"""
mod_shared.py -- Constants and helpers shared across all routlin modules.
"""

import ipaddress
import os
from pathlib import Path
import mod_validation as validation

PRODUCT_NAME     = "routlin"
SCRIPT_DIR       = Path(__file__).parent
DNSMASQ_CONF_DIR = Path(f"/etc/dnsmasq-{PRODUCT_NAME}")
LEASES_DIR       = Path("/var/lib/misc")
SYSTEMD_DIR      = Path("/etc/systemd/system")


# ===================================================================
# Process / error helpers
# ===================================================================

def is_root():
    return os.geteuid() == 0


def service_warning(action, svc, stderr):
    msg = stderr.strip()
    print(f"WARNING: Failed to {action} {svc}: {msg}")
    if "not found" in msg.lower() or "not-found" in msg.lower():
        print(f"  -> Package may not be installed. Run: sudo python3 install.py")


def chown_to_script_dir_owner(path):
    try:
        stat = SCRIPT_DIR.stat()
        os.chown(path, stat.st_uid, stat.st_gid)
    except OSError:
        pass


# ===================================================================
# Network / VLAN utilities
# ===================================================================

def prefix_to_dotted(n):
    mask = (0xFFFFFFFF << (32 - int(n))) & 0xFFFFFFFF
    return '.'.join(str((mask >> (8 * i)) & 0xFF) for i in (3, 2, 1, 0))


def network_for(vlan):
    return ipaddress.IPv4Network(f"{vlan['subnet']}/{vlan['subnet_mask']}", strict=False)


def lowest_quartet_ip(vlan):
    """Return the server_identity IP with the lowest last-octet value, or None if there are no valid identities."""
    identities = vlan.get("server_identities", [])
    ips = []
    for s in identities:
        try:
            ips.append(ipaddress.IPv4Address(s["ip"]))
        except (KeyError, ValueError):
            pass
    if not ips:
        return None
    return str(min(ips, key=lambda ip: ip.packed[-1]))


def resolve_vlan_options(vlan):
    """
    Resolve gateway, dns_server, and ntp_server for a VLAN.

    For both WG and non-WG VLANs: gateway defaults to the lowest-last-octet
    server_identity IP unless overridden in explicit_overrides. The gateway
    override must be one of the server_identity IPs.

    WG VLANs: ntp_server is None (WireGuard has no DHCP so NTP cannot be
    advertised to peers). Overrides live in vpn_information.explicit_overrides.

    Non-WG VLANs: overrides live in dhcp_information.explicit_overrides.
    Returns a dict with keys: gateway, dns_server, ntp_server.
    """
    if validation.is_wg(vlan):
        vpi       = vlan["vpn_information"]
        overrides = vpi.get("explicit_overrides", {})
        default   = lowest_quartet_ip(vlan) or str(next(network_for(vlan).hosts()))
        gateway   = overrides.get("gateway", "") or default
        dns       = overrides.get("dns_servers", "") or gateway
        return {
            "gateway":    gateway,
            "dns_servers": dns,
            "ntp_servers": None,
        }
    overrides = vlan.get("dhcp_information", {}).get("explicit_overrides", {})
    default   = lowest_quartet_ip(vlan)
    def _resolve(key):
        v = overrides.get(key, "")
        if isinstance(v, list):
            return ','.join(v) if v else default
        return v or default
    return {
        "gateway":    overrides.get("gateway", "") or default,
        "dns_servers": _resolve("dns_servers"),
        "ntp_servers": _resolve("ntp_servers"),
    }


def is_physical(vlan):
    return vlan.get("vlan_id") == 1


# ===================================================================
# VLAN naming / path helpers
# ===================================================================

def networkd_stem(vlan):
    return f"10-{PRODUCT_NAME}-{vlan['name']}"


def vlan_service_name(vlan, iface):
    if validation.is_wg(vlan):
        return f"dnsmasq-{PRODUCT_NAME}-{vlan['name']}-{iface}"
    return f"dnsmasq-{PRODUCT_NAME}-{vlan['name']}"


def vlan_service_file(vlan, iface):
    return SYSTEMD_DIR / f"{vlan_service_name(vlan, iface)}.service"


def vlan_conf_file(vlan):
    return DNSMASQ_CONF_DIR / f"{vlan['name']}.conf"


def vlan_leases_file(vlan):
    return LEASES_DIR / f"dnsmasq-{PRODUCT_NAME}-{vlan['name']}.leases"


def vlan_pid_file(vlan):
    return Path("/run") / f"dnsmasq-{PRODUCT_NAME}-{vlan['name']}.pid"