import type { LinkedField, LinkedType } from '../types';
import startsWith from 'lodash.startswith';

export function getFieldFromPath(root: LinkedType | undefined, path: string[]) {
  let current: LinkedField | undefined;

  if (!root) throw new Error('root type is not provided');

  if (path.length === 0) throw new Error(`path is empty`);

  path.forEach((f) => {
    const type = current ? current.type : root;

    if (!type.fields) throw new Error(`type \`${type.name}\` does not have fields`);

    const possibleTypes = Object.keys(type.fields)
      .filter((i) => startsWith(i, 'on_'))
      .reduce(
        (types, fieldName) => {
          const field = type.fields && type.fields[fieldName];
          if (field) types.push(field.type);
          return types;
        },
        [type],
      );

    let field: LinkedField | null = null;

    possibleTypes.forEach((type) => {
      const found = type.fields && type.fields[f];
      if (found) field = found;
    });

    if (!field) throw new Error(`type \`${type.name}\` does not have a field \`${f}\``);

    current = field;
  });

  return current as LinkedField;
}