/**
 * Crew Agent identity (Phase 0)
 * ─────────────────────────────
 * The Crew Agent ("🐝 Sasquatch") is a Nostr identity that belongs to a crew.
 * Its key is DETERMINISTICALLY DERIVED from the crew's addressable coordinate,
 * so any client can reproduce the same agent identity for a given crew without
 * storing a key anywhere.
 *
 * ⚠️ SECURITY TRADEOFF (documented, deliberate for v1):
 * Because the key is derived from public data (the crew coordinate) plus a
 * fixed, public salt in this source, ANYONE who reads this code can derive the
 * same private key. This is acceptable for v1 because the agent only ever:
 *   - publishes its own kind-0 profile, and
 *   - (later, Phase 3) posts helper replies into its own crew's chat.
 * It holds no funds and speaks only for itself. It is NOT a secure identity and
 * must never be trusted for signing anything sensitive. A future version can
 * swap this for a founder-controlled stored key without changing call sites.
 */

import { getPublicKey, finalizeEvent, nip19, type EventTemplate } from 'nostr-tools';
import { sha256 } from '@noble/hashes/sha2.js';
import { bytesToHex } from '@noble/hashes/utils.js';
import { SKATE_CREW_KIND } from '@/lib/types';

/** Public, fixed salt — versioned so we can rotate the scheme later if needed. */
const AGENT_KEY_SALT = 'skatespots:crew-agent:v1';

export interface CrewAgentIdentity {
  /** 32-byte private key (hex). */
  secretKeyHex: string;
  /** 32-byte private key (bytes) — for signing. */
  secretKey: Uint8Array;
  /** Public key (hex). */
  pubkey: string;
  /** npub encoding of the public key. */
  npub: string;
}

/**
 * Build the crew's addressable coordinate `kind:pubkey:identifier`.
 * This is the stable, public seed for the agent identity.
 */
export function crewCoord(crewPubkey: string, identifier: string): string {
  return `${SKATE_CREW_KIND}:${crewPubkey}:${identifier}`;
}

/**
 * Deterministically derive the crew agent's keypair from the crew coordinate.
 * Same crew → same agent identity, everywhere, with no stored state.
 */
export function deriveCrewAgentIdentity(crewPubkey: string, identifier: string): CrewAgentIdentity {
  const coord = crewCoord(crewPubkey, identifier);
  // 32-byte secret = sha256(salt | coord). secp256k1 accepts any 32-byte scalar
  // in range; sha256 output is overwhelmingly within range, and nostr-tools /
  // noble will reject the astronomically unlikely invalid case at sign time.
  const secretKey = sha256(new TextEncoder().encode(`${AGENT_KEY_SALT}|${coord}`));
  const secretKeyHex = bytesToHex(secretKey);
  const pubkey = getPublicKey(secretKey);
  const npub = nip19.npubEncode(pubkey);
  return { secretKeyHex, secretKey, pubkey, npub };
}

/** Just the agent pubkey — cheap when you don't need to sign. */
export function crewAgentPubkey(crewPubkey: string, identifier: string): string {
  return deriveCrewAgentIdentity(crewPubkey, identifier).pubkey;
}

/** Sasquatch mascot avatar used for the agent's profile. */
export const CREW_AGENT_AVATAR =
  'https://npub1yrnuj56rnen08zp2h9h7p74ghgjx6ma39spmpj6w9hzxywutevsst7k5cx.blossom.band/2ff0cb5bd8622fed54a80784f5cc9d1f569714e9a16de65857a727e63404f5c2.png';

/**
 * Build (unsigned) the agent's kind-0 profile metadata for a crew.
 * `bot: true` follows NIP-24 so clients can honestly label it as automated.
 */
export function buildCrewAgentProfile(crewName: string): EventTemplate {
  const metadata = {
    name: `🐝 Sasquatch · ${crewName}`,
    display_name: `Sasquatch · ${crewName}`,
    about: `The AI crew guide for ${crewName} on SkateSpots. Ask me about spots, events, coaches, gear and more — I answer with live data. 🛹`,
    picture: CREW_AGENT_AVATAR,
    bot: true,
  };
  return {
    kind: 0,
    content: JSON.stringify(metadata),
    tags: [],
    created_at: Math.floor(Date.now() / 1000),
  };
}

/**
 * Sign an event template AS the crew agent (using its derived key).
 * Used to publish the agent's profile now, and its chat replies in Phase 3.
 */
export function signAsCrewAgent(
  crewPubkey: string,
  identifier: string,
  template: EventTemplate,
) {
  const { secretKey } = deriveCrewAgentIdentity(crewPubkey, identifier);
  return finalizeEvent(template, secretKey);
}