export type SkipReason = "too_short" | "too_long" | "code_like";

export interface SkipRuleOptions {
	minWords: number;
	maxChars: number;
}

const CODE_FENCE_RE = /```/;
const SHELL_PROMPT_RE = /^\s*[$#>]\s/m;
const STACK_TRACE_RE = /\bat\s+\S+\s*\(.*:\d+:\d+\)/;
const PATH_HEAVY_RE = /(\/[\w.-]+){3,}|([A-Za-z]:\\[\w.-]+){2,}/;
const CODE_SYMBOL_RE = /[{};()<>=]/g;

export function countWords(text: string): number {
	return text.trim().split(/\s+/).filter(Boolean).length;
}

/** Fence markers, prompts, stack traces, dense paths, or a high symbol density all read as code, not prose. */
function isCodeLike(text: string): boolean {
	if (CODE_FENCE_RE.test(text)) return true;
	if (SHELL_PROMPT_RE.test(text)) return true;
	if (STACK_TRACE_RE.test(text)) return true;
	if (PATH_HEAVY_RE.test(text)) return true;

	const symbolCount = text.match(CODE_SYMBOL_RE)?.length ?? 0;
	return text.length > 40 && symbolCount / text.length > 0.05;
}

/**
 * Both a cost and a privacy control: anything skipped here is never transmitted
 * to the correction provider at all.
 */
export function shouldSkip(text: string, options: SkipRuleOptions): SkipReason | null {
	const trimmed = text.trim();
	if (trimmed.length > options.maxChars) return "too_long";
	if (isCodeLike(trimmed)) return "code_like";
	if (countWords(trimmed) < options.minWords) return "too_short";
	return null;
}