Understanding Business Logic

package main

import "fmt"

type order struct {
	subtotal int    // taka, already worked out from the menu prices
	hour     int    // when it was placed, 0-23
	newUser  bool   // first order ever?
	payment  string // "card" or "cash"
}

// quote holds the shop's business rules, and nothing else: no HTTP, no database.
// It returns the amount to pay, or the reason the order can't be placed.
func quote(o order) (int, string) {
	if o.hour < 10 || o.hour >= 22 {
		return 0, "we deliver 10:00-22:00 only"
	}
	if o.subtotal < 200 {
		return 0, "minimum order is 200 taka"
	}
	if o.payment == "cash" && o.subtotal > 3000 {
		return 0, "cash on delivery only up to 3000"
	}
	delivery := 60
	if o.subtotal >= 500 {
		delivery = 0 // free delivery from 500
	}
	discount := 0
	if o.newUser {
		discount = min(o.subtotal*20/100, 100) // 20% off the first order, at most 100
	}
	return o.subtotal - discount + delivery, ""
}

func main() {
	cases := []struct {
		name string
		o    order
	}{
		{"small lunch", order{150, 13, false, "card"}},
		{"regular lunch", order{350, 13, false, "card"}},
		{"family dinner", order{600, 20, false, "cash"}},
		{"first order, big", order{600, 20, true, "card"}},
		{"first order, small", order{400, 13, true, "cash"}},
		{"office party", order{3500, 12, false, "cash"}},
		{"midnight snack", order{300, 23, false, "card"}},
	}
	fmt.Printf("%-19s %8s %5s %-4s %-5s %s\n", "order", "subtotal", "time", "new", "pay", "result")
	for _, c := range cases {
		total, reason := quote(c.o)
		result := fmt.Sprintf("pay %d", total)
		if reason != "" {
			result = "refused: " + reason
		}
		isNew := map[bool]string{true: "yes", false: "no"}[c.o.newUser]
		fmt.Printf("%-19s %8d %02d:00 %-4s %-5s %s\n", c.name, c.o.subtotal, c.o.hour, isNew, c.o.payment, result)
	}
}

// quote holds the shop's business rules, and nothing else: no HTTP, no database.
// It returns [amount to pay, ""] or [0, the reason the order can't be placed].
function quote({ subtotal, hour, newUser, payment }) {
  if (hour < 10 || hour >= 22) return [0, "we deliver 10:00-22:00 only"];
  if (subtotal < 200) return [0, "minimum order is 200 taka"];
  if (payment === "cash" && subtotal > 3000) return [0, "cash on delivery only up to 3000"];
  const delivery = subtotal >= 500 ? 0 : 60; // free delivery from 500
  const discount = newUser ? Math.min(Math.floor((subtotal * 20) / 100), 100) : 0; // 20% off the first order, at most 100
  return [subtotal - discount + delivery, ""];
}

const cases = [
  ["small lunch", { subtotal: 150, hour: 13, newUser: false, payment: "card" }],
  ["regular lunch", { subtotal: 350, hour: 13, newUser: false, payment: "card" }],
  ["family dinner", { subtotal: 600, hour: 20, newUser: false, payment: "cash" }],
  ["first order, big", { subtotal: 600, hour: 20, newUser: true, payment: "card" }],
  ["first order, small", { subtotal: 400, hour: 13, newUser: true, payment: "cash" }],
  ["office party", { subtotal: 3500, hour: 12, newUser: false, payment: "cash" }],
  ["midnight snack", { subtotal: 300, hour: 23, newUser: false, payment: "card" }],
];
console.log(`${"order".padEnd(19)} ${"subtotal".padStart(8)} ${"time".padStart(5)} ${"new".padEnd(4)} ${"pay".padEnd(5)} result`);
for (const [name, o] of cases) {
  const [total, reason] = quote(o);
  const result = reason ? `refused: ${reason}` : `pay ${total}`;
  const time = `${String(o.hour).padStart(2, "0")}:00`;
  console.log(`${name.padEnd(19)} ${String(o.subtotal).padStart(8)} ${time} ${(o.newUser ? "yes" : "no").padEnd(4)} ${o.payment.padEnd(5)} ${result}`);
}

struct Order {
    subtotal: i64,          // taka, already worked out from the menu prices
    hour: u32,              // when it was placed, 0-23
    new_user: bool,         // first order ever?
    payment: &'static str, // "card" or "cash"
}

// quote holds the shop's business rules, and nothing else: no HTTP, no database.
// It returns the amount to pay, or the reason the order can't be placed.
fn quote(o: &Order) -> Result<i64, &'static str> {
    if o.hour < 10 || o.hour >= 22 {
        return Err("we deliver 10:00-22:00 only");
    }
    if o.subtotal < 200 {
        return Err("minimum order is 200 taka");
    }
    if o.payment == "cash" && o.subtotal > 3000 {
        return Err("cash on delivery only up to 3000");
    }
    let delivery = if o.subtotal >= 500 { 0 } else { 60 }; // free delivery from 500
    let discount = if o.new_user { (o.subtotal * 20 / 100).min(100) } else { 0 }; // 20% off the first order, at most 100
    Ok(o.subtotal - discount + delivery)
}

fn main() {
    let cases = [
        ("small lunch", Order { subtotal: 150, hour: 13, new_user: false, payment: "card" }),
        ("regular lunch", Order { subtotal: 350, hour: 13, new_user: false, payment: "card" }),
        ("family dinner", Order { subtotal: 600, hour: 20, new_user: false, payment: "cash" }),
        ("first order, big", Order { subtotal: 600, hour: 20, new_user: true, payment: "card" }),
        ("first order, small", Order { subtotal: 400, hour: 13, new_user: true, payment: "cash" }),
        ("office party", Order { subtotal: 3500, hour: 12, new_user: false, payment: "cash" }),
        ("midnight snack", Order { subtotal: 300, hour: 23, new_user: false, payment: "card" }),
    ];
    println!("{:<19} {:>8} {:>5} {:<4} {:<5} result", "order", "subtotal", "time", "new", "pay");
    for (name, o) in &cases {
        let result = match quote(o) {
            Ok(total) => format!("pay {total}"),
            Err(reason) => format!("refused: {reason}"),
        };
        let new = if o.new_user { "yes" } else { "no" };
        println!("{:<19} {:>8} {:02}:00 {:<4} {:<5} {}", name, o.subtotal, o.hour, new, o.payment, result);
    }
}

from dataclasses import dataclass


@dataclass
class Order:
    subtotal: int  # taka, already worked out from the menu prices
    hour: int  # when it was placed, 0-23
    new_user: bool  # first order ever?
    payment: str  # "card" or "cash"


def quote(o):
    """The shop's business rules, and nothing else: no HTTP, no database.
    Returns (amount to pay, "") or (0, the reason the order can't be placed)."""
    if o.hour < 10 or o.hour >= 22:
        return 0, "we deliver 10:00-22:00 only"
    if o.subtotal < 200:
        return 0, "minimum order is 200 taka"
    if o.payment == "cash" and o.subtotal > 3000:
        return 0, "cash on delivery only up to 3000"
    delivery = 0 if o.subtotal >= 500 else 60  # free delivery from 500
    discount = min(o.subtotal * 20 // 100, 100) if o.new_user else 0  # 20% off the first order, at most 100
    return o.subtotal - discount + delivery, ""


cases = [
    ("small lunch", Order(150, 13, False, "card")),
    ("regular lunch", Order(350, 13, False, "card")),
    ("family dinner", Order(600, 20, False, "cash")),
    ("first order, big", Order(600, 20, True, "card")),
    ("first order, small", Order(400, 13, True, "cash")),
    ("office party", Order(3500, 12, False, "cash")),
    ("midnight snack", Order(300, 23, False, "card")),
]
print(f"{'order':<19} {'subtotal':>8} {'time':>5} {'new':<4} {'pay':<5} result")
for name, o in cases:
    total, reason = quote(o)
    result = f"refused: {reason}" if reason else f"pay {total}"
    new = "yes" if o.new_user else "no"
    print(f"{name:<19} {o.subtotal:>8} {o.hour:02d}:00 {new:<4} {o.payment:<5} {result}")

public class Main {
    // subtotal in taka (already worked out from the menu prices), hour 0-23,
    // newUser = first order ever, payment = "card" or "cash".
    record Order(int subtotal, int hour, boolean newUser, String payment) {}

    // The answer: the amount to pay, or the reason the order can't be placed.
    record Quote(int total, String reason) {}

    // quote holds the shop's business rules, and nothing else: no HTTP, no database.
    static Quote quote(Order o) {
        if (o.hour() < 10 || o.hour() >= 22) return new Quote(0, "we deliver 10:00-22:00 only");
        if (o.subtotal() < 200) return new Quote(0, "minimum order is 200 taka");
        if (o.payment().equals("cash") && o.subtotal() > 3000) return new Quote(0, "cash on delivery only up to 3000");
        int delivery = o.subtotal() >= 500 ? 0 : 60; // free delivery from 500
        int discount = o.newUser() ? Math.min(o.subtotal() * 20 / 100, 100) : 0; // 20% off the first order, at most 100
        return new Quote(o.subtotal() - discount + delivery, "");
    }

    public static void main(String[] args) {
        Object[][] cases = {
            {"small lunch", new Order(150, 13, false, "card")},
            {"regular lunch", new Order(350, 13, false, "card")},
            {"family dinner", new Order(600, 20, false, "cash")},
            {"first order, big", new Order(600, 20, true, "card")},
            {"first order, small", new Order(400, 13, true, "cash")},
            {"office party", new Order(3500, 12, false, "cash")},
            {"midnight snack", new Order(300, 23, false, "card")},
        };
        System.out.printf("%-19s %8s %5s %-4s %-5s %s%n", "order", "subtotal", "time", "new", "pay", "result");
        for (Object[] c : cases) {
            Order o = (Order) c[1];
            Quote q = quote(o);
            String result = q.reason().isEmpty() ? "pay " + q.total() : "refused: " + q.reason();
            System.out.printf("%-19s %8d %02d:00 %-4s %-5s %s%n", c[0], o.subtotal(), o.hour(), o.newUser() ? "yes" : "no", o.payment(), result);
        }
    }
}