package server

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

	"housecarl/internal/api"
	"housecarl/internal/engine"
	"housecarl/internal/model"
)

// Every configuration change is an operation (model.Op): applied at once,
// or staged in a changeset and replayed when the changeset is applied.
// applyOp is the one place an operation becomes an edit.

// applyOp makes an operation's change to st. It returns the ID of the
// object it made or changed (0 for deletes and settings).
func applyOp(st *model.State, op *model.Op) (int64, error) {
	switch op.Op {
	case model.OpCreate:
		return createOp(st, op)
	case model.OpUpdate:
		return updateOp(st, op)
	case model.OpDelete:
		return 0, deleteOp(st, op)
	case model.OpMove:
		return moveOp(st, op)
	case model.OpSettings:
		return 0, settingsOp(st, op)
	case model.OpRevert:
		var h model.HistoryEntry
		if err := json.Unmarshal(op.Data, &h); err != nil {
			return 0, badRequest("revert: %v", err)
		}
		return 0, engine.Undo(st, &h)
	}
	return 0, badRequest("unknown operation %q", op.Op)
}

func createOp(st *model.State, op *model.Op) (int64, error) {
	o, err := decodeObject(op.Kind, op.Data)
	if err != nil {
		return 0, err
	}
	if svc, ok := o.(*model.Service); ok {
		svc.Builtin = false
	}
	if rule, ok := o.(*model.Rule); ok && rule.Action == "" {
		rule.Action = model.ActionAccept
	}
	if f, ok := o.(*model.PortForward); ok && len(f.Protocols) == 0 {
		f.Protocols = []string{"tcp"}
	}
	if st.ByID(op.Kind, op.ID) != nil {
		return 0, conflict("%s %d exists already", op.Kind, op.ID)
	}
	setID(o, op.ID)
	if pos := position(o); pos != nil && *pos == 0 {
		*pos = lastPosition(st, op.Kind, chainOf(o))
	}
	data, _ := json.Marshal(o)
	if err := st.Put(op.Kind, op.ID, data); err != nil {
		return 0, err
	}
	// Placed in the same change, so it is never in force anywhere else.
	if len(op.Place) > 0 {
		if _, err := moveOp(st, &model.Op{Op: model.OpMove, Kind: op.Kind, Ref: strconv.FormatInt(op.ID, 10), Data: op.Place}); err != nil {
			return 0, err
		}
	}
	return op.ID, nil
}

func updateOp(st *model.State, op *model.Op) (int64, error) {
	var patch map[string]json.RawMessage
	if err := json.Unmarshal(op.Data, &patch); err != nil {
		return 0, badRequest("%s: %v", op.Kind, err)
	}
	delete(patch, "id")
	o, err := findObject(st, op.Kind, op.Ref)
	if err != nil {
		return 0, err
	}
	id := o.GetID()
	// The patch's fields over the object's.
	var cur map[string]json.RawMessage
	b, _ := json.Marshal(o)
	json.Unmarshal(b, &cur)
	for k, v := range patch {
		if string(v) == "null" {
			delete(cur, k)
		} else {
			cur[k] = v
		}
	}
	merged, _ := json.Marshal(cur)
	next, err := decodeObject(op.Kind, merged)
	if err != nil {
		return 0, err
	}
	setID(next, id)
	if old, now := o.Label(), next.Label(); old != now && isNamed(op.Kind) {
		if set, ok := o.(*model.AddressSet); ok && set.Dynamic {
			return 0, conflict("set %s is dynamic: its entries, and the API tokens and programs that fill it, go by its name; make a new set instead", old)
		}
		renameRefs(st, op.Kind, old, now)
	}
	data, _ := json.Marshal(next)
	return id, st.Put(op.Kind, id, data)
}

// isNamed reports whether other objects refer to a kind by name.
func isNamed(kind string) bool {
	return kind == model.KindZone || kind == model.KindSet || kind == model.KindService
}

func deleteOp(st *model.State, op *model.Op) error {
	o, err := findObject(st, op.Kind, op.Ref)
	if err != nil {
		return err
	}
	if used := usedBy(st, op.Kind, o); used != "" {
		return conflict("%s %s is used by %s; change that first", op.Kind, o.Label(), used)
	}
	return st.Put(op.Kind, o.GetID(), nil)
}

// moveOp reorders a rule or NAT rule: before or after another, or to the
// start or end; a rule can change chain at the same time.
func moveOp(st *model.State, op *model.Op) (int64, error) {
	var in api.MoveInput
	if err := json.Unmarshal(op.Data, &in); err != nil {
		return 0, badRequest("move: %v", err)
	}
	o, err := findObject(st, op.Kind, op.Ref)
	if err != nil {
		return 0, err
	}
	id := o.GetID()
	pos := position(o)
	if pos == nil {
		return 0, badRequest("only rules, port forwards, source NAT rules and redirects have an order")
	}
	if rule, ok := o.(*model.Rule); ok && in.Chain != "" {
		rule.Chain = in.Chain
	}
	chain := chainOf(o)
	// The others in order.
	var others []model.Object
	for _, x := range st.Objects(op.Kind) {
		if x.GetID() != id && chainOf(x) == chain {
			others = append(others, x)
		}
	}
	sort.SliceStable(others, func(i, j int) bool { return *position(others[i]) < *position(others[j]) })
	place := func(i int) { // before others[i] (i == len: at the end)
		switch {
		case len(others) == 0:
			*pos = 1
		case i == 0:
			*pos = *position(others[0]) - 1
		case i == len(others):
			*pos = *position(others[len(others)-1]) + 1
		default:
			*pos = (*position(others[i-1]) + *position(others[i])) / 2
		}
	}
	index := func(ref int64) (int, error) {
		for i, x := range others {
			if x.GetID() == ref {
				return i, nil
			}
		}
		return 0, badRequest("%d isn't another %s of the same chain", ref, op.Kind)
	}
	switch {
	case in.Before != 0:
		i, err := index(in.Before)
		if err != nil {
			return 0, err
		}
		place(i)
	case in.After != 0:
		i, err := index(in.After)
		if err != nil {
			return 0, err
		}
		place(i + 1)
	case in.To == "start":
		place(0)
	case in.To == "end" || in.Chain != "":
		place(len(others))
	default:
		return 0, badRequest("say where: before, after, or to start or end")
	}
	data, _ := json.Marshal(o)
	return id, st.Put(op.Kind, id, data)
}

func settingsOp(st *model.State, op *model.Op) error {
	var patch map[string]json.RawMessage
	if err := json.Unmarshal(op.Data, &patch); err != nil {
		return badRequest("settings: %v", err)
	}
	var cur map[string]json.RawMessage
	b, _ := json.Marshal(st.Settings)
	json.Unmarshal(b, &cur)
	for k, v := range patch {
		// Built-ins merge one by one.
		if k == "builtins" {
			var cb, pb map[string]json.RawMessage
			json.Unmarshal(cur[k], &cb)
			if err := json.Unmarshal(v, &pb); err != nil {
				return badRequest("builtins: %v", err)
			}
			for bk, bv := range pb {
				cb[bk] = bv
			}
			v, _ = json.Marshal(cb)
		}
		cur[k] = v
	}
	merged, _ := json.Marshal(cur)
	var next model.Settings
	dec := json.NewDecoder(strings.NewReader(string(merged)))
	dec.DisallowUnknownFields()
	if err := dec.Decode(&next); err != nil {
		return badRequest("settings: %v", err)
	}
	st.Settings = next
	return nil
}

// replay applies a changeset's operations to st, in order. An operation
// that fails is named in the error (opError).
func replay(st *model.State, ops []model.Op) error {
	for i := range ops {
		if _, err := applyOp(st, &ops[i]); err != nil {
			return &opError{seq: ops[i].Seq, summary: ops[i].Summary, err: err}
		}
	}
	return nil
}

// opError: an operation of a changeset that can't be applied (the
// objects it names changed since it was staged, say).
type opError struct {
	seq     int
	summary string
	err     error
}

func (e *opError) Error() string {
	return fmt.Sprintf("operation %d (%s) can't be applied: %v", e.seq, e.summary, e.err)
}

func (e *opError) Unwrap() error { return e.err }

// info is the error for the API, with the inner error's status.
func (e *opError) info() (api.ErrorInfo, int) {
	info := api.ErrorInfo{Code: "conflict", Message: e.Error(), Op: e.seq}
	status := http.StatusConflict
	var he *httpError
	if errors.As(e.err, &he) {
		info.Code, status = he.code, he.status
	}
	if ee, ok := engine.AsError(e.err); ok {
		info.Code, info.Problems, status = ee.Kind, ee.Problems, engineStatus(ee.Kind)
	}
	return info, status
}

// objectOf picks what an operation's answer returns from a state.
func objectOf(op *model.Op, id int64) func(st *model.State) any {
	switch op.Op {
	case model.OpDelete:
		return nil
	case model.OpSettings:
		return func(st *model.State) any { return st.Settings }
	}
	return func(st *model.State) any {
		if o := st.ByID(op.Kind, id); o != nil {
			return o
		}
		return nil
	}
}