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

//! Extracts and parses signed and unsigned integers from surrounding text and whitespace.
//!
//! A common pattern in Advent of Code is to parse and return `123`, `456` and `789` from input
//! resembling:
//!
//! ```none
//!   Lorem ipsum 123 dolor 456 sit 789 amet
//! ```
//!
//! This module provides two [`&str`] extension methods [`iter_signed`] and [`iter_unsigned`]. The
//! reason for the separate methods is that some Advent of Code inputs contains the `-` character
//! as a delimeter and this would cause numbers to be incorrectly parsed as negative.
//!
//! [`iter_unsigned`]: ParseOps::iter_unsigned
//! [`iter_signed`]: ParseOps::iter_signed
use crate::util::integer::*;
use std::marker::PhantomData;
use std::str::Bytes;

pub trait ParseByte {
    fn to_decimal(self) -> u8;
}

impl ParseByte for u8 {
    #[inline]
    fn to_decimal(self) -> u8 {
        self.wrapping_sub(b'0')
    }
}

pub struct ParseUnsigned<'a, T> {
    bytes: Bytes<'a>,
    phantom: PhantomData<T>,
}

pub struct ParseSigned<'a, T> {
    bytes: Bytes<'a>,
    phantom: PhantomData<T>,
}

pub trait ParseOps {
    fn unsigned<T: Unsigned<T>>(&self) -> T;
    fn signed<T: Signed<T>>(&self) -> T;
    fn iter_unsigned<T: Unsigned<T>>(&self) -> ParseUnsigned<'_, T>;
    fn iter_signed<T: Signed<T>>(&self) -> ParseSigned<'_, T>;
}

impl ParseOps for &str {
    fn unsigned<T: Unsigned<T>>(&self) -> T {
        match try_unsigned(&mut self.bytes()) {
            Some(t) => t,
            None => panic!("Unable to parse \"{self}\""),
        }
    }

    fn signed<T: Signed<T>>(&self) -> T {
        match try_signed(&mut self.bytes()) {
            Some(t) => t,
            None => panic!("Unable to parse \"{self}\""),
        }
    }

    fn iter_unsigned<T: Unsigned<T>>(&self) -> ParseUnsigned<'_, T> {
        ParseUnsigned { bytes: self.bytes(), phantom: PhantomData }
    }

    fn iter_signed<T: Signed<T>>(&self) -> ParseSigned<'_, T> {
        ParseSigned { bytes: self.bytes(), phantom: PhantomData }
    }
}

impl<T: Unsigned<T>> Iterator for ParseUnsigned<'_, T> {
    type Item = T;

    fn size_hint(&self) -> (usize, Option<usize>) {
        let (lower, upper) = self.bytes.size_hint();
        (lower / 3, upper.map(|u| u / 3))
    }

    fn next(&mut self) -> Option<Self::Item> {
        try_unsigned(&mut self.bytes)
    }
}

impl<T: Signed<T>> Iterator for ParseSigned<'_, T> {
    type Item = T;

    fn size_hint(&self) -> (usize, Option<usize>) {
        let (lower, upper) = self.bytes.size_hint();
        (lower / 3, upper.map(|u| u / 3))
    }

    fn next(&mut self) -> Option<Self::Item> {
        try_signed(&mut self.bytes)
    }
}

fn try_unsigned<T: Unsigned<T>>(bytes: &mut Bytes<'_>) -> Option<T> {
    let mut n = loop {
        let byte = bytes.next()?;
        let digit = byte.to_decimal();

        if digit < 10 {
            break T::from(digit);
        }
    };

    loop {
        let Some(byte) = bytes.next() else { break Some(n) };
        let digit = byte.to_decimal();

        if digit < 10 {
            n = T::TEN * n + T::from(digit);
        } else {
            break Some(n);
        }
    }
}

fn try_signed<T: Signed<T>>(bytes: &mut Bytes<'_>) -> Option<T> {
    let (mut n, negative) = loop {
        let byte = bytes.next()?;
        let digit = byte.to_decimal();

        if digit == 253 {
            break (T::ZERO, true);
        }
        if digit < 10 {
            break (T::from(digit), false);
        }
    };

    loop {
        let Some(byte) = bytes.next() else {
            break Some(if negative { -n } else { n });
        };
        let digit = byte.to_decimal();

        if digit < 10 {
            n = T::TEN * n + T::from(digit);
        } else {
            break Some(if negative { -n } else { n });
        }
    }
}