Phase2: Invoicecomputation/AdminpricingUI/Ainvoicemgnt

src/lib/billing-i18n.ts

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+/**
+ * Shared billing localization. Used by:
+ *   - billing.ts (compute path) — pre-renders the localized
+ *     line description and stores it on the invoice line at issue
+ *     time. Descriptions are then frozen in the customer's locale.
+ *   - billing-pdf.tsx (render path) — can fall back to this if a
+ *     stored description is missing (e.g. legacy invoice from the
+ *     pre-i18n era) or if the PDF is re-rendered in a different
+ *     locale (Phase 7).
+ *
+ * Locale set matches the portal's next-intl locales: de, en, fr, it.
+ * Unknown locales fall back to German (Swiss B2B default).
+ */
+
+import type { InvoiceLineKind } from "@/types";
+
+export type BillingLocale = "de" | "en" | "fr" | "it";
+
+function normaliseLocale(locale: string): BillingLocale {
+  if (locale === "en" || locale === "fr" || locale === "it" || locale === "de") {
+    return locale;
+  }
+  return "de";
+}
+
+/**
+ * Localized "N day(s)" — covers the only plural case in billing
+ * line descriptions. Other plurals (months, requests, messages)
+ * either don't change form in the supported languages or are
+ * always >1 in practice.
+ */
+function days(n: number, locale: BillingLocale): string {
+  const labels = {
+    de: { one: "Tag", many: "Tage" },
+    en: { one: "day", many: "days" },
+    fr: { one: "jour", many: "jours" },
+    it: { one: "giorno", many: "giorni" },
+  } as const;
+  const label = labels[locale];
+  return `${n} ${n === 1 ? label.one : label.many}`;
+}
+
+/** Subset of InvoiceLine needed for description formatting. */
+export interface LineForDescription {
+  kind: InvoiceLineKind;
+  tenantName: string | null;
+  metadata: Record<string, unknown> | null;
+}
+
+/**
+ * Build the localized line description from a line's kind +
+ * metadata. Pure function — no DB/IO. Output mirrors what the
+ * PDF and admin preview show in the description column.
+ *
+ * Metadata expectations per kind (must match what billing.ts
+ * stores when emitting the line):
+ *   tenant_monthly:    { billable_days, days_in_month }
+ *   tenant_setup:      {} (uses tenantName only)
+ *   ai_usage:          { requests }
+ *   threema_messages:  { in_count, out_count }
+ *   skill_usage:       { skill_id, billable_days }
+ *   skill_setup:       { skill_id }
+ *   adjustment:        { reason? }
+ *
+ * Missing fields fall back to "?" so a malformed line still
+ * renders something readable rather than crashing the PDF.
+ */
+export function formatLineDescription(
+  line: LineForDescription,
+  locale: string
+): string {
+  const L = normaliseLocale(locale);
+  const m = line.metadata ?? {};
+  const tenant = line.tenantName ?? "—";
+  // Helper to fetch a metadata field with a safe fallback.
+  const f = (key: string): string | number => {
+    const v = (m as Record<string, unknown>)[key];
+    if (v === undefined || v === null) return "?";
+    return v as string | number;
+  };
+
+  switch (line.kind) {
+    case "tenant_monthly": {
+      const bd = f("billable_days");
+      const dim = f("days_in_month");
+      return {
+        de: `Monatliche Grundgebühr für ${tenant} (${bd}/${dim} Tage)`,
+        en: `Monthly fee for ${tenant} (${bd}/${dim} days)`,
+        fr: `Forfait mensuel pour ${tenant} (${bd}/${dim} jours)`,
+        it: `Canone mensile per ${tenant} (${bd}/${dim} giorni)`,
+      }[L];
+    }
+
+    case "tenant_setup":
+      return {
+        de: `Einrichtungsgebühr für ${tenant}`,
+        en: `Setup fee for ${tenant}`,
+        fr: `Frais de configuration pour ${tenant}`,
+        it: `Spese di attivazione per ${tenant}`,
+      }[L];
+
+    case "ai_usage": {
+      const r = f("requests");
+      return {
+        de: `KI-Inferenz-Nutzung (${r} Anfragen)`,
+        en: `AI inference usage (${r} requests)`,
+        fr: `Utilisation IA (${r} requêtes)`,
+        it: `Utilizzo IA (${r} richieste)`,
+      }[L];
+    }
+
+    case "threema_messages": {
+      const inC = f("in_count");
+      const outC = f("out_count");
+      return {
+        de: `Threema-Nachrichten (${inC} eingehend + ${outC} ausgehend)`,
+        en: `Threema messages (${inC} in + ${outC} out)`,
+        fr: `Messages Threema (${inC} entrants + ${outC} sortants)`,
+        it: `Messaggi Threema (${inC} in entrata + ${outC} in uscita)`,
+      }[L];
+    }
+
+    case "skill_usage": {
+      const skill = f("skill_id");
+      const bdRaw = (m as Record<string, unknown>)["billable_days"];
+      const bd = typeof bdRaw === "number" ? bdRaw : 0;
+      return {
+        de: `Skill: ${skill} (${days(bd, "de")})`,
+        en: `Skill: ${skill} (${days(bd, "en")})`,
+        fr: `Skill: ${skill} (${days(bd, "fr")})`,
+        it: `Skill: ${skill} (${days(bd, "it")})`,
+      }[L];
+    }
+
+    case "skill_setup": {
+      const skill = f("skill_id");
+      return {
+        de: `Einrichtungsgebühr Skill: ${skill}`,
+        en: `Setup fee skill: ${skill}`,
+        fr: `Frais de configuration skill: ${skill}`,
+        it: `Spese di attivazione skill: ${skill}`,
+      }[L];
+    }
+
+    case "adjustment": {
+      const reasonRaw = (m as Record<string, unknown>)["reason"];
+      const reason = typeof reasonRaw === "string" ? reasonRaw : null;
+      const base = {
+        de: "Anpassung",
+        en: "Adjustment",
+        fr: "Ajustement",
+        it: "Rettifica",
+      }[L];
+      return reason ? `${base}: ${reason}` : base;
+    }
+  }
+}