From ec8c24e5b6be2b8bab842d945185bca684f899ce Mon Sep 17 00:00:00 2001
From: Colin McMillen <colin@semicolin.games>
Date: Wed, 25 Mar 2020 15:16:31 -0400
Subject: [PATCH] FSM: deal with IStates directly, don't parametrize on an
 input type.

---
 Shared/FSM.cs | 22 ++++++++++++----------
 Shared/NPC.cs | 33 ++++++++++++++++++++++-----------
 2 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/Shared/FSM.cs b/Shared/FSM.cs
index 23f8704..42d0812 100644
--- a/Shared/FSM.cs
+++ b/Shared/FSM.cs
@@ -1,27 +1,29 @@
 using System.Collections.Generic;
 
 namespace SemiColinGames {
-  public interface IState<T> {
+  public interface IState {
+    // Called automatically whenever this state is transitioned to. Should reset whichever
+    // state-specific variables need resetting.
     public void Enter();
 
     // Returns the name of the new state, or null if we should stay in the same state.
-    public string Update(T obj, float modelTime, World world);
+    public string Update(float modelTime, World world);
   }
 
-  public class FSM<T> {
-    readonly Dictionary<string, IState<T>> states;
-    IState<T> state;
+  public class FSM {
+    readonly Dictionary<string, IState> states;
+    IState state;
 
-    public FSM(Dictionary<string, IState<T>> states, string initial) {
+    public FSM(string initialStateName, Dictionary<string, IState> states) {
       this.states = states;
-      StateName = initial;
+      StateName = initialStateName;
       Transition(StateName);
     }
 
     public string StateName { get; private set; }
 
-    public void Update(T obj, float modelTime, World world) {
-      string newState = state.Update(obj, modelTime, world);
+    public void Update(float modelTime, World world) {
+      string newState = state.Update(modelTime, world);
       if (newState != null) {
         Transition(newState);
       }
@@ -29,7 +31,7 @@ namespace SemiColinGames {
 
     void Transition(string state) {
       StateName = state;
-      IState<T> newState = states[state];
+      IState newState = states[state];
       this.state = newState;
       this.state.Enter();
     }
diff --git a/Shared/NPC.cs b/Shared/NPC.cs
index bcd4dcc..1541be3 100644
--- a/Shared/NPC.cs
+++ b/Shared/NPC.cs
@@ -3,14 +3,19 @@ using Microsoft.Xna.Framework.Graphics;
 using System.Collections.Generic;
 
 namespace SemiColinGames {
-  class IdleState : IState<NPC> {
-    float timeInState = 0;
+  class IdleState : IState {
+    private NPC npc;
+    private float timeInState = 0;
+
+    public IdleState(NPC npc) {
+      this.npc = npc;
+    }
 
     public void Enter() {
       timeInState = 0;
     }
 
-    public string Update(NPC npc, float modelTime, World world) {
+    public string Update(float modelTime, World world) {
       timeInState += modelTime;
       if (timeInState > 1.0f) {
         npc.Facing *= -1;
@@ -20,10 +25,16 @@ namespace SemiColinGames {
     }
   }
 
-  class RunState : IState<NPC> {
+  class RunState : IState {
+    private NPC npc;
+
+    public RunState(NPC npc) {
+      this.npc = npc;
+    }
+
     public void Enter() {}
 
-    public string Update(NPC npc, float modelTime, World world) {
+    public string Update(float modelTime, World world) {
       float moveSpeed = 120;
       float desiredX = npc.Position.X + moveSpeed * npc.Facing * modelTime;
       float testPoint = desiredX + npc.Box.HalfSize.X * npc.Facing;
@@ -52,7 +63,7 @@ namespace SemiColinGames {
     private readonly Vector2 spriteCenter;
     private readonly Vector2 eyeOffset = new Vector2(4, -9);
 
-    private readonly FSM<NPC> fsm;
+    private readonly FSM fsm;
     private readonly Vector2 halfSize = new Vector2(11, 24);
 
     public NPC(Vector2 position, int facing) {
@@ -64,10 +75,10 @@ namespace SemiColinGames {
       Box = new AABB(Position, halfSize);
       Facing = facing;
 
-      fsm = new FSM<NPC>(new Dictionary<string, IState<NPC>> {
-        { "idle", new IdleState() },
-        { "run", new RunState() }
-      }, "run");
+      fsm = new FSM("run", new Dictionary<string, IState> {
+        { "idle", new IdleState(this) },
+        { "run", new RunState(this) }
+      });
     }
 
     public int Facing;
@@ -99,7 +110,7 @@ namespace SemiColinGames {
     }
 
     public void Update(float modelTime, World world) {
-      fsm.Update(this, modelTime, world);
+      fsm.Update(modelTime, world);
       Box = new AABB(Position, halfSize);
       Debug.AddRect(Box, Color.White);
     }