add basic entity component system

3 files changed, 123 insertions, 45 deletions

diff --git a/src/ecs/component.zig b/src/ecs/component.zig
new file mode 100644
index 0000000..4a10172
--- /dev/null
+++ b/src/ecs/component.zig
@@ -0,0 +1,39 @@
+const std = @import("std");
+
+pub const ComponentStub = struct {
+    pub fn init(args: ComponentStub) ComponentStub {
+        _ = args;
+        return .{};
+    }
+
+    pub fn deinit(self: *ComponentStub) void {
+        _ = self;
+    }
+};
+
+pub const ComponentType = enum(usize) {
+    component_stub = 0,
+};
+
+pub const Component = union(ComponentType) {
+    component_stub: ComponentStub,
+
+    pub fn init(t: ComponentType, args: anytype) Component {
+        switch (t) {
+            ComponentType.component_stub => return Component{
+                .component_stub = ComponentStub.init(args),
+            },
+        }
+    }
+
+    pub fn deinit(self: *Component) void {
+        switch (self.*) {
+            .component_stub => |*comp| comp.deinit(),
+        }
+    }
+};
+
+test "stub component" {
+    var stub = Component.init(ComponentType.component_stub, .{});
+    defer stub.deinit();
+}
diff --git a/src/ecs/ecs.zig b/src/ecs/ecs.zig
new file mode 100644
index 0000000..542de34
--- /dev/null
+++ b/src/ecs/ecs.zig
@@ -0,0 +1,84 @@
+const std = @import("std");
+const component = @import("component.zig");
+
+const ComponentList = struct {
+    entities: std.AutoHashMap(usize, component.Component),
+};
+
+pub const EntityComponentSystem = struct {
+    entities: std.ArrayList(usize),
+    components: std.AutoHashMap(usize, ComponentList),
+    available_ids: std.ArrayList(usize),
+    next_id: usize,
+
+    pub fn init(allocator: std.mem.Allocator) !EntityComponentSystem {
+        var ecs = EntityComponentSystem{
+            .entities = std.ArrayList(usize).init(allocator),
+            .components = std.AutoHashMap(usize, ComponentList).init(allocator),
+            .available_ids = std.ArrayList(usize).init(allocator),
+            .next_id = 0,
+        };
+
+        inline for (std.meta.fields(component.ComponentType)) |comp| {
+            try ecs.components.put(comp.value, ComponentList{
+                .entities = std.AutoHashMap(usize, component.Component).init(allocator),
+            });
+        }
+
+        return ecs;
+    }
+
+    pub fn deinit(self: *EntityComponentSystem) void {
+        self.entities.deinit();
+        self.available_ids.deinit();
+
+        var component_iterator = self.components.iterator();
+        while (component_iterator.next()) |component_entry| {
+            var comp = component_entry.value_ptr;
+
+            var entity_iterator = comp.entities.iterator();
+            while (entity_iterator.next()) |entity_entry| {
+                var entity = entity_entry.value_ptr;
+
+                entity.deinit();
+            }
+
+            comp.entities.deinit();
+        }
+        self.components.deinit();
+    }
+
+    pub fn createEntity(self: *EntityComponentSystem) !usize {
+        const reuse_id = self.available_ids.popOrNull();
+        if (reuse_id != null and reuse_id.? < self.entities.items.len) {
+            self.entities.items[reuse_id.?] = reuse_id.?;
+            return reuse_id.?;
+        }
+
+        const id = self.next_id;
+        try self.entities.append(id);
+        self.next_id += 1;
+        return id;
+    }
+
+    pub fn componentAddEntity(
+        self: *EntityComponentSystem,
+        comp: component.ComponentType,
+        entity: usize,
+        args: anytype,
+    ) !void {
+        var comp_list = self.components.getPtr(@intFromEnum(comp)) orelse return;
+
+        try comp_list.entities.put(entity, component.Component.init(comp, args));
+    }
+};
+
+test "add entities to components" {
+    var ecs = try EntityComponentSystem.init(std.testing.allocator);
+    defer ecs.deinit();
+
+    const entity = try ecs.createEntity();
+    try std.testing.expectEqual(0, entity);
+
+    try ecs.componentAddEntity(component.ComponentType.component_stub, entity, .{});
+}
diff --git a/src/ecs/entity.zig b/src/ecs/entity.zig
deleted file mode 100644
index 2ad8556..0000000
--- a/src/ecs/entity.zig
+++ /dev/null
@@ -1,45 +0,0 @@
-const std = @import("std");
-
-pub const Entity = struct {
-    id: usize,
-};
-
-pub const EntityCollection = struct {
-    allocator: std.mem.Allocator,
-    next_id: usize,
-    entities: std.AutoHashMap(usize, Entity),
-
-    pub fn addEntity(self: *EntityCollection) !usize {
-        try self.entities.put(self.next_id, .{
-            .id = self.next_id,
-        });
-
-        self.next_id += 1;
-
-        return self.next_id - 1;
-    }
-
-    pub fn init(allocator: std.mem.Allocator) EntityCollection {
-        return .{
-            .allocator = allocator,
-            .next_id = 0,
-            .entities = std.AutoHashMap(usize, Entity).init(allocator),
-        };
-    }
-
-    pub fn deinit(self: *EntityCollection) void {
-        self.entities.deinit();
-    }
-};
-
-test "create entities" {
-    try std.testing.expect(true);
-
-    var ec = EntityCollection.init(std.testing.allocator);
-    defer ec.deinit();
-
-    for (0..128) |i| {
-        const id = ec.addEntity();
-        try std.testing.expectEqual(i, id);
-    }
-}