h.logger, "notifications: count", apierror.Internal(err))
		return
	}

	out := notificationsPageResp{Items: make([]notificationResp, 0, len(rows)), UnreadCount: unread}
	for _, row := range rows {
		rendered := notifications.Render(notifications.Kind(row.Kind), row.Payload)
		item := notificationResp{
			ID:        uuidToString(row.ID),
			Kind:      row.Kind,
			Title:     rendered.Title,
			Body:      rendered.Body,
			Link:      rendered.Link,
			CreatedAt: row.CreatedAt.Time,
		}
		if row.ReadAt.Valid {
			t := row.ReadAt.Time
			item.ReadAt = &t
		}
		out.Items = append(out.Items, item)
	}
	if len(rows) == limit {
		last := rows[len(rows)-1]
		out.NextBefore = formatNotificationCursor(last.CreatedAt, last.ID)
	}
	writeJSON(w, http.StatusOK, out)
}

// handleMyUnreadNotificationCount implements GET /api/me/notifications/unread-count,
// the cheap call behind the badge.
func (h *handlers) handleMyUnreadNotificationCount(w http.ResponseWriter, r *http.Request) {
	user, ok := requireUser(w, r)
	if !ok {
		return
	}
	n, err := dbq.New(h.pool).CountUnreadNotifications(r.Context(), user.ID)
	if err != nil {
		writeErrWithLog(w, h.logger, "notifications: count", apierror.Internal(err))
		return
	}
	writeJSON(w, http.StatusOK, unreadCountResp{UnreadCount: n})
}

// handleMarkMyNotificationRead implements POST /api/me/notifications/{id}/read.
// Repeating it is harmless; another user's id is a 404, the same answer as a
// malformed one, so ids can't be probed.
func (h *handlers) handleMarkMyNotificationRead(w http.ResponseWriter, r *http.Request) {
	user, ok := requireUser(w, r)
	if !ok {
		return
	}
	id, ok := parseUUID(chi.URLParam(r, "id"))
	if !ok {
		writeErr(w, apierror.NotFound("notification"))
		return
	}
	n, err := dbq.New(h.pool).MarkNotificationRead(r.Context(), dbq.MarkNotificationReadParams{ID: id, UserID: user.ID})
	if err != nil {
		writeErrWithLog(w, h.logger, "notifications: mark read", apierror.Internal(err))
		return
	}
	if n == 0 {
		writeErr(w, apierror.NotFound("notification"))
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// handleMarkAllMyNotificationsRead implements POST /api/me/notifications/read-all.
func (h *handlers) handleMarkAllMyNotificationsRead(w http.ResponseWriter, r *http.Request) {
	user, ok := requireUser(w, r)
	if !ok {
		return
	}
	// Optional {"up_to": RFC3339}: only what existed then. A client replaying
	// an offline "mark all read" sends the moment the user asked.
	var body struct {
		UpTo *time.Time `json:"up_to"`
	}
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil && !errors.Is(err, io.EOF) {
		writeErr(w, apierror.BadRequest("bad_body", "invalid JSON body"))
		return
	}
	params := dbq.MarkAllNotificationsReadParams{UserID: user.ID}
	if body.UpTo != nil {
		params.UpTo = pgtype.Timestamptz{Time: *body.UpTo, Valid: true}
	}
	if _, err := dbq.New(h.pool).MarkAllNotificationsRead(r.Context(), params); err != nil {
		writeErrWithLog(w, h.logger, "notifications: mark all read", apierror.Internal(err))
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// handleGetMyNotificationSettings implements GET /api/me/notification-settings.
func (h *handlers) handleGetMyNotificationSettings(w http.ResponseWriter, r *http.Request) {
	user, ok := requireUser(w, r)
	if !ok {
		return
	}
	q := dbq.New(h.pool)
	kinds, err := notifications.LoadSettings(r.Context(), q, user.ID, user.IsAdmin)
	if err != nil {
		writeErrWithLog(w, h.logger, "notifications: load settings", apierror.Internal(err))
		return
	}
	h.writeNotificationSettings(w, r, q, user, kinds)
}

// handlePutMyNotificationSettings implements PUT /api/me/notification-settings.
// A partial update: only the kinds and channels named change.
func (h *handlers) handlePutMyNotificationSettings(w http.ResponseWriter, r *http.Request) {
	user, ok := requireUser(w, r)
	if !ok {
		return
	}
	var body notificationSettingsReq
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		writeErr(w, apierror.BadRequest("bad_body", "invalid JSON body"))
		return
	}
	q := dbq.New(h.pool)
	kinds, err := notifications.SaveSettings(r.Context(), q, user.ID, user.IsAdmin, body.Kinds)
	if errors.Is(err, notifications.ErrSettingInvalid) {
		writeErr(w, apierror.BadRequest("invalid_notification_setting", err.Error()))
		return
	}
	if err != nil {
		writeErrWithLog(w, h.logger, "notifications: save settings", apierror.Internal(err))
		return
	}
	h.writeNotificationSettings(w, r, q, user, kinds)
}

func (h *handlers) writeNotificationSettings(w http.ResponseWriter, r *http.Request, q *dbq.Queries, user dbq.User, kinds []notifications.KindSetting) {
	resp := notificationSettingsResp{Kinds: kinds, EmailAvailable: true}
	if user.Email == nil || strings.TrimSpace(*user.Email) == "" {
		resp.EmailAvailable, resp.EmailUnavailableReason = false, "no_address"
	} else {
		// A failed read is an error, not "not configured": that would tell
		// the user something about the server the read never established.
		cfg, err := q.GetSMTPConfig(r.Context())
		if err != nil {
			writeErrWithLog(w, h.logger, "notifications: read smtp config", apierror.Internal(err))
			return
		}
		if !mailer.Configured(cfg) {
			resp.EmailAvailable, resp.EmailUnavailableReason = false, "smtp_not_configured"
		}
	}
	writeJSON(w, http.StatusOK, resp)
}

// The cursor is the last row's (created_at, id), opaque to clients.
func formatNotificationCursor(at pgtype.Timestamptz, id pgtype.UUID) string {
	return at.Time.UTC().Format(time.RFC3339Nano) + "_" + uuidToString(id)
}

func parseNotificationCursor(raw string) (pgtype.Timestamptz, pgtype.UUID, bool) {
	ts, idStr, found := strings.Cut(raw, "_")
	if !found {
		return pgtype.Timestamptz{}, pgtype.UUID{}, false
	}
	at, err := time.Parse(time.RFC3339Nano, ts)
	if err != nil {
		return pgtype.Timestamptz{}, pgtype.UUID{}, false
	}
	id, ok := parseUUID(idStr)
	if !ok {
		return pgtype.Timestamptz{}, pgtype.UUID{}, false
	}
	return pgtype.Timestamptz{Time: at, Valid: true}, id, true
}