Module: Scrapetor::Dom::Selectors

Defined in:
lib/scrapetor/dom/selectors.rb

Overview

CSS selector engine over the pure-Ruby DOM.

Pipeline:

1. Compile the selector string into a list of "atoms" with
   combinators (reuses `Scrapetor::Selector.compile`).
2. Find candidates matching the rightmost atom by walking the
   subtree once (no global indexes — the DOM is small enough
   that one scan is faster than maintaining indexes for the
   typical scraping document).
3. For each candidate, walk ancestors right-to-left to verify
   the rest of the chain.

Atom matching delegates to ‘Scrapetor::Selector.atom_matches?`, so pseudo-class support (`:has`, `:not`, `:is`, `:nth-child`, etc.) lives in one place.

Constant Summary collapse

GROUPS_CACHE =

Cached comma-splitter. Frozen-literal selector strings hit the cache 100% of the time after first call, so a fallback loop that re-runs the same selector pays the per-char scan once across the whole iteration.

{}
GROUPS_CACHE_CAP = 
1024
DOM_COMPILE_CACHE =

Cache compiled plans by selector string so a dom-mode document that re-runs the same selector dozens of times in a fallback loop only pays the parse cost once. Selector strings tend to come from frozen literals in parser code, so the cache hit rate is effectively 100%.

{}
DOM_COMPILE_CACHE_CAP = 
1024

Class Method Summary collapse

Class Method Details

.atom_document(scope) ⇒ Object 



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# File 'lib/scrapetor/dom/selectors.rb', line 129

def self.atom_document(scope)
  return scope if scope.is_a?(Document)
  cur = scope
  cur = cur.parent while cur && cur.respond_to?(:parent) && cur.parent
  cur
end

.atom_matches?(atom, node) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/scrapetor/dom/selectors.rb', line 151

def self.atom_matches?(atom, node)
  Scrapetor::Selector.atom_matches?(atom, node)
end

.candidates_for_atom(scope, atom) ⇒ Object 



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# File 'lib/scrapetor/dom/selectors.rb', line 97

def self.candidates_for_atom(scope, atom)
  # Use the document's lazy structural indexes when the atom has a
  # narrowing anchor (id / class / tag). Falling back to a full
  # walk_descendants on every fallback selector dominated parse
  # time on 100KB SERP-style fixtures.
  doc = atom_document(scope)
  if doc.is_a?(Document) && atom.id
    node = doc.id_index[atom.id]
    return [] if node.nil?
    return Scrapetor::Selector.atom_matches?(atom, node) && in_scope?(node, scope) ? [node] : []
  end
  if doc.is_a?(Document) && atom.classes && !atom.classes.empty?
    # Pick the narrowest class index entry as the candidate seed.
    sets = atom.classes.map { |c| doc.class_index[c] || [] }
    seed = sets.min_by(&:size) || []
    return seed.select do |node|
      in_scope?(node, scope) && Scrapetor::Selector.atom_matches?(atom, node)
    end
  end
  if doc.is_a?(Document) && atom.tag
    seed = doc.tag_index[atom.tag.to_s] || []
    return seed.select do |node|
      in_scope?(node, scope) && Scrapetor::Selector.atom_matches?(atom, node)
    end
  end
  result = []
  walk_descendants(scope) do |node|
    result << node if Scrapetor::Selector.atom_matches?(atom, node)
  end
  result
end

.compile(selector) ⇒ Object 



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# File 'lib/scrapetor/dom/selectors.rb', line 81

def self.compile(selector)
  cached = DOM_COMPILE_CACHE[selector]
  return cached if cached
  plan = Scrapetor::Selector.compile(selector)
  DOM_COMPILE_CACHE.shift while DOM_COMPILE_CACHE.size >= DOM_COMPILE_CACHE_CAP
  DOM_COMPILE_CACHE[selector] = plan
end

.css(scope, selector_str) ⇒ Object 



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# File 'lib/scrapetor/dom/selectors.rb', line 21

def self.css(scope, selector_str)
  results = []
  seen = {}
  selector_groups(selector_str).each do |group|
    plan = compile(group)
    next if plan.empty?
    execute(scope, plan).each do |n|
      oid = n.object_id
      next if seen[oid]
      seen[oid] = true
      results << n
    end
  end
  results
end

.execute(scope, plan) ⇒ Object 



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# File 'lib/scrapetor/dom/selectors.rb', line 89

def self.execute(scope, plan)
  return [] if plan.empty?
  last_idx = plan.size - 1
  candidates = candidates_for_atom(scope, plan[last_idx])
  return candidates if plan.size == 1
  candidates.select { |n| match_chain_backwards?(n, plan, last_idx - 1, scope) }
end

.in_scope?(node, scope) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/scrapetor/dom/selectors.rb', line 197

def self.in_scope?(node, scope)
  return true if scope.is_a?(Document)
  cur = node
  while cur
    return true if cur.equal?(scope)
    cur = cur.parent
  end
  false
end

.match_chain_backwards?(node, plan, idx, scope) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/scrapetor/dom/selectors.rb', line 155

def self.match_chain_backwards?(node, plan, idx, scope)
  return true if idx < 0
  atom = plan[idx]
  combinator = plan[idx + 1].combinator
  case combinator
  when :child
    parent = node.parent
    return false unless parent.is_a?(Element)
    return false unless in_scope?(parent, scope)
    return false unless atom_matches?(atom, parent)
    match_chain_backwards?(parent, plan, idx - 1, scope)
  when :descendant, nil
    cur = node.parent
    while cur.is_a?(Element)
      if in_scope?(cur, scope) && atom_matches?(atom, cur) &&
         match_chain_backwards?(cur, plan, idx - 1, scope)
        return true
      end
      cur = cur.parent
    end
    false
  when :adj
    prev = node.previous_element_sibling
    return false unless prev.is_a?(Element)
    return false unless in_scope?(prev, scope)
    return false unless atom_matches?(atom, prev)
    match_chain_backwards?(prev, plan, idx - 1, scope)
  when :gen
    prev = node.previous_element_sibling
    while prev.is_a?(Element)
      if in_scope?(prev, scope) && atom_matches?(atom, prev) &&
         match_chain_backwards?(prev, plan, idx - 1, scope)
        return true
      end
      prev = prev.previous_element_sibling
    end
    false
  else
    false
  end
end

.selector_groups(s) ⇒ Object 



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# File 'lib/scrapetor/dom/selectors.rb', line 44

def self.selector_groups(s)
  cached = GROUPS_CACHE[s]
  return cached if cached
  depth = 0
  paren = 0
  groups = []
  buf = +""
  s.each_char do |ch|
    if ch == "["
      depth += 1; buf << ch
    elsif ch == "]"
      depth -= 1 if depth.positive?; buf << ch
    elsif ch == "("
      paren += 1; buf << ch
    elsif ch == ")"
      paren -= 1 if paren.positive?; buf << ch
    elsif ch == "," && depth.zero? && paren.zero?
      groups << buf.strip
      buf = +""
    else
      buf << ch
    end
  end
  groups << buf.strip
  out = groups.reject(&:empty?).each(&:freeze).freeze
  GROUPS_CACHE.shift while GROUPS_CACHE.size >= GROUPS_CACHE_CAP
  GROUPS_CACHE[s] = out
end

.walk_descendants(scope, &block) ⇒ Object 



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# File 'lib/scrapetor/dom/selectors.rb', line 136

def self.walk_descendants(scope, &block)
  children =
    if scope.is_a?(Document) || scope.is_a?(Element)
      scope.children
    else
      []
    end
  children.each do |c|
    if c.element?
      block.call(c)
      walk_descendants(c, &block)
    end
  end
end