package notification

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"log/slog"
	"sync"
	"time"

	"gitea.dcglab.co.uk/steve/restic-manager/internal/crypto"
	"gitea.dcglab.co.uk/steve/restic-manager/internal/store"
)

// Hub fans Payload events out to every enabled channel and persists
// the result to notification_log. One Hub per process; thread-safe.
type Hub struct {
	store       *store.Store
	aead        *crypto.AEAD
	baseURL     string // e.g. https://restic-manager.example
	msgIDDomain string // hostname extracted from baseURL for SMTP Message-ID
}

// NewHub constructs a Hub. baseURL is the public root of the server
// (used to build /alerts/<id> links and the SMTP Message-ID domain).
func NewHub(st *store.Store, aead *crypto.AEAD, baseURL string) *Hub {
	return &Hub{
		store:       st,
		aead:        aead,
		baseURL:     baseURL,
		msgIDDomain: extractDomain(baseURL),
	}
}

// Dispatch fans out to every enabled channel. Best-effort — failures
// are logged to notification_log but do not propagate to the caller.
// Each channel runs in its own goroutine; Dispatch returns only when
// all goroutines have settled, so the caller can block briefly for
// the test-button case.
func (h *Hub) Dispatch(ctx context.Context, p Payload) {
	chans, err := h.store.ListEnabledNotificationChannels(ctx)
	if err != nil {
		slog.Error("notification: list channels", "err", err)
		return
	}
	// Stamp the alert link if the caller left it empty.
	if p.Link == "" {
		p.Link = h.baseURL + "/alerts/" + p.AlertID
	}

	var wg sync.WaitGroup
	for _, c := range chans {
		wg.Add(1)
		go func(c store.NotificationChannel) {
			defer wg.Done()
			h.send(ctx, c, p)
		}(c)
	}
	wg.Wait()
}

// DispatchOne fires a single channel — used by the "Send test
// notification" button. Returns the log entry that was persisted so
// the handler can render the result inline.
func (h *Hub) DispatchOne(ctx context.Context, channelID string, p Payload) (store.NotificationLogEntry, error) {
	c, err := h.store.GetNotificationChannel(ctx, channelID)
	if err != nil {
		return store.NotificationLogEntry{}, err
	}
	if p.Link == "" {
		p.Link = h.baseURL + "/alerts/" + p.AlertID
	}
	return h.send(ctx, *c, p), nil
}

// send builds the channel impl, delivers the payload, and persists a
// notification_log row regardless of success or failure.
func (h *Hub) send(ctx context.Context, c store.NotificationChannel, p Payload) store.NotificationLogEntry {
	ch, buildErr := h.buildChannel(c)
	logEntry := store.NotificationLogEntry{
		ID:        newID(),
		ChannelID: c.ID,
		Event:     string(p.Event),
		FiredAt:   time.Now().UTC(),
	}
	if p.AlertID != "" {
		aid := p.AlertID
		logEntry.AlertID = &aid
	}
	if buildErr != nil {
		errStr := buildErr.Error()
		logEntry.OK = false
		logEntry.Error = &errStr
		_ = h.store.AppendNotificationLog(ctx, logEntry)
		return logEntry
	}

	code, latency, sendErr := ch.Send(ctx, p)
	statusCode := code
	latencyMS := int(latency.Milliseconds())
	logEntry.StatusCode = &statusCode
	logEntry.LatencyMS = &latencyMS
	if sendErr != nil {
		errStr := sendErr.Error()
		logEntry.OK = false
		logEntry.Error = &errStr
	} else {
		logEntry.OK = true
	}
	if err := h.store.AppendNotificationLog(ctx, logEntry); err != nil {
		slog.Warn("notification: persist log", "err", err)
	}
	return logEntry
}

// buildChannel decrypts the channel config and returns a concrete
// Channel implementation for the channel's kind.
func (h *Hub) buildChannel(row store.NotificationChannel) (Channel, error) {
	plain, err := h.aead.Decrypt(string(row.Config), []byte("notification-channel:"+row.ID))
	if err != nil {
		return nil, err
	}
	switch row.Kind {
	case "webhook":
		var cfg WebhookConfig
		if err := json.Unmarshal(plain, &cfg); err != nil {
			return nil, err
		}
		return NewWebhookChannel(cfg), nil
	case "ntfy":
		var cfg NtfyConfig
		if err := json.Unmarshal(plain, &cfg); err != nil {
			return nil, err
		}
		dp := ""
		if row.DefaultPriority != nil {
			dp = *row.DefaultPriority
		}
		return NewNtfyChannel(cfg, dp), nil
	case "smtp":
		var cfg SMTPConfig
		if err := json.Unmarshal(plain, &cfg); err != nil {
			return nil, err
		}
		return NewSMTPChannel(cfg, h.msgIDDomain), nil
	}
	return nil, errUnknownKind(row.Kind)
}

// newID returns a 32-hex-char random identifier for notification_log rows.
func newID() string {
	var b [16]byte
	_, _ = rand.Read(b[:])
	return hex.EncodeToString(b[:])
}

// extractDomain strips the scheme and path from baseURL, leaving only
// the host[:port] component. Used as the right-hand side of SMTP
// Message-IDs.
func extractDomain(baseURL string) string {
	s := baseURL
	if i := indexOf(s, "://"); i >= 0 {
		s = s[i+3:]
	}
	if i := indexOf(s, "/"); i >= 0 {
		s = s[:i]
	}
	if s == "" {
		return "restic-manager.local"
	}
	return s
}

// indexOf returns the index of the first occurrence of sub in s, or -1.
func indexOf(s, sub string) int {
	for i := 0; i+len(sub) <= len(s); i++ {
		if s[i:i+len(sub)] == sub {
			return i
		}
	}
	return -1
}

type errUnknownKind string

func (e errUnknownKind) Error() string { return "notification: unknown kind: " + string(e) }