import { type RefObject, useEffect, useMemo, useRef, useState } from "react";
import type { DirectorySession } from "../workspace/types";

const focusableSelector =
	'button:not(:disabled), input:not(:disabled), [href], [tabindex]:not([tabindex="-1"])';

function sessionTitle(session: DirectorySession) {
	return session.name ?? session.firstMessage ?? "Untitled session";
}

function messageCountLabel(count: number) {
	return `${count} ${count === 1 ? "message" : "messages"}`;
}

function matchesQuery(session: DirectorySession, query: string) {
	return [session.name, session.firstMessage, session.id].some((value) =>
		value?.toLocaleLowerCase().includes(query),
	);
}

function SessionRow({
	session,
	onOpen,
}: {
	session: DirectorySession;
	onOpen: (session: DirectorySession) => void;
}) {
	const showPreview = Boolean(
		session.name &&
			session.firstMessage &&
			session.firstMessage !== session.name,
	);
	return (
		<li>
			<button className="session-row" onClick={() => onOpen(session)}>
				<span className="session-row-content">
					<strong>{sessionTitle(session)}</strong>
					{showPreview ? (
						<span className="session-preview">{session.firstMessage}</span>
					) : null}
					<small className="session-metadata">
						<span>{messageCountLabel(session.messageCount)}</span>
						<time dateTime={session.modified}>
							Modified {new Date(session.modified).toLocaleDateString()}
						</time>
					</small>
				</span>
				{session.runtimeId ? <span className="session-open">Open</span> : null}
			</button>
		</li>
	);
}

function SessionResults({
	sessions,
	query,
	onOpen,
}: {
	sessions: DirectorySession[];
	query: string;
	onOpen: (session: DirectorySession) => void;
}) {
	if (sessions.length === 0)
		return <p className="muted">No saved sessions match “{query}”.</p>;
	return (
		<ul id="session-results" className="session-list">
			{sessions.map((session) => (
				<SessionRow key={session.path} session={session} onOpen={onOpen} />
			))}
		</ul>
	);
}

function useDialogFocus(
	dialogRef: RefObject<HTMLElement | null>,
	searchRef: RefObject<HTMLInputElement | null>,
	onClose: () => void,
) {
	const openerRef = useRef<HTMLElement | null>(
		document.activeElement as HTMLElement | null,
	);
	useEffect(() => {
		const dialog = dialogRef.current;
		const controls = () => [
			...(dialog?.querySelectorAll<HTMLElement>(focusableSelector) ?? []),
		];
		searchRef.current?.focus();
		const keydown = (event: KeyboardEvent) => {
			if (event.key === "Escape") {
				event.preventDefault();
				onClose();
				return;
			}
			if (event.key !== "Tab") return;
			const focusable = controls();
			const first = focusable[0];
			const last = focusable[focusable.length - 1];
			if (!first || !last) return;
			if (event.shiftKey && document.activeElement === first) {
				event.preventDefault();
				last.focus();
			} else if (!event.shiftKey && document.activeElement === last) {
				event.preventDefault();
				first.focus();
			}
		};
		window.addEventListener("keydown", keydown);
		return () => {
			window.removeEventListener("keydown", keydown);
			openerRef.current?.focus();
		};
	}, [dialogRef, onClose, searchRef]);
}

export function SessionPicker({
	sessions,
	onOpen,
	onClose,
}: {
	sessions: DirectorySession[];
	onOpen: (session: DirectorySession) => void;
	onClose: () => void;
}) {
	const [query, setQuery] = useState("");
	const dialogRef = useRef<HTMLElement>(null);
	const searchRef = useRef<HTMLInputElement>(null);
	const normalizedQuery = query.trim().toLocaleLowerCase();
	const filteredSessions = useMemo(
		() => sessions.filter((session) => matchesQuery(session, normalizedQuery)),
		[normalizedQuery, sessions],
	);
	useDialogFocus(dialogRef, searchRef, onClose);
	const resultLabel = `${filteredSessions.length} saved session${filteredSessions.length === 1 ? "" : "s"}`;
	return (
		<div className="modal-backdrop">
			<section
				ref={dialogRef}
				className="session-picker"
				role="dialog"
				aria-modal="true"
				aria-labelledby="session-picker-title"
			>
				<div className="picker-heading">
					<h2 id="session-picker-title">Saved sessions</h2>
					<button onClick={onClose}>Close</button>
				</div>
				<div className="session-search">
					<label className="sr-only" htmlFor="session-search">
						Search saved sessions
					</label>
					<input
						ref={searchRef}
						id="session-search"
						type="search"
						value={query}
						onChange={(event) => setQuery(event.target.value)}
						placeholder="Search by name, message, or ID"
						aria-controls="session-results"
					/>
				</div>
				<p className="session-result-count" role="status" aria-live="polite">
					{sessions.length ? resultLabel : "No saved sessions"}
				</p>
				{sessions.length === 0 ? (
					<p className="muted">No saved sessions for this directory.</p>
				) : (
					<SessionResults
						sessions={filteredSessions}
						query={query}
						onOpen={onOpen}
					/>
				)}
			</section>
		</div>
	);
}