import { derived, type Readable } from 'svelte/store';
import { json } from 'svelte-i18n';
import type { Locale } from '$lib/Locale/layout';

type FormatXMLElementFn<T, R = string | T | (string | T)[]> = (parts: Array<string | T>) => R;

type InterpolationValue =
  | string
  | number
  | boolean
  | Date
  | FormatXMLElementFn<unknown>
  | null
  | undefined;

type InterpolationValues = Record<string, InterpolationValue> | undefined;

interface Options {
  id?: string;
  locale?: string;
  format?: string;
  default?: string;
  values?: InterpolationValues;
}

const createLocale = () => {
  return derived(json, ($json) => {
    return (options: Options = {}) =>
      new Proxy(
        {},
        {
          get(_target, key) {
            const localisation = $json(key.toString(), options.locale);

            if (localisation === key.toString()) return undefined;

            const replaceValues = (
              localisation: InterpolationValues,
              values: InterpolationValues
            ) => {
              if (typeof localisation !== 'object' || localisation === null) return localisation;

              const updatedLocalisation: InterpolationValues = {};

              for (const [key, value] of Object.entries(localisation)) {
                if (typeof value === 'string') {
                  updatedLocalisation[key] = value.replace(
                    /\{(\w+)\}/g,
                    (match, name) => (values ? values[name] : match) as string
                  );
                } else {
                  updatedLocalisation[key] = replaceValues(
                    value as InterpolationValues,
                    values
                  ) as InterpolationValue;
                }
              }

              return updatedLocalisation;
            };

            if (options.values)
              return replaceValues(localisation as unknown as InterpolationValues, options.values);

            return localisation;
          }
        }
      );
  }) as Readable<(options?: Options) => Locale>;
};

const locale = createLocale();

export default locale;