import { Injectable, computed, signal } from '@angular/core';
import { DICTS, type Messages } from '@shared/i18n';
import type { AppSettings, SupportedLocale } from '@shared/types';
import { formatDate, formatSize, formatSpeed } from './format';

type Params = Record<string, string | number>;

function lookup(dict: Messages, key: string): string | Messages | undefined {
  let node: string | Messages | undefined = dict;
  for (const part of key.split('.')) {
    if (typeof node !== 'object') return undefined;
    node = node[part];
  }
  return node;
}

function interpolate(template: string, params?: Params): string {
  if (!params) return template;
  return template.replace(/\{(\w+)\}/g, (_, name: string) =>
    name in params ? String(params[name]) : `{${name}}`,
  );
}

/**
 * Runtime translator. `t()` reads the `locale` signal, so any template binding
 * that calls it re-renders live on a language switch (the same reactive
 * function-call tracking the file-list icon classes rely on). Missing keys fall
 * back to English, then to the raw key so gaps are visible in dev.
 */
@Injectable({ providedIn: 'root' })
export class I18nService {
  readonly locale = signal<SupportedLocale>('en');
  private readonly dict = computed(() => DICTS[this.locale()]);

  t(key: string, params?: Params): string {
    let value = lookup(this.dict(), key) ?? lookup(DICTS.en, key);
    // plural map: pick the CLDR category for params.count (fallback to English)
    if (value && typeof value === 'object') {
      const count = Number(params?.['count'] ?? NaN);
      if (Number.isFinite(count)) {
        const rule = new Intl.PluralRules(this.locale()).select(count);
        const picked = value[rule] ?? value['other'] ?? lookup(DICTS.en, `${key}.other`);
        value = typeof picked === 'string' ? picked : undefined;
      } else {
        value = undefined;
      }
    }
    return typeof value === 'string' ? interpolate(value, params) : key;
  }

  // Locale-reactive formatting (live-updates the file list on switch).
  date(epochMs: number): string {
    return formatDate(epochMs, this.locale());
  }
  size(bytes: number): string {
    return formatSize(bytes, this.locale());
  }
  speed(bytesPerSec: number, unit: AppSettings['speedUnit']): string {
    return formatSpeed(bytesPerSec, unit, this.locale());
  }
}