package server

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/netip"
	"sort"
	"strconv"
	"strings"

	"steward/internal/api"
	"steward/internal/auth"
	"steward/internal/dhcp4"
	"steward/internal/engine"
	"steward/internal/model"
	"steward/internal/store"
)

// change applies a configuration change and answers with what changed.
// object, if set, returns the object to include from the new state.
func (s *Server) change(w http.ResponseWriter, r *http.Request, p *auth.Principal, description string, edit engine.Edit, object func(st *model.State) any) error {
	if err := require(p, auth.ResConfig, true); err != nil {
		return err
	}
	res, err := s.eng.Apply(r.Context(), p, description, engine.Options{DryRun: queryBool(r, "dry_run"), Via: via(r, p)}, edit)
	if err != nil {
		s.writeErr(w, r, err, res)
		return nil
	}
	s.respondChange(w, r, res, object, r.Method == http.MethodPost)
	return nil
}

// respondChange answers a change: 201 when it created something.
func (s *Server) respondChange(w http.ResponseWriter, r *http.Request, res *engine.Result, object func(st *model.State) any, creates bool) {
	out := api.MutationResponse{Applied: res.Applied, DryRun: res.DryRun, HistoryID: res.HistoryID, Changes: res.Changes, Warnings: res.Warnings}
	if out.Changes == nil {
		out.Changes = []model.Change{}
	}
	if object != nil && res.Applied {
		if v := object(s.eng.State()); v != nil {
			out.Object, _ = json.Marshal(v)
		}
	}
	status := http.StatusOK
	if res.Applied && creates {
		status = http.StatusCreated
	}
	writeJSON(w, status, out)
}

// optionsFrom reads options given by name or number.
func optionsFrom(in []api.OptionInput) ([]model.OptionValue, error) {
	out := []model.OptionValue{}
	for _, o := range in {
		def, ok := dhcp4.Lookup(o.Option)
		if !ok {
			return nil, badRequest("unknown option %q: use a name from 'steward option list' or a number from 1 to 254", o.Option)
		}
		if why, reserved := dhcp4.Reserved[def.Code]; reserved {
			return nil, badRequest("option %s (%d) can't be set: %s", o.Option, def.Code, why)
		}
		v := model.OptionValue{Code: int(def.Code), Value: o.Value}
		if !dhcp4.Known(def.Code) {
			v.Type = o.Type
			if v.Type == "" {
				v.Type = dhcp4.TypeHex
			}
		} else if o.Type != "" && o.Type != def.Type {
			return nil, badRequest("option %s has type %s; a type can only be given for options Steward doesn't know", def.Name, def.Type)
		}
		out = append(out, v)
	}
	return out, nil
}

// ---- settings

func (s *Server) getSettings(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, s.eng.State().Settings)
	return nil
}

func (s *Server) updateSettings(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	var in api.SettingsInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	var opts []model.OptionValue
	if in.Options != nil {
		var err error
		if opts, err = optionsFrom(*in.Options); err != nil {
			return err
		}
	}
	return s.change(w, r, p, "", func(st *model.State, _ func() int64) error {
		set := &st.Settings
		if in.LeaseTime != nil {
			set.LeaseTime = *in.LeaseTime
		}
		if in.Options != nil {
			set.Options = opts
		}
		if in.PingCheck != nil {
			set.PingCheck = *in.PingCheck
		}
		if in.PingTimeout != nil {
			set.PingTimeout = *in.PingTimeout
		}
		if in.DeclineHold != nil {
			set.DeclineHold = *in.DeclineHold
		}
		if in.NotAuthoritative != nil {
			set.NotAuthoritative = *in.NotAuthoritative
		}
		return nil
	}, func(st *model.State) any { return st.Settings })
}

// ---- subnets

func (s *Server) presentSubnet(sn *model.Subnet, st *model.State, leases []*model.Lease) api.Subnet {
	out := api.Subnet{Subnet: sn}
	now := s.nowFn()
	for _, p := range sn.Pools {
		out.Usage.PoolSize += p.Size()
	}
	reserved := map[netip.Addr]bool{}
	for _, res := range st.Reservations {
		if sn.Prefix.Contains(res.IP) {
			out.Usage.Reservations++
			reserved[res.IP] = true
			for _, p := range sn.Pools {
				if p.Contains(res.IP) {
					out.Usage.PoolSize-- // reserved addresses aren't handed out
				}
			}
		}
	}
	for _, l := range leases {
		if !sn.Prefix.Contains(l.IP) {
			continue
		}
		switch {
		case reserved[l.IP] && l.ActiveAt(now):
			out.Usage.ReservationsLeased++
		case l.ActiveAt(now):
			out.Usage.Leased++
		case l.HeldAt(now):
			out.Usage.Declined++
		}
	}
	return out
}

func (s *Server) listSubnets(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	st := s.eng.State()
	leases := s.dhcp.Leases()
	out := []api.Subnet{}
	for _, sn := range st.Subnets {
		out = append(out, s.presentSubnet(sn, st, leases))
	}
	writeJSON(w, http.StatusOK, out)
	return nil
}

// subnetRef finds a subnet by ID, name or prefix (10.0.10.0/24 or
// 10.0.10.0_24 in a path).
func subnetRef(st *model.State, ref string) (*model.Subnet, error) {
	if sn := st.FindSubnet(strings.Replace(ref, "_", "/", 1)); sn != nil {
		return sn, nil
	}
	return nil, notFound("no subnet %q (give its ID, name or prefix)", ref)
}

func (s *Server) getSubnet(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	st := s.eng.State()
	sn, err := subnetRef(st, r.PathValue("ref"))
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, s.presentSubnet(sn, st, s.dhcp.Leases()))
	return nil
}

// applySubnetInput sets the given fields.
func applySubnetInput(sn *model.Subnet, in *api.SubnetInput) error {
	if in.Name != nil {
		sn.Name = strings.TrimSpace(*in.Name)
	}
	if in.Interface != nil {
		sn.Interface = strings.TrimSpace(*in.Interface)
	}
	if in.Prefix != nil {
		pfx, err := netip.ParsePrefix(strings.TrimSpace(*in.Prefix))
		if err != nil {
			return badRequest("prefix %q: write the network as 10.0.10.0/24", *in.Prefix)
		}
		sn.Prefix = pfx
	}
	if in.Pools != nil {
		sn.Pools = []model.Pool{}
		for _, ps := range *in.Pools {
			pool, err := model.ParsePool(ps)
			if err != nil {
				return badRequest("%v", err)
			}
			sn.Pools = append(sn.Pools, pool)
		}
	}
	if in.LeaseTime != nil {
		sn.LeaseTime = *in.LeaseTime
	}
	if in.Options != nil {
		opts, err := optionsFrom(*in.Options)
		if err != nil {
			return err
		}
		sn.Options = opts
	}
	if in.Disabled != nil {
		sn.Disabled = *in.Disabled
	}
	if in.Comment != nil {
		sn.Comment = *in.Comment
	}
	return nil
}

func (s *Server) createSubnet(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	var in api.SubnetInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	if in.Prefix == nil || in.Interface == nil {
		return badRequest("a subnet needs its prefix and its interface")
	}
	var id int64
	return s.change(w, r, p, "", func(st *model.State, newID func() int64) error {
		sn := &model.Subnet{Pools: []model.Pool{}, Options: []model.OptionValue{}}
		if err := applySubnetInput(sn, &in); err != nil {
			return err
		}
		id = newID()
		sn.ID = id
		st.Subnets = append(st.Subnets, sn)
		return nil
	}, func(st *model.State) any { return st.SubnetByID(id) })
}

func (s *Server) updateSubnet(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	var in api.SubnetInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	var id int64
	return s.change(w, r, p, "", func(st *model.State, _ func() int64) error {
		sn, err := subnetRef(st, r.PathValue("ref"))
		if err != nil {
			return err
		}
		id = sn.ID
		return applySubnetInput(sn, &in)
	}, func(st *model.State) any { return st.SubnetByID(id) })
}

func (s *Server) deleteSubnet(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	return s.change(w, r, p, "", func(st *model.State, _ func() int64) error {
		sn, err := subnetRef(st, r.PathValue("ref"))
		if err != nil {
			return err
		}
		var keep []*model.Subnet
		for _, x := range st.Subnets {
			if x.ID != sn.ID {
				keep = append(keep, x)
			}
		}
		st.Subnets = keep
		// Its reservations go with it (they can't be anywhere else).
		var kr []*model.Reservation
		for _, res := range st.Reservations {
			if !sn.Prefix.Contains(res.IP) || st.SubnetFor(res.IP) != nil {
				kr = append(kr, res)
			}
		}
		st.Reservations = kr
		return nil
	}, nil)
}

// ---- reservations

func (s *Server) presentReservation(res *model.Reservation, st *model.State) api.Reservation {
	out := api.Reservation{Reservation: res}
	if sn := st.SubnetFor(res.IP); sn != nil {
		out.SubnetID, out.SubnetName = sn.ID, sn.Name
		if out.SubnetName == "" {
			out.SubnetName = sn.Prefix.String()
		}
	}
	if l := s.dhcp.Lease(res.IP); l != nil && l.ActiveAt(s.nowFn()) {
		out.Lease = s.presentLease(l, st)
	}
	return out
}

func (s *Server) listReservations(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	st := s.eng.State()
	var only *model.Subnet
	if ref := r.URL.Query().Get("subnet"); ref != "" {
		var err error
		if only, err = subnetRef(st, ref); err != nil {
			return err
		}
	}
	out := []api.Reservation{}
	for _, res := range st.Reservations {
		if only != nil && !only.Prefix.Contains(res.IP) {
			continue
		}
		out = append(out, s.presentReservation(res, st))
	}
	writeJSON(w, http.StatusOK, out)
	return nil
}

// reservationRef finds a reservation by ID, address or MAC address.
func reservationRef(st *model.State, ref string) (*model.Reservation, error) {
	if id, err := strconv.ParseInt(ref, 10, 64); err == nil {
		if res := st.ReservationByID(id); res != nil {
			return res, nil
		}
	}
	if a, err := netip.ParseAddr(ref); err == nil {
		for _, res := range st.Reservations {
			if res.IP == a {
				return res, nil
			}
		}
	}
	if m, err := model.NormalizeMAC(ref); err == nil {
		var found []*model.Reservation
		for _, res := range st.Reservations {
			if res.MAC == m {
				found = append(found, res)
			}
		}
		if len(found) == 1 {
			return found[0], nil
		}
		if len(found) > 1 {
			return nil, badRequest("%s has %d reservations; give the address or the ID", m, len(found))
		}
	}
	return nil, notFound("no reservation %q (give its ID, address or MAC address)", ref)
}

func (s *Server) getReservation(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	st := s.eng.State()
	res, err := reservationRef(st, r.PathValue("ref"))
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, s.presentReservation(res, st))
	return nil
}

func applyReservationInput(res *model.Reservation, in *api.ReservationInput) error {
	if in.MAC != nil {
		res.MAC = ""
		if strings.TrimSpace(*in.MAC) != "" {
			m, err := model.NormalizeMAC(*in.MAC)
			if err != nil {
				return badRequest("%v", err)
			}
			res.MAC = m
		}
	}
	if in.ClientID != nil {
		res.ClientID = ""
		if strings.TrimSpace(*in.ClientID) != "" {
			id, err := model.NormalizeClientID(*in.ClientID)
			if err != nil {
				return badRequest("%v", err)
			}
			res.ClientID = id
		}
	}
	if in.IP != nil {
		a, err := netip.ParseAddr(strings.TrimSpace(*in.IP))
		if err != nil || !a.Is4() {
			return badRequest("%q is not an IPv4 address", *in.IP)
		}
		res.IP = a
	}
	if in.Hostname != nil {
		res.Hostname = strings.TrimSpace(*in.Hostname)
	}
	if in.Options != nil {
		opts, err := optionsFrom(*in.Options)
		if err != nil {
			return err
		}
		res.Options = opts
	}
	if in.Comment != nil {
		res.Comment = *in.Comment
	}
	return nil
}

func (s *Server) createReservation(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	var in api.ReservationInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	if in.IP == nil {
		return badRequest("a reservation needs an address")
	}
	var id int64
	return s.change(w, r, p, "", func(st *model.State, newID func() int64) error {
		res := &model.Reservation{Options: []model.OptionValue{}}
		if err := applyReservationInput(res, &in); err != nil {
			return err
		}
		id = newID()
		res.ID = id
		st.Reservations = append(st.Reservations, res)
		return nil
	}, func(st *model.State) any {
		if res := st.ReservationByID(id); res != nil {
			return s.presentReservation(res, st)
		}
		return nil
	})
}

func (s *Server) updateReservation(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	var in api.ReservationInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	var id int64
	return s.change(w, r, p, "", func(st *model.State, _ func() int64) error {
		res, err := reservationRef(st, r.PathValue("ref"))
		if err != nil {
			return err
		}
		id = res.ID
		return applyReservationInput(res, &in)
	}, func(st *model.State) any {
		if res := st.ReservationByID(id); res != nil {
			return s.presentReservation(res, st)
		}
		return nil
	})
}

func (s *Server) deleteReservation(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	return s.change(w, r, p, "", func(st *model.State, _ func() int64) error {
		res, err := reservationRef(st, r.PathValue("ref"))
		if err != nil {
			return err
		}
		var keep []*model.Reservation
		for _, x := range st.Reservations {
			if x.ID != res.ID {
				keep = append(keep, x)
			}
		}
		st.Reservations = keep
		return nil
	}, nil)
}

// ---- history

func (s *Server) listHistory(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	hs, err := s.store.ListHistory(r.Context(), queryInt(r, "limit", 100), int64(queryInt(r, "before", 0)))
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, hs)
	return nil
}

func (s *Server) getHistory(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	id, err := pathID(r, "id")
	if err != nil {
		return err
	}
	h, err := s.store.GetHistory(r.Context(), id)
	if errors.Is(err, store.ErrNotFound) {
		return notFound("history entry %d not found", id)
	}
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, h)
	return nil
}

func (s *Server) revertHistory(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, true); err != nil {
		return err
	}
	id, err := pathID(r, "id")
	if err != nil {
		return err
	}
	res, err := s.eng.Revert(r.Context(), p, id, engine.Options{DryRun: queryBool(r, "dry_run"), Via: via(r, p)})
	if err != nil {
		s.writeErr(w, r, err, res)
		return nil
	}
	s.respondChange(w, r, res, nil, false)
	return nil
}

// ---- catalog and interfaces

func (s *Server) catalog(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	out := api.Catalog{Types: dhcp4.Types, Reserved: map[int]string{}, Roles: map[string][]string{}}
	for _, d := range dhcp4.Catalog {
		out.Options = append(out.Options, api.OptionDef{Code: int(d.Code), Name: d.Name, Type: d.Type, Help: d.Help, Common: d.Common})
	}
	for c, why := range dhcp4.Reserved {
		out.Reserved[int(c)] = why
	}
	for n, gs := range auth.Roles {
		out.Roles[n] = grantStrings(gs)
	}
	writeJSON(w, http.StatusOK, out)
	return nil
}

func (s *Server) interfaces(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	all, err := s.ifaces.All()
	if err != nil {
		return fmt.Errorf("reading the interfaces: %w", err)
	}
	st := s.eng.State()
	out := []api.HostInterface{}
	for name, ps := range all {
		hi := api.HostInterface{Name: name, Addresses: []string{}, Subnets: []int64{}}
		for _, a := range ps {
			hi.Addresses = append(hi.Addresses, a.String())
		}
		for _, sn := range st.Subnets {
			if sn.Interface == name {
				hi.Subnets = append(hi.Subnets, sn.ID)
			}
		}
		out = append(out, hi)
	}
	// Subnets may name interfaces that don't exist (yet).
	for _, sn := range st.Subnets {
		if _, ok := all[sn.Interface]; !ok && sn.Interface != "" {
			found := false
			for i := range out {
				if out[i].Name == sn.Interface {
					out[i].Subnets = append(out[i].Subnets, sn.ID)
					found = true
				}
			}
			if !found {
				out = append(out, api.HostInterface{Name: sn.Interface, Addresses: []string{}, Subnets: []int64{sn.ID}})
			}
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
	writeJSON(w, http.StatusOK, out)
	return nil
}