— Scene III —

What are Plato's Pizzas best and worst selling pizzas?

package database 
 
type PlatosPizzaDatabase interface { 
	InsertMetadata(MetadataEntry) error 
	InsertOrder(Order) error 
	InsertOrderDetail(OrderDetail) error 
	InsertPizza(Pizza) error 
	InsertPizzaType(PizzaType) error 
	... 
}

// Order represents an order of pizzas, one or many pizzas per order 
type Order struct { 
 
	// Unique identifier for each order placed by a table 
	Id int 
 
	// Date & time the order was placed 
	// (entered into the system prior to cooking & serving) 
	Datetime time.Time 
}

// OrderDetail represents a specific pizza type order, one or more pizzas, 
// within an order 
type OrderDetail struct { 
 
	// Unique identifier for each pizza placed within each order 
	// (pizzas of the same type and size are kept in the same row, and the quantity increases) 
	Id int 
 
	// Foreign key that ties the details in each order to the order itself 
	OrderId int 
 
	// Foreign key that ties the pizza ordered to its details, like size and price 
	PizzaId string 
 
	// Quantity ordered for each pizza of the same type and size 
	Quantity int 
}

// Pizza represents a specific pizza type at a specific size 
type Pizza struct { 
 
	// Unique identifier for each pizza (constituted by its type and size) 
	Id string 
 
	// Foreign key that ties each pizza to its broader pizza type 
	TypeId string 
 
	// Size of the pizza (Small, Medium, Large, X Large, or XX Large) 
	Size string 
 
	// Price of the pizza in USD 
	Price float64 
}

type PizzaType struct { 
 
	// Unique identifier for each pizza type 
	Id string 
 
	// Name of the pizza as shown in the menu 
	Name string 
 
	// Category that the pizza fall under in the menu 
	// (Classic, Chicken, Supreme, or Veggie) 
	Category string 
 
	// Comma-delimited ingredients used in the pizza as shown in the menu 
	// (they all include Mozzarella Cheese, even if not specified; and they all 
	// include Tomato Sauce, unless another sauce is specified) 
	Ingredients string 
}

package database 
 
type inMemory struct { 
	dataDictionaries []MetadataEntry 
	orders           []Order 
	orderDetails     []OrderDetail 
	pizzas           []Pizza 
	pizzaTypes       []PizzaType 
} 
 
func NewInMemoryDatabase() *inMemory { 
	return &inMemory{} 
} 
 
... 
 
func (db *inMemory) InsertOrder(order Order) error { 
	db.orders = append(db.orders, order) 
	return nil 
} 
 
...

const ( 
	DatetimeFormat = "2006-01-02 15:04:05" 
)

func InsertOrdersFromCSV(db PlatosPizzaDatabase, filename string) error { 
	records, e := readCSV(filename) 
	if e != nil { 
		return ErrDatabase.CausedBy(e, "Failure to read orders %q", filename) 
	} 
 
	orders := make([]Order, len(records)) 
	for i, record := range records { 
		id, e := strconv.Atoi(record[0]) 
		if e != nil { 
			return ErrDatabase.CausedBy(e, "Bad order ID discovered") 
		} 
 
		datetime, e := time.Parse(DatetimeFormat, record[1]+" "+record[2]) 
		if e != nil { 
			return ErrDatabase.CausedBy(e, "Bad order date or time discovered") 
		} 
 
		orders[i] = Order{ 
			Id:       id, 
			Datetime: datetime, 
		} 
	} 
 
	if e = db.InsertOrders(orders...); e != nil { 
		return ErrDatabase.Wrap(e) 
	} 
 
	return nil 
}

func readCSV(filename string) ([][]string, error) { 
	f, e := os.Open(filename) 
	if e != nil { 
		return nil, ErrCSVFile.CausedBy(e, "Could not open file %q", filename) 
	} 
	defer f.Close() 
 
	r := csv.NewReader(f) 
	records, e := r.ReadAll() 
 
	if e != nil { 
		return nil, ErrCSVFile.CausedBy(e, "Could not read file %q", filename) 
	} 
 
	records = records[1:] // Remove header 
	return records, nil 
}

package workflow 
 
import ( 
	"github.com/PaulioRandall/analytics-platos-pizza/act-3/pkg/database" 
	"github.com/PaulioRandall/analytics-platos-pizza/act-3/pkg/err" 
) 
 
var ErrExecuting = err.Track("Failed to execute workflow") 
 
func Execute() error { 
	db := database.NewInMemoryDatabase() 
 
	if e := insertCSVData(db); e != nil { 
		return ErrExecuting.TraceWrap(e, "Inserting CSV data into database") 
	} 
 
	return nil 
} 
 
func insertCSVData(db database.PlatosPizzaDatabase) error { 
 
	... 
 
	e = database.InsertOrdersFromCSV(db, "../data/orders.csv") 
	if e != nil { 
		return err.Wrap(e, "Failed to insert orders") 
	} 
 
	... 
 
	return nil 
}