parseJSONnumber.jsonnet

local xtd = import 'github.com/jsonnet-libs/xtd/main.libsonnet';

local cp = std.codepoint;

//                           "1"            "9"
local onenine(c) = (cp(c) >= 49 && cp(c) <= 57);

//                         "0"
local digit(c) = (cp(c) == 48 || onenine(c));

local digits(str) =
  std.length(str) > 0
  && std.all(
    std.foldl(
      function(acc, c)
        acc + [digit(c)],
      std.stringChars(str),
      [],
    )
  );

local fraction(str) =
  str == ''
  || (str[0] == '.' && digits(str[1:]));

local sign(c) = (c == '-' || c == '+');

local exponent(str) =
  str == ''
  || (str[0] == 'E' && digits(str[1:]))
  || (str[0] == 'e' && digits(str[1:]))
  || (std.length(str) > 1 && str[0] == 'E' && sign(str[1]) && digits(str[2:]))
  || (std.length(str) > 1 && str[0] == 'e' && sign(str[1]) && digits(str[2:]));


local integer(str) =
  (std.length(str) == 1 && digit(str[0]))
  || (std.length(str) > 0 && onenine(str[0]) && digits(str[1:]))
  || (std.length(str) > 1 && str[0] == '-' && digit(str[1]))
  || (std.length(str) > 1 && str[0] == '-' && onenine(str[1]) && digits(str[2:]));

local number(str) =
  local expectInteger =
    if std.member(str, '.')
    then std.split(str, '.')[0]
    else if std.member(str, 'e')
    then std.split(str, 'e')[0]
    else if std.member(str, 'E')
    then std.split(str, 'E')[0]
    else str;

  local expectFraction =
    if std.member(str, 'e')
    then std.split(str[std.length(expectInteger):], 'e')[0]
    else if std.member(str, 'E')
    then std.split(str[std.length(expectInteger):], 'E')[0]
    else str[std.length(expectInteger):];

  local expectExponent = str[std.length(expectInteger) + std.length(expectFraction):];
  //[str]
  //+ [expectInteger, expectFraction, expectExponent]
  //+ [
  //  integer(expectInteger),
  //  fraction(expectFraction),
  //  exponent(expectExponent),
  //];
  std.all([
    integer(expectInteger),
    fraction(expectFraction),
    exponent(expectExponent),
  ]);

local parseIntegerFromString(str, strict=true) =
  local s = ['-', '+', '.', 'e', 'E'];
  if !(integer(str[0]) || str[0] == '-')
  then ''
  else
    local aux(index=0, return='') =
      if index < std.length(str) && number(return + str[index])
      then aux(index + 1, return + str[index])
      else if index + 1 < std.length(str) && std.member(s, str[index])
      then aux(index + 1, return + str[index])
      else if strict && index + 1 <= std.length(str) && std.member(s, str[index])
      then error "Couldn't lex number, junk after %s" % str[index]
      else if number(return)
      then return
      else '';
    std.trace(str, aux)();


std.map(
  parseIntegerFromString, [
    '15',
    '1.5',
    '-1.5',
    '1e5',
    '1E5',
    '1.5e5',
    '1.5E5',
    '1.5e-5',
    '1.5E+5',

    '15e5garbage',
    //'15e',  // fails on strict
    '1garbag5e5garbage',
    //'1.',  // fails on strict

    'garbage15e5garbage',
    '+',
    '+1E5',
    '.5',
    'E5',
    'e5',

  ]
)
/*
'next are true',
number(parseIntegerFromString(a)),
number(parseIntegerFromString(b)),
'15',
'1.5',
'-1.5',
'1e5',
'1E5',
'1.5e5',
'1.5E5',
'1.5e-5',
'1.5E+5',

'+1E5',
'.5',
'e5',
'E5',
]
*/