// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0

// Package webhooks notifies external services about post changes.
//
// Hooks come from two places with the same shape: [[webhooks]] tables in
// config.toml (read-only, applied at start) and webhooks.toml beside the
// users file, which the admin edits and which applies without a
// restart. Each event payload is POSTed as JSON, signed with HMAC-SHA256
// when the hook carries a secret:
//
//	X-Volumen-Event: post.created
//	X-Volumen-Delivery: 0f3b1c9e2a4d
//	X-Volumen-Signature: sha256=<hex digest of the raw body>
//
// Delivery runs in background goroutines so admin requests never block
// on a third-party endpoint; failures are retried with a short backoff
// and recorded in an in-memory delivery history (lost on restart).
package webhooks

import (
	"bytes"
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	json "encoding/json/v2"
	"fmt"
	"io"
	"log/slog"
	"maps"
	"net/http"
	"slices"
	"strings"
	"sync"
	"time"
)

const (
	requestTimeout = 10 * time.Second
	maxAttempts    = 3
	historyLimit   = 50

	// maxConcurrentDeliveries bounds the deliveries in flight at once.
	maxConcurrentDeliveries = 8
)

var retryBackoff = []time.Duration{time.Second, 4 * time.Second}

// Webhook is one configured endpoint.
type Webhook struct {
	URL     string
	Secret  string
	Events  []string // empty = every event
	Enabled bool
}

// Accepts reports whether the hook wants event (ignoring ping, which
// is always delivered on demand).
func (h Webhook) Accepts(event string) bool {
	if !h.Enabled {
		return false
	}
	if len(h.Events) == 0 {
		return true
	}
	return slices.Contains(h.Events, event)
}

// Delivery is the outcome of one delivery attempt series.
type Delivery struct {
	ID         string
	HookURL    string
	Event      string
	Timestamp  string
	Status     string // "ok" | "failed"
	StatusCode int
	Attempts   int
	Error      string
}

// Manager delivers signed JSON payloads to the configured webhooks.
type Manager struct {
	mu      sync.Mutex
	hooks   []Webhook
	version string
	client  *http.Client

	// deliveries bounds how many deliveries run at once, so a burst of
	// post writes cannot spawn an unbounded number of goroutines that
	// each retry with a backoff.
	deliveries chan struct{}
	inflight   sync.WaitGroup

	history []Delivery
}

// NewManager builds the manager from the configured hooks.
func NewManager(hooks []Webhook, version string) *Manager {
	return &Manager{
		hooks:      hooks,
		version:    version,
		client:     &http.Client{Timeout: requestTimeout},
		deliveries: make(chan struct{}, maxConcurrentDeliveries),
	}
}

// SetHooks replaces the hook set: the admin edits the persisted list and
// the change applies without a restart. Deliveries already in flight
// finish against the hook they hold.
func (m *Manager) SetHooks(hooks []Webhook) {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.hooks = hooks
}

// Hooks returns a copy of the configured hooks.
func (m *Manager) Hooks() []Webhook {
	m.mu.Lock()
	defer m.mu.Unlock()
	return slices.Clone(m.hooks)
}

// Wait blocks until the asynchronous deliveries started by Fire have
// finished, so a short-lived command can flush before it exits.
func (m *Manager) Wait() { m.inflight.Wait() }

// Deliveries returns recorded deliveries, newest first, optionally
// filtered by hook URL.
func (m *Manager) Deliveries(hookURL string) []Delivery {
	m.mu.Lock()
	defer m.mu.Unlock()
	out := make([]Delivery, 0, len(m.history))
	for _, v := range slices.Backward(m.history) {
		if hookURL == "" || v.HookURL == hookURL {
			out = append(out, v)
		}
	}
	return out
}

// Fire schedules event delivery to every matching hook and returns the
// number of hooks contacted. With wait the deliveries run inline, so
// short-lived CLI commands finish before the process exits.
func (m *Manager) Fire(event string, payload map[string]any, wait bool) int {
	body := map[string]any{
		"event":     event,
		"timestamp": nowISO(),
		"version":   m.version,
	}
	maps.Copy(body, payload)
	encoded, err := json.Marshal(body)
	if err != nil {
		slog.Warn("webhook: cannot encode payload", "error", err)
		return 0
	}
	targets := 0
	for _, hook := range m.Hooks() {
		if event != "ping" && !hook.Accepts(event) {
			continue
		}
		targets++
		if wait {
			m.deliver(hook, event, encoded)
			continue
		}
		m.inflight.Go(func() {
			m.deliveries <- struct{}{}
			defer func() { <-m.deliveries }()
			m.deliver(hook, event, encoded)
		})
	}
	return targets
}

// TestHook delivers a ping event to one hook, inline, regardless of
// the hook's filters, and returns the delivery outcome.
func (m *Manager) TestHook(hook Webhook) Delivery {
	encoded, err := json.Marshal(map[string]any{
		"event": "ping", "timestamp": nowISO(), "version": m.version,
	})
	if err != nil {
		return Delivery{HookURL: hook.URL, Event: "ping", Status: "failed", Error: err.Error()}
	}
	return m.deliver(hook, "ping", encoded)
}

func (m *Manager) deliver(hook Webhook, event string, body []byte) Delivery {
	deliveryID := randomID()
	startedAt := nowISO()
	lastError := ""
	statusCode := 0
	for attempt := 1; attempt <= maxAttempts; attempt++ {
		code, err := m.post(hook, event, body, deliveryID)
		statusCode = code
		if err == nil && code >= 200 && code < 300 {
			return m.record(Delivery{
				ID: deliveryID, HookURL: hook.URL, Event: event,
				Timestamp: startedAt, Status: "ok", StatusCode: code, Attempts: attempt,
			})
		}
		if err != nil {
			lastError = err.Error()
		} else {
			lastError = fmt.Sprintf("HTTP %d", code)
		}
		if attempt < maxAttempts {
			time.Sleep(retryBackoff[attempt-1])
		}
	}
	return m.record(Delivery{
		ID: deliveryID, HookURL: hook.URL, Event: event,
		Timestamp: startedAt, Status: "failed", StatusCode: statusCode,
		Attempts: maxAttempts, Error: lastError,
	})
}

func (m *Manager) post(hook Webhook, event string, body []byte, deliveryID string) (int, error) {
	req, err := http.NewRequest(http.MethodPost, hook.URL, bytes.NewReader(body))
	if err != nil {
		return 0, err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("User-Agent", "volumen/"+m.version)
	req.Header.Set("X-Volumen-Event", event)
	req.Header.Set("X-Volumen-Delivery", deliveryID)
	if hook.Secret != "" {
		mac := hmac.New(sha256.New, []byte(hook.Secret))
		mac.Write(body)
		req.Header.Set("X-Volumen-Signature", "sha256="+hex.EncodeToString(mac.Sum(nil)))
	}
	resp, err := m.client.Do(req)
	if err != nil {
		return 0, err
	}
	defer resp.Body.Close()
	_, _ = io.Copy(io.Discard, resp.Body)
	return resp.StatusCode, nil
}

func (m *Manager) record(delivery Delivery) Delivery {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.history = append(m.history, delivery)
	if len(m.history) > historyLimit {
		m.history = m.history[len(m.history)-historyLimit:]
	}
	if delivery.Status == "ok" {
		slog.Info("webhook delivered", "url", delivery.HookURL, "event", delivery.Event,
			"status", delivery.StatusCode, "attempt", delivery.Attempts)
	} else {
		slog.Warn("webhook failed", "url", delivery.HookURL, "event", delivery.Event,
			"error", delivery.Error)
	}
	return delivery
}

func nowISO() string {
	return time.Now().UTC().Format("2006-01-02T15:04:05-07:00")
}

func randomID() string {
	buf := make([]byte, 6)
	if _, err := rand.Read(buf); err != nil {
		return strings.Repeat("0", 12)
	}
	return hex.EncodeToString(buf)
}