Update README for room list store
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@ -7,20 +7,21 @@ It's so complicated it needs its own README.
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There's two main kinds of algorithms involved in the room list store: list ordering and tag sorting.
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Throughout the code an intentional decision has been made to call them the List Algorithm and Sorting
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Algorithm respectively. The list algorithm determines the behaviour of the room list whereas the sorting
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algorithm determines how individual tags (lists of rooms, sometimes called sublists) are ordered.
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algorithm determines how rooms get ordered within tags affected by the list algorithm.
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Behaviour of the room list takes the shape of default sorting on tags in most cases, though it can
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override what is happening at the tag level depending on the algorithm used (as is the case with the
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importance algorithm, described later).
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Behaviour of the room list takes the shape of determining what features the room list supports, as well
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as determining where and when to apply the sorting algorithm in a tag. The importance algorithm, which
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is described later in this doc, is an example of an algorithm which makes heavy behavioural changes
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to the room list.
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Tag sorting is effectively the comparator supplied to the list algorithm. This gives the list algorithm
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the power to decide when and how to apply the tag sorting, if at all.
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### Tag sorting algorithm: Alphabetical
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When used, rooms in a given tag will be sorted alphabetically, where the alphabet is determined by a
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simple string comparison operation (essentially giving the browser the problem of figuring out if A
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comes before Z).
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When used, rooms in a given tag will be sorted alphabetically, where the alphabet's order is a problem
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for the browser. All we do is a simple string comparison and expect the browser to return something
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useful.
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### Tag sorting algorithm: Manual
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@ -30,7 +31,7 @@ of `order` cause rooms to appear closer to the top of the list.
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### Tag sorting algorithm: Recent
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Rooms are ordered by the timestamp of the most recent useful message. Usefulness is yet another algorithm
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Rooms get ordered by the timestamp of the most recent useful message. Usefulness is yet another algorithm
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in the room list system which determines whether an event type is capable of bubbling up in the room list.
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Normally events like room messages, stickers, and room security changes will be considered useful enough
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to cause a shift in time.
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@ -49,7 +50,7 @@ its relative deterministic behaviour.
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### List ordering algorithm: Importance
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On the other end of the spectrum, this is the most complicated algorithm which exists. There's major
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behavioural changes and the tag sorting algorithm is selectively applied depending on circumstances.
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behavioural changes, and the tag sorting algorithm gets selectively applied depending on circumstances.
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Each tag which is not manually ordered gets split into 4 sections or "categories". Manually ordered tags
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simply get the manual sorting algorithm applied to them with no further involvement from the importance
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@ -58,34 +59,37 @@ relative (perceived) importance to the user:
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* **Red**: The room has unread mentions waiting for the user.
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* **Grey**: The room has unread notifications waiting for the user. Notifications are simply unread
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messages which cause a push notification or badge count. Typically this is the default as rooms are
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messages which cause a push notification or badge count. Typically, this is the default as rooms get
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set to 'All Messages'.
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* **Bold**: The room has unread messages waiting for the user. Essentially this is a grey room without
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a badge/notification count (or 'Mentions Only'/'Muted').
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* **Idle**: No relevant activity has occurred in the room since the user last read it.
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* **Idle**: No useful (see definition of useful above) activity has occurred in the room since the user
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last read it.
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Conveniently, each tag is ordered by those categories as presented: red rooms appear above grey, grey
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above idle, etc.
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Conveniently, each tag gets ordered by those categories as presented: red rooms appear above grey, grey
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above bold, etc.
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Once the algorithm has determined which rooms belong in which categories, the tag sorting algorithm
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is applied to each category in a sub-sub-list fashion. This should result in the red rooms (for example)
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being sorted alphabetically amongst each other and the grey rooms sorted amongst each other, but
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gets applied to each category in a sub-sub-list fashion. This should result in the red rooms (for example)
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being sorted alphabetically amongst each other as well as the grey rooms sorted amongst each other, but
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collectively the tag will be sorted into categories with red being at the top.
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<!-- TODO: Implement sticky rooms as described below -->
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The algorithm also has a concept of a 'sticky' room which is the room the user is currently viewing.
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The sticky room will remain in position on the room list regardless of other factors going on as typically
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clicking on a room will cause it to change categories into 'idle'. This is done by preserving N rooms
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above the selected room at all times where N is the number of rooms above the selected rooms when it was
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above the selected room at all times, where N is the number of rooms above the selected rooms when it was
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selected.
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For example, if the user has 3 red rooms and selects the middle room, they will always see exactly one
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room above their selection at all times. If they receive another notification and the tag ordering is set
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to Recent, they'll see the new notification go to the top position and the one that was previously there
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fall behind the sticky room.
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room above their selection at all times. If they receive another notification, and the tag ordering is
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specified as Recent, they'll see the new notification go to the top position, and the one that was previously
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there fall behind the sticky room.
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The sticky room's category is technically 'idle' while being viewed and is explicitly pulled out of the
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tag sorting algorithm's input as it must maintain its position in the list. When the user moves to another
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room, the previous sticky room is recalculated to determine which category it needs to be in as the user
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room, the previous sticky room gets recalculated to determine which category it needs to be in as the user
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could have been scrolled up while new messages were received.
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Further, the sticky room is not aware of category boundaries and thus the user can see a shift in what
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@ -112,7 +116,10 @@ all kinds of filtering.
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The `RoomListStore` is the major coordinator of various `Algorithm` implementations, which take care
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of the various `ListAlgorithm` and `SortingAlgorithm` options. The `Algorithm` superclass is also
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responsible for figuring out which tags get which rooms, as Matrix specifies them as a reverse map:
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tags are defined on rooms and are not defined as a collection of rooms (unlike how they are presented
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tags get defined on rooms and are not defined as a collection of rooms (unlike how they are presented
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to the user). Various list-specific utilities are also included, though they are expected to move
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somewhere more general when needed. For example, the `membership` utilities could easily be moved
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elsewhere as needed.
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The various bits throughout the room list store should also have jsdoc of some kind to help describe
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what they do and how they work.
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