1 files changed, 83 insertions, 0 deletions
diff --git a/gui/src/types/balanceToBudgetRatio.ts b/gui/src/types/balanceToBudgetRatio.ts
new file mode 100644
index 0000000..2f8000c
--- /dev/null
+++ b/gui/src/types/balanceToBudgetRatio.ts
@@ -0,0 +1,83 @@
+import { Budget } from "./budget";
+import Currency from "./currency/currency";
+
+class BalanceToBudgetRatio {
+  toString(): string {
+    return this._ratio?.toFixed(2) ?? "";
+  }
+
+  public readonly recommendedAction: "arrears" | "save" | "spend" | null;
+  public readonly normalisedRatio: number | null;
+
+  private constructor(
+    private readonly _ratio: number | null,
+    private readonly _normalisationFactor: number,
+  ) {
+    if (this._ratio === null) {
+      this.normalisedRatio = null;
+      this.recommendedAction = null;
+      return;
+    }
+
+    this.normalisedRatio = this._ratio * this._normalisationFactor;
+
+    if (this._ratio < 0) {
+      this.recommendedAction = "arrears";
+    } else if (this._ratio >= 1) {
+      this.recommendedAction = "spend";
+    } else {
+      this.recommendedAction = "save";
+    }
+  }
+
+  static new(balance: Currency, budget: Budget | null) {
+    if (budget === null || budget.quantity === 0 || budget.quantity === -0) {
+      return null;
+    }
+
+    return new BalanceToBudgetRatio(
+      balance.valueOf() / budget.quantity.valueOf(),
+      1,
+    );
+  }
+
+  static makeNormaliser(
+    ...balanceToBudgetRatios: (BalanceToBudgetRatio | null)[]
+  ): (r: BalanceToBudgetRatio | null) => BalanceToBudgetRatio {
+    const validRatios = balanceToBudgetRatios.filter(
+      (r) =>
+        r &&
+        r._ratio &&
+        !isNaN(r._ratio) &&
+        Infinity > r._ratio &&
+        -Infinity < r._ratio,
+    );
+
+    const maxAbsRatio = Math.max(
+      ...validRatios.map((r) => Math.abs(r?._ratio ?? 0)),
+    );
+
+    const normalisationFactor = 1 / maxAbsRatio;
+    return (r) =>
+      new BalanceToBudgetRatio(r?._ratio ?? null, normalisationFactor);
+  }
+
+  static compare(
+    lhs: BalanceToBudgetRatio | null,
+    rhs: BalanceToBudgetRatio | null,
+  ): number {
+    if (lhs === null || lhs._ratio === null) {
+      if (rhs === null || rhs._ratio === null) {
+        return 0;
+      }
+      return 1;
+    }
+    if (rhs === null || rhs._ratio === null) {
+      return -1;
+    }
+
+    return rhs._ratio - lhs._ratio;
+  }
+}
+
+export { BalanceToBudgetRatio };