// Secondary index: index + main table in one transaction
// Textbook section: Volume II, chapter 8, "Secondary indexes", section "Maintaining consistency".
// What it demonstrates: the main "users" table and a secondary index
//   "role → list of IDs"; updating both tables in one transaction;
//   deleting a record together with its index references; a query via the index.
// Build: g++ -std=c++17 -I<libmdbx-include> -I../common 09-secondary-index.c++ -lmdbx
// Run: ./09-secondary-index
// Expected output:
//   admins via index: user1 user3
//   ok: secondary index maintained in one txn
// On failure — message to stderr and exit 1.
//
// SPDX-License-Identifier: Apache-2.0

#include <iostream>
#include <string>

#include "common.h++"
#include <mdbx.h++>

int main() {
  try {
    const std::string path = std::string(example::tmpdir()) + "/mdbx-09-secondary-index.mdbx";
    mdbx::env::remove(path);
    mdbx::env_managed env = example::env_open(path);

    {
      auto txn = env.start_write();
      auto users = txn.create_map("users", mdbx::key_mode::usual, mdbx::value_mode::single);
      // The index: key is a role, values are user IDs (multi-values).
      auto by_role = txn.create_map("by_role", mdbx::key_mode::usual, mdbx::value_mode::multi);

      // Inserting users and maintaining the index — in one transaction.
      txn.insert(users, mdbx::slice("user1"), mdbx::slice("Alice|admin"));
      txn.upsert(by_role, mdbx::slice("admin"), mdbx::slice("user1"));
      txn.insert(users, mdbx::slice("user2"), mdbx::slice("Bob|dev"));
      txn.upsert(by_role, mdbx::slice("dev"), mdbx::slice("user2"));
      txn.insert(users, mdbx::slice("user3"), mdbx::slice("Carol|admin"));
      txn.upsert(by_role, mdbx::slice("admin"), mdbx::slice("user3"));
      txn.commit();
    }

    // Deleting a user together with his record in the index.
    {
      auto txn = env.start_write();
      auto users = txn.open_map("users", mdbx::key_mode::usual, mdbx::value_mode::single);
      auto by_role = txn.open_map("by_role", mdbx::key_mode::usual, mdbx::value_mode::multi);
      txn.erase(users, mdbx::slice("user2"));
      // the value of a specific key
      txn.erase(by_role, mdbx::slice("dev"), mdbx::slice("user2"));
      txn.commit();
    }

    // The "all admins" query via the index.
    auto rtxn = env.start_read();
    auto by_role = rtxn.open_map("by_role", mdbx::key_mode::usual, mdbx::value_mode::multi);
    auto cur = rtxn.open_cursor(by_role);
    std::string admins;
    for (auto r = cur.to_key_exact(mdbx::slice("admin")); r; r = cur.to_current_next_multi(false))
      admins += r.value.as_string() + " ";
    std::cout << "admins via index: " << admins << "\n";
    rtxn.abort();

    std::cout << "ok: secondary index maintained in one txn\n";
    return EXIT_SUCCESS;
  } catch (const std::exception &ex) {
    std::cerr << "error: " << ex.what() << "\n";
    return EXIT_FAILURE;
  }
}