module Ruco
  class TextArea
    attr_reader :content

    def initialize(content, options)
      @content = tabs_to_spaces(content)
      @options = options
      @line = 0
      @column = 0
      @cursor_line = 0
      @cursor_column = 0
      @scrolled_lines = 0
      @scrolled_columns = 0
      @options[:line_scrolling_offset] ||= @options[:lines] / 2
      @options[:column_scrolling_offset] ||= @options[:columns] / 2
    end

    def view
      lines = self.lines
      Array.new(@options[:lines]).map_with_index do |_,i|
        (lines[i + @scrolled_lines] || "").slice(@scrolled_columns, @options[:columns])
      end * "\n" + "\n"
    end

    def move(where, *args)
      case where
      when :relative then
        @line += args.first
        @column += args.last
      when :to then
        @line, @column = args
      when :to_bol then move_to_bol(*args)
      when :to_eol then move_to_eol(*args)
      when :to_line then @line = args.first
      when :to_column then @column = args.first
      when :page_down then
        shift = @options[:lines] - 1
        @line += shift
        @scrolled_lines += shift
      when :page_up then
        shift = @options[:lines] - 1
        @line -= shift
        @scrolled_lines -= shift
      else
        raise "Unknown move type #{where} with #{args.inspect}"
      end
      adjust_view
    end

    def insert(text)
      text = tabs_to_spaces(text)
      insert_into_content cursor_index, text
      move_according_to_insert(text)
    end

    def delete(count)
      if count > 0
        @content.slice!(cursor_index, count)
      else
        backspace(count.abs)
      end
    end

    # TODO this should go into editor
    def delete_line
      old_position = position
      move :to_column, 0
      delete line_length
      if position == [0,0]
        delete(1)
      else
        delete(-1)
      end
      move :to, *old_position
    end

    def cursor
      Cursor.new @cursor_line, @cursor_column
    end

    def cursor_index
      index = lines[0...@line].join("\n").size + @column
      index += 1 if @line > 0 # account for missing newline
      index
    end

    def cursor_for_index(index)
      jump = @content.slice(0, index).to_s.naive_split("\n")
      [jump.size - 1, jump.last.size]
    end

    protected

    def line_length
      lines[@line].size
    end

    def position
      [@line, @column]
    end

    def move_to_eol
      after_last_word = current_line.index(/\s*$/)
      after_last_whitespace = current_line.size

      if @column == after_last_whitespace or @column < after_last_word
        move :to_column, after_last_word
      else
        move :to_column, after_last_whitespace
      end
    end

    def move_to_bol
      before_first_word = current_line.index(/[^\s]/) || 0
      column = if @column == 0 or @column > before_first_word
        before_first_word
      else
        0
      end
      move :to_column, column
    end

    def backspace(count)
      start_index = cursor_index - count
      if start_index < 0
        count += start_index
        start_index = 0
      end

      @content.slice!(start_index, count)
      move :to, *cursor_for_index(start_index)
    end

    def lines
      @content.naive_split("\n")
    end

    def adjust_view
      @line =    [[@line,   0].max, lines.size - 1].min
      @column =  [[@column, 0].max, (lines[@line]||'').size].min
      reposition_cursor
      scroll_column_into_view
      scroll_line_into_view
      reposition_cursor
    end

    def scroll_column_into_view
      offset = [@options[:column_scrolling_offset], @options[:columns]].min

      if @cursor_column >= @options[:columns]
        @scrolled_columns = @column - @options[:columns] + offset
      end

      if @cursor_column < 0
        @scrolled_columns = @column - offset
      end

      @scrolled_columns = [[@scrolled_columns, 0].max, @column].min
    end

    def scroll_line_into_view
      offset = [@options[:line_scrolling_offset], @options[:lines]].min

      if @cursor_line >= @options[:lines]
        @scrolled_lines = @line - @options[:lines] + offset
      end

      if @cursor_line < 0
        @scrolled_lines = @line - offset
      end

      @scrolled_lines = [[@scrolled_lines, 0].max, @line].min
    end

    def reposition_cursor
      @cursor_column = @column - @scrolled_columns
      @cursor_line = @line - @scrolled_lines
    end

    def insert_into_content(index, text)
      # expand with newlines when inserting after maximum position
      if index > @content.size
        @content << "\n" * (index - @content.size)
      end
      @content.insert(index, text)
    end

    def current_line
      lines[@line] || ''
    end

    def move_according_to_insert(text)
      inserted_lines = text.naive_split("\n")
      if inserted_lines.size > 1
        # column position does not add up when hitting return
        @column = inserted_lines.last.size
        move(:relative, inserted_lines.size - 1, 0)
      else
        move(:relative, inserted_lines.size - 1, inserted_lines.last.size)
      end
    end

    def tabs_to_spaces(text)
      text.gsub("\t",' ' * Ruco::TAB_SIZE)
    end
  end
end