package node

import (
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"time"

	"go-blockchain/blockchain"
	"go-blockchain/identity"
	"go-blockchain/relay"
)

// RelayConfig holds dependencies for the relay HTTP API.
type RelayConfig struct {
	Mailbox *relay.Mailbox

	// Send seals a message for recipientX25519PubHex and broadcasts it.
	// Returns the envelope ID. nil disables POST /relay/send.
	Send func(recipientPubHex string, msg []byte) (string, error)

	// Broadcast publishes a pre-sealed Envelope on gossipsub and stores it in the mailbox.
	// nil disables POST /relay/broadcast.
	Broadcast func(env *relay.Envelope) error

	// ContactRequests returns incoming contact records for the given Ed25519 pubkey.
	ContactRequests func(pubKey string) ([]blockchain.ContactInfo, error)

	// ResolveX25519 returns the X25519 hex published by the Ed25519 identity,
	// or "" if the identity has not registered or does not exist. Used by
	// authenticated mutating endpoints (e.g. DELETE /relay/inbox) to link a
	// signing key back to its mailbox pubkey. nil disables those endpoints.
	ResolveX25519 func(ed25519PubHex string) string
}

// registerRelayRoutes wires relay mailbox endpoints onto mux.
//
//	POST   /relay/send             {recipient_pub, msg_b64}
//	POST   /relay/broadcast        {envelope: <Envelope JSON>}
//	GET    /relay/inbox            ?pub=<x25519hex>[&since=<unix_ts>][&limit=N]
//	GET    /relay/inbox/count      ?pub=<x25519hex>
//	DELETE /relay/inbox/{envID}    ?pub=<x25519hex>
//	GET    /relay/contacts         ?pub=<ed25519hex>
func registerRelayRoutes(mux *http.ServeMux, rc RelayConfig) {
	// Writes go through withSubmitTxGuards: per-IP rate limit (10/s, burst 20)
	// + 256 KiB body cap. Without these, a single attacker could spam
	// 500 envelopes per victim in a few seconds and evict every real message
	// via the mailbox FIFO cap.
	mux.HandleFunc("/relay/send", withSubmitTxGuards(relaySend(rc)))
	mux.HandleFunc("/relay/broadcast", withSubmitTxGuards(relayBroadcast(rc)))

	// Reads go through withReadLimit: per-IP rate limit (20/s, burst 40).
	// Protects against inbox-scraping floods from a single origin.
	mux.HandleFunc("/relay/inbox/count", withReadLimit(relayInboxCount(rc)))
	mux.HandleFunc("/relay/inbox/", withReadLimit(relayInboxDelete(rc)))
	mux.HandleFunc("/relay/inbox", withReadLimit(relayInboxList(rc)))
	mux.HandleFunc("/relay/contacts", withReadLimit(relayContacts(rc)))
}

// relayInboxList handles GET /relay/inbox?pub=<hex>[&since=<ts>][&limit=N]
func relayInboxList(rc RelayConfig) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet {
			jsonErr(w, fmt.Errorf("method not allowed"), 405)
			return
		}
		pub := r.URL.Query().Get("pub")
		if pub == "" {
			jsonErr(w, fmt.Errorf("pub parameter required"), 400)
			return
		}
		since := int64(0)
		if s := r.URL.Query().Get("since"); s != "" {
			if v, err := parseInt64(s); err == nil && v > 0 {
				since = v
			}
		}
		limit := queryIntMin0(r, "limit")
		if limit == 0 {
			limit = 50
		}

		envelopes, err := rc.Mailbox.List(pub, since, limit)
		if err != nil {
			jsonErr(w, err, 500)
			return
		}

		type item struct {
			ID           string `json:"id"`
			SenderPub    string `json:"sender_pub"`
			RecipientPub string `json:"recipient_pub"`
			FeeUT        uint64 `json:"fee_ut,omitempty"`
			SentAt       int64  `json:"sent_at"`
			SentAtHuman  string `json:"sent_at_human"`
			Nonce        []byte `json:"nonce"`
			Ciphertext   []byte `json:"ciphertext"`
		}

		out := make([]item, 0, len(envelopes))
		for _, env := range envelopes {
			out = append(out, item{
				ID:           env.ID,
				SenderPub:    env.SenderPub,
				RecipientPub: env.RecipientPub,
				FeeUT:        env.FeeUT,
				SentAt:       env.SentAt,
				SentAtHuman:  time.Unix(env.SentAt, 0).UTC().Format(time.RFC3339),
				Nonce:        env.Nonce,
				Ciphertext:   env.Ciphertext,
			})
		}

		hasMore := len(out) == limit
		jsonOK(w, map[string]any{
			"pub":      pub,
			"count":    len(out),
			"has_more": hasMore,
			"items":    out,
		})
	}
}

// relayInboxDelete handles DELETE /relay/inbox/{envelopeID}?pub=<x25519hex>
//
// Auth model:
//   Query:  ?pub=<x25519hex>
//   Body:   {"ed25519_pub":"<hex>", "sig":"<base64>", "ts":<unix_seconds>}
//   sig   = Ed25519(privEd25519,
//                   "inbox-delete:" + envID + ":" + x25519Pub + ":" + ts)
//   ts    must be within ±5 minutes of server clock (anti-replay).
//
// Server then:
//   1. Verifies sig over the canonical bytes above.
//   2. Looks up identity(ed25519_pub).X25519Pub — must equal the ?pub= query.
//
// This links the signing key to the mailbox key without exposing the user's
// X25519 private material.
func relayInboxDelete(rc RelayConfig) http.HandlerFunc {
	const inboxDeleteSkewSecs = 300 // ±5 minutes

	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodDelete {
			// Also serve GET /relay/inbox/{id} for convenience (fetch single envelope)
			if r.Method == http.MethodGet {
				relayInboxList(rc)(w, r)
				return
			}
			jsonErr(w, fmt.Errorf("method not allowed"), 405)
			return
		}

		envID := strings.TrimPrefix(r.URL.Path, "/relay/inbox/")
		if envID == "" {
			jsonErr(w, fmt.Errorf("envelope ID required in path"), 400)
			return
		}
		pub := r.URL.Query().Get("pub")
		if pub == "" {
			jsonErr(w, fmt.Errorf("pub parameter required"), 400)
			return
		}

		// Auth. Unauthenticated DELETE historically let anyone wipe any
		// mailbox by just knowing the pub — fixed in v1.0.2 via signed
		// Ed25519 identity linked to the x25519 via identity registry.
		if rc.ResolveX25519 == nil {
			jsonErr(w, fmt.Errorf("mailbox delete not available on this node"), 503)
			return
		}
		var body struct {
			Ed25519Pub string `json:"ed25519_pub"`
			Sig        string `json:"sig"`
			Ts         int64  `json:"ts"`
		}
		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
			jsonErr(w, fmt.Errorf("invalid JSON body: %w", err), 400)
			return
		}
		if body.Ed25519Pub == "" || body.Sig == "" || body.Ts == 0 {
			jsonErr(w, fmt.Errorf("ed25519_pub, sig, ts are required"), 400)
			return
		}
		now := time.Now().Unix()
		if body.Ts < now-inboxDeleteSkewSecs || body.Ts > now+inboxDeleteSkewSecs {
			jsonErr(w, fmt.Errorf("timestamp out of range (±%ds)", inboxDeleteSkewSecs), 400)
			return
		}
		sigBytes, err := base64.StdEncoding.DecodeString(body.Sig)
		if err != nil {
			// Also try URL-safe for defensive UX.
			sigBytes, err = base64.RawURLEncoding.DecodeString(body.Sig)
			if err != nil {
				jsonErr(w, fmt.Errorf("sig: invalid base64"), 400)
				return
			}
		}
		if _, err := hex.DecodeString(body.Ed25519Pub); err != nil {
			jsonErr(w, fmt.Errorf("ed25519_pub: invalid hex"), 400)
			return
		}
		msg := []byte(fmt.Sprintf("inbox-delete:%s:%s:%d", envID, pub, body.Ts))
		ok, err := identity.Verify(body.Ed25519Pub, msg, sigBytes)
		if err != nil || !ok {
			jsonErr(w, fmt.Errorf("signature invalid"), 403)
			return
		}
		// Link ed25519 → x25519 via identity registry.
		registeredX := rc.ResolveX25519(body.Ed25519Pub)
		if registeredX == "" {
			jsonErr(w, fmt.Errorf("identity has no registered X25519 key"), 403)
			return
		}
		if !strings.EqualFold(registeredX, pub) {
			jsonErr(w, fmt.Errorf("pub does not match identity's registered X25519"), 403)
			return
		}

		if err := rc.Mailbox.Delete(pub, envID); err != nil {
			jsonErr(w, err, 500)
			return
		}
		jsonOK(w, map[string]string{"id": envID, "status": "deleted"})
	}
}

// relayInboxCount handles GET /relay/inbox/count?pub=<hex>
func relayInboxCount(rc RelayConfig) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		pub := r.URL.Query().Get("pub")
		if pub == "" {
			jsonErr(w, fmt.Errorf("pub parameter required"), 400)
			return
		}
		count, err := rc.Mailbox.Count(pub)
		if err != nil {
			jsonErr(w, err, 500)
			return
		}
		jsonOK(w, map[string]any{"pub": pub, "count": count})
	}
}

// relaySend handles POST /relay/send
//
// Request body:
//
//	{
//	  "recipient_pub": "<hex X25519 pub key>",
//	  "msg_b64":       "<base64-encoded plaintext>",
//	}
//
// WARNING — NOT END-TO-END ENCRYPTED.
// The relay node seals the message using its OWN X25519 keypair, not the
// sender's. That means:
//   - The relay can read the plaintext (msg_b64 arrives in the clear).
//   - The recipient cannot authenticate the sender — they only see "a
//     message from the relay".
// For real E2E messaging, clients should seal the envelope themselves and
// use POST /relay/broadcast instead. This endpoint is retained only for
// backwards compatibility with legacy integrations and for bootstrap
// scenarios where the sender doesn't have a long-lived X25519 key yet.
func relaySend(rc RelayConfig) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			jsonErr(w, fmt.Errorf("method not allowed"), 405)
			return
		}
		if rc.Send == nil {
			jsonErr(w, fmt.Errorf("relay send not available on this node"), 503)
			return
		}

		var req struct {
			RecipientPub string `json:"recipient_pub"`
			MsgB64       string `json:"msg_b64"`
		}
		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			jsonErr(w, fmt.Errorf("invalid JSON: %w", err), 400)
			return
		}
		if req.RecipientPub == "" {
			jsonErr(w, fmt.Errorf("recipient_pub is required"), 400)
			return
		}
		if req.MsgB64 == "" {
			jsonErr(w, fmt.Errorf("msg_b64 is required"), 400)
			return
		}

		msg, err := decodeBase64(req.MsgB64)
		if err != nil {
			jsonErr(w, fmt.Errorf("msg_b64: %w", err), 400)
			return
		}
		if len(msg) == 0 {
			jsonErr(w, fmt.Errorf("msg_b64: empty message"), 400)
			return
		}

		envID, err := rc.Send(req.RecipientPub, msg)
		if err != nil {
			jsonErr(w, fmt.Errorf("send failed: %w", err), 500)
			return
		}
		jsonOK(w, map[string]string{
			"id":            envID,
			"recipient_pub": req.RecipientPub,
			"status":        "sent",
		})
	}
}

// decodeBase64 accepts both standard and URL-safe base64.
func decodeBase64(s string) ([]byte, error) {
	// Try URL-safe first (no padding required), then standard.
	if b, err := base64.RawURLEncoding.DecodeString(s); err == nil {
		return b, nil
	}
	return base64.StdEncoding.DecodeString(s)
}

// relayBroadcast handles POST /relay/broadcast
//
// Request body: {"envelope": <relay.Envelope JSON>}
//
// Light clients use this to publish pre-sealed envelopes without a direct
// libp2p connection. The relay node stores it in the mailbox and gossips it.
func relayBroadcast(rc RelayConfig) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			jsonErr(w, fmt.Errorf("method not allowed"), 405)
			return
		}
		if rc.Broadcast == nil {
			jsonErr(w, fmt.Errorf("relay broadcast not available on this node"), 503)
			return
		}

		var req struct {
			Envelope *relay.Envelope `json:"envelope"`
		}
		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			jsonErr(w, fmt.Errorf("invalid JSON: %w", err), 400)
			return
		}
		if req.Envelope == nil {
			jsonErr(w, fmt.Errorf("envelope is required"), 400)
			return
		}
		if req.Envelope.ID == "" {
			jsonErr(w, fmt.Errorf("envelope.id is required"), 400)
			return
		}
		if len(req.Envelope.Ciphertext) == 0 {
			jsonErr(w, fmt.Errorf("envelope.ciphertext is required"), 400)
			return
		}

		if err := rc.Broadcast(req.Envelope); err != nil {
			jsonErr(w, fmt.Errorf("broadcast failed: %w", err), 500)
			return
		}
		jsonOK(w, map[string]string{
			"id":     req.Envelope.ID,
			"status": "broadcast",
		})
	}
}

// relayContacts handles GET /relay/contacts?pub=<ed25519hex>
//
// Returns all incoming contact requests for the given Ed25519 public key.
func relayContacts(rc RelayConfig) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet {
			jsonErr(w, fmt.Errorf("method not allowed"), 405)
			return
		}
		if rc.ContactRequests == nil {
			jsonErr(w, fmt.Errorf("contacts not available on this node"), 503)
			return
		}
		pub := r.URL.Query().Get("pub")
		if pub == "" {
			jsonErr(w, fmt.Errorf("pub parameter required"), 400)
			return
		}

		contacts, err := rc.ContactRequests(pub)
		if err != nil {
			jsonErr(w, err, 500)
			return
		}
		jsonOK(w, map[string]any{
			"pub":      pub,
			"count":    len(contacts),
			"contacts": contacts,
		})
	}
}

// parseInt64 parses a string as int64.
func parseInt64(s string) (int64, error) {
	var v int64
	if err := json.Unmarshal([]byte(s), &v); err != nil {
		return 0, err
	}
	return v, nil
}