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Filename : around_block_scan.rb
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# frozen_string_literal: true

require_relative "scan_history"

module SyntaxSuggest
  # This class is useful for exploring contents before and after
  # a block
  #
  # It searches above and below the passed in block to match for
  # whatever criteria you give it:
  #
  # Example:
  #
  #   def dog         # 1
  #     puts "bark"   # 2
  #     puts "bark"   # 3
  #   end             # 4
  #
  #   scan = AroundBlockScan.new(
  #     code_lines: code_lines
  #     block: CodeBlock.new(lines: code_lines[1])
  #   )
  #
  #   scan.scan_while { true }
  #
  #   puts scan.before_index # => 0
  #   puts scan.after_index  # => 3
  #
  class AroundBlockScan
    def initialize(code_lines:, block:)
      @code_lines = code_lines
      @orig_indent = block.current_indent

      @stop_after_kw = false
      @force_add_empty = false
      @force_add_hidden = false
      @target_indent = nil

      @scanner = ScanHistory.new(code_lines: code_lines, block: block)
    end

    # When using this flag, `scan_while` will
    # bypass the block it's given and always add a
    # line that responds truthy to `CodeLine#hidden?`
    #
    # Lines are hidden when they've been evaluated by
    # the parser as part of a block and found to contain
    # valid code.
    def force_add_hidden
      @force_add_hidden = true
      self
    end

    # When using this flag, `scan_while` will
    # bypass the block it's given and always add a
    # line that responds truthy to `CodeLine#empty?`
    #
    # Empty lines contain no code, only whitespace such
    # as leading spaces a newline.
    def force_add_empty
      @force_add_empty = true
      self
    end

    # Tells `scan_while` to look for mismatched keyword/end-s
    #
    # When scanning up, if we see more keywords then end-s it will
    # stop. This might happen when scanning outside of a method body.
    # the first scan line up would be a keyword and this setting would
    # trigger a stop.
    #
    # When scanning down, stop if there are more end-s than keywords.
    def stop_after_kw
      @stop_after_kw = true
      self
    end

    # Main work method
    #
    # The scan_while method takes a block that yields lines above and
    # below the block. If the yield returns true, the @before_index
    # or @after_index are modified to include the matched line.
    #
    # In addition to yielding individual lines, the internals of this
    # object give a mini DSL to handle common situations such as
    # stopping if we've found a keyword/end mis-match in one direction
    # or the other.
    def scan_while
      stop_next_up = false
      stop_next_down = false

      @scanner.scan(
        up: ->(line, kw_count, end_count) {
          next false if stop_next_up
          next true if @force_add_hidden && line.hidden?
          next true if @force_add_empty && line.empty?

          if @stop_after_kw && kw_count > end_count
            stop_next_up = true
          end

          yield line
        },
        down: ->(line, kw_count, end_count) {
          next false if stop_next_down
          next true if @force_add_hidden && line.hidden?
          next true if @force_add_empty && line.empty?

          if @stop_after_kw && end_count > kw_count
            stop_next_down = true
          end

          yield line
        }
      )

      self
    end

    # Scanning is intentionally conservative because
    # we have no way of rolling back an agressive block (at this time)
    #
    # If a block was stopped for some trivial reason, (like an empty line)
    # but the next line would have caused it to be balanced then we
    # can check that condition and grab just one more line either up or
    # down.
    #
    # For example, below if we're scanning up, line 2 might cause
    # the scanning to stop. This is because empty lines might
    # denote logical breaks where the user intended to chunk code
    # which is a good place to stop and check validity. Unfortunately
    # it also means we might have a "dangling" keyword or end.
    #
    #   1 def bark
    #   2
    #   3 end
    #
    # If lines 2 and 3 are in the block, then when this method is
    # run it would see it is unbalanced, but that acquiring line 1
    # would make it balanced, so that's what it does.
    def lookahead_balance_one_line
      kw_count = 0
      end_count = 0
      lines.each do |line|
        kw_count += 1 if line.is_kw?
        end_count += 1 if line.is_end?
      end

      return self if kw_count == end_count # nothing to balance

      @scanner.commit_if_changed # Rollback point if we don't find anything to optimize

      # Try to eat up empty lines
      @scanner.scan(
        up: ->(line, _, _) { line.hidden? || line.empty? },
        down: ->(line, _, _) { line.hidden? || line.empty? }
      )

      # More ends than keywords, check if we can balance expanding up
      next_up = @scanner.next_up
      next_down = @scanner.next_down
      case end_count - kw_count
      when 1
        if next_up&.is_kw? && next_up.indent >= @target_indent
          @scanner.scan(
            up: ->(line, _, _) { line == next_up },
            down: ->(line, _, _) { false }
          )
          @scanner.commit_if_changed
        end
      when -1
        if next_down&.is_end? && next_down.indent >= @target_indent
          @scanner.scan(
            up: ->(line, _, _) { false },
            down: ->(line, _, _) { line == next_down }
          )
          @scanner.commit_if_changed
        end
      end
      # Rollback any uncommitted changes
      @scanner.stash_changes

      self
    end

    # Finds code lines at the same or greater indentation and adds them
    # to the block
    def scan_neighbors_not_empty
      @target_indent = @orig_indent
      scan_while { |line| line.not_empty? && line.indent >= @target_indent }
    end

    # Scan blocks based on indentation of next line above/below block
    #
    # Determines indentaion of the next line above/below the current block.
    #
    # Normally this is called when a block has expanded to capture all "neighbors"
    # at the same (or greater) indentation and needs to expand out. For example
    # the `def/end` lines surrounding a method.
    def scan_adjacent_indent
      before_after_indent = []

      before_after_indent << (@scanner.next_up&.indent || 0)
      before_after_indent << (@scanner.next_down&.indent || 0)

      @target_indent = before_after_indent.min
      scan_while { |line| line.not_empty? && line.indent >= @target_indent }

      self
    end

    # Return the currently matched lines as a `CodeBlock`
    #
    # When a `CodeBlock` is created it will gather metadata about
    # itself, so this is not a free conversion. Avoid allocating
    # more CodeBlock's than needed
    def code_block
      CodeBlock.new(lines: lines)
    end

    # Returns the lines matched by the current scan as an
    # array of CodeLines
    def lines
      @scanner.lines
    end

    # Managable rspec errors
    def inspect
      "#<#{self.class}:0x0000123843lol >"
    end
  end
end