class Regexp::Parser

def self.parse(input, syntax = nil, options: nil, &block)
  new.parse(input, syntax, options: options, &block)
end

def active_opts
  options_stack.last
end

def anchor(token)
  case token.token
  when :bol;              node << Anchor::BeginningOfLine.new(token, active_opts)
  when :bos;              node << Anchor::BOS.new(token, active_opts)
  when :eol;              node << Anchor::EndOfLine.new(token, active_opts)
  when :eos;              node << Anchor::EOS.new(token, active_opts)
  when :eos_ob_eol;       node << Anchor::EOSobEOL.new(token, active_opts)
  when :match_start;      node << Anchor::MatchStart.new(token, active_opts)
  when :nonword_boundary; node << Anchor::NonWordBoundary.new(token, active_opts)
  when :word_boundary;    node << Anchor::WordBoundary.new(token, active_opts)
  else
    raise UnknownTokenError.new('Anchor', token)
  end
end

def assign_effective_number(exp)
  exp.effective_number =
    exp.number + total_captured_group_count + (exp.number < 0 ? 1 : 0)
  exp.effective_number > 0 ||
    raise(ParserError, "Invalid reference: #{exp.reference}")
end

def assign_referenced_expressions
  # find all referenceable and referring expressions
  targets = { 0 => root }
  referrers = []
  root.each_expression do |exp|
    exp.is_a?(Group::Capture) && targets[exp.identifier] = exp
    referrers << exp if exp.referential?
  end
  # assign reference expression to referring expressions
  # (in a second iteration because there might be forward references)
  referrers.each do |exp|
    exp.referenced_expression = targets[exp.reference] ||
      raise(ParserError, "Invalid reference #{exp.reference} at pos #{exp.ts}")
  end
end

def backref(token)
  case token.token
  when :name_ref
    node << Backreference::Name.new(token, active_opts)
  when :name_recursion_ref
    node << Backreference::NameRecursionLevel.new(token, active_opts)
  when :name_call
    node << Backreference::NameCall.new(token, active_opts)
  when :number, :number_ref # TODO: split in v3.0.0
    node << Backreference::Number.new(token, active_opts)
  when :number_recursion_ref
    node << Backreference::NumberRecursionLevel.new(token, active_opts).tap do |exp|
      # TODO: should split off new token number_recursion_rel_ref and new
      # class NumberRelativeRecursionLevel in v3.0.0 to get rid of this
      if exp.text =~ /[<'][+-]/
        assign_effective_number(exp)
      else
        exp.effective_number = exp.number
      end
    end
  when :number_call
    node << Backreference::NumberCall.new(token, active_opts)
  when :number_rel_ref
    node << Backreference::NumberRelative.new(token, active_opts).tap do |exp|
      assign_effective_number(exp)
    end
  when :number_rel_call
    node << Backreference::NumberCallRelative.new(token, active_opts).tap do |exp|
      assign_effective_number(exp)
    end
  else
    raise UnknownTokenError.new('Backreference', token)
  end
end

def captured_group_count_at_level
  captured_group_counts[node]
end

def close_completed_character_set_range
  decrease_nesting if node.instance_of?(CharacterSet::Range) && node.complete?
end

def close_group
  options_stack.pop unless switching_options
  self.switching_options = false
  decrease_nesting
end

def close_set
  decrease_nesting(&:close)
end

def conditional(token)
  case token.token
  when :open
    nest_conditional(Conditional::Expression.new(token, active_opts))
  when :condition
    conditional_nesting.last.condition = Conditional::Condition.new(token, active_opts)
    conditional_nesting.last.add_sequence(active_opts, { ts: token.te })
  when :separator
    conditional_nesting.last.add_sequence(active_opts, { ts: token.te })
    self.node = conditional_nesting.last.branches.last
  when :close
    conditional_nesting.pop
    decrease_nesting
    self.node =
      if conditional_nesting.empty?
        nesting.last
      else
        conditional_nesting.last
      end
  else
    raise UnknownTokenError.new('Conditional', token)
  end
end

def count_captured_group
  captured_group_counts[node] += 1
end

def decrease_nesting
  while nesting.last.is_a?(SequenceOperation)
    nesting.pop
    self.node = nesting.last
  end
  nesting.pop
  yield(node) if block_given?
  self.node = nesting.last
  self.node = node.last if node.last.is_a?(SequenceOperation)
end

def escape(token)
  case token.token
  when :backspace;      node << EscapeSequence::Backspace.new(token, active_opts)
  when :escape;         node << EscapeSequence::AsciiEscape.new(token, active_opts)
  when :bell;           node << EscapeSequence::Bell.new(token, active_opts)
  when :form_feed;      node << EscapeSequence::FormFeed.new(token, active_opts)
  when :newline;        node << EscapeSequence::Newline.new(token, active_opts)
  when :carriage;       node << EscapeSequence::Return.new(token, active_opts)
  when :tab;            node << EscapeSequence::Tab.new(token, active_opts)
  when :vertical_tab;   node << EscapeSequence::VerticalTab.new(token, active_opts)
  when :codepoint;      node << EscapeSequence::Codepoint.new(token, active_opts)
  when :codepoint_list; node << EscapeSequence::CodepointList.new(token, active_opts)
  when :hex;            node << EscapeSequence::Hex.new(token, active_opts)
  when :octal;          node << EscapeSequence::Octal.new(token, active_opts)
  when :control
    if token.text =~ /\A(?:\\C-\\M|\\c\\M)/
      # TODO: emit :meta_control_sequence token in v3.0.0
      node << EscapeSequence::MetaControl.new(token, active_opts)
    else
      node << EscapeSequence::Control.new(token, active_opts)
    end
  when :meta_sequence
    if token.text =~ /\A\\M-\\[Cc]/
      # TODO: emit :meta_control_sequence token in v3.0.0:
      node << EscapeSequence::MetaControl.new(token, active_opts)
    else
      node << EscapeSequence::Meta.new(token, active_opts)
    end
  else
    # treating everything else as a literal
    # TODO: maybe split this up a bit more in v3.0.0?
    # E.g. escaped quantifiers or set meta chars are not the same
    # as stuff that would be a literal even without the backslash.
    # Right now, they all end up here.
    node << EscapeSequence::Literal.new(token, active_opts)
  end
end

def extract_options(input, options)
  if options && !input.is_a?(String)
    raise ArgumentError, 'options cannot be supplied unless parsing a String'
  end
  options = input.options if input.is_a?(::Regexp)
  return {} unless options
  enabled_options = {}
  enabled_options[:i] = true if options & ::Regexp::IGNORECASE != 0
  enabled_options[:m] = true if options & ::Regexp::MULTILINE  != 0
  enabled_options[:x] = true if options & ::Regexp::EXTENDED   != 0
  enabled_options
end

def free_space(token)
  case token.token
  when :comment
    node << Comment.new(token, active_opts)
  when :whitespace
    node << WhiteSpace.new(token, active_opts)
  else
    raise UnknownTokenError.new('FreeSpace', token)
  end
end

def group(token)
  case token.token
  when :options, :options_switch
    options_group(token)
  when :close
    close_group
  when :comment
    node << Group::Comment.new(token, active_opts)
  else
    open_group(token)
  end
end

def increase_group_level(exp)
  exp.level += 1
  exp.quantifier.level += 1 if exp.quantifier
  exp.terminal? || exp.each { |subexp| increase_group_level(subexp) }
end

def intersection(token)
  sequence_operation(CharacterSet::Intersection, token)
end

def keep(token)
  node << Keep::Mark.new(token, active_opts)
end

def literal(token)
  node << Literal.new(token, active_opts)
end

def meta(token)
  case token.token
  when :dot
    node << CharacterType::Any.new(token, active_opts)
  when :alternation
    sequence_operation(Alternation, token)
  else
    raise UnknownTokenError.new('Meta', token)
  end
end

def negate_set
  node.negate
end

def nest(exp)
  nesting.push(exp)
  node << exp
  self.node = exp
end

def nest_conditional(exp)
  conditional_nesting.push(exp)
  nest(exp)
end

def open_group(token)
  group_class =
    case token.token
    when :absence;     Group::Absence
    when :atomic;      Group::Atomic
    when :capture;     Group::Capture
    when :named;       Group::Named
    when :passive;     Group::Passive
    when :lookahead;   Assertion::Lookahead
    when :lookbehind;  Assertion::Lookbehind
    when :nlookahead;  Assertion::NegativeLookahead
    when :nlookbehind; Assertion::NegativeLookbehind
    else
      raise UnknownTokenError.new('Group type open', token)
    end
  group = group_class.new(token, active_opts)
  if group.capturing?
    group.number          = total_captured_group_count + 1
    group.number_at_level = captured_group_count_at_level + 1
    count_captured_group
  end
  # Push the active options to the stack again. This way we can simply pop the
  # stack for any group we close, no matter if it had its own options or not.
  options_stack << active_opts
  nest(group)
end

def open_set(token)
  # TODO: this and Quantifier are the only cases where Expression#token
  # does not match the scanner/lexer output. Fix in v3.0.0.
  token.token = :character
  nest(CharacterSet.new(token, active_opts))
end

def options_group(token)
  positive, negative = token.text.split('-', 2)
  negative ||= ''
  self.switching_options = token.token.equal?(:options_switch)
  opt_changes = {}
  new_active_opts = active_opts.dup
  MOD_FLAGS.each do |flag|
    if positive.include?(flag.to_s)
      opt_changes[flag] = new_active_opts[flag] = true
    end
    if negative.include?(flag.to_s)
      opt_changes[flag] = false
      new_active_opts.delete(flag)
    end
  end
  if (enc_flag = positive.reverse[/[adu]/])
    enc_flag = enc_flag.to_sym
    (ENC_FLAGS - [enc_flag]).each do |other|
      opt_changes[other] = false if new_active_opts[other]
      new_active_opts.delete(other)
    end
    opt_changes[enc_flag] = new_active_opts[enc_flag] = true
  end
  options_stack << new_active_opts
  options_group = Group::Options.new(token, active_opts)
  options_group.option_changes = opt_changes
  nest(options_group)
end

def parse(input, syntax = nil, options: nil, &block)
  root = Root.construct(options: extract_options(input, options))
  self.root = root
  self.node = root
  self.nesting = [root]
  self.options_stack = [root.options]
  self.switching_options = false
  self.conditional_nesting = []
  self.captured_group_counts = Hash.new(0)
  Regexp::Lexer.scan(input, syntax, options: options, collect_tokens: false) do |token|
    parse_token(token)
  end
  # Trigger recursive setting of #nesting_level, which reflects how deep
  # a node is in the tree. Do this at the end to account for tree rewrites.
  root.nesting_level = 0
  assign_referenced_expressions
  if block_given?
    block.call(root)
  else
    root
  end
end

def parse_token(token)
  case token.type
  when :anchor;                     anchor(token)
  when :assertion, :group;          group(token)
  when :backref;                    backref(token)
  when :conditional;                conditional(token)
  when :escape;                     escape(token)
  when :free_space;                 free_space(token)
  when :keep;                       keep(token)
  when :literal;                    literal(token)
  when :meta;                       meta(token)
  when :posixclass, :nonposixclass; posixclass(token)
  when :property, :nonproperty;     property(token)
  when :quantifier;                 quantifier(token)
  when :set;                        set(token)
  when :type;                       type(token)
  else
    raise UnknownTokenTypeError.new(token.type, token)
  end
  close_completed_character_set_range
end

def posixclass(token)
  node << PosixClass.new(token, active_opts)
end

def property(token)
  case token.token
  when :alnum;                  node << UP::Alnum.new(token, active_opts)
  when :alpha;                  node << UP::Alpha.new(token, active_opts)
  when :ascii;                  node << UP::Ascii.new(token, active_opts)
  when :blank;                  node << UP::Blank.new(token, active_opts)
  when :cntrl;                  node << UP::Cntrl.new(token, active_opts)
  when :digit;                  node << UP::Digit.new(token, active_opts)
  when :graph;                  node << UP::Graph.new(token, active_opts)
  when :lower;                  node << UP::Lower.new(token, active_opts)
  when :print;                  node << UP::Print.new(token, active_opts)
  when :punct;                  node << UP::Punct.new(token, active_opts)
  when :space;                  node << UP::Space.new(token, active_opts)
  when :upper;                  node << UP::Upper.new(token, active_opts)
  when :word;                   node << UP::Word.new(token, active_opts)
  when :xdigit;                 node << UP::Xdigit.new(token, active_opts)
  when :xposixpunct;            node << UP::XPosixPunct.new(token, active_opts)
  # only in Oniguruma (old rubies)
  when :newline;                node << UP::Newline.new(token, active_opts)
  when :any;                    node << UP::Any.new(token, active_opts)
  when :assigned;               node << UP::Assigned.new(token, active_opts)
  when :letter;                 node << UP::Letter::Any.new(token, active_opts)
  when :cased_letter;           node << UP::Letter::Cased.new(token, active_opts)
  when :uppercase_letter;       node << UP::Letter::Uppercase.new(token, active_opts)
  when :lowercase_letter;       node << UP::Letter::Lowercase.new(token, active_opts)
  when :titlecase_letter;       node << UP::Letter::Titlecase.new(token, active_opts)
  when :modifier_letter;        node << UP::Letter::Modifier.new(token, active_opts)
  when :other_letter;           node << UP::Letter::Other.new(token, active_opts)
  when :mark;                   node << UP::Mark::Any.new(token, active_opts)
  when :combining_mark;         node << UP::Mark::Combining.new(token, active_opts)
  when :nonspacing_mark;        node << UP::Mark::Nonspacing.new(token, active_opts)
  when :spacing_mark;           node << UP::Mark::Spacing.new(token, active_opts)
  when :enclosing_mark;         node << UP::Mark::Enclosing.new(token, active_opts)
  when :number;                 node << UP::Number::Any.new(token, active_opts)
  when :decimal_number;         node << UP::Number::Decimal.new(token, active_opts)
  when :letter_number;          node << UP::Number::Letter.new(token, active_opts)
  when :other_number;           node << UP::Number::Other.new(token, active_opts)
  when :punctuation;            node << UP::Punctuation::Any.new(token, active_opts)
  when :connector_punctuation;  node << UP::Punctuation::Connector.new(token, active_opts)
  when :dash_punctuation;       node << UP::Punctuation::Dash.new(token, active_opts)
  when :open_punctuation;       node << UP::Punctuation::Open.new(token, active_opts)
  when :close_punctuation;      node << UP::Punctuation::Close.new(token, active_opts)
  when :initial_punctuation;    node << UP::Punctuation::Initial.new(token, active_opts)
  when :final_punctuation;      node << UP::Punctuation::Final.new(token, active_opts)
  when :other_punctuation;      node << UP::Punctuation::Other.new(token, active_opts)
  when :separator;              node << UP::Separator::Any.new(token, active_opts)
  when :space_separator;        node << UP::Separator::Space.new(token, active_opts)
  when :line_separator;         node << UP::Separator::Line.new(token, active_opts)
  when :paragraph_separator;    node << UP::Separator::Paragraph.new(token, active_opts)
  when :symbol;                 node << UP::Symbol::Any.new(token, active_opts)
  when :math_symbol;            node << UP::Symbol::Math.new(token, active_opts)
  when :currency_symbol;        node << UP::Symbol::Currency.new(token, active_opts)
  when :modifier_symbol;        node << UP::Symbol::Modifier.new(token, active_opts)
  when :other_symbol;           node << UP::Symbol::Other.new(token, active_opts)
  when :other;                  node << UP::Codepoint::Any.new(token, active_opts)
  when :control;                node << UP::Codepoint::Control.new(token, active_opts)
  when :format;                 node << UP::Codepoint::Format.new(token, active_opts)
  when :surrogate;              node << UP::Codepoint::Surrogate.new(token, active_opts)
  when :private_use;            node << UP::Codepoint::PrivateUse.new(token, active_opts)
  when :unassigned;             node << UP::Codepoint::Unassigned.new(token, active_opts)
  when *UPTokens::Age;          node << UP::Age.new(token, active_opts)
  when *UPTokens::Derived;      node << UP::Derived.new(token, active_opts)
  when *UPTokens::Emoji;        node << UP::Emoji.new(token, active_opts)
  when *UPTokens::Enumerated;   node << UP::Enumerated.new(token, active_opts)
  when *UPTokens::Script;       node << UP::Script.new(token, active_opts)
  when *UPTokens::UnicodeBlock; node << UP::Block.new(token, active_opts)
  else
    raise UnknownTokenError.new('UnicodeProperty', token)
  end
end

def quantifier(token)
  target_node = node.extract_quantifier_target(token.text)
  # in case of chained quantifiers, wrap target in an implicit passive group
  # description of the problem: https://github.com/ammar/regexp_parser/issues/3
  # rationale for this solution: https://github.com/ammar/regexp_parser/pull/69
  if target_node.quantified?
    new_group = Group::Passive.construct(
      token:             :passive,
      ts:                target_node.ts,
      level:             target_node.level,
      set_level:         target_node.set_level,
      conditional_level: target_node.conditional_level,
      options:           active_opts,
    )
    new_group.implicit = true
    new_group << target_node
    increase_group_level(target_node)
    node.expressions[node.expressions.index(target_node)] = new_group
    target_node = new_group
  end
  unless token.token =~ /\A(?:zero_or_one|zero_or_more|one_or_more|interval)
                           (?:_greedy|_reluctant|_possessive)?\z/x
    raise UnknownTokenError.new('Quantifier', token)
  end
  target_node.quantify(token, active_opts)
end

def range(token)
  exp = CharacterSet::Range.new(token, active_opts)
  scope = node.last.instance_of?(CharacterSet::IntersectedSequence) ? node.last : node
  exp << scope.expressions.pop
  nest(exp)
end

def sequence_operation(klass, token)
  unless node.instance_of?(klass)
    operator = klass.new(token, active_opts)
    sequence = operator.add_sequence(active_opts, { ts: token.ts })
    sequence.expressions = node.expressions
    node.expressions = []
    nest(operator)
  end
  node.add_sequence(active_opts, { ts: token.te })
end

def set(token)
  case token.token
  when :open;         open_set(token)
  when :close;        close_set
  when :negate;       negate_set
  when :range;        range(token)
  when :intersection; intersection(token)
  else
    raise UnknownTokenError.new('CharacterSet', token)
  end
end

def total_captured_group_count
  captured_group_counts.values.reduce(0, :+)
end

def type(token)
  case token.token
  when :digit;     node << CharacterType::Digit.new(token, active_opts)
  when :hex;       node << CharacterType::Hex.new(token, active_opts)
  when :linebreak; node << CharacterType::Linebreak.new(token, active_opts)
  when :nondigit;  node << CharacterType::NonDigit.new(token, active_opts)
  when :nonhex;    node << CharacterType::NonHex.new(token, active_opts)
  when :nonspace;  node << CharacterType::NonSpace.new(token, active_opts)
  when :nonword;   node << CharacterType::NonWord.new(token, active_opts)
  when :space;     node << CharacterType::Space.new(token, active_opts)
  when :word;      node << CharacterType::Word.new(token, active_opts)
  when :xgrapheme; node << CharacterType::ExtendedGrapheme.new(token, active_opts)
  else
    raise UnknownTokenError.new('CharacterType', token)
  end
end