You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: chase_ai_system.rs
    path of file: ./repos/rustrogueliketutorial/chapter-59-caverns2/src/ai
    
    the code of the file until where you have to start completion: use specs::prelude::*;
use crate::{MyTurn, Chasing, Position, Map, Viewshed, EntityMoved};
use std::collections::HashMap;

pub struct ChaseAI {}

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

    fn run(&mut self, data : Self::SystemData) {
        let (mut turns, mut chasing, mut positions,
    
    fn run(&mut self, data : Self::SystemData) {
        let (mut turns, mut chasing, mut positions, mut map,
            mut viewsheds, mut entity_moved, entities) = data;

        let mut targets : HashMap<Entity, (i32, i32)> = HashMap::new();
        let mut end_chase : Vec<Entity> = Vec::new();
        for (entity, _turn, chasing) in (&entities, &turns, &chasing).join() {
            let target_pos = positions.get(chasing.target);
            if let Some(target_pos) = target_pos {
                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();

        let mut turn_done : Vec<Entity> = Vec::new();
        for (entity, mut pos, _chase, mut viewshed, _myturn) in
            (&entities, &mut positions, &chasing, &mut viewsheds, &turns).join()
        {
            turn_done.push(entity);
            let target_pos = targets[&entity];
            let path = rltk::a_star_search(
                map.xy_idx(pos.x, pos.y),
                map.xy_idx(target_pos.0, target_pos.1),
                &mut *map
            );
            if path.success && path.steps.len()>1 && path.steps.len()<15 {
                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("Unable to insert marker");
                let new_idx = map.xy_idx(pos.x, pos.y);
                viewshed.dirty = true;
                crate::spatial::move_entity(entity, idx, new_idx);
                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);
        }
    }