import { isString } from '@sindresorhus/is';
import { DateTime } from 'luxon';
import { decompressFromBase64, decompressFromBuffer } from '../../compress.ts';

// TODO: Delete this decode-only support, legacy.spec.ts, and the single call
// site in impl/base.ts once pre-envelope entries have expired.

export interface LegacyEntry {
  value: unknown;
  expiry: DateTime | undefined;
}

interface LegacyJsonEntry {
  value: unknown;
  expiry: unknown;
}

export async function decodeLegacyEntry(data: Buffer): Promise<LegacyEntry> {
  if (data[0] === 0x7b) {
    return await decodeLegacyJsonEntry(data);
  }

  return await decodeLegacySqliteEntry(data);
}

async function decodeLegacyJsonEntry(data: Buffer): Promise<LegacyEntry> {
  const cached = JSON.parse(data.toString('utf8')) as LegacyJsonEntry;

  if (!isString(cached.value) || !isString(cached.expiry)) {
    throw new Error('Invalid legacy JSON package cache entry');
  }

  const json = await decompressFromBase64(cached.value);

  return {
    value: JSON.parse(json),
    expiry: DateTime.fromISO(cached.expiry),
  };
}

async function decodeLegacySqliteEntry(data: Buffer): Promise<LegacyEntry> {
  const json = await decompressFromBuffer(data);

  return {
    value: JSON.parse(json),
    expiry: undefined,
  };
}