Goal planner backend (#132)

* refactor avghelper

* #59 backend

Co-authored-by: DarK-rtfm <44683230+DarK-rtfm@users.noreply.github.com>

filcnaplo/lib/helpers/average_helper.dart

@@ -1,26 +1,24 @@
+// ignore_for_file: no_leading_underscores_for_local_identifiers
+
 import 'package:filcnaplo_kreta_api/models/grade.dart';
 
 class AverageHelper {
   static double averageEvals(List<Grade> grades, {bool finalAvg = false}) {
-    double average = 0.0;
-
     List<String> ignoreInFinal = ["5,SzorgalomErtek", "4,MagatartasErtek"];
+    if (finalAvg) grades.removeWhere((e) => (e.value.value == 0) || (ignoreInFinal.contains(e.gradeType?.id)));
 
-    if (finalAvg) {
+    double average =
-      grades.removeWhere((e) =>
+        grades.map((e) => e.value.value * e.value.weight / 100.0).fold(0.0, (double a, double b) => a + b) / weightSum(grades, finalAvg: finalAvg);
-          (e.value.value == 0) ||
-          (ignoreInFinal.contains(e.gradeType?.id)));
-    }
-
-    for (var e in grades) {
-      average += e.value.value * ((finalAvg ? 100 : e.value.weight) / 100);
-    }
-
-    average = average /
-        grades
-            .map((e) => (finalAvg ? 100 : e.value.weight) / 100)
-            .fold(0.0, (a, b) => a + b);
-
     return average.isNaN ? 0.0 : average;
   }
-}
+
+  static double weightSum(List<Grade> grades, {bool finalAvg = false}) =>
+      grades.map((e) => finalAvg ? 1 : e.value.weight / 100).fold(0, (a, b) => a + b);
+
+  static int howManyNeeded(int grade, List<Grade> base, double goal, {bool filcgrade = true, double avg = 0, double wsum = 0}) {
+    double _avg = filcgrade ? averageEvals(base) : avg;
+    double _wsum = filcgrade ? weightSum(base) : wsum;
+    if (_avg >= goal) return 0;
+    return (_wsum * (_avg - goal) / (goal - grade)).ceil();
+  }
+}

filcnaplo/lib/helpers/goalplanner_helper.dart

@@ -0,0 +1,117 @@
+/* 
+ * Maintainer: DarK
+ * Translated from C version
+ * ##Please do NOT modify if you don't know whats going on##
+ * 
+ * Issue: #59
+ * 
+ * Future changes / ideas:
+ *  - `best` should be configurable
+ */
+import 'dart:math';
+
+import 'package:filcnaplo/helpers/average_helper.dart';
+import 'package:filcnaplo_kreta_api/models/grade.dart';
+
+/// Generate list of grades that achieve the wanted goal.
+/// After generating possible options, it (when doing so would NOT result in empty list) filters with two criteria:
+///  - Plan should not contain more than 15 grades
+///  - Plan should not contain only one type of grade
+///
+/// **Usage**:
+///
+/// ```dart
+/// List<int> GoalPlanner(double goal, List<Grade> grades).solve().plan
+/// ```
+class GoalPlanner {
+  final double goal;
+  final List<Grade> grades;
+  List<Plan> plans = [];
+  GoalPlanner(this.goal, this.grades);
+
+  bool _allowed(int grade) => grade > goal;
+
+  Avg _addToAvg(Avg base, int grade, int n) => Avg((base.avg * base.n + grade * n) / (base.n + n), base.n + n);
+  List<T> _addToList<T>(List<T> l, T e, int n) {
+    if (n == 0) return l;
+    List<T> tmp = l;
+    for (int i = 0; i < n; i++) tmp.add(e);
+    return tmp;
+  }
+
+  void _generate(Generator g) {
+    // Exit condition 1: Generator has working plan.
+    if (g.currentAvg.avg >= goal) {
+      plans.add(Plan(g.plan));
+      return;
+    }
+    // Exit condition 2: Generator plan will never work.
+    if (!_allowed(g.gradeToAdd)) return;
+    for (int i = 0; i < g.max; i++) {
+      int newGradeToAdd = g.gradeToAdd - 1;
+      List<int> newPlan = _addToList<int>(g.plan, g.gradeToAdd, i);
+      Avg newAvg = _addToAvg(g.currentAvg, g.gradeToAdd, i);
+      int newN = AverageHelper.howManyNeeded(newGradeToAdd, [], goal);
+
+      _generate(Generator(newGradeToAdd, newN, newAvg, newPlan));
+    }
+  }
+
+  Plan solve() {
+    _generate(
+      Generator(
+        5,
+        AverageHelper.howManyNeeded(
+          5,
+          [],
+          goal,
+          filcgrade: false,
+          avg: AverageHelper.averageEvals(grades),
+          wsum: AverageHelper.weightSum(grades),
+        ),
+        Avg(AverageHelper.averageEvals(grades), AverageHelper.weightSum(grades)),
+        [],
+      ),
+    );
+
+    // Calculate Statistics
+    plans.forEach((e) {
+      e.sum = e.plan.fold(0, (int a, b) => a + b);
+      e.avg = e.sum / e.plan.length;
+      e.sigma = sqrt(e.plan.map((i) => pow(i - e.avg, 2)).fold(0, (num a, b) => a + b) / e.plan.length);
+    });
+
+    // filter without aggression
+    if (plans.where((e) => e.plan.length < 15).isNotEmpty) plans.removeWhere((e) => !(e.plan.length < 15));
+    if (plans.where((e) => e.sigma > 1).isNotEmpty) plans.removeWhere((e) => !(e.sigma > 1));
+
+    return plans[Random().nextInt(plans.length)];
+  }
+}
+
+class Avg {
+  final double avg;
+  final double n;
+
+  Avg(this.avg, this.n);
+}
+
+class Generator {
+  final int gradeToAdd;
+  final int max;
+  final Avg currentAvg;
+  final List<int> plan;
+
+  Generator(this.gradeToAdd, this.max, this.currentAvg, this.plan);
+}
+
+class Plan {
+  final List<int> plan;
+  int sum = 0;
+  double avg = 0;
+  int med = 0; // currently
+  int mod = 0; // unused
+  double sigma = 0;
+
+  Plan(this.plan);
+}