/*
 * 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 ielr::input::{Node, ProdIdx};
use std::collections::HashMap;

use super::{next_word, parse_number};

pub(super) fn parse_precedence(
    line: &str,
    nodes: &HashMap<&str, (Node, Vec<ProdIdx>)>,
) -> Result<(ProdIdx, Option<u16>, Option<u16>), String> {
    let line = match line.strip_prefix('(') {
        Some(line) => line.trim_start(),
        None => return Err(String::from("expected '(' after '@precedence'")),
    };
    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 '@precedence('",
            ))
        }
    };
    let line = if let Some(line) = line.strip_prefix(',') {
        line.trim_start()
    } else {
        return Err(format!(
            "expected ',' after the node {node_name} in @precedence"
        ));
    };
    let (line, index) = parse_number(line)?;
    let production = productions[index as usize];
    let line = if let Some(line) = line.strip_prefix(',') {
        line.trim_start()
    } else {
        return Err(format!("expected ',' after {index} in @precedence"));
    };
    let (line, left_prec, maybe_right) = if let Some(line) = line.strip_prefix("left") {
        let line = if let Some(line) = line.trim_start().strip_prefix('=') {
            line.trim_start()
        } else {
            return Err(String::from("expected '=' after 'left' in @precedence"));
        };
        let (line, n) = parse_number(line)?;
        let (line, maybe_right) = if let Some(line) = line.strip_prefix(',') {
            (line.trim_start(), true)
        } else {
            (line, false)
        };
        (line, Some(n as u16), maybe_right)
    } else {
        (line, None, true)
    };
    if !maybe_right {
        if let Some(line) = line.strip_prefix(')') {
            if !line.trim().is_empty() {
                return Err(format!(
                    "incorrect syntax after closing ')' in @precedence:\n\"{line}\""
                ));
            }
            return Ok((production, left_prec, None));
        } else {
            return Err(String::from("expected ')' at the end of @precedence"));
        };
    }
    let (line, right_prec) = if let Some(line) = line.strip_prefix("right") {
        let line = if let Some(line) = line.trim_start().strip_prefix('=') {
            line.trim_start()
        } else {
            return Err(String::from("expected '=' after 'right' in @precedence"));
        };
        let (line, n) = parse_number(line)?;
        let line = if let Some(line) = line.strip_prefix(',') {
            line.trim_start()
        } else {
            line
        };
        (line, Some(n as u16))
    } else {
        (line, None)
    };
    if let Some(line) = line.strip_prefix(')') {
        if !line.trim().is_empty() {
            Err(format!(
                "incorrect syntax after closing ')' in @precedence:\n\"{line}\""
            ))
        } else {
            Ok((production, left_prec, right_prec))
        }
    } else {
        Err(String::from("expected ')' at the end of @precedence"))
    }
}