package events

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"net/http"
	"time"

	"git.knownelement.com/reachableceo/MOPAC/harness/internal/config"
)

// maxBodyBytes bounds webhook payloads; bigger deliveries are rejected
// before parsing (413).
const maxBodyBytes = 1 << 20

// Dispatcher is the conductor-side event sink. Turn dispatch is a stub
// call for now: the conductor implements it, real event->turn wiring lands
// after the skeleton (phase 3).
type Dispatcher interface {
	DispatchEvent(ctx context.Context, ev Event)
}

// Server is the `harness events` webhook receiver. Routes:
//
//	POST /hooks/redmine    shared-secret header
//	POST /hooks/discourse  shared-secret header
//	POST /hooks/gitea      HMAC-SHA256 X-Gitea-Signature
//	GET  /healthz
//
// Unsigned or unverified requests get 401 without any detail beyond
// "unverified"; secrets and header values are never logged.
type Server struct {
	cfg     config.EventsConfig
	store   *Store
	disp    Dispatcher
	logger  *log.Logger
	secrets map[string]string // resolved at startup; never logged, never persisted
}

// NewServer resolves the webhook secrets (fail-fast: at least one source
// must be configured) and opens the event store.
func NewServer(cfg config.EventsConfig, disp Dispatcher, out io.Writer) (*Server, error) {
	secrets := map[string]string{
		SourceRedmine:   "",
		SourceDiscourse: "",
		SourceGitea:     "",
	}
	for source, sc := range map[string]config.EventSourceConfig{
		SourceRedmine:   cfg.Redmine,
		SourceDiscourse: cfg.Discourse,
		SourceGitea:     cfg.Gitea,
	} {
		if sc.SecretRef == "" {
			continue
		}
		v, err := config.ResolveKeyRef(sc.SecretRef)
		if err != nil {
			return nil, fmt.Errorf("[events.%s]: resolve secret: %w", source, err)
		}
		secrets[source] = v
	}
	if secrets[SourceRedmine] == "" && secrets[SourceDiscourse] == "" && secrets[SourceGitea] == "" {
		return nil, fmt.Errorf("[events]: no webhook secrets configured; set secret_ref for at least one of redmine/discourse/gitea")
	}
	store, err := OpenStore(cfg.StateDir)
	if err != nil {
		return nil, err
	}
	return &Server{
		cfg:     cfg,
		store:   store,
		disp:    disp,
		logger:  log.New(out, "events: ", log.LstdFlags|log.Lmsgprefix),
		secrets: secrets,
	}, nil
}

// Handler builds the receiver's HTTP routes.
func (s *Server) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "application/json")
		fmt.Fprint(w, `{"status":"ok"}`)
	})
	mux.HandleFunc("/hooks/redmine", s.hook(SourceRedmine))
	mux.HandleFunc("/hooks/discourse", s.hook(SourceDiscourse))
	mux.HandleFunc("/hooks/gitea", s.hook(SourceGitea))
	return mux
}

// Close releases the event store.
func (s *Server) Close() error { return s.store.Close() }

func (s *Server) hook(source string) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			w.Header().Set("Allow", http.MethodPost)
			s.writeJSON(w, http.StatusMethodNotAllowed, map[string]string{"error": "POST only"})
			return
		}
		body, ok := s.readBody(w, r)
		if !ok {
			return
		}

		if err := s.verify(source, r.Header, body); err != nil {
			// Log the class of failure only; never header values.
			s.logger.Printf("rejected source=%s remote=%s reason=%v", source, r.RemoteAddr, err)
			s.writeJSON(w, http.StatusUnauthorized, map[string]string{"error": "unverified webhook"})
			return
		}

		ev, err := Normalize(source, r.Header, body, time.Now())
		if err != nil {
			s.logger.Printf("malformed source=%s remote=%s", source, r.RemoteAddr)
			s.writeJSON(w, http.StatusBadRequest, map[string]string{"error": "malformed webhook payload"})
			return
		}

		stored, err := s.store.Append(ev)
		if err != nil {
			s.logger.Printf("store error source=%s: %v", source, err)
			s.writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "event log write failed"})
			return
		}

		status := "stored"
		if !stored {
			status = "duplicate"
		}
		// One audit line per delivery: normalized fields + digest, no
		// headers, no secrets, no payload contents.
		s.logger.Printf(
			"source=%s kind=%s actor=%s subject_id=%s repo=%s action=%s provider_id=%s digest=%s %s",
			ev.Source, ev.Kind, ev.Actor, ev.SubjectID, ev.Repo, ev.Action,
			ev.ProviderID, shortDigest(ev.PayloadDigest), status,
		)

		if stored && ev.Action != ActionIgnore && s.disp != nil {
			s.disp.DispatchEvent(r.Context(), ev)
		}
		s.writeJSON(w, http.StatusOK, map[string]string{
			"status": status,
			"id":     ev.DedupKey(),
			"action": ev.Action,
		})
	}
}

func (s *Server) verify(source string, header http.Header, body []byte) error {
	secret := s.secrets[source]
	if secret == "" {
		return fmt.Errorf("%w: no secret configured for source %s", ErrUnverified, source)
	}
	switch source {
	case SourceGitea:
		return VerifyGiteaHMAC(body, header.Get(giteaSignatureHeader), secret)
	case SourceRedmine:
		name := s.cfg.Redmine.SecretHeader
		if name == "" {
			name = DefaultRedmineSecretHeader
		}
		return VerifySharedSecret(name, header.Get(name), secret)
	case SourceDiscourse:
		name := s.cfg.Discourse.SecretHeader
		if name == "" {
			name = DefaultDiscourseSecretHeader
		}
		return VerifySharedSecret(name, header.Get(name), secret)
	}
	return fmt.Errorf("%w: unknown source %s", ErrUnverified, source)
}

func (s *Server) readBody(w http.ResponseWriter, r *http.Request) ([]byte, bool) {
	body, err := io.ReadAll(io.LimitReader(r.Body, maxBodyBytes+1))
	if err != nil {
		s.writeJSON(w, http.StatusBadRequest, map[string]string{"error": "unreadable body"})
		return nil, false
	}
	if len(body) > maxBodyBytes {
		s.writeJSON(w, http.StatusRequestEntityTooLarge, map[string]string{"error": "payload too large"})
		return nil, false
	}
	return body, true
}

func (s *Server) writeJSON(w http.ResponseWriter, code int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(code)
	_ = json.NewEncoder(w).Encode(v)
}

func shortDigest(d string) string {
	if len(d) > 16 {
		return d[:16]
	}
	return d
}

// IsUnverified reports whether err is a verification failure (CLI/tests).
func IsUnverified(err error) bool { return errors.Is(err, ErrUnverified) }