import { untrack } from 'svelte'
import { fromStore } from 'svelte/store'
import { SvelteMap } from 'svelte/reactivity'
import { userStore, workspaceStore, type UserExt } from '$lib/stores'
import { getWorkspaceRole, type RoleLookup } from '$lib/user'

/**
 * The user acting in a workspace that is not necessarily the one the top nav points at — an AI
 * session or a workspace-specific variant acts on a workspace the nav deliberately is not on.
 *
 * `$userStore` answers for the navigation workspace at no cost, exactly as every permission check
 * in the app did before this hook existed — including when it holds nobody, which reads as unknown
 * and refuses. Every other workspace is looked up, and an unresolved user there is `undefined`: it
 * must never fall back to the navigation user, whose rights belong to another workspace.
 * `canWrite`/`isOwner` refuse for an unknown user, which is the only safe answer. A caller that
 * must not render that refusal as a denial asks `resolved` first.
 */
export function useActingUser(workspace: () => string | undefined) {
	const navWorkspace = fromStore(workspaceStore)
	const navUser = fromStore(userStore)
	const looked = new SvelteMap<string, RoleLookup>()
	// The workspace this effect last acted on, so arriving at one is distinguishable from the
	// effect re-running while already there.
	let asking: string | undefined

	$effect(() => {
		const ws = workspace()
		if (asking !== ws) {
			asking = ws
			// Dropped on the way *in*, not on the way out: a lookup that fails after the acting
			// workspace has already moved on has no entry to clear at the moment it is left, so
			// clearing it there would keep a refusal that no attempt is behind any more.
			if (ws && untrack(() => looked.get(ws)?.kind) === 'lookup_failed') looked.delete(ws)
		}
		if (!ws || ws === navWorkspace.current) return
		// Any settled answer stops the asking, a failure included — otherwise recording one
		// would re-enter this effect and loop.
		if (looked.has(ws)) return
		untrack(() => {
			// Memoized process-wide, so two components pointed at the same workspace share one
			// request rather than each issuing their own.
			getWorkspaceRole(ws).then((lookup) => looked.set(ws, lookup))
		})
	})

	function userIn(ws: string | undefined): UserExt | undefined {
		if (!ws) return undefined
		if (ws === navWorkspace.current) return navUser.current
		const lookup = looked.get(ws)
		return lookup?.kind === 'resolved' ? lookup.user : undefined
	}

	return {
		/** The acting user in `ws`, or `undefined` when it is not known. Only workspaces this
		 *  hook has been pointed at are looked up; the rest read as unknown. */
		in: userIn,
		/** Whether `ws` has an answer at all — a user, or a lookup that came back without one.
		 *  The navigation workspace always has one: `$userStore`, "nobody" included. */
		resolved: (ws: string | undefined): boolean =>
			!!ws && (ws === navWorkspace.current || looked.has(ws)),
		get current(): UserExt | undefined {
			return userIn(workspace())
		},
		/** Drop the lookups that came back empty so they are asked again. Arriving at a
		 *  workspace already does this; a long-lived editor must call this too when it starts a
		 *  fresh session on the workspace it is already on, or a `whoami` that happened to fail
		 *  pins it to "unknown user" for as long as it stays there. */
		forgetFailures(): void {
			for (const [ws, lookup] of looked) {
				if (lookup.kind === 'lookup_failed') looked.delete(ws)
			}
		}
	}
}