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module JsonPointer
# Evaluates a JSON pointer within a JSON document.
#
# Note that this class is designed to evaluate references across a plain JSON
# data object _or_ an instance of `JsonSchema::Schema`, so the constructor's
# `data` argument can be of either type.
class Evaluator
def initialize(data)
@data = data
end
def evaluate(original_path)
path = original_path
# the leading # can either be included or not
path = path[1..-1] if path[0] == "#"
# special case on "" or presumably "#"
if path.empty?
return @data
end
if path[0] != "/"
raise ArgumentError, %{Path must begin with a leading "/": #{original_path}.}
end
path_parts = split(path)
evaluate_segment(@data, path_parts)
end
private
def evaluate_segment(data, path_parts)
if path_parts.empty?
data
elsif data == nil
# spec doesn't define how to handle this, so we'll return `nil`
nil
else
key = transform_key(path_parts.shift)
if data.is_a?(Array)
unless key =~ /^\d+$/
raise ArgumentError, %{Key operating on an array must be a digit or "-": #{key}.}
end
evaluate_segment(data[key.to_i], path_parts)
else
evaluate_segment(data[key], path_parts)
end
end
end
# custom split method to account for blank segments
def split(path)
parts = []
last_index = 0
while index = path.index("/", last_index)
if index == last_index
parts << ""
else
parts << path[last_index...index]
end
last_index = index + 1
end
# and also get that last segment
parts << path[last_index..-1]
# it should begin with a blank segment from the leading "/"; kill that
parts.shift
parts
end
def transform_key(key)
# ~ has special meaning to JSON pointer to allow keys containing "/", so
# perform some transformations first as defined by the spec
# first as defined by the spec
key = key.gsub('~1', '/')
key = key.gsub('~0', '~')
key
end
end
end
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