package provider

import (
	"fmt"
	"net/url"
	"regexp"
)

// KVMConfig configures a kvm provider instance: one or more libvirt/KVM
// hypervisors reached over SSH (the libvirt unix socket is forwarded through
// the SSH connection, so hosts need no libvirtd TCP/TLS listener).
// placement.zone on a Proxy selects a host by name; with a single host it may
// be omitted.
type KVMConfig struct {
	// SSHKeyFile is the path to the private key used for every host. Required.
	SSHKeyFile string `json:"sshKeyFile"`
	// KnownHostsFile is an OpenSSH known_hosts file used to verify host keys.
	// Required unless InsecureIgnoreHostKey is set.
	KnownHostsFile string `json:"knownHostsFile,omitempty"`
	// InsecureIgnoreHostKey skips host-key verification entirely.
	InsecureIgnoreHostKey bool `json:"insecureIgnoreHostKey,omitempty"`
	// DiskSizeGB is the capacity of each VM's overlay disk. Default 10. The
	// guest's cloud-init growpart expands the root filesystem into it.
	DiskSizeGB int64 `json:"diskSizeGb,omitempty"`
	// VendorData is optional cloud-init vendor-data placed on every seed next
	// to the Proxy's own user-data. cloud-init drops any top-level key here
	// that the user-data also defines. The qemu-guest-agent bootstrap does
	// not live here: the provider merges it into each Proxy's cloud-config.
	VendorData string `json:"vendorData,omitempty"`
	// Images are named base images; placement.image names a key here (or is
	// an http(s) URL directly). The provider downloads each image into a
	// host's storage pool on first use and caches it there.
	Images map[string]KVMImage `json:"images,omitempty"`
	// MachineTypes are named size profiles; placement.machineType names a
	// key here. Required, at least one.
	MachineTypes map[string]KVMMachineType `json:"machineTypes"`
	// Hosts are the hypervisors. Required, at least one, unique names.
	Hosts []KVMHost `json:"hosts"`
}

// KVMImage is one downloadable base image (a distro cloud image with
// cloud-init preinstalled, e.g. Debian's generic qcow2).
type KVMImage struct {
	// URL is where to fetch the image from. Required, http or https.
	URL string `json:"url"`
	// SHA256 is the expected hex digest of the file. Optional; when set it is
	// verified after download and a later change triggers a re-download.
	SHA256 string `json:"sha256,omitempty"`
	// Format is the image's disk format, "qcow2" (default) or "raw".
	Format string `json:"format,omitempty"`
	// Firmware is how VMs from this image boot: "uefi" (default; OVMF with
	// secure boot off) or "bios" (SeaBIOS) for images with no EFI system
	// partition. Current Debian, Ubuntu, Fedora and Rocky cloud images all
	// boot UEFI, and Debian 13's BIOS path was found not to boot at all.
	Firmware string `json:"firmware,omitempty"`
}

// KVMMachineType is a VM size profile.
type KVMMachineType struct {
	VCPUs     int32 `json:"vcpus"`
	MemoryMiB int64 `json:"memoryMiB"`
}

// KVMHost is one hypervisor.
type KVMHost struct {
	// Name is the placement.zone value that selects this host. Required.
	Name string `json:"name"`
	// Address is the SSH endpoint, host:port. Required.
	Address string `json:"address"`
	// User is the SSH user; it must be allowed to use the libvirt socket
	// (typically a member of the libvirt group). Required.
	User string `json:"user"`
	// Socket is the libvirt unix socket path on the host.
	// Default /var/run/libvirt/libvirt-sock.
	Socket string `json:"socket,omitempty"`
	// Pool is the libvirt storage pool for base images, overlay disks and
	// seed ISOs. Default "default".
	Pool string `json:"pool,omitempty"`
	// Bridge is the host bridge the VM's NIC attaches to; it must lead to a
	// network the cluster can reach and that hands out DHCP leases. Required.
	Bridge string `json:"bridge"`
}

var sha256Hex = regexp.MustCompile(`^[0-9a-fA-F]{64}$`)

// kvmIdentifier constrains the config names that are pasted into
// identifiers elsewhere: a host name goes into the providerID
// hosts/<name>/domains/<vm>, which is split on "/" to parse, and an image
// key becomes the file name of the cached base volume. A slash in either
// produces an ID or a path that never resolves again, so the VM leaks with
// nothing able to address it.
var kvmIdentifier = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9_.-]*$`)

func validateKVM(prefix string, c *KVMConfig) error {
	if c == nil {
		return fmt.Errorf("%s: kvm block is required", prefix)
	}
	if c.SSHKeyFile == "" {
		return fmt.Errorf("%s: kvm.sshKeyFile is required", prefix)
	}
	if c.KnownHostsFile == "" && !c.InsecureIgnoreHostKey {
		return fmt.Errorf("%s: kvm.knownHostsFile is required unless kvm.insecureIgnoreHostKey is true", prefix)
	}
	if c.DiskSizeGB < 0 {
		return fmt.Errorf("%s: kvm.diskSizeGb must not be negative", prefix)
	}
	for name, img := range c.Images {
		p := fmt.Sprintf("%s: kvm.images[%q]", prefix, name)
		if !kvmIdentifier.MatchString(name) {
			return fmt.Errorf("%s: key must be letters, digits, dots, dashes or underscores"+
				" — it becomes the cached volume name base-<key>.<format>", p)
		}
		u, err := url.Parse(img.URL)
		if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
			return fmt.Errorf("%s.url must be an http(s) URL (got %q)", p, img.URL)
		}
		if img.SHA256 != "" && !sha256Hex.MatchString(img.SHA256) {
			return fmt.Errorf("%s.sha256 must be 64 hex characters", p)
		}
		if img.Format != "" && img.Format != "qcow2" && img.Format != "raw" {
			return fmt.Errorf("%s.format must be qcow2 or raw (got %q)", p, img.Format)
		}
		if img.Firmware != "" && img.Firmware != "uefi" && img.Firmware != "bios" {
			return fmt.Errorf("%s.firmware must be uefi or bios (got %q)", p, img.Firmware)
		}
	}
	if len(c.MachineTypes) == 0 {
		return fmt.Errorf("%s: kvm.machineTypes must define at least one profile", prefix)
	}
	for name, mt := range c.MachineTypes {
		if mt.VCPUs <= 0 || mt.MemoryMiB <= 0 {
			return fmt.Errorf("%s: kvm.machineTypes[%q] needs vcpus > 0 and memoryMiB > 0", prefix, name)
		}
	}
	if len(c.Hosts) == 0 {
		return fmt.Errorf("%s: kvm.hosts must list at least one host", prefix)
	}
	seen := make(map[string]bool, len(c.Hosts))
	for i, h := range c.Hosts {
		p := fmt.Sprintf("%s: kvm.hosts[%d]", prefix, i)
		if h.Name == "" {
			return fmt.Errorf("%s: name is required", p)
		}
		if !kvmIdentifier.MatchString(h.Name) {
			return fmt.Errorf("%s: name %q must be letters, digits, dots, dashes or underscores"+
				" — it becomes part of the providerID hosts/<name>/domains/<vm>", p, h.Name)
		}
		if seen[h.Name] {
			return fmt.Errorf("%s: duplicate host name %q", p, h.Name)
		}
		seen[h.Name] = true
		if h.Address == "" {
			return fmt.Errorf("%s %q: address is required", p, h.Name)
		}
		if h.User == "" {
			return fmt.Errorf("%s %q: user is required", p, h.Name)
		}
		if h.Bridge == "" {
			return fmt.Errorf("%s %q: bridge is required", p, h.Name)
		}
	}
	return nil
}