use regex::Regex;
use std::collections::{HashMap, HashSet};

static DAY: u8 = 14;

fn main() {
    let input = advent::read_lines(DAY);
    println!("{DAY}a: {}", safety_factor(&input, Position { x: 101, y: 103 }));
    println!("{DAY}b: {}", find_tree(&input, Position { x: 101, y: 103 }));
}

#[derive(Eq, PartialEq, Hash, Clone, Copy)]
struct Position {
    x: isize,
    y: isize,
}

struct Robot {
    pos: Position,
    velocity: Position,
}

impl Robot {
    fn new(input: &str) -> Robot {
        let re = Regex::new(r"p=([0-9]+),([0-9]+) v=([-0-9]+),([-0-9]+)").unwrap();
        let caps = re.captures(input).unwrap();
        let x = caps.get(1).unwrap().as_str().parse::<isize>().unwrap();
        let y = caps.get(2).unwrap().as_str().parse::<isize>().unwrap();
        let dx = caps.get(3).unwrap().as_str().parse::<isize>().unwrap();
        let dy = caps.get(4).unwrap().as_str().parse::<isize>().unwrap();

        Robot {
            pos: Position { x, y },
            velocity: Position { x: dx, y: dy },
        }
    }

    fn travel(&mut self, area: &Position) {
        self.pos.x = (self.pos.x + self.velocity.x + area.x) % area.x;
        self.pos.y = (self.pos.y + self.velocity.y + area.y) % area.y;
    }

    fn quadrant(&self, area: &Position) -> u8 {
        if self.pos.x < area.x / 2 && self.pos.y < area.y / 2 {
            1
        } else if self.pos.x < area.x / 2 && self.pos.y > area.y / 2 {
            2
        } else if self.pos.x > area.x / 2 && self.pos.y < area.y / 2 {
            3
        } else if self.pos.x > area.x / 2 && self.pos.y > area.y / 2 {
            4
        } else {
            0
        }
    }
}

struct RobotMap {
    robots: Vec<Robot>,
    area: Position,
}

impl RobotMap {
    fn new(input: &[String], area: Position) -> RobotMap {
        let robots = input.iter()
                          .map(|line| Robot::new(line))
                          .collect::<Vec<_>>();
        RobotMap { robots, area }
    }

    fn tick(&mut self) {
        for robot in self.robots.iter_mut() {
            robot.travel(&self.area);
        }
    }

    fn safety_factor(&self) -> u32 {
        let mut quadrants = HashMap::new();
        for robot in &self.robots {
            let quadrant = robot.quadrant(&self.area);
            if quadrant != 0 {
                let entry = quadrants.entry(quadrant).or_insert(0);
                *entry += 1;
            }
        }
        quadrants.values().product()
    }

    fn to_text(&self) -> String {
        let mut map = String::new();

        let positions = self.robots.iter()
                                   .map(|robot| robot.pos)
                                   .collect::<HashSet<_>>();
        for y in 0 .. self.area.y {
            for x in 0 .. self.area.x {
                if positions.contains(&Position { x, y }) {
                    map += "*";
                } else {
                    map += ".";
                }
            }
            map += "\n";
        }
        map
    }

    fn draw(&self) {
        println!("{}", self.to_text());
    }
}

fn safety_factor(input: &[String], area: Position) -> u32 {
    let mut robotmap = RobotMap::new(input, area);

    for _ in 0 .. 100 {
        robotmap.tick();
    }
    robotmap.safety_factor()
}

fn find_tree(input: &[String], area: Position) -> u32 {
    let mut robotmap = RobotMap::new(input, area);
    let mut i = 0;
    loop {
        robotmap.tick();
        i += 1;
        /* output likely contains a lot of robots closely together */
        if robotmap.to_text().contains("*********") {
            robotmap.draw();
            return i;
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test() {
        let input = [
            "p=0,4 v=3,-3",
            "p=6,3 v=-1,-3",
            "p=10,3 v=-1,2",
            "p=2,0 v=2,-1",
            "p=0,0 v=1,3",
            "p=3,0 v=-2,-2",
            "p=7,6 v=-1,-3",
            "p=3,0 v=-1,-2",
            "p=9,3 v=2,3",
            "p=7,3 v=-1,2",
            "p=2,4 v=2,-3",
            "p=9,5 v=-3,-3",
        ].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
        assert_eq!(safety_factor(&input, Position { x: 11, y: 7}), 12);
    }
}