-- Mutable source version can be anything (e.g. number, string, immutable data structure)
-- so long as it changes every time any part of the source changes.

export type MutableSourceVersion = NonMaybeType<any>

export type MutableSourceGetSnapshotFn<Source, Snapshot> = (source: Source) -> Snapshot

export type MutableSourceSubscribeFn<Source, Snapshot> = (
	source: Source,
	callback: (snapshot: Snapshot) -> ()
) -> (() -> ())

export type MutableSourceGetVersionFn = (
	_source: NonMaybeType<any>
) -> MutableSourceVersion

export type MutableSource<Source> = {
	_source: Source,

	_getVersion: MutableSourceGetVersionFn,

	-- Tracks the version of this source at the time it was most recently read.
	-- Used to determine if a source is safe to read from before it has been subscribed to.
	-- Version number is only used during mount,
	-- since the mechanism for determining safety after subscription is expiration time.
	--
	-- As a workaround to support multiple concurrent renderers,
	-- we categorize some renderers as primary and others as secondary.
	-- We only expect there to be two concurrent renderers at most:
	-- React Native (primary) and Fabric (secondary);
	-- React DOM (primary) and React ART (secondary).
	-- Secondary renderers store their context values on separate fields.
	-- We use the same approach for Context.
	_workInProgressVersionPrimary: nil | MutableSourceVersion,
	_workInProgressVersionSecondary: nil | MutableSourceVersion,

	-- DEV only
	-- Used to detect multiple renderers using the same mutable source.
	_currentPrimaryRenderer: Object | nil,
	_currentSecondaryRenderer: Object | nil,
}
