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

mod eval;

struct Program {
    data: Vec<String>,
    pc: usize,
    vars: HashMap<char, String>,
    funcs: 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(),
            funcs: 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 mut value: String = argument_vec[1..].into_iter().collect();
        value = self.args_or_funcs(&value);

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

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

        self.funcs.insert(name, body);
    }

    fn parse_funcs(&mut self, instruction: &String) -> u32 {
        // Opcode is the first character, arguments are everything after the first char
        let opcode = instruction.chars().collect::<Vec<char>>()[0];
        let arguments = &instruction[1..];

        // Only a subset of opcodes, because the others don't make sense in a function
        match opcode {
            'a' => eval::do_math(self.args_or_funcs(&self.args_or_vars(arguments)), '+'),
            's' => eval::do_math(self.args_or_funcs(&self.args_or_vars(arguments)), '-'),
            'm' => eval::do_math(self.args_or_funcs(&self.args_or_vars(arguments)), '*'),
            'd' => eval::do_math(self.args_or_funcs(&self.args_or_vars(arguments)), '/'),
            'l' => {self.add_var(arguments);0}
            _ => panic!("SyntaxError: No such opcode: {}", self.pc),
        }
    }

    fn args_or_funcs(&mut self, arguments: &str) -> String {
        let mut builder = String::from("");
        let argument_vec: Vec<char> = arguments.chars().collect();

        for index in 0..argument_vec.len() {
            let current_char = argument_vec[index];
            let str_to_push: String;

            if index > 0 {
                if argument_vec[index-1] == '*' {
                    continue;
                }
            }

            if current_char == '*' {
                let func_name = argument_vec[index+1];
                let body: String;

                let key = (self).funcs.get(&func_name);
                match key {
                    Some(content) => body = content.to_owned(),
                    None => panic!("ValueError: function {} has not been defined yet!", func_name)
                }

                str_to_push = self.parse_funcs(&body).to_string();
            } else {
                str_to_push = current_char.to_string();
            }

            builder.push_str(&str_to_push);
        }

        builder
    }

    fn run_external(&mut self, filename: String) {
        // 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();
    }

    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 = eval::args_or_comments(&instruction[1..]);

        if opcode != '#' {
            match opcode {
                'p' => println!("{}", self.args_or_funcs(&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),
                'f' => self.add_func(&arguments),
                'i' => self.run_external(arguments),
                _ => panic!("SyntaxError at opcode {}: Unknown opcode {}", self.pc, opcode),
            }
        }
    }

    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();
    }

    #[test]
    #[should_panic]
    fn test_undefined_function() {
        make_program("p*x").run();
    }

    #[test]
    fn test_factory() {
        let prog = make_program("lhHello\nlwWorld\np$h $w");
        let vec_to_check: Vec<String> = vec!["lhHello", "lwWorld", "p$h $w"].into_iter().map(|s| s.to_string()).collect();

        assert_eq!(prog.data, vec_to_check);
    }

    #[test]
    fn test_args() {
        let mut prog = make_program("lhHello\nlwWorld\np$h $w");
        prog.run();

        let args_to_check: HashMap<char, String> = [('h', String::from("Hello")), ('w', String::from("World"))].iter().cloned().collect();

        assert_eq!(prog.vars, args_to_check);
    }
    
    #[test]
    fn test_funcs() {
        let mut prog = make_program("fxa10-10\nfys10-5\np*x *y");
        prog.run();

        let funcs_to_check: HashMap<char, String> = [('x', String::from("a10-10")), ('y', String::from("s10-5"))].iter().cloned().collect();

        assert_eq!(prog.funcs, funcs_to_check);
    }
}