// Market-basket analysis: transactions of (order, product) lines. Compute
// product popularity, basket sizes per order, and the average order value.
// Demonstrates group_by to size baskets, agg for revenue, and count_by.

cell Basket {
    on lines() {
        return list(
            map("order", "o1", "product", "milk",  "price", 2),
            map("order", "o1", "product", "bread", "price", 3),
            map("order", "o1", "product", "eggs",  "price", 4),
            map("order", "o2", "product", "milk",  "price", 2),
            map("order", "o2", "product", "eggs",  "price", 4),
            map("order", "o3", "product", "bread", "price", 3),
            map("order", "o3", "product", "milk",  "price", 2),
            map("order", "o3", "product", "jam",   "price", 5)
        )
    }

    // How many times each product was bought, most popular first.
    on popularity() {
        return lines()
            |> agg("product", "price:count")
            |> sort_by("price_count", "desc")
    }

    // Basket size (number of lines) per order, via agg's per-group count.
    on basket_sizes() {
        return lines()
            |> agg("order", "price:count")
            |> sort_by("count", "desc")
    }

    // Order value per order.
    on order_values() {
        return lines() |> agg("order", "price:sum") |> sort_by("price_sum", "desc")
    }

    on milk_count() { return count_by(lines(), "product", "milk") }

    on run() {
        for r in popularity() { print("{r.product}: {r.price_count}") }
        for r in basket_sizes() { print("{r.order}: {r.count} items") }
        return order_values()
    }
}

cell test BasketTests {
    rules {
        // milk appears in 3 orders
        assert milk_count() == 3
        assert popularity()[0].product == "milk"
        // 4 distinct products: milk, bread, eggs, jam
        assert len(popularity()) == 4
        // o1 value = 2 + 3 + 4 = 9; o3 = 3 + 2 + 5 = 10 (highest)
        assert order_values()[0].order == "o3"
        assert order_values()[0].price_sum == 10
        // o2 value = 2 + 4 = 6
        assert (order_values() |> filter_by("order", "=", "o2"))[0].price_sum == 6
    }
}