Add health condition list, tick, and save for phase 77.

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

src/HSchool.People/HealthCondition.cs

@@ -0,0 +1,94 @@
+using System.Text.Json.Serialization;
+
+namespace HSchool.People;
+
+/// <summary>
+/// One medical condition on a person (hediff-like). Needs stay separate — a disease may
+/// later modify decay, but hunger is still a need.
+/// </summary>
+public sealed class HealthCondition
+{
+    public required string DefName { get; init; }
+
+    /// <summary>0…1. Stages and effects read this; DiseaseDef curves land in phase 78.</summary>
+    public float Severity { get; set; }
+
+    /// <summary>Immunity / treatment progress 0…1.</summary>
+    public float Progress { get; set; }
+
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? Source { get; init; }
+
+    public DateTime StartedAt { get; init; }
+
+    /// <summary>
+    /// Base severity change per game day before the person+day seed factor.
+    /// Artificial conditions carry this until DiseaseDef owns the curve (phase 78).
+    /// </summary>
+    public float SeverityPerDay { get; init; }
+
+    /// <summary>Base progress change per game day before the person+day seed factor.</summary>
+    public float ProgressPerDay { get; init; }
+}
+
+/// <summary>Mutates the sparse <see cref="Person.Conditions"/> list and ticks severity deterministically.</summary>
+public static class HealthConditions
+{
+    public static void Add(Person person, HealthCondition condition)
+    {
+        ArgumentNullException.ThrowIfNull(person);
+        ArgumentNullException.ThrowIfNull(condition);
+
+        var list = person.Conditions;
+        if (list is null)
+        {
+            list = [];
+            person.Conditions = list;
+        }
+
+        list.Add(condition);
+    }
+
+    /// <summary>
+    /// Advances severity/progress for everyone with conditions. Same
+    /// <paramref name="peopleSeed"/>, person id and <paramref name="dayNumber"/> yield the same curve.
+    /// </summary>
+    public static bool Tick(Person person, int peopleSeed, int dayNumber, double gameMinutes)
+    {
+        ArgumentNullException.ThrowIfNull(person);
+        var list = person.Conditions;
+        if (list is null || list.Count == 0 || gameMinutes <= 0)
+        {
+            return false;
+        }
+
+        var daySeed = Seed.Mix(peopleSeed, person.Id, dayNumber, Seed.HealthSalt);
+        var unit = (daySeed & int.MaxValue) / (float)int.MaxValue;
+        var dayFactor = 0.5f + unit;
+        var days = gameMinutes / (24d * 60d);
+        var changed = false;
+
+        foreach (var condition in list)
+        {
+            var severityDelta = (float)(condition.SeverityPerDay * dayFactor * days);
+            var progressDelta = (float)(condition.ProgressPerDay * dayFactor * days);
+            if (severityDelta == 0f && progressDelta == 0f)
+            {
+                continue;
+            }
+
+            var nextSeverity = Math.Clamp(condition.Severity + severityDelta, 0f, 1f);
+            var nextProgress = Math.Clamp(condition.Progress + progressDelta, 0f, 1f);
+            if (nextSeverity == condition.Severity && nextProgress == condition.Progress)
+            {
+                continue;
+            }
+
+            condition.Severity = nextSeverity;
+            condition.Progress = nextProgress;
+            changed = true;
+        }
+
+        return changed;
+    }
+}

src/HSchool.People/Roster.cs

@@ -75,6 +75,12 @@ public sealed record Person
     /// </summary>
     public List<OffenseRecord>? Offenses { get; set; }
 
+    /// <summary>
+    /// Active medical conditions. Null when healthy (empty) so people.json stays compact.
+    /// Needs are not replaced by this list.
+    /// </summary>
+    public List<HealthCondition>? Conditions { get; set; }
+
     public int AgeOn(DateTime asOf) => SchoolYears.AgeYears(BirthDate, asOf);
 }
 

src/HSchool.People/Seed.cs

@@ -21,6 +21,7 @@ public static class Seed
     public const int OrientationSalt = 13;
     public const int ConflictSalt = 14;
     public const int HomeSalt = 15;
+    public const int HealthSalt = 16;
 
     /// <summary>A stream that belongs to the school rather than to one family.</summary>
     public static int ForSchool(int schoolSeed, int salt) => Mix(schoolSeed, familyIndex: -1, salt);

src/HSchool.Simulation/HealthConditionSystem.cs

@@ -0,0 +1,26 @@
+using HSchool.People;
+
+namespace HSchool.Simulation;
+
+/// <summary>
+/// Ticks medical condition severity on the roster. Contagion and DiseaseDef outbreaks are later phases.
+/// </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;
+    }
+}

src/HSchool.Simulation/School.cs

@@ -348,7 +348,7 @@ public sealed class School : IDisposable
         }
     }
 
-    /// <summary>Runs one fixed step of the school: calendar, yearly intake, applicant refresh, presence, actions, need decay, then apparel wear.</summary>
+    /// <summary>Runs one fixed step of the school: calendar, yearly intake, applicant refresh, presence, actions, need decay, apparel wear, then health conditions.</summary>
     /// <returns><see langword="true"/> when the roster, applicant pool or wardrobe changed this step.</returns>
     public bool Tick(double deltaTime, double gameMinutesPerRealSecond)
     {
@@ -442,6 +442,7 @@ public sealed class School : IDisposable
             peopleChanged |= AffinitySystem.Apply(this, talked);
         }
 
+        peopleChanged |= HealthConditionSystem.Apply(this, gameMinutes);
         peopleChanged |= RosterTalkDirty;
         RosterTalkDirty = false;
         return peopleChanged;