1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145

/* 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 `Err(())` for a syntax error.
pub fn parse_nth<'i, 't>(input: &mut Parser<'i, 't>) -> 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" => Ok(parse_b(input, a)?),
                "n-" => Ok(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" => Ok(parse_b(input, 1)?),
                "-n" => Ok(parse_b(input, -1)?),
                "n-" => Ok(parse_signless_b(input, 1, -1)?),
                "-n-" => Ok(parse_signless_b(input, -1, -1)?),
                _ => {
                    let (slice, a) = if value.starts_with("-") {
                        (&value[1..], -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, 't>(input: &mut Parser<'i, 't>, 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, 't>(
    input: &mut Parser<'i, 't>,
    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| matches!(c, b'0'..=b'9'))
    {
        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)
}