Support subpage and bi-directional links

[tzhangchi]

[doodlewind]

Updated TODOs:

• Rich text
  • [x] New rich text node (blot-like cursor behavior)
  • [x] [[ markdown shortcuts
• Model layer
  • [x] API (events) for receiving linked page title change
  • [x] API for querying filtered page list inside workspace
  • [ ] Import from markdown
  • [x] Export to markdown and HTML
• UI components
  • [x] Filtered page list popup UI
• Misc
  • [ ] Clipboard support
  • [x] Multiple page testing in BlockSuite playground

To be clarified:

• Behavior (fallback) state when linked page is deleted

Note:

• Cross-workspace bi-directional link support is a non-goal.

[tzhangchi]

@lawvs

[lawvs]

Some design ideas related to subpage:

Basic Principles

• Use the field pageMeta as the data source

For example:

<page title="page1" pageMeta={["page-id-foo", "bar"]}>
  <paragraph text={<>
      <page-ref type="subpage" link-id="page-id-foo">subpage text</page-ref>
      <page-ref type="bi-directional" link-id="foo">bi-directional link text</page-ref>
    </>}
  />
</page>

Scenario 1 - Add/Delete subpage by sidebar

• Update pageMeta
• If page1 is opened and page-ref node rendered
  • The page-ref can receive notification, then remove itself
• Else do nothing
• If someone opens the readonly page, the page-ref will check page.subpages and render nothing.
• When the page1 opens and before page-ref rendered
  • page-ref can check pageMeta and then remove itself

Scenario 2 - Add/Delete subpage by operate text node

• Update pageMeta
• Add/Remove page-ref node

Scenario 3 - data out of sync 1

• pageMeta is empty, but has a subpage node
  • It's expected scenario, the page-ref will remove itself before render

Options (happens when removing an unopened subpage from sidebar):

• Not removing subpage link from page content immediately, lazy-remove it at next render -> may lead to side effect.
• Try removing subpage link after page tree updated -> requires loading subdoc and may fail, also more time-costly.

<page title="page1" pageMeta={[]}>
  <paragraph text={<>
      <page-ref type="subpage" link-id="foo">subpage text</page-ref>
      <page-ref type="bi-directional" link-id="page-id-foo">bi-directional link text</page-ref>
    </>}
  />
</page>

Scenario 4 - data out of sync 2

• pageMeta has some pages, but no corresponding page-ref text node
  • left side would have a ghost page, once remove it manually, it will return to normal

Happens when adding new subpage from sidebar, need similar options as Scenario 3.

<page title="page1" subpages={["page-id-foo"]}>
  <paragraph text="" />
</page>

Note: All of the above names are temporary.

[doodlewind]

We need to maintain the page tree hierarchy in pageMeta, which is a common sub-doc across the workspace. In this case, we may not need another page-level field (page.subpage in CRDT model) marking the subpage relationship, only having the sys:refs: id[] property on the paragraph/list block that contains subpage could be adequate.

TODOs:

• API for adding/querying/removing/updating subpage link in one page
• API for querying all bi-directional links in one page