Add solution for Challenge 7 by onomica (#1884)

Auto-merged after 2 days with all checks passing.

PR: #1884
Author: @onomica

Author: onomica

challenge-7/submissions/onomica/solution-template.go

@@ -0,0 +1,154 @@
+package challenge7
+
+import (
+	"fmt"
+	"sync"
+)
+
+type BankAccount struct {
+	ID         string
+	Owner      string
+	Balance    float64
+	MinBalance float64
+	mu         sync.Mutex
+}
+
+const (
+	MaxTransactionAmount = 10000.0
+)
+
+type AccountError struct {
+	ID    string
+	Owner string
+}
+
+func (e *AccountError) Error() string {
+	return fmt.Sprintf("account error: %s: %s", e.ID, e.Owner)
+}
+
+type InsufficientFundsError struct {
+	Balance float64
+	Amount  float64
+}
+
+func (e *InsufficientFundsError) Error() string {
+	return fmt.Sprintf("insufficient funds: balance $%.2f, attempted to withdraw $%.2f", e.Balance, e.Amount)
+}
+
+type NegativeAmountError struct {
+	Amount float64
+}
+
+func (e *NegativeAmountError) Error() string {
+	return fmt.Sprintf("negative amount: $%.2f", e.Amount)
+}
+
+type ExceedsLimitError struct {
+	Amount float64
+	Limit  float64
+}
+
+func (e *ExceedsLimitError) Error() string {
+	return fmt.Sprintf("amount $%.2f exceeds limit $%.2f", e.Amount, e.Limit)
+}
+
+func NewBankAccount(id, owner string, initialBalance, minBalance float64) (*BankAccount, error) {
+	if id == "" || owner == "" {
+		return nil, &AccountError{
+			ID:    id,
+			Owner: owner,
+		}
+	}
+
+	if initialBalance < 0 {
+		return nil, &NegativeAmountError{Amount: initialBalance}
+	}
+	if minBalance < 0 {
+		return nil, &NegativeAmountError{Amount: minBalance}
+	}
+	if initialBalance < minBalance {
+		return nil, &InsufficientFundsError{
+			Balance: initialBalance,
+			Amount:  minBalance,
+		}
+	}
+
+	return &BankAccount{
+		ID:         id,
+		Owner:      owner,
+		Balance:    initialBalance,
+		MinBalance: minBalance,
+	}, nil
+}
+
+func (a *BankAccount) Deposit(amount float64) error {
+	if err := validateAmount(amount); err != nil {
+		return err
+	}
+
+	a.mu.Lock()
+	defer a.mu.Unlock()
+	a.Balance += amount
+	return nil
+}
+
+func (a *BankAccount) Withdraw(amount float64) error {
+	if err := validateAmount(amount); err != nil {
+		return err
+	}
+
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	if a.Balance-amount < a.MinBalance {
+		return &InsufficientFundsError{
+			Balance: a.Balance,
+			Amount:  amount,
+		}
+	}
+
+	a.Balance -= amount
+	return nil
+}
+
+func (a *BankAccount) Transfer(amount float64, target *BankAccount) error {
+	if a == target {
+		return nil
+	}
+
+	if err := validateAmount(amount); err != nil {
+		return err
+	}
+
+	first, second := a, target
+	if first.ID > second.ID {
+		first, second = second, first
+	}
+
+	first.mu.Lock()
+	defer first.mu.Unlock()
+	second.mu.Lock()
+	defer second.mu.Unlock()
+
+	if a.Balance-amount < a.MinBalance {
+		return &InsufficientFundsError{
+			Balance: a.Balance,
+			Amount:  amount,
+		}
+	}
+
+	a.Balance -= amount
+	target.Balance += amount
+
+	return nil
+}
+
+func validateAmount(amount float64) error {
+	if amount < 0 {
+		return &NegativeAmountError{Amount: amount}
+	}
+	if amount > MaxTransactionAmount {
+		return &ExceedsLimitError{Amount: amount, Limit: MaxTransactionAmount}
+	}
+	return nil
+}