Add Lab: Group Discount (Section 1: Composing Types: Part II)

01-composing-types-part-2/lab/README.md

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+# Lab: Group Discount 🛍️
+
+> **Section 1: Composing Types: Part II**
+
+We're trying to group the discounts that we offer in our online store, but we're
+having a tough time creating the types for these groups. Can you help us?!
+
+## Requirements
+
+We got stuck creating the `GroupedDiscounts` type, so it currently allows for `any`
+type of value.
+
+1. Change the `GroupedDiscounts` type into a mapped type that allows for grouping
+discounts by their `kind` property.
+2. Test that your code runs correctly with `npx tsx index.ts`.
+
+### Extra Credit
+
+The `DiscountBase` has a wide type of `string` for the `code` property, but we'd
+like to ensure that the discount code for each kind of discount matches a specific
+format.
+
+Use the existing `code` values to help you establish the formats, and then create
+template literal types to enforce a specific format for each kind of discount.

01-composing-types-part-2/lab/solution/index.ts

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+type DiscountBase = {
+  description: string;
+};
+
+type PercentageDiscount = DiscountBase & {
+  kind: "percentage";
+  code: `PERCENT_OFF_${number}`;
+  percentage: number;
+};
+
+type AmountDiscount = DiscountBase & {
+  kind: "amount";
+  code: `AMOUNT_OFF_${number}`;
+  amount: number;
+};
+
+type QuantityDiscount = DiscountBase & {
+  kind: "quantity";
+  code: `BUY_${number}_GET_${number}_FREE`;
+  quantity: number;
+  free: number;
+};
+
+type Discount = PercentageDiscount | AmountDiscount | QuantityDiscount;
+
+// -- Discounts --
+
+const discounts: Discount[] = [
+  {
+    code: "PERCENT_OFF_10",
+    description: "10% off",
+    kind: "percentage",
+    percentage: 10,
+  },
+  {
+    code: "AMOUNT_OFF_5",
+    description: "$5 off",
+    kind: "amount",
+    amount: 5,
+  },
+  {
+    code: "PERCENT_OFF_30",
+    description: "30% off",
+    kind: "percentage",
+    percentage: 30,
+  },
+  {
+    kind: "quantity",
+    code: "BUY_1_GET_1_FREE",
+    description: "Buy 1 get 1 free",
+    quantity: 1,
+    free: 1,
+  },
+  {
+    kind: "amount",
+    code: "AMOUNT_OFF_15",
+    description: "$15 off",
+    amount: 15,
+  },
+  {
+    kind: "quantity",
+    code: "BUY_3_GET_1_FREE",
+    description: "Buy 3 get 1 free",
+    quantity: 3,
+    free: 1,
+  },
+];
+
+// -- Grouped discounts --
+
+type GroupedDiscounts = {
+  [Key in Discount["kind"]]?: Discount[];
+};
+
+// Alternative `GroupedDiscounts` type using built-in utility types.
+{
+  type GroupedDiscounts = Partial<Record<Discount["kind"], Discount[]>>;
+}
+
+function groupDiscounts(discounts: Discount[]): GroupedDiscounts {
+  const groups: GroupedDiscounts = {};
+
+  for (let discount of discounts) {
+    groups[discount.kind] = groups[discount.kind] ?? [];
+    groups[discount.kind]?.push(discount);
+  }
+
+  return groups;
+}
+
+const groupedDiscounts = groupDiscounts(discounts);
+
+console.log(groupedDiscounts);

01-composing-types-part-2/lab/solution/tsconfig.json

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+{
+  "extends": "@total-typescript/tsconfig/tsc/no-dom/app"
+}

01-composing-types-part-2/lab/start/index.ts

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+type DiscountBase = {
+  code: string;
+  description: string;
+};
+
+type PercentageDiscount = DiscountBase & {
+  kind: "percentage";
+  percentage: number;
+};
+
+type AmountDiscount = DiscountBase & {
+  kind: "amount";
+  amount: number;
+};
+
+type QuantityDiscount = DiscountBase & {
+  kind: "quantity";
+  quantity: number;
+  free: number;
+};
+
+type Discount = PercentageDiscount | AmountDiscount | QuantityDiscount;
+
+// -- Discounts --
+
+const discounts: Discount[] = [
+  {
+    code: "PERCENT_OFF_10",
+    description: "10% off",
+    kind: "percentage",
+    percentage: 10,
+  },
+  {
+    code: "AMOUNT_OFF_5",
+    description: "$5 off",
+    kind: "amount",
+    amount: 5,
+  },
+  {
+    code: "PERCENT_OFF_30",
+    description: "30% off",
+    kind: "percentage",
+    percentage: 30,
+  },
+  {
+    kind: "quantity",
+    code: "BUY_1_GET_1_FREE",
+    description: "Buy 1 get 1 free",
+    quantity: 1,
+    free: 1,
+  },
+  {
+    kind: "amount",
+    code: "AMOUNT_OFF_15",
+    description: "$15 off",
+    amount: 15,
+  },
+  {
+    kind: "quantity",
+    code: "BUY_3_GET_1_FREE",
+    description: "Buy 3 get 1 free",
+    quantity: 3,
+    free: 1,
+  },
+];
+
+// -- Grouped discounts --
+
+type GroupedDiscounts = any;
+
+function groupDiscounts(discounts: Discount[]): GroupedDiscounts {
+  const groups: GroupedDiscounts = {};
+
+  for (let discount of discounts) {
+    groups[discount.kind] = groups[discount.kind] ?? [];
+    groups[discount.kind]?.push(discount);
+  }
+
+  return groups;
+}
+
+const groupedDiscounts = groupDiscounts(discounts);
+
+console.log(groupedDiscounts);

01-composing-types-part-2/lab/start/tsconfig.json

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+{
+  "extends": "@total-typescript/tsconfig/tsc/no-dom/app"
+}