// Copyright 2018 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// This package implements support for smartcard-based hardware wallets such as
// the one written by Status: https://github.com/status-im/hardware-wallet
//
// This implementation of smartcard wallets have a different interaction process
// to other types of hardware wallet. The process works like this:
//
// 1. (First use with a given client) Establish a pairing between hardware
//    wallet and client. This requires a secret value called a 'PUK'. You can
//    pair with an unpaired wallet with `personal.openWallet(URI, PUK)`.
// 2. (First use only) Initialize the wallet, which generates a keypair, stores
//    it on the wallet, and returns it so the user can back it up. You can
//    initialize a wallet with `personal.initializeWallet(URI)`.
// 3. Connect to the wallet using the pairing information established in step 1.
//    You can connect to a paired wallet with `personal.openWallet(URI, PIN)`.
// 4. Interact with the wallet as normal.

package scwallet

import (
	"encoding/json"
	"io/ioutil"
	"os"
	"sort"
	"sync"
	"time"

	"github.com/ebfe/scard"
	"github.com/ethereum/go-ethereum/accounts"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/event"
	"github.com/ethereum/go-ethereum/log"
)

// Scheme is the URI prefix for smartcard wallets.
const Scheme = "pcsc"

// refreshCycle is the maximum time between wallet refreshes (if USB hotplug
// notifications don't work).
const refreshCycle = time.Second

// refreshThrottling is the minimum time between wallet refreshes to avoid thrashing.
const refreshThrottling = 500 * time.Millisecond

// smartcardPairing contains information about a smart card we have paired with
// or might pair with the hub.
type smartcardPairing struct {
	PublicKey    []byte                                     `json:"publicKey"`
	PairingIndex uint8                                      `json:"pairingIndex"`
	PairingKey   []byte                                     `json:"pairingKey"`
	Accounts     map[common.Address]accounts.DerivationPath `json:"accounts"`
}

// Hub is a accounts.Backend that can find and handle generic PC/SC hardware wallets.
type Hub struct {
	scheme string // Protocol scheme prefixing account and wallet URLs.

	context  *scard.Context
	datadir  string
	pairings map[string]smartcardPairing

	refreshed   time.Time               // Time instance when the list of wallets was last refreshed
	wallets     map[string]*Wallet      // Mapping from reader names to wallet instances
	updateFeed  event.Feed              // Event feed to notify wallet additions/removals
	updateScope event.SubscriptionScope // Subscription scope tracking current live listeners
	updating    bool                    // Whether the event notification loop is running

	quit chan chan error

	stateLock sync.RWMutex // Protects the internals of the hub from racey access
}

func (hub *Hub) readPairings() error {
	hub.pairings = make(map[string]smartcardPairing)
	pairingFile, err := os.Open(hub.datadir + "/smartcards.json")
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return err
	}

	pairingData, err := ioutil.ReadAll(pairingFile)
	if err != nil {
		return err
	}
	var pairings []smartcardPairing
	if err := json.Unmarshal(pairingData, &pairings); err != nil {
		return err
	}

	for _, pairing := range pairings {
		hub.pairings[string(pairing.PublicKey)] = pairing
	}
	return nil
}

func (hub *Hub) writePairings() error {
	pairingFile, err := os.OpenFile(hub.datadir+"/smartcards.json", os.O_RDWR|os.O_CREATE, 0755)
	if err != nil {
		return err
	}

	pairings := make([]smartcardPairing, 0, len(hub.pairings))
	for _, pairing := range hub.pairings {
		pairings = append(pairings, pairing)
	}

	pairingData, err := json.Marshal(pairings)
	if err != nil {
		return err
	}

	if _, err := pairingFile.Write(pairingData); err != nil {
		return err
	}

	return pairingFile.Close()
}

func (hub *Hub) pairing(wallet *Wallet) *smartcardPairing {
	pairing, ok := hub.pairings[string(wallet.PublicKey)]
	if ok {
		return &pairing
	}
	return nil
}

func (hub *Hub) setPairing(wallet *Wallet, pairing *smartcardPairing) error {
	if pairing == nil {
		delete(hub.pairings, string(wallet.PublicKey))
	} else {
		hub.pairings[string(wallet.PublicKey)] = *pairing
	}
	return hub.writePairings()
}

// NewHub creates a new hardware wallet manager for smartcards.
func NewHub(scheme string, datadir string) (*Hub, error) {
	context, err := scard.EstablishContext()
	if err != nil {
		return nil, err
	}
	hub := &Hub{
		scheme:  scheme,
		context: context,
		datadir: datadir,
		wallets: make(map[string]*Wallet),
		quit:    make(chan chan error),
	}
	if err := hub.readPairings(); err != nil {
		return nil, err
	}
	hub.refreshWallets()
	return hub, nil
}

// Wallets implements accounts.Backend, returning all the currently tracked smart
// cards that appear to be hardware wallets.
func (hub *Hub) Wallets() []accounts.Wallet {
	// Make sure the list of wallets is up to date
	hub.refreshWallets()

	hub.stateLock.RLock()
	defer hub.stateLock.RUnlock()

	cpy := make([]accounts.Wallet, 0, len(hub.wallets))
	for _, wallet := range hub.wallets {
		cpy = append(cpy, wallet)
	}
	sort.Sort(accounts.WalletsByURL(cpy))
	return cpy
}

// refreshWallets scans the devices attached to the machine and updates the
// list of wallets based on the found devices.
func (hub *Hub) refreshWallets() {
	// Don't scan the USB like crazy it the user fetches wallets in a loop
	hub.stateLock.RLock()
	elapsed := time.Since(hub.refreshed)
	hub.stateLock.RUnlock()

	if elapsed < refreshThrottling {
		return
	}
	// Retrieve all the smart card reader to check for cards
	readers, err := hub.context.ListReaders()
	if err != nil {
		// This is a perverted hack, the scard library returns an error if no card
		// readers are present instead of simply returning an empty list. We don't
		// want to fill the user's log with errors, so filter those out.
		if err.Error() != "scard: Cannot find a smart card reader." {
			log.Error("Failed to enumerate smart card readers", "err", err)
		}
	}
	// Transform the current list of wallets into the new one
	hub.stateLock.Lock()

	events := []accounts.WalletEvent{}
	seen := make(map[string]struct{})

	for _, reader := range readers {
		// Mark the reader as present
		seen[reader] = struct{}{}

		// If we alreay know about this card, skip to the next reader, otherwise clean up
		if wallet, ok := hub.wallets[reader]; ok {
			if err := wallet.ping(); err == nil {
				continue
			}
			wallet.Close()
			events = append(events, accounts.WalletEvent{Wallet: wallet, Kind: accounts.WalletDropped})
			delete(hub.wallets, reader)
		}
		// New card detected, try to connect to it
		card, err := hub.context.Connect(reader, scard.ShareShared, scard.ProtocolAny)
		if err != nil {
			log.Debug("Failed to open smart card", "reader", reader, "err", err)
			continue
		}
		wallet := NewWallet(hub, card)
		if err = wallet.connect(); err != nil {
			log.Debug("Failed to connect to smart card", "reader", reader, "err", err)
			card.Disconnect(scard.LeaveCard)
			continue
		}
		// Card connected, start tracking in amongs the wallets
		hub.wallets[reader] = wallet
		events = append(events, accounts.WalletEvent{Wallet: wallet, Kind: accounts.WalletArrived})
	}
	// Remove any wallets no longer present
	for reader, wallet := range hub.wallets {
		if _, ok := seen[reader]; !ok {
			wallet.Close()
			events = append(events, accounts.WalletEvent{Wallet: wallet, Kind: accounts.WalletDropped})
			delete(hub.wallets, reader)
		}
	}
	hub.refreshed = time.Now()
	hub.stateLock.Unlock()

	for _, event := range events {
		hub.updateFeed.Send(event)
	}
}

// Subscribe implements accounts.Backend, creating an async subscription to
// receive notifications on the addition or removal of smart card wallets.
func (hub *Hub) Subscribe(sink chan<- accounts.WalletEvent) event.Subscription {
	// We need the mutex to reliably start/stop the update loop
	hub.stateLock.Lock()
	defer hub.stateLock.Unlock()

	// Subscribe the caller and track the subscriber count
	sub := hub.updateScope.Track(hub.updateFeed.Subscribe(sink))

	// Subscribers require an active notification loop, start it
	if !hub.updating {
		hub.updating = true
		go hub.updater()
	}
	return sub
}

// updater is responsible for maintaining an up-to-date list of wallets managed
// by the smart card hub, and for firing wallet addition/removal events.
func (hub *Hub) updater() {
	for {
		// TODO: Wait for a USB hotplug event (not supported yet) or a refresh timeout
		// <-hub.changes
		time.Sleep(refreshCycle)

		// Run the wallet refresher
		hub.refreshWallets()

		// If all our subscribers left, stop the updater
		hub.stateLock.Lock()
		if hub.updateScope.Count() == 0 {
			hub.updating = false
			hub.stateLock.Unlock()
			return
		}
		hub.stateLock.Unlock()
	}
}