// HPC cluster: one head node (the single entry point, public SSH + private
// cluster network) and N compute nodes (private network only, internet egress
// through an OVH gateway for package installation). The cloud provider
// credentials and the project (OVH_CLOUD_PROJECT_SERVICE) reach the provider
// from the runner environment, never from module inputs.

data "ovh_cloud_project_flavors" "head" {
  service_name = var.project_id
  name_filter  = var.head_flavor
  region       = var.region
}

data "ovh_cloud_project_flavors" "compute" {
  service_name = var.project_id
  name_filter  = var.compute_flavor
  region       = var.region
}

data "ovh_cloud_project_images" "all" {
  service_name = var.project_id
  region       = var.region
}

locals {
  selected_image          = one([for m in data.ovh_cloud_project_images.all.images : m if m.name == var.image])
  selected_head_flavor    = one(data.ovh_cloud_project_flavors.head.flavors)
  selected_compute_flavor = one(data.ovh_cloud_project_flavors.compute.flavors)

  head_hostname = "${var.name_prefix}-head-${var.deployment_id}"
  head_ip       = cidrhost(var.cluster_cidr, 50)

  compute_hostnames = [for i in range(var.compute_node_count) : "${var.name_prefix}-compute${i + 1}-${var.deployment_id}"]
  compute_ips       = [for i in range(var.compute_node_count) : cidrhost(var.cluster_cidr, 60 + i)]
}

// Private cluster network (vRack) with one subnet. Fixed addresses are
// assigned outside the DHCP pool; DHCP stays enabled so the instances
// configure their private interface from the OpenStack metadata.
resource "ovh_cloud_project_network_private" "cluster" {
  service_name = var.project_id
  name         = "${var.name_prefix}-hpc-${var.deployment_id}"
  regions      = [var.region]
  vlan_id      = var.vlan_id
}

resource "ovh_cloud_project_network_private_subnet" "cluster" {
  service_name = var.project_id
  network_id   = ovh_cloud_project_network_private.cluster.id
  region       = var.region
  network      = var.cluster_cidr
  // The allocation pool must cover the fixed addresses: the OVH API refuses
  // an instance ip outside it ("instance ip must be in subnet allocation
  // pool"). The DHCP agent ports allocate from the start of the pool, so the
  // fixed addresses (head at 50, compute nodes from 60) stay clear of them:
  // an instance on a DHCP-port address is silently canceled by the cloud.
  start = cidrhost(var.cluster_cidr, 10)
  end   = cidrhost(var.cluster_cidr, 200)
  dhcp  = true
}

locals {
  openstack_network_id = one([
    for r in ovh_cloud_project_network_private.cluster.regions_attributes : r.openstackid if r.region == var.region
  ])
}

// Internet egress for the whole cluster: the gateway attaches to the
// cluster subnet and DHCP distributes it as the default route. A NAT
// through a dual-homed head node is not an option: the cloud's port
// anti-spoofing silently drops the forwarded return traffic.
resource "ovh_cloud_project_gateway" "egress" {
  service_name = var.project_id
  name         = "${var.name_prefix}-hpc-gw-${var.deployment_id}"
  model        = var.gateway_model
  region       = var.region
  network_id   = local.openstack_network_id
  subnet_id    = ovh_cloud_project_network_private_subnet.cluster.id
}

// One project SSH key per deployment, managed by the module so it is removed
// on destroy. The instance level ssh_key_create is avoided on purpose: keys it
// creates outlive the instance and collide on the next deployment.
resource "ovh_cloud_project_ssh_key" "admin" {
  service_name = var.project_id
  name         = "${var.name_prefix}-${var.deployment_id}-key"
  public_key   = trimspace(tls_private_key.admin.public_key_openssh)
}

resource "ovh_cloud_project_instance" "head" {
  service_name   = var.project_id
  region         = var.region
  billing_period = "hourly"
  name           = local.head_hostname

  boot_from {
    image_id = local.selected_image.id
  }

  flavor {
    flavor_id = local.selected_head_flavor.id
  }

  ssh_key {
    name = ovh_cloud_project_ssh_key.admin.name
  }

  // The head node cannot sit on the public network: the cloud refuses an
  // instance attached to both the public network and a subnet served by a
  // gateway. Public reachability comes from a floating ip routed through
  // the gateway instead. The fixed address stays clear of the DHCP agent
  // ports at the start of the pool: an instance on a DHCP-port address is
  // silently canceled by the cloud, which also broke the floating ip
  // creation until the address moved.
  network {
    private {
      ip = local.head_ip
      floating_ip_create {
        description = "${var.name_prefix}-hpc-head-${var.deployment_id}"
      }
      network {
        id        = local.openstack_network_id
        subnet_id = ovh_cloud_project_network_private_subnet.cluster.id
      }
    }
  }

  user_data = data.cloudinit_config.head.rendered

  depends_on = [ovh_cloud_project_gateway.egress]
}

// Resolves the public (floating) address of the head node: the instance
// addresses only carry the fixed private ip, the floating ip is matched
// through the port it is associated with.
data "ovh_cloud_project_floatingips" "all" {
  service_name = var.project_id
  region_name  = var.region

  depends_on = [ovh_cloud_project_instance.head]
}

resource "ovh_cloud_project_instance" "compute" {
  count          = var.compute_node_count
  service_name   = var.project_id
  region         = var.region
  billing_period = "hourly"
  name           = local.compute_hostnames[count.index]

  boot_from {
    image_id = local.selected_image.id
  }

  flavor {
    flavor_id = local.selected_compute_flavor.id
  }

  ssh_key {
    name = ovh_cloud_project_ssh_key.admin.name
  }

  network {
    private {
      ip = local.compute_ips[count.index]
      network {
        id        = local.openstack_network_id
        subnet_id = ovh_cloud_project_network_private_subnet.cluster.id
      }
    }
  }

  user_data = data.cloudinit_config.compute[count.index].rendered

  depends_on = [ovh_cloud_project_gateway.egress]
}

locals {
  head_public_ip = one([
    for f in data.ovh_cloud_project_floatingips.all.cloud_project_floatingips : f.ip
    if try(f.associated_entity.ip, "") == local.head_ip
  ])
}