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const std = @import("std");

const MyApp = App(i32);

fn myLoad(context: *MyApp.Context) !void {
    std.debug.warn("load: {}\n", .{context.model});
    context.model += 1;
}

fn myUnload(context: *MyApp.Context) void {
    std.debug.warn("load: {}\n", .{context.model});
}

pub fn main() !void {
    var app = try MyApp.init(.{
        .allocator = null,
        .model = 42,
        .load = myLoad,
        .unload = myUnload,
    });
    defer app.deinit();
}

pub fn AppContext(comptime T: type) type {
    return struct {
        const Self = @This();

// Set by user.
        allocator: ?*std.mem.Allocator,
        model: T,

load: fn(context: *Self) anyerror!void,
        unload: fn(context: *Self) void,

// Internal.
        err: ?anyerror = null,

pub fn foo(self: *Self, yes: bool) void { }
    };
}

pub fn AppConfig(comptime Context: type, comptime Model: type) type {
    return struct {
        allocator: ?*std.mem.Allocator,
        model: Model,

load: ?fn(context: *Context) anyerror!void = null,
        unload: ?fn(context: *Context) void = null,
    };
}

pub fn App(comptime Model: type) type {
    return struct {
        const Self = @This();
        pub const Context = AppContext(Model);
        pub const Config = AppConfig(Context, Model);

context: Context,

pub fn init(config: Config) !Self {
            var self = Self{
                .context = .{
                    .allocator = config.allocator,
                    .model = config.model,
                    .load = config.load orelse noopLoad,
                    .unload = config.unload orelse noopUnload,
                },
            };
            try self.context.load(&self.context);
            return self;
        }

pub fn deinit(self: *Self) void {
            self.context.unload(&self.context);
        }

pub fn run(self: *Self) !void {
            while (true) {
                // event loop
            }
        }
        
        fn noopLoad(ctx: *Context) !void { }
        fn noopUnload(ctx: *Context) void { }
    };
}