import { readdirSync, existsSync, readFileSync } from "node:fs";
import { join, extname } from "node:path";
import type { ContextCandidate, DiscoveryOptions } from "./types.js";

const CODE_EXTS = new Set([".ts", ".tsx", ".js", ".jsx", ".py", ".go", ".rs", ".java"]);

function estimateTokens(text: string): number {
  return Math.ceil(text.length / 4);
}

function scanDir(dir: string, limit: number): ContextCandidate[] {
  const results: ContextCandidate[] = [];
  try {
    for (const entry of readdirSync(dir, { withFileTypes: true })) {
      if (results.length >= limit) break;
      const full = join(dir, entry.name);
      if (entry.isDirectory() && !entry.name.startsWith(".") && entry.name !== "node_modules") {
        results.push(...scanDir(full, limit - results.length));
      } else if (entry.isFile() && CODE_EXTS.has(extname(entry.name))) {
        try {
          const content = readFileSync(full, "utf8").slice(0, 8000);
          results.push({
            id: full,
            kind: "source",
            path: full,
            title: entry.name,
            content,
            tokens: estimateTokens(content),
            trust: "high",
            tags: [extname(entry.name).replace(".", "")],
          });
        } catch { /* skip unreadable */ }
      }
    }
  } catch { /* skip inaccessible */ }
  return results;
}

export function discoverContext(root: string, options: Omit<DiscoveryOptions, "root"> = {}): ContextCandidate[] {
  const limit = options.limit ?? 50;
  return scanDir(root, limit);
}