"""
mod_networkd.py -- systemd-networkd configuration for VLAN interfaces.

Generates .netdev and .network files for each VLAN, removes legacy
conflicting files, and triggers a networkd reload when content changes.
"""

import subprocess
from pathlib import Path

import mod_shared as shared
import mod_validation as validation

NETWORKD_DIR = Path("/etc/systemd/network")


# ===================================================================
# Build
# ===================================================================

def build_netdev(vlan, vid, iface):
    return "\n".join([
        "# Generated by core.py -- do not edit manually.",
        "# Edit config.json and re-run: sudo python3 core.py --apply",
        "",
        "[NetDev]",
        f"Name={iface}",
        "Kind=vlan",
        "",
        "[VLAN]",
        f"Id={vid}",
        "",
    ])

def build_network(vlan, vid, iface, all_vlan_ids):
    network = shared.network_for(vlan)
    prefix  = network.prefixlen
    lines   = [
        "# Generated by core.py -- do not edit manually.",
        "# Edit config.json and re-run: sudo python3 core.py --apply",
        "",
        "[Match]",
        f"Name={iface}",
        "",
        "[Network]",
        "DHCP=no",
        "LinkLocalAddressing=no",
    ]
    for ident in vlan["server_identities"]:
        lines.append(f"# {ident['description']}")
        lines.append(f"Address={ident['ip']}/{prefix}")

    if shared.is_physical(vlan):
        lines.append("")
        for v in all_vlan_ids:
            if v != 1:
                lines.append(f"VLAN={iface}.{v}")

    lines.append("")
    return "\n".join(lines)


# ===================================================================
# Apply
# ===================================================================

def find_legacy_files(managed_interfaces):
    to_remove = []
    for pattern in ("*.network", "*.netdev"):
        for f in NETWORKD_DIR.glob(pattern):
            if f.name.startswith(f"10-{shared.PRODUCT_NAME}-"):
                continue
            try:
                content = f.read_text()
            except OSError:
                continue
            for iface in managed_interfaces:
                if f"Name={iface}" in content:
                    to_remove.append(f)
                    break
    return to_remove

def apply_networkd(data, dry_run=False, only_if_changed=False):
    """Write systemd-networkd files and reload.
    If only_if_changed=True, write files only when content differs from disk
    and skip the networkd reload if nothing changed. Used by --apply mode.
    """
    all_vlan_ids   = [v.get('vlan_id') for v in data["vlans"] if not validation.is_wg(v)]
    managed_ifaces = [validation.derive_interface(v, data) for v in data["vlans"]]
    changed        = False

    legacy = find_legacy_files(managed_ifaces)
    if legacy:
        print("Removing legacy networkd files:")
        for f in legacy:
            if not dry_run:
                f.unlink()
                changed = True
            print(f"  {'[dry-run] would remove' if dry_run else 'Removed'}: {f}")
        print()

    for vlan in data["vlans"]:
        if validation.is_wg(vlan):
            continue
        iface = validation.derive_interface(vlan, data)
        vid   = vlan.get('vlan_id')
        stem  = shared.networkd_stem(vlan)

        if not shared.is_physical(vlan):
            netdev_path    = NETWORKD_DIR / f"{stem}.netdev"
            netdev_content = build_netdev(vlan, vid, iface)
            if dry_run:
                print(f"# -- {netdev_path} (dry-run) --")
                print(netdev_content)
            else:
                existing = netdev_path.read_text() if netdev_path.exists() else None
                if existing != netdev_content:
                    netdev_path.write_text(netdev_content)
                    print(f"Written: {netdev_path}")
                    changed = True
                elif not only_if_changed:
                    print(f"Unchanged: {netdev_path}")

        network_path    = NETWORKD_DIR / f"{stem}.network"
        network_content = build_network(vlan, vid, iface, all_vlan_ids)
        if dry_run:
            print(f"# -- {network_path} (dry-run) --")
            print(network_content)
        else:
            existing = network_path.read_text() if network_path.exists() else None
            if existing != network_content:
                network_path.write_text(network_content)
                print(f"Written: {network_path}")
                changed = True
            elif not only_if_changed:
                print(f"Unchanged: {network_path}")

    if not dry_run:
        if changed:
            print("Reloading systemd-networkd...")
            result = subprocess.run(
                ["networkctl", "reload"], capture_output=True, text=True
            )
            if result.returncode != 0:
                print(f"WARNING: networkctl reload returned non-zero:\n{result.stderr.strip()}")
            else:
                print("systemd-networkd reloaded.")
        elif only_if_changed:
            print("systemd-networkd: no changes. Good.")