/*
 * Copyright 2022 Arnaud Golfouse
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

use super::{next_word, parse_number};
use ielr::input::{Node, ProdIdx};
use std::collections::HashMap;

pub(super) fn parse_forbid(
    mut line: &str,
    nodes: &HashMap<&str, (Node, Vec<ProdIdx>)>,
) -> Result<(ProdIdx, usize, ProdIdx), String> {
    line = match line.strip_prefix('(') {
        Some(line) => line,
        None => return Err(String::from("expected '(' after '@forbid'")),
    };
    let (line, prod_idx) = parse_prod_idx(line, nodes)?;
    let line = if let Some(line) = line.strip_prefix(',') {
        line.trim_start()
    } else {
        return Err("expected ',' after the first production in @forbid".to_string());
    };
    let (line, index) = parse_number(line)?;
    let line = if let Some(line) = line.strip_prefix(',') {
        line.trim_start()
    } else {
        return Err("expected ',' after the symbol index in @forbid".to_string());
    };
    let (line, forbidden_prod_idx) = parse_prod_idx(line, nodes)?;
    let line = if let Some(line) = line.strip_prefix(')') {
        line.trim_start()
    } else {
        return Err("expected ')' after the second production in @forbid".to_string());
    };
    if line.is_empty() {
        Ok((
            prod_idx,
            TryInto::<usize>::try_into(index).map_err(|err| err.to_string())?,
            forbidden_prod_idx,
        ))
    } else {
        Err(format!("unknown characters after @forbid : {line:?}"))
    }
}

fn parse_prod_idx<'a>(
    line: &'a str,
    nodes: &HashMap<&str, (Node, Vec<ProdIdx>)>,
) -> Result<(&'a str, ProdIdx), String> {
    let (node_name, productions, line) = match next_word(line) {
        Some((word, line)) => {
            if let Some((_, productions)) = nodes.get(word) {
                (word, productions, line)
            } else {
                return Err(format!("unknown node: {word}"));
            }
        }
        None => return Err(String::from("expected node identifier after '@forbid('")),
    };
    let line = if let Some(line) = line.strip_prefix(',') {
        line.trim_start()
    } else {
        return Err(format!(
            "expected ',' after the node {node_name} in @forbid"
        ));
    };
    let (line, index) = parse_number(line)?;
    let prod_idx = productions[index as usize];
    Ok((line, prod_idx))
}