#--
# Copyright (c) 2006 Assaf Arkin (http://labnotes.org)
# Under MIT and/or CC By license.
#++
module HTML
# Selects HTML elements using CSS 2 selectors.
#
# The +Selector+ class uses CSS selector expressions to match and select
# HTML elements.
#
# For example:
# selector = HTML::Selector.new "form.login[action=/login]"
# creates a new selector that matches any +form+ element with the class
# +login+ and an attribute +action+ with the value <tt>/login</tt>.
#
# === Matching Elements
#
# Use the #match method to determine if an element matches the selector.
#
# For simple selectors, the method returns an array with that element,
# or +nil+ if the element does not match. For complex selectors (see below)
# the method returns an array with all matched elements, of +nil+ if no
# match found.
#
# For example:
# if selector.match(element)
# puts "Element is a login form"
# end
#
# === Selecting Elements
#
# Use the #select method to select all matching elements starting with
# one element and going through all children in depth-first order.
#
# This method returns an array of all matching elements, an empty array
# if no match is found
#
# For example:
# selector = HTML::Selector.new "input[type=text]"
# matches = selector.select(element)
# matches.each do |match|
# puts "Found text field with name #{match.attributes['name']}"
# end
#
# === Expressions
#
# Selectors can match elements using any of the following criteria:
# * <tt>name</tt> -- Match an element based on its name (tag name).
# For example, <tt>p</tt> to match a paragraph. You can use <tt>*</tt>
# to match any element.
# * <tt>#</tt><tt>id</tt> -- Match an element based on its identifier (the
# <tt>id</tt> attribute). For example, <tt>#</tt><tt>page</tt>.
# * <tt>.class</tt> -- Match an element based on its class name, all
# class names if more than one specified.
# * <tt>[attr]</tt> -- Match an element that has the specified attribute.
# * <tt>[attr=value]</tt> -- Match an element that has the specified
# attribute and value. (More operators are supported see below)
# * <tt>:pseudo-class</tt> -- Match an element based on a pseudo class,
# such as <tt>:nth-child</tt> and <tt>:empty</tt>.
# * <tt>:not(expr)</tt> -- Match an element that does not match the
# negation expression.
#
# When using a combination of the above, the element name comes first
# followed by identifier, class names, attributes, pseudo classes and
# negation in any order. Do not separate these parts with spaces!
# Space separation is used for descendant selectors.
#
# For example:
# selector = HTML::Selector.new "form.login[action=/login]"
# The matched element must be of type +form+ and have the class +login+.
# It may have other classes, but the class +login+ is required to match.
# It must also have an attribute called +action+ with the value
# <tt>/login</tt>.
#
# This selector will match the following element:
# <form class="login form" method="post" action="/login">
# but will not match the element:
# <form method="post" action="/logout">
#
# === Attribute Values
#
# Several operators are supported for matching attributes:
# * <tt>name</tt> -- The element must have an attribute with that name.
# * <tt>name=value</tt> -- The element must have an attribute with that
# name and value.
# * <tt>name^=value</tt> -- The attribute value must start with the
# specified value.
# * <tt>name$=value</tt> -- The attribute value must end with the
# specified value.
# * <tt>name*=value</tt> -- The attribute value must contain the
# specified value.
# * <tt>name~=word</tt> -- The attribute value must contain the specified
# word (space separated).
# * <tt>name|=word</tt> -- The attribute value must start with specified
# word.
#
# For example, the following two selectors match the same element:
# #my_id
# [id=my_id]
# and so do the following two selectors:
# .my_class
# [class~=my_class]
#
# === Alternatives, siblings, children
#
# Complex selectors use a combination of expressions to match elements:
# * <tt>expr1 expr2</tt> -- Match any element against the second expression
# if it has some parent element that matches the first expression.
# * <tt>expr1 > expr2</tt> -- Match any element against the second expression
# if it is the child of an element that matches the first expression.
# * <tt>expr1 + expr2</tt> -- Match any element against the second expression
# if it immediately follows an element that matches the first expression.
# * <tt>expr1 ~ expr2</tt> -- Match any element against the second expression
# that comes after an element that matches the first expression.
# * <tt>expr1, expr2</tt> -- Match any element against the first expression,
# or against the second expression.
#
# Since children and sibling selectors may match more than one element given
# the first element, the #match method may return more than one match.
#
# === Pseudo classes
#
# Pseudo classes were introduced in CSS 3. They are most often used to select
# elements in a given position:
# * <tt>:root</tt> -- Match the element only if it is the root element
# (no parent element).
# * <tt>:empty</tt> -- Match the element only if it has no child elements,
# and no text content.
# * <tt>:only-child</tt> -- Match the element if it is the only child (element)
# of its parent element.
# * <tt>:only-of-type</tt> -- Match the element if it is the only child (element)
# of its parent element and its type.
# * <tt>:first-child</tt> -- Match the element if it is the first child (element)
# of its parent element.
# * <tt>:first-of-type</tt> -- Match the element if it is the first child (element)
# of its parent element of its type.
# * <tt>:last-child</tt> -- Match the element if it is the last child (element)
# of its parent element.
# * <tt>:last-of-type</tt> -- Match the element if it is the last child (element)
# of its parent element of its type.
# * <tt>:nth-child(b)</tt> -- Match the element if it is the b-th child (element)
# of its parent element. The value <tt>b</tt> specifies its index, starting with 1.
# * <tt>:nth-child(an+b)</tt> -- Match the element if it is the b-th child (element)
# in each group of <tt>a</tt> child elements of its parent element.
# * <tt>:nth-child(-an+b)</tt> -- Match the element if it is the first child (element)
# in each group of <tt>a</tt> child elements, up to the first <tt>b</tt> child
# elements of its parent element.
# * <tt>:nth-child(odd)</tt> -- Match element in the odd position (i.e. first, third).
# Same as <tt>:nth-child(2n+1)</tt>.
# * <tt>:nth-child(even)</tt> -- Match element in the even position (i.e. second,
# fourth). Same as <tt>:nth-child(2n+2)</tt>.
# * <tt>:nth-of-type(..)</tt> -- As above, but only counts elements of its type.
# * <tt>:nth-last-child(..)</tt> -- As above, but counts from the last child.
# * <tt>:nth-last-of-type(..)</tt> -- As above, but counts from the last child and
# only elements of its type.
# * <tt>:not(selector)</tt> -- Match the element only if the element does not
# match the simple selector.
#
# As you can see, <tt>:nth-child<tt> pseudo class and its variant can get quite
# tricky and the CSS specification doesn't do a much better job explaining it.
# But after reading the examples and trying a few combinations, it's easy to
# figure out.
#
# For example:
# table tr:nth-child(odd)
# Selects every second row in the table starting with the first one.
#
# div p:nth-child(4)
# Selects the fourth paragraph in the +div+, but not if the +div+ contains
# other elements, since those are also counted.
#
# div p:nth-of-type(4)
# Selects the fourth paragraph in the +div+, counting only paragraphs, and
# ignoring all other elements.
#
# div p:nth-of-type(-n+4)
# Selects the first four paragraphs, ignoring all others.
#
# And you can always select an element that matches one set of rules but
# not another using <tt>:not</tt>. For example:
# p:not(.post)
# Matches all paragraphs that do not have the class <tt>.post</tt>.
#
# === Substitution Values
#
# You can use substitution with identifiers, class names and element values.
# A substitution takes the form of a question mark (<tt>?</tt>) and uses the
# next value in the argument list following the CSS expression.
#
# The substitution value may be a string or a regular expression. All other
# values are converted to strings.
#
# For example:
# selector = HTML::Selector.new "#?", /^\d+$/
# matches any element whose identifier consists of one or more digits.
#
# See http://www.w3.org/TR/css3-selectors/
class Selector
# An invalid selector.
class InvalidSelectorError < StandardError #:nodoc:
end
class << self
# :call-seq:
# Selector.for_class(cls) => selector
#
# Creates a new selector for the given class name.
def for_class(cls)
self.new([".?", cls])
end
# :call-seq:
# Selector.for_id(id) => selector
#
# Creates a new selector for the given id.
def for_id(id)
self.new(["#?", id])
end
end
# :call-seq:
# Selector.new(string, [values ...]) => selector
#
# Creates a new selector from a CSS 2 selector expression.
#
# The first argument is the selector expression. All other arguments
# are used for value substitution.
#
# Throws InvalidSelectorError is the selector expression is invalid.
def initialize(selector, *values)
raise ArgumentError, "CSS expression cannot be empty" if selector.empty?
@source = ""
values = values[0] if values.size == 1 && values[0].is_a?(Array)
# We need a copy to determine if we failed to parse, and also
# preserve the original pass by-ref statement.
statement = selector.strip.dup
# Create a simple selector, along with negation.
simple_selector(statement, values).each { |name, value| instance_variable_set("@#{name}", value) }
@alternates = []
@depends = nil
# Alternative selector.
if statement.sub!(/^\s*,\s*/, "")
second = Selector.new(statement, values)
@alternates << second
# If there are alternate selectors, we group them in the top selector.
if alternates = second.instance_variable_get(:@alternates)
second.instance_variable_set(:@alternates, [])
@alternates.concat alternates
end
@source << " , " << second.to_s
# Sibling selector: create a dependency into second selector that will
# match element immediately following this one.
elsif statement.sub!(/^\s*\+\s*/, "")
second = next_selector(statement, values)
@depends = lambda do |element, first|
if element = next_element(element)
second.match(element, first)
end
end
@source << " + " << second.to_s
# Adjacent selector: create a dependency into second selector that will
# match all elements following this one.
elsif statement.sub!(/^\s*~\s*/, "")
second = next_selector(statement, values)
@depends = lambda do |element, first|
matches = []
while element = next_element(element)
if subset = second.match(element, first)
if first && !subset.empty?
matches << subset.first
break
else
matches.concat subset
end
end
end
matches.empty? ? nil : matches
end
@source << " ~ " << second.to_s
# Child selector: create a dependency into second selector that will
# match a child element of this one.
elsif statement.sub!(/^\s*>\s*/, "")
second = next_selector(statement, values)
@depends = lambda do |element, first|
matches = []
element.children.each do |child|
if child.tag? && subset = second.match(child, first)
if first && !subset.empty?
matches << subset.first
break
else
matches.concat subset
end
end
end
matches.empty? ? nil : matches
end
@source << " > " << second.to_s
# Descendant selector: create a dependency into second selector that
# will match all descendant elements of this one. Note,
elsif statement =~ /^\s+\S+/ && statement != selector
second = next_selector(statement, values)
@depends = lambda do |element, first|
matches = []
stack = element.children.reverse
while node = stack.pop
next unless node.tag?
if subset = second.match(node, first)
if first && !subset.empty?
matches << subset.first
break
else
matches.concat subset
end
elsif children = node.children
stack.concat children.reverse
end
end
matches.empty? ? nil : matches
end
@source << " " << second.to_s
else
# The last selector is where we check that we parsed
# all the parts.
unless statement.empty? || statement.strip.empty?
raise ArgumentError, "Invalid selector: #{statement}"
end
end
end
# :call-seq:
# match(element, first?) => array or nil
#
# Matches an element against the selector.
#
# For a simple selector this method returns an array with the
# element if the element matches, nil otherwise.
#
# For a complex selector (sibling and descendant) this method
# returns an array with all matching elements, nil if no match is
# found.
#
# Use +first_only=true+ if you are only interested in the first element.
#
# For example:
# if selector.match(element)
# puts "Element is a login form"
# end
def match(element, first_only = false)
# Match element if no element name or element name same as element name
if matched = (!@tag_name || @tag_name == element.name)
# No match if one of the attribute matches failed
for attr in @attributes
if element.attributes[attr[0]] !~ attr[1]
matched = false
break
end
end
end
# Pseudo class matches (nth-child, empty, etc).
if matched
for pseudo in @pseudo
unless pseudo.call(element)
matched = false
break
end
end
end
# Negation. Same rules as above, but we fail if a match is made.
if matched && @negation
for negation in @negation
if negation[:tag_name] == element.name
matched = false
else
for attr in negation[:attributes]
if element.attributes[attr[0]] =~ attr[1]
matched = false
break
end
end
end
if matched
for pseudo in negation[:pseudo]
if pseudo.call(element)
matched = false
break
end
end
end
break unless matched
end
end
# If element matched but depends on another element (child,
# sibling, etc), apply the dependent matches instead.
if matched && @depends
matches = @depends.call(element, first_only)
else
matches = matched ? [element] : nil
end
# If this selector is part of the group, try all the alternative
# selectors (unless first_only).
if !first_only || !matches
@alternates.each do |alternate|
break if matches && first_only
if subset = alternate.match(element, first_only)
if matches
matches.concat subset
else
matches = subset
end
end
end
end
matches
end
# :call-seq:
# select(root) => array
#
# Selects and returns an array with all matching elements, beginning
# with one node and traversing through all children depth-first.
# Returns an empty array if no match is found.
#
# The root node may be any element in the document, or the document
# itself.
#
# For example:
# selector = HTML::Selector.new "input[type=text]"
# matches = selector.select(element)
# matches.each do |match|
# puts "Found text field with name #{match.attributes['name']}"
# end
def select(root)
matches = []
stack = [root]
while node = stack.pop
if node.tag? && subset = match(node, false)
subset.each do |match|
matches << match unless matches.any? { |item| item.equal?(match) }
end
elsif children = node.children
stack.concat children.reverse
end
end
matches
end
# Similar to #select but returns the first matching element. Returns +nil+
# if no element matches the selector.
def select_first(root)
stack = [root]
while node = stack.pop
if node.tag? && subset = match(node, true)
return subset.first if !subset.empty?
elsif children = node.children
stack.concat children.reverse
end
end
nil
end
def to_s #:nodoc:
@source
end
# Return the next element after this one. Skips sibling text nodes.
#
# With the +name+ argument, returns the next element with that name,
# skipping other sibling elements.
def next_element(element, name = nil)
if siblings = element.parent.children
found = false
siblings.each do |node|
if node.equal?(element)
found = true
elsif found && node.tag?
return node if (name.nil? || node.name == name)
end
end
end
nil
end
protected
# Creates a simple selector given the statement and array of
# substitution values.
#
# Returns a hash with the values +tag_name+, +attributes+,
# +pseudo+ (classes) and +negation+.
#
# Called the first time with +can_negate+ true to allow
# negation. Called a second time with false since negation
# cannot be negated.
def simple_selector(statement, values, can_negate = true)
tag_name = nil
attributes = []
pseudo = []
negation = []
# Element name. (Note that in negation, this can come at
# any order, but for simplicity we allow if only first).
statement.sub!(/^(\*|[[:alpha:]][\w\-]*)/) do |match|
match.strip!
tag_name = match.downcase unless match == "*"
@source << match
"" # Remove
end
# Get identifier, class, attribute name, pseudo or negation.
while true
# Element identifier.
next if statement.sub!(/^#(\?|[\w\-]+)/) do |match|
id = $1
if id == "?"
id = values.shift
end
@source << "##{id}"
id = Regexp.new("^#{Regexp.escape(id.to_s)}$") unless id.is_a?(Regexp)
attributes << ["id", id]
"" # Remove
end
# Class name.
next if statement.sub!(/^\.([\w\-]+)/) do |match|
class_name = $1
@source << ".#{class_name}"
class_name = Regexp.new("(^|\s)#{Regexp.escape(class_name)}($|\s)") unless class_name.is_a?(Regexp)
attributes << ["class", class_name]
"" # Remove
end
# Attribute value.
next if statement.sub!(/^\[\s*([[:alpha:]][\w\-:]*)\s*((?:[~|^$*])?=)?\s*('[^']*'|"[^*]"|[^\]]*)\s*\]/) do |match|
name, equality, value = $1, $2, $3
if value == "?"
value = values.shift
else
# Handle single and double quotes.
value.strip!
if (value[0] == ?" || value[0] == ?') && value[0] == value[-1]
value = value[1..-2]
end
end
@source << "[#{name}#{equality}'#{value}']"
attributes << [name.downcase.strip, attribute_match(equality, value)]
"" # Remove
end
# Root element only.
next if statement.sub!(/^:root/) do |match|
pseudo << lambda do |element|
element.parent.nil? || !element.parent.tag?
end
@source << ":root"
"" # Remove
end
# Nth-child including last and of-type.
next if statement.sub!(/^:nth-(last-)?(child|of-type)\((odd|even|(\d+|\?)|(-?\d*|\?)?n([+\-]\d+|\?)?)\)/) do |match|
reverse = $1 == "last-"
of_type = $2 == "of-type"
@source << ":nth-#{$1}#{$2}("
case $3
when "odd"
pseudo << nth_child(2, 1, of_type, reverse)
@source << "odd)"
when "even"
pseudo << nth_child(2, 2, of_type, reverse)
@source << "even)"
when /^(\d+|\?)$/ # b only
b = ($1 == "?" ? values.shift : $1).to_i
pseudo << nth_child(0, b, of_type, reverse)
@source << "#{b})"
when /^(-?\d*|\?)?n([+\-]\d+|\?)?$/
a = ($1 == "?" ? values.shift :
$1 == "" ? 1 : $1 == "-" ? -1 : $1).to_i
b = ($2 == "?" ? values.shift : $2).to_i
pseudo << nth_child(a, b, of_type, reverse)
@source << (b >= 0 ? "#{a}n+#{b})" : "#{a}n#{b})")
else
raise ArgumentError, "Invalid nth-child #{match}"
end
"" # Remove
end
# First/last child (of type).
next if statement.sub!(/^:(first|last)-(child|of-type)/) do |match|
reverse = $1 == "last"
of_type = $2 == "of-type"
pseudo << nth_child(0, 1, of_type, reverse)
@source << ":#{$1}-#{$2}"
"" # Remove
end
# Only child (of type).
next if statement.sub!(/^:only-(child|of-type)/) do |match|
of_type = $1 == "of-type"
pseudo << only_child(of_type)
@source << ":only-#{$1}"
"" # Remove
end
# Empty: no child elements or meaningful content (whitespaces
# are ignored).
next if statement.sub!(/^:empty/) do |match|
pseudo << lambda do |element|
empty = true
for child in element.children
if child.tag? || !child.content.strip.empty?
empty = false
break
end
end
empty
end
@source << ":empty"
"" # Remove
end
# Content: match the text content of the element, stripping
# leading and trailing spaces.
next if statement.sub!(/^:content\(\s*(\?|'[^']*'|"[^"]*"|[^)]*)\s*\)/) do |match|
content = $1
if content == "?"
content = values.shift
elsif (content[0] == ?" || content[0] == ?') && content[0] == content[-1]
content = content[1..-2]
end
@source << ":content('#{content}')"
content = Regexp.new("^#{Regexp.escape(content.to_s)}$") unless content.is_a?(Regexp)
pseudo << lambda do |element|
text = ""
for child in element.children
unless child.tag?
text << child.content
end
end
text.strip =~ content
end
"" # Remove
end
# Negation. Create another simple selector to handle it.
if statement.sub!(/^:not\(\s*/, "")
raise ArgumentError, "Double negatives are not missing feature" unless can_negate
@source << ":not("
negation << simple_selector(statement, values, false)
raise ArgumentError, "Negation not closed" unless statement.sub!(/^\s*\)/, "")
@source << ")"
next
end
# No match: moving on.
break
end
# Return hash. The keys are mapped to instance variables.
{:tag_name=>tag_name, :attributes=>attributes, :pseudo=>pseudo, :negation=>negation}
end
# Create a regular expression to match an attribute value based
# on the equality operator (=, ^=, |=, etc).
def attribute_match(equality, value)
regexp = value.is_a?(Regexp) ? value : Regexp.escape(value.to_s)
case equality
when "=" then
# Match the attribute value in full
Regexp.new("^#{regexp}$")
when "~=" then
# Match a space-separated word within the attribute value
Regexp.new("(^|\s)#{regexp}($|\s)")
when "^="
# Match the beginning of the attribute value
Regexp.new("^#{regexp}")
when "$="
# Match the end of the attribute value
Regexp.new("#{regexp}$")
when "*="
# Match substring of the attribute value
regexp.is_a?(Regexp) ? regexp : Regexp.new(regexp)
when "|=" then
# Match the first space-separated item of the attribute value
Regexp.new("^#{regexp}($|\s)")
else
raise InvalidSelectorError, "Invalid operation/value" unless value.empty?
# Match all attributes values (existence check)
//
end
end
# Returns a lambda that can match an element against the nth-child
# pseudo class, given the following arguments:
# * +a+ -- Value of a part.
# * +b+ -- Value of b part.
# * +of_type+ -- True to test only elements of this type (of-type).
# * +reverse+ -- True to count in reverse order (last-).
def nth_child(a, b, of_type, reverse)
# a = 0 means select at index b, if b = 0 nothing selected
return lambda { |element| false } if a == 0 && b == 0
# a < 0 and b < 0 will never match against an index
return lambda { |element| false } if a < 0 && b < 0
b = a + b + 1 if b < 0 # b < 0 just picks last element from each group
b -= 1 unless b == 0 # b == 0 is same as b == 1, otherwise zero based
lambda do |element|
# Element must be inside parent element.
return false unless element.parent && element.parent.tag?
index = 0
# Get siblings, reverse if counting from last.
siblings = element.parent.children
siblings = siblings.reverse if reverse
# Match element name if of-type, otherwise ignore name.
name = of_type ? element.name : nil
found = false
for child in siblings
# Skip text nodes/comments.
if child.tag? && (name == nil || child.name == name)
if a == 0
# Shortcut when a == 0 no need to go past count
if index == b
found = child.equal?(element)
break
end
elsif a < 0
# Only look for first b elements
break if index > b
if child.equal?(element)
found = (index % a) == 0
break
end
else
# Otherwise, break if child found and count == an+b
if child.equal?(element)
found = (index % a) == b
break
end
end
index += 1
end
end
found
end
end
# Creates a only child lambda. Pass +of-type+ to only look at
# elements of its type.
def only_child(of_type)
lambda do |element|
# Element must be inside parent element.
return false unless element.parent && element.parent.tag?
name = of_type ? element.name : nil
other = false
for child in element.parent.children
# Skip text nodes/comments.
if child.tag? && (name == nil || child.name == name)
unless child.equal?(element)
other = true
break
end
end
end
!other
end
end
# Called to create a dependent selector (sibling, descendant, etc).
# Passes the remainder of the statement that will be reduced to zero
# eventually, and array of substitution values.
#
# This method is called from four places, so it helps to put it here
# for reuse. The only logic deals with the need to detect comma
# separators (alternate) and apply them to the selector group of the
# top selector.
def next_selector(statement, values)
second = Selector.new(statement, values)
# If there are alternate selectors, we group them in the top selector.
if alternates = second.instance_variable_get(:@alternates)
second.instance_variable_set(:@alternates, [])
@alternates.concat alternates
end
second
end
end
# See HTML::Selector.new
def self.selector(statement, *values)
Selector.new(statement, *values)
end
class Tag
def select(selector, *values)
selector = HTML::Selector.new(selector, values)
selector.select(self)
end
end
end
