RosettaCodeData/Task/URL-decoding/Jq/url-decoding-1.jq

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# Emit . and stop as soon as "condition" is true.
def until(condition; next):
def u: if condition then . else (next|u) end;
u;
def url_decode:
# The helper function converts the input string written in the given
# "base" to an integer
def to_i(base):
explode
| reverse
| map(if 65 <= . and . <= 90 then . + 32 else . end) # downcase
| map(if . > 96 then . - 87 else . - 48 end) # "a" ~ 97 => 10 ~ 87
| reduce .[] as $c
# base: [power, ans]
([1,0]; (.[0] * base) as $b | [$b, .[1] + (.[0] * $c)]) | .[1];
. as $in
| length as $length
| [0, ""] # i, answer
| until ( .[0] >= $length;
.[0] as $i
| if $in[$i:$i+1] == "%"
then [ $i + 3, .[1] + ([$in[$i+1:$i+3] | to_i(16)] | implode) ]
else [ $i + 1, .[1] + $in[$i:$i+1] ]
end)
| .[1]; # answer