import type { ClassificationResult, PromptCategory } from './types.js';

// ── Keyword patterns for classification ────────────────────────

const CODE_PATTERNS = [
  /\b(function|const |let |var |class |import |export |return |async |await )\b/,
  /\b(def |print\(|if __name__|lambda )\b/,
  /[{}();]=>/,
  /```[\s\S]*```/,
  /\b(typescript|javascript|python|rust|golang|java|kotlin|swift|sql|html|css|react|node)\b/i,
  /\b(debug|refactor|compile|build|deploy|lint|test|api|endpoint|route|middleware)\b/i,
  /\b(fix|bug|error|exception|stack trace|undefined|null|NaN)\b/i,
];

const MATH_PATTERNS = [
  /\b(calculate|compute|solve|equation|formula|integral|derivative|matrix)\b/i,
  /\b(probability|statistics|regression|correlation|variance|median|mean)\b/i,
  /\b(algebra|geometry|calculus|theorem|proof|hypothesis)\b/i,
  /[+\-*/^=]{2,}/,
  /\d+\s*[+\-*/^]\s*\d+/,
];

const REASONING_PATTERNS = [
  /\b(explain|analyze|compare|evaluate|reason|logic|argument|conclusion)\b/i,
  /\b(why|how does|what if|pros and cons|trade-?offs|implications)\b/i,
  /\b(step[- ]by[- ]step|chain of thought|think through|break down)\b/i,
  /\b(strategy|approach|methodology|framework|architecture|design)\b/i,
];

const CREATIVE_PATTERNS = [
  /\b(write|compose|draft|create|generate|story|poem|essay|blog|article)\b/i,
  /\b(creative|imaginative|brainstorm|ideas|fiction|narrative|dialogue)\b/i,
  /\b(rewrite|rephrase|summarize|translate|tone|style|voice)\b/i,
];

// ── Token estimation ───────────────────────────────────────────

/**
 * Rough token estimate: ~4 chars per token for English text.
 * Good enough for routing decisions.
 */
function estimateTokens(text: string): number {
  return Math.ceil(text.length / 4);
}

// ── Classifier ─────────────────────────────────────────────────

function countMatches(text: string, patterns: RegExp[]): number {
  let count = 0;
  for (const pattern of patterns) {
    if (pattern.test(text)) count++;
  }
  return count;
}

/**
 * Classify a prompt into a category based on keyword matching.
 * No LLM needed — pure regex heuristics.
 */
export function classifyPrompt(
  messages: { role: string; content: string }[]
): ClassificationResult {
  const fullText = messages.map(m => m.content).join('\n');
  const estimatedTokens = estimateTokens(fullText);

  const scores: Record<PromptCategory, number> = {
    code: countMatches(fullText, CODE_PATTERNS),
    math: countMatches(fullText, MATH_PATTERNS),
    reasoning: countMatches(fullText, REASONING_PATTERNS),
    creative: countMatches(fullText, CREATIVE_PATTERNS),
    general: 1, // baseline
  };

  // Pick highest scoring category
  let best: PromptCategory = 'general';
  let bestScore = 0;
  for (const [cat, score] of Object.entries(scores) as [PromptCategory, number][]) {
    if (score > bestScore) {
      bestScore = score;
      best = cat;
    }
  }

  return { category: best, estimatedTokens };
}