package mockalertreceiver

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"io"
	"log/slog"
	"net/http"
	"strconv"
	"strings"
	"sync"
	"time"
)

const maxBodyBytes = 64 * 1024

type Options struct {
	Secret    string
	ClockSkew time.Duration
}

type Event struct {
	EventID    string          `json:"event_id"`
	EventType  string          `json:"event_type"`
	TestRef    string          `json:"test_ref,omitempty"`
	Data       json.RawMessage `json:"data"`
	ReceivedAt time.Time       `json:"received_at"`
}

type envelope struct {
	EventID   string          `json:"event_id"`
	EventType string          `json:"event_type"`
	Data      json.RawMessage `json:"data"`
}

type Server struct {
	secret    []byte
	clockSkew time.Duration
	logger    *slog.Logger
	now       func() time.Time
	mu        sync.RWMutex
	events    []Event
}

func New(options Options, logger *slog.Logger) (*Server, error) {
	options.Secret = strings.TrimSpace(options.Secret)
	if len(options.Secret) < 32 {
		return nil, errors.New("mock alert receiver secret must contain at least 32 characters")
	}
	if options.ClockSkew <= 0 {
		return nil, errors.New("mock alert receiver clock skew must be positive")
	}
	if logger == nil {
		return nil, errors.New("mock alert receiver logger is required")
	}
	return &Server{secret: []byte(options.Secret), clockSkew: options.ClockSkew, logger: logger, now: time.Now, events: []Event{}}, nil
}

func (s *Server) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /health/live", func(w http.ResponseWriter, _ *http.Request) {
		writeJSON(w, http.StatusOK, map[string]string{"status": "alive", "service": "mock-alert-receiver"})
	})
	mux.HandleFunc("POST /webhooks/alerts", s.receive)
	mux.HandleFunc("GET /events", s.list)
	return mux
}

func (s *Server) receive(w http.ResponseWriter, r *http.Request) {
	body, err := io.ReadAll(io.LimitReader(r.Body, maxBodyBytes+1))
	if err != nil || len(body) > maxBodyBytes {
		http.Error(w, "invalid body", http.StatusBadRequest)
		return
	}
	timestamp := strings.TrimSpace(r.Header.Get("X-Voice-Timestamp"))
	eventID := strings.TrimSpace(r.Header.Get("X-Voice-Event-ID"))
	unixSeconds, err := strconv.ParseInt(timestamp, 10, 64)
	if err != nil || eventID == "" || s.now().UTC().Sub(time.Unix(unixSeconds, 0).UTC()).Abs() > s.clockSkew || !validSignature(s.secret, timestamp, body, r.Header.Get("X-Voice-Signature")) {
		http.Error(w, "invalid webhook authentication", http.StatusUnauthorized)
		return
	}
	var incoming envelope
	if err = json.Unmarshal(body, &incoming); err != nil || incoming.EventID != eventID || incoming.EventType == "" || !json.Valid(incoming.Data) {
		http.Error(w, "invalid webhook envelope", http.StatusBadRequest)
		return
	}
	var metadata struct {
		TestRef string `json:"test_ref"`
	}
	_ = json.Unmarshal(incoming.Data, &metadata)
	received := Event{EventID: incoming.EventID, EventType: incoming.EventType, TestRef: metadata.TestRef, Data: incoming.Data, ReceivedAt: s.now().UTC()}
	s.mu.Lock()
	found := false
	for index := range s.events {
		if s.events[index].EventID == received.EventID {
			s.events[index] = received
			found = true
			break
		}
	}
	if !found {
		s.events = append([]Event{received}, s.events...)
		if len(s.events) > 100 {
			s.events = s.events[:100]
		}
	}
	s.mu.Unlock()
	s.logger.InfoContext(r.Context(), "mock alert webhook received", "event_id", received.EventID, "event_type", received.EventType, "test_ref", received.TestRef)
	w.WriteHeader(http.StatusNoContent)
}

func (s *Server) list(w http.ResponseWriter, r *http.Request) {
	testRef := strings.TrimSpace(r.URL.Query().Get("test_ref"))
	s.mu.RLock()
	items := make([]Event, 0, len(s.events))
	for _, item := range s.events {
		if testRef == "" || item.TestRef == testRef {
			items = append(items, item)
		}
	}
	s.mu.RUnlock()
	w.Header().Set("Cache-Control", "no-store")
	writeJSON(w, http.StatusOK, map[string]any{"items": items})
}

func validSignature(secret []byte, timestamp string, body []byte, provided string) bool {
	mac := hmac.New(sha256.New, secret)
	_, _ = mac.Write([]byte(timestamp))
	_, _ = mac.Write([]byte("."))
	_, _ = mac.Write(body)
	want := mac.Sum(nil)
	provided = strings.TrimSpace(provided)
	if !strings.HasPrefix(provided, "v1=") {
		return false
	}
	provided = strings.TrimPrefix(provided, "v1=")
	got, err := hex.DecodeString(provided)
	return err == nil && hmac.Equal(want, got)
}

func writeJSON(w http.ResponseWriter, status int, value any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(value)
}