"""WireGuard VPN management service.

Handles key generation, peer management, config file sync, and RouterOS command generation.
"""

import base64
import ipaddress
import json
import os
import uuid
from datetime import datetime, timezone
from pathlib import Path
from typing import Optional

import structlog
from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey
from cryptography.hazmat.primitives.serialization import (
    Encoding,
    NoEncryption,
    PrivateFormat,
    PublicFormat,
)
from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.config import settings
from app.models.device import Device
from app.models.vpn import VpnConfig, VpnPeer
from app.services.crypto import decrypt_credentials, encrypt_credentials, encrypt_credentials_transit

logger = structlog.get_logger(__name__)


# ── Key Generation ──


def generate_wireguard_keypair() -> tuple[str, str]:
    """Generate a WireGuard X25519 keypair. Returns (private_key_b64, public_key_b64)."""
    private_key = X25519PrivateKey.generate()
    priv_bytes = private_key.private_bytes(Encoding.Raw, PrivateFormat.Raw, NoEncryption())
    pub_bytes = private_key.public_key().public_bytes(Encoding.Raw, PublicFormat.Raw)
    return base64.b64encode(priv_bytes).decode(), base64.b64encode(pub_bytes).decode()


def generate_preshared_key() -> str:
    """Generate a WireGuard preshared key (32 random bytes, base64)."""
    return base64.b64encode(os.urandom(32)).decode()


# ── Global Server Key & Subnet Allocation ──


async def _get_or_create_global_server_key(db: AsyncSession) -> tuple[str, str]:
    """Get (or create on first call) the global WireGuard server keypair.

    Returns (private_key_b64, public_key_b64). Private key is decrypted.
    Uses an advisory lock to prevent race conditions on first-time generation.
    """
    from sqlalchemy import text as sa_text

    # Advisory lock prevents two simultaneous first-calls from generating different keypairs
    await db.execute(sa_text("SELECT pg_advisory_xact_lock(hashtext('vpn_server_keygen'))"))

    result = await db.execute(
        sa_text("SELECT key, value, encrypted_value FROM system_settings WHERE key IN ('vpn_server_public_key', 'vpn_server_private_key')")
    )
    rows = {row[0]: row for row in result.fetchall()}

    if "vpn_server_public_key" in rows and "vpn_server_private_key" in rows:
        public_key = rows["vpn_server_public_key"][1]
        encrypted_private = rows["vpn_server_private_key"][2]
        key_bytes = settings.get_encryption_key_bytes()
        private_key = decrypt_credentials(encrypted_private, key_bytes)
        return private_key, public_key

    # First call on fresh install — generate and store
    private_key_b64, public_key_b64 = generate_wireguard_keypair()
    key_bytes = settings.get_encryption_key_bytes()
    encrypted_private = encrypt_credentials(private_key_b64, key_bytes)

    await db.execute(
        sa_text("""
            INSERT INTO system_settings (key, value, updated_at)
            VALUES ('vpn_server_public_key', :pub, now())
            ON CONFLICT (key) DO UPDATE SET value = :pub, updated_at = now()
        """),
        {"pub": public_key_b64},
    )
    await db.execute(
        sa_text("""
            INSERT INTO system_settings (key, value, encrypted_value, updated_at)
            VALUES ('vpn_server_private_key', NULL, :enc, now())
            ON CONFLICT (key) DO UPDATE SET encrypted_value = :enc, updated_at = now()
        """),
        {"enc": encrypted_private},
    )
    await db.flush()

    logger.info("vpn_global_server_keypair_generated", audit=True)
    return private_key_b64, public_key_b64


def _allocate_subnet_index_from_used(used: set[int]) -> int:
    """Find the first available subnet index in [1, 255] not in `used`.

    Pure function for unit testing. Raises ValueError if pool exhausted.
    """
    for i in range(1, 256):
        if i not in used:
            return i
    raise ValueError("VPN subnet pool exhausted")


async def _allocate_subnet_index(db: AsyncSession) -> int:
    """Allocate next available subnet_index from the database.

    Uses an admin session to see ALL tenants' subnet indices (bypasses RLS).
    The UNIQUE constraint on subnet_index protects against races.
    """
    from app.database import AdminAsyncSessionLocal
    from sqlalchemy import text as sa_text

    async with AdminAsyncSessionLocal() as admin_db:
        result = await admin_db.execute(sa_text("SELECT subnet_index FROM vpn_config"))
        used = {row[0] for row in result.fetchall()}
    return _allocate_subnet_index_from_used(used)


_VPN_ADDRESS_SPACE = ipaddress.ip_network("10.10.0.0/16")


def _validate_additional_allowed_ips(additional_allowed_ips: str | None) -> None:
    """Reject additional_allowed_ips that overlap the VPN address space (10.10.0.0/16)."""
    if not additional_allowed_ips:
        return
    for entry in additional_allowed_ips.split(","):
        entry = entry.strip()
        if not entry:
            continue
        try:
            network = ipaddress.ip_network(entry, strict=False)
        except ValueError:
            continue  # let WireGuard reject malformed entries
        if network.overlaps(_VPN_ADDRESS_SPACE):
            raise ValueError(
                "Additional allowed IPs must not overlap the VPN address space (10.10.0.0/16)"
            )


# ── Config File Management ──


def _get_wg_config_path() -> Path:
    """Return the path to the shared WireGuard config directory."""
    return Path(os.getenv("WIREGUARD_CONFIG_PATH", "/data/wireguard"))


async def _commit_and_sync(db: AsyncSession) -> None:
    """Commit the caller's transaction then regenerate wg0.conf.

    sync_wireguard_config opens its own DB session, so callers must commit
    first for their changes to be visible. This helper combines both steps
    and provides a single patch point for tests.
    """
    await db.commit()
    await sync_wireguard_config()


async def sync_wireguard_config() -> None:
    """Regenerate wg0.conf with ALL tenants' peers and write to shared volume.

    Uses AdminAsyncSessionLocal to bypass RLS (must see all tenants).
    Callers MUST commit their transaction before calling this function,
    since it opens a separate DB session that cannot see uncommitted data.
    Uses a PostgreSQL advisory lock to prevent concurrent writes.
    Writes atomically via temp file + rename.
    """
    from app.database import AdminAsyncSessionLocal
    from sqlalchemy import text as sa_text

    async with AdminAsyncSessionLocal() as admin_db:
        # Acquire advisory lock (released when this session closes)
        await admin_db.execute(sa_text("SELECT pg_advisory_lock(hashtext('wireguard_config'))"))

        try:
            # Get global server private key
            private_key_b64, _ = await _get_or_create_global_server_key(admin_db)

            # Query ALL enabled VPN configs (admin session bypasses RLS)
            configs_result = await admin_db.execute(
                select(VpnConfig).where(VpnConfig.is_enabled.is_(True)).order_by(VpnConfig.subnet_index)
            )
            configs = configs_result.scalars().all()

            # Build wg0.conf
            lines = [
                "[Interface]",
                "Address = 10.10.0.1/16",
                f"ListenPort = {configs[0].server_port if configs else 51820}",
                f"PrivateKey = {private_key_b64}",
                "",
            ]

            key_bytes = settings.get_encryption_key_bytes()
            total_peers = 0

            for config in configs:
                # Get tenant name for comment
                tenant_result = await admin_db.execute(
                    sa_text("SELECT name FROM tenants WHERE id = :tid"),
                    {"tid": config.tenant_id},
                )
                tenant_row = tenant_result.fetchone()
                tenant_name = tenant_row[0] if tenant_row else str(config.tenant_id)

                peers_result = await admin_db.execute(
                    select(VpnPeer).where(
                        VpnPeer.tenant_id == config.tenant_id,
                        VpnPeer.is_enabled.is_(True),
                    )
                )
                peers = peers_result.scalars().all()

                if peers:
                    lines.append(f"# --- Tenant: {tenant_name} ({config.subnet}) ---")

                for peer in peers:
                    peer_ip = peer.assigned_ip.split("/")[0]
                    allowed_ips = [f"{peer_ip}/32"]
                    if peer.additional_allowed_ips:
                        extra = [s.strip() for s in peer.additional_allowed_ips.split(",") if s.strip()]
                        allowed_ips.extend(extra)
                    lines.append("[Peer]")
                    lines.append(f"PublicKey = {peer.peer_public_key}")
                    if peer.preshared_key:
                        psk = decrypt_credentials(peer.preshared_key, key_bytes)
                        lines.append(f"PresharedKey = {psk}")
                    lines.append(f"AllowedIPs = {', '.join(allowed_ips)}")
                    lines.append("")
                    total_peers += 1

            # Atomic write: temp file + rename
            config_dir = _get_wg_config_path()
            wg_confs_dir = config_dir / "wg_confs"
            wg_confs_dir.mkdir(parents=True, exist_ok=True)

            conf_path = wg_confs_dir / "wg0.conf"
            tmp_path = wg_confs_dir / "wg0.conf.tmp"
            tmp_path.write_text("\n".join(lines))
            os.rename(str(tmp_path), str(conf_path))

            # Write per-tenant SNAT rules for poller→device routing
            # Docker traffic (172.16.0.0/12) going to each tenant's subnet
            # gets SNATted to that tenant's gateway IP (.1) so the router
            # can route replies back through the tunnel.
            nat_lines = ["#!/bin/sh",
                         "# Auto-generated per-tenant SNAT rules",
                         "# Remove old rules",
                         "iptables -t nat -F POSTROUTING 2>/dev/null",
                         "# Re-add Docker DNS rules",
                         ]
            for config in configs:
                gateway_ip = config.server_address.split("/")[0]  # e.g. 10.10.3.1
                subnet = config.subnet  # e.g. 10.10.3.0/24
                nat_lines.append(
                    f"iptables -t nat -A POSTROUTING -s 172.16.0.0/12 -d {subnet} -o wg0 -j SNAT --to-source {gateway_ip}"
                )
            nat_path = wg_confs_dir / "nat_rules.sh"
            nat_tmp = wg_confs_dir / "nat_rules.sh.tmp"
            nat_tmp.write_text("\n".join(nat_lines) + "\n")
            os.rename(str(nat_tmp), str(nat_path))
            os.chmod(str(nat_path), 0o755)

            # Signal WireGuard container to reload
            reload_flag = wg_confs_dir / ".reload"
            reload_flag.write_text("1")

            logger.info("wireguard_config_synced", audit=True,
                        tenants=len(configs), peers=total_peers)

        finally:
            # Release advisory lock explicitly (session-level lock, not xact-level)
            await admin_db.execute(sa_text("SELECT pg_advisory_unlock(hashtext('wireguard_config'))"))


# ── Live Status ──


def read_wg_status() -> dict[str, dict]:
    """Read live WireGuard peer status from the shared volume.

    The WireGuard container writes wg_status.json every 15 seconds
    with output from `wg show wg0 dump`. Returns a dict keyed by
    peer public key with handshake timestamp and transfer stats.
    """
    status_path = _get_wg_config_path() / "wg_status.json"
    if not status_path.exists():
        return {}
    try:
        data = json.loads(status_path.read_text())
        return {entry["public_key"]: entry for entry in data}
    except (json.JSONDecodeError, KeyError, OSError):
        return {}


def get_peer_handshake(wg_status: dict[str, dict], public_key: str) -> Optional[datetime]:
    """Get last_handshake datetime for a peer from live WireGuard status."""
    entry = wg_status.get(public_key)
    if not entry:
        return None
    ts = entry.get("last_handshake", 0)
    if ts and ts > 0:
        return datetime.fromtimestamp(ts, tz=timezone.utc)
    return None


# ── CRUD Operations ──


async def get_vpn_config(db: AsyncSession, tenant_id: uuid.UUID) -> Optional[VpnConfig]:
    """Get the VPN config for a tenant."""
    result = await db.execute(select(VpnConfig).where(VpnConfig.tenant_id == tenant_id))
    return result.scalar_one_or_none()


async def setup_vpn(
    db: AsyncSession, tenant_id: uuid.UUID, endpoint: Optional[str] = None
) -> VpnConfig:
    """Initialize VPN for a tenant — allocates unique subnet, uses global server key."""
    existing = await get_vpn_config(db, tenant_id)
    if existing:
        raise ValueError("VPN already configured for this tenant")

    # Auto-set endpoint from CORS_ORIGINS if not provided
    if not endpoint:
        origins = getattr(settings, "CORS_ORIGINS", "")
        if isinstance(origins, list):
            host = origins[0] if origins else ""
        else:
            host = str(origins).split(",")[0].strip()
        # Extract hostname from URL, append WireGuard port
        if host:
            host = host.replace("https://", "").replace("http://", "").split("/")[0]
            endpoint = f"{host}:51820"

    # Get or create global server keypair
    _, public_key_b64 = await _get_or_create_global_server_key(db)

    # Allocate unique subnet
    subnet_index = await _allocate_subnet_index(db)
    subnet = f"10.10.{subnet_index}.0/24"
    server_address = f"10.10.{subnet_index}.1/24"

    # Generate a per-tenant key for the deprecated server_private_key column.
    # This column is NOT NULL and kept for rollback safety. The global key
    # in system_settings is authoritative; this per-tenant key is unused.
    private_key_b64, _ = generate_wireguard_keypair()
    key_bytes = settings.get_encryption_key_bytes()
    encrypted_private = encrypt_credentials(private_key_b64, key_bytes)

    config = VpnConfig(
        tenant_id=tenant_id,
        server_private_key=encrypted_private,
        server_public_key=public_key_b64,
        subnet_index=subnet_index,
        subnet=subnet,
        server_address=server_address,
        endpoint=endpoint,
        is_enabled=True,
    )
    db.add(config)
    await db.flush()

    logger.info("vpn_subnet_allocated", audit=True,
                tenant_id=str(tenant_id), subnet_index=subnet_index, subnet=subnet)

    await _commit_and_sync(db)
    return config


async def update_vpn_config(
    db: AsyncSession, tenant_id: uuid.UUID, endpoint: Optional[str] = None, is_enabled: Optional[bool] = None
) -> VpnConfig:
    """Update VPN config settings."""
    config = await get_vpn_config(db, tenant_id)
    if not config:
        raise ValueError("VPN not configured for this tenant")

    if endpoint is not None:
        config.endpoint = endpoint
    if is_enabled is not None:
        config.is_enabled = is_enabled

    await db.flush()
    await _commit_and_sync(db)
    return config


async def get_peers(db: AsyncSession, tenant_id: uuid.UUID) -> list[VpnPeer]:
    """List all VPN peers for a tenant."""
    result = await db.execute(
        select(VpnPeer).where(VpnPeer.tenant_id == tenant_id).order_by(VpnPeer.created_at)
    )
    return list(result.scalars().all())


async def _next_available_ip(db: AsyncSession, tenant_id: uuid.UUID, config: VpnConfig) -> str:
    """Allocate the next available IP in the VPN subnet."""
    # Parse subnet: e.g. "10.10.0.0/24" → start from .2 (server is .1)
    network = ipaddress.ip_network(config.subnet, strict=False)
    hosts = list(network.hosts())

    # Get already assigned IPs
    result = await db.execute(select(VpnPeer.assigned_ip).where(VpnPeer.tenant_id == tenant_id))
    used_ips = {row[0].split("/")[0] for row in result.all()}
    used_ips.add(config.server_address.split("/")[0])  # exclude server IP

    for host in hosts[1:]:  # skip .1 (server)
        if str(host) not in used_ips:
            return f"{host}/24"

    raise ValueError("No available IPs in VPN subnet")


async def add_peer(db: AsyncSession, tenant_id: uuid.UUID, device_id: uuid.UUID, additional_allowed_ips: Optional[str] = None) -> VpnPeer:
    """Add a device as a VPN peer."""
    config = await get_vpn_config(db, tenant_id)
    if not config:
        raise ValueError("VPN not configured — enable VPN first")

    # Check device exists
    device = await db.execute(select(Device).where(Device.id == device_id, Device.tenant_id == tenant_id))
    if not device.scalar_one_or_none():
        raise ValueError("Device not found")

    # Check if already a peer
    existing = await db.execute(select(VpnPeer).where(VpnPeer.device_id == device_id))
    if existing.scalar_one_or_none():
        raise ValueError("Device is already a VPN peer")

    _validate_additional_allowed_ips(additional_allowed_ips)

    private_key_b64, public_key_b64 = generate_wireguard_keypair()
    psk = generate_preshared_key()

    key_bytes = settings.get_encryption_key_bytes()
    encrypted_private = encrypt_credentials(private_key_b64, key_bytes)
    encrypted_psk = encrypt_credentials(psk, key_bytes)

    assigned_ip = await _next_available_ip(db, tenant_id, config)

    peer = VpnPeer(
        tenant_id=tenant_id,
        device_id=device_id,
        peer_private_key=encrypted_private,
        peer_public_key=public_key_b64,
        preshared_key=encrypted_psk,
        assigned_ip=assigned_ip,
        additional_allowed_ips=additional_allowed_ips,
    )
    db.add(peer)
    await db.flush()

    await _commit_and_sync(db)
    return peer


async def remove_peer(db: AsyncSession, tenant_id: uuid.UUID, peer_id: uuid.UUID) -> None:
    """Remove a VPN peer."""
    result = await db.execute(
        select(VpnPeer).where(VpnPeer.id == peer_id, VpnPeer.tenant_id == tenant_id)
    )
    peer = result.scalar_one_or_none()
    if not peer:
        raise ValueError("Peer not found")

    await db.delete(peer)
    await db.flush()
    await _commit_and_sync(db)


async def get_peer_config(db: AsyncSession, tenant_id: uuid.UUID, peer_id: uuid.UUID) -> dict:
    """Get the full config for a peer — includes private key for device setup."""
    config = await get_vpn_config(db, tenant_id)
    if not config:
        raise ValueError("VPN not configured")

    result = await db.execute(
        select(VpnPeer).where(VpnPeer.id == peer_id, VpnPeer.tenant_id == tenant_id)
    )
    peer = result.scalar_one_or_none()
    if not peer:
        raise ValueError("Peer not found")

    key_bytes = settings.get_encryption_key_bytes()
    private_key = decrypt_credentials(peer.peer_private_key, key_bytes)
    psk = decrypt_credentials(peer.preshared_key, key_bytes) if peer.preshared_key else None

    endpoint = config.endpoint or "YOUR_SERVER_IP:51820"
    peer_ip_no_cidr = peer.assigned_ip.split("/")[0]

    routeros_commands = [
        f'/interface wireguard add name=wg-portal listen-port=13231 private-key="{private_key}"',
        f'/interface wireguard peers add interface=wg-portal public-key="{config.server_public_key}" '
        f'endpoint-address={endpoint.split(":")[0]} endpoint-port={endpoint.split(":")[-1]} '
        f'allowed-address=10.10.0.0/16 persistent-keepalive=25'
        + (f' preshared-key="{psk}"' if psk else ""),
        f"/ip address add address={peer.assigned_ip} interface=wg-portal",
    ]

    return {
        "peer_private_key": private_key,
        "peer_public_key": peer.peer_public_key,
        "assigned_ip": peer.assigned_ip,
        "server_public_key": config.server_public_key,
        "server_endpoint": endpoint,
        "allowed_ips": config.subnet,
        "routeros_commands": routeros_commands,
    }


async def onboard_device(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    hostname: str,
    username: str,
    password: str,
) -> dict:
    """Create device + VPN peer in one transaction. Returns device, peer, and RouterOS commands.

    Unlike regular device creation, this skips TCP connectivity checks because
    the VPN tunnel isn't up yet. The device IP is set to the VPN-assigned address.
    """
    config = await get_vpn_config(db, tenant_id)
    if not config:
        raise ValueError("VPN not configured — enable VPN first")

    # Allocate VPN IP before creating device
    assigned_ip = await _next_available_ip(db, tenant_id, config)
    vpn_ip_no_cidr = assigned_ip.split("/")[0]

    # Create device with VPN IP (skip TCP check — tunnel not up yet)
    credentials_json = json.dumps({"username": username, "password": password})
    transit_ciphertext = await encrypt_credentials_transit(credentials_json, str(tenant_id))

    device = Device(
        tenant_id=tenant_id,
        hostname=hostname,
        ip_address=vpn_ip_no_cidr,
        api_port=8728,
        api_ssl_port=8729,
        encrypted_credentials_transit=transit_ciphertext,
        status="unknown",
    )
    db.add(device)
    await db.flush()

    # Create VPN peer linked to this device
    private_key_b64, public_key_b64 = generate_wireguard_keypair()
    psk = generate_preshared_key()

    key_bytes = settings.get_encryption_key_bytes()
    encrypted_private = encrypt_credentials(private_key_b64, key_bytes)
    encrypted_psk = encrypt_credentials(psk, key_bytes)

    peer = VpnPeer(
        tenant_id=tenant_id,
        device_id=device.id,
        peer_private_key=encrypted_private,
        peer_public_key=public_key_b64,
        preshared_key=encrypted_psk,
        assigned_ip=assigned_ip,
    )
    db.add(peer)
    await db.flush()

    await _commit_and_sync(db)

    # Generate RouterOS commands
    endpoint = config.endpoint or "YOUR_SERVER_IP:51820"
    psk_decrypted = decrypt_credentials(encrypted_psk, key_bytes)

    routeros_commands = [
        f'/interface wireguard add name=wg-portal listen-port=13231 private-key="{private_key_b64}"',
        f'/interface wireguard peers add interface=wg-portal public-key="{config.server_public_key}" '
        f'endpoint-address={endpoint.split(":")[0]} endpoint-port={endpoint.split(":")[-1]} '
        f'allowed-address=10.10.0.0/16 persistent-keepalive=25'
        f' preshared-key="{psk_decrypted}"',
        f"/ip address add address={assigned_ip} interface=wg-portal",
    ]

    return {
        "device_id": device.id,
        "peer_id": peer.id,
        "hostname": hostname,
        "assigned_ip": assigned_ip,
        "routeros_commands": routeros_commands,
    }