// Configuration model and INI-style loader.
//
// Format:
//   [section]
//   key = value          # comment
//   list_key = a, b, c
//
// Durations accept a unit suffix: "30s", "5m", "1h", "250ms". Bare numbers are
// seconds. Keeping the format boring is intentional -- config bugs at 3am are
// worse than a missing feature.
#pragma once

#include <chrono>
#include <cstdint>
#include <map>
#include <string>
#include <vector>

#include "common/logging.h"

namespace ovg {

using Millis = std::chrono::milliseconds;

struct Credential {
  std::string username;
  // Stored as sha256(salt || password), hex. Never the plaintext.
  std::string salt_hex;
  std::string hash_hex;
};

struct Socks5Config {
  std::string listen_address = "127.0.0.1";
  uint16_t listen_port = 1080;
  bool require_auth = true;
  // Address handed back in the UDP ASSOCIATE reply. Must be reachable *by the
  // client*, which is why it cannot just be the listen address when that is
  // 0.0.0.0. Empty means "derive from the control connection's local address".
  std::string advertise_address;
  bool udp_associate_enabled = true;
  size_t max_sessions = 1200;
  Millis handshake_timeout{10000};
  Millis connect_timeout{20000};
  Millis idle_timeout{300000};
  Millis udp_idle_timeout{60000};
  size_t relay_buffer_size = 16384;
  int io_threads = 0;  // 0 = min(hardware_concurrency, 4)
  std::string auth_file;
  std::vector<Credential> users;
};

struct VpnGateConfig {
  std::vector<std::string> api_urls{
      "http://www.vpngate.net/api/iphone/",
      "http://www.vpngate.net/api/iphone/",  // retried; mirrors can be added
  };
  Millis refresh_interval{1800000};  // 30m
  Millis http_timeout{30000};
  std::string cache_path = "var/vpngate_cache.csv";
  Millis cache_max_age{21600000};  // 6h -- stale cache still beats no nodes
  size_t max_response_bytes = 32u * 1024 * 1024;
};

struct SelectorConfig {
  std::vector<std::string> country_allow;  // empty = all
  std::vector<std::string> country_deny;
  bool prefer_udp = true;
  size_t probe_candidates = 12;
  size_t probe_samples = 3;
  Millis probe_timeout{3000};
  size_t probe_concurrency = 8;

  // Prior (API-derived) weights.
  double w_score = 0.35;
  double w_speed = 0.30;
  double w_sessions = 0.20;
  double w_uptime = 0.15;

  // Final blend.
  double w_rtt = 0.45;
  double w_prior = 0.30;
  double w_history = 0.25;

  std::string history_path = "var/node_history.tsv";
  Millis failure_backoff_initial{60000};
  Millis failure_backoff_max{3600000};
};

struct SwitchConfig {
  enum class Mode {
    Graceful,  // make-before-break with a bounded drain window
    Hard,      // promote and immediately close every old session
  };
  Mode mode = Mode::Graceful;
  Millis drain_grace{120000};
  size_t max_draining = 2;
  Millis min_interval{60000};
  double improvement_margin = 0.20;  // candidate must beat current by this much
  Millis backoff_initial{30000};
  Millis backoff_max{480000};
  bool retry_zero_progress = true;  // transparently re-home untouched sessions
  bool rehome_udp = true;           // UDP associations survive a switch

  // How often to go looking for a *better* node while the current one is
  // perfectly healthy. Off by default, and deliberately so: a scan probes a
  // dozen volunteer-run servers, and switching a healthy tunnel costs every
  // session that has moved bytes. Degradation-driven switching (health/) is
  // what the requirement actually asks for; this is the optional upgrade path.
  Millis opportunistic_interval{0};  // 0 = disabled
};

struct HealthConfig {
  Millis interval{15000};
  int unhealthy_windows = 3;
  Millis probe_timeout{5000};
  // The probe dials this host:port *through the egress* and drops the stream
  // as soon as it is up. A TCP handshake is used rather than a bare DNS lookup
  // because a lookup can be answered from the resolver cache without a single
  // byte crossing the tunnel -- which would report a dead tunnel as healthy.
  std::string probe_domain = "www.google.com";
  uint16_t probe_port = 80;
  double min_score = 0.40;
  double max_connect_failure_rate = 0.50;
  Millis stall_threshold{45000};
};

struct OvpnConfig {
  bool allow_legacy_algorithms = true;  // VPNGate is AES-128-CBC / SHA1
  std::string username = "vpn";         // fallback for nodes that demand it
  std::string password = "vpn";
  int connect_timeout_s = 30;
  bool compression = true;
  int tunnel_up_timeout_s = 45;
  // SO_SNDBUF/SO_RCVBUF for the tun socketpair; too small drops IP packets
  // under burst (recoverable, but hurts throughput).
  int packet_socket_buffer = 2 * 1024 * 1024;
};

struct DnsConfig {
  std::vector<std::string> fallback_servers{"1.1.1.1", "8.8.8.8"};
  Millis timeout{5000};
  size_t cache_entries = 4096;
  Millis min_ttl{5000};
  Millis max_ttl{3600000};
  bool prefer_ipv4 = true;
};

struct AdminConfig {
  bool enabled = true;
  std::string listen_address = "127.0.0.1";
  uint16_t listen_port = 9080;
};

struct LogConfig {
  log::Level level = log::Level::Info;
  std::string file = "-";
  std::map<std::string, log::Level> module_levels;
};

struct Config {
  Socks5Config socks5;
  VpnGateConfig vpngate;
  SelectorConfig selector;
  SwitchConfig switching;
  HealthConfig health;
  OvpnConfig ovpn;
  DnsConfig dns;
  AdminConfig admin;
  LogConfig logging;

  // Egress backend. "tunnel" = OpenVPN+lwIP, "direct" = host sockets (testing).
  std::string egress_mode = "tunnel";

  // Loads and validates. Returns false and fills `err` on any problem; a
  // partially-applied config is never returned.
  static bool load_file(const std::string &path, Config *out, std::string *err);
  static bool load_string(const std::string &text, Config *out,
                          std::string *err);

  bool validate(std::string *err) const;
};

// Parses "250ms" / "30s" / "5m" / "2h"; bare numbers are seconds.
bool parse_duration(const std::string &text, Millis *out);

// Loads "user:password" or "user:sha256$salt$hash" lines.
bool load_auth_file(const std::string &path, std::vector<Credential> *out,
                    std::string *err);

// Builds a credential with a fresh random salt.
Credential make_credential(const std::string &user, const std::string &password);

// Constant-time verification.
bool verify_credential(const Credential &c, const std::string &password);

}  // namespace ovg