import { readdirSync, readFileSync } from "node:fs";
import { join } from "node:path";
import type { Db } from "./connect";

const MIGRATIONS_DIR = join(import.meta.dir, "..", "migrations");

function statements(text: string): string[] {
  const noComments = text.split("\n").filter((l) => !l.trim().startsWith("--")).join("\n");
  return noComments.split(";").map((s) => s.trim()).filter(Boolean);
}

/** Migration folders contributed by feature packages, keyed by package name. */
export type PackageMigrations = Record<string, string[]>;

/**
 * Applies pending migrations: core (`packages/db/migrations`) first, then each package's folders in alphabetical
 * order of package name, files in name order within a folder. `schema_migrations` is keyed by file name, so file
 * names must be unique across packages (each package prefixes its files, e.g. `0001_learner_auth.sql`).
 */
export async function migrate(db: Db, packages: PackageMigrations = {}): Promise<string[]> {
  await db.sql.unsafe("CREATE TABLE IF NOT EXISTS schema_migrations (name TEXT PRIMARY KEY, applied_at TEXT NOT NULL)");
  const done = new Set((await db.sql`SELECT name FROM schema_migrations`).map((r: { name: string }) => r.name));
  const dirs = [MIGRATIONS_DIR, ...Object.keys(packages).sort().flatMap((k) => packages[k]!)];
  const seen = new Map<string, string>();
  const applied: string[] = [];
  for (const dir of dirs) {
    for (const name of readdirSync(dir).filter((f) => f.endsWith(".sql")).sort()) {
      const other = seen.get(name);
      if (other && other !== dir) throw new Error(`migration ${name} exists in both ${other} and ${dir}`);
      seen.set(name, dir);
      if (done.has(name)) continue;
      const stmts = statements(readFileSync(join(dir, name), "utf8"));
      await db.sql.begin(async (tx) => {
        for (const s of stmts) await tx.unsafe(s);
        await tx`INSERT INTO schema_migrations (name, applied_at) VALUES (${name}, ${new Date().toISOString()})`;
      });
      done.add(name);
      applied.push(name);
    }
  }
  return applied;
}