/**
 * Assistant-message dot transformer (pure, no pi imports — unit-testable).
 *
 * Prepend a "● " to assistant text messages, mirroring Claude Code. Thinking
 * blocks and user messages pass through untouched, as does any message that
 * opens with a code fence (a "● " before "```" would break code-block
 * parsing).
 *
 * Streaming: partial updates re-run this transform every frame with the raw
 * markdown as input, so the prefix never accumulates. A fence can arrive one
 * backtick at a time ("`", "``", "```js") — while isStreaming is true, any
 * leading backtick is treated as a fence start to avoid a "● `" flicker on
 * intermediate frames. The final frame keeps the full ``` check, so replies
 * that merely open with inline code (e.g. "`foo` and `bar`") still get the
 * dot.
 */

export const ASSISTANT_DOT = "\u2B24 ";

export interface AssistantDotContext {
	/** "user" | "assistant" | "assistant-thinking". */
	messageType?: string;
	/** True for partial assistant updates. */
	isStreaming?: boolean;
}

export function assistantDotTransformer(
	markdown: string,
	{ messageType, isStreaming }: AssistantDotContext = {},
): string {
	// Only assistant text gets the dot; user messages and thinking blocks
	// (assistant-thinking) pass through untouched.
	if (messageType !== "assistant") return markdown;
	const trimmed = markdown.trimStart();
	if (!trimmed) return markdown;
	// Idempotent: never stack a second dot if the text already starts with one
	// (e.g. a previous transformer output fed back in).
	if (trimmed.startsWith(ASSISTANT_DOT)) return markdown;
	const fenceStart = isStreaming ? trimmed.startsWith("`") : trimmed.startsWith("```");
	if (fenceStart) return markdown;
	return ASSISTANT_DOT + trimmed;
}