sandwich/src/main.rs

use std::fs;
use std::env;
use std::fmt;
use std::usize;
use std::collections::HashMap;

mod eval;

struct Program {
    data: Vec<String>,
    pc: usize,
    vars: HashMap<char, String>
}

impl Program {
    fn from_string(program: String) -> Program {
        let mut op_list: Vec<String> = Vec::new();
        
        for opcode in program.split("\n").collect::<Vec<&str>>() {
            let new_op = opcode.to_owned();

            if new_op.len() != 0 {
                op_list.push(new_op.to_owned());
            }
        }

        return Program{ data: op_list, pc: 0, vars: HashMap::new() };
    }

    // Reads the arguments passed to an opcode, and inserts variables where necessary
    fn args_or_vars(&self, arguments: &str) -> String {
        let mut builder = String::from(""); // Empty string that will be rebuilt based on the loop
        let argument_vec: Vec<char> = arguments.chars().collect(); // Deconstructed arguments

        // Iterate through each char
        for index in 0..argument_vec.len() {
            let current_char = argument_vec[index];
            let str_to_push: String;

            if index > 0 {
                // Only test for the dollar sign if it's not the first character
                // This is because there can't be anything before the first character, otherwise it's not the first
                if argument_vec[index-1] == '$' {
                    // If the previous character is a dollar sign, we can skip this iteration because we know the variable has already been handled
                    continue;
                }
            }
            
            if current_char == '$' {
                // If the current char is a $, we know that the next char should be a variable
                let variable = argument_vec[index+1];

                let key = self.vars.get(&variable);
                match key {
                    Some(value) => str_to_push = value.to_string(),
                    None => panic!("NotFoundError: Variable {} has not been defined", variable)
                }

            } else {
                // If there's no variable, then just push the char that was already there
                str_to_push = current_char.to_string();
            }


            builder.push_str(&str_to_push);
        }

        builder
    }

    fn add_var(&mut self, arguments: &str) {
        let argument_vec: Vec<char> = arguments.chars().collect();
        let name = argument_vec[0];
        let value: String = argument_vec[1..].into_iter().collect();

        self.vars.insert(name, value);
    }

    fn parse(&mut self, instruction: &String) {
        // Opcode is the first character, arguments are everything after the first char
        let opcode = instruction.chars().collect::<Vec<char>>()[0];
        let arguments = &instruction[1..];

        match opcode {
            'p' => println!("{}", self.args_or_vars(arguments)),
            'a' => println!("{}", eval::do_math(self.args_or_vars(arguments), '+')),
            's' => println!("{}", eval::do_math(self.args_or_vars(arguments), '-')),
            'm' => println!("{}", eval::do_math(self.args_or_vars(arguments), '*')),
            'd' => println!("{}", eval::do_math(self.args_or_vars(arguments), '/')),
            'l' => self.add_var(arguments),
            '#' => {}, // Do nothing for comments
            _ => panic!("SyntaxError: No such opcode: {}", self.pc)
        }
    }

    fn run(&mut self) {
        println!("{}", self);
        while self.pc < self.data.len() {
            // Grab instruction from op list and parse the instruction
            let instruction = self.data[self.pc].to_owned();

            self.parse(&instruction);

            self.pc += 1;
        }
    }
}

impl fmt::Display for Program {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "Program ({:?})", self.data)
    }
}

fn main() {
    // Grab args and a filename
    let args: Vec<String> = env::args().collect();
    if args.len() == 1 {
        // Args will always have at least 1 argument, which is the name of the executable. 
        // That's why we're checking index 1, not index 0.
        panic!("You must provide a filename!");
    }

    let filename = &args[1];

    // Read contents of the provided file and construct a symbolic Program from it
    let contents = fs::read_to_string(filename).expect("Something went wrong reading the file");
    let mut prog = Program::from_string(contents);
    prog.run();
}

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

    fn make_program(contents: &str) -> Program {
        Program::from_string(contents.to_string())
    }

    #[test]
    fn test_math() {
        assert_eq!(eval::do_math("2-2".to_string(), '+'), 4);
    }

    #[test]
    #[should_panic]
    fn test_undefined_opcode() {
        make_program("Hello\nWorld!").run();
    }

    #[test]
    #[should_panic]
    fn test_undefined_variable() {
        make_program("p$v").run();
    }

}