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* A file that has not been read yet, dragged.
*
* Every drop target in this application was written for one of two things: an
* operating-system drag carrying `DataTransfer.files`, or a track row being
* moved between the map's edges (`TRACK_DRAG_TYPE`). A row in the Files panel is
* neither. It names a file in a connected folder — a key on a bucket, an entry
* in a granted directory — and there are no bytes behind it until somebody asks
* for them, which is the whole reason the panel can list four hundred rows
* without reading anything.
*
* So it travels as a third type, and the targets learn one more branch. That is
* the same shape `TRACK_DRAG_TYPE` established and it is here for the same
* reason: `types` is all a browser exposes *during* a drag, and a target has to
* decide whether to light up long before it can look at what it is being handed.
*
* **A row of a store is the same thing** (§24.2): a file nobody has read, named
* by an address rather than by a folder. It travels under the same type, so
* every target that takes a Files row takes a store row too — a map's edges and
* middle, a cell of the deck, the Tracks card, an analysis form's file box, the
* landing page — and none of them can tell which list the hand came from.
*
* ## Two payloads, and only one of them is trustworthy
*
* The custom type carries JSON — the folder's id and the entry's path, or, for
* a store row, a token naming the drag ({@link writePickedDrag}) — which is
* what {@link readFileDrag} resolves back into a real file. It is readable only
* at `drop`, like every other `getData`.
*
* `text/plain` is set as well and carries the **name** — a store row's address,
* which is the useful thing about it outside this app — so dragging a row into
* a text box somewhere else does something sensible instead of nothing. Nothing
* in this app ever reads it: a plain string is what a text selection dragged out
* of any input carries too, and a target that trusted it would offer to load a
* file because somebody dragged a word across the map.
*
* ## Resolving happens at the drop, never at the drag
*
* A drag may end anywhere or nowhere, and reading a file for one that is going
* to be cancelled is a permission prompt or a network request for a gesture the
* reader abandoned. {@link readFileDrag} is therefore async and is called by the
* target that accepted the drop, once.
*/
import { folderById } from '../browse/connected'
import type { PickedFile } from '../browse/folder'
import { noteLocation } from '../state/locations'
/**
* The type a dragged **unread file** carries.
*
* Lowercase, because a browser lowercases every type it stores and a comparison
* against a capital would never match — the note `TRACK_DRAG_TYPE` carries, for
* the same reason.
*/
export const FILE_DRAG_TYPE = 'application/x-chromosomix-file'
/** Whether a drag is carrying a row out of the Files panel. */
export function dragHasFileRow(event: DragEvent): boolean {
return Array.from(event.dataTransfer?.types ?? []).includes(FILE_DRAG_TYPE)
}
/** Mark a drag as carrying `path` in the folder `folderId`. */
export function writeFileDrag(
event: DragEvent,
folderId: string,
path: string,
name: string,
): void {
const transfer = event.dataTransfer
if (transfer === null) return
transfer.effectAllowed = 'copy'
transfer.setData(FILE_DRAG_TYPE, JSON.stringify({ folder: folderId, path, name }))
// For everywhere that is not this app. See the header on why nothing here
// reads it back.
transfer.setData('text/plain', name)
}
/**
* The file a drag out of a store is carrying, held here and named in the
* payload by its token — see {@link writePickedDrag}.
*/
let carried: { token: string; picked: PickedFile; taken?: () => void } | null = null
/** How many such drags this page has started, which is what a token is minted from. */
let carriedCount = 0
/**
* Mark a drag as carrying a file this window already has the address of — a
* row of a store (§24.2) — rather than an entry of a connected folder.
*
* The payload names a **token**, and the file stays here. An address in the
* payload would make this type a way for any page to have this one open any
* URL, by dragging something across it with the right label on; a token
* resolves only to the drag this window started, as a folder id resolves only
* to a folder this window is connected to. A drag from another window of the
* app resolves to nothing, as a row of a folder that window never connected
* does. One is held at a time, since there is one hand.
*
* `taken` runs when a target takes the file, before it is opened: a store row
* registers the tracks it brings with it there (`App.noteShelf`), as its two
* buttons do — and a drag that was abandoned registers nothing.
*/
export function writePickedDrag(event: DragEvent, picked: PickedFile, taken?: () => void): void {
const transfer = event.dataTransfer
if (transfer === null) return
const token = `drag-${++carriedCount}`
carried = { token, picked, ...(taken === undefined ? {} : { taken }) }
transfer.effectAllowed = 'copy'
transfer.setData(FILE_DRAG_TYPE, JSON.stringify({ held: token, name: picked.name ?? picked.uri }))
// The address: a store's file is somewhere anybody can fetch it, so its URL
// is what a terminal or a notebook it is dropped into can use.
transfer.setData('text/plain', picked.uri)
}
/**
* The file a drop was carrying, or `null`.
*
* `null` covers every way this can fail to produce a file — a payload that is
* not ours, a folder disconnected between the drag and the drop, an entry that
* has been deleted since it was listed, a lapsed grant, a store row's drag
* that another has replaced — because there is one thing a drop target does
* about all of them, which is nothing. The panel the drag came from is still on
* screen with the same row on it, and a message about a drag the reader has
* already finished is a message with nowhere to go.
*/
export async function readFileDrag(event: DragEvent): Promise<PickedFile | null> {
const raw = event.dataTransfer?.getData(FILE_DRAG_TYPE) ?? ''
if (raw === '') return null
let parsed: unknown
try {
parsed = JSON.parse(raw)
} catch {
return null
}
if (typeof parsed !== 'object' || parsed === null) return null
const payload = parsed as { folder?: unknown; path?: unknown; name?: unknown; held?: unknown }
if (typeof payload.held === 'string') {
if (carried === null || carried.token !== payload.held) return null
carried.taken?.()
return carried.picked
}
if (typeof payload.folder !== 'string' || typeof payload.path !== 'string') return null
if (typeof payload.name !== 'string') return null
const folder = folderById(payload.folder)
if (folder === null) return null
try {
const picked = await folder.pick({ kind: 'file', name: payload.name, path: payload.path, size: null })
// As a row opened by a click is (`FilesCard`): where it came from (§20.6).
noteLocation(picked)
return picked
} catch {
return null
}
}
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