import {
  AUTH_ATTEMPT_WINDOW_SECONDS,
  AUTH_MAX_ATTEMPTS_PER_WINDOW,
  AUTH_RECENT_NONCE_WINDOW_SIZE,
  type BuiltinEnvelope,
  type HelloPayload,
  type PairConfirmPayload,
  YONEXUS_PROTOCOL_VERSION,
  buildAuthFailed,
  buildAuthSuccess,
  buildError,
  buildHelloAck,
  buildPairFailed,
  buildPairRequest,
  buildPairSuccess,
  buildRePairRequired,
  decodeBuiltin,
  encodeBuiltin,
  extractAuthRequestSigningInput,
  isBuiltinMessage,
  isTimestampFresh,
  isValidAuthNonce,
  type AuthRequestPayload
} from "../../../Yonexus.Protocol/src/index.js";
import type { YonexusServerConfig } from "./config.js";
import {
  canAuthenticate,
  createClientRecord,
  hasPendingPairing,
  isPairingExpired,
  type ClientRecord,
  type ServerRegistry
} from "./persistence.js";
import { verifySignature } from "../../../Yonexus.Client/plugin/crypto/keypair.js";
import type { YonexusServerStore } from "./store.js";
import { type ClientConnection, type ServerTransport } from "./transport.js";
import { createPairingService, type PairingService } from "../services/pairing.js";
import {
  createDiscordNotificationService,
  type DiscordNotificationService
} from "../notifications/discord.js";

export interface YonexusServerRuntimeOptions {
  config: YonexusServerConfig;
  store: YonexusServerStore;
  transport: ServerTransport;
  now?: () => number;
}

export interface ServerLifecycleState {
  readonly isStarted: boolean;
  readonly registry: ServerRegistry;
}

export class YonexusServerRuntime {
  private readonly options: YonexusServerRuntimeOptions;
  private readonly now: () => number;
  private readonly registry: ServerRegistry;
  private readonly pairingService: PairingService;
  private readonly notificationService: DiscordNotificationService;
  private started = false;

  constructor(options: YonexusServerRuntimeOptions) {
    this.options = options;
    this.now = options.now ?? (() => Math.floor(Date.now() / 1000));
    this.registry = {
      clients: new Map(),
      sessions: new Map()
    };
    this.pairingService = createPairingService({ now: this.now });
    this.notificationService = createDiscordNotificationService({
      botToken: options.config.notifyBotToken,
      adminUserId: options.config.adminUserId
    });
  }

  get state(): ServerLifecycleState {
    return {
      isStarted: this.started,
      registry: this.registry
    };
  }

  async start(): Promise<void> {
    if (this.started) {
      return;
    }

    const persisted = await this.options.store.load();
    for (const record of persisted.clients.values()) {
      this.registry.clients.set(record.identifier, record);
    }

    for (const identifier of this.options.config.followerIdentifiers) {
      if (!this.registry.clients.has(identifier)) {
        this.registry.clients.set(identifier, createClientRecord(identifier));
      }
    }

    await this.options.transport.start();
    this.started = true;
  }

  async stop(): Promise<void> {
    if (!this.started) {
      return;
    }

    await this.persist();
    this.registry.sessions.clear();
    await this.options.transport.stop();
    this.started = false;
  }

  handleDisconnect(identifier: string | null): void {
    if (!identifier) {
      return;
    }

    const existing = this.registry.sessions.get(identifier);
    if (!existing) {
      return;
    }

    const record = this.registry.clients.get(identifier);
    if (record) {
      record.status = "offline";
      record.updatedAt = this.now();
    }

    this.registry.sessions.delete(identifier);
  }

  async handleMessage(connection: ClientConnection, raw: string): Promise<void> {
    if (!isBuiltinMessage(raw)) {
      return;
    }

    const envelope = decodeBuiltin(raw);

    if (envelope.type === "hello") {
      await this.handleHello(connection, envelope as BuiltinEnvelope<"hello", HelloPayload>);
      return;
    }

    if (envelope.type === "pair_confirm") {
      await this.handlePairConfirm(
        connection,
        envelope as BuiltinEnvelope<"pair_confirm", PairConfirmPayload>
      );
      return;
    }

    if (envelope.type === "auth_request") {
      await this.handleAuthRequest(
        connection,
        envelope as BuiltinEnvelope<"auth_request", AuthRequestPayload>
      );
    }
  }

  private async handleHello(
    connection: ClientConnection,
    envelope: BuiltinEnvelope<"hello", HelloPayload>
  ): Promise<void> {
    const payload = envelope.payload;
    if (!payload) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(buildError({ code: "MALFORMED_MESSAGE", message: "hello payload is required" }, { timestamp: this.now() }))
      );
      return;
    }

    const helloIdentifier = payload.identifier?.trim();
    if (!helloIdentifier || !this.options.config.followerIdentifiers.includes(helloIdentifier)) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(buildError({ code: "IDENTIFIER_NOT_ALLOWED", message: "identifier is not allowed" }, { timestamp: this.now() }))
      );
      return;
    }

    if (payload.protocolVersion !== YONEXUS_PROTOCOL_VERSION) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildError(
            {
              code: "UNSUPPORTED_PROTOCOL_VERSION",
              message: `Unsupported protocol version: ${payload.protocolVersion}`
            },
            { requestId: envelope.requestId, timestamp: this.now() }
          )
        )
      );
      connection.ws.close(1002, "Unsupported protocol version");
      return;
    }

    const record = this.ensureClientRecord(helloIdentifier);
    record.updatedAt = this.now();

    this.options.transport.registerConnection(helloIdentifier, connection.ws);
    this.registry.sessions.set(helloIdentifier, {
      identifier: helloIdentifier,
      socket: connection.ws,
      isAuthenticated: false,
      connectedAt: connection.connectedAt,
      lastActivityAt: this.now(),
      publicKey: payload.publicKey
    });

    const nextAction = this.determineNextAction(record);
    this.options.transport.sendToConnection(
      { ...connection, identifier: helloIdentifier },
      encodeBuiltin(
        buildHelloAck(
          {
            identifier: helloIdentifier,
            nextAction
          },
          { requestId: envelope.requestId, timestamp: this.now() }
        )
      )
    );

    if (nextAction === "pair_required" || nextAction === "waiting_pair_confirm") {
      await this.beginPairing({
        record,
        connection: { ...connection, identifier: helloIdentifier },
        requestId: envelope.requestId,
        reusePending: nextAction === "waiting_pair_confirm"
      });
    }

    await this.persist();
  }

  private async handlePairConfirm(
    connection: ClientConnection,
    envelope: BuiltinEnvelope<"pair_confirm", PairConfirmPayload>
  ): Promise<void> {
    const payload = envelope.payload;
    if (!payload) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildError(
            { code: "MALFORMED_MESSAGE", message: "pair_confirm payload is required" },
            { requestId: envelope.requestId, timestamp: this.now() }
          )
        )
      );
      return;
    }

    const identifier = payload.identifier?.trim();
    if (!identifier || !this.options.config.followerIdentifiers.includes(identifier)) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildPairFailed(
            {
              identifier: identifier || "unknown",
              reason: "identifier_not_allowed"
            },
            { requestId: envelope.requestId, timestamp: this.now() }
          )
        )
      );
      return;
    }

    const record = this.ensureClientRecord(identifier);
    const submittedCode = payload.pairingCode?.trim();
    if (!submittedCode) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildError(
            { code: "MALFORMED_MESSAGE", message: "pairingCode is required" },
            { requestId: envelope.requestId, timestamp: this.now() }
          )
        )
      );
      return;
    }

    const result = this.pairingService.confirmPairing(record, submittedCode);
    if (!result.success || !result.secret || !result.pairedAt) {
      const reason = result.reason === "not_pending" ? "internal_error" : result.reason ?? "internal_error";
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildPairFailed(
            {
              identifier,
              reason
            },
            { requestId: envelope.requestId, timestamp: this.now() }
          )
        )
      );

      await this.persist();
      return;
    }

    if (connection.identifier !== identifier) {
      this.options.transport.registerConnection(identifier, connection.ws);
    }

    const session = this.registry.sessions.get(identifier);
    record.publicKey = session?.publicKey ?? record.publicKey;
    record.updatedAt = this.now();

    this.options.transport.sendToConnection(
      { ...connection, identifier },
      encodeBuiltin(
        buildPairSuccess(
          {
            identifier,
            secret: result.secret,
            pairedAt: result.pairedAt
          },
          { requestId: envelope.requestId, timestamp: this.now() }
        )
      )
    );

    await this.persist();
  }

  private async handleAuthRequest(
    connection: ClientConnection,
    envelope: BuiltinEnvelope<"auth_request", AuthRequestPayload>
  ): Promise<void> {
    const payload = envelope.payload;
    if (!payload) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildError(
            { code: "MALFORMED_MESSAGE", message: "auth_request payload is required" },
            { requestId: envelope.requestId, timestamp: this.now() }
          )
        )
      );
      return;
    }

    const identifier = payload.identifier?.trim();
    if (!identifier || !this.options.config.followerIdentifiers.includes(identifier)) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildAuthFailed(
            {
              identifier: identifier || "unknown",
              reason: "unknown_identifier"
            },
            { requestId: envelope.requestId, timestamp: this.now() }
          )
        )
      );
      return;
    }

    const record = this.ensureClientRecord(identifier);
    const session = this.registry.sessions.get(identifier);
    if (!session || !canAuthenticate(record) || !record.secret || !record.publicKey) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildAuthFailed(
            {
              identifier,
              reason: "not_paired"
            },
            { requestId: envelope.requestId, timestamp: this.now() }
          )
        )
      );
      return;
    }

    const now = this.now();
    record.recentHandshakeAttempts = record.recentHandshakeAttempts.filter(
      (timestamp) => now - timestamp < AUTH_ATTEMPT_WINDOW_SECONDS
    );
    record.recentHandshakeAttempts.push(now);

    if (record.recentHandshakeAttempts.length > AUTH_MAX_ATTEMPTS_PER_WINDOW) {
      await this.triggerRePairRequired(connection, record, envelope.requestId, "rate_limited");
      return;
    }

    if (!isValidAuthNonce(payload.nonce)) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildAuthFailed(
            {
              identifier,
              reason: "invalid_signature"
            },
            { requestId: envelope.requestId, timestamp: now }
          )
        )
      );
      return;
    }

    const freshness = isTimestampFresh(payload.proofTimestamp, now);
    if (!freshness.ok) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildAuthFailed(
            {
              identifier,
              reason: freshness.reason
            },
            { requestId: envelope.requestId, timestamp: now }
          )
        )
      );
      return;
    }

    const hasNonceCollision = record.recentNonces.some((entry) => entry.nonce === payload.nonce);
    if (hasNonceCollision) {
      await this.triggerRePairRequired(connection, record, envelope.requestId, "nonce_collision");
      return;
    }

    const publicKey = payload.publicKey?.trim() || session.publicKey || record.publicKey;
    if (!publicKey || publicKey !== record.publicKey) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildAuthFailed(
            {
              identifier,
              reason: "invalid_signature"
            },
            { requestId: envelope.requestId, timestamp: now }
          )
        )
      );
      return;
    }

    const isValidSignature = await verifySignature(
      publicKey,
      extractAuthRequestSigningInput(payload, record.secret),
      payload.signature
    );

    if (!isValidSignature) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildAuthFailed(
            {
              identifier,
              reason: "invalid_signature"
            },
            { requestId: envelope.requestId, timestamp: now }
          )
        )
      );
      return;
    }

    record.recentNonces = [...record.recentNonces, { nonce: payload.nonce, timestamp: now }].slice(
      -AUTH_RECENT_NONCE_WINDOW_SIZE
    );
    record.lastAuthenticatedAt = now;
    record.lastHeartbeatAt = now;
    record.status = "online";
    record.updatedAt = now;

    if (session) {
      session.isAuthenticated = true;
      session.lastActivityAt = now;
      session.publicKey = publicKey;
    }
    this.options.transport.markAuthenticated(identifier);
    this.options.transport.sendToConnection(
      { ...connection, identifier },
      encodeBuiltin(
        buildAuthSuccess(
          {
            identifier,
            authenticatedAt: now,
            status: "online"
          },
          { requestId: envelope.requestId, timestamp: now }
        )
      )
    );

    await this.persist();
  }

  private determineNextAction(record: ClientRecord): "pair_required" | "auth_required" | "waiting_pair_confirm" {
    if (hasPendingPairing(record) && !isPairingExpired(record, this.now())) {
      return "waiting_pair_confirm";
    }

    if (canAuthenticate(record)) {
      return "auth_required";
    }

    return "pair_required";
  }

  private ensureClientRecord(identifier: string): ClientRecord {
    const existing = this.registry.clients.get(identifier);
    if (existing) {
      return existing;
    }

    const created = createClientRecord(identifier);
    this.registry.clients.set(identifier, created);
    return created;
  }

  private async beginPairing(options: {
    record: ClientRecord;
    connection: ClientConnection;
    requestId?: string;
    reusePending?: boolean;
  }): Promise<void> {
    const { record, connection, requestId, reusePending = false } = options;

    const request =
      reusePending && hasPendingPairing(record) && !isPairingExpired(record, this.now())
        ? {
            identifier: record.identifier,
            pairingCode: record.pairingCode ?? "",
            expiresAt: record.pairingExpiresAt ?? this.now(),
            ttlSeconds: this.pairingService.getRemainingTtl(record),
            createdAt: record.updatedAt
          }
        : this.pairingService.createPairingRequest(record);

    const notified = reusePending
      ? record.pairingNotifyStatus === "sent"
      : await this.notificationService.sendPairingNotification(request);

    if (notified) {
      this.pairingService.markNotificationSent(record);
    } else {
      this.pairingService.markNotificationFailed(record);
    }

    this.options.transport.sendToConnection(
      connection,
      encodeBuiltin(
        buildPairRequest(
          {
            identifier: record.identifier,
            expiresAt: request.expiresAt,
            ttlSeconds: this.pairingService.getRemainingTtl(record),
            adminNotification: notified ? "sent" : "failed",
            codeDelivery: "out_of_band"
          },
          { requestId, timestamp: this.now() }
        )
      )
    );

    if (!notified) {
      this.options.transport.sendToConnection(
        connection,
        encodeBuiltin(
          buildPairFailed(
            {
              identifier: record.identifier,
              reason: "admin_notification_failed"
            },
            { requestId, timestamp: this.now() }
          )
        )
      );
      this.pairingService.clearPairingState(record);
    }
  }

  private async triggerRePairRequired(
    connection: ClientConnection,
    record: ClientRecord,
    requestId: string | undefined,
    reason: "nonce_collision" | "rate_limited"
  ): Promise<void> {
    record.secret = undefined;
    record.pairingStatus = "revoked";
    record.pairingCode = undefined;
    record.pairingExpiresAt = undefined;
    record.pairingNotifyStatus = undefined;
    record.recentNonces = [];
    record.recentHandshakeAttempts = [];
    record.status = "offline";
    record.updatedAt = this.now();

    this.options.transport.sendToConnection(
      connection,
      encodeBuiltin(
        buildRePairRequired(
          {
            identifier: record.identifier,
            reason
          },
          { requestId, timestamp: this.now() }
        )
      )
    );

    await this.persist();
  }

  private async persist(): Promise<void> {
    await this.options.store.save(this.registry.clients.values());
  }
}

export function createYonexusServerRuntime(
  options: YonexusServerRuntimeOptions
): YonexusServerRuntime {
  return new YonexusServerRuntime(options);
}