rust-rl/src/ai/chase_ai_system.rs

use crate::{ Chasing, EntityMoved, Map, Position, TakingTurn, Telepath, Viewshed };
use bracket_lib::prelude::*;
use specs::prelude::*;
use std::collections::HashMap;
use super::approach_ai_system::get_adjacent_unblocked;

// If the target is beyond this distance, they're no longer being detected,
// so stop following them. This is essentially a combined value of the sound
// the target might be making, noise, light, etc., anything they could do to
// be detected. As those constituent systems are developed, this value should
// be changed to being a result of some calculations between them.
const MAX_CHASE_DISTANCE: usize = 15;
pub struct ChaseAI {}

impl<'a> System<'a> for ChaseAI {
    #[allow(clippy::type_complexity)]
    type SystemData = (
        WriteStorage<'a, TakingTurn>,
        WriteStorage<'a, Chasing>,
        WriteStorage<'a, Position>,
        WriteExpect<'a, Map>,
        WriteStorage<'a, Viewshed>,
        WriteStorage<'a, Telepath>,
        WriteStorage<'a, EntityMoved>,
        Entities<'a>,
    );

    fn run(&mut self, data: Self::SystemData) {
        let (
            mut turns,
            mut chasing,
            mut positions,
            mut map,
            mut viewsheds,
            mut telepaths,
            mut entity_moved,
            entities,
        ) = data;
        let mut targets: HashMap<Entity, (i32, i32)> = HashMap::new();
        let mut end_chase: Vec<Entity> = Vec::new();
        // For every chasing entity with a turn, look for a valid target position,
        // and if found, store that position in a temporary HashMap. This gets around
        // needing to read Position twice - that would cause borrowchecker issues.
        // If there's no valid target found, remove the chasing component.
        for (entity, _turn, chasing) in (&entities, &turns, &chasing).join() {
            if let Some(target_pos) = positions.get(chasing.target) {
                targets.insert(entity, (target_pos.x, target_pos.y));
            } else {
                end_chase.push(entity);
            }
        }
        for done in end_chase.iter() {
            chasing.remove(*done);
        }
        end_chase.clear();
        // Iterate over everyone who is *still* chasing, and path to the target
        // stored in the HashMap. If successful, follow the path. If not, remove
        // the chasing component.
        let mut turn_done: Vec<Entity> = Vec::new();
        for (entity, _turn, mut pos, _chase, mut viewshed) in (
            &entities,
            &turns,
            &mut positions,
            &chasing,
            &mut viewsheds,
        ).join() {
            turn_done.push(entity);
            let target_pos = targets[&entity];
            let target_idx = map.xy_idx(target_pos.0, target_pos.1);
            let target_idxs = if let Some(paths) = get_adjacent_unblocked(&map, target_idx) {
                paths
            } else {
                continue;
            };
            let mut path: Option<NavigationPath> = None;
            let idx = map.xy_idx(pos.x, pos.y);
            for tar_idx in target_idxs {
                let potential_path = a_star_search(idx, tar_idx, &mut *map);
                if potential_path.success && potential_path.steps.len() > 1 {
                    if
                        path.is_none() ||
                        potential_path.steps.len() < path.as_ref().unwrap().steps.len()
                    {
                        path = Some(potential_path);
                    }
                }
            }
            let path = if path.is_some() {
                path.unwrap()
            } else {
                continue;
            };
            if path.success && path.steps.len() > 1 && path.steps.len() < MAX_CHASE_DISTANCE {
                let idx = map.xy_idx(pos.x, pos.y);
                pos.x = (path.steps[1] as i32) % map.width;
                pos.y = (path.steps[1] as i32) / map.width;
                entity_moved.insert(entity, EntityMoved {}).expect("Failed to insert EntityMoved");
                let new_idx = map.xy_idx(pos.x, pos.y);
                crate::spatial::move_entity(entity, idx, new_idx);
                viewshed.dirty = true;
                if let Some(is_telepath) = telepaths.get_mut(entity) {
                    is_telepath.dirty = true;
                }
                turn_done.push(entity);
            } else {
                end_chase.push(entity);
            }
        }
        for done in end_chase.iter() {
            chasing.remove(*done);
        }
        for done in turn_done.iter() {
            turns.remove(*done);
        }
    }
}