Backlog/engine/core/src/engineObject.zig

const std = @import("std");
const logging = @import("logging.zig");
const p2 = @import("p2");
const engine_logs = logging.engine_logs;

const ObjectHandle = p2.ObjectHandle;
const Name = p2.Name;
const MakeName = p2.MakeName;

const ArrayList = std.ArrayList;
const AutoHashMap = std.AutoHashMap;

const ArrayListUnmanaged = std.ArrayListUnmanaged;
const AutoHashMapUnmanaged = std.AutoHashMapUnmanaged;

pub fn InterfaceRef(comptime Vtable: type) type {
    return struct {
        ptr: *anyopaque,
        vtable: *const Vtable,
    };
}

pub fn InterfaceRef2(comptime Vtable: type) type {
    return struct {
        ptr: *anyopaque,
        vtable: *Vtable,
    };
}

pub fn MakeTypeName(comptime TargetType: type) Name {
    const hashedName = comptime std.fmt.comptimePrint("{s}_{d}", .{ @typeName(TargetType), @sizeOf(TargetType) });

    return MakeName(hashedName);
}

// todo.. engineObject is not the right word for this

pub const EngineDataEventError = error{
    UnknownStatePanic,
    BadInit,
    JobsAbortShutdown,
    UnknownError,
    OutOfMemory,
};

const FuncInfo = struct {
    name: []const u8,
    ptr: *const anyopaque,
};

pub const FieldInfo = struct {
    name: []const u8,
    size: u32,
    offset: u32,
    alignment: u32,
};

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

pub fn updateEngineVTable(comptime T: type) void {
    const ref = core.getEngineObjectRef(T).?;
    const vtable: *EngineObjectVTable = @constCast(ref.vtable);
    const version = vtable.version;

    if (ref.vtable.fieldList) |fieldList| {
        core.PatchStruct(T, @ptrCast(@alignCast(ref.ptr)), fieldList);
    }

    vtable.* = T.NeonObjectTable;
    vtable.version = version + 1;
}

pub fn PatchStruct(comptime T: type, p: *T, old: []const FieldInfo) void {
    const t = @typeInfo(T).@"struct";

    var new: T = .{};

    inline for (t.fields) |field| {
        var oldField: ?FieldInfo = null;

        for (old) |oldFieldSearch| {
            if (std.mem.eql(u8, field.name, oldFieldSearch.name)) {
                oldField = oldFieldSearch;
                break;
            }
        }

        if (oldField) |of| {
            var src: []const u8 = undefined;
            src.ptr = @ptrCast(p);
            src.ptr += of.offset;
            src.len = @sizeOf(@TypeOf(@field(p, field.name)));

            var dest: []u8 = undefined;
            dest.ptr = @ptrCast(&@field(new, field.name));
            dest.len = @sizeOf(@TypeOf(@field(new, field.name)));

            //  std.debug.print(
            //      "patching field {s} {d} bytes {d}  ->  {d} {s}\n",
            //      .{
            //          field.name,
            //          src.len,
            //          of.offset,
            //          @offsetOf(T, field.name),
            //          if (of.offset == @offsetOf(T, field.name)) "" else "change!",
            //      },
            //  );

            std.mem.copyForwards(u8, dest, src);
        } else {
            std.debug.print("new field added {s}", .{field.name});
        }
    }

    p.* = new;
}

pub fn EngineObjectDelegate(comptime T: type) type {
    return struct {
        func: ?T = null,
        target: *anyopaque,

        functionName: []const u8,
        version: i32 = -1,
        vtable: *EngineObjectVTable,

        pub fn make(ptr: anytype, comptime funcName: []const u8) @This() {
            const TargetType = @typeInfo(@TypeOf(ptr)).pointer.child;
            const func = @field(TargetType, funcName);

            return .{
                .func = func,
                .functionName = funcName,
                .target = ptr,
                .vtable = &TargetType.NeonObjectTable,
            };
        }

        pub fn call(self: *@This(), args: anytype) void {
            //if (!core.BuildOption("static_build")) {  todo; disable this vtable check in non-static builds
            if (self.vtable.version != self.version) {
                self.version = self.vtable.version;
                if (self.vtable.findFunc(self.functionName)) |p| {
                    self.func = @ptrCast(@alignCast(p));
                } else {
                    core.engine_log("unable to find function {s} in {s}", .{ self.functionName, self.vtable.typeName });
                    self.func = null;
                }
            }
            //}

            if (self.func) |func| {
                func(self.target, args);
            }
        }
    };
}

pub const EngineObjectVTable = struct {
    typeName: []const u8,
    typeSize: usize,
    typeAlign: usize,

    singletonName: ?[]const u8 = null,

    // new init_function passes in an already created object
    init_func: *const fn (*anyopaque, std.mem.Allocator, bool) EngineDataEventError!void,
    tick_func: ?*const fn (*anyopaque, f64) void = null,
    engineDraw_func: ?*const fn (*anyopaque, f64) void = null,
    preTick_func: ?*const fn (*anyopaque, f64) EngineDataEventError!void = null,
    deinit_func: ?*const fn (*anyopaque) void = null,
    postInit_func: ?*const fn (*anyopaque) EngineDataEventError!void = null,
    processEvents: ?*const fn (*anyopaque, u64) EngineDataEventError!void = null,
    exitSignal_func: ?*const fn (*anyopaque) EngineDataEventError!void = null,
    readyToExit_func: ?*const fn (*anyopaque) bool = null,

    prepare_func: ?*const fn (*anyopaque) EngineDataEventError!void = null,
    fieldListHash: ?usize = null,
    fieldList: ?[]const FieldInfo = null,
    slackSize: ?usize = null,

    funcList: ?[]const FuncInfo = null,
    version: i32 = 0,

    pub fn findFunc(self: *const @This(), name: []const u8) ?*const anyopaque {
        if (self.funcList) |flist| {
            for (flist) |fi| {
                // core.engine_log("checking func {s} vs {s}.", .{ fi.name, name });
                if (std.mem.eql(u8, fi.name, name)) {
                    return fi.ptr;
                }
            }
        }
        return null;
    }

    pub fn addFunctionsList(self: *@This(), comptime TargetType: type) void {
        const ti = @typeInfo(TargetType);

        const funcList = blk: {
            comptime var f: []const FuncInfo = &.{};
            inline for (ti.@"struct".decls) |decl| {
                if (std.mem.eql(u8, decl.name, "NeonObjectTable")) {
                    continue;
                }

                const t = @typeInfo(@TypeOf(@field(TargetType, decl.name)));

                switch (t) {
                    .@"fn" => {
                        // @compileLog(decl.name);
                        f = f ++ .{FuncInfo{
                            .name = decl.name,
                            .ptr = @ptrCast(@alignCast(&@field(TargetType, decl.name))),
                        }};
                    },
                    else => {},
                }
            }

            break :blk f;
        };

        self.funcList = funcList;
    }

    fn fieldInfoCompare(_: void, a: FieldInfo, b: FieldInfo) bool {
        return a.offset < b.offset;
    }

    pub fn addFieldList(self: *@This(), comptime TargetType: type) void {
        if (!@hasDecl(TargetType, "Slack")) {
            return;
        }

        self.slackSize = @sizeOf(TargetType.Slack);
        const typeinfo = @typeInfo(TargetType).@"struct";
        const fieldList = blk: {
            comptime var f: []const FieldInfo = &.{};
            inline for (typeinfo.fields) |field| {
                f = f ++ .{FieldInfo{
                    .name = field.name,
                    .offset = @intCast(@offsetOf(TargetType, field.name)),
                    .size = @intCast(@sizeOf(field.type)),
                    .alignment = @alignOf(field.type),
                }};
            }

            break :blk f;
        };

        self.fieldList = fieldList;
    }

    pub fn from(comptime TargetType: type, comptime engineObjectName: ?[]const u8) EngineObjectVTable {
        var self = EngineObjectVTable{
            .typeName = @typeName(TargetType),
            .typeSize = @sizeOf(TargetType),
            .typeAlign = @alignOf(TargetType),
            .init_func = undefined,
        };
        self.addFieldList(TargetType);
        self.addFunctionsList(TargetType);

        if (engineObjectName) |eon| {
            self.singletonName = eon;
        }

        if (@hasDecl(TargetType, "init")) {
            const wrappedInit = struct {
                pub fn func(p: *anyopaque, allocator: std.mem.Allocator, first: bool) EngineDataEventError!void {
                    const newObject: *TargetType = @ptrCast(@alignCast(p)); // funcFind(allocator) catch return error.BadInit;
                    newObject.init(allocator, first) catch return error.BadInit;
                    // return @as(*anyopaque, @ptrCast(newObject));
                }
            };

            self.init_func = wrappedInit.func;
        }

        if (@hasDecl(TargetType, "create")) {
            const wrappedInit = struct {
                pub fn func(p: *anyopaque, allocator: std.mem.Allocator, first: bool) EngineDataEventError!void {
                    const newObject: *TargetType = @ptrCast(@alignCast(p)); // funcFind(allocator) catch return error.BadInit;
                    newObject.create(allocator, first) catch return error.BadInit;
                    // return @as(*anyopaque, @ptrCast(newObject));
                }
            };

            self.init_func = wrappedInit.func;
        }

        // function used for objects created before engine loop starts;
        // this is a defferred startup
        //
        // will run normally during create if in systems thread
        //
        // or else will run
        if (@hasDecl(TargetType, "prepare")) {
            const wrap = struct {
                pub fn func(pointer: *anyopaque) EngineDataEventError!void {
                    var ptr = @as(*TargetType, @ptrCast(@alignCast(pointer)));
                    ptr.prepare() catch return error.BadInit;
                }
            };

            self.prepare_func = wrap.func;
        }

        if (@hasDecl(TargetType, "postInit")) {
            const wrappedPostInit = struct {
                pub fn func(pointer: *anyopaque) EngineDataEventError!void {
                    var ptr = @as(*TargetType, @ptrCast(@alignCast(pointer)));
                    try ptr.postInit();
                }
            };

            self.postInit_func = wrappedPostInit.func;
        }

        if (@hasDecl(TargetType, "preTick")) {
            const Wrapped = struct {
                pub fn func(pointer: *anyopaque, deltaTime: f64) EngineDataEventError!void {
                    var ptr = @as(*TargetType, @ptrCast(@alignCast(pointer)));
                    ptr.preTick(deltaTime) catch return error.UnknownStatePanic;
                }
            };

            self.preTick_func = Wrapped.func;
        }

        if (@hasDecl(TargetType, "engineDraw")) {
            const Wrapped = struct {
                pub fn func(pointer: *anyopaque, deltaTime: f64) void {
                    var ptr = @as(*TargetType, @ptrCast(@alignCast(pointer)));
                    ptr.engineDraw(deltaTime);
                }
            };

            self.engineDraw_func = Wrapped.func;
        }

        if (@hasDecl(TargetType, "tick")) {
            const Wrapped = struct {
                pub fn func(pointer: *anyopaque, deltaTime: f64) void {
                    var ptr = @as(*TargetType, @ptrCast(@alignCast(pointer)));
                    ptr.tick(deltaTime);
                }
            };

            self.tick_func = Wrapped.func;
        }

        if (@hasDecl(TargetType, "processEvents")) {
            const wrappedProcessEvents = struct {
                pub fn func(pointer: *anyopaque, frameNumber: u64) EngineDataEventError!void {
                    var ptr = @as(*TargetType, @ptrCast(@alignCast(pointer)));
                    try ptr.processEvents(frameNumber);
                }
            };

            self.processEvents = wrappedProcessEvents.func;
        }

        if (@hasDecl(TargetType, "onExitSignal")) {
            if (!@hasDecl(TargetType, "readyToExit")) {
                @compileError("engine object implemented onExitSignal but did not implement fn readyToExit() bool");
            }

            const wrappedProcessEvents = struct {
                pub fn onExitSignal(pointer: *anyopaque) EngineDataEventError!void {
                    var ptr = @as(*TargetType, @ptrCast(@alignCast(pointer)));
                    try ptr.onExitSignal();
                }

                pub fn readyToExit(pointer: *anyopaque) bool {
                    var ptr = @as(*TargetType, @ptrCast(@alignCast(pointer)));
                    return ptr.readyToExit();
                }
            };

            self.exitSignal_func = wrappedProcessEvents.onExitSignal;
            self.readyToExit_func = wrappedProcessEvents.readyToExit;
        }

        if (@hasDecl(TargetType, "deinit")) {
            const wrappedDeinit = struct {
                pub fn func(pointer: *anyopaque) void {
                    var ptr = @as(*TargetType, @ptrCast(@alignCast(pointer)));
                    ptr.deinit();
                }
            };

            self.deinit_func = wrappedDeinit.func;
        }

        if (@hasDecl(TargetType, "destroy")) {
            const wrappedDeinit = struct {
                pub fn func(pointer: *anyopaque) void {
                    var ptr = @as(*TargetType, @ptrCast(@alignCast(pointer)));
                    ptr.destroy();
                }
            };

            self.deinit_func = wrappedDeinit.func;
        }

        return self;
    }
};

pub const EngineObjectRef = InterfaceRef2(EngineObjectVTable);