add basic entity component system

1 files changed, 84 insertions, 0 deletions

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, .{});
+}