const POSTGRES_JSON_REPLACEMENT_CHARACTER = '\uFFFD';
const POSTGRES_JSON_SUSPECT_CODE_UNIT_RE = /[\u0000\uD800-\uDFFF]/;

function sanitizePostgresJsonString(value: string): string {
  if (!POSTGRES_JSON_SUSPECT_CODE_UNIT_RE.test(value)) return value;

  let sanitized = '';
  let changed = false;

  for (let index = 0; index < value.length; index += 1) {
    const codeUnit = value.charCodeAt(index);
    if (codeUnit === 0) {
      changed = true;
      continue;
    }

    if (codeUnit >= 0xd800 && codeUnit <= 0xdbff) {
      const nextCodeUnit = value.charCodeAt(index + 1);
      if (nextCodeUnit >= 0xdc00 && nextCodeUnit <= 0xdfff) {
        sanitized += value[index] + value[index + 1];
        index += 1;
        continue;
      }
      sanitized += POSTGRES_JSON_REPLACEMENT_CHARACTER;
      changed = true;
      continue;
    }

    if (codeUnit >= 0xdc00 && codeUnit <= 0xdfff) {
      sanitized += POSTGRES_JSON_REPLACEMENT_CHARACTER;
      changed = true;
      continue;
    }

    sanitized += value[index];
  }

  return changed ? sanitized : value;
}

function postgresJsonReplacer(_key: string, value: unknown): unknown {
  if (typeof value === 'string') {
    return sanitizePostgresJsonString(value);
  }
  if (value === null || typeof value !== 'object' || Array.isArray(value)) {
    return value;
  }

  const keys = Object.keys(value);
  if (!keys.some((key) => sanitizePostgresJsonString(key) !== key)) {
    return value;
  }
  const sanitizedEntries: Array<[string, unknown]> = [];
  const sanitizedKeys = new Set<string>();
  for (const key of keys) {
    const sanitizedKey = sanitizePostgresJsonString(key);
    if (sanitizedKeys.has(sanitizedKey)) {
      throw new TypeError(
        'Postgres JSON key normalization produced a duplicate object key.',
      );
    }
    sanitizedKeys.add(sanitizedKey);
    sanitizedEntries.push([
      sanitizedKey,
      (value as Record<string, unknown>)[key],
    ]);
  }
  return Object.fromEntries(sanitizedEntries);
}

export function sanitizePostgresJsonValue<T>(value: T): T {
  const serialized = stringifyPostgresJson(value);
  return serialized === undefined ? value : (JSON.parse(serialized) as T);
}

export function stringifyPostgresJson(value: unknown): string | undefined {
  return JSON.stringify(value, postgresJsonReplacer);
}