module EditorCore
  class Cursor
    attr_reader :row, :col

    def initialize(row = 0, col = 0)
      @row = row
      @col = col
      freeze
    end

    def move(buffer,row,col); self.class.new(row,col).clamp(buffer); end
    def up(buffer,   offset = 1); move(buffer, row-offset,col); end
    def down(buffer, offset = 1); move(buffer, row+offset,col); end

    def left(buffer, offset = 1)
      return Cursor.new(row, col - offset) if offset <= col
      return self if beginning_of_file?
      return move(buffer,row-1,buffer.line_length(row-1))
    end

    def right(buffer, offset = 1)
      #buffer.right(self,offset)
      return Cursor.new(row, col + offset).clamp(buffer) unless end_of_line?(buffer)
      return self if final_line?(buffer)
      Cursor.new(row + 1, 0)
    end

    def clamp(buffer)
      row = @row.clamp(0, buffer.lines_count - 1)
      # FIXME: Is this `buffer.lines` check needed? It ought not to be.
      if !buffer.lines(row)
        col = 0
      else
        col = @col.clamp(0, buffer.line_length(row))
      end
      Cursor.new(row,col)
    end

    def enter(buffer)
      down(buffer).line_home
    end

    def line_home
      Cursor.new(row, 0)
    end

    def line_end(buffer)
      Cursor.new(row, buffer.line_length(row))
    end

    def end_of_line?(buffer)
      if buffer.lines(row)
        col == buffer.line_length(row)
      else
        true
      end
    end

    def final_line?(buffer)
      row == buffer.lines_count - 1
    end

    def end_of_file?(buffer)
      final_line?(buffer) && end_of_line?(buffer)
    end

    def beginning_of_file?
      row == 0 && col == 0
    end
  end
end