From a8e5e723b7e1891c9b352261a3ee4c3d3563e8cf Mon Sep 17 00:00:00 2001
From: Elizabeth Hunt <me@liz.coffee>
Date: Sun, 26 Oct 2025 21:38:22 -0700
Subject: Checkpoint two

---
 .../kotlin/coffee/liz/ecs/grid/Components.kt       |  8 ++++
 .../commonMain/kotlin/coffee/liz/ecs/grid/Grid.kt  | 54 ++++++++++++++++++++++
 .../kotlin/coffee/liz/ecs/grid/GridSystem.kt       | 17 +++++++
 3 files changed, 79 insertions(+)
 create mode 100644 composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/Components.kt
 create mode 100644 composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/Grid.kt
 create mode 100644 composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/GridSystem.kt

(limited to 'composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid')

diff --git a/composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/Components.kt b/composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/Components.kt
new file mode 100644
index 0000000..b559aa7
--- /dev/null
+++ b/composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/Components.kt
@@ -0,0 +1,8 @@
+package coffee.liz.ecs.grid
+
+import coffee.liz.ecs.Component
+import coffee.liz.ecs.Vec2
+
+data class GridPosition(
+    val position: Vec2,
+) : Component
diff --git a/composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/Grid.kt b/composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/Grid.kt
new file mode 100644
index 0000000..f4eef43
--- /dev/null
+++ b/composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/Grid.kt
@@ -0,0 +1,54 @@
+package coffee.liz.ecs.grid
+
+import coffee.liz.ecs.Entity
+import coffee.liz.ecs.Rect
+import coffee.liz.ecs.Vec2
+
+data class Grid(
+    val dimensions: Vec2,
+    val grid: MutableList<MutableList<MutableSet<Entity>>> =
+        MutableList(dimensions.y.toInt()) {
+            MutableList(dimensions.x.toInt()) { mutableSetOf() }
+        },
+) {
+    fun at(position: Vec2): MutableSet<Entity> {
+        if (!Rect(Vec2(0f, 0f), dimensions).contains(position)) {
+            throw IllegalArgumentException()
+        }
+        return grid[position.y.toInt()][position.x.toInt()]
+    }
+
+    fun add(entity: Entity) {
+        if (!entity.has(GridPosition::class)) {
+            throw IllegalArgumentException("Entity must have a GridPosition component to be added to the grid")
+        }
+        val position = entity.get(GridPosition::class).position
+        at(position).add(entity)
+    }
+
+    fun reassignCellEntities(entities: Collection<Entity>) {
+        val remainingEntities = entities.filter { it.has(GridPosition::class) }.toMutableSet()
+        for (y in grid.indices) {
+            for (x in grid[y].indices) {
+                val vec = Vec2(x.toFloat(), y.toFloat())
+                val entities = at(vec)
+                entities.retainAll(
+                    entities
+                        .filter {
+                            if (!it.has(GridPosition::class)) {
+                                return@filter false
+                            }
+                            val currentPosition = it.get(GridPosition::class).position
+                            (vec == currentPosition).also { stillInCell ->
+                                if (!stillInCell) {
+                                    at(currentPosition).add(it)
+                                }
+                            }
+                        }.toSet(),
+                )
+                remainingEntities.removeAll(entities)
+            }
+        }
+        remainingEntities.forEach { add(it) }
+    }
+}
diff --git a/composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/GridSystem.kt b/composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/GridSystem.kt
new file mode 100644
index 0000000..50d784d
--- /dev/null
+++ b/composeApp/src/commonMain/kotlin/coffee/liz/ecs/grid/GridSystem.kt
@@ -0,0 +1,17 @@
+package coffee.liz.ecs.grid
+
+import coffee.liz.ecs.System
+import coffee.liz.ecs.World
+import coffee.liz.ecs.physics.PhysicsSystem
+import kotlin.reflect.KClass
+import kotlin.time.Duration
+
+class GridSystem<Outside>(
+    private val grid: Grid
+): System<Outside> {
+    override val dependencies = setOf(PhysicsSystem::class)
+
+    override fun update(world: World<Outside>, state: Outside, deltaTime: Duration) {
+
+    }
+}
\ No newline at end of file
-- 
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