nff 0.1.2

//! You can use this crate as a library for your own library instead of a command line program
// This file is part of "nff", which is free software: you
// can redistribute it and/or modify it under the terms of the GNU General
// Public License version 3 as published by the Free Software Foundation. See
// <https://www.gnu.org/licenses/> for a copy.

// libraries to read files defined by program caller
//use std::env::Args;
use std::fs::File;
use std::io::prelude::*;

use hashbrown::HashMap; // use hashmaps to associate lefthand and righthand sides

type Rule = Vec<Token>;

#[derive(Debug)]
enum Token {
    NONTERMINAL(char),
    TERMINAL(char),
    NULL,
}
/// Put all nonterminals in a single struct, one hashmap for rules and one each for
/// nullable, first, and follow.
pub struct NonTerminals {
    nullable_map: HashMap<char, bool>,
    first_map: HashMap<char, Vec<char>>,
    follow_map: HashMap<char, Vec<char>>,
    rule_map: HashMap<char, Vec<Rule>>,
}

impl NonTerminals {
    /// Init takes the grammar in the form of a string
    /// and initializes all the hashmaps.
    pub fn init(grammar: String) -> Self {
        let mut nullable_map = HashMap::new();
        let mut first_map = HashMap::new();
        let mut follow_map = HashMap::new();
        let mut rule_map = HashMap::new();

        // go line by line eg A -> B c
        for line in grammar.split("\n") {
            // split line into two sides ["A ", " B c"]
            let mut side = line.split("->");
            let mut lhs = side.next().expect("Missing left hand side").trim().chars();
            let nonterminal = lhs.next();
            match nonterminal {
                Some(c) if c.is_ascii_uppercase() => {
                    nullable_map.entry(c).or_insert(false);
                    first_map.entry(c).or_insert(Vec::new());
                    follow_map.entry(c).or_insert(Vec::new());
                    rule_map.entry(c).or_insert(Vec::new());
                }
                _ => panic!("Something with the left hand side of a rule went very wrong"),
            }
            if let Some(_) = lhs.next() {
                panic!("left hand side too long");
            }
            // for the right hand side we need to a bit more work.
            // first we remove all non ascii characters or 0s and give them tokens
            // then we put them in a vector and add them to the hashmaps
            let mut rhs = side.next().expect("Missing right hand side").trim().chars();
            let rule = rhs
                .filter(|c| (c.is_ascii() || *c == '0') && !c.is_whitespace())
                .map(|c| match c {
                    '0' => Token::NULL,
                    _ if c.is_uppercase() => Token::NONTERMINAL(c),
                    _ => Token::TERMINAL(c),
                })
                .collect();

            rule_map
                .entry(nonterminal.unwrap())
                .and_modify(|rule_set| rule_set.push(rule));
        }

        NonTerminals {
            nullable_map,
            first_map,
            follow_map,
            rule_map,
        }
    }
    /// Determines which nonterminals are nullable
    pub fn calculate_null_set(&mut self) {
        let mut changed = true;
        while changed {
            changed = false;
            for (non_terminal, rules) in self.rule_map.iter() {
                for rule in rules {
                    let nullable = rule.iter().all(|token| match token {
                        Token::NONTERMINAL(c) => *self.nullable_map.get(c).unwrap(),
                        Token::TERMINAL(_) => false,
                        Token::NULL => true,
                    });
                    if nullable == true && nullable != *self.nullable_map.get(non_terminal).unwrap()
                    {
                        self.nullable_map.insert(*non_terminal, true);
                        changed = true;
                    }
                }
            }
        }
    }
    /// Determines the first set of each nonterminal
    pub fn calculate_first_set(&mut self) {
        let mut changed = true;
        while changed {
            changed = false;
            for (non_terminal, rules) in self.rule_map.iter() {
                for rule in rules {
                    for token in rule {
                        match token {
                            // push all first, if not nullable break
                            Token::NONTERMINAL(c) => {
                                let potential_new_firsts =
                                    (*self.first_map.get(c).unwrap()).clone();
                                for f in potential_new_firsts {
                                    if !self.first_map.get(non_terminal).unwrap().contains(&f) {
                                        self.first_map
                                            .entry(*non_terminal)
                                            .and_modify(|first_set| first_set.push(f));
                                        changed = true;
                                    }
                                }
                                if !*self.nullable_map.get(c).unwrap() {
                                    break;
                                }
                            }
                            Token::TERMINAL(f) => {
                                if !self.first_map.get(non_terminal).unwrap().contains(f) {
                                    self.first_map
                                        .entry(*non_terminal)
                                        .and_modify(|first_set| first_set.push(*f));
                                    changed = true;
                                }
                                break;
                            }
                            Token::NULL => (),
                        };
                    }
                }
            }
        }
    }
    /// Determines the follow set of each nonterminal
    pub fn calculate_follow_set(&mut self) {
        let mut changed = true;
        while changed {
            changed = false;
            for (nonterminal, _) in self.rule_map.iter() {
                for (lhs_nonterminal, rules) in self.rule_map.iter() {
                    for rule in rules {
                        // state 0 waiting nonterminal to appear
                        // state 1 nonterminal appeared
                        let mut state = 0;

                        // if a nonterminal is last in a rule, or everything after it is nullable
                        // then it inherits all follows from left hand side nonterminal
                        let mut nullable_til_end = false;
                        for token in rule {
                            match token {
                                Token::NONTERMINAL(c) => {
                                    // if we are waiting for nonterminal, and we find it
                                    // stop waiting for it
                                    if state == 0 && c == nonterminal {
                                        state += 1;
                                        nullable_til_end = true;
                                    } else if state == 1 && c != nonterminal {
                                        // get list of potential_new_follows
                                        // make sure they are not already in the list
                                        for f in self.first_map.get(c).unwrap() {
                                            if !self
                                                .follow_map
                                                .get(nonterminal)
                                                .unwrap()
                                                .contains(&f)
                                            {
                                                self.follow_map
                                                    .entry(*nonterminal)
                                                    .and_modify(|follow_set| follow_set.push(*f));
                                                changed = true;
                                            }
                                        }
                                        // if it is nullable, keep adding more follows
                                        if !*self.nullable_map.get(c).unwrap() {
                                            state += 1;
                                            nullable_til_end = false;
                                        }
                                    } else {
                                        continue;
                                    }
                                }
                                Token::TERMINAL(f) => {
                                    nullable_til_end = false;
                                    // if nonterminal not found yet, keep waiting
                                    if state == 0 {
                                        continue;
                                    // if we found nonterminal, we have potential new follow
                                    } else if state == 1 {
                                        if !self.follow_map.get(nonterminal).unwrap().contains(&f) {
                                            self.follow_map
                                                .entry(*nonterminal)
                                                .and_modify(|follow_set| follow_set.push(*f));
                                            changed = true;
                                        }
                                        state += 1;
                                    } else {
                                        break;
                                    }
                                }
                                Token::NULL => (),
                            };
                        }
                        if nullable_til_end && lhs_nonterminal != nonterminal {
                            // get list of potential_new_follows
                            let potential_new_follows =
                                (*self.follow_map.get(lhs_nonterminal).unwrap()).clone();
                            // make sure they are not already in the list
                            for f in potential_new_follows {
                                if !(*self.follow_map.get(nonterminal).unwrap()).contains(&f) {
                                    self.follow_map
                                        .entry(*nonterminal)
                                        .and_modify(|follow_set| follow_set.push(f));
                                    changed = true;
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    /// You can use this function to verify that nff understood your rules correctly
    pub fn print_rules(&self) {
        for (non_terminal, rule) in self.rule_map.iter() {
            println!("{}\n{:?}", non_terminal, rule);
        }
    }
    /// Print results
    pub fn print_results(&self) {
        for (nonterminal, _) in self.rule_map.iter() {
            println!("{}", nonterminal);
            println!("Nullable: {}", self.nullable_map.get(nonterminal).unwrap());
            println!("First: {:?}", self.first_map.get(nonterminal).unwrap());
            println!("Follow: {:?}", self.follow_map.get(nonterminal).unwrap());
        }
    }
}

/// Opens the file defined by the first argument
pub fn open_file(mut args: std::env::Args) -> String {
    if args.len() > 2 {
        println!("Program only supports 1 file");
    }
    args.next();
    let filename = match args.next() {
        Some(arg) => arg,
        None => panic!("Specify file with grammars"),
    };
    let mut f = File::open(filename).expect("File not found");
    let mut contents = String::new();
    f.read_to_string(&mut contents).expect("Error reading file");

    contents
}