import { Key, KeyPath, Value } from "./types";
import valueToKey from "./valueToKey";

// http://www.w3.org/TR/2015/REC-IndexedDB-20150108/#dfn-steps-for-extracting-a-key-from-a-value-using-a-key-path
const extractKey = (keyPath: KeyPath, value: Value) => {
  if (Array.isArray(keyPath)) {
    const result: Key[] = [];

    for (let item of keyPath) {
      // This doesn't make sense to me based on the spec, but it is needed to pass the W3C KeyPath tests (see same
      // comment in validateKeyPath)
      if (
        item !== undefined &&
        item !== null &&
        typeof item !== "string" &&
        (item as any).toString
      ) {
        item = (item as any).toString();
      }
      result.push(valueToKey(extractKey(item, value)));
    }

    return result;
  }

  if (keyPath === "") {
    return value;
  }

  let remainingKeyPath: string | null = keyPath;
  let object = value;

  while (remainingKeyPath !== null) {
    let identifier;

    const i = remainingKeyPath.indexOf(".");
    if (i >= 0) {
      identifier = remainingKeyPath.slice(0, i);
      remainingKeyPath = remainingKeyPath.slice(i + 1);
    } else {
      identifier = remainingKeyPath;
      remainingKeyPath = null;
    }

    if (!object.hasOwnProperty(identifier)) {
      return;
    }

    object = object[identifier];
  }

  return object;
};

export default extractKey;