5 files changed, 242 insertions, 1 deletions
diff --git a/2020/rust/Cargo.toml b/2020/rust/Cargo.toml
index 3949f7e..6ace855 100644
--- a/2020/rust/Cargo.toml
+++ b/2020/rust/Cargo.toml
@@ -8,7 +8,7 @@ members = [
     "day05",
     "day06",
     "day07",
-#    "day08",
+    "day08",
 #    "day09",
 #    "day10",
 #    "day11",
diff --git a/2020/rust/day08/Cargo.toml b/2020/rust/day08/Cargo.toml
new file mode 100644
index 0000000..bb718df
--- /dev/null
+++ b/2020/rust/day08/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "day08"
+version = "0.1.0"
+authors = ["cos <cos>"]
+edition = "2018"
+
+[dependencies]
+aoc = { path = "../aoc" }
+anyhow = "1.0"
diff --git a/2020/rust/day08/src/intcode/mod.rs b/2020/rust/day08/src/intcode/mod.rs
new file mode 100644
index 0000000..5ec50e3
--- /dev/null
+++ b/2020/rust/day08/src/intcode/mod.rs
@@ -0,0 +1,134 @@
+use std::convert::TryFrom;
+use std::error::Error;
+use std::fmt;
+
+const DEBUG: bool = false;
+
+#[derive(Clone,Debug)]
+pub enum Instruction {
+    Acc(Wordsize),
+    Jmp(Wordsize),
+    Nop(Wordsize),
+}
+
+#[derive(Debug)]
+pub enum InstructionError {
+    InvalidOperation,
+    InvalidArgument,
+    Parse(std::num::ParseIntError),
+}
+
+impl fmt::Display for InstructionError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "InstructionError")
+    }
+}
+
+impl Error for InstructionError { }
+
+impl TryFrom<String> for Instruction {
+    type Error = InstructionError;
+
+    fn try_from(string: String) -> Result<Self, Self::Error> {
+        Instruction::try_from(string.as_str())
+    }
+}
+
+impl TryFrom<&str> for Instruction {
+    type Error = InstructionError;
+
+    fn try_from(string: &str) -> Result<Self, Self::Error> {
+        let mut iter = string.split(" ");
+        let (op, arg) = (iter.next().ok_or(InstructionError::InvalidOperation)?,
+            iter.next().ok_or(InstructionError::InvalidArgument)?);
+        let num = arg.parse().map_err(InstructionError::Parse)?;
+        match op {
+            "nop" => Ok(Instruction::Nop(num)),
+            "jmp" => Ok(Instruction::Jmp(num)),
+            "acc" => Ok(Instruction::Acc(num)),
+            _ => Err(InstructionError::InvalidOperation),
+        }
+    }
+}
+
+pub type Wordsize = i128;
+
+#[derive(Clone,Debug)]
+pub struct Registers {
+    pub ip: usize,
+    pub accumulator: Wordsize,
+}
+
+pub struct Intcode {
+  program: Vec<Instruction>,
+  registers: Registers,
+}
+
+impl Intcode {
+    pub fn new() -> Intcode {
+        Intcode {
+            program: vec![],
+            registers: Registers {
+                accumulator: 0,
+                ip: 0,
+            }
+        }
+    }
+
+    fn op_acc(&mut self, arg: &Wordsize) {
+        self.registers.accumulator += arg;
+    }
+
+    fn op_jmp(&mut self, arg: &Wordsize) {
+        if *arg >= 0 {
+            self.registers.ip += *arg as usize;
+        } else {
+            self.registers.ip -= (*arg * -1) as usize;
+        }
+    }
+
+    pub fn load(&mut self, program: &[Instruction]) {
+        if DEBUG {
+            eprintln!("{:?}", program);
+        }
+        self.program = program.into();
+    }
+
+    pub fn regdump(&self) -> Registers {
+        self.registers.clone()
+    }
+
+    pub fn step(&mut self) -> Result<(), IntcodeError>{
+        let op = match self.program.get(self.registers.ip) {
+            Some(v) => v.clone(),
+            None => return Err(IntcodeError::MemoryAccessViolation),
+        };
+        if DEBUG {
+            eprintln!("ip: {}, op: {:?}", self.registers.ip, op);
+        }
+        match op {
+            Instruction::Acc(arg) => self.op_acc(&arg),
+            Instruction::Jmp(arg) => self.op_jmp(&arg),
+            Instruction::Nop(_) => {},
+        }
+        match op {
+            Instruction::Jmp(_) => {},
+            _ => self.registers.ip += 1,
+        }
+
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+pub enum IntcodeError {
+    MemoryAccessViolation,
+}
+
+impl fmt::Display for IntcodeError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "IntcodeError")
+    }
+}
+
+impl Error for IntcodeError { }
diff --git a/2020/rust/day08/src/lib.rs b/2020/rust/day08/src/lib.rs
new file mode 100644
index 0000000..b6b007e
--- /dev/null
+++ b/2020/rust/day08/src/lib.rs
@@ -0,0 +1 @@
+pub mod intcode;
diff --git a/2020/rust/day08/src/main.rs b/2020/rust/day08/src/main.rs
new file mode 100644
index 0000000..884ba54
--- /dev/null
+++ b/2020/rust/day08/src/main.rs
@@ -0,0 +1,97 @@
+use anyhow::Result;
+use std::convert::TryFrom;
+use std::env::args;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::path::Path;
+
+use day08::intcode::{Instruction, Intcode};
+use day08::intcode;
+
+fn read_input<T: AsRef<Path>>(filename: T) -> Result<Vec<Instruction>> {
+    let f = File::open(filename)?;
+    let reader = BufReader::new(f);
+
+    reader.lines()
+        .map(|v| Ok(Instruction::try_from(v?)?))
+        .collect()
+}
+
+fn part1(program: &[Instruction]) -> Result<intcode::Wordsize> {
+    let mut visited = vec![];
+    let mut intcode = Intcode::new();
+    intcode.load(program);
+
+    loop {
+        let registers = intcode.regdump();
+        if visited.contains(&registers.ip) {
+            return Ok(registers.accumulator);
+        }
+        visited.push(registers.ip);
+        intcode.step()?
+    }
+}
+
+fn part2(program: &[Instruction]) -> Option<intcode::Wordsize> {
+    'reset: for i in 0..program.len() {
+        let mut modified = program.to_vec();
+        match modified.get_mut(i) {
+            Some(instruction) => match instruction {
+                Instruction::Jmp(arg) => *instruction = Instruction::Nop(*arg),
+                Instruction::Nop(arg) => *instruction = Instruction::Jmp(*arg),
+                _ => {},
+            },
+            None => panic!("Invalid loop index"),
+        }
+
+        let mut visited = vec![];
+        let mut intcode = Intcode::new();
+        intcode.load(&modified);
+
+        loop {
+            let registers = intcode.regdump();
+            if visited.contains(&registers.ip) {
+                continue 'reset;
+            }
+            visited.push(registers.ip);
+            match intcode.step() {
+                Ok(_) => {},
+                Err(_) => {
+                    // Weird as it might seem, Error is Success in this aoc case.
+                    let registers = intcode.regdump();
+                    return Some(registers.accumulator);
+                }
+            }
+        }
+    }
+    None
+}
+
+fn main() {
+    let (do_part_1, do_part_2) = aoc::do_parts();
+
+    let filename = match args().nth(1) {
+        Some(f) => f,
+        None => {
+            eprintln!("Missing input filename");
+            std::process::exit(1);
+        },
+    };
+    match read_input(filename) {
+        Ok(input) => {
+            if do_part_1 {
+                match part1(&input) {
+                    Ok(solution) => println!("Part1, {}", solution),
+                    Err(err) => eprintln!("Part1, {}", err),
+                }
+            }
+            if do_part_2 {
+                match part2(&input) {
+                    Some(solution) => println!("Part2, {}", solution),
+                    None => eprintln!("Part2, no solution found"),
+                }
+            }
+        },
+        Err(err) => eprintln!("Could not read input: {}", err),
+    }
+}