implement helper function findMeanInt

src/lib/utils/math.ts

@@ -42,6 +42,51 @@ function findMinPositive<T>(items: T[], evaluate: (item: T) => number) {
     return bestItem;
 }
 
+function findMeanInt(sum: number, constraints: { min: number, max: number }[]) {
+    let mean = Math.floor(sum / constraints.length);
+    while (true) {
+        let actualSum = 0;
+        let increasable = 0;
+        let decreasable = 0;
+        let low = -Infinity;
+        let high = Infinity;
+        for (const constraint of constraints) {
+            const value = clamp(mean, constraint.min, constraint.max);
+            actualSum += value;
+            if (mean > constraint.min) {
+                decreasable++;
+                if (value > low) {
+                    low = value;
+                }
+            }
+            if (mean < constraint.max) {
+                increasable++;
+                if (value < high) {
+                    high = value;
+                }
+            }
+        }
+
+        const oldMean = mean;
+        const error = actualSum - sum;
+        if (error > 0) {
+            // need to decrease mean
+            if (decreasable > 0) {
+                mean = Math.floor(low - error / decreasable);
+            }
+        } else if (error < 0) {
+            // need to increase mean
+            if (increasable > 0) {
+                mean = Math.floor(high - error / increasable);
+            }
+        }
+
+        if (mean === oldMean) {
+            return mean;
+        }
+    }
+}
+
 function rectEquals(a: QmlRect, b: QmlRect) {
     return a.x === b.x &&
         a.y === b.y &&

src/tests/units/utils/findMean.ts

@@ -0,0 +1,93 @@
+tests.register("findMean", 1, () => {
+    const testCases: {
+        sum: number,
+        constraints: { min: number, max: number }[],
+        check: (result: number) => boolean,
+    }[] = [
+        {
+            sum: 600,
+            constraints: [
+                { min: 10, max: 600 },
+                { min: 10, max: 600 },
+            ],
+            check: r => r === 300,
+        },
+        {
+            sum: 600,
+            constraints: [
+                { min: 10, max: 250 },
+                { min: 10, max: 500 },
+            ],
+            check: r => r === 350,
+        },
+        {
+            sum: 600,
+            constraints: [
+                { min: 10, max: 250 },
+                { min: 400, max: 500 },
+            ],
+            check: r => r === 200,
+        },
+        {
+            sum: 765,
+            constraints: [
+                { min: 10, max: 250 },
+                { min: 10, max: 254 },
+                { min: 10, max: 500 },
+            ],
+            check: r => r === 261,
+        },
+        {
+            sum: 600,
+            constraints: [
+                { min: 10, max: 150 },
+                { min: 400, max: 500 },
+            ],
+            check: r => r === 450,
+        },
+        {
+            sum: 750,
+            constraints: [
+                { min: 10, max: 250 },
+                { min: 10, max: 250 },
+                { min: 400, max: 500 },
+                { min: 10, max: 300 },
+            ],
+            check: r => r === 116,
+        },
+        {
+            sum: 750,
+            constraints: [
+                { min: 10, max: 250 },
+                { min: 120, max: 250 },
+                { min: 400, max: 500 },
+                { min: 10, max: 300 },
+            ],
+            check: r => r === 115,
+        },
+        {
+            sum: 1200,
+            constraints: [
+                { min: 10, max: 250 },
+                { min: 10, max: 500 },
+            ],
+            check: r => r >= 500,
+        },
+        {
+            sum: 5,
+            constraints: [
+                { min: 10, max: 250 },
+                { min: 10, max: 500 },
+            ],
+            check: r => r <= 10,
+        },
+    ];
+
+    for (const testCase of testCases) {
+        const result = findMeanInt(testCase.sum, testCase.constraints);
+        Assert.assert(
+            testCase.check(result),
+            { message: `got ${result} for test case ${JSON.stringify(testCase)}` },
+        );
+    }
+});