1 files changed, 154 insertions, 0 deletions
diff --git a/2020/src/bin/day_8.rs b/2020/src/bin/day_8.rs
new file mode 100644
index 0000000..2c0c227
--- /dev/null
+++ b/2020/src/bin/day_8.rs
@@ -0,0 +1,154 @@
+use bevy::{app::AppExit, prelude::*};
+use std::convert::TryFrom;
+use std::io::{BufRead, BufReader};
+use std::{collections::BTreeSet, fs::File};
+
+fn main() {
+    App::build()
+        .add_resource(WindowDescriptor {
+            title: "Advent of Code".to_string(),
+            width: 1920,
+            height: 1080,
+            ..Default::default()
+        })
+        .add_resource(ClearColor(Color::rgb(0., 0., 0.)))
+        .add_startup_system(setup_camera.system())
+        .add_startup_system(read_input_file.system())
+        .add_stage("check_line")
+        .add_system_to_stage("check_line", track_program_line_execution.system())
+        .add_system_to_stage("check_line", track_program_termination.system())
+        .add_stage("exec")
+        .add_system_to_stage("exec", tick_computer.system())
+        .add_system_to_stage("exec", exit.system())
+        .add_plugins(DefaultPlugins)
+        .run();
+}
+
+fn setup_camera(mut commands: Commands) {
+    commands.spawn(Camera2dComponents::default());
+}
+
+struct Program {
+    ops: Vec<Op>,
+}
+#[derive(Clone)]
+enum Op {
+    Acc(i32),
+    Jmp(i32),
+    Nop(i32),
+}
+struct UnalteredProgram;
+#[derive(Default)]
+struct Computer {
+    program_counter: i32,
+    accumulator: i32,
+    termiated: bool,
+}
+#[derive(Default)]
+struct LineTracker(BTreeSet<i32>);
+
+impl Computer {
+    fn exec(&mut self, program: &Program) {
+        if self.termiated {
+            return;
+        }
+
+        let x = usize::try_from(self.program_counter).ok();
+        match x.and_then(|x| program.ops.get(x)) {
+            None => {}
+            Some(Op::Acc(val)) => {
+                self.accumulator += val;
+                self.program_counter += 1;
+            }
+            Some(Op::Jmp(val)) => {
+                self.program_counter += val;
+            }
+            Some(Op::Nop(_)) => {
+                self.program_counter += 1;
+            }
+        }
+        if self.program_counter >= program.ops.len() as i32 {
+            self.termiated = true;
+        }
+    }
+}
+
+fn read_input_file(mut commands: Commands) {
+    let f = File::open("./inputs/day_8.txt").unwrap();
+
+    let ops: Vec<Op> = BufReader::new(f)
+        .lines()
+        .map(|line| {
+            let line = line.unwrap();
+            let line = line.trim();
+
+            let mut line_parts = line.split_whitespace();
+            let opcode = line_parts.next().unwrap();
+            let val: i32 = line_parts.next().unwrap().parse().unwrap();
+            let op = match opcode {
+                "acc" => Op::Acc(val),
+                "jmp" => Op::Jmp(val),
+                "nop" => Op::Nop(val),
+                _ => panic!("Invalid opcode"),
+            };
+            op
+        })
+        .collect();
+    commands.spawn((
+        UnalteredProgram,
+        Program { ops: ops.clone() },
+        Computer::default(),
+        LineTracker::default(),
+    ));
+
+    for i in 0..ops.len() {
+        let mut ops = ops.clone();
+        ops[i] = match ops[i] {
+            Op::Nop(v) => Op::Jmp(v),
+            Op::Jmp(v) => Op::Nop(v),
+            Op::Acc(v) => Op::Acc(v),
+        };
+        commands.spawn((
+            Program { ops: ops.clone() },
+            Computer::default(),
+            LineTracker::default(),
+        ));
+    }
+}
+
+fn track_program_line_execution(
+    mut commands: Commands,
+    entity: Entity,
+    mut line_tracker: Mut<LineTracker>,
+    computer: &Computer,
+    unaltered: Option<&UnalteredProgram>,
+) {
+    if line_tracker.0.contains(&computer.program_counter) {
+        if unaltered.is_some() {
+            println!(
+                "About to execute a line for the second time! Line {}. Accumulator: {}",
+                computer.program_counter, computer.accumulator
+            );
+        }
+        commands.despawn(entity);
+    } else {
+        line_tracker.0.insert(computer.program_counter);
+    }
+}
+
+fn track_program_termination(mut commands: Commands, entity: Entity, computer: &Computer) {
+    if computer.termiated {
+        println!("Program terminated! Accumulator: {}", computer.accumulator);
+        commands.despawn(entity);
+    }
+}
+
+fn tick_computer(mut computer: Mut<Computer>, program: &Program) {
+    computer.exec(program);
+}
+
+fn exit(mut exit_events: ResMut<Events<AppExit>>, computers: Query<&Computer>) {
+    if computers.iter().len() == 0 {
+        exit_events.send(AppExit);
+    }
+}