Refactor Copy/Paste

[bantic]

Copy/Paste behavior is somewhat under-specced in mobiledoc-kit at the moment (and in general — I cannot find a general-purpose algorithm described online for pasting structured content into a document).
This issue attempts to define some declarative behaviors for copy-pasting that align with user expectations. It addresses #249 as well.

Paste Algorithm for mobiledoc-kit

• pasting when in a blank section
  • replaces that section with the entirety of the pasted post
  • update cursor to end of pasted content
• pasting when cursor is in non-markerable section
  • if cursor is at start of section
    • for each pasted section
      • insert if before the cursor section
      • update cursor to be end of inserted section
  • else
    • for each pasted section
      • insert it after the cursor section
      • update cursor to be end of inserted section
• pasting when cursor is in non-nested markerable (e.g., MarkupSection)
  • if pasted post first leaf section is not markerable
    • if cursor position is at start of section
      • insert each pasted section before the cursor section except the last one
      • if the last one is markerable:
        • prepend its content to the cursor section
        • update cursor position to be the end of the prepended content
      • else
        • insert it before the cursor section
        • update cursor position to be the end of the inserted section
    • else if cursor position is in middle of section
      • split the cursor section into pre- and post-split
      • for each pasted section except the last:
        • insert it before the post-split section
        • update cursor position to be the end of the inserted section
      • if last section is markerable:
        • prepend its content to the cursor section
        • update the cursor position to be the end of the prepended content
      • else
        • insert it before the post-split section
        • update cursor position to be the end of the inserted section
    • else if cursor is at the end of the section
      • for each pasted section
        • insert it after the cursor section
        • update cursor position to be the end of the inserted section
  • else if pasted post first leaf section is non-nested markerable (e.g. MarkupSection)
    • insert leaf section markers at cursor position
    • update cursor position to be end of inserted content
    • if additional sections:
      • break cursor section at updated cursor position into pre- and post-split
      • for each section except the last:
        • insert it before post-split
        • update cursor position to be end of inserted section
      • for last section
        • if it is markerable:
          • insert its contents at start of post-split
          • update cursor position to be end of inserted content
        • else
          • insert it before post-split
          • update cursor position to be end of inserted section
  • else if pasted post first leaf section is nested markerable (e.g. ListItem)
    • insert content from 1st item at cursor position
    • update cursor position to be end of inserted content
    • if more items in the list or more sections to paste (aka “should insert linebreak”)
      • split the cursor section at updated position into pre- and post-split
      • if any remaining items:
        • create a new list with the remaining items
        • insert the list before post-split
        • update cursor position to be end of inserted list
      • if additional pasted sections:
        • for each section except the last
          • insert it before post-split
          • update cursor position to be end of inserted section
        • for last section
          • if it is markerable
            • insert its contents at start of post-split
            • update cursor position to be end of inserted content
          • else
            • insert it before post-split
            • update cursor position to be end of inserted section
• pasting when cursor is in nested markerable (e.g. ListItem)
  • if pasted post first leaf section is not markerable
    • break list at list item/position (pre-split and post-split lists)
    • for each pasted section including the last:
      • insert it before post-split
      • update cursor position to be end of inserted section
  • if pasted post first leaf section is non-nested markerable (markup section)
    • insert contents of 1st section at cursor position
    • update cursor position to be end of inserted contents
    • if additional sections:
      • break list at list item/position (pre-split and post-split lists)
      • for each section except the last
        • insert it before post-split
        • update cursor position to be the end of the inserted section
      • for last section
        • if it is markerable
          • insert its contents at start of 1st item in post-split list
          • update cursor position to be end of inserted content
        • else
          • insert it before post-split
          • update cursor position to be end of inserted section
  • if pasted post first leaf section is nested markerable (ListItem):
    • insert contents of 1st item at cursor position
    • update cursor position to be end of inserted contents
    • let hasAdditionalSections be true if pasted content has sections after the list section
    • let sectionToInsertBefore be the section after the cursor’s list section if hasAdditionalSections
    • if additional list items
      • split cursor list item into pre- and post-split list items
      • for each list item except last
        • insert it before post-split list item
        • update cursor position to be end of inserted section
      • if hasAdditionalSections
        • break cursor list section between the last inserted item and the post-split list item (the post-split list section has the post-split list item and all remaining items)
        • insert the new list after existing list
        • update sectionToInsertBefore be the inserted list
      • else
        • insert contents of last list item at start of post-split list item
        • update cursor position to end of inserted content
    • if hasAdditionalSections
      • for each section including the last
        • insert it before sectionToInsertBefore
        • update cursor position to be end of inserted section

[bantic]

Here's some research I did on how Google Docs does copy/paste in different scenarios, for reference:
https://www.evernote.com/shard/s62/sh/88f31509-54c7-4b39-a93a-2e0876f1bf73/a1d9b7be0fb28ef9

[bantic]

closed by #267