use ecs::event::component::Changed;
use ecs::pair::Pair;
use ecs::phase::UPDATE as UPDATE_PHASE;
use ecs::system::observer::Observe;
use ecs::{Component, Query, World};

#[derive(Component)]
struct SomeData
{
    num: u64,
}

#[derive(Component)]
struct Greeting
{
    greeting: String,
}

fn say_hello(query: Query<(&SomeData, &mut Greeting)>)
{
    for (data, mut greeting) in &query {
        println!("{}: {}", greeting.greeting, data.num);

        if greeting.greeting == "Good evening" {
            greeting.greeting = "Good morning".to_string();
            greeting.set_changed();
        }
    }
}

fn print_changed_greetings(observe: Observe<'_, Pair<Changed, Greeting>>)
{
    println!("\nChanged greetings:");

    for ent in &observe {
        let Some(greeting) = ent.get::<Greeting>() else {
            unreachable!();
        };

        println!("A greeting changed to {}", greeting.greeting);
    }

    println!("");
}

fn main()
{
    let mut world = World::new();

    world.register_system(*UPDATE_PHASE, say_hello);

    world.register_observer(print_changed_greetings);

    world.create_entity((
        SomeData { num: 987_654 },
        Greeting {
            greeting: "Good afternoon".to_string(),
        },
    ));

    world.create_entity((
        SomeData { num: 345 },
        Greeting { greeting: "Good evening".to_string() },
    ));

    world.step();

    world.step();

    for (mut greeting,) in &world.query::<(&mut Greeting,), ()>() {
        if greeting.greeting == "Good afternoon" {
            greeting.greeting = "Yo yo".to_string();
            greeting.set_changed();
        }
    }

    world.step();

    world.step();
}