Merge branch 'phase/78-diseases'

Co-authored-by: Cursor <cursoragent@cursor.com>

src/HSchool.Simulation/AttendanceSystem.cs

@@ -117,6 +117,15 @@ internal static class AttendanceSystem
                 continue;
             }
 
+            var reason = DiseaseEffects.ShouldStayHome(
+                    person,
+                    school.Catalog!,
+                    school.PeopleSeed,
+                    school.Clock.Time)
+                || DiseaseEffects.StayHomeChance(person, school.Catalog!, school.Clock.Time) >= 0.5f
+                    ? AbsenceReasons.Illness
+                    : AbsenceReasons.Truancy;
+
             if (AttendanceMemory.Record(
                     person,
                     lesson.Subject,
@@ -124,7 +133,7 @@ internal static class AttendanceSystem
                     school.Clock.Time,
                     period,
                     rules,
-                    AbsenceReasons.Truancy))
+                    reason))
             {
                 school.RosterTalkDirty = true;
             }

src/HSchool.Simulation/DiseaseSystem.cs

@@ -0,0 +1,163 @@
+using HSchool.Content;
+using HSchool.People;
+
+namespace HSchool.Simulation;
+
+/// <summary>
+/// DiseaseDef onset from weather vectors and ticks that follow stage curves.
+/// Person-to-person contagion is phase 79.
+/// </summary>
+internal static class DiseaseSystem
+{
+    public static bool Apply(School school, double gameMinutes)
+    {
+        if (school.Roster is null || school.Catalog is null)
+        {
+            return false;
+        }
+
+        var catalog = school.Catalog;
+        var changed = false;
+        var dayNumber = DateOnly.FromDateTime(school.Clock.Time).DayNumber;
+        var now = school.Clock.Time;
+
+        foreach (var person in school.Roster.People)
+        {
+            changed |= DiseaseImmunities.Expire(person, now);
+        }
+
+        if (school.LastDiseaseDay != dayNumber)
+        {
+            school.LastDiseaseDay = dayNumber;
+            changed |= TryOnset(school);
+        }
+
+        if (gameMinutes > 0)
+        {
+            foreach (var person in school.Roster.People)
+            {
+                changed |= HealthConditions.Tick(
+                    person,
+                    school.PeopleSeed,
+                    dayNumber,
+                    gameMinutes,
+                    catalog,
+                    now);
+            }
+        }
+
+        return changed;
+    }
+
+    private static bool TryOnset(School school)
+    {
+        var catalog = school.Catalog!;
+        var rules = catalog.BehaviorRules;
+        if (rules is null || rules.DiseaseVectorScale <= 0f || catalog.Diseases.Count == 0)
+        {
+            return false;
+        }
+
+        var weather = school.Weather;
+        var dayNumber = DateOnly.FromDateTime(school.Clock.Time).DayNumber;
+        var changed = false;
+
+        foreach (var person in school.Roster!.People)
+        {
+            if (!person.IsStudent && !person.IsStaff)
+            {
+                continue;
+            }
+
+            foreach (var disease in catalog.Diseases.Values)
+            {
+                if (disease.Abstract
+                    || HealthConditions.Has(person, disease.DefName)
+                    || DiseaseImmunities.IsImmune(person, disease.DefName, school.Clock.Time))
+                {
+                    continue;
+                }
+
+                var chance = OnsetChance(disease, weather, rules.DiseaseVectorScale);
+                if (chance <= 0f)
+                {
+                    continue;
+                }
+
+                var salt = Seed.DiseaseSalt + Stable(disease.DefName);
+                var roll = Seed.Mix(school.PeopleSeed, person.Id, dayNumber, salt);
+                var unit = (roll & int.MaxValue) / (float)int.MaxValue;
+                if (unit >= chance)
+                {
+                    continue;
+                }
+
+                HealthConditions.Add(
+                    person,
+                    new HealthCondition
+                    {
+                        DefName = disease.DefName,
+                        Severity = 0.05f,
+                        Progress = 0f,
+                        Source = SourceOf(disease, weather),
+                        StartedAt = school.Clock.Time,
+                    });
+                changed = true;
+            }
+        }
+
+        return changed;
+    }
+
+    internal static float OnsetChance(DiseaseDef disease, OutdoorWeather weather, float vectorScale)
+    {
+        if (vectorScale <= 0f)
+        {
+            return 0f;
+        }
+
+        var chance = disease.BaseChancePerDay;
+        if (disease.ColdBelowC is { } below && weather.TemperatureC <= below)
+        {
+            chance += disease.ColdChancePerDay;
+        }
+
+        chance += weather.Precipitation switch
+        {
+            Precipitation.Rain => disease.RainChancePerDay,
+            Precipitation.Snow => disease.SnowChancePerDay,
+            _ => 0f,
+        };
+
+        return Math.Clamp(chance * vectorScale, 0f, 1f);
+    }
+
+    private static string SourceOf(DiseaseDef disease, OutdoorWeather weather)
+    {
+        if (disease.ColdBelowC is { } below && weather.TemperatureC <= below)
+        {
+            return "cold";
+        }
+
+        return weather.Precipitation switch
+        {
+            Precipitation.Rain => "rain",
+            Precipitation.Snow => "snow",
+            _ => "idiopathic",
+        };
+    }
+
+    private static int Stable(string value)
+    {
+        unchecked
+        {
+            var hash = 17;
+            foreach (var character in value)
+            {
+                hash = (hash * 31) + character;
+            }
+
+            return hash & 0xFFFF;
+        }
+    }
+}

src/HSchool.Simulation/HealthConditionSystem.cs

@@ -3,24 +3,10 @@ using HSchool.People;
 namespace HSchool.Simulation;
 
 /// <summary>
-/// Ticks medical condition severity on the roster. Contagion and DiseaseDef outbreaks are later phases.
+/// Ticks medical conditions. DiseaseDef onset and stage curves live in <see cref="DiseaseSystem"/>.
+/// Kept so older call sites and phase-77 tests still have a named entry.
 /// </summary>
 internal static class HealthConditionSystem
 {
-    public static bool Apply(School school, double gameMinutes)
-    {
-        if (gameMinutes <= 0 || school.Roster is null)
-        {
-            return false;
-        }
-
-        var dayNumber = DateOnly.FromDateTime(school.Clock.Time).DayNumber;
-        var changed = false;
-        foreach (var person in school.Roster.People)
-        {
-            changed |= HealthConditions.Tick(person, school.PeopleSeed, dayNumber, gameMinutes);
-        }
-
-        return changed;
-    }
+    public static bool Apply(School school, double gameMinutes) => DiseaseSystem.Apply(school, gameMinutes);
 }

src/HSchool.Simulation/LessonLearningSystem.cs

@@ -110,6 +110,7 @@ internal static class LessonLearningSystem
                 }
 
                 textbookFactor *= TalkCircles.LessonWhisperFactor(activity.ActionId, rules);
+                textbookFactor *= DiseaseEffects.LessonLearningFactor(person, catalog, school.Clock.Time);
 
                 IReadOnlyDictionary<string, float> taught = teacherSkills.TryGetValue(lesson.TeacherId, out var found)
                     ? found

src/HSchool.Simulation/School.cs

@@ -119,6 +119,9 @@ public sealed class School : IDisposable
     /// <summary>Last slot <see cref="AttendanceSystem"/> observed — detects leaving a lesson to finalize absents.</summary>
     internal DaySlot? LastAttendanceSlot { get; set; }
 
+    /// <summary>Calendar day of the last DiseaseDef onset pass (one roll per person per day).</summary>
+    internal int LastDiseaseDay { get; set; } = int.MinValue;
+
     internal Dictionary<string, DayPlan> Plans { get; } = new(StringComparer.Ordinal);
 
     internal Queue<string> DecisionQueue { get; } = new();
@@ -227,6 +230,7 @@ public sealed class School : IDisposable
         PlanDay = null;
         LastDecisionSlot = null;
         LastAttendanceSlot = null;
+        LastDiseaseDay = int.MinValue;
         Plans.Clear();
         DecisionQueue.Clear();
         LoggedActivity.Clear();