#include <union.h>
#include <iostream>

// This example shows how to use union relationships. Union relationships behave
// much like exclusive relationships in that entities can have only one instance
// and that adding an instance removes the previous instance.
//
// What makes union relationships stand out is that changing the relationship
// target doesn't change the archetype of an entity. This allows for quick
// switching of tags, which can be useful when encoding state machines in ECS.
//
// There is a tradeoff, and that is that because a single archetype can contain
// entities with multiple targets, queries need to do a bit of extra work to
// only return the requested target. 
//
// This code uses enumeration relationships. See the enum_relations example for
// more details.

enum Movement {
    Walking,
    Running
};

enum Direction {
    Front,
    Back,
    Left,
    Right
};

int main(int argc, char *argv[]) {
    flecs::world ecs(argc, argv);

    ecs.component<Movement>().add(flecs::Union);
    ecs.component<Direction>().add(flecs::Union);

    // Create a query that subscribes for all entities that have a Direction
    // and that are walking
    flecs::query<> q = ecs.query_builder()
        .with(Walking)
        .with<Direction>(flecs::Wildcard)
        .build();

    // Create a few entities with various state combinations
    ecs.entity("e1")
        .add(Walking)
        .add(Front);

    ecs.entity("e2")
        .add(Running)
        .add(Left);

    flecs::entity e3 = ecs.entity("e3")
        .add(Running)
        .add(Back);

    // Add Walking to e3. This will remove the Running case
    e3.add(Walking);

    // Iterate the query
    q.iter([&](const flecs::iter& it) {
        // Get the column with direction states. This is stored as an array
        // with identifiers to the individual states
        auto movement = it.field<flecs::entity_t>(1);
        auto direction = it.field<flecs::entity_t>(2);

        for (auto i : it) {
            // Movement will always be Walking, Direction can be any state
            std::cout << it.entity(i).name() 
                << ": Movement: " 
                << it.world().get_alive(movement[i]).name()
                << ", Direction: "
                << it.world().get_alive(direction[i]).name()
                << std::endl;
        }
    });

    // Output:
    //   e3: Movement: Walking, Direction: Back
    //   e1: Movement: Walking, Direction: Front

    return 0;
}