snake/src/snake.rs

use crate::components as c;
use bevy::prelude::*;

fn spawn_segment(
    mut commands: Commands,
    material: &Handle<ColorMaterial>,
    position: c::Position,
) -> Entity {
    commands
        .spawn_bundle(SpriteBundle {
            material: material.clone(),
            ..Default::default()
        })
        .insert(c::SnakeSegment)
        .insert(position)
        .insert(c::GridSize::square(0.65))
        .id()
}

pub fn spawn(
    mut commands: Commands,
    materials: Res<c::Materials>,
    mut segments: ResMut<c::SnakeSegments>,
) {
    segments.segments = vec![
        commands
            .spawn_bundle(SpriteBundle {
                material: materials.head_material.clone(),
                sprite: Sprite::new(Vec2::new(10.0, 10.0)),
                ..Default::default()
            })
            .insert(c::SnakeHead {
                direction: c::Direction::Up,
            })
            .insert(c::Position { x: 3, y: 3 })
            .insert(c::GridSize::square(0.8))
            .id(),
        spawn_segment(
            commands,
            &materials.segment_material,
            c::Position { x: 3, y: 2 },
        ),
    ]
}

pub fn input(keyboard_input: Res<Input<KeyCode>>, mut heads: Query<&mut c::SnakeHead>) {
    if let Some(mut head) = heads.iter_mut().next() {
        let dir = if keyboard_input.pressed(KeyCode::Left) {
            c::Direction::Left
        } else if keyboard_input.pressed(KeyCode::Down) {
            c::Direction::Down
        } else if keyboard_input.pressed(KeyCode::Up) {
            c::Direction::Up
        } else if keyboard_input.pressed(KeyCode::Right) {
            c::Direction::Right
        } else {
            head.direction
        };
        if dir != head.direction.opposite() {
            head.direction = dir;
        }
    }
}

pub fn movement(
    segments: ResMut<c::SnakeSegments>,
    mut heads: Query<(Entity, &c::SnakeHead)>,
    mut positions: Query<&mut c::Position>,
) {
    if let Some((head_entity, head)) = heads.iter_mut().next() {
        let segment_positions = segments
            .segments
            .iter()
            .map(|e| *positions.get_mut(*e).unwrap())
            .collect::<Vec<c::Position>>();
        let mut head_pos = positions.get_mut(head_entity).unwrap();
        match &head.direction {
            c::Direction::Left => head_pos.x -= 1,
            c::Direction::Right => head_pos.x += 1,
            c::Direction::Up => head_pos.y += 1,
            c::Direction::Down => head_pos.y -= 1,
        }
        segment_positions
            .iter()
            .zip(segments.segments.iter().skip(1))
            .for_each(|(pos, segment)| {
                *positions.get_mut(*segment).unwrap() = *pos;
            });
    }
}

pub fn eating(
    mut commands: Commands,
    mut growth_writer: EventWriter<c::GrowthEvent>,
    food_positions: Query<(Entity, &c::Position), With<c::Food>>,
    head_positions: Query<&c::Position, With<c::SnakeHead>>,
) {
    for head_pos in head_positions.iter() {
        for (ent, food_pos) in food_positions.iter() {
            if food_pos == head_pos {
                commands.entity(ent).despawn();
                growth_writer.send(c::GrowthEvent);
            }
        }
    }
}