add simplification steps

csharp-fp1/Application/AccountApplicationService.cs

@@ -0,0 +1,17 @@
+using CsharpFp1.Domain;
+
+namespace CsharpFp1.Application;
+
+public static class AccountApplicationService
+{
+    public static void WithdrawMoney(IAccountRepository repository, Guid accountId, decimal amount)
+    {
+        var account =
+            repository.GetById(new AccountId(accountId))
+            ?? throw new InvalidOperationException("Account not found.");
+
+        account.Withdraw(new Money(amount));
+
+        repository.Save(account);
+    }
+}

csharp-fp1/Domain/Account.cs

@@ -0,0 +1,36 @@
+namespace CsharpFp1.Domain;
+
+/// Domain entity / aggregate root representing a bank account
+public sealed class Account : AggregateRoot<AccountId>
+{
+    public Money Balance { get; private set; }
+
+    // Often present to satisfy serializers / ORMs.
+    private Account()
+    {
+        Balance = new Money(0);
+    }
+
+    public Account(AccountId id, Money openingBalance)
+    {
+        if (openingBalance.Amount < 0)
+            throw new ArgumentOutOfRangeException(nameof(openingBalance));
+
+        Id = id;
+
+        Balance = openingBalance;
+    }
+
+    // Domain behaviour attached to the entity.
+    public void Withdraw(Money amount)
+    {
+        if (amount.Amount <= 0)
+            throw new InvalidOperationException("Withdrawal amount must be positive.");
+
+        // Sometimes, validation is modelled with custom exceptions instead
+        if (Balance.Amount - amount.Amount < 0)
+            throw new InsufficientBalanceException(Balance, amount);
+
+        Balance = Balance.Subtract(amount);
+    }
+}

csharp-fp1/Domain/AccountId.cs

@@ -0,0 +1,4 @@
+namespace CsharpFp1.Domain;
+
+/// Value object used to wrap the aggregate identity
+public sealed record AccountId(Guid Value);

csharp-fp1/Domain/AggregateRoot.cs

@@ -0,0 +1,7 @@
+namespace CsharpFp1.Domain;
+
+/// Conventional DDD base type for aggregates
+public abstract class AggregateRoot<TId>
+{
+    public TId Id { get; protected set; } = default!;
+}

csharp-fp1/Domain/IAccountRepository.cs

@@ -0,0 +1,8 @@
+namespace CsharpFp1.Domain;
+
+/// Repository abstraction used to load and save accounts
+public interface IAccountRepository
+{
+    Account? GetById(AccountId id);
+    void Save(Account account);
+}

csharp-fp1/Domain/InsufficientBalanceException.cs

@@ -0,0 +1,17 @@
+namespace CsharpFp1.Domain;
+
+/// Custom domain exception thrown when a withdrawal would cause the balance to go below zero
+public sealed class InsufficientBalanceException : InvalidOperationException
+{
+    public Money CurrentBalance { get; }
+    public Money RequestedAmount { get; }
+
+    public InsufficientBalanceException(Money currentBalance, Money requestedAmount)
+        : base(
+            $"Insufficient balance. Current: {currentBalance.Amount:0.00}, Requested: {requestedAmount.Amount:0.00}"
+        )
+    {
+        CurrentBalance = currentBalance;
+        RequestedAmount = requestedAmount;
+    }
+}

csharp-fp1/Domain/Money.cs

@@ -0,0 +1,33 @@
+namespace CsharpFp1.Domain;
+
+/// Value object used to represent money and enforce simple invariants.
+/// Note that this implementation uses immutable patterns for the data
+/// by returning a new instance for each modification. This is an early
+/// recommendation for DDD with OO, but not necessarily the common practice
+/// in many real-world implementations.
+public sealed class Money
+{
+    // Potentially with a setter - see note above
+    public decimal Amount { get; }
+
+    public Money(decimal amount)
+    {
+        Amount = amount;
+    }
+
+    // In many existing DDD/OO codebases you may actually see the use
+    // of mutable value types.
+    //
+    // public void Add(Money other)
+    // {
+    //     this.Amount += other.Amount;
+    // }
+
+    // On the other hand, sometimes these helpers may be left out
+    // and operations encoded directly "from the outside":
+    // newBalance = new Money(oldBalance.Amount - charge.Amount)
+    //
+    public Money Add(Money other) => new(Amount + other.Amount);
+
+    public Money Subtract(Money other) => new(Amount - other.Amount);
+}

csharp-fp1/Infrastructure/InMemoryAccountRepository.cs

@@ -0,0 +1,27 @@
+using CsharpFp1.Domain;
+
+namespace CsharpFp1.Infrastructure;
+
+/// Simple in-memory repository for demonstration
+public class InMemoryAccountRepository : IAccountRepository
+{
+    private readonly Dictionary<AccountId, Account> _accounts = new();
+
+    public Account? GetById(AccountId id)
+    {
+        var found = _accounts.TryGetValue(id, out var account);
+        Console.WriteLine(
+            found ? $"[Repo] Loaded account {id.Value}" : $"[Repo] Account {id.Value} not found"
+        );
+
+        return found ? account : null;
+    }
+
+    public void Save(Account account)
+    {
+        _accounts[account.Id] = account;
+        Console.WriteLine(
+            $"[Repo] Saved account {account.Id.Value} with balance {account.Balance.Amount:0.00}"
+        );
+    }
+}

csharp-fp1/Program.cs

@@ -0,0 +1,25 @@
+using CsharpFp1.Application;
+using CsharpFp1.Domain;
+using CsharpFp1.Infrastructure;
+
+namespace CsharpFp1;
+
+public class Program
+{
+    public static void Main()
+    {
+        Console.WriteLine("[csharp-fp1] Starting withdraw money demo...");
+
+        var repository = new InMemoryAccountRepository();
+
+        var accountId = Guid.NewGuid();
+        Console.WriteLine($"[csharp-fp1] Seeding account {accountId} with opening balance 200.00");
+        repository.Save(new Account(new AccountId(accountId), new Money(200m)));
+
+        decimal amount = 100m;
+        Console.WriteLine($"[csharp-fp1] Executing withdrawal {amount:0.00} from account {accountId}");
+        AccountApplicationService.WithdrawMoney(repository, accountId, amount);
+
+        Console.WriteLine("[csharp-fp1] Demo completed.");
+    }
+}

csharp-fp1/csharp-fp1.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <RootNamespace>csharp_fp1</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+</Project>

csharp-fp2/Application/AccountApplicationService.cs

@@ -0,0 +1,17 @@
+using CsharpFp2.Domain;
+
+namespace CsharpFp2.Application;
+
+public static class AccountApplicationService
+{
+    public static void WithdrawMoney(IAccountRepository repository, Guid accountId, decimal amount)
+    {
+        var account =
+            repository.GetById(accountId)
+            ?? throw new InvalidOperationException("Account not found.");
+
+        account.Withdraw(new Money(amount));
+
+        repository.Save(account);
+    }
+}

csharp-fp2/Domain/Account.cs

@@ -0,0 +1,37 @@
+namespace CsharpFp2.Domain;
+
+/// Domain entity / aggregate root representing a bank account
+public sealed class Account
+{
+    public Guid Id { get; private set; }
+    public Money Balance { get; private set; }
+
+    // Often present to satisfy serializers / ORMs.
+    private Account()
+    {
+        Balance = new Money(0);
+    }
+
+    public Account(Guid id, Money openingBalance)
+    {
+        if (openingBalance.Amount < 0)
+            throw new ArgumentOutOfRangeException(nameof(openingBalance));
+
+        Id = id;
+
+        Balance = openingBalance;
+    }
+
+    // Domain behaviour attached to the entity.
+    public void Withdraw(Money amount)
+    {
+        if (amount.Amount <= 0)
+            throw new InvalidOperationException("Withdrawal amount must be positive.");
+
+        // Sometimes, validation is modelled with custom exceptions instead
+        if (Balance.Amount - amount.Amount < 0)
+            throw new InsufficientBalanceException(Balance, amount);
+
+        Balance = Balance.Subtract(amount);
+    }
+}

csharp-fp2/Domain/IAccountRepository.cs

@@ -0,0 +1,8 @@
+namespace CsharpFp2.Domain;
+
+/// Repository abstraction used to load and save accounts
+public interface IAccountRepository
+{
+    Account? GetById(Guid id);
+    void Save(Account account);
+}

csharp-fp2/Domain/InsufficientBalanceException.cs

@@ -0,0 +1,17 @@
+namespace CsharpFp2.Domain;
+
+/// Custom domain exception thrown when a withdrawal would cause the balance to go below zero
+public sealed class InsufficientBalanceException : InvalidOperationException
+{
+    public Money CurrentBalance { get; }
+    public Money RequestedAmount { get; }
+
+    public InsufficientBalanceException(Money currentBalance, Money requestedAmount)
+        : base(
+            $"Insufficient balance. Current: {currentBalance.Amount:0.00}, Requested: {requestedAmount.Amount:0.00}"
+        )
+    {
+        CurrentBalance = currentBalance;
+        RequestedAmount = requestedAmount;
+    }
+}

csharp-fp2/Domain/Money.cs

@@ -0,0 +1,33 @@
+namespace CsharpFp2.Domain;
+
+/// Value object used to represent money and enforce simple invariants.
+/// Note that this implementation uses immutable patterns for the data
+/// by returning a new instance for each modification. This is an early
+/// recommendation for DDD with OO, but not necessarily the common practice
+/// in many real-world implementations.
+public sealed class Money
+{
+    // Potentially with a setter - see note above
+    public decimal Amount { get; }
+
+    public Money(decimal amount)
+    {
+        Amount = amount;
+    }
+
+    // In many existing DDD/OO codebases you may actually see the use
+    // of mutable value types.
+    //
+    // public void Add(Money other)
+    // {
+    //     this.Amount += other.Amount;
+    // }
+
+    // On the other hand, sometimes these helpers may be left out
+    // and operations encoded directly "from the outside":
+    // newBalance = new Money(oldBalance.Amount - charge.Amount)
+    //
+    public Money Add(Money other) => new(Amount + other.Amount);
+
+    public Money Subtract(Money other) => new(Amount - other.Amount);
+}

csharp-fp2/Infrastructure/InMemoryAccountRepository.cs

@@ -0,0 +1,25 @@
+using CsharpFp2.Domain;
+
+namespace CsharpFp2.Infrastructure;
+
+/// Simple in-memory repository for demonstration
+public class InMemoryAccountRepository : IAccountRepository
+{
+    private readonly Dictionary<Guid, Account> _accounts = new();
+
+    public Account? GetById(Guid id)
+    {
+        var found = _accounts.TryGetValue(id, out var account);
+        Console.WriteLine(found ? $"[Repo] Loaded account {id}" : $"[Repo] Account {id} not found");
+
+        return found ? account : null;
+    }
+
+    public void Save(Account account)
+    {
+        _accounts[account.Id] = account;
+        Console.WriteLine(
+            $"[Repo] Saved account {account.Id} with balance {account.Balance.Amount:0.00}"
+        );
+    }
+}

csharp-fp2/Program.cs

@@ -0,0 +1,27 @@
+using CsharpFp2.Application;
+using CsharpFp2.Domain;
+using CsharpFp2.Infrastructure;
+
+namespace CsharpFp2;
+
+public class Program
+{
+    public static void Main()
+    {
+        Console.WriteLine("[csharp-fp2] Starting withdraw money demo...");
+
+        var repository = new InMemoryAccountRepository();
+
+        var accountId = Guid.NewGuid();
+        Console.WriteLine($"[csharp-fp2] Seeding account {accountId} with opening balance 200.00");
+        repository.Save(new Account(accountId, new Money(200m)));
+
+        decimal amount = 100m;
+        Console.WriteLine(
+            $"[csharp-fp2] Executing withdrawal {amount:0.00} from account {accountId}"
+        );
+        AccountApplicationService.WithdrawMoney(repository, accountId, amount);
+
+        Console.WriteLine("[csharp-fp2] Demo completed.");
+    }
+}

csharp-fp2/csharp-fp2.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <RootNamespace>csharp_fp2</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+</Project>

csharp-oop/Program.cs

@@ -9,22 +9,22 @@ public class Program
 {
     public static void Main()
     {
-        Console.WriteLine("[Program] Starting withdraw money demo...");
+        Console.WriteLine("[csharp-oop] Starting withdraw money demo...");
 
         var repository = new InMemoryAccountRepository();
         var handler = new WithdrawMoneyHandler(repository);
 
         var accountId = Guid.NewGuid();
-        Console.WriteLine($"[Program] Seeding account {accountId} with opening balance 200.00");
+        Console.WriteLine($"[csharp-oop] Seeding account {accountId} with opening balance 200.00");
         repository.Save(new Account(new AccountId(accountId), new Money(200m)));
 
         var command = new WithdrawMoneyCommand { AccountId = accountId, Amount = 100m };
         Console.WriteLine(
-            $"[Program] Dispatching command: withdraw {command.Amount:0.00} from account {command.AccountId}"
+            $"[csharp-oop] Dispatching command: withdraw {command.Amount:0.00} from account {command.AccountId}"
         );
 
         handler.Handle(command);
 
-        Console.WriteLine("[Program] Demo completed.");
+        Console.WriteLine("[csharp-oop] Demo completed.");
     }
 }

csharp.sln

@@ -9,6 +9,12 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "csharp-oop", "csharp-oop\cs
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "csharp-oop.Tests", "csharp-oop.Tests\csharp-oop.Tests.csproj", "{9FD0C8F4-A23B-4C68-A365-86E7EF5623D8}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "FP", "FP", "{89C53051-77F9-4C1C-ABE5-6D54AB398471}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "csharp-fp1", "csharp-fp1\csharp-fp1.csproj", "{561BCA96-76DF-4A33-B767-4AD7CD3246B4}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "csharp-fp2", "csharp-fp2\csharp-fp2.csproj", "{7237398A-2E8B-4161-BA15-DB090395A1F2}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -43,6 +49,30 @@ Global
 		{9FD0C8F4-A23B-4C68-A365-86E7EF5623D8}.Release|x64.Build.0 = Release|Any CPU
 		{9FD0C8F4-A23B-4C68-A365-86E7EF5623D8}.Release|x86.ActiveCfg = Release|Any CPU
 		{9FD0C8F4-A23B-4C68-A365-86E7EF5623D8}.Release|x86.Build.0 = Release|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Debug|x64.Build.0 = Debug|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Debug|x86.Build.0 = Debug|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Release|Any CPU.Build.0 = Release|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Release|x64.ActiveCfg = Release|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Release|x64.Build.0 = Release|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Release|x86.ActiveCfg = Release|Any CPU
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4}.Release|x86.Build.0 = Release|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Debug|x64.Build.0 = Debug|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Debug|x86.Build.0 = Debug|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Release|Any CPU.Build.0 = Release|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Release|x64.ActiveCfg = Release|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Release|x64.Build.0 = Release|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Release|x86.ActiveCfg = Release|Any CPU
+		{7237398A-2E8B-4161-BA15-DB090395A1F2}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -50,5 +80,7 @@ Global
 	GlobalSection(NestedProjects) = preSolution
 		{E00F4E4F-8D52-49CE-8754-ED8378A5278F} = {CEC0EC27-0CEC-90C6-CABA-E58AB278E4DA}
 		{9FD0C8F4-A23B-4C68-A365-86E7EF5623D8} = {CEC0EC27-0CEC-90C6-CABA-E58AB278E4DA}
+		{561BCA96-76DF-4A33-B767-4AD7CD3246B4} = {89C53051-77F9-4C1C-ABE5-6D54AB398471}
+		{7237398A-2E8B-4161-BA15-DB090395A1F2} = {89C53051-77F9-4C1C-ABE5-6D54AB398471}
 	EndGlobalSection
 EndGlobal