import { syncConfigReviewFingerprint } from "./config.js";
import type { RemoteHead, SyncBackend } from "./sync-backend.js";
import { safeTerminalText } from "./sync-format.js";
import {
	inspectRemoteSelection,
	type RemoteSelectionState,
	remoteSelectionMismatch,
	sameSyncInclude,
	snapshotSelectionInclude,
} from "./sync-policy.js";
import type { AnySyncConfig, Snapshot } from "./types.js";

export async function readSnapshotForHead(
	backend: SyncBackend,
	head: RemoteHead,
	signal?: AbortSignal,
) {
	const snapshot = await backend.readSnapshot(head.snapshotRef, signal);
	if (signal?.aborted) {
		throw signal.reason instanceof Error
			? signal.reason
			: new DOMException("The operation was aborted", "AbortError");
	}
	if (snapshot.id !== head.snapshotId) {
		throw new Error(
			`Remote head ${head.snapshotId} resolved to unexpected snapshot ${snapshot.id}.`,
		);
	}
	if (head.selection) {
		const snapshotInclude = snapshotSelectionInclude(snapshot);
		if (!snapshotInclude || !sameSyncInclude(head.selection.include, snapshotInclude)) {
			throw new Error("Remote head selection does not match its immutable snapshot.");
		}
	}
	return snapshot;
}

export function requireCompatibleRemoteSelection(config: AnySyncConfig, snapshot: Snapshot) {
	const state = inspectRemoteSelection(config.include, snapshot);
	if (state.kind === "different") {
		throw remoteSelectionMismatch(config, state.include, syncConfigReviewFingerprint(config));
	}
}

export function formatRemoteSelectionStatus(state: RemoteSelectionState | undefined) {
	if (!state) return "remote included content: unavailable (remote is empty)";
	if (state.kind === "same") return "remote included content: matches this setup";
	if (state.kind === "legacy") {
		return `remote included content: unavailable in legacy snapshot (${state.discovered.length} path${state.discovered.length === 1 ? "" : "s"} discovered, partial)`;
	}
	return [
		"remote included content: differs from this setup",
		`remote-only selection: ${safeList(state.remoteOnly)}`,
		`local-only selection: ${safeList(state.localOnly)}`,
	].join("\n");
}

function safeList(values: readonly string[]) {
	return values.length > 0 ? values.map(safeTerminalText).join(", ") : "none";
}