dhcpsvc

type Config struct {
	// Interfaces stores configurations of DHCP server specific for the network
	// interface identified by its name.  It must not be empty and must only
	// contain valid interface names and configurations.
	Interfaces map[string]*InterfaceConfig

	// NetworkDeviceManager is the manager of network devices.  It must not be
	// nil.
	//
	// TODO(e.burkov):  Set.
	NetworkDeviceManager NetworkDeviceManager

	// Logger will be used to log the DHCP events.  It must not be nil.
	Logger *slog.Logger

	// LocalDomainName is the top-level domain name to use for resolving DHCP
	// clients' hostnames.  It must be a valid domain name.
	LocalDomainName string

	// DBFilePath is the path to the database file containing the DHCP leases.
	// It must not be empty.
	DBFilePath string

	// ICMPTimeout is the timeout for checking another DHCP server's presence.
	// It must be non-negative.  If it is zero, the check will be skipped.
	ICMPTimeout time.Duration

	// Enabled is the state of the service, whether it is enabled or not.
	Enabled bool
}

type DHCPServer struct {
	// contains filtered or unexported fields
}

type Empty struct{}

type EmptyNetworkDevice struct{}

type EmptyNetworkDeviceManager struct{}

type IPv4Config struct {
	// Clock is used to get current time.  It should not be nil.
	Clock timeutil.Clock

	// GatewayIP is the IPv4 address of the network's gateway.  It is used as
	// the default gateway for DHCP clients and also used for calculating the
	// network-specific broadcast address.  It should be a valid IPv4 address,
	// should be within the subnet, and should be outside the address range.
	GatewayIP netip.Addr

	// SubnetMask is the IPv4 subnet mask of the network.  It should be a valid
	// IPv4 CIDR (i.e. all 1s followed by all 0s).
	SubnetMask netip.Addr

	// RangeStart is the first address in the range to assign to DHCP clients.
	// It should be a valid IPv4 address, should be within the subnet, and
	// should be less or equal to RangeEnd.
	RangeStart netip.Addr

	// RangeEnd is the last address in the range to assign to DHCP clients.  It
	// should be a valid IPv4 address, should be within the subnet, and should
	// be greater or equal to RangeStart.
	RangeEnd netip.Addr

	// Options is the list of explicitly configured DHCP options to send to
	// clients.  Options with nil Data field are removed from responses.
	//
	// TODO(e.burkov):  Validate.
	Options layers.DHCPOptions

	// LeaseDuration is the TTL of a DHCP lease.  It should be positive.
	LeaseDuration time.Duration

	// Enabled is the state of the DHCPv4 service, whether it is enabled or not
	// on the specific interface.
	Enabled bool
}

type IPv6Config struct {
	// RangeStart is the first address in the range to assign to DHCP clients.
	// It should be a valid IPv6 address.
	RangeStart netip.Addr

	// Options is the list of explicit DHCP options to send to clients.  The
	// options with zero length are treated as deletions of the corresponding
	// options, either implicit or explicit.
	Options layers.DHCPv6Options

	// LeaseDuration is the TTL of a DHCP lease.  It should be positive.
	LeaseDuration time.Duration

	// RASlaacOnly defines whether the DHCP clients should only use SLAAC for
	// address assignment.
	RASLAACOnly bool

	// RAAllowSlaac defines whether the DHCP clients may use SLAAC for address
	// assignment.
	RAAllowSLAAC bool

	// Enabled is the state of the DHCPv6 service, whether it is enabled or not
	// on the specific interface.
	Enabled bool
}

type Interface interface {
	agh.ServiceWithConfig[*Config]

	// Enabled returns true if DHCP provides information about clients.
	Enabled() (ok bool)

	// HostByIP returns the hostname of the DHCP client with the given IP
	// address.  The address will be netip.Addr{} if there is no such client,
	// due to an assumption that a DHCP client must always have an IP address.
	HostByIP(ip netip.Addr) (host string)

	// MACByIP returns the MAC address for the given IP address leased.  It
	// returns nil if there is no such client, due to an assumption that a DHCP
	// client must always have a MAC address.
	//
	// TODO(e.burkov):  Think of a contract for the returned value.
	MACByIP(ip netip.Addr) (mac net.HardwareAddr)

	// IPByHost returns the IP address of the DHCP client with the given
	// hostname.  The hostname will be an empty string if there is no such
	// client, due to an assumption that a DHCP client must always have a
	// hostname, either set or generated.
	IPByHost(host string) (ip netip.Addr)

	// Leases returns all the active DHCP leases.  The returned slice should be
	// a clone.  The order of leases is undefined.
	//
	// TODO(e.burkov):  Consider implementing iterating methods with appropriate
	// signatures instead of cloning the whole list.
	Leases() (ls []*Lease)

	// AddLease adds a new DHCP lease.  l must be valid.  It returns an error if
	// l already exists.
	AddLease(ctx context.Context, l *Lease) (err error)

	// UpdateStaticLease replaces an existing static DHCP lease.  l must be
	// valid.  It returns an error if the lease with the given hardware address
	// doesn't exist or if other values match another existing lease.
	UpdateStaticLease(ctx context.Context, l *Lease) (err error)

	// RemoveLease removes an existing DHCP lease.  l must be valid.  It returns
	// an error if there is no lease equal to l.
	RemoveLease(ctx context.Context, l *Lease) (err error)

	// Reset removes all the DHCP leases.
	//
	// TODO(e.burkov):  If it's really needed?
	Reset(ctx context.Context) (err error)
}

type InterfaceConfig struct {
	// IPv4 is the configuration of DHCP protocol for IPv4.
	IPv4 *IPv4Config

	// IPv6 is the configuration of DHCP protocol for IPv6.
	IPv6 *IPv6Config
}

type Lease struct {
	// IP is the IP address leased to the client.  It must not be empty.
	IP netip.Addr

	// Expiry is the expiration time of the lease or its blocking expiration
	// time.
	Expiry time.Time

	// Hostname of the client.  It may be empty if the lease is blocked.
	Hostname string

	// HWAddr is the physical hardware (MAC) address.  It must not be nil.
	HWAddr net.HardwareAddr

	// IsStatic defines if the lease is static.
	IsStatic bool
}

type NetworkDevice interface {
	gopacket.PacketDataSource

	// No methods of a device should be called after Close.
	io.Closer

	// Addresses returns all IP addresses assigned to the device.
	Addresses() (ips []netip.Addr)

	// LinkType returns the link type of the network interface.
	LinkType() (lt layers.LinkType)

	// WritePacketData writes a serialized packet to the network interface.
	WritePacketData(data []byte) (err error)
}

type NetworkDeviceConfig struct {
	// Name is the name of the network device.  It must be a valid interface
	// name on the system.
	Name string
}

type NetworkDeviceManager interface {
	// Open opens a network device.  conf must be valid.
	//
	// An attempt to open the same device multiple times may return an error.
	Open(ctx context.Context, conf *NetworkDeviceConfig) (dev NetworkDevice, err error)
}