.zflecs = .{ .path = "libs/zflecs" },

pub fn build(b: *std.Build) void {
    const exe = b.addExecutable(.{ ... });

    const zflecs = b.dependency("zflecs", .{});
    exe.root_module.addImport("zflecs", zflecs.module("root"));
    exe.linkLibrary(zflecs.artifact("flecs"));
}

const std = @import("std");
const ecs = @import("zflecs");

const Position = struct { x: f32, y: f32 };
const Velocity = struct { x: f32, y: f32 };
const Eats = struct {};
const Apples = struct {};

fn move(it: *ecs.iter_t) callconv(.C) void {
    const p = ecs.field(it, Position, 1).?;
    const v = ecs.field(it, Velocity, 2).?;

    const type_str = ecs.table_str(it.world, it.table).?;
    std.debug.print("Move entities with [{s}]\n", .{type_str});
    defer ecs.os.free(type_str);

    for (0..it.count()) |i| {
        p[i].x += v[i].x;
        p[i].y += v[i].y;
    }
}

pub fn main() !void {
    const world = ecs.init();
    defer _ = ecs.fini(world);

    ecs.COMPONENT(world, Position);
    ecs.COMPONENT(world, Velocity);

    ecs.TAG(world, Eats);
    ecs.TAG(world, Apples);

    {
        var system_desc = ecs.system_desc_t{};
        system_desc.callback = move;
        system_desc.query.filter.terms[0] = .{ .id = ecs.id(Position) };
        system_desc.query.filter.terms[1] = .{ .id = ecs.id(Velocity) };
        ecs.SYSTEM(world, "move system", ecs.OnUpdate, &system_desc);
    }

    const bob = ecs.new_entity(world, "Bob");
    _ = ecs.set(world, bob, Position, .{ .x = 0, .y = 0 });
    _ = ecs.set(world, bob, Velocity, .{ .x = 1, .y = 2 });
    ecs.add_pair(world, bob, ecs.id(Eats), ecs.id(Apples));

    _ = ecs.progress(world, 0);
    _ = ecs.progress(world, 0);

    const p = ecs.get(world, bob, Position).?;
    std.debug.print("Bob's position is ({d}, {d})\n", .{ p.x, p.y });
}