// Package model holds Steward's data: the configuration (State), leases,
// users and tokens, the history of changes and the audit log.
package model

import (
	"encoding/json"
	"fmt"
	"net"
	"net/netip"
	"sort"
	"strings"
	"time"
)

// Defaults for settings that are 0 or unset.
const (
	DefaultLeaseTime   = 12 * 60 * 60 // seconds
	DefaultPingTimeout = 500          // milliseconds
	DefaultDeclineHold = 24 * 60 * 60 // seconds
	MinLeaseTime       = 60
	MaxLeaseTime       = 365 * 24 * 60 * 60
)

// State is the whole configuration. It is small and changed as a whole
// (internal/engine).
type State struct {
	Settings     Settings       `json:"settings"`
	Subnets      []*Subnet      `json:"subnets"`
	Reservations []*Reservation `json:"reservations"`
}

// Settings are the server-wide settings and the options every subnet
// starts from.
type Settings struct {
	// LeaseTime is the default lease time in seconds (0: DefaultLeaseTime).
	LeaseTime int `json:"lease_time"`
	// Options apply to every subnet; a subnet's or a reservation's own
	// options of the same code win.
	Options []OptionValue `json:"options"`
	// PingCheck pings an address before offering it, and skips it if
	// something answers. PingTimeout is how long to wait, in ms.
	PingCheck   bool `json:"ping_check"`
	PingTimeout int  `json:"ping_timeout_ms"`
	// DeclineHold is how long an address a client declined (or that
	// answered a ping) is held back, in seconds.
	DeclineHold int `json:"decline_hold"`
	// NotAuthoritative stops Steward from refusing (DHCPNAK) requests for
	// addresses that don't belong on the interface, for networks where
	// another DHCP server shares the segment. Off by default.
	NotAuthoritative bool `json:"not_authoritative"`
}

// DefaultSettings are the settings of a new database.
func DefaultSettings() Settings {
	return Settings{LeaseTime: DefaultLeaseTime, PingCheck: true, PingTimeout: DefaultPingTimeout, DeclineHold: DefaultDeclineHold, Options: []OptionValue{}}
}

// EffectiveLeaseTime is the lease time with its default.
func (s Settings) EffectiveLeaseTime() int {
	if s.LeaseTime > 0 {
		return s.LeaseTime
	}
	return DefaultLeaseTime
}

// EffectivePingTimeout is the ping timeout with its default.
func (s Settings) EffectivePingTimeout() time.Duration {
	ms := s.PingTimeout
	if ms <= 0 {
		ms = DefaultPingTimeout
	}
	return time.Duration(ms) * time.Millisecond
}

// EffectiveDeclineHold is the decline hold with its default.
func (s Settings) EffectiveDeclineHold() time.Duration {
	sec := s.DeclineHold
	if sec <= 0 {
		sec = DefaultDeclineHold
	}
	return time.Duration(sec) * time.Second
}

// OptionValue is an option set in the configuration: its code and its
// value as text ("10.0.10.1, 10.0.10.2"). Name is the catalog's name,
// filled in for display. Type is only stored for options the catalog
// doesn't know (default hex).
type OptionValue struct {
	Code  int    `json:"code"`
	Name  string `json:"name,omitempty"`
	Type  string `json:"type,omitempty"`
	Value string `json:"value"`
}

// Subnet is an IPv4 network served on one interface.
type Subnet struct {
	ID int64 `json:"id"`
	// Name is a label for people ("office", "iot"); optional, unique.
	Name string `json:"name"`
	// Interface is the network interface the subnet is served on.
	Interface string       `json:"interface"`
	Prefix    netip.Prefix `json:"prefix"`
	Pools     []Pool       `json:"pools"`
	// LeaseTime overrides the settings' lease time (0: inherit).
	LeaseTime int           `json:"lease_time"`
	Options   []OptionValue `json:"options"`
	// Disabled subnets keep their configuration and leases but get no
	// answers.
	Disabled bool   `json:"disabled"`
	Comment  string `json:"comment"`
}

// Label names the subnet in messages: "office (10.0.10.0/24)".
func (s *Subnet) Label() string {
	if s.Name != "" {
		return s.Name + " (" + s.Prefix.String() + ")"
	}
	return s.Prefix.String()
}

// Pool is a range of addresses handed out to any client.
type Pool struct {
	Start netip.Addr `json:"start"`
	End   netip.Addr `json:"end"`
}

func (p Pool) String() string { return p.Start.String() + "-" + p.End.String() }

// Contains reports whether a is in the pool.
func (p Pool) Contains(a netip.Addr) bool {
	return a.Is4() && p.Start.Compare(a) <= 0 && a.Compare(p.End) <= 0
}

// Size is the number of addresses in the pool.
func (p Pool) Size() int {
	if !p.Start.Is4() || !p.End.Is4() || p.End.Less(p.Start) {
		return 0
	}
	return int(U32(p.End)-U32(p.Start)) + 1
}

// ParsePool reads "10.0.10.100-10.0.10.199" (spaces around the dash are
// fine) or a prefix, "10.0.10.128/25".
func ParsePool(s string) (Pool, error) {
	s = strings.TrimSpace(s)
	if a, b, ok := strings.Cut(s, "-"); ok {
		start, err1 := netip.ParseAddr(strings.TrimSpace(a))
		end, err2 := netip.ParseAddr(strings.TrimSpace(b))
		if err1 != nil || err2 != nil || !start.Is4() || !end.Is4() {
			return Pool{}, fmt.Errorf("pool %q: write it as FIRST-LAST, with IPv4 addresses", s)
		}
		if end.Less(start) {
			return Pool{}, fmt.Errorf("pool %q ends before it starts", s)
		}
		return Pool{Start: start, End: end}, nil
	}
	pfx, err := netip.ParsePrefix(s)
	if err != nil || !pfx.Addr().Is4() {
		return Pool{}, fmt.Errorf("pool %q: write it as FIRST-LAST (10.0.10.100-10.0.10.199) or as a prefix", s)
	}
	pfx = pfx.Masked()
	return Pool{Start: pfx.Addr(), End: Last(pfx)}, nil
}

// U32 is an IPv4 address as a number.
func U32(a netip.Addr) uint32 {
	b := a.As4()
	return uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3])
}

// FromU32 is the address of a number.
func FromU32(v uint32) netip.Addr {
	return netip.AddrFrom4([4]byte{byte(v >> 24), byte(v >> 16), byte(v >> 8), byte(v)})
}

// Last is the last address of a prefix (its broadcast address).
func Last(p netip.Prefix) netip.Addr {
	p = p.Masked()
	return FromU32(U32(p.Addr()) | (1<<(32-p.Bits()) - 1))
}

// Mask is the prefix's netmask.
func Mask(p netip.Prefix) netip.Addr {
	return FromU32(^uint32(0) << (32 - p.Bits()))
}

// Reservation gives a client a fixed address. The client is known by its
// MAC address, or by its client identifier (option 61) when ClientID is
// set. The subnet is the one whose prefix holds the address.
type Reservation struct {
	ID       int64      `json:"id"`
	MAC      string     `json:"mac,omitempty"`
	ClientID string     `json:"client_id,omitempty"`
	IP       netip.Addr `json:"ip"`
	// Hostname is sent to the client (option 12).
	Hostname string        `json:"hostname"`
	Options  []OptionValue `json:"options"`
	Comment  string        `json:"comment"`
}

// Label names the reservation in messages.
func (r *Reservation) Label() string {
	who := r.MAC
	if r.ClientID != "" {
		who = "client id " + r.ClientID
	}
	if r.Hostname != "" {
		return r.Hostname + " (" + r.IP.String() + ", " + who + ")"
	}
	return r.IP.String() + " (" + who + ")"
}

// NormalizeMAC writes a MAC address as aa:bb:cc:dd:ee:ff. It accepts
// colons, dashes, dots (Cisco) or no separators.
func NormalizeMAC(s string) (string, error) {
	s = strings.TrimSpace(s)
	if len(s) == 12 && !strings.ContainsAny(s, ":-.") {
		var parts []string
		for i := 0; i < 12; i += 2 {
			parts = append(parts, s[i:i+2])
		}
		s = strings.Join(parts, ":")
	}
	hw, err := net.ParseMAC(s)
	if err != nil || len(hw) != 6 {
		return "", fmt.Errorf("%q is not a MAC address (write it as aa:bb:cc:dd:ee:ff)", s)
	}
	return hw.String(), nil
}

// NormalizeClientID writes a client identifier as lower-case hex without
// separators. It accepts hex with colons or dashes.
func NormalizeClientID(s string) (string, error) {
	h := strings.ToLower(strings.NewReplacer(":", "", "-", "", " ", "").Replace(strings.TrimSpace(s)))
	if h == "" || len(h)%2 != 0 || strings.Trim(h, "0123456789abcdef") != "" {
		return "", fmt.Errorf("%q is not a client identifier in hex (01:aa:bb:cc:dd:ee:ff)", s)
	}
	return h, nil
}

// SubnetByID finds a subnet.
func (st *State) SubnetByID(id int64) *Subnet {
	for _, s := range st.Subnets {
		if s.ID == id {
			return s
		}
	}
	return nil
}

// SubnetFor returns the subnet whose prefix holds a (the first, in
// order), or nil.
func (st *State) SubnetFor(a netip.Addr) *Subnet {
	for _, s := range st.Subnets {
		if s.Prefix.Contains(a) {
			return s
		}
	}
	return nil
}

// ReservationByID finds a reservation.
func (st *State) ReservationByID(id int64) *Reservation {
	for _, r := range st.Reservations {
		if r.ID == id {
			return r
		}
	}
	return nil
}

// FindSubnet finds a subnet by ID, name or prefix.
func (st *State) FindSubnet(ref string) *Subnet {
	ref = strings.TrimSpace(ref)
	var id int64
	if _, err := fmt.Sscan(ref, &id); err == nil && fmt.Sprint(id) == ref {
		if s := st.SubnetByID(id); s != nil {
			return s
		}
	}
	for _, s := range st.Subnets {
		if strings.EqualFold(s.Name, ref) && s.Name != "" {
			return s
		}
	}
	if p, err := netip.ParsePrefix(ref); err == nil {
		for _, s := range st.Subnets {
			if s.Prefix == p.Masked() {
				return s
			}
		}
	}
	return nil
}

// Clone returns a deep copy.
func (st *State) Clone() *State {
	b, err := json.Marshal(st)
	if err != nil {
		panic(err)
	}
	var out State
	if err := json.Unmarshal(b, &out); err != nil {
		panic(err)
	}
	return &out
}

// Sort puts subnets and reservations in display order: subnets by
// interface then address, reservations by address.
func (st *State) Sort() {
	sort.SliceStable(st.Subnets, func(i, j int) bool {
		a, b := st.Subnets[i], st.Subnets[j]
		if a.Interface != b.Interface {
			return a.Interface < b.Interface
		}
		return a.Prefix.Addr().Less(b.Prefix.Addr())
	})
	sort.SliceStable(st.Reservations, func(i, j int) bool {
		return st.Reservations[i].IP.Less(st.Reservations[j].IP)
	})
}

// Interfaces lists the interfaces subnets are served on (enabled ones).
func (st *State) Interfaces() []string {
	seen := map[string]bool{}
	var out []string
	for _, s := range st.Subnets {
		if !s.Disabled && s.Interface != "" && !seen[s.Interface] {
			seen[s.Interface] = true
			out = append(out, s.Interface)
		}
	}
	sort.Strings(out)
	return out
}