harden business rules

core/racing/domain/value-objects/StrengthOfField.ts

@@ -0,0 +1,75 @@
+/**
+ * Domain Value Object: StrengthOfField
+ * 
+ * Represents the strength of field (SOF) rating for a race or league.
+ * Enforces valid range and provides domain-specific operations.
+ */
+
+import type { IValueObject } from '@core/shared/domain';
+import { RacingDomainValidationError } from '../errors/RacingDomainError';
+
+export interface StrengthOfFieldProps {
+  value: number;
+}
+
+export class StrengthOfField implements IValueObject<StrengthOfFieldProps> {
+  readonly value: number;
+
+  private constructor(value: number) {
+    this.value = value;
+  }
+
+  static create(value: number): StrengthOfField {
+    if (!Number.isInteger(value)) {
+      throw new RacingDomainValidationError('Strength of field must be an integer');
+    }
+
+    if (value < 0 || value > 100) {
+      throw new RacingDomainValidationError('Strength of field must be between 0 and 100');
+    }
+
+    return new StrengthOfField(value);
+  }
+
+  /**
+   * Get the strength category
+   */
+  getCategory(): 'beginner' | 'intermediate' | 'advanced' | 'expert' {
+    if (this.value < 25) return 'beginner';
+    if (this.value < 50) return 'intermediate';
+    if (this.value < 75) return 'advanced';
+    return 'expert';
+  }
+
+  /**
+   * Check if this SOF is suitable for the given participant count
+   */
+  isSuitableForParticipants(count: number): boolean {
+    // Higher SOF should generally have more participants
+    const minExpected = Math.floor(this.value / 10);
+    return count >= minExpected;
+  }
+
+  /**
+   * Calculate difference from another SOF
+   */
+  differenceFrom(other: StrengthOfField): number {
+    return Math.abs(this.value - other.value);
+  }
+
+  get props(): StrengthOfFieldProps {
+    return { value: this.value };
+  }
+
+  toNumber(): number {
+    return this.value;
+  }
+
+  equals(other: IValueObject<StrengthOfFieldProps>): boolean {
+    return this.value === other.props.value;
+  }
+
+  toString(): string {
+    return this.value.toString();
+  }
+}