"""
mod_avahi.py -- Avahi mDNS reflector configuration and management.

Patches avahi-daemon.conf with the correct interface list and manages
the avahi-daemon service lifecycle.
"""

import re
import shutil
import subprocess
from pathlib import Path

import mod_shared as shared
import mod_validation as validation

AVAHI_CONF_FILE = Path("/etc/avahi/avahi-daemon.conf")


# ===================================================================
# State helpers
# ===================================================================

def avahi_enabled(data):
    """Return True if at least one non-WireGuard VLAN has mdns_reflection enabled."""
    return any(v.get("mdns_reflection") is True
               for v in data.get("vlans", [])
               if not validation.is_wg(v))

def avahi_interfaces(data):
    """Return list of interface names for VLANs with mdns_reflection enabled."""
    return [
        validation.derive_interface(v, data)
        for v in data.get("vlans", [])
        if v.get("mdns_reflection") is True and not validation.is_wg(v)
    ]


# ===================================================================
# Config generation
# ===================================================================

def build_avahi_conf(data):
    """Patch avahi-daemon.conf directives needed for cross-VLAN mDNS reflection.
    Reads the existing file (default or previously patched) and modifies only
    the specific directives we need, leaving everything else untouched.
    Returns the patched config as a string. Caller is responsible for ensuring
    the file exists before calling (apply_avahi guards this).
    """
    ifaces = avahi_interfaces(data)
    content = AVAHI_CONF_FILE.read_text()

    def set_directive(text, directive, value):
        """Enable and set a directive, whether it is commented out or already set."""
        pattern = re.compile(
            rf"^#?\s*{re.escape(directive)}\s*=.*$", re.MULTILINE
        )
        replacement = f"{directive}={value}"
        if pattern.search(text):
            return pattern.sub(replacement, text)
        return text + f"\n{replacement}\n"

    content = set_directive(content, "use-ipv6",              "no")
    content = set_directive(content, "disallow-other-stacks", "yes")
    content = set_directive(content, "allow-interfaces",      ",".join(ifaces))
    content = set_directive(content, "enable-reflector",      "yes")
    content = set_directive(content, "disable-publishing",    "yes")

    return content


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

def apply_avahi(data):
    """Write avahi-daemon.conf and ensure service is running."""
    if not shutil.which("avahi-daemon"):
        print("avahi-daemon is not installed.")
        print("  -> Run: sudo python3 install.py")
        return

    ifaces = avahi_interfaces(data)

    if len(ifaces) < 2:
        print("mDNS reflection requires at least two VLANs in reflect_vlans. Skipping.")
        return

    if not AVAHI_CONF_FILE.exists():
        print(f"WARNING: {AVAHI_CONF_FILE} not found. Run: sudo python3 install.py")
        return

    content  = build_avahi_conf(data)
    existing = AVAHI_CONF_FILE.read_text()
    changed  = existing != content
    if changed:
        AVAHI_CONF_FILE.write_text(content)
        print(f"Written: {AVAHI_CONF_FILE}")
        print(f"  Reflecting mDNS across: {', '.join(ifaces)}")
    else:
        print(f"Unchanged: {AVAHI_CONF_FILE}")

    svc   = "avahi-daemon"
    state = subprocess.run(
        ["systemctl", "is-active", svc], capture_output=True, text=True
    ).stdout.strip()

    if state == "active":
        if changed:
            result = subprocess.run(["systemctl", "restart", svc],
                                    capture_output=True, text=True)
            if result.returncode == 0:
                print("avahi-daemon restarted.")
            else:
                shared.service_warning("restart", "avahi-daemon", result.stderr)
        else:
            print("avahi-daemon: running, config unchanged.")
    else:
        subprocess.run(["systemctl", "enable", svc], capture_output=True, text=True)
        result = subprocess.run(["systemctl", "start", svc],
                                capture_output=True, text=True)
        if result.returncode == 0:
            print("avahi-daemon started.")
        else:
            shared.service_warning("start", "avahi-daemon", result.stderr)

def disable_avahi():
    """Stop and disable avahi-daemon."""
    result = subprocess.run(
        ["systemctl", "is-active", "avahi-daemon"], capture_output=True, text=True
    )
    if result.stdout.strip() == "active":
        subprocess.run(["systemctl", "disable", "--now", "avahi-daemon"],
                       capture_output=True, text=True)
        print("avahi-daemon stopped and disabled.")
    else:
        print("avahi-daemon: not running, skipping.")