Initial computer reading.

src/main.rs

@@ -1,4 +1,6 @@
 use clap::{App,Arg,SubCommand};
+use std::fs;
+use std::str;
 
 fn is_number(s: String) -> Result<(), String> {
     match u64::from_str_radix(&s, 10) {
@@ -7,6 +9,14 @@ fn is_number(s: String) -> Result<(), String> {
     }
 }
 
+fn is_file(s: String) -> Result<(), String> {
+    match fs::metadata(&s) {
+        Err(e) => Err(e.to_string()),
+        Ok(md) if md.is_file() => Ok(()),
+        _      => Err(format!("{} is not a file.", s))
+    }
+}
+
 fn calculate_base_fuel(mass: u64) -> u64 {
     let div3 = mass / 3;
 
@@ -32,6 +42,48 @@ fn calculate_fuel(mass: u64) -> u64 {
     }
 }
 
+struct Computer {
+    memory: Vec<u64>,
+    position: usize
+}
+
+impl Computer {
+    fn load(path: &str, position: usize) -> Computer {
+        let mut memory = vec![];
+        let byte_buffer = fs::read(path).unwrap();
+        let char_buffer = str::from_utf8(&byte_buffer).unwrap();
+
+        let mut current = 0;
+        for c in char_buffer.chars() {
+            match c {
+                ',' => {
+                    memory.push(current);
+                    current = 0;
+                }
+                _ if c.is_digit(10) => {
+                    let val = c.to_digit(10).unwrap() as u64;
+                    current = (current * 10) + val;
+                }
+                _ if c.is_whitespace() => {
+                }
+                _ => {
+                    panic!("Unrecognized character: '{}'", c);
+                }
+            }
+        }
+        memory.push(current);
+
+        Computer{ memory, position }
+    }
+
+    fn show(&self) {
+       for (idx, val) in self.memory.iter().enumerate() {
+           println!("{:08}: {}", idx, val);
+       }
+       println!("POSITION: {}", self.position);
+    }
+}
+
 fn main() {
     let matches = App::new("My Advent of Code Thing")
                       .version("1.0")
@@ -42,7 +94,22 @@ fn main() {
                                     .arg(Arg::with_name("NUM")
                                              .help("The mass of the ship")
                                              .multiple(true)
-                                             .validator(is_number)))
+                                             .validator(is_number))
+                                    )
+                      .subcommand(SubCommand::with_name("compute")
+                                    .about("run the given computer")
+                                    .arg(Arg::with_name("START_POSITION")
+                                             .short("p")
+                                             .long("start-position")
+                                             .help("The starting position to execute from.")
+                                             .default_value("0")
+                                             .validator(is_number))
+                                    .arg(Arg::with_name("COMPUTER")
+                                             .index(1)
+                                             .help("The computer to run.")
+                                             .required(true)
+                                             .validator(is_file))
+                                    )
                       .get_matches();
 
     if let Some(problem1) = matches.subcommand_matches("fuel") {
@@ -65,5 +132,13 @@ fn main() {
         }
     }
 
+    if let Some(problem2) = matches.subcommand_matches("compute") {
+        let start_pos_str = problem2.value_of("START_POSITION").unwrap();
+        let start_pos = usize::from_str_radix(&start_pos_str, 10).unwrap();
+        let mut computer = Computer::load(problem2.value_of("COMPUTER").unwrap(), start_pos);
+        println!("Initial Computer:");
+        computer.show();
+    }
+
     println!("Failed to run a reasonable command.");
 }