//! The Death Creation Step: the one place minions leave play.
//!
//! Damage and destroy effects only mark a minion (0 or less Health, or pending
//! destroy). It stays in play, and keeps triggering, until the outermost Phase
//! ends. Then this step removes every marked minion at once.

use super::event::Event;
use super::world::{EntityId, World, Zone};

/// Remove every mortally wounded or pending-destroy minion from play, simultaneously.
/// Returns their Death Events in order of play; empty if nothing died.
pub fn death_creation_step(world: &mut World) -> Vec<Event> {
    // Every neighbour is read before anything moves: removal is simultaneous. Each Death
    // Event remembers where its minion stood as a handle, the minion that stays to its
    // right, not as a board index: an index goes stale as soon as a minion further left
    // leaves play in the same step (Module 1: hold handles, not indexes).
    let mut deaths = Vec::new();
    for id in world.minions_in_play() {
        if world.is_doomed(id) {
            let before = survivor_to_the_right(world, id);
            deaths.push(Event::Destroyed { id, before });
        }
    }
    for death in &deaths {
        if let Event::Destroyed { id, before } = *death {
            world.kill(id, before);
        }
    }
    deaths
}

/// The nearest minion to the right of `id` on its board that is not leaving play in this step, if any.
fn survivor_to_the_right(world: &World, id: EntityId) -> Option<EntityId> {
    world
        .zone(world.owner_of(id), Zone::Board)
        .iter()
        .copied()
        .skip_while(|&other| other != id)
        .skip(1)
        .find(|&other| !world.is_doomed(other))
}