/**
 * ChatThread renders the conversation: user prompts, streamed agent answers
 * (markdown) and inline errors, auto-scrolled to the latest entry.
 *
 * @example
 * <ChatThread thread={[{ kind: "user", text: "hi" }]} turnActive={false} />
 */

import { useEffect, useRef } from "react";
import type { ThreadItem } from "../reducer";
import { Markdown } from "./Markdown";
import { ToolCallCard } from "./ToolCallCard";

interface ChatThreadProps {
	thread: ThreadItem[];
	turnActive: boolean;
}

export function ChatThread({ thread, turnActive }: ChatThreadProps) {
	const endRef = useRef<HTMLDivElement>(null);

	// biome-ignore lint/correctness/useExhaustiveDependencies: thread and turnActive intentionally retrigger the scroll-to-bottom on every conversation change.
	useEffect(() => {
		// Optional call: test DOMs (jsdom) do not implement scrollIntoView.
		endRef.current?.scrollIntoView?.({ behavior: "smooth" });
	}, [thread, turnActive]);

	return (
		<section className="thread" aria-label="conversation">
			{thread.length === 0 && (
				<p className="thread-empty">
					Send a prompt to start working with the agent.
				</p>
			)}
			{thread.map((item, index) => (
				// biome-ignore lint/suspicious/noArrayIndexKey: the thread is append-only (never reordered or spliced), so the index is a stable identity.
				<ThreadEntry key={index} item={item} />
			))}
			{turnActive && (
				<output className="thread-working">the agent is working…</output>
			)}
			<div ref={endRef} />
		</section>
	);
}

function ThreadEntry({ item }: { item: ThreadItem }) {
	switch (item.kind) {
		case "user":
			return <div className="message message-user">{item.text}</div>;
		case "agent":
			return (
				<div className="message message-agent">
					<Markdown text={item.text} />
				</div>
			);
		case "thought":
			return (
				<details className="thought">
					<summary className="thought-summary">💭 Thinking</summary>
					<div className="thought-body">
						<Markdown text={item.text} />
					</div>
				</details>
			);
		case "tool":
			return <ToolCallCard call={item.call} />;
		case "error":
			return (
				<div className="message message-error" role="alert">
					{item.text}
				</div>
			);
	}
}