"""
validation.py -- Shared structural validators for config.json fields.

Lives alongside core.py in ~/routlin/ and is volume-mounted into the
routlin-dash container at /app/validation.py.  Importable by both
core.py (router host) and the Flask app directly.

Convention: primitive validators accept a raw string and return the
normalised valid value, or '' / None if the input is invalid.
"""
import ipaddress
import os
import re

VALID_PROTOCOLS         = {'tcp', 'udp', 'both'}
VALID_BLOCKLIST_FORMATS = {'dnsmasq', 'hosts'}
VALID_DDNS_PROVIDERS    = ('noip', 'cloudflare', 'duckdns')


# ===================================================================
# IP / CIDR
# ===================================================================

def ip(value):
    """Return value if it is a valid IPv4 or IPv6 address, else ''."""
    if not value:
        return ''
    v = str(value).strip()
    try:
        ipaddress.ip_address(v)
        return v
    except ValueError:
        return ''


def ip_or_cidr(value):
    """Return value if it is a valid IPv4/IPv6 address or CIDR network, else ''."""
    if not value:
        return ''
    v = str(value).strip()
    try:
        ipaddress.ip_address(v)
        return v
    except ValueError:
        pass
    try:
        ipaddress.ip_network(v, strict=False)
        return v
    except ValueError:
        return ''


def ipv4(value):
    """Return value if it is a valid IPv4 address, else ''."""
    if not value:
        return ''
    v = str(value).strip()
    try:
        ipaddress.IPv4Address(v)
        return v
    except ValueError:
        return ''


def ipv4_or_cidr(value):
    """Return value if it is a valid IPv4 address or IPv4 CIDR network, else ''."""
    if not value:
        return ''
    v = str(value).strip()
    try:
        ipaddress.IPv4Address(v)
        return v
    except ValueError:
        pass
    try:
        ipaddress.IPv4Network(v, strict=False)
        return v
    except ValueError:
        return ''


# ===================================================================
# Port
# ===================================================================

def port(value):
    """Return port as string if valid 1-65535, else ''."""
    try:
        p = int(re.sub(r'[^0-9]', '', str(value)))
        if 1 <= p <= 65535:
            return str(p)
    except (ValueError, TypeError):
        pass
    return ''


# ===================================================================
# Time
# ===================================================================

def time_24h(value):
    """Return value if it is a valid 24-hour HH:MM time string, else ''."""
    if not value:
        return ''
    v = str(value).strip()
    if re.fullmatch(r'([01]\d|2[0-3]):[0-5]\d', v):
        return v
    return ''


# ===================================================================
# Integer range
# ===================================================================

def int_range(value, lo, hi):
    """Return value as int if it is an integer within [lo, hi], else None.

    lo and hi may be None to indicate no lower or upper bound respectively.
    """
    try:
        v = int(str(value).strip())
        if (lo is None or v >= lo) and (hi is None or v <= hi):
            return v
    except (ValueError, TypeError):
        pass
    return None


# ===================================================================
# Domain name
# ===================================================================

def domainname(value):
    """Return value if it is a valid domain name, else ''.

    Rules: labels separated by dots; each label contains only
    letters, digits, and hyphens; no label may start or end with a
    hyphen; no consecutive dots; total length <= 253.
    """
    if not value:
        return ''
    v = str(value).strip().lower()
    if len(v) > 253:
        return ''
    if '..' in v or v.startswith('.') or v.endswith('.'):
        return ''
    labels = v.split('.')
    for label in labels:
        if not label:
            return ''
        if not re.match(r'^[a-zA-Z0-9]([a-zA-Z0-9\-]*[a-zA-Z0-9])?$|^[a-zA-Z0-9]$', label):
            return ''
    return v


# ===================================================================
# Banned-IP pattern
# ===================================================================

def banned_ip(value):
    """
    Return value if it is a valid banned_ip pattern, else ''.

    Accepted formats (mirrors core.py expand_banned_ip):
      IPv4:
        Single address    192.0.2.1
        CIDR              192.0.2.0/24
        Wildcard octet    192.0.2.*
        Octet range       192.0.2.10-20
        (combinations that expand to <=1024 entries are accepted)
      IPv6:
        Single address    2001:db8::1
        CIDR              2001:db8::/32
        Trailing wildcard 2001:db8:c17:*
    """
    if not value:
        return ''
    v = str(value).strip()
    try:
        _check_banned_ip(v)
        return v
    except (ValueError, TypeError):
        return ''


def _check_banned_ip(ip_str):
    if ':' in ip_str:
        _check_banned_ipv6(ip_str)
    else:
        _check_banned_ipv4(ip_str)


def _check_banned_ipv4(ip_str):
    if '/' in ip_str:
        ipaddress.IPv4Network(ip_str, strict=False)
        return

    parts = ip_str.split('.')
    if len(parts) != 4:
        raise ValueError(f"Expected 4 octets: {ip_str!r}")

    def parse_octet(s):
        if s == '*':
            return (0, 255)
        if '-' in s:
            a, b = s.split('-', 1)
            lo, hi = int(a), int(b)
            if not (0 <= lo <= hi <= 255):
                raise ValueError(f"Invalid octet range {s!r}")
            return (lo, hi)
        v = int(s)
        if not 0 <= v <= 255:
            raise ValueError(f"Octet {v} out of 0-255")
        return (v, v)

    ranges = [parse_octet(p) for p in parts]

    trailing = 0
    for lo, hi in reversed(ranges):
        if lo == 0 and hi == 255:
            trailing += 1
        else:
            break

    total = 1
    for lo, hi in ranges[:4 - trailing]:
        total *= (hi - lo + 1)
    if total > 1024:
        raise ValueError(f"Pattern expands to {total} entries (limit 1024); use CIDR")


def _check_banned_ipv6(ip_str):
    if '/' in ip_str:
        ipaddress.IPv6Network(ip_str, strict=False)
        return
    if '*' not in ip_str:
        ipaddress.IPv6Address(ip_str)
        return
    if not ip_str.endswith(':*'):
        raise ValueError(f"Unsupported IPv6 wildcard: {ip_str!r}; use 'prefix:*' or CIDR")
    prefix_part = ip_str[:-2]
    if '::' in prefix_part:
        left, right = prefix_part.split('::', 1)
        lg = [g for g in left.split(':')  if g] if left  else []
        rg = [g for g in right.split(':') if g] if right else []
        zeros = 8 - len(lg) - len(rg) - 1
        if zeros < 0:
            raise ValueError(f"Too many groups in {ip_str!r}")
        groups = lg + ['0000'] * zeros + rg
    else:
        groups = [g for g in prefix_part.split(':') if g]
    if not (1 <= len(groups) <= 7):
        raise ValueError(f"IPv6 wildcard must have 1-7 prefix groups: {ip_str!r}")


# ===================================================================
# Cross-VLAN uniqueness checks (callable independently by action.py)
# ===================================================================

def check_vlan_name_unique(vlans, name, exclude_idx=None):
    """Return error string if name is already used by another VLAN, else None."""
    for i, v in enumerate(vlans):
        if exclude_idx is not None and i == exclude_idx:
            continue
        if v.get('name') == name:
            return f'VLAN name "{name}" is already in use (VLAN ID {v.get("vlan_id")}).'
    return None


def check_vlan_id_unique(vlans, vlan_id, exclude_idx=None):
    """Return error string if vlan_id is already used by another VLAN, else None."""
    for i, v in enumerate(vlans):
        if exclude_idx is not None and i == exclude_idx:
            continue
        if v.get('vlan_id') == vlan_id:
            return f'VLAN ID {vlan_id} is already in use (VLAN "{v.get("name")}").'
    return None


def check_radius_default_unique(vlans, exclude_idx=None):
    """Return error string if another VLAN (not exclude_idx) is already the RADIUS default, else None."""
    for i, v in enumerate(vlans):
        if exclude_idx is not None and i == exclude_idx:
            continue
        if v.get('radius_default'):
            return f'VLAN "{v.get("name", "?")}" is already the RADIUS default. Only one VLAN may be the default.'
    return None


def check_mdns_vpn(is_vpn, mdns_reflection):
    """Return error string if mDNS reflection is enabled on a VPN VLAN, else None."""
    if is_vpn and mdns_reflection:
        return 'mDNS reflection is not supported on VPN VLANs.'
    return None


# ===================================================================
# Blocklist checks (callable independently by action.py)
# ===================================================================

def check_blocklist_name_unique(blocklists, name, exclude_idx=None):
    """Return error string if name is already used by another blocklist entry, else None."""
    for i, b in enumerate(blocklists):
        if exclude_idx is not None and i == exclude_idx:
            continue
        if b.get('name') == name:
            return f'A blocklist named "{name}" already exists.'
    return None


# ===================================================================
# DHCP reservation checks (callable independently by action.py)
# ===================================================================

def check_reservation_ip_conflicts(ip, vlan):
    """Return error string if ip conflicts with the VLAN's pool range or server identities, else None."""
    if not ip or ip == 'dynamic':
        return None
    dhcp = vlan.get('dhcp_information', {})
    pool_start = dhcp.get('dynamic_pool_start')
    pool_end   = dhcp.get('dynamic_pool_end')
    if pool_start and pool_end:
        try:
            if (ipaddress.IPv4Address(pool_start) <= ipaddress.IPv4Address(ip)
                    <= ipaddress.IPv4Address(pool_end)):
                return f'{ip} falls within the dynamic pool range ({pool_start}-{pool_end}).'
        except Exception:
            pass
    identity_ips = {s['ip'] for s in vlan.get('server_identities', []) if s.get('ip')}
    if ip in identity_ips:
        return f'{ip} is already assigned as a server identity IP.'
    return None


# ===================================================================
# Host override checks (callable independently by action.py)
# ===================================================================

def check_host_override_ip_in_vlans(ip_str, cfg):
    """Return error string if ip_str is not within any configured VLAN subnet, else None."""
    try:
        addr = ipaddress.IPv4Address(ip_str)
    except ValueError:
        return f"'{ip_str}' is not a valid IPv4 address."
    nets = []
    for v in cfg.get('vlans', []):
        subnet = v.get('subnet', '')
        mask   = v.get('subnet_mask', '')
        if subnet and mask:
            try:
                nets.append(ipaddress.IPv4Network(f'{subnet}/{mask}', strict=False))
            except ValueError:
                pass
    if not nets:
        return None
    if not any(addr in net for net in nets):
        return 'IP address does not fall within any configured VLAN subnet.'
    return None


# ===================================================================
# VPN uniqueness checks (callable independently by action.py)
# ===================================================================

def check_vpn_listen_port_unique(vlans, listen_port, exclude_vlan_name=None):
    """Return error string if listen_port is already used by another VPN VLAN, else None."""
    for v in vlans:
        if not v.get('is_vpn'):
            continue
        if exclude_vlan_name is not None and v.get('name') == exclude_vlan_name:
            continue
        if v.get('vpn_information', {}).get('listen_port') == listen_port:
            return f'Listen port {listen_port} is already used by another VPN VLAN.'
    return None


def check_peer_name_unique(peers, name, exclude_idx=None):
    """Return error string if name is already used by another peer, else None."""
    for i, p in enumerate(peers):
        if exclude_idx is not None and i == exclude_idx:
            continue
        if p.get('name') == name:
            return f'A peer named "{name}" already exists.'
    return None


# ===================================================================
# Physical interface checks (callable independently by action.py)
# ===================================================================

def check_wan_lan_unique(wan, lan):
    """Return error string if WAN and LAN resolve to the same interface, else None."""
    if wan and lan and wan == lan:
        return 'WAN and LAN interfaces must be different.'
    return None


def check_interface_exists(iface, available):
    """Return error string if iface is absent from the available set (when non-empty), else None."""
    if available and iface not in available:
        return f"Interface '{iface}' does not exist on this system."
    return None


# ===================================================================
# VLAN / interface helpers (shared with core.py apply logic)
# ===================================================================

def is_wg(vlan):
    return vlan.get("is_vpn", False)


def is_dynamic_ip(r):
    """Return True if a reservation has no pinned IP (DHCP assigns from pool)."""
    ip = r.get("ip", "dynamic")
    return ip in ("", "dynamic") or ip is None


def derive_vlan_id(subnet, prefix):
    """Return VLAN ID (1-4094) derived from the active octet of the network address, or None."""
    try:
        network  = ipaddress.IPv4Network(f'{subnet}/{prefix}', strict=False)
        octets   = list(network.network_address.packed)
        byte_idx = (int(prefix) - 1) // 8
        vlan_id  = octets[byte_idx]
        if 1 <= vlan_id <= 4094:
            return vlan_id
        return None
    except Exception:
        return None


def derive_interface(vlan, data):
    """Derive the interface name for a VLAN without mutating data."""
    lan = data.get('network_interfaces', {}).get('lan_interface', 'eth0')
    if is_wg(vlan):
        wg_vlans = [v for v in data.get('vlans', []) if is_wg(v)]
        wg_sorted = sorted(wg_vlans, key=lambda v: (v.get('vlan_id') is None, v.get('vlan_id') or 0))
        idx = next((i for i, v in enumerate(wg_sorted) if v is vlan), 0)
        return f'wg{idx}'
    vid = vlan.get('vlan_id')
    return lan if vid == 1 else f'{lan}.{vid}'


# ===================================================================
# Full config validation (shared with core.py --apply)
# ===================================================================

def validate_config(data):
    """Validate config.json structure and content. Returns list of error strings."""
    errors = []
    seen_interfaces   = {}
    seen_listen_ports = {}

    # Pre-compute per-VLAN vlan_ids and interface names without mutating data
    _lan       = data.get("network_interfaces", {}).get("lan_interface", "eth0")
    _all_vlans = data.get("vlans", [])
    _stored_ids = [_v.get("vlan_id") for _v in _all_vlans]
    _wg_sorted = sorted(
        [(i, _stored_ids[i]) for i, _v in enumerate(_all_vlans) if is_wg(_v)],
        key=lambda x: (x[1] is None, x[1] or 0)
    )
    _wg_order = {orig_i: wg_idx for wg_idx, (orig_i, _) in enumerate(_wg_sorted)}
    vlan_ifaces = []
    for i, _vlan in enumerate(_all_vlans):
        if is_wg(_vlan):
            vlan_ifaces.append(f"wg{_wg_order[i]}")
        else:
            _vid = _stored_ids[i]
            vlan_ifaces.append(_lan if _vid == 1 else f"{_lan}.{_vid}")

    # upstream_dns block ============================================
    if not data.get("upstream_dns", {}).get("upstream_servers"):
        errors.append("upstream_dns.upstream_servers is missing or empty.")

    # WAN / LAN interfaces ==========================================
    gen = data.get("network_interfaces", {})
    wan = gen.get("wan_interface", "")
    lan = gen.get("lan_interface", "")
    if not wan:
        errors.append("network_interfaces.wan_interface is missing or empty.")
    if not lan:
        errors.append("network_interfaces.lan_interface is missing or empty.")
    if wan and lan:
        available_interfaces = set()
        try:
            available_interfaces = set(os.listdir('/sys/class/net'))
        except Exception:
            pass
        err = check_interface_exists(wan, available_interfaces)
        if err:
            errors.append(f"network_interfaces.wan_interface: {err}")
        err = check_interface_exists(lan, available_interfaces)
        if err:
            errors.append(f"network_interfaces.lan_interface: {err}")
        err = check_wan_lan_unique(wan, lan)
        if err:
            errors.append(f"network_interfaces: {err}")

    # Blocklist library =============================================
    blocklists_by_name = {}
    for idx, bl in enumerate(data.get("dns_blocking", {}).get("blocklists", [])):
        name  = bl.get("name", "")
        label = f"dns_blocking.blocklists[{idx}] '{name}'"
        for field in ("name", "description", "save_as", "url", "format"):
            if not bl.get(field):
                errors.append(f"{label}: missing or empty field '{field}'.")
        if bl.get("format") and bl["format"] not in VALID_BLOCKLIST_FORMATS:
            errors.append(f"{label}: format must be one of: {', '.join(sorted(VALID_BLOCKLIST_FORMATS))}.")
        if name:
            err = check_blocklist_name_unique(
                data.get("dns_blocking", {}).get("blocklists", []), name, exclude_idx=idx
            )
            if err:
                errors.append(f"{label}: {err}")
            else:
                blocklists_by_name[name] = bl

    # Per-VLAN validation ===========================================
    vlan_networks = {}  # iface -> IPv4Network (used for NAT section)

    for i, (vlan, iface) in enumerate(zip(_all_vlans, vlan_ifaces)):
        vlan_id = _stored_ids[i]
        name    = vlan.get("name", "?")
        label   = f"vlan '{name}' (id={vlan_id})"

        if vlan_id is None or not isinstance(vlan_id, int) or not (1 <= vlan_id <= 4094):
            errors.append(f"vlan '{name}': vlan_id must be an integer 1-4094 (got {vlan_id!r}).")

        err = check_vlan_name_unique(_all_vlans, name, exclude_idx=i)
        if err:
            errors.append(f"{label}: {err}")

        err = check_vlan_id_unique(_all_vlans, vlan_id, exclude_idx=i)
        if err:
            errors.append(f"{label}: {err}")

        if iface in seen_interfaces:
            errors.append(f"{label}: duplicate interface '{iface}' "
                          f"(also used by '{seen_interfaces[iface]}').")
        else:
            seen_interfaces[iface] = name

        err = check_mdns_vpn(is_wg(vlan), vlan.get('mdns_reflection'))
        if err:
            errors.append(f"{label}: {err}")

        if is_wg(vlan):
            # vpn_information =======================================
            vpi = vlan.get("vpn_information")
            if not isinstance(vpi, dict):
                errors.append(f"{label}: vpn_information must be a plain object.")
                vpi = {}
            else:
                lp = vpi.get("listen_port")
                if int_range(lp, 1, 65535) is None:
                    errors.append(f"{label}: vpn_information.listen_port must be an integer 1-65535.")
                elif lp in seen_listen_ports:
                    errors.append(f"{label}: vpn_information.listen_port {lp} is already used by "
                                  f"'{seen_listen_ports[lp]}'.")
                else:
                    seen_listen_ports[lp] = name

            # subnet/subnet_mask ====================================
            for field in ("subnet", "subnet_mask"):
                if not vlan.get(field):
                    errors.append(f"{label}: missing required field '{field}'.")
            wg_net = None
            if vlan.get("subnet") and vlan.get("subnet_mask"):
                try:
                    wg_net = ipaddress.IPv4Network(f"{vlan['subnet']}/{vlan['subnet_mask']}", strict=False)
                    vlan_networks[iface] = wg_net
                except ValueError as e:
                    errors.append(f"{label}: invalid subnet/subnet_mask: {e}")

            # server_identities =====================================
            if not vlan.get("server_identities"):
                errors.append(f"{label}: server_identities is empty or missing.")
            identity_ips = []
            for idx, ident in enumerate(vlan.get("server_identities", [])):
                ip_str = ident.get("ip", "")
                ilabel = f"{label} server_identities[{idx}] '{ident.get('description', '?')}'"
                if not ip_str:
                    errors.append(f"{ilabel}: missing 'ip' field.")
                    continue
                if not ipv4(ip_str):
                    errors.append(f"{ilabel}: ip '{ip_str}' is not a valid IPv4 address.")
                    continue
                ip_addr = ipaddress.IPv4Address(ip_str)
                if wg_net and ip_addr not in wg_net:
                    errors.append(f"{ilabel}: ip '{ip_str}' is not within subnet {wg_net}.")
                else:
                    identity_ips.append(ip_addr)

            # vpn_information.explicit_overrides ====================
            eo = vpi.get("explicit_overrides", {}) if isinstance(vpi, dict) else {}
            if not isinstance(eo, dict):
                errors.append(f"{label}: vpn_information.explicit_overrides must be a plain object.")
            else:
                gw = eo.get("gateway", "")
                if gw:
                    if not ipv4(gw):
                        errors.append(f"{label}: vpn_information.explicit_overrides.gateway '{gw}' is not a valid IPv4 address.")
                    else:
                        gw_ip = ipaddress.IPv4Address(gw)
                        if identity_ips and gw_ip not in identity_ips:
                            errors.append(
                                f"{label}: vpn_information.explicit_overrides.gateway '{gw}' does not match "
                                f"any server_identity IP. Must be one of: "
                                f"{[str(ip) for ip in identity_ips]}."
                            )
                dns = eo.get("dns_servers", "")
                if dns and not ipv4(dns):
                    errors.append(f"{label}: vpn_information.explicit_overrides.dns_server '{dns}' is not a valid IPv4 address.")
                mtu = eo.get("mtu", "")
                if mtu and int_range(mtu, 576, 9000) is None:
                    errors.append(f"{label}: vpn_information.explicit_overrides.mtu '{mtu}' must be an integer in range 576-9000.")
                domain_val = vpi.get("domain", "") if isinstance(vpi, dict) else ""
                if domain_val and not domainname(domain_val):
                    errors.append(f"{label}: vpn_information.domain '{domain_val}' is not a valid domain name.")

            # peers =================================================
            seen_peer_names = {}
            seen_peer_ips   = {}
            for pidx, peer in enumerate(vlan.get("peers", [])):
                pname  = peer.get("name", "")
                plabel = f"{label} peer[{pidx}] '{pname}'"
                if not pname:
                    errors.append(f"{plabel}: missing 'name' field.")
                elif pname in seen_peer_names:
                    errors.append(f"{plabel}: duplicate peer name '{pname}'.")
                else:
                    seen_peer_names[pname] = pidx
                if not peer.get("public_key"):
                    errors.append(f"{plabel}: missing 'public_key' field.")
                pip_str = peer.get("ip", "")
                if not pip_str:
                    errors.append(f"{plabel}: missing 'ip' field.")
                elif not ipv4(pip_str):
                    errors.append(f"{plabel}: ip '{pip_str}' is not a valid IPv4 address.")
                else:
                    pip = ipaddress.IPv4Address(pip_str)
                    if wg_net and pip not in wg_net:
                        errors.append(f"{plabel}: ip '{pip_str}' is not within subnet {wg_net}.")
                    if pip in identity_ips:
                        errors.append(f"{plabel}: ip '{pip_str}' conflicts with a server_identity.")
                    if pip_str in seen_peer_ips:
                        errors.append(
                            f"{plabel}: duplicate peer ip '{pip_str}' "
                            f"(also used by peer '{seen_peer_ips[pip_str]}')."
                        )
                    else:
                        seen_peer_ips[pip_str] = pname
            continue

        if not vlan.get("server_identities"):
            errors.append(f"{label}: server_identities is empty or missing.")
            continue

        for field in ("subnet", "subnet_mask"):
            if not vlan.get(field):
                errors.append(f"{label}: missing required top-level field '{field}'.")
        if not vlan.get("subnet") or not vlan.get("subnet_mask"):
            continue

        try:
            network = ipaddress.IPv4Network(f"{vlan['subnet']}/{vlan['subnet_mask']}", strict=False)
            vlan_networks[iface] = network
        except ValueError as e:
            errors.append(f"{label}: invalid subnet/subnet_mask: {e}")
            continue

        d = vlan.get("dhcp_information", {})
        required_dhcp = {"dynamic_pool_start", "dynamic_pool_end", "lease_time"}
        missing = required_dhcp - set(d.keys())
        if missing:
            errors.append(f"{label}: missing dhcp_information fields: {missing}")
            continue

        def check_ip(field_label, ip_str, allow_none=False):
            if ip_str is None:
                if not allow_none:
                    errors.append(f"{label}: {field_label} is null/missing.")
                return None
            if not ipv4(ip_str):
                errors.append(f"{label}: {field_label} '{ip_str}' is not a valid IPv4 address.")
                return None
            addr = ipaddress.IPv4Address(ip_str)
            if addr not in network:
                errors.append(f"{label}: {field_label} '{ip_str}' is not within subnet {network}.")
            return addr

        identity_ips = []
        for idx, ident in enumerate(vlan["server_identities"]):
            ip = check_ip(
                f"server_identities[{idx}] '{ident.get('description', '?')}'",
                ident.get("ip")
            )
            if ip:
                identity_ips.append(ip)

        # Validate explicit_overrides ===============================
        eo = d.get("explicit_overrides", {})
        if not isinstance(eo, dict):
            errors.append(f"{label}: explicit_overrides must be a plain object.")
        else:
            gw = eo.get("gateway", "")
            if gw:
                gw_ip = check_ip("explicit_overrides.gateway", gw)
                if gw_ip and gw_ip not in identity_ips:
                    errors.append(
                        f"{label}: explicit_overrides.gateway '{gw}' does not match "
                        f"any server_identity IP. Must be one of: "
                        f"{[str(ip) for ip in identity_ips]}."
                    )
            dns = eo.get("dns_servers", "")
            if dns:
                for _ip in (dns if isinstance(dns, list) else [dns]):
                    check_ip("explicit_overrides.dns_servers", _ip)
            ntp = eo.get("ntp_servers", "")
            if ntp:
                for _ip in (ntp if isinstance(ntp, list) else [ntp]):
                    check_ip("explicit_overrides.ntp_servers", _ip)

        pool_start = check_ip("dynamic_pool_start", d["dynamic_pool_start"])
        pool_end   = check_ip("dynamic_pool_end",   d["dynamic_pool_end"])

        if pool_start and pool_end and pool_start > pool_end:
            errors.append(
                f"{label}: dynamic_pool_start '{pool_start}' is greater than "
                f"dynamic_pool_end '{pool_end}'."
            )

        if pool_start and pool_end:
            for ip in identity_ips:
                if pool_start <= ip <= pool_end:
                    errors.append(
                        f"{label}: server_identity '{ip}' falls inside the dynamic "
                        f"pool ({pool_start} - {pool_end})."
                    )

        seen_res_ips       = {}
        seen_res_macs      = {}
        seen_res_hostnames = {}
        vlan_name_key = vlan.get("name", "")
        for r in [r for r in data.get("dhcp_reservations", []) if r.get("vlan") == vlan_name_key]:
            rdesc = r.get("description", "?")
            rmac  = r.get("mac", "").lower().strip()

            if is_dynamic_ip(r):
                rip = None
            else:
                rip = check_ip(f"reservation '{rdesc}' ip", r.get("ip"))

            if rip:
                if pool_start and pool_end and pool_start <= rip <= pool_end:
                    errors.append(
                        f"{label}: reservation '{rdesc}' ip '{rip}' falls inside "
                        f"the dynamic pool ({pool_start} - {pool_end})."
                    )
                rip_str = str(rip)
                if rip_str in seen_res_ips:
                    # Allow same IP for different MACs (multi-interface device)
                    if rmac and rmac in seen_res_ips[rip_str]:
                        errors.append(
                            f"{label}: reservation '{rdesc}' ip '{rip}' and MAC '{rmac}' "
                            f"duplicates '{seen_res_ips[rip_str][rmac]}'."
                        )
                    else:
                        seen_res_ips[rip_str][rmac] = rdesc
                else:
                    seen_res_ips[rip_str] = {rmac: rdesc}
                if rip in identity_ips:
                    errors.append(
                        f"{label}: reservation '{rdesc}' ip '{rip}' conflicts "
                        f"with a server_identity."
                    )

            if rmac:
                if rmac in seen_res_macs:
                    errors.append(
                        f"{label}: reservation '{rdesc}' MAC '{rmac}' duplicates "
                        f"'{seen_res_macs[rmac]}'."
                    )
                else:
                    seen_res_macs[rmac] = rdesc

            rhost = r.get("hostname", "").strip().lower()
            if rhost:
                if rhost in seen_res_hostnames:
                    errors.append(
                        f"{label}: reservation '{rdesc}' hostname '{rhost}' duplicates "
                        f"'{seen_res_hostnames[rhost]}'."
                    )
                else:
                    seen_res_hostnames[rhost] = rdesc

        for bl_name in vlan.get("use_blocklists", []):
            if bl_name not in blocklists_by_name:
                errors.append(f"{label}: use_blocklists references unknown blocklist '{bl_name}'.")

    # NAT / firewall validation =====================================
    valid_protos     = VALID_PROTOCOLS
    known_interfaces = set(seen_interfaces.keys())

    def nat_check_port(label, port):
        if int_range(port, 1, 65535) is None:
            errors.append(f"{label}: '{port}' is not a valid port number (1-65535).")

    def nat_check_ip(label, ip_str):
        if not ipv4(ip_str):
            errors.append(f"{label}: '{ip_str}' is not a valid IPv4 address.")
            return None
        return ipaddress.IPv4Address(ip_str)

    def nat_check_ip_in_network(label, ip_str, network):
        ip = nat_check_ip(label, ip_str)
        if ip and ip not in network:
            errors.append(f"{label}: '{ip_str}' is not within subnet {network}.")

    # port_wrangling validation (top-level) =========================
    _vlan_name_to_net = {
        v.get("name", ""): vlan_networks.get(iface)
        for v, iface in zip(data.get("vlans", []), vlan_ifaces)
    }
    for idx, r in enumerate(data.get("port_wrangling", [])):
        desc      = r.get("description", "?")
        vlan_name = r.get("vlan", "?")
        label     = f"port_wrangling[{idx}] (vlan '{vlan_name}') '{desc}'"
        if r.get("protocol") not in valid_protos:
            errors.append(f"{label}: invalid protocol '{r.get('protocol')}'. "
                          f"Must be tcp, udp, or both.")
        nat_check_port(f"{label} dest_port", r.get("dest_port"))
        net = _vlan_name_to_net.get(vlan_name)
        if net:
            nat_check_ip_in_network(f"{label} redirect_to", r.get("redirect_to", ""), net)

    # port_forwarding validation (top-level) ========================
    for idx, r in enumerate(data.get("port_forwarding", [])):
        desc  = r.get("description", "?")
        label = f"port_forwarding[{idx}] '{desc}'"
        if r.get("protocol") not in valid_protos:
            errors.append(f"{label}: invalid protocol '{r.get('protocol')}'. "
                          f"Must be tcp, udp, or both.")
        nat_check_port(f"{label} dest_port", r.get("dest_port"))
        nat_check_port(f"{label} nat_port",  r.get("nat_port"))
        nat_check_ip(f"{label} nat_ip", r.get("nat_ip", ""))

    for r in data.get("inter_vlan_exceptions", []):
        desc  = r.get("description", "?")
        label = f"inter_vlan_exceptions '{desc}'"
        if r.get("protocol") not in valid_protos:
            errors.append(f"{label}: invalid protocol '{r.get('protocol')}'. "
                          f"Must be tcp, udp, or both.")
        if "src_ip_or_subnet" not in r:
            errors.append(f"{label}: missing field 'src_ip_or_subnet'.")
        else:
            val = r["src_ip_or_subnet"]
            if not ipv4_or_cidr(val):
                errors.append(f"{label}: src_ip_or_subnet '{val}' is not a valid "
                              f"IPv4 address or network.")
        dst = r.get("dst_ip_or_subnet") or r.get("dst_ip", "")
        if not dst:
            errors.append(f"{label}: missing field 'dst_ip_or_subnet'.")
        else:
            if not ipv4_or_cidr(dst):
                errors.append(f"{label}: dst_ip_or_subnet '{dst}' is not a valid "
                              f"IPv4 address or network.")
        if r.get("dest_port_start"):
            nat_check_port(f"{label} dest_port_start", r.get("dest_port_start"))
        if r.get("dest_port_end"):
            nat_check_port(f"{label} dest_port_end", r.get("dest_port_end"))
        min_p, max_p = r.get("dest_port_start", ""), r.get("dest_port_end", "")
        if min_p and max_p:
            try:
                if int(min_p) > int(max_p):
                    errors.append(f"{label}: dest_port_start {min_p} is greater than dest_port_end {max_p}.")
            except (ValueError, TypeError):
                pass

    # radius_default uniqueness check ===============================
    _rd_idx = next(
        (i for i, v in enumerate(data.get('vlans', [])) if v.get('radius_default')), None
    )
    if _rd_idx is not None:
        err = check_radius_default_unique(data.get('vlans', []), exclude_idx=_rd_idx)
        if err:
            defaults = [v.get('name', '?') for v in data.get('vlans', []) if v.get('radius_default')]
            errors.append(f"Multiple VLANs have radius_default: true ({', '.join(defaults)}). "
                          f"Only one VLAN may be the RADIUS default.")

    # RADIUS requires multiple VLANs ================================
    non_wg_vlans = [v for v in data.get("vlans", []) if not is_wg(v)]
    non_wg_names = {v.get("name") for v in non_wg_vlans}
    has_radius_clients = any(
        r.get("radius_client")
        for r in data.get("dhcp_reservations", [])
        if r.get("vlan") in non_wg_names
    )
    if has_radius_clients and len(non_wg_vlans) < 2:
        errors.append(
            "RADIUS clients are configured but only one non-VPN VLAN exists. "
            "Dynamic VLAN assignment requires at least two VLANs."
        )

    # host_overrides validation =====================================
    all_vlan_nets = list(vlan_networks.values())
    for idx, entry in enumerate(data.get("host_overrides", [])):
        lbl = f"host_overrides[{idx}] '{entry.get('host', '?')}'"
        if not entry.get("host"):
            errors.append(f"{lbl}: missing 'host' field.")
        ip_str = entry.get("ip", "")
        if not ip_str:
            errors.append(f"{lbl}: missing 'ip' field.")
        elif not ipv4(ip_str):
            errors.append(f"{lbl}: '{ip_str}' is not a valid IPv4 address.")
        else:
            ip_addr = ipaddress.IPv4Address(ip_str)
            if all_vlan_nets and not any(ip_addr in net for net in all_vlan_nets):
                errors.append(f"{lbl}: '{ip_str}' does not fall within any configured VLAN subnet.")

    # banned_ips validation =========================================
    for idx, entry in enumerate(data.get("banned_ips", [])):
        ip_val = entry.get("ip", "")
        lbl    = f"banned_ips[{idx}] '{entry.get('description', '')}'"
        if not ip_val:
            errors.append(f"{lbl}: missing 'ip' field.")
            continue
        if not banned_ip(ip_val):
            errors.append(f"{lbl}: '{ip_val}' is not a valid IP, CIDR, or wildcard pattern.")

    return errors