# The relay: one small CVM in Tencent Cloud that terminates TLS for the .cn
# domain and forwards over WireGuard to the homelab ingress.
#
# Why a relay and not Cloudflare: mainland clients reach a Tencent edge far
# faster than a Cloudflare edge, and Cloudflare's China network is an
# Enterprise product. The homelab keeps zero inbound exposure because the
# tunnel is dialled outbound from the cluster.
#
# ICP FILING: a mainland resource serving HTTP/HTTPS for a domain requires an
# ICP filing naming that domain. Without it this instance accepts the
# connection and the mainland network resets the HTTP layer. Put the relay in a
# non-mainland region (ap-hongkong, ap-singapore) when no filing exists.

resource "tencentcloud_vpc" "edge" {
  name       = "${replace(var.china_domain, ".", "_")}_edge"
  cidr_block = var.edge_vpc_cidr
}

resource "tencentcloud_subnet" "edge" {
  name              = "${replace(var.china_domain, ".", "_")}_edge"
  vpc_id            = tencentcloud_vpc.edge.id
  availability_zone = var.tencent_availability_zone
  cidr_block        = var.edge_subnet_cidr
}

resource "tencentcloud_key_pair" "edge" {
  key_name   = "${replace(var.china_domain, ".", "_")}_edge"
  public_key = var.relay_ssh_public_key
}

resource "tencentcloud_security_group" "edge" {
  name        = "${replace(var.china_domain, ".", "_")}_edge"
  description = "TLS + WireGuard for the ${var.china_domain} relay; SSH from the operator only"
}

resource "tencentcloud_security_group_rule" "ssh" {
  security_group_id = tencentcloud_security_group.edge.id
  type              = "ingress"
  ip_protocol       = "tcp"
  port_range        = "22"
  cidr_ip           = var.relay_admin_cidr
  policy            = "accept"
}

resource "tencentcloud_security_group_rule" "tls" {
  security_group_id = tencentcloud_security_group.edge.id
  type              = "ingress"
  ip_protocol       = "tcp"
  port_range        = "80,443"
  cidr_ip           = "0.0.0.0/0"
  policy            = "accept"
}

resource "tencentcloud_security_group_rule" "wireguard" {
  security_group_id = tencentcloud_security_group.edge.id
  type              = "ingress"
  ip_protocol       = "udp"
  port_range        = tostring(var.wireguard_port)
  cidr_ip           = var.relay_admin_cidr
  policy            = "accept"
}

# cloud-init: WireGuard listener, forwarding sysctls, and Caddy for TLS.
# The relay never holds application credentials; it forwards bytes.
#
# NOTE ON THE PRIVATE KEY: user_data is visible in the instance metadata and in
# Terraform state. That is a known limitation of bootstrapping WireGuard this
# way. The argument is wrapped in sensitive() to keep it out of plan/apply
# output, but anyone with console or state access can read it. Rotate the key
# if the state or the instance metadata is ever exposed.
locals {
  china_fqdns = [for host in var.china_hostnames : "${host}.${var.china_domain}"]

  caddyfile = templatefile("${path.module}/templates/Caddyfile.tpl", {
    acme_email       = var.acme_email
    hosts            = join(", ", local.china_fqdns)
    ingress_upstream = var.ingress_upstream
  })

  relay_user_data = <<-EOT
    #cloud-config
    package_update: true
    package_upgrade: false
    manage_etc_hosts: true
    timezone: Asia/Shanghai
    packages: [wireguard, wireguard-tools, caddy]
    write_files:
      - path: /etc/wireguard/wg0.conf
        permissions: "0600"
        content: |
          [Interface]
          Address = ${var.wireguard_relay_address}
          ListenPort = ${var.wireguard_port}
          PrivateKey = ${var.wireguard_relay_private_key}
          # Masquerade forwarded traffic so the homelab peer only has to accept
          # packets sourced from the relay's tunnel address. Without this the
          # homelab peer's AllowedIPs would drop the original client source IP.
          PostUp = iptables -t nat -A POSTROUTING -o wg0 -j MASQUERADE
          PostDown = iptables -t nat -D POSTROUTING -o wg0 -j MASQUERADE
          [Peer]
          PublicKey = ${var.wireguard_homelab_public_key}
          AllowedIPs = ${var.wireguard_homelab_allowed_ips}
          PersistentKeepalive = 25
      - path: /etc/sysctl.d/99-wireguard.conf
        content: |
          net.ipv4.ip_forward = 1
      - path: /etc/caddy/Caddyfile
        permissions: "0644"
        content: ${jsonencode(local.caddyfile)}
    runcmd:
      - sysctl --system
      - systemctl enable --now wg-quick@wg0
      - caddy validate --config /etc/caddy/Caddyfile
      - systemctl enable --now caddy
      - systemctl restart caddy
  EOT
}

resource "tencentcloud_instance" "relay" {
  instance_name     = "${replace(var.china_domain, ".", "_")}_edge"
  availability_zone = var.tencent_availability_zone
  image_id          = var.relay_image_id
  instance_type     = var.relay_instance_type

  vpc_id             = tencentcloud_vpc.edge.id
  subnet_id          = tencentcloud_subnet.edge.id
  security_groups    = [tencentcloud_security_group.edge.id]
  key_ids            = [tencentcloud_key_pair.edge.id]
  allocate_public_ip = true

  # Outbound only needs a few Mbps; inbound TLS is the same order.
  internet_max_bandwidth_out = var.relay_internet_max_bandwidth_out
  system_disk_type           = var.relay_system_disk_type
  system_disk_size           = var.relay_system_disk_size

  # The private key is embedded in this bootstrap script. sensitive() keeps it
  # out of CLI output; it does not remove it from state or instance metadata.
  user_data = sensitive(local.relay_user_data)

  tags = {
    role   = "china-edge"
    domain = var.china_domain
  }

  # Accidental `terraform destroy` would take the only China-facing edge down.
  # Remove this block deliberately when a replacement path exists.
  lifecycle {
    prevent_destroy = true
  }
}

# DNS for the .cn domain lives at DNSPod (Tencent). Each subdomain resolves to
# the relay's public address, and the relay proxies to the homelab over the
# tunnel. The "中国境内" line is the default line; no separate line records.
resource "tencentcloud_dnspod_record" "china" {
  for_each = toset(var.china_hostnames)

  domain      = var.china_domain
  sub_domain  = each.value
  record_type = "A"
  record_line = var.china_dns_record_line
  value       = tencentcloud_instance.relay.public_ip
  ttl         = var.china_dns_ttl
  remark      = "China edge relay; origin is the homelab ingress over WireGuard"
}