Backlog/engine/core/src/gameObject.zig

// ok
//
// lets really cook a good API here

pub const SpawnObjectResult = struct { ptr: *anyopaque, entity: core.Entity };

pub const ObjectCreateFn = *const fn (allocator: std.mem.Allocator, entity: core.Entity, parameters: SpawnParameters) ObjectError!*anyopaque;
pub const MessageHandlerFunc = *const fn (*anyopaque, *const MessageInfo, *anyopaque) void;

pub const GameObjectInterfaceVTable = struct {
    destroy: *const fn (*anyopaque, std.mem.Allocator) void,
    tick: ?*const fn (*anyopaque, f64) void,
    objectTypeName: core.Name = core.DefineName("UnknownType"),
    objectBaseName: core.Name = core.DefineName("UnknownObject"),
    create: ObjectCreateFn,
    messageHandlers: std.AutoHashMapUnmanaged(u32, MessageHandlerFunc) = .{},

    pub fn deinit(self: *@This(), allocator: std.mem.Allocator) void {
        self.messageHandlers.deinit(allocator);
    }
};

pub const ObjectError = error{
    OutOfMemory,
    BadInit,
    UnknownState,
    UnknownObject,
};

pub const MessageInfo = struct {
    tag: core.Name,
    sourceEntity: ?core.Entity = null,
    sourceSystem: ?core.Name = null,
    // maybe add like a filter type? or an invoker?
};

pub const GameObjectRef = struct {
    table: *GameObjectInterfaceVTable,
    ptr: *anyopaque,
};

pub const GameObject = struct {
    pub var BaseContainer: *core.SparseSet(GameObject) = undefined;
    pub const ComponentName = "GameObjectComponent";
    pub const ScriptExports: []const []const u8 = &.{};

    // set by GameObjectSystem when it calls Entity
    objectRef: GameObjectRef = undefined,
    destroyed: bool = false,

    pub fn deinitECS(self: *@This(), handle: core.ObjectHandle) void {
        _ = handle;
        if (!self.destroyed) {
            self.objectRef.table.destroy(self.objectRef.ptr, core.get(GameObjectSystem).allocator);
            self.destroyed = true;
        }
    }
};

pub const SpawnParameters = struct {
    posRot: core.ScenePosRot = .{},
    scale: core.Vectorf = .{ .z = 1.0, .y = 1.0, .x = 1.0 },
};

pub const SpawnEvent = struct {
    interface: GameObjectInterfaceVTable,
};

pub const GameObjectSystem = struct {

    // this is the new one, GameObjectList should be deleted after this passes initial usability
    pub var NeonObjectTable = core.EngineObjectVTable.from(@This(), "core.GameObjectSystem");

    allocator: std.mem.Allocator = undefined,
    objectDefinitions: std.AutoHashMapUnmanaged(u32, GameObjectInterfaceVTable) = .{},
    typesArena: std.heap.ArenaAllocator = undefined,

    objectSpawnEvents: std.ArrayListUnmanaged(SpawnEvent) = .{},

    pub fn create(self: *@This(), allocator: std.mem.Allocator, first: bool) !void {
        if (!first)
            return;

        self.* = .{
            .allocator = allocator,
            .typesArena = std.heap.ArenaAllocator.init(self.allocator),
        };
    }

    pub fn spawnObject(self: *@This(), comptime T: type, objectName: []const u8, parameters: SpawnParameters) !*T {
        var n = core.MakeName(objectName);
        return self.spawnObjectByName(T, &n, parameters);
    }

    pub fn spawnObjectByName(self: *@This(), comptime T: type, objectName: *core.Name, parameters: SpawnParameters) !*T {
        return @ptrCast(@alignCast((try self.spawnObjectFromTableByName(objectName, parameters)).ptr));
    }

    pub fn spawnObjectFromTableByName(self: *@This(), objectName: *core.Name, parameters: SpawnParameters) !SpawnObjectResult {
        const interface: *GameObjectInterfaceVTable = self.objectDefinitions.getPtr(objectName.handle()) orelse {
            return ObjectError.UnknownObject;
        };

        const entity = try core.createEntity();
        const objectComponent = entity.addComponent(GameObject).?;
        const rv = SpawnObjectResult{ .ptr = try interface.create(self.allocator, entity, parameters), .entity = entity };

        objectComponent.objectRef = .{
            .table = interface,
            .ptr = rv.ptr,
        };

        return rv;
    }

    // registers an object for spawning with the object name
    pub fn registerObject(self: *@This(), objectName: []const u8, comptime T: type) !void {
        try self.registerObjectAdvanced(objectName, T, "create");
    }

    pub fn registerObjectAdvanced(self: *@This(), name: []const u8, comptime T: type, comptime createFunctionName: []const u8) !void {
        var n = core.MakeName(name);

        const Wrap = struct {
            pub fn create(allocator: std.mem.Allocator, entity: core.Entity, parameters: SpawnParameters) ObjectError!*anyopaque {
                return @field(T, createFunctionName)(allocator, entity, parameters) catch {
                    return ObjectError.BadInit;
                };
            }

            pub fn destroy(p: *anyopaque, alloc: std.mem.Allocator) void {
                T.destroy(@ptrCast(@alignCast(p)), alloc);
            }

            pub fn tick(p: *anyopaque, dt: f64) void {
                T.tick(@ptrCast(@alignCast(p)), dt);
            }
        };

        var interface = GameObjectInterfaceVTable{
            .create = Wrap.create,
            .tick = if (@hasDecl(T, "tick")) Wrap.tick else null,
            .destroy = Wrap.destroy,
            .objectTypeName = core.MakeTypeName(T),
            .objectBaseName = n,
            .messageHandlers = .{},
        };

        if (@hasDecl(T, "MessageHandlers")) {
            inline for (T.MessageHandlers) |handlerName| {
                var messageHandlerName = core.MakeName(handlerName);
                // const handlerFunc = @field(T, handlerName);
                // const handlerTypeInfo = @typeInfo(@TypeOf(handlerFunc));
                // const M = @typeInfo(handlerTypeInfo.@"fn".params[3].type.?).pointer.child;

                const HandlerWrap = struct {
                    pub fn messageHandler(p: *anyopaque, info: *const MessageInfo, message: *anyopaque) void {
                        @field(T, handlerName)(@ptrCast(@alignCast(p)), info, @ptrCast(@alignCast(message)));
                    }
                };

                try interface.messageHandlers.put(self.typesArena.allocator(), messageHandlerName.handle(), HandlerWrap.messageHandler);
            }
        }

        try self.objectDefinitions.put(self.typesArena.allocator(), n.handle(), interface);
    }

    pub fn tick(self: *@This(), dt: f64) void {
        // for (self.objects.items) |object| {
        // if (object.vtable.tick) |tick_fn| {
        // tick_fn(object.ptr, dt);
        // }
        // }
        _ = self;
        _ = dt;
    }

    pub fn destroy(self: *@This()) void {
        self.typesArena.deinit();
    }
};

const core = @import("core.zig");
const std = @import("std");