// Package service — NotificationService is the single seam every
// user-facing event flows through ("the notification plugin"). Today it
// does two things per event:
//
//  1. Persists a row in `notifications` (so an in-app notification center
//     and, later, websocket + push delivery can read the same history).
//  2. Sends an email to the recipient via the shared mailer.
//
// Everything here is fire-and-forget from the caller's perspective: a
// follow request must succeed even if the email bounces or the insert
// fails, so Notify* never returns an error — failures are logged. When
// websocket/push land they hook in right here alongside the email send.
package service

import (
	"bytes"
	"context"
	"fmt"
	"html/template"
	"strings"
	"time"

	"github.com/prabhupadasays/spsays-bff/internal/model"
	"github.com/prabhupadasays/spsays-bff/internal/repository"
	"github.com/prabhupadasays/spsays-bff/pkg/mailer"
	"github.com/prabhupadasays/spsays-bff/pkg/realtime"
	"go.uber.org/zap"
)

// Notification kinds — short machine strings stored in notifications.kind.
const (
	NotifFollowRequest  = "follow_request"
	NotifFollowAccepted = "follow_accepted"
	NotifPostLike       = "post_like"

	// Reminder kinds are delivered live (email + push + a websocket toast)
	// but NOT persisted — they're ephemeral nudges, not history.
	NotifChantReminder   = "chant_reminder"
	NotifQuoteReminder   = "quote_reminder"
	NotifChantIncomplete = "chant_incomplete_reminder"
)

type NotificationService struct {
	notifs      *repository.NotificationRepo
	users       *repository.UserRepo
	mail        mailer.Mailer
	rt          *realtime.SoketiClient // optional — nil disables WebSocket push
	push        *PushSender            // optional — nil disables Web Push
	logger      *zap.Logger
	frontendURL string
}

func NewNotificationService(notifs *repository.NotificationRepo, users *repository.UserRepo, mail mailer.Mailer, rt *realtime.SoketiClient, push *PushSender, logger *zap.Logger, frontendURL string) *NotificationService {
	return &NotificationService{
		notifs:      notifs,
		users:       users,
		mail:        mail,
		rt:          rt,
		push:        push,
		logger:      logger,
		frontendURL: strings.TrimRight(frontendURL, "/"),
	}
}

// List returns the caller's notifications, newest first.
func (s *NotificationService) List(ctx context.Context, userID string, limit, offset int) ([]model.Notification, error) {
	if limit <= 0 || limit > 100 {
		limit = 30
	}
	if offset < 0 {
		offset = 0
	}
	return s.notifs.ListByUser(ctx, userID, limit, offset)
}

// UnreadCount returns the caller's unread notification count (for the bell
// badge).
func (s *NotificationService) UnreadCount(ctx context.Context, userID string) (int, error) {
	return s.notifs.CountUnread(ctx, userID)
}

// MarkAllRead marks all of the caller's notifications read.
func (s *NotificationService) MarkAllRead(ctx context.Context, userID string) error {
	return s.notifs.MarkAllRead(ctx, userID)
}

// LikeEmailPref / SetLikeEmailPref back the Settings → Notifications toggle
// for aggregated like emails.
func (s *NotificationService) LikeEmailPref(ctx context.Context, userID string) (bool, error) {
	return s.notifs.LikeEmailsEnabled(ctx, userID)
}

func (s *NotificationService) SetLikeEmailPref(ctx context.Context, userID string, enabled bool) error {
	return s.notifs.SetLikeEmailsEnabled(ctx, userID, enabled)
}

// NotifyFollowRequest tells `recipientID` that `actorID` asked to follow
// them. Persists the row and emails the recipient (if they have an email
// on file).
func (s *NotificationService) NotifyFollowRequest(ctx context.Context, recipientID, actorID string) {
	s.dispatch(ctx, recipientID, actorID, NotifFollowRequest,
		"%s requested to follow you — Prabhupāda Says")
}

// NotifyFollowAccepted tells `recipientID` that `actorID` accepted their
// follow request (i.e. the recipient can now see actor's activity).
func (s *NotificationService) NotifyFollowAccepted(ctx context.Context, recipientID, actorID string) {
	s.dispatch(ctx, recipientID, actorID, NotifFollowAccepted,
		"%s accepted your follow request — Prabhupāda Says")
}

// NotifyPostLike tells the post author that `likerID` liked their post. Sent
// only when the liker isn't the author (callers also guard). Unlike follows,
// likes are high-volume, so this delivers a persisted row + realtime nudge +
// Web Push but NO email. The push is tagged per-post so repeated likes on the
// same post collapse into one notification rather than stacking.
func (s *NotificationService) NotifyPostLike(ctx context.Context, postID, authorID, likerID string) {
	if authorID == "" || likerID == "" || authorID == likerID {
		return
	}
	// Aggregate into the single (author, post) like-notification row. Returns
	// the new liker count and whether an aggregated email is due (throttled).
	count, emailDue, err := s.notifs.UpsertLike(ctx, authorID, likerID, postID, likeEmailThrottle)
	if err != nil {
		s.logger.Warn("aggregate like notification failed",
			zap.String("recipient", authorID), zap.Error(err))
		count, emailDue = 1, false
	}

	actorUser, _ := s.users.FindByID(ctx, likerID)
	who := "Someone"
	if actorUser != nil {
		who = actorDisplay(actorUser)
	}
	body := likeMessage(who, count)

	// Realtime nudge — carry actor_count so the toast can read "and N others".
	if s.rt != nil {
		payload := map[string]any{"kind": NotifPostLike, "actor_count": count}
		if actorUser != nil {
			payload["actor_name"] = actorDisplay(actorUser)
			payload["actor_handle"] = actorUser.Handle
			payload["actor_avatar_url"] = actorUser.AvatarURL
		}
		if err := s.rt.Trigger(ctx, "notifications."+authorID, "notification", payload); err != nil {
			s.logger.Warn("realtime like publish failed", zap.String("recipient", authorID), zap.Error(err))
		}
	}

	// Tapping a notification opens the author's own feed anchored to the post.
	author, _ := s.users.FindByID(ctx, authorID)
	url := s.frontendURL + "/notifications"
	if author != nil {
		url = s.frontendURL + "/u/" + author.Handle + "/posts#post-" + postID
	}

	// Web Push — tagged per-post so repeated likes collapse into one.
	if s.push != nil {
		s.push.SendToUser(ctx, authorID, PushPayload{
			Title: "New Like",
			Body:  body,
			URL:   url,
			Icon:  s.iconURL(),
			Tag:   NotifPostLike + ":" + postID,
		})
	}

	// Aggregated email — only when the throttle says one is due (so a burst of
	// likes yields a single email), the author has an address, and they
	// haven't opted out. `body` already aggregates ("X and N others …").
	if !emailDue || author == nil || author.Email == nil || strings.TrimSpace(*author.Email) == "" {
		return
	}
	if enabled, perr := s.notifs.LikeEmailsEnabled(ctx, authorID); perr != nil || !enabled {
		return
	}
	var buf bytes.Buffer
	if err := likeEmailTpl.Execute(&buf, map[string]any{
		"RecipientName": author.Name,
		"Message":       body,
		"URL":           url,
	}); err != nil {
		s.logger.Warn("render like email failed", zap.Error(err))
		return
	}
	if err := s.mail.Send(strings.TrimSpace(*author.Email), "New likes on your post — Prabhupāda Says", buf.String()); err != nil {
		s.logger.Warn("like email send failed", zap.String("to", *author.Email), zap.Error(err))
	}
}

// likeEmailThrottle is the minimum gap between aggregated like emails for a
// single post — a burst of likes within the window produces one email.
const likeEmailThrottle = 6 * time.Hour

// likeMessage renders the aggregated like text: "X liked your post" or
// "X and N others liked your post".
func likeMessage(who string, count int) string {
	if count <= 1 {
		return who + " liked your post"
	}
	others := count - 1
	noun := "others"
	if others == 1 {
		noun = "other"
	}
	return fmt.Sprintf("%s and %d %s liked your post", who, others, noun)
}

// dispatch persists the notification and sends the matching email. All
// failures are logged, never propagated.
func (s *NotificationService) dispatch(ctx context.Context, recipientID, actorID, kind, subjectFmt string) {
	actor := actorID
	if _, err := s.notifs.Create(ctx, recipientID, &actor, kind); err != nil {
		s.logger.Warn("persist notification failed",
			zap.String("recipient", recipientID), zap.String("kind", kind), zap.Error(err))
		// Persistence failed, but still try the other channels.
	}

	// Look up the actor once — both the realtime push and the email use it.
	actorUser, aerr := s.users.FindByID(ctx, actorID)
	if aerr != nil {
		s.logger.Warn("notification actor lookup failed", zap.String("actor", actorID), zap.Error(aerr))
	}

	// Realtime push (best-effort) — a lightweight nudge so the client can
	// bump the bell + toast immediately. Fires regardless of whether the
	// recipient has an email; authoritative data still comes from REST.
	s.publishRealtime(ctx, recipientID, kind, actorUser)

	// Web Push (best-effort) — reaches the recipient even with the app
	// closed. Same seam as realtime/email; nil sender is a no-op.
	s.publishPush(ctx, recipientID, kind, actorUser)

	// Email (best-effort).
	recipient, err := s.users.FindByID(ctx, recipientID)
	if err != nil {
		s.logger.Warn("notification recipient lookup failed", zap.String("recipient", recipientID), zap.Error(err))
		return
	}
	if recipient.Email == nil || strings.TrimSpace(*recipient.Email) == "" {
		// No email on file (OAuth-only account that never added one) —
		// the persisted row + realtime push are the notification.
		return
	}
	if actorUser == nil {
		// Can't render the email body without the actor's name.
		return
	}

	body, err := s.render(kind, recipient, actorUser)
	if err != nil {
		s.logger.Warn("render notification email failed", zap.String("kind", kind), zap.Error(err))
		return
	}
	subject := strings.Replace(subjectFmt, "%s", actorDisplay(actorUser), 1)
	if err := s.mail.Send(strings.TrimSpace(*recipient.Email), subject, body); err != nil {
		s.logger.Warn("notification email send failed",
			zap.String("to", *recipient.Email), zap.String("kind", kind), zap.Error(err))
	}
}

// publishRealtime pushes a lightweight notification event to the
// recipient's Soketi channel. PUBLIC channel for now ("notifications.{id}")
// — switch to a "private-" prefix once Soketi App auth is wired up. The
// payload carries just enough for a toast; the client refetches the
// authoritative unread count + list from REST.
func (s *NotificationService) publishRealtime(ctx context.Context, recipientID, kind string, actor *model.User) {
	if s.rt == nil {
		return
	}
	payload := map[string]any{"kind": kind}
	if actor != nil {
		payload["actor_name"] = actorDisplay(actor)
		payload["actor_handle"] = actor.Handle
		payload["actor_avatar_url"] = actor.AvatarURL
	}
	if err := s.rt.Trigger(ctx, "notifications."+recipientID, "notification", payload); err != nil {
		s.logger.Warn("realtime notification publish failed",
			zap.String("recipient", recipientID), zap.String("kind", kind), zap.Error(err))
	}
}

// SendReminder delivers an ephemeral sādhana reminder across all live
// channels — a websocket toast (no unread bump, not persisted), a Web Push,
// and an email. Best-effort; nothing is persisted to the notification
// center. `url` is where tapping the notification lands.
func (s *NotificationService) SendReminder(ctx context.Context, userID, kind, title, body, url string) {
	// Realtime toast — a distinct "reminder" event so the client toasts
	// without bumping the unread badge (reminders have no DB row).
	if s.rt != nil {
		_ = s.rt.Trigger(ctx, "notifications."+userID, "reminder", map[string]any{
			"kind": kind, "title": title, "body": body, "url": url,
		})
	}

	// Web Push (reaches closed apps).
	if s.push != nil {
		s.push.SendToUser(ctx, userID, PushPayload{Title: title, Body: body, URL: url, Icon: s.iconURL(), Tag: kind, RequireInteraction: true})
	}

	// Email (only if there's an address on file).
	recipient, err := s.users.FindByID(ctx, userID)
	if err != nil || recipient == nil || recipient.Email == nil || strings.TrimSpace(*recipient.Email) == "" {
		return
	}
	var buf bytes.Buffer
	if err := reminderEmailTpl.Execute(&buf, map[string]any{
		"RecipientName": recipient.Name,
		"Message":       body,
		"URL":           url,
	}); err != nil {
		s.logger.Warn("render reminder email failed", zap.String("kind", kind), zap.Error(err))
		return
	}
	if err := s.mail.Send(strings.TrimSpace(*recipient.Email), title, buf.String()); err != nil {
		s.logger.Warn("reminder email send failed", zap.String("to", *recipient.Email), zap.String("kind", kind), zap.Error(err))
	}
}

// publishPush delivers a Web Push notification to the recipient's devices.
// The body quotes the actor; tapping it opens their profile (where a pending
// follow request can be accepted). Best-effort; nil sender is a no-op.
func (s *NotificationService) publishPush(ctx context.Context, recipientID, kind string, actor *model.User) {
	if s.push == nil {
		return
	}
	who := "Someone"
	url := s.frontendURL + "/notifications"
	if actor != nil {
		who = actorDisplay(actor)
		url = s.frontendURL + "/u/" + actor.Handle
	}
	// Title must be meaningful, not the app name: iOS renders installed-PWA
	// notifications as "<title> from <app name>", so a generic "Prabhupāda
	// Says" title reads as "Prabhupāda Says from Prabhupāda Says".
	var title, body string
	switch kind {
	case NotifFollowRequest:
		title = "New Friend Request"
		body = who + " requested to follow you"
	case NotifFollowAccepted:
		title = "Friend Request Accepted"
		body = who + " accepted your follow request"
	default:
		title = "New notification"
		body = "You have a new notification"
	}
	s.push.SendToUser(ctx, recipientID, PushPayload{
		Title: title,
		Body:  body,
		URL:   url,
		Icon:  s.iconURL(),
		Tag:   kind,
	})
}

// iconURL is the absolute URL of the notification icon (the app's square
// icon), so it renders regardless of the client's base path.
func (s *NotificationService) iconURL() string {
	return strings.TrimRight(s.frontendURL, "/") + "/icon-192.png"
}

func (s *NotificationService) render(kind string, recipient, actor *model.User) (string, error) {
	data := map[string]any{
		"RecipientName": recipient.Name,
		"ActorName":     actorDisplay(actor),
		"ActorHandle":   actor.Handle,
		"ProfileURL":    s.frontendURL + "/u/" + actor.Handle,
	}
	var tpl *template.Template
	switch kind {
	case NotifFollowRequest:
		tpl = followRequestEmailTpl
	case NotifFollowAccepted:
		tpl = followAcceptedEmailTpl
	default:
		tpl = followRequestEmailTpl
	}
	var buf bytes.Buffer
	if err := tpl.Execute(&buf, data); err != nil {
		return "", err
	}
	return buf.String(), nil
}

// actorDisplay prefers the display name, falling back to @handle.
func actorDisplay(u *model.User) string {
	if n := strings.TrimSpace(u.Name); n != "" {
		return n
	}
	return "@" + u.Handle
}

// Vaishnava-styled, 17px base to match the feedback emails. Both quote
// the actor and link to their profile (where the recipient can accept a
// pending request).
var followRequestEmailTpl = template.Must(template.New("followRequest").Parse(`<div style="font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;color:#2a2118;max-width:560px;margin:0 auto;font-size:17px;line-height:1.7">
  <p style="font-size:18px;color:#9a6b2f;letter-spacing:0.04em;margin-bottom:1em">Hare Kṛṣṇa{{if .RecipientName}}, {{.RecipientName}}{{end}} 🙏</p>

  <p><strong>{{.ActorName}}</strong> (<a href="{{.ProfileURL}}" style="color:#9a6b2f;font-weight:600">@{{.ActorHandle}}</a>)
  has requested to follow you on Prabhupāda Says.</p>

  <p>You can review and accept or decline the request from their profile:</p>

  <p style="margin:1.25em 0">
    <a href="{{.ProfileURL}}" style="display:inline-block;background:#9a6b2f;color:#fff;text-decoration:none;padding:0.6em 1.3em;border-radius:8px;font-weight:600">View request</a>
  </p>

  <p style="margin-top:1.5em">Your servants,<br>
  <strong>The Prabhupāda Says team</strong></p>
</div>`))

var followAcceptedEmailTpl = template.Must(template.New("followAccepted").Parse(`<div style="font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;color:#2a2118;max-width:560px;margin:0 auto;font-size:17px;line-height:1.7">
  <p style="font-size:18px;color:#9a6b2f;letter-spacing:0.04em;margin-bottom:1em">Hare Kṛṣṇa{{if .RecipientName}}, {{.RecipientName}}{{end}} 🙏</p>

  <p><strong>{{.ActorName}}</strong> (<a href="{{.ProfileURL}}" style="color:#9a6b2f;font-weight:600">@{{.ActorHandle}}</a>)
  has accepted your follow request. You're now following them on Prabhupāda Says.</p>

  <p style="margin:1.25em 0">
    <a href="{{.ProfileURL}}" style="display:inline-block;background:#9a6b2f;color:#fff;text-decoration:none;padding:0.6em 1.3em;border-radius:8px;font-weight:600">Visit profile</a>
  </p>

  <p style="margin-top:1.5em">Your servants,<br>
  <strong>The Prabhupāda Says team</strong></p>
</div>`))

// Daily sādhana reminder. The Message is the recency-aware nudge; the CTA
// opens the streak page.
var reminderEmailTpl = template.Must(template.New("reminder").Parse(`<div style="font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;color:#2a2118;max-width:560px;margin:0 auto;font-size:17px;line-height:1.7">
  <p style="font-size:18px;color:#9a6b2f;letter-spacing:0.04em;margin-bottom:1em">Hare Kṛṣṇa{{if .RecipientName}}, {{.RecipientName}}{{end}} 🙏</p>

  <p>{{.Message}}</p>

  <p style="margin:1.25em 0">
    <a href="{{.URL}}" style="display:inline-block;background:#9a6b2f;color:#fff;text-decoration:none;padding:0.6em 1.3em;border-radius:8px;font-weight:600">Open your sādhana</a>
  </p>

  <p style="margin-top:1.5em;font-size:14px;color:#7a6a55">You can turn these reminders off any time in Settings → Notifications.</p>

  <p style="margin-top:1em">Your servants,<br>
  <strong>The Prabhupāda Says team</strong></p>
</div>`))

// Aggregated like email. Message is "X and N others liked your post"; the CTA
// opens the author's post.
var likeEmailTpl = template.Must(template.New("postLike").Parse(`<div style="font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;color:#2a2118;max-width:560px;margin:0 auto;font-size:17px;line-height:1.7">
  <p style="font-size:18px;color:#9a6b2f;letter-spacing:0.04em;margin-bottom:1em">Hare Kṛṣṇa{{if .RecipientName}}, {{.RecipientName}}{{end}} 🙏</p>

  <p>{{.Message}}.</p>

  <p style="margin:1.25em 0">
    <a href="{{.URL}}" style="display:inline-block;background:#9a6b2f;color:#fff;text-decoration:none;padding:0.6em 1.3em;border-radius:8px;font-weight:600">View your post</a>
  </p>

  <p style="margin-top:1.5em;font-size:14px;color:#7a6a55">You can turn off like emails any time in Settings → Notifications.</p>

  <p style="margin-top:1em">Your servants,<br>
  <strong>The Prabhupāda Says team</strong></p>
</div>`))