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require "nokogiri"
require "open_graph_reader/parser/graph"
module OpenGraphReader
# Parse OpenGraph tags in a HTML document into a graph.
#
# @api private
class Parser
# Some helper methods for Nokogiri
module XPathHelpers
# Helper to lowercase all given properties
def self.ci_starts_with node_set, string
node_set.select {|node|
node.to_s.downcase.start_with? string.downcase
}
end
end
# Namespaces found in the passed documents head tag
#
# @return [Array<String>]
attr_reader :additional_namespaces
# Create a new parser.
#
# @param [#to_s, Nokogiri::XML::Node] html the document to parse.
def initialize html
@doc = to_doc html
@additional_namespaces = []
end
# Whether there are any OpenGraph tags at all.
#
# @return [Bool]
def any_tags?
graph.exist?("og")
end
# Build and return the {Graph}.
#
# @return [Graph]
def graph
@graph ||= build_graph
end
# The value of the title tag of the passed document.
#
# @return [String]
def title
@doc.xpath("/html/head/title").first.text
end
private
def build_graph
graph = Graph.new
meta_tags.each do |tag|
*path, leaf = tag["property"].downcase.split(":")
node = graph.find_or_create_path path
# @todo make stripping configurable?
node << Graph::Node.new(leaf, tag["content"].strip)
end
graph
end
def meta_tags
head = @doc.xpath("/html/head").first
raise NoOpenGraphDataError, "There's no head tag in #{@doc}" unless head
head.xpath("meta[#{xpath_condition(head)}]", XPathHelpers)
end
def xpath_condition head
condition = "ci_starts_with(@property, 'og:')"
if head["prefix"]
@additional_namespaces = head["prefix"].scan(/(\w+):\s*([^ ]+)/)
@additional_namespaces.map! {|prefix, _| prefix.downcase }
@additional_namespaces.each do |additional_namespace|
next if additional_namespace == "og"
condition << " or ci_starts_with(@property, '#{additional_namespace}')"
end
end
"(#{condition}) and @content"
end
def to_doc html
case html
when Nokogiri::XML::Node
html
else
Nokogiri::HTML.parse(html.to_s)
end
end
end
end
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