/**
 * Per-provider runtime state and upstream registration.
 *
 * Each configured provider gets its own ProviderState instance tracking
 * registration status, public IP, and the periodic REGISTER cycle.
 */

import { Buffer } from 'node:buffer';
import {
  SipMessage,
  generateCallId,
  generateTag,
  generateBranch,
  parseDigestChallenge,
  computeDigestAuth,
} from './sip/index.ts';
import type { IEndpoint } from './sip/index.ts';
import type { IProviderConfig } from './config.ts';

// ---------------------------------------------------------------------------
// Provider state
// ---------------------------------------------------------------------------

export class ProviderState {
  readonly config: IProviderConfig;
  publicIp: string | null;
  isRegistered = false;
  registeredAor: string;

  // Registration transaction state.
  private regCallId: string;
  private regCSeq = 0;
  private regFromTag: string;
  private regTimer: ReturnType<typeof setInterval> | null = null;
  private sendSip: ((buf: Buffer, dest: IEndpoint) => void) | null = null;
  private logFn: ((msg: string) => void) | null = null;
  private onRegistrationChange: ((provider: ProviderState) => void) | null = null;

  constructor(config: IProviderConfig, publicIpSeed: string | null) {
    this.config = config;
    this.publicIp = publicIpSeed;
    this.registeredAor = `sip:${config.username}@${config.domain}`;
    this.regCallId = generateCallId();
    this.regFromTag = generateTag();
  }

  private log(msg: string): void {
    this.logFn?.(`[provider:${this.config.id}] ${msg}`);
  }

  // -------------------------------------------------------------------------
  // Upstream registration
  // -------------------------------------------------------------------------

  /**
   * Start the periodic REGISTER cycle with this provider.
   */
  startRegistration(
    lanIp: string,
    lanPort: number,
    sendSip: (buf: Buffer, dest: IEndpoint) => void,
    log: (msg: string) => void,
    onRegistrationChange: (provider: ProviderState) => void,
  ): void {
    this.sendSip = sendSip;
    this.logFn = log;
    this.onRegistrationChange = onRegistrationChange;

    // Initial registration.
    this.sendRegister(lanIp, lanPort);

    // Re-register periodically.
    const intervalMs = (this.config.registerIntervalSec * 0.85) * 1000;
    this.regTimer = setInterval(() => this.sendRegister(lanIp, lanPort), intervalMs);
  }

  stopRegistration(): void {
    if (this.regTimer) {
      clearInterval(this.regTimer);
      this.regTimer = null;
    }
  }

  private sendRegister(lanIp: string, lanPort: number): void {
    this.regCSeq++;
    const pub = this.publicIp || lanIp;
    const { config } = this;

    const register = SipMessage.createRequest('REGISTER', `sip:${config.domain}`, {
      via: { host: pub, port: lanPort },
      from: { uri: this.registeredAor, tag: this.regFromTag },
      to: { uri: this.registeredAor },
      callId: this.regCallId,
      cseq: this.regCSeq,
      contact: `<sip:${config.username}@${pub}:${lanPort}>`,
      maxForwards: 70,
      extraHeaders: [
        ['Expires', String(config.registerIntervalSec)],
        ['User-Agent', 'SipRouter/1.0'],
        ['Allow', 'INVITE, ACK, OPTIONS, CANCEL, BYE, SUBSCRIBE, NOTIFY, INFO, REFER, UPDATE'],
      ],
    });

    this.log(`REGISTER -> ${config.outboundProxy.address}:${config.outboundProxy.port} (CSeq ${this.regCSeq})`);
    this.sendSip!(register.serialize(), config.outboundProxy);
  }

  /**
   * Handle an incoming SIP response that belongs to this provider's registration.
   * Returns true if the message was consumed.
   */
  handleRegistrationResponse(msg: SipMessage): boolean {
    if (!msg.isResponse) return false;
    if (msg.callId !== this.regCallId) return false;
    if (msg.cseqMethod?.toUpperCase() !== 'REGISTER') return false;

    const code = msg.statusCode ?? 0;
    this.log(`REGISTER <- ${code}`);

    if (code === 200) {
      const wasRegistered = this.isRegistered;
      this.isRegistered = true;
      if (!wasRegistered) {
        this.log('registered');
        this.onRegistrationChange?.(this);
      }
      return true;
    }

    if (code === 401 || code === 407) {
      const challengeHeader = code === 401
        ? msg.getHeader('WWW-Authenticate')
        : msg.getHeader('Proxy-Authenticate');

      if (!challengeHeader) {
        this.log(`${code} but no challenge header`);
        return true;
      }

      const challenge = parseDigestChallenge(challengeHeader);
      if (!challenge) {
        this.log(`${code} could not parse digest challenge`);
        return true;
      }

      const authValue = computeDigestAuth({
        username: this.config.username,
        password: this.config.password,
        realm: challenge.realm,
        nonce: challenge.nonce,
        method: 'REGISTER',
        uri: `sip:${this.config.domain}`,
        algorithm: challenge.algorithm,
        opaque: challenge.opaque,
      });

      // Resend REGISTER with auth.
      this.regCSeq++;
      const pub = this.publicIp || 'unknown';
      // We need lanIp/lanPort but don't have them here — reconstruct from Via.
      const via = msg.getHeader('Via') || '';
      const viaHost = via.match(/SIP\/2\.0\/UDP\s+([^;:]+)/)?.[1] || pub;
      const viaPort = parseInt(via.match(/:(\d+)/)?.[1] || '5070', 10);

      const register = SipMessage.createRequest('REGISTER', `sip:${this.config.domain}`, {
        via: { host: viaHost, port: viaPort },
        from: { uri: this.registeredAor, tag: this.regFromTag },
        to: { uri: this.registeredAor },
        callId: this.regCallId,
        cseq: this.regCSeq,
        contact: `<sip:${this.config.username}@${viaHost}:${viaPort}>`,
        maxForwards: 70,
        extraHeaders: [
          [code === 401 ? 'Authorization' : 'Proxy-Authorization', authValue],
          ['Expires', String(this.config.registerIntervalSec)],
          ['User-Agent', 'SipRouter/1.0'],
          ['Allow', 'INVITE, ACK, OPTIONS, CANCEL, BYE, SUBSCRIBE, NOTIFY, INFO, REFER, UPDATE'],
        ],
      });

      this.log(`REGISTER -> (with auth, CSeq ${this.regCSeq})`);
      this.sendSip!(register.serialize(), this.config.outboundProxy);
      return true;
    }

    if (code >= 400) {
      const wasRegistered = this.isRegistered;
      this.isRegistered = false;
      if (wasRegistered) {
        this.log(`registration lost (${code})`);
        this.onRegistrationChange?.(this);
      }
      return true;
    }

    return true; // consume 1xx etc.
  }

  /**
   * Update public IP from Via received= parameter.
   */
  detectPublicIp(via: string): void {
    const m = via.match(/received=([\d.]+)/);
    if (m && m[1] !== this.publicIp) {
      this.log(`publicIp = ${m[1]}`);
      this.publicIp = m[1];
    }
  }
}

// ---------------------------------------------------------------------------
// Provider state management
// ---------------------------------------------------------------------------

let providerStates: Map<string, ProviderState>;

export function initProviderStates(
  providers: IProviderConfig[],
  publicIpSeed: string | null,
): Map<string, ProviderState> {
  providerStates = new Map();
  for (const p of providers) {
    providerStates.set(p.id, new ProviderState(p, publicIpSeed));
  }
  return providerStates;
}

export function getProviderState(id: string): ProviderState | null {
  return providerStates?.get(id) ?? null;
}

/**
 * Sync running provider states with updated config.
 * - New providers: create state + start registration.
 * - Removed providers: stop registration + delete state.
 * - Changed providers: stop old, create new, start registration (preserves detected publicIp).
 */
export function syncProviderStates(
  newProviders: IProviderConfig[],
  publicIpSeed: string | null,
  lanIp: string,
  lanPort: number,
  sendSip: (buf: Buffer, dest: IEndpoint) => void,
  log: (msg: string) => void,
  onRegistrationChange: (provider: ProviderState) => void,
): void {
  if (!providerStates) return;

  const newIds = new Set(newProviders.map(p => p.id));
  const oldIds = new Set(providerStates.keys());

  // Remove providers no longer in config.
  for (const id of oldIds) {
    if (!newIds.has(id)) {
      const ps = providerStates.get(id)!;
      ps.stopRegistration();
      providerStates.delete(id);
      log(`[provider:${id}] removed`);
    }
  }

  for (const p of newProviders) {
    if (!oldIds.has(p.id)) {
      // New provider.
      const ps = new ProviderState(p, publicIpSeed);
      providerStates.set(p.id, ps);
      ps.startRegistration(lanIp, lanPort, sendSip, log, onRegistrationChange);
      log(`[provider:${p.id}] added — registration started`);
    } else {
      // Existing provider — check if config changed.
      const existing = providerStates.get(p.id)!;
      if (JSON.stringify(existing.config) !== JSON.stringify(p)) {
        existing.stopRegistration();
        const ps = new ProviderState(p, existing.publicIp || publicIpSeed);
        providerStates.set(p.id, ps);
        ps.startRegistration(lanIp, lanPort, sendSip, log, onRegistrationChange);
        log(`[provider:${p.id}] config changed — re-registering`);
      }
    }
  }
}

/**
 * Find which provider sent a packet, by matching the source address
 * against all providers' outbound proxy addresses.
 */
export function getProviderByUpstreamAddress(address: string, port: number): ProviderState | null {
  if (!providerStates) return null;
  for (const ps of providerStates.values()) {
    if (ps.config.outboundProxy.address === address && ps.config.outboundProxy.port === port) {
      return ps;
    }
  }
  return null;
}

/**
 * Check whether a response belongs to any provider's registration transaction.
 */
export function handleProviderRegistrationResponse(msg: SipMessage): boolean {
  if (!providerStates || !msg.isResponse) return false;
  for (const ps of providerStates.values()) {
    if (ps.handleRegistrationResponse(msg)) return true;
  }
  return false;
}