export type TestCommandArgumentCompletion = {
	value: string;
	label: string;
	description: string;
};

const TEST_COMMAND_FLAG_COMPLETIONS: TestCommandArgumentCompletion[] = [
	{
		value: "--info",
		label: "--info",
		description: "Show full command output",
	},
	{
		value: "--tags",
		label: "--tags",
		description: "Run with Go build tags",
	},
	{
		value: "--comment",
		label: "--comment",
		description: "Ask the model to analyze the test results",
	},
];

export function completeTestCommandArguments(
	argumentPrefix: string,
): TestCommandArgumentCompletion[] | null {
	if (isCompletingTagValue(argumentPrefix)) return null;

	const usedFlags = collectUsedFlags(argumentPrefix);
	const currentToken = currentCompletionToken(argumentPrefix);
	const matches = TEST_COMMAND_FLAG_COMPLETIONS.filter(
		(item) => !usedFlags.has(item.value) && item.value.startsWith(currentToken),
	);

	return matches.length > 0 ? matches : null;
}

/**
 * Detects whether the cursor is inside a `/test` args context and returns
 * the text after `/test ` (or "" right after the command). Returns
 * undefined when the line is not a `/test` command line.
 */
export function testCommandTailBeforeCursor(
	line: string,
	cursorCol: number,
): string | undefined {
	const beforeCursor = line.slice(0, cursorCol);
	if (beforeCursor === "/test") return "";
	if (!beforeCursor.startsWith("/test ")) return undefined;
	return beforeCursor.slice("/test ".length);
}

export function currentCompletionToken(argumentPrefix: string): string {
	if (argumentPrefix.trim() === "" || /\s$/.test(argumentPrefix)) return "";
	return argumentPrefix.trim().split(/\s+/).at(-1) ?? "";
}

function collectUsedFlags(argumentPrefix: string): Set<string> {
	const usedFlags = new Set<string>();
	const tokens =
		argumentPrefix.trim() === "" ? [] : argumentPrefix.trim().split(/\s+/);

	for (const token of tokens) {
		if (token === "--info") usedFlags.add("--info");
		if (token === "--comment") usedFlags.add("--comment");
		if (token === "--tags" || token.startsWith("--tags=")) {
			usedFlags.add("--tags");
		}
	}

	return usedFlags;
}

function isCompletingTagValue(argumentPrefix: string): boolean {
	return /(?:^|\s)--tags\s+\S+$/.test(argumentPrefix);
}