feat: add internationalization message platform

src/presentation/i18n/formatters.ts

@@ -0,0 +1,96 @@
+import { normalizeLocale, type SupportedLocale } from "./message-contract.js";
+
+const FORMAT_FALLBACK = "—";
+
+export type DateFormatStyle = "short" | "medium" | "long";
+
+export function formatDate(
+  locale: SupportedLocale,
+  value: Date | number,
+  options: Readonly<{
+    dateStyle?: DateFormatStyle;
+    timeZone?: string;
+  }> = {},
+): string {
+  try {
+    const date = value instanceof Date ? value : new Date(value);
+    if (Number.isNaN(date.getTime())) return FORMAT_FALLBACK;
+    return new Intl.DateTimeFormat(normalizeLocale(locale), {
+      dateStyle: options.dateStyle ?? "medium",
+      timeZone: options.timeZone ?? "UTC",
+    }).format(date);
+  } catch {
+    return FORMAT_FALLBACK;
+  }
+}
+
+export function formatNumber(
+  locale: SupportedLocale,
+  value: number,
+  options: Readonly<{
+    style?: "decimal" | "percent";
+    maximumFractionDigits?: number;
+  }> = {},
+): string {
+  try {
+    if (!Number.isFinite(value)) return FORMAT_FALLBACK;
+    return new Intl.NumberFormat(normalizeLocale(locale), options).format(value);
+  } catch {
+    return FORMAT_FALLBACK;
+  }
+}
+
+export function formatRelativeTime(
+  locale: SupportedLocale,
+  value: number,
+  unit: Intl.RelativeTimeFormatUnit,
+): string {
+  try {
+    if (!Number.isFinite(value)) return FORMAT_FALLBACK;
+    return new Intl.RelativeTimeFormat(normalizeLocale(locale), {
+      numeric: "auto",
+    }).format(value, unit);
+  } catch {
+    return FORMAT_FALLBACK;
+  }
+}
+
+export function formatList(
+  locale: SupportedLocale,
+  values: readonly string[],
+): string {
+  try {
+    return new Intl.ListFormat(normalizeLocale(locale), {
+      style: "long",
+      type: "conjunction",
+    }).format(values);
+  } catch {
+    return values.join(", ");
+  }
+}
+
+export function selectPlural(
+  locale: SupportedLocale,
+  value: number,
+  choices: Readonly<
+    Partial<Record<Intl.LDMLPluralRule, string>> & { other: string }
+  >,
+): string {
+  try {
+    if (!Number.isFinite(value)) return choices.other;
+    return choices[
+      new Intl.PluralRules(normalizeLocale(locale)).select(value)
+    ] ?? choices.other;
+  } catch {
+    return choices.other;
+  }
+}
+
+export function selectMessage(
+  value: string,
+  choices: Readonly<Record<string, string> & { other: string }>,
+): string {
+  return choices[value] ?? choices.other;
+}
+
+export { FORMAT_FALLBACK };