Add configurable application settings

.env.example

@@ -0,0 +1,16 @@
+# Example environment variables for Docker deployment
+# Copy this file to .env and adjust values as needed
+
+# Predictor Settings
+PREDICTOR__MAXCALCULATIONPERIODMONTHS=36
+PREDICTOR__DEFAULTINITIALBUDGET=48750
+PREDICTOR__ENABLEEXAMPLEDATA=true
+PREDICTOR__MAXALLOWEDCALCULATIONPERIOD=120
+
+# ASP.NET Core Settings
+ASPNETCORE_ENVIRONMENT=Production
+ASPNETCORE_URLS=http://+:8080
+
+# Logging
+LOGGING__LOGLEVEL__DEFAULT=Information
+LOGGING__LOGLEVEL__MICROSOFT_ASPNETCORE=Warning

docs/CONFIGURATION.md

@@ -0,0 +1,84 @@
+# Configuration Guide
+
+## Application Settings
+
+The Predictor application is fully configurable through the `PredictorSettings` section in `appsettings.json`. All settings can be overridden using environment variables or other ASP.NET Core configuration sources.
+
+### Available Settings
+
+| Setting                       | Default | Description                                                    |
+| ----------------------------- | ------- | -------------------------------------------------------------- |
+| `MaxCalculationPeriodMonths`  | 36      | Maximum number of months to calculate predictions for          |
+| `DefaultInitialBudget`        | 48750   | Default initial budget used in example data                    |
+| `EnableExampleData`           | true    | Enable/disable the `/example-data` endpoint                    |
+| `MaxAllowedCalculationPeriod` | 120     | Maximum allowed calculation period to prevent abuse (10 years) |
+
+### Configuration Examples
+
+#### appsettings.json
+
+```json
+{
+  "PredictorSettings": {
+    "MaxCalculationPeriodMonths": 24,
+    "DefaultInitialBudget": 25000,
+    "EnableExampleData": true,
+    "MaxAllowedCalculationPeriod": 60
+  }
+}
+```
+
+#### Environment Variables
+
+```bash
+# Docker/Container deployment
+PREDICTOR__MAXCALCULATIONPERIODMONTHS=24
+PREDICTOR__DEFAULTINITIALBUDGET=25000
+PREDICTOR__ENABLEEXAMPLEDATA=true
+PREDICTOR__MAXALLOWEDCALCULATIONPERIOD=60
+
+# Or use the ASPNETCORE prefix
+ASPNETCORE_PREDICTORSETTINGS__MAXCALCULATIONPERIODMONTHS=24
+```
+
+#### Docker Compose
+
+```yaml
+version: "3.8"
+services:
+  predictor:
+    image: predictor:latest
+    environment:
+      - PREDICTOR__MAXCALCULATIONPERIODMONTHS=24
+      - PREDICTOR__DEFAULTINITIALBUDGET=25000
+      - PREDICTOR__ENABLEEXAMPLEDATA=true
+      - PREDICTOR__MAXALLOWEDCALCULATIONPERIOD=60
+    ports:
+      - "8080:8080"
+```
+
+### Environment-Specific Configuration
+
+The application uses standard ASP.NET Core configuration layering:
+
+1. **appsettings.json** - Base configuration
+2. **appsettings.{Environment}.json** - Environment-specific overrides
+3. **Environment variables** - Runtime overrides
+4. **Command line arguments** - Highest priority
+
+#### Development vs Production
+
+- **Development**: Uses `appsettings.Development.json` with shorter calculation periods for faster testing
+- **Production**: Uses `appsettings.json` with full calculation periods
+
+### Configuration Validation
+
+The application validates configuration at startup and uses sensible defaults if values are missing. The calculation period is automatically capped at `MaxAllowedCalculationPeriod` to prevent resource abuse.
+
+### Why This Matters
+
+✅ **Deployment Flexibility**: Change limits without code changes  
+✅ **Environment-Specific**: Different settings for dev/staging/production  
+✅ **Docker Ready**: Full support for container deployment  
+✅ **Twelve-Factor**: Follows twelve-factor app configuration principles  
+✅ **Security**: Sensitive settings can be injected via environment variables

src/.gitignore

@@ -6,6 +6,13 @@
 # Project private files
 DownloadResults/
 
+# Environment files
+.env
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
 # User-specific files
 *.rsuser
 *.suo

src/Predictor.Web/ExampleData.cs

@@ -4,17 +4,22 @@ namespace Predictor.Web;
 
 public static class ExampleData
 {
-    public static CalculateInput CalculateInputExample { get; } = new(
-    InitialBudget: 48_750,
-    StartCalculationMonth: MonthDate.Now,
-    Incomes: [
-        // Infinite recurring income (no EndDate)
-        new("Primary Salary", 5_400, MonthDate.Now, new RecurringConfig(1)),
-        new("Spouse Salary", 4_100, MonthDate.Now, new RecurringConfig(1)),
-        new("Rental Property A", 1_500, MonthDate.Now, new RecurringConfig(1)),
-        new("Rental Property B", 1_100, MonthDate.Now.AddMonths(3), new RecurringConfig(1)),
-        new("Investment Dividends", 320, MonthDate.Now.AddMonths(1), new RecurringConfig(3)),
-        new("Side Business", 850, MonthDate.Now.AddMonths(2), new RecurringConfig(1)),
+    [Obsolete("Use GetCalculateInputExample(PredictorSettings settings) instead")]
+    public static CalculateInput CalculateInputExample => GetCalculateInputExample(new PredictorSettings());
+
+    public static CalculateInput GetCalculateInputExample(PredictorSettings settings)
+    {
+        return new CalculateInput(
+            InitialBudget: settings.DefaultInitialBudget,
+            StartCalculationMonth: MonthDate.Now,
+            Incomes: [
+                // Infinite recurring income (no EndDate)
+                new("Primary Salary", 5_400, MonthDate.Now, new RecurringConfig(1)),
+                new("Spouse Salary", 4_100, MonthDate.Now, new RecurringConfig(1)),
+                new("Rental Property A", 1_500, MonthDate.Now, new RecurringConfig(1)),
+                new("Rental Property B", 1_100, MonthDate.Now.AddMonths(3), new RecurringConfig(1)),
+                new("Investment Dividends", 320, MonthDate.Now.AddMonths(1), new RecurringConfig(3)),
+                new("Side Business", 850, MonthDate.Now.AddMonths(2), new RecurringConfig(1)),
 
         // Finite recurring income (with EndDate)
         new("Contract Work", 2_200, MonthDate.Now, new RecurringConfig(1, MonthDate.Now.AddMonths(18))),
@@ -123,4 +128,5 @@ public static class ExampleData
         new("Luxury Purchase", 18_000, MonthDate.Now.AddMonths(42)),
         new("Investment Property Down Payment", 25_000, MonthDate.Now.AddMonths(45)),
         new("Retirement Catch-up", 30_000, MonthDate.Now.AddMonths(48))]);
+    }
 }

src/Predictor.Web/Models/PredictorSettings.cs

@@ -0,0 +1,26 @@
+namespace Predictor.Web.Models;
+
+public class PredictorSettings
+{
+    public const string SectionName = "PredictorSettings";
+
+    /// <summary>
+    /// Maximum number of months to calculate predictions for
+    /// </summary>
+    public int MaxCalculationPeriodMonths { get; set; } = 36;
+
+    /// <summary>
+    /// Default initial budget for examples
+    /// </summary>
+    public decimal DefaultInitialBudget { get; set; } = 48_750m;
+
+    /// <summary>
+    /// Enable/disable example data endpoint
+    /// </summary>
+    public bool EnableExampleData { get; set; } = true;
+
+    /// <summary>
+    /// Maximum allowed calculation period to prevent abuse
+    /// </summary>
+    public int MaxAllowedCalculationPeriod { get; set; } = 120; // 10 years
+}

src/Predictor.Web/Program.cs

@@ -3,6 +3,10 @@
 
 var builder = WebApplication.CreateBuilder(args);
 
+// Configure PredictorSettings
+builder.Services.Configure<PredictorSettings>(
+    builder.Configuration.GetSection(PredictorSettings.SectionName));
+
 builder.Services.AddControllers();
 builder.Services.AddEndpointsApiExplorer();
 builder.Services.AddSwaggerGen();
@@ -19,20 +23,31 @@
 app.UseAuthorization();
 app.MapControllers();
 
-app.MapGet("/example-data", () => ExampleData.CalculateInputExample);
+// Get settings
+var settings = app.Services.GetRequiredService<IConfiguration>()
+    .GetSection(PredictorSettings.SectionName)
+    .Get<PredictorSettings>() ?? new PredictorSettings();
+
+// Conditionally register example data endpoint
+if (settings.EnableExampleData)
+{
+    app.MapGet("/example-data", () => ExampleData.GetCalculateInputExample(settings));
+}
 
 app.MapPost("/calc", (CalculateInput input) =>
 {
     var months = new List<MonthOutput>();
     var budget = input.InitialBudget;
-    foreach (var currentMonth in MonthDate.Range(input.StartCalculationMonth, 12 * 3 - 1))
+    var calculationPeriod = Math.Min(settings.MaxCalculationPeriodMonths, settings.MaxAllowedCalculationPeriod);
+
+    foreach (var currentMonth in MonthDate.Range(input.StartCalculationMonth, calculationPeriod - 1))
     {
         var month = Calculator.CalculateMonth(input, currentMonth, budget);
         budget = month.BudgetAfter;
         months.Add(month);
     }
 
-    return new CalculationOutput([.. months]);
+    return Results.Ok(new CalculationOutput([.. months]));
 });
 
 app.Run();

src/Predictor.Web/appsettings.Development.json

@@ -4,5 +4,11 @@
       "Default": "Information",
       "Microsoft.AspNetCore": "Warning"
     }
+  },
+  "PredictorSettings": {
+    "MaxCalculationPeriodMonths": 24,
+    "DefaultInitialBudget": 25000,
+    "EnableExampleData": true,
+    "MaxAllowedCalculationPeriod": 60
   }
 }

src/Predictor.Web/appsettings.json

@@ -5,5 +5,11 @@
       "Microsoft.AspNetCore": "Warning"
     }
   },
-  "AllowedHosts": "*"
+  "AllowedHosts": "*",
+  "PredictorSettings": {
+    "MaxCalculationPeriodMonths": 36,
+    "DefaultInitialBudget": 48750,
+    "EnableExampleData": true,
+    "MaxAllowedCalculationPeriod": 120
+  }
 }