/*
 *  Copyright (c) 2026 Kaiy Ragur
 *
 *  This Source Code Form is subject to the terms of the Mozilla Public
 *  License, v. 2.0. If a copy of the MPL was not distributed with this
 *  file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
package remote

import (
	"crypto/ed25519"
	"fmt"
	"sync"
	"time"

	pb "github.com/neilalexander/yggmail/internal/remote/types"
	"github.com/neilalexander/yggmail/internal/utils"
	"google.golang.org/protobuf/proto"
)

type ReqValidator struct {
	r      map[string]time.Time
	m      sync.RWMutex
	window time.Duration
}

func NewValidator(window time.Duration) *ReqValidator {
	r := &ReqValidator{
		window: window,
		r:      map[string]time.Time{},
	}
	go r.Cleaner()
	return r
}
func (rv *ReqValidator) Validate(req *pb.Request, pub ed25519.PublicKey) (bool, error) {
	diff := time.Since(time.Unix(0, req.Timestamp))
	if diff < 0 {
		diff = -diff
	}
	if diff > rv.window {
		return false, fmt.Errorf("request timestamp is too old or too far in future")
	}

	ok, err := VerifyRequest(req, pub)
	if err != nil || !ok {
		return false, err
	}
	rv.m.Lock()
	defer rv.m.Unlock()

	if _, exist := rv.r[utils.EncodeString(req.Signature)]; exist {
		return false, nil
	}
	rv.r[utils.EncodeString(req.Signature)] = time.Now()
	return true, nil
}

func (rv *ReqValidator) Cleaner() {
	for tn := range time.NewTicker(time.Minute).C {
		rv.clean(tn)
	}
}

func (rv *ReqValidator) clean(tn time.Time) {
	rv.m.Lock()
	defer rv.m.Unlock()
	for s, tr := range rv.r {
		if tr.Add(rv.window).Before(tn) {
			delete(rv.r, s)
		}
	}
}

type Signer func([]byte) ([]byte, error)

func PrepareToSign(req *pb.Request) ([]byte, error) {
	clone := proto.Clone(req).(*pb.Request)

	clone.Signature = nil

	opts := proto.MarshalOptions{Deterministic: true}
	return opts.Marshal(clone)
}

func SignRequest(req *pb.Request, signer Signer) error {
	data, err := PrepareToSign(req)
	if err != nil {
		return err
	}

	req.Signature, err = signer(data)
	if err != nil {
		return err
	}
	return nil
}

func VerifyRequest(req *pb.Request, pubKey ed25519.PublicKey) (bool, error) {
	if len(req.Signature) == 0 {
		return false, fmt.Errorf("missing signature")
	}
	data, err := PrepareToSign(req)
	if err != nil {
		return false, err
	}
	if !ed25519.Verify(pubKey, data, req.Signature) {
		return false, fmt.Errorf("cryptographic signature mismatch")
	}

	return true, nil
}