Add support for the diminished state.

shared/src/commonMain/kotlin/com/pixelized/shared/lwa/model/campaign/Campaign.kt

@@ -6,6 +6,7 @@ data class Campaign(
 ) {
     data class CharacterInstance(
         val characteristic: Map<Characteristic, Int>,
+        val diminished: Int,
     ) {
         data class Id(
             val characterSheetId: String,
@@ -16,6 +17,13 @@ data class Campaign(
             Damage,
             Power,
         }
+
+        companion object {
+            fun empty() = CharacterInstance(
+                characteristic = emptyMap(),
+                diminished = 0,
+            )
+        }
     }
 
     companion object {
@@ -27,15 +35,11 @@ data class Campaign(
 }
 
 fun Campaign.character(id: Campaign.CharacterInstance.Id): Campaign.CharacterInstance {
-    return characters[id] ?: Campaign.CharacterInstance(
-        characteristic = emptyMap(),
-    )
+    return characters[id] ?: Campaign.CharacterInstance.empty()
 }
 
 fun Campaign.npc(id: Campaign.CharacterInstance.Id): Campaign.CharacterInstance {
-    return npcs[id] ?: Campaign.CharacterInstance(
-        characteristic = emptyMap(),
-    )
+    return npcs[id] ?: Campaign.CharacterInstance.empty()
 }
 
 val Campaign.CharacterInstance.level

shared/src/commonMain/kotlin/com/pixelized/shared/lwa/model/campaign/CampaignJsonFactory.kt

@@ -47,6 +47,7 @@ class CampaignJsonFactory {
             characteristic = characterInstanceJson.characteristic
                 .map { char -> convertFromV1(characteristicJson = char.key) to char.value }
                 .toMap(),
+            diminished = characterInstanceJson.diminished ?: 0,
         )
     }
 
@@ -85,6 +86,7 @@ class CampaignJsonFactory {
             characteristic = data.characteristic
                 .map { char -> convertToJson(characteristic = char.key) to char.value }
                 .toMap(),
+            diminished = data.diminished,
         )
     }
 

shared/src/commonMain/kotlin/com/pixelized/shared/lwa/model/campaign/CampaignJsonV1.kt

@@ -11,6 +11,7 @@ data class CampaignJsonV1(
     @Serializable
     data class CharacterInstanceJson(
         val characteristic: Map<Characteristic, Int>,
+        val diminished: Int?,
     ) {
         enum class Characteristic {
             Damage,

shared/src/commonMain/kotlin/com/pixelized/shared/lwa/protocol/websocket/payload/CampaignMessage.kt

@@ -0,0 +1,25 @@
+package com.pixelized.shared.lwa.protocol.websocket.payload
+
+import com.pixelized.shared.lwa.model.campaign.CampaignJsonV1
+import kotlinx.serialization.Serializable
+
+@Serializable
+sealed interface CampaignMessage : MessagePayload {
+    val characterSheetId: String
+    val instanceId: Int
+
+    @Serializable
+    data class UpdateCharacteristic(
+        override val characterSheetId: String,
+        override val instanceId: Int,
+        val characteristic: CampaignJsonV1.CharacterInstanceJson.Characteristic,
+        val value: Int,
+    ) : CampaignMessage
+
+    @Serializable
+    data class UpdateDiminished(
+        override val characterSheetId: String,
+        override val instanceId: Int,
+        val diminished: Int,
+    ) : CampaignMessage
+}

shared/src/commonMain/kotlin/com/pixelized/shared/lwa/protocol/websocket/payload/UpdatePlayerCharacteristicMessage.kt

@@ -1,11 +0,0 @@
-package com.pixelized.shared.lwa.protocol.websocket.payload
-
-import com.pixelized.shared.lwa.model.campaign.CampaignJsonV1
-import kotlinx.serialization.Serializable
-
-@Serializable
-data class UpdatePlayerCharacteristicMessage(
-    val characterInstanceId: String,
-    val characteristic: CampaignJsonV1.CharacterInstanceJson.Characteristic,
-    val value: Int,
-) : MessagePayload

shared/src/commonMain/kotlin/com/pixelized/shared/lwa/usecase/CampaignUseCase.kt

@@ -5,14 +5,23 @@ import com.pixelized.shared.lwa.model.campaign.Campaign
 class CampaignUseCase {
 
     fun updateCharacteristic(
-        character: Campaign.CharacterInstance,
+        instance: Campaign.CharacterInstance,
         characteristic: Campaign.CharacterInstance.Characteristic,
         value: Int,
     ): Campaign.CharacterInstance {
-        return character.copy(
-            characteristic = character.characteristic.toMutableMap().also {
+        return instance.copy(
+            characteristic = instance.characteristic.toMutableMap().also {
                 it[characteristic] = value
             }
         )
     }
+
+    fun updateDiminished(
+        instance: Campaign.CharacterInstance,
+        diminished: Int,
+    ): Campaign.CharacterInstance {
+        return instance.copy(
+            diminished = diminished,
+        )
+    }
 }

shared/src/commonMain/kotlin/com/pixelized/shared/lwa/usecase/ExpressionUseCase.kt

@@ -24,6 +24,7 @@ class ExpressionUseCase(
     fun computeSkillValue(
         sheet: CharacterSheet,
         alterations: Map<String, List<FieldAlteration>>,
+        diminished: Int,
         skill: CharacterSheet.Skill,
     ): Int {
         val context = Context(
@@ -51,7 +52,7 @@ class ExpressionUseCase(
             context.evaluate(it.expression)
         } ?: 0
 
-        return max(base + bonus + level + alteration, 0)
+        return max(base + bonus + level + alteration - diminished, 0)
     }
 
     fun computeRoll(