import { get, set, merge } from 'lodash';

export function decoder<TOut, TIn = unknown>(paths: [string, object, object][], obj: TIn): TOut {
  const output: Partial<TOut> = {};

  const array_notation_test = /(.+)\[](\..+)?/;
  const paths_to_process = paths.slice();
  while (paths_to_process.length > 0) {
    const [path, from, to] = paths_to_process.pop() as [string, object, object];
    let value = get(obj, path) as unknown;
    const matches = array_notation_test.exec(Array.isArray(value) ? `${path}[]` : path);
    // Array Expansion logic
    if (matches) {
      const [, pre_path, post_path] = matches;

      const base = get(obj, pre_path, []) as unknown[];
      paths_to_process.push(
        ...base.map<[string, object, object]>((_, index) => [`${pre_path}[${index}]${post_path || ''}`, from, to])
      );
    } else {
      // Correct for the enum value being reversed
      if (typeof value !== 'number' && (value as never) in from) {
        value = from[value as never];
      }

      if ((value as never) in from && (value as never) in to) {
        set(output, path, to[value as never]);
      } else if (
        ((value as never) in from && !((value as never) in to)) ||
        ((value as never) in to && !((value as never) in from))
      ) {
        throw new Error(`Failed to decode value at '${path}': MISMATCH`);
      }
    }
  }

  return merge({}, obj, output) as unknown as TOut;
}