init

app/lib/units.ts

@@ -0,0 +1,54 @@
+import type { BaseUnit, RecipeUnit, StoreItem } from "@/app/types";
+
+// ---------------------------------------------------------------------------
+// Unit conversion: recipe units → the catalog item's base unit.
+//
+// Weight ↔ volume crossings (e.g. "1 cup rice" for a rice bag sold by weight)
+// use the item's `gramsPerMl`. Anything else that doesn't line up is a data
+// bug, so we throw loudly instead of guessing.
+// ---------------------------------------------------------------------------
+
+const GRAMS_PER: Partial<Record<RecipeUnit, number>> = { g: 1, oz: 28.35, lb: 453.6 };
+const ML_PER: Partial<Record<RecipeUnit, number>> = { ml: 1, tsp: 4.93, tbsp: 14.79, cup: 236.6 };
+
+export function toBaseUnit(amount: number, unit: RecipeUnit, item: StoreItem): number {
+  const base = item.baseUnit;
+
+  if (base === "each") {
+    if (unit === "each") return amount;
+    throw new Error(`"${item.id}" is sold by count; recipe used "${unit}"`);
+  }
+
+  if (base === "g") {
+    if (GRAMS_PER[unit] !== undefined) return amount * GRAMS_PER[unit]!;
+    if (ML_PER[unit] !== undefined && item.gramsPerMl) return amount * ML_PER[unit]! * item.gramsPerMl;
+  }
+
+  if (base === "ml") {
+    if (ML_PER[unit] !== undefined) return amount * ML_PER[unit]!;
+  }
+
+  throw new Error(`Can't convert ${unit} → ${base} for "${item.id}" (missing gramsPerMl?)`);
+}
+
+/** Pretty-print a base-unit amount using US kitchen units. */
+export function formatAmount(amount: number, base: BaseUnit): string {
+  if (base === "each") {
+    const rounded = Math.round(amount * 10) / 10;
+    return `${rounded}`;
+  }
+  if (base === "g") {
+    const lb = amount / 453.6;
+    return lb >= 1 ? `${lb.toFixed(1)} lb` : `${(amount / 28.35).toFixed(1)} oz`;
+  }
+  // ml
+  const cups = amount / 236.6;
+  // Number(...) drops trailing zeros: 2.50 → 2.5, 2.00 → 2
+  if (cups >= 0.25) return `${Number(cups.toFixed(cups >= 4 ? 0 : 2))} cup`;
+  const tbsp = amount / 14.79;
+  return tbsp >= 1 ? `${tbsp.toFixed(1)} tbsp` : `${(amount / 4.93).toFixed(1)} tsp`;
+}
+
+export function formatUsd(value: number): string {
+  return value.toLocaleString("en-US", { style: "currency", currency: "USD" });
+}