package gateway

import (
	"context"
	"fmt"
	"net/http"
	"sort"
	"strconv"
	"strings"
	"time"
	"unicode/utf8"

	apperr "git.yeij.top/AskaEth/Cyrene_v2/internal/errors"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/services/backthink"
)

// Notification feed limits (design/10 §3 #16). Compile-time constants so no bare
// magic number appears in the run path (project rule §10).
const (
	defaultNotificationLimit = 50
	maxNotificationLimit     = 200
	// notificationFetchFactor widens the per-source read. The merged page must be
	// the newest N of the union, which the per-source newest-N always contains,
	// but with a `before` cursor one source can dominate the newest window and
	// starve the other — the factor pays for that.
	notificationFetchFactor = 4
	// notificationBodyRunes caps a backthink summary in the feed; the full text
	// stays available on GET /api/v1/admin/backthink.
	notificationBodyRunes = 200
)

// The unified feed's families, used both as the item `type` and as the `?type=`
// filter. They are derived from the sources the composition root already has
// (design/10 §3 #16: 先聚合现有源为统一 feed，避免新建重模型).
const (
	// NotificationTypeSystem is a system/security operation: backup & restore,
	// JWT rotation, API-key revocation, plugin install/uninstall, tool policy.
	NotificationTypeSystem = "system"
	// NotificationTypeChannel is a channel lifecycle or connection event
	// (channel.open / close / save / reject / login).
	NotificationTypeChannel = "channel"
	// NotificationTypeBackthink is one proactive push the background thinker
	// decided to send.
	NotificationTypeBackthink = "backthink"
	// NotificationTypeAudit is the remaining admin audit trail: personas, memory,
	// users, RAG, sessions, uploads, audio.
	NotificationTypeAudit = "audit"
)

// Provenance labels carried on an item's `source` field.
const (
	notificationSourceAudit     = "audit"
	notificationSourceBackthink = "backthink"
	// notificationIDPrefixAudit / ...Backthink namespace the source's own record id
	// so the merged feed has stable, collision-free, client-dedupable ids.
	notificationIDPrefixAudit     = "audit:"
	notificationIDPrefixBackthink = "backthink:"
)

// AdminNotification is one item of the unified notification feed (design/10 §3
// #16). It is a read-only projection of an existing record — audit rows and
// backthink records — never a new persisted model: `id` is "<source>:<原生 id>",
// `title`/`body` are derived from the source record, and `createdAt` is epoch
// milliseconds.
type AdminNotification struct {
	ID        string `json:"id"`
	Type      string `json:"type"`
	Title     string `json:"title"`
	Body      string `json:"body,omitempty"`
	Source    string `json:"source"`
	CreatedAt int64  `json:"createdAt"`
}

// adminListNotifications returns the unified notification feed (owner/admin
// read): the admin audit trail and the background thinker's proactive pushes,
// merged newest-first and filterable by family and by a `before` cursor.
//
// A source that is not injected contributes no items — the feed reports what
// actually exists instead of fabricating a family — so a deployment without the
// backthink service simply has no `backthink` items.
func (s *Server) adminListNotifications(w http.ResponseWriter, r *http.Request) {
	limit := parseNotificationLimit(r)
	typ := strings.TrimSpace(r.URL.Query().Get("type"))
	if typ != "" && !validNotificationType(typ) {
		writeError(w, apperr.Wrap(apperr.ErrBadRequest, "invalid_type",
			"type must be one of system|channel|backthink|audit"))
		return
	}
	before, hasBefore := parseNotificationBefore(r)

	items, err := s.notificationItems(r.Context(), notificationFetchLimit(limit))
	if err != nil {
		s.log.Error("list notifications", "err", err)
		writeError(w, apperr.Wrap(apperr.ErrInternal, "notifications_failed",
			"failed to list notifications"))
		return
	}

	out := make([]AdminNotification, 0, limit)
	for _, it := range items {
		if typ != "" && it.Type != typ {
			continue
		}
		if hasBefore && it.CreatedAt > before {
			continue
		}
		out = append(out, it)
		if len(out) == limit {
			break
		}
	}
	writeJSON(w, http.StatusOK, out)
}

// notificationItems reads both sources and returns their merge, newest first. A
// source failure is returned (never swallowed into a silently shorter feed), so
// the endpoint answers a clear error instead of pretending there was no event.
func (s *Server) notificationItems(ctx context.Context, fetch int) ([]AdminNotification, error) {
	auditItems, err := s.notificationsFromAudit(ctx, fetch)
	if err != nil {
		return nil, err
	}
	btItems, err := s.notificationsFromBackthink(ctx, fetch)
	if err != nil {
		return nil, err
	}
	items := append(auditItems, btItems...)
	sort.SliceStable(items, func(i, j int) bool {
		if items[i].CreatedAt != items[j].CreatedAt {
			return items[i].CreatedAt > items[j].CreatedAt
		}
		// Descending id keeps the order deterministic for items sharing a
		// millisecond (the cursor can split one millisecond across pages).
		return items[i].ID > items[j].ID
	})
	return items, nil
}

// notificationsFromAudit projects the admin audit trail (audit_logs, persisted
// by NewSQLiteAuditStore) into feed items. The fallback in-memory store holds
// only records really appended in this process, so an unwired store yields an
// empty family rather than fabricated entries.
func (s *Server) notificationsFromAudit(ctx context.Context, fetch int) ([]AdminNotification, error) {
	if s.obs == nil || s.obs.audit == nil {
		return nil, nil
	}
	records, err := s.obs.audit.List(ctx, fetch)
	if err != nil {
		return nil, fmt.Errorf("gateway: notification audit source: %w", err)
	}
	out := make([]AdminNotification, 0, len(records))
	for _, rec := range records {
		out = append(out, AdminNotification{
			ID:        notificationIDPrefixAudit + strconv.FormatInt(rec.ID, 10),
			Type:      notificationTypeOfAudit(rec.What),
			Title:     rec.What,
			Body:      notificationAuditBody(rec),
			Source:    notificationSourceAudit,
			CreatedAt: notificationAuditAt(rec.When),
		})
	}
	return out, nil
}

// notificationsFromBackthink projects the background thinker's records into feed
// items. Only records that decided to push are notifications (a plain thinking
// record is not an event the owner needs to be told about); each carries the
// delivery state so the feed never claims an undelivered push was sent.
func (s *Server) notificationsFromBackthink(ctx context.Context, fetch int) ([]AdminNotification, error) {
	if s.backthink == nil {
		return nil, nil
	}
	records, err := s.backthink.List(ctx, fetch)
	if err != nil {
		return nil, fmt.Errorf("gateway: notification backthink source: %w", err)
	}
	out := make([]AdminNotification, 0, len(records))
	for _, rec := range records {
		if !rec.ShouldPush {
			continue
		}
		out = append(out, AdminNotification{
			ID:        notificationIDPrefixBackthink + strconv.FormatInt(rec.ID, 10),
			Type:      NotificationTypeBackthink,
			Title:     backthinkNotificationTitle(rec),
			Body:      clipRunes(strings.TrimSpace(rec.Conclusion), notificationBodyRunes),
			Source:    notificationSourceBackthink,
			CreatedAt: rec.At.UnixMilli(),
		})
	}
	return out, nil
}

// notificationTypeOfAudit classifies an audit operation into a feed family: the
// channel lifecycle is `channel`, and the system/plugin/policy operations are
// `system`; everything else stays `audit`.
func notificationTypeOfAudit(what string) string {
	switch {
	case strings.HasPrefix(what, "channel."):
		return NotificationTypeChannel
	case strings.HasPrefix(what, "system."),
		strings.HasPrefix(what, "plugin."),
		strings.HasPrefix(what, "policy."):
		return NotificationTypeSystem
	default:
		return NotificationTypeAudit
	}
}

// notificationAuditBody derives an audit item's body from its who/what/result
// trail, e.g. "owner:owner · ok".
func notificationAuditBody(rec AuditRecord) string {
	parts := make([]string, 0, 2)
	if who := strings.TrimSpace(rec.Who); who != "" {
		parts = append(parts, who)
	}
	if result := strings.TrimSpace(rec.Result); result != "" {
		parts = append(parts, result)
	}
	return strings.Join(parts, " · ")
}

// notificationAuditAt parses an audit record's RFC3339 timestamp into epoch
// milliseconds. An unparseable timestamp yields 0: the item still appears (oldest
// first) instead of being dropped or stamped with a made-up time.
func notificationAuditAt(when string) int64 {
	ts, err := time.Parse(time.RFC3339Nano, strings.TrimSpace(when))
	if err != nil {
		return 0
	}
	return ts.UnixMilli()
}

// backthinkNotificationTitle labels one proactive push with its trigger and
// delivery state, so the feed distinguishes "sent" from "decided but not
// delivered" (route none / no online client / push failure).
func backthinkNotificationTitle(rec backthink.Record) string {
	state := "未送达"
	if rec.PushResult.Pushed {
		state = "已送达"
	}
	if trigger := strings.TrimSpace(rec.Trigger); trigger != "" {
		return "主动推送（" + trigger + " · " + state + "）"
	}
	return "主动推送（" + state + "）"
}

// clipRunes truncates s to at most max runes, appending an ellipsis when it was
// cut. It never splits a multi-byte rune.
func clipRunes(s string, max int) string {
	if max <= 0 || utf8.RuneCountInString(s) <= max {
		return s
	}
	runes := []rune(s)
	return string(runes[:max]) + "…"
}

// parseNotificationLimit parses the ?limit= query param, clamping to
// [1, maxNotificationLimit] and selecting defaultNotificationLimit when absent or
// invalid.
func parseNotificationLimit(r *http.Request) int {
	n, err := strconv.Atoi(r.URL.Query().Get("limit"))
	if err != nil || n <= 0 {
		return defaultNotificationLimit
	}
	if n > maxNotificationLimit {
		return maxNotificationLimit
	}
	return n
}

// parseNotificationBefore parses the ?before= epoch-millisecond cursor. The
// cursor is inclusive (items with createdAt <= before are returned): the sources
// resolve to milliseconds, so a page boundary can fall inside one millisecond,
// and the client deduplicates by id. An absent or malformed cursor means "from
// the newest item".
func parseNotificationBefore(r *http.Request) (int64, bool) {
	raw := strings.TrimSpace(r.URL.Query().Get("before"))
	if raw == "" {
		return 0, false
	}
	ms, err := strconv.ParseInt(raw, 10, 64)
	if err != nil || ms <= 0 {
		return 0, false
	}
	return ms, true
}

// notificationFetchLimit widens a page request into the per-source read window,
// capped at maxObsLimit (the audit store's own ceiling) and never below the page.
func notificationFetchLimit(limit int) int {
	fetch := limit * notificationFetchFactor
	if fetch > maxObsLimit {
		fetch = maxObsLimit
	}
	if fetch < limit {
		fetch = limit
	}
	return fetch
}

// validNotificationType reports whether t names a feed family. An unknown family
// is rejected with 400 rather than answered with a silently empty feed.
func validNotificationType(t string) bool {
	switch t {
	case NotificationTypeSystem, NotificationTypeChannel, NotificationTypeBackthink, NotificationTypeAudit:
		return true
	default:
		return false
	}
}