Kez/nodejs/packages/kez-core/src/encodings.ts

// Four wire encodings: JSON, compact (kez:z1:...), Markdown fence, legacy
// DNS (kez1:...). Round-trips match Rust exactly.

import { base64url } from "@scure/base";
import { zstdCompressSync, zstdDecompressSync } from "node:zlib";
import {
  type SignedClaimEnvelope,
  COMPACT_PROOF_PREFIX,
} from "./envelope.js";
import { Identity } from "./identity.js";

const MARKDOWN_FENCE = "```kez";

// ─────────────────────────────────────────────────────────────────────────────
// JSON
// ─────────────────────────────────────────────────────────────────────────────

export function toPrettyJson(envelope: SignedClaimEnvelope): string {
  return JSON.stringify(envelope, null, 2);
}

export function fromJson(json: string): SignedClaimEnvelope {
  return JSON.parse(json) as SignedClaimEnvelope;
}

// ─────────────────────────────────────────────────────────────────────────────
// Compact: kez:z1:<base64url-no-pad(zstd(json))>
// ─────────────────────────────────────────────────────────────────────────────

export function toCompact(envelope: SignedClaimEnvelope): string {
  const json = new TextEncoder().encode(JSON.stringify(envelope));
  const compressed = zstdCompressSync(json);
  return (
    COMPACT_PROOF_PREFIX +
    base64url.encode(new Uint8Array(compressed)).replace(/=+$/, "")
  );
}

export function fromCompact(value: string): SignedClaimEnvelope {
  const trimmed = value.trim();
  if (!trimmed.startsWith(COMPACT_PROOF_PREFIX)) {
    throw new Error("compact proof missing kez:z1: prefix");
  }
  const body = trimmed.slice(COMPACT_PROOF_PREFIX.length);
  // @scure/base's base64url requires standard padding; restore it.
  const padded = body + "=".repeat((4 - (body.length % 4)) % 4);
  const compressed = base64url.decode(padded);
  const json = zstdDecompressSync(compressed);
  return JSON.parse(new TextDecoder().decode(json)) as SignedClaimEnvelope;
}

// ─────────────────────────────────────────────────────────────────────────────
// Markdown fence: ```kez ... ```
// ─────────────────────────────────────────────────────────────────────────────

export function toMarkdown(envelope: SignedClaimEnvelope): string {
  const json = toPrettyJson(envelope);
  return [
    "# KEZ Proof",
    "",
    "This account publishes a signed KEZ identity claim.",
    "",
    `- Primary: \`${envelope.payload.primary}\``,
    `- Subject: \`${envelope.payload.subject}\``,
    `- Created: \`${envelope.payload.created_at}\``,
    "",
    MARKDOWN_FENCE,
    json,
    "```",
    "",
  ].join("\n");
}

export function extractMarkdownProof(markdown: string): SignedClaimEnvelope {
  const start = markdown.indexOf(MARKDOWN_FENCE);
  if (start < 0) {
    throw new Error("missing ```kez proof block");
  }
  const bodyStart = start + MARKDOWN_FENCE.length;
  const endRel = markdown.slice(bodyStart).indexOf("```");
  if (endRel < 0) {
    throw new Error("unterminated ```kez proof block");
  }
  const json = markdown.slice(bodyStart, bodyStart + endRel).trim();
  return JSON.parse(json) as SignedClaimEnvelope;
}

// ─────────────────────────────────────────────────────────────────────────────
// DNS TXT
// ─────────────────────────────────────────────────────────────────────────────

export function dnsTxtName(identity: Identity): string {
  if (identity.scheme !== "dns") {
    throw new Error(`dns_txt_name requires dns: identity, got: ${identity}`);
  }
  return `_kez.${identity.id}`;
}

/** Legacy `kez1:` DNS encoding — Rust parser still accepts it. */
export function dnsTxtValue(envelope: SignedClaimEnvelope): string {
  return "kez1:" + JSON.stringify(envelope);
}

export function parseDnsTxtValue(value: string): SignedClaimEnvelope {
  if (!value.startsWith("kez1:")) {
    throw new Error("DNS TXT proof missing kez1: prefix");
  }
  return JSON.parse(value.slice("kez1:".length)) as SignedClaimEnvelope;
}