module: build addressable event handler names, runtime invocation

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

src/module.zig

@@ -1,6 +1,6 @@
 const builtin = @import("builtin");
 const std = @import("std");
-const testing = std.testing;
+const testing = @import("testing.zig");
 
 // TODO: eliminate dependency on ECS here.
 const EntityID = @import("ecs/entities.zig").EntityID;
@@ -39,9 +39,82 @@ pub fn Modules(comptime mods: anytype) type {
             _ = m;
             _ = allocator;
         }
+
+        inline fn call(event_name: EventName(mods), args: anytype) void {
+            switch (event_name) {
+                inline else => |name| {
+                    inline for (modules) |M| {
+                        if (@hasDecl(M, @tagName(name))) {
+                            switch (@typeInfo(@TypeOf(@field(M, @tagName(name))))) {
+                                .Fn => {
+                                    const handler = @field(M, @tagName(name));
+                                    callHandler(handler, args);
+                                },
+                                else => {},
+                            }
+                        }
+                    }
+                },
+            }
+        }
+
+        inline fn callHandler(handler: anytype, args: anytype) void {
+            @call(.auto, handler, args);
+        }
     };
 }
 
+/// enum describing every possible comptime-known event name
+fn EventName(comptime mods: anytype) type {
+    var enum_fields: []const std.builtin.Type.EnumField = &[0]std.builtin.Type.EnumField{};
+    var i: u32 = 0;
+    for (mods) |M| {
+        // Global event handlers
+        for (@typeInfo(M).Struct.decls) |decl| {
+            switch (@typeInfo(@TypeOf(@field(M, decl.name)))) {
+                .Fn => {
+                    const exists_already = blk2: {
+                        for (enum_fields) |existing| if (std.mem.eql(u8, existing.name, decl.name)) break :blk2 true;
+                        break :blk2 false;
+                    };
+                    if (!exists_already) {
+                        enum_fields = enum_fields ++ [_]std.builtin.Type.EnumField{.{ .name = decl.name, .value = i }};
+                        i += 1;
+                    }
+                },
+                else => {},
+            }
+        }
+
+        // Local event handlers
+        if (@hasDecl(M, "local")) {
+            for (@typeInfo(M.local).Struct.decls) |decl| {
+                switch (@typeInfo(@TypeOf(@field(M.local, decl.name)))) {
+                    .Fn => {
+                        const exists_already = blk2: {
+                            for (enum_fields) |existing| if (std.mem.eql(u8, existing.name, decl.name)) break :blk2 true;
+                            break :blk2 false;
+                        };
+                        if (!exists_already) {
+                            enum_fields = enum_fields ++ [_]std.builtin.Type.EnumField{.{ .name = decl.name, .value = i }};
+                            i += 1;
+                        }
+                    },
+                    else => {},
+                }
+            }
+        }
+    }
+    return @Type(.{
+        .Enum = .{
+            .tag_type = std.math.IntFittingRange(0, enum_fields.len - 1),
+            .fields = enum_fields,
+            .decls = &[_]std.builtin.Type.Declaration{},
+            .is_exhaustive = true,
+        },
+    });
+}
+
 fn NamespacedComponents(comptime modules: anytype) type {
     var fields: []const std.builtin.Type.StructField = &[0]std.builtin.Type.StructField{};
     inline for (modules) |M| {
@@ -171,9 +244,123 @@ test Modules {
     testing.refAllDeclsRecursive(Sprite2D);
 
     // access namespaced components
-    try testing.expectEqual(Physics.components.location, @TypeOf(modules).components.engine_physics.location);
-    try testing.expectEqual(Renderer.components, @TypeOf(modules).components.engine_renderer);
+    try testing.expect(type, Physics.components.location).eql(@TypeOf(modules).components.engine_physics.location);
+    try testing.expect(type, Renderer.components).eql(@TypeOf(modules).components.engine_renderer);
 
     // implicitly generated
     _ = @TypeOf(modules).components.entity.id;
 }
+
+test EventName {
+    const Physics = Module(struct {
+        pub const name = .engine_physics;
+        pub const components = struct {};
+
+        pub fn foo() !void {}
+        pub fn bar() !void {}
+
+        pub const local = struct {
+            pub fn baz() !void {}
+            pub fn bam() !void {}
+        };
+    });
+
+    const Renderer = Module(struct {
+        pub const name = .engine_renderer;
+        pub const components = struct {};
+
+        pub fn tick() !void {}
+        pub fn foo() !void {} // same .foo name as .engine_physics.foo
+        pub fn bar() !void {} // same .bar name as .engine_physics.bar
+    });
+
+    const Sprite2D = Module(struct {
+        pub const name = .engine_sprite2d;
+
+        pub fn tick() void {} // same .tick as .engine_renderer.tick
+        pub const local = struct {
+            pub fn foobar() void {}
+        };
+    });
+
+    const Mods = Modules(.{
+        Physics,
+        Renderer,
+        Sprite2D,
+    });
+    const info = @typeInfo(EventName(Mods.modules)).Enum;
+
+    try testing.expect(type, u3).eql(info.tag_type);
+    try testing.expect(usize, 6).eql(info.fields.len);
+    try testing.expect([]const u8, "foo").eql(info.fields[0].name);
+    try testing.expect([]const u8, "bar").eql(info.fields[1].name);
+    try testing.expect([]const u8, "baz").eql(info.fields[2].name);
+    try testing.expect([]const u8, "bam").eql(info.fields[3].name);
+    try testing.expect([]const u8, "tick").eql(info.fields[4].name);
+    try testing.expect([]const u8, "foobar").eql(info.fields[5].name);
+}
+
+test "event name calling" {
+    // TODO: verify that event handlers error return signatures are correct
+    const global = struct {
+        var ticks: usize = 0;
+        var physics_updates: usize = 0;
+        var renderer_updates: usize = 0;
+    };
+    const Physics = Module(struct {
+        pub const name = .engine_physics;
+        pub const components = struct {};
+
+        pub fn tick() void {
+            global.ticks += 1;
+        }
+
+        pub const local = struct {
+            pub fn update() void {
+                global.physics_updates += 1;
+            }
+        };
+    });
+    const Renderer = Module(struct {
+        pub const name = .engine_physics;
+        pub const components = struct {};
+
+        pub fn tick() void {
+            global.ticks += 1;
+        }
+
+        pub const local = struct {
+            pub fn update() void {
+                global.renderer_updates += 1;
+            }
+        };
+    });
+
+    var modules: Modules(.{
+        Physics,
+        Renderer,
+    }) = undefined;
+    try modules.init(testing.allocator);
+    defer modules.deinit(testing.allocator);
+
+    @TypeOf(modules).call(.tick, .{});
+    try testing.expect(usize, 2).eql(global.ticks);
+
+    // Check we can use .call() with a runtime-known value.
+    const alloc = try testing.allocator.create(u3);
+    defer testing.allocator.destroy(alloc);
+    const E = EventName(@TypeOf(modules).modules);
+    alloc.* = @intFromEnum(@as(E, .tick));
+
+    var event_name = @as(E, @enumFromInt(alloc.*));
+    @TypeOf(modules).call(event_name, .{});
+    try testing.expect(usize, 4).eql(global.ticks);
+
+    // Now check call() with a valid enum, but not a valid global event handler
+    alloc.* = @intFromEnum(@as(E, .update));
+    event_name = @as(E, @enumFromInt(alloc.*));
+    @TypeOf(modules).call(event_name, .{});
+    try testing.expect(usize, 4).eql(global.ticks);
+    try testing.expect(usize, 0).eql(global.physics_updates);
+    try testing.expect(usize, 0).eql(global.renderer_updates);
+}