/* 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 http://mozilla.org/MPL/2.0/. */

use super::{BasicParseError, Parser, ParserInput, Token};

/// Parse the *An+B* notation, as found in the `:nth-child()` selector.

/// The input is typically the arguments of a function,

/// in which case the caller needs to check if the arguments’ parser is exhausted.

/// Return `Ok((A, B))`, or an `Err(..)` for a syntax error.

pub fn parse_nth<'i>(input: &mut Parser<'i, '_>) -> Result<(i32, i32), BasicParseError<'i>> {

    match *input.next()? {

        Token::Number {

            int_value: Some(b), ..

        } => Ok((0, b)),

        Token::Dimension {

            int_value: Some(a),

            ref unit,

            ..

        } => {

            match_ignore_ascii_case! {

                unit,

                "n" => parse_b(input, a),

                "n-" => parse_signless_b(input, a, -1),

                _ => match parse_n_dash_digits(unit) {

                    Ok(b) => Ok((a, b)),

                    Err(()) => {

                        let unit = unit.clone();

                        Err(input.new_basic_unexpected_token_error(Token::Ident(unit)))

                    }

                }

            }

        }

        Token::Ident(ref value) => {

            match_ignore_ascii_case! { value,

                "even" => Ok((2, 0)),

                "odd" => Ok((2, 1)),

                "n" => parse_b(input, 1),

                "-n" => parse_b(input, -1),

                "n-" => parse_signless_b(input, 1, -1),

                "-n-" => parse_signless_b(input, -1, -1),

                _ => {

                    let (slice, a) = if let Some(stripped) = value.strip_prefix('-') {

                        (stripped, -1)

                    } else {

                        (&**value, 1)

                    };

                    match parse_n_dash_digits(slice) {

                        Ok(b) => Ok((a, b)),

                        Err(()) => {

                            let value = value.clone();

                            Err(input.new_basic_unexpected_token_error(Token::Ident(value)))

                        }

                    }

                }

            }

        }

        Token::Delim('+') => match *input.next_including_whitespace()? {

            Token::Ident(ref value) => {

                match_ignore_ascii_case! { value,

                    "n" => parse_b(input, 1),

                    "n-" => parse_signless_b(input, 1, -1),

                    _ => match parse_n_dash_digits(value) {

                        Ok(b) => Ok((1, b)),

                        Err(()) => {

                            let value = value.clone();

                            Err(input.new_basic_unexpected_token_error(Token::Ident(value)))

                        }

                    }

                }

            }

            ref token => {

                let token = token.clone();

                Err(input.new_basic_unexpected_token_error(token))

            }

        },

        ref token => {

            let token = token.clone();

            Err(input.new_basic_unexpected_token_error(token))

        }

    }

}

fn parse_b<'i>(input: &mut Parser<'i, '_>, a: i32) -> Result<(i32, i32), BasicParseError<'i>> {

    let start = input.state();

    match input.next() {

        Ok(&Token::Delim('+')) => parse_signless_b(input, a, 1),

        Ok(&Token::Delim('-')) => parse_signless_b(input, a, -1),

        Ok(&Token::Number {

            has_sign: true,

            int_value: Some(b),

            ..

        }) => Ok((a, b)),

        _ => {

            input.reset(&start);

            Ok((a, 0))

        }

    }

}

fn parse_signless_b<'i>(

    input: &mut Parser<'i, '_>,

    a: i32,

    b_sign: i32,

) -> Result<(i32, i32), BasicParseError<'i>> {

    // FIXME: remove .clone() when lifetimes are non-lexical.

    match input.next()?.clone() {

        Token::Number {

            has_sign: false,

            int_value: Some(b),

            ..

        } => Ok((a, b_sign * b)),

        token => Err(input.new_basic_unexpected_token_error(token)),

    }

}

fn parse_n_dash_digits(string: &str) -> Result<i32, ()> {

    let bytes = string.as_bytes();

    if bytes.len() >= 3

        && bytes[..2].eq_ignore_ascii_case(b"n-")

        && bytes[2..].iter().all(|&c| c.is_ascii_digit())

    {

        Ok(parse_number_saturate(&string[1..]).unwrap()) // Include the minus sign

    } else {

        Err(())

    }

}

fn parse_number_saturate(string: &str) -> Result<i32, ()> {

    let mut input = ParserInput::new(string);

    let mut parser = Parser::new(&mut input);

    let int = if let Ok(&Token::Number {

        int_value: Some(int),

        ..

    }) = parser.next_including_whitespace_and_comments()

    {

        int

    } else {

        return Err(());

    };

    if !parser.is_exhausted() {

        return Err(());

    }

    Ok(int)

}