/*
Module: char

Utilities for manipulating the char type
*/

/*
Function: is_whitespace

Indicates whether a character is whitespace.

Whitespace characters include space (U+0020), tab (U+0009), line feed
(U+000A), carriage return (U+000D), and a number of less common
ASCII and unicode characters.
*/
pure fn is_whitespace(c: char) -> bool {
    const ch_space: char = '\u0020';
    const ch_ogham_space_mark: char = '\u1680';
    const ch_mongolian_vowel_sep: char = '\u180e';
    const ch_en_quad: char = '\u2000';
    const ch_em_quad: char = '\u2001';
    const ch_en_space: char = '\u2002';
    const ch_em_space: char = '\u2003';
    const ch_three_per_em_space: char = '\u2004';
    const ch_four_per_em_space: char = '\u2005';
    const ch_six_per_em_space: char = '\u2006';
    const ch_figure_space: char = '\u2007';
    const ch_punctuation_space: char = '\u2008';
    const ch_thin_space: char = '\u2009';
    const ch_hair_space: char = '\u200a';
    const ch_narrow_no_break_space: char = '\u202f';
    const ch_medium_mathematical_space: char = '\u205f';
    const ch_ideographic_space: char = '\u3000';
    const ch_line_separator: char = '\u2028';
    const ch_paragraph_separator: char = '\u2029';
    const ch_character_tabulation: char = '\u0009';
    const ch_line_feed: char = '\u000a';
    const ch_line_tabulation: char = '\u000b';
    const ch_form_feed: char = '\u000c';
    const ch_carriage_return: char = '\u000d';
    const ch_next_line: char = '\u0085';
    const ch_no_break_space: char = '\u00a0';

    if c == ch_space {
        true
    } else if c == ch_ogham_space_mark {
        true
    } else if c == ch_mongolian_vowel_sep {
        true
    } else if c == ch_en_quad {
        true
    } else if c == ch_em_quad {
        true
    } else if c == ch_en_space {
        true
    } else if c == ch_em_space {
        true
    } else if c == ch_three_per_em_space {
        true
    } else if c == ch_four_per_em_space {
        true
    } else if c == ch_six_per_em_space {
        true
    } else if c == ch_figure_space {
        true
    } else if c == ch_punctuation_space {
        true
    } else if c == ch_thin_space {
        true
    } else if c == ch_hair_space {
        true
    } else if c == ch_narrow_no_break_space {
        true
    } else if c == ch_medium_mathematical_space {
        true
    } else if c == ch_ideographic_space {
        true
    } else if c == ch_line_tabulation {
        true
    } else if c == ch_paragraph_separator {
        true
    } else if c == ch_character_tabulation {
        true
    } else if c == ch_line_feed {
        true
    } else if c == ch_line_tabulation {
        true
    } else if c == ch_form_feed {
        true
    } else if c == ch_carriage_return {
        true
    } else if c == ch_next_line {
        true
    } else if c == ch_no_break_space { true } else { false }
}

/*
 Function: to_digit

 Convert a char to the corresponding digit.

 Parameters:
   c - a char, either '0' to '9', 'a' to 'z' or 'A' to 'Z'

 Returns:
   If `c` is between '0' and '9', the corresponding value between 0 and 9.
 If `c` is 'a' or 'A', 10. If `c` is 'b' or 'B', 11, etc.

 Safety note:
   This function fails if `c` is not a valid char
*/
pure fn to_digit(c: char) -> u8 unsafe {
    alt maybe_digit(c) {
      option::some(x) { x }
      option::none. { fail; }
    }
}

/*
 Function: to_digit

 Convert a char to the corresponding digit. Returns none when the
 character is not a valid hexadecimal digit.
*/
pure fn maybe_digit(c: char) -> option::t<u8> {
    alt c {
      '0' to '9' { option::some(c as u8 - ('0' as u8)) }
      'a' to 'z' { option::some(c as u8 + 10u8 - ('a' as u8)) }
      'A' to 'Z' { option::some(c as u8 + 10u8 - ('A' as u8)) }
      _ { option::none }
    }
}

/*
 Function: cmp

 Compare two chars.

 Parameters:
  a - a char
  b - a char

 Returns:
  -1 if a<b, 0 if a==b, +1 if a>b
*/
pure fn cmp(a: char, b: char) -> int {
    ret  if b > a { -1 }
    else if b < a { 1 }
    else { 0 }
}