dchain/client-app/lib/api.ts

/**
 * DChain REST API client.
 * All requests go to the configured node URL (e.g. http://192.168.1.10:8081).
 */

import type { Envelope, TxRecord, NetStats, Contact } from './types';
import { base64ToBytes, bytesToBase64, bytesToHex, hexToBytes } from './crypto';

// ─── Base ─────────────────────────────────────────────────────────────────────

let _nodeUrl = 'http://localhost:8081';

/**
 * Listeners invoked AFTER _nodeUrl changes. The WS client registers here so
 * that switching nodes in Settings tears down the old socket and re-dials
 * the new one (without this, a user who pointed their app at node A would
 * keep receiving A's events forever after flipping to B).
 */
const nodeUrlListeners = new Set<(url: string) => void>();

export function setNodeUrl(url: string) {
  const normalised = url.replace(/\/$/, '');
  if (_nodeUrl === normalised) return;
  _nodeUrl = normalised;
  for (const fn of nodeUrlListeners) {
    try { fn(_nodeUrl); } catch { /* ignore — listeners are best-effort */ }
  }
}

export function getNodeUrl(): string {
  return _nodeUrl;
}

/** Register a callback for node-URL changes. Returns an unsubscribe fn. */
export function onNodeUrlChange(fn: (url: string) => void): () => void {
  nodeUrlListeners.add(fn);
  return () => { nodeUrlListeners.delete(fn); };
}

async function get<T>(path: string): Promise<T> {
  const res = await fetch(`${_nodeUrl}${path}`);
  if (!res.ok) throw new Error(`GET ${path} → ${res.status}`);
  return res.json() as Promise<T>;
}

/**
 * Enhanced error reporter for POST failures. The node's `jsonErr` writes
 * `{"error": "..."}` as the response body; we parse that out so the UI layer
 * can show a meaningful message instead of a raw status code.
 *
 * Rate-limit and timestamp-skew rejections produce specific strings the UI
 * can translate to user-friendly Russian via matcher functions below.
 */
async function post<T>(path: string, body: unknown): Promise<T> {
  const res = await fetch(`${_nodeUrl}${path}`, {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(body),
  });
  if (!res.ok) {
    const text = await res.text();
    // Try to extract {"error":"..."} payload for a cleaner message.
    let detail = text;
    try {
      const parsed = JSON.parse(text);
      if (parsed?.error) detail = parsed.error;
    } catch { /* keep raw text */ }
    // Include HTTP status so `humanizeTxError` can branch on 429/400/etc.
    throw new Error(`${res.status}: ${detail}`);
  }
  return res.json() as Promise<T>;
}

/**
 * Turn a submission error from `post()` / `submitTx()` into a user-facing
 * Russian message with actionable hints. Preserves the raw detail at the end
 * so advanced users can still copy the original for support.
 */
export function humanizeTxError(e: unknown): string {
  const raw = e instanceof Error ? e.message : String(e);
  if (raw.startsWith('429')) {
    return 'Too many requests to the node. Wait a couple of seconds and try again.';
  }
  if (raw.startsWith('400') && raw.includes('timestamp')) {
    return 'Device clock is out of sync with the node. Check the time on your phone (±1 hour).';
  }
  if (raw.startsWith('400') && raw.includes('signature')) {
    return 'Transaction signature is invalid. Try again; if this persists the client and node versions may be incompatible.';
  }
  if (raw.startsWith('400')) {
    return `Node rejected transaction: ${raw.replace(/^400:\s*/, '')}`;
  }
  if (raw.startsWith('5')) {
    return `Node error (${raw}). Please try again later.`;
  }
  // Network-level
  if (raw.toLowerCase().includes('network request failed')) {
    return 'Cannot reach the node. Check the URL in settings and that the server is online.';
  }
  return raw;
}

// ─── Chain API ────────────────────────────────────────────────────────────────

export async function getNetStats(): Promise<NetStats> {
  return get<NetStats>('/api/netstats');
}

interface AddrResponse {
  balance_ut:   number;
  balance:      string;
  transactions: Array<{
    id:         string;
    type:       string;
    from:       string;
    to?:        string;
    amount_ut:  number;
    fee_ut:     number;
    time:       string;   // ISO-8601 e.g. "2025-01-01T12:00:00Z"
    block_index: number;
  }>;
  tx_count:  number;
  has_more:  boolean;
}

export async function getBalance(pubkey: string): Promise<number> {
  const data = await get<AddrResponse>(`/api/address/${pubkey}`);
  return data.balance_ut ?? 0;
}

/**
 * Transaction as sent to /api/tx — maps 1-to-1 to blockchain.Transaction JSON.
 * Key facts:
 *   - `payload`   is base64-encoded JSON bytes  (Go []byte → base64 in JSON)
 *   - `signature` is base64-encoded Ed25519 sig (Go []byte → base64 in JSON)
 *   - `timestamp` is RFC3339 string             (Go time.Time → string in JSON)
 *   - There is NO nonce field; dedup is by `id`
 */
export interface RawTx {
  id:        string;   // "tx-<nanoseconds>" or sha256-based
  type:      string;   // "TRANSFER", "CONTACT_REQUEST", etc.
  from:      string;   // hex Ed25519 pub key
  to:        string;   // hex Ed25519 pub key (empty string if N/A)
  amount:    number;   // µT (uint64)
  fee:       number;   // µT (uint64)
  memo?:     string;   // optional
  payload:   string;   // base64(json.Marshal(TypeSpecificPayload))
  signature: string;   // base64(ed25519.Sign(canonical_bytes, priv))
  timestamp: string;   // RFC3339 e.g. "2025-01-01T12:00:00Z"
}

export async function submitTx(tx: RawTx): Promise<{ id: string; status: string }> {
  console.log('[submitTx] →', {
    id:        tx.id,
    type:      tx.type,
    from:      tx.from.slice(0, 12) + '…',
    to:        tx.to ? tx.to.slice(0, 12) + '…' : '',
    amount:    tx.amount,
    fee:       tx.fee,
    timestamp: tx.timestamp,
    transport: 'auto',
  });

  // Try the WebSocket path first: no HTTP round-trip, and we get a proper
  // submit_ack correlated back to our tx id. Falls through to HTTP if WS is
  // unavailable (old node, disconnected, timeout, etc.) so legacy setups
  // keep working.
  try {
    // Lazy import avoids a circular dep with lib/ws.ts (which itself
    // imports getNodeUrl from this module).
    const { getWSClient } = await import('./ws');
    const ws = getWSClient();
    if (ws.isConnected()) {
      try {
        const res = await ws.submitTx(tx);
        console.log('[submitTx] ← accepted via WS', res);
        return { id: res.id || tx.id, status: 'accepted' };
      } catch (e) {
        console.warn('[submitTx] WS path failed, falling back to HTTP:', e);
      }
    }
  } catch { /* circular import edge case — ignore and use HTTP */ }

  try {
    const res = await post<{ id: string; status: string }>('/api/tx', tx);
    console.log('[submitTx] ← accepted via HTTP', res);
    return res;
  } catch (e) {
    console.warn('[submitTx] ← rejected', e);
    throw e;
  }
}

export async function getTxHistory(pubkey: string, limit = 50): Promise<TxRecord[]> {
  const data = await get<AddrResponse>(`/api/address/${pubkey}?limit=${limit}`);
  return (data.transactions ?? []).map(tx => ({
    hash:      tx.id,
    type:      tx.type,
    from:      tx.from,
    to:        tx.to,
    amount:    tx.amount_ut,
    fee:       tx.fee_ut,
    // Convert ISO-8601 string → unix seconds
    timestamp: tx.time ? Math.floor(new Date(tx.time).getTime() / 1000) : 0,
    status:    'confirmed' as const,
  }));
}

// ─── Relay API ────────────────────────────────────────────────────────────────
//
// Endpoints are mounted at the ROOT of the node HTTP server (not under /api):
//   POST /relay/broadcast  — publish pre-sealed envelope (proper E2E)
//   GET  /relay/inbox      — fetch envelopes addressed to <pub>
//
// Why /relay/broadcast, not /relay/send?
//   /relay/send takes plaintext (msg_b64) и SEAL'ит его ключом релей-ноды —
//   это ломает end-to-end шифрование (получатель не сможет расшифровать
//   своим ключом). Для E2E всегда используем /relay/broadcast с уже
//   запечатанным на клиенте envelope'ом.

/**
 * Shape of envelope item returned by GET /relay/inbox (server item type).
 * Go `[]byte` поля сериализуются как base64 в JSON — поэтому `nonce` и
 * `ciphertext` приходят base64, а не hex. Мы декодируем их в hex для
 * совместимости с crypto.ts (decryptMessage принимает hex).
 */
interface InboxItemWire {
  id:            string;
  sender_pub:    string;
  recipient_pub: string;
  fee_ut?:       number;
  sent_at:       number;
  sent_at_human?: string;
  nonce:         string;   // base64
  ciphertext:    string;   // base64
}

interface InboxResponseWire {
  pub:      string;
  count:    number;
  has_more: boolean;
  items:    InboxItemWire[];
}

/**
 * Клиент собирает envelope через encryptMessage и шлёт на /relay/broadcast.
 * Серверный формат: `{envelope: <relay.Envelope JSON>}`. Nonce/ciphertext
 * там — base64 (Go []byte), а у нас в crypto.ts — hex, так что на wire
 * конвертим hex→bytes→base64.
 */
export async function sendEnvelope(params: {
  senderPub:    string;   // X25519 hex
  recipientPub: string;   // X25519 hex
  nonce:        string;   // hex
  ciphertext:   string;   // hex
  senderEd25519Pub?: string;  // optional — для будущих fee-релеев
}): Promise<{ id: string; status: string }> {
  const sentAt = Math.floor(Date.now() / 1000);
  const nonceB64 = bytesToBase64(hexToBytes(params.nonce));
  const ctB64    = bytesToBase64(hexToBytes(params.ciphertext));

  // envelope.id — 16 байт, hex. Сервер только проверяет что поле не
  // пустое и использует его как ключ mailbox'а. Первые 16 байт nonce
  // уже криптографически-случайны (nacl.randomBytes), так что берём их.
  const id = bytesToHex(hexToBytes(params.nonce).slice(0, 16));

  return post<{ id: string; status: string }>('/relay/broadcast', {
    envelope: {
      id,
      sender_pub:         params.senderPub,
      recipient_pub:      params.recipientPub,
      sender_ed25519_pub: params.senderEd25519Pub ?? '',
      fee_ut:             0,
      fee_sig:            null,
      nonce:              nonceB64,
      ciphertext:         ctB64,
      sent_at:            sentAt,
    },
  });
}

/**
 * Fetch envelopes адресованные нам из relay-почтовика.
 * Server: `GET /relay/inbox?pub=<x25519hex>` → `{pub, count, has_more, items}`.
 * Нормализуем item'ы к clientскому Envelope type: sent_at → timestamp,
 * base64 nonce/ciphertext → hex.
 */
export async function fetchInbox(x25519PubHex: string): Promise<Envelope[]> {
  const resp = await get<InboxResponseWire>(`/relay/inbox?pub=${x25519PubHex}`);
  const items = Array.isArray(resp?.items) ? resp.items : [];
  return items.map((it): Envelope => ({
    id:            it.id,
    sender_pub:    it.sender_pub,
    recipient_pub: it.recipient_pub,
    nonce:         bytesToHex(base64ToBytes(it.nonce)),
    ciphertext:    bytesToHex(base64ToBytes(it.ciphertext)),
    timestamp:     it.sent_at ?? 0,
  }));
}


// ─── Contact requests (on-chain) ─────────────────────────────────────────────

/**
 * Maps blockchain.ContactInfo returned by GET /relay/contacts?pub=...
 * The response shape is { pub, count, contacts: ContactInfo[] }.
 */
export interface ContactRequestRaw {
  requester_pub:  string;   // Ed25519 pubkey of requester
  requester_addr: string;   // DChain address (DC…)
  status:         string;   // "pending" | "accepted" | "blocked"
  intro:          string;   // plaintext intro message (may be empty)
  fee_ut:         number;   // anti-spam fee paid in µT
  tx_id:          string;   // transaction ID
  created_at:     number;   // unix seconds
}

export async function fetchContactRequests(edPubHex: string): Promise<ContactRequestRaw[]> {
  const data = await get<{ contacts: ContactRequestRaw[] }>(`/relay/contacts?pub=${edPubHex}`);
  return data.contacts ?? [];
}

// ─── Identity API ─────────────────────────────────────────────────────────────

export interface IdentityInfo {
  pub_key:    string;
  address:    string;
  x25519_pub: string;   // hex Curve25519 key; empty string if not published
  nickname:   string;
  registered: boolean;
}

/** Fetch identity info for any pubkey or DC address. Returns null on 404. */
export async function getIdentity(pubkeyOrAddr: string): Promise<IdentityInfo | null> {
  try {
    return await get<IdentityInfo>(`/api/identity/${pubkeyOrAddr}`);
  } catch {
    return null;
  }
}

// ─── Contract API ─────────────────────────────────────────────────────────────

/**
 * Response shape from GET /api/contracts/{id}/state/{key}.
 * The node handler (node/api_contract.go:handleContractState) returns either:
 *   { value_b64: null, value_hex: null, ... }        when the key is missing
 * or
 *   { value_b64: "...", value_hex: "...", value_u64?: 0 }  when the key exists.
 */
interface ContractStateResponse {
  contract_id: string;
  key:         string;
  value_b64:   string | null;
  value_hex:   string | null;
  value_u64?:  number;
}

/**
 * Decode a hex string (lowercase/uppercase) back to the original string value
 * it represents. The username registry contract stores values as plain ASCII
 * bytes (pubkey hex strings / username strings), so `value_hex` on the wire
 * is the hex-encoding of UTF-8 bytes. We hex-decode to bytes, then interpret
 * those bytes as UTF-8.
 */
function hexToUtf8(hex: string): string {
  if (hex.length % 2 !== 0) return '';
  const bytes = new Uint8Array(hex.length / 2);
  for (let i = 0; i < hex.length; i += 2) {
    bytes[i / 2] = parseInt(hex.substr(i, 2), 16);
  }
  // TextDecoder is available in Hermes / RN's JS runtime.
  try {
    return new TextDecoder('utf-8').decode(bytes);
  } catch {
    // Fallback for environments without TextDecoder.
    let s = '';
    for (const b of bytes) s += String.fromCharCode(b);
    return s;
  }
}

/** username → address (hex pubkey). Returns null if unregistered. */
export async function resolveUsername(contractId: string, username: string): Promise<string | null> {
  try {
    const data = await get<ContractStateResponse>(`/api/contracts/${contractId}/state/name:${username}`);
    if (!data.value_hex) return null;
    const decoded = hexToUtf8(data.value_hex).trim();
    return decoded || null;
  } catch {
    return null;
  }
}

/** address (hex pubkey) → username. Returns null if this address hasn't registered a name. */
export async function reverseResolve(contractId: string, address: string): Promise<string | null> {
  try {
    const data = await get<ContractStateResponse>(`/api/contracts/${contractId}/state/addr:${address}`);
    if (!data.value_hex) return null;
    const decoded = hexToUtf8(data.value_hex).trim();
    return decoded || null;
  } catch {
    return null;
  }
}

// ─── Well-known contracts ─────────────────────────────────────────────────────

/**
 * Per-entry shape returned by GET /api/well-known-contracts.
 * Matches node/api_well_known.go:WellKnownContract.
 */
export interface WellKnownContract {
  contract_id: string;
  name:        string;
  version?:    string;
  deployed_at: number;
}

/**
 * Response from GET /api/well-known-contracts.
 * `contracts` is keyed by ABI name (e.g. "username_registry").
 */
export interface WellKnownResponse {
  count:     number;
  contracts: Record<string, WellKnownContract>;
}

/**
 * Fetch the node's view of canonical system contracts so the client doesn't
 * have to force the user to paste contract IDs into settings.
 *
 * The node returns the earliest-deployed contract per ABI name; this means
 * every peer in the same chain reports the same mapping.
 *
 * Returns `null` on failure (old node, network hiccup, endpoint missing).
 */
export async function fetchWellKnownContracts(): Promise<WellKnownResponse | null> {
  try {
    return await get<WellKnownResponse>('/api/well-known-contracts');
  } catch {
    return null;
  }
}

// ─── Node version / update-check ─────────────────────────────────────────────
//
// The three calls below let the client:
//   1. fetchNodeVersion() — see what tag/commit/features the connected node
//      exposes. Used on first boot + on every chain-switch so we can warn if
//      a required feature is missing.
//   2. checkNodeVersion(required)  — thin wrapper that returns {supported,
//      missing} by diffing a client-expected feature list against the node's.
//   3. fetchUpdateCheck() — ask the node whether its operator has a newer
//      release available from their configured release source (Gitea). For
//      messenger UX this is purely informational ("the node you're on is N
//      versions behind"), never used to update the node automatically.

/** The shape returned by GET /api/well-known-version. */
export interface NodeVersionInfo {
  node_version: string;
  protocol_version: number;
  features: string[];
  chain_id?: string;
  build?: {
    tag: string;
    commit: string;
    date: string;
    dirty: string;
  };
}

/** Client-expected protocol version. Bumped only when wire-protocol breaks. */
export const CLIENT_PROTOCOL_VERSION = 1;

/**
 * Minimum feature set this client build relies on. A node missing any of
 * these is considered "unsupported" — caller should surface an upgrade
 * prompt to the user instead of silently failing on the first feature call.
 */
export const CLIENT_REQUIRED_FEATURES = [
  'chain_id',
  'feed_v2',           // social feed (v2.0.0) — PostCard, timeline, forYou
  'identity_registry',
  'media_scrub',       // server-side EXIF strip — we rely on this for privacy
  'onboarding_api',
  'relay_broadcast',   // /relay/broadcast for E2E envelopes (not /relay/send)
  'relay_mailbox',
  'ws_submit_tx',
];

/** GET /api/well-known-version. Returns null on failure (old node, network hiccup). */
export async function fetchNodeVersion(): Promise<NodeVersionInfo | null> {
  try {
    return await get<NodeVersionInfo>('/api/well-known-version');
  } catch {
    return null;
  }
}

/**
 * Check whether the connected node supports this client's required features
 * and protocol version. Returns a decision blob the UI can render directly.
 *
 *   { supported: true }                       → everything fine
 *   { supported: false, reason: "...", ... }  → show update prompt
 *   { supported: null, reason: "unreachable" } → couldn't reach the endpoint,
 *                                                likely old node — assume OK
 *                                                but warn quietly.
 */
export async function checkNodeVersion(
  required: string[] = CLIENT_REQUIRED_FEATURES,
): Promise<{
  supported: boolean | null;
  reason?: string;
  missing?: string[];
  info?: NodeVersionInfo;
}> {
  const info = await fetchNodeVersion();
  if (!info) {
    return { supported: null, reason: 'unreachable' };
  }
  if (info.protocol_version !== CLIENT_PROTOCOL_VERSION) {
    return {
      supported: false,
      reason: `protocol v${info.protocol_version} but client expects v${CLIENT_PROTOCOL_VERSION}`,
      info,
    };
  }
  const have = new Set(info.features || []);
  const missing = required.filter((f) => !have.has(f));
  if (missing.length > 0) {
    return {
      supported: false,
      reason: `node missing features: ${missing.join(', ')}`,
      missing,
      info,
    };
  }
  return { supported: true, info };
}

/** The shape returned by GET /api/update-check. */
export interface UpdateCheckResponse {
  current: { tag: string; commit: string; date: string; dirty: string };
  latest?: { tag: string; commit?: string; url?: string; published_at?: string };
  update_available: boolean;
  checked_at: string;
  source?: string;
}

/**
 * GET /api/update-check. Returns null when:
 *   - the node operator hasn't configured DCHAIN_UPDATE_SOURCE_URL (503),
 *   - upstream Gitea call failed (502),
 *   - request errored out.
 * All three are non-fatal for the client; the UI just doesn't render the
 * "update available" banner.
 */
export async function fetchUpdateCheck(): Promise<UpdateCheckResponse | null> {
  try {
    return await get<UpdateCheckResponse>('/api/update-check');
  } catch {
    return null;
  }
}

// ─── Transaction builder helpers ─────────────────────────────────────────────

import { signBase64 } from './crypto';

/** Minimum blockchain tx fee paid to the block validator (matches blockchain.MinFee = 1000 µT). */
const MIN_TX_FEE = 1000;

const _encoder = new TextEncoder();

/** RFC3339 timestamp with second precision — matches Go time.Time JSON output. */
function rfc3339Now(): string {
  const d = new Date();
  d.setMilliseconds(0);
  // toISOString() gives "2025-01-01T12:00:00.000Z" → replace ".000Z" with "Z"
  return d.toISOString().replace('.000Z', 'Z');
}

/** Unique transaction ID (nanoseconds-like using Date.now + random). */
function newTxID(): string {
  return `tx-${Date.now()}${Math.floor(Math.random() * 1_000_000)}`;
}

/**
 * Canonical bytes for signing — must match identity.txSignBytes in Go exactly.
 *
 * Go struct field order: id, type, from, to, amount, fee, payload, timestamp.
 * JS JSON.stringify preserves insertion order, so we rely on that here.
 */
function txCanonicalBytes(tx: {
  id: string; type: string; from: string; to: string;
  amount: number; fee: number; payload: string; timestamp: string;
}): Uint8Array {
  const s = JSON.stringify({
    id:        tx.id,
    type:      tx.type,
    from:      tx.from,
    to:        tx.to,
    amount:    tx.amount,
    fee:       tx.fee,
    payload:   tx.payload,
    timestamp: tx.timestamp,
  });
  return _encoder.encode(s);
}

/** Encode a JS string (UTF-8) to base64. */
function strToBase64(s: string): string {
  return bytesToBase64(_encoder.encode(s));
}

export function buildTransferTx(params: {
  from:    string;
  to:      string;
  amount:  number;
  fee:     number;
  privKey: string;
  memo?:   string;
}): RawTx {
  const id        = newTxID();
  const timestamp = rfc3339Now();
  const payloadObj = params.memo ? { memo: params.memo } : {};
  const payload    = strToBase64(JSON.stringify(payloadObj));

  const canonical = txCanonicalBytes({
    id, type: 'TRANSFER', from: params.from, to: params.to,
    amount: params.amount, fee: params.fee, payload, timestamp,
  });

  return {
    id, type: 'TRANSFER', from: params.from, to: params.to,
    amount: params.amount, fee: params.fee,
    memo: params.memo,
    payload, timestamp,
    signature: signBase64(canonical, params.privKey),
  };
}

/**
 * CONTACT_REQUEST transaction.
 *
 * blockchain.Transaction fields:
 *   Amount = contactFee  — anti-spam fee, paid directly to recipient (>= 5000 µT)
 *   Fee    = MIN_TX_FEE  — blockchain tx fee to the block validator (1000 µT)
 *   Payload = ContactRequestPayload { intro? } as base64 JSON bytes
 */
export function buildContactRequestTx(params: {
  from:       string;  // sender Ed25519 pubkey
  to:         string;  // recipient Ed25519 pubkey
  contactFee: number;  // anti-spam amount paid to recipient (>= 5000 µT)
  intro?:     string;  // optional plaintext intro message (≤ 280 chars)
  privKey:    string;
}): RawTx {
  const id        = newTxID();
  const timestamp = rfc3339Now();
  // Payload matches ContactRequestPayload{Intro: "..."} in Go
  const payloadObj = params.intro ? { intro: params.intro } : {};
  const payload    = strToBase64(JSON.stringify(payloadObj));

  const canonical = txCanonicalBytes({
    id, type: 'CONTACT_REQUEST', from: params.from, to: params.to,
    amount: params.contactFee, fee: MIN_TX_FEE, payload, timestamp,
  });

  return {
    id, type: 'CONTACT_REQUEST', from: params.from, to: params.to,
    amount: params.contactFee, fee: MIN_TX_FEE, payload, timestamp,
    signature: signBase64(canonical, params.privKey),
  };
}

/**
 * ACCEPT_CONTACT transaction.
 * AcceptContactPayload is an empty struct in Go — no fields needed.
 */
export function buildAcceptContactTx(params: {
  from:    string;  // acceptor Ed25519 pubkey (us — the recipient of the request)
  to:      string;  // requester Ed25519 pubkey
  privKey: string;
}): RawTx {
  const id        = newTxID();
  const timestamp = rfc3339Now();
  const payload   = strToBase64(JSON.stringify({}));   // AcceptContactPayload{}

  const canonical = txCanonicalBytes({
    id, type: 'ACCEPT_CONTACT', from: params.from, to: params.to,
    amount: 0, fee: MIN_TX_FEE, payload, timestamp,
  });

  return {
    id, type: 'ACCEPT_CONTACT', from: params.from, to: params.to,
    amount: 0, fee: MIN_TX_FEE, payload, timestamp,
    signature: signBase64(canonical, params.privKey),
  };
}

// ─── Contract call ────────────────────────────────────────────────────────────

/** Minimum base fee for CALL_CONTRACT (matches blockchain.MinCallFee). */
const MIN_CALL_FEE = 1000;

/**
 * CALL_CONTRACT transaction.
 *
 * Payload shape (CallContractPayload):
 *   { contract_id, method, args_json?, gas_limit }
 *
 * `amount` is the payment attached to the call and made available to the
 * contract as `tx.Amount`. Whether it's collected depends on the contract
 * — e.g. username_registry.register requires exactly 10_000 µT. Contracts
 * that don't need payment should be called with `amount: 0` (default).
 *
 * The on-chain tx envelope carries `amount` openly, so the explorer shows
 * the exact cost of a call rather than hiding it in a contract-internal
 * debit — this was the UX motivation for this field.
 *
 * `fee` is the NETWORK fee paid to the block validator (not the contract).
 * `gas` costs are additional and billed at the live gas price.
 */
export function buildCallContractTx(params: {
  from:       string;
  contractId: string;
  method:     string;
  args?:      unknown[];      // JSON-serializable arguments
  amount?:    number;         // µT attached to the call (default 0)
  gasLimit?:  number;         // default 1_000_000
  privKey:    string;
}): RawTx {
  const id        = newTxID();
  const timestamp = rfc3339Now();
  const amount    = params.amount ?? 0;

  const argsJson = params.args && params.args.length > 0
    ? JSON.stringify(params.args)
    : '';

  const payloadObj = {
    contract_id: params.contractId,
    method:      params.method,
    args_json:   argsJson,
    gas_limit:   params.gasLimit ?? 1_000_000,
  };
  const payload = strToBase64(JSON.stringify(payloadObj));

  const canonical = txCanonicalBytes({
    id, type: 'CALL_CONTRACT', from: params.from, to: '',
    amount, fee: MIN_CALL_FEE, payload, timestamp,
  });

  return {
    id, type: 'CALL_CONTRACT', from: params.from, to: '',
    amount, fee: MIN_CALL_FEE, payload, timestamp,
    signature: signBase64(canonical, params.privKey),
  };
}

/**
 * Flat registration fee for a username, in µT.
 *
 * The native username_registry charges a single flat fee (10 000 µT = 0.01 T)
 * per register() call regardless of name length, replacing the earlier
 * length-based formula. Flat pricing is easier to communicate and the
 * 4-char minimum (enforced both in the client UI and the on-chain contract)
 * already removes the squatting pressure that tiered pricing mitigated.
 */
export const USERNAME_REGISTRATION_FEE = 10_000;

/** Minimum/maximum allowed username length. Match blockchain/native_username.go. */
export const MIN_USERNAME_LENGTH = 4;
export const MAX_USERNAME_LENGTH = 32;

/** @deprecated Kept for backward compatibility; always returns the flat fee. */
export function usernameRegistrationFee(_name: string): number {
  return USERNAME_REGISTRATION_FEE;
}