// Copyright (c) 2013-2016 The btcsuite developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package chain

import (
	"errors"
	"sync"
	"time"

	"github.com/btcsuite/btcd/btcjson"
	"github.com/btcsuite/btcd/chaincfg"
	"github.com/btcsuite/btcd/chaincfg/chainhash"
	"github.com/btcsuite/btcd/rpcclient"
	"github.com/btcsuite/btcutil"
	"github.com/btcsuite/btcwallet/waddrmgr"
	"github.com/btcsuite/btcwallet/wtxmgr"
)

// RPCClient represents a persistent client connection to a bitcoin RPC server
// for information regarding the current best block chain.
type RPCClient struct {
	*rpcclient.Client
	connConfig        *rpcclient.ConnConfig // Work around unexported field
	chainParams       *chaincfg.Params
	reconnectAttempts int

	enqueueNotification chan interface{}
	dequeueNotification chan interface{}
	currentBlock        chan *waddrmgr.BlockStamp

	quit    chan struct{}
	wg      sync.WaitGroup
	started bool
	quitMtx sync.Mutex
}

// NewRPCClient creates a client connection to the server described by the
// connect string.  If disableTLS is false, the remote RPC certificate must be
// provided in the certs slice.  The connection is not established immediately,
// but must be done using the Start method.  If the remote server does not
// operate on the same bitcoin network as described by the passed chain
// parameters, the connection will be disconnected.
func NewRPCClient(chainParams *chaincfg.Params, connect, user, pass string, certs []byte,
	disableTLS bool, reconnectAttempts int) (*RPCClient, error) {

	if reconnectAttempts < 0 {
		return nil, errors.New("reconnectAttempts must be positive")
	}

	client := &RPCClient{
		connConfig: &rpcclient.ConnConfig{
			Host:                 connect,
			Endpoint:             "ws",
			User:                 user,
			Pass:                 pass,
			Certificates:         certs,
			DisableAutoReconnect: false,
			DisableConnectOnNew:  true,
			DisableTLS:           disableTLS,
		},
		chainParams:         chainParams,
		reconnectAttempts:   reconnectAttempts,
		enqueueNotification: make(chan interface{}),
		dequeueNotification: make(chan interface{}),
		currentBlock:        make(chan *waddrmgr.BlockStamp),
		quit:                make(chan struct{}),
	}
	ntfnCallbacks := &rpcclient.NotificationHandlers{
		OnClientConnected:   client.onClientConnect,
		OnBlockConnected:    client.onBlockConnected,
		OnBlockDisconnected: client.onBlockDisconnected,
		OnRecvTx:            client.onRecvTx,
		OnRedeemingTx:       client.onRedeemingTx,
		OnRescanFinished:    client.onRescanFinished,
		OnRescanProgress:    client.onRescanProgress,
	}
	rpcClient, err := rpcclient.New(client.connConfig, ntfnCallbacks)
	if err != nil {
		return nil, err
	}
	client.Client = rpcClient
	return client, nil
}

// BackEnd returns the name of the driver.
func (c *RPCClient) BackEnd() string {
	return "btcd"
}

// Start attempts to establish a client connection with the remote server.
// If successful, handler goroutines are started to process notifications
// sent by the server.  After a limited number of connection attempts, this
// function gives up, and therefore will not block forever waiting for the
// connection to be established to a server that may not exist.
func (c *RPCClient) Start() error {
	err := c.Connect(c.reconnectAttempts)
	if err != nil {
		return err
	}

	// Verify that the server is running on the expected network.
	net, err := c.GetCurrentNet()
	if err != nil {
		c.Disconnect()
		return err
	}
	if net != c.chainParams.Net {
		c.Disconnect()
		return errors.New("mismatched networks")
	}

	c.quitMtx.Lock()
	c.started = true
	c.quitMtx.Unlock()

	c.wg.Add(1)
	go c.handler()
	return nil
}

// Stop disconnects the client and signals the shutdown of all goroutines
// started by Start.
func (c *RPCClient) Stop() {
	c.quitMtx.Lock()
	select {
	case <-c.quit:
	default:
		close(c.quit)
		c.Client.Shutdown()

		if !c.started {
			close(c.dequeueNotification)
		}
	}
	c.quitMtx.Unlock()
}

// WaitForShutdown blocks until both the client has finished disconnecting
// and all handlers have exited.
func (c *RPCClient) WaitForShutdown() {
	c.Client.WaitForShutdown()
	c.wg.Wait()
}

// Notifications returns a channel of parsed notifications sent by the remote
// bitcoin RPC server.  This channel must be continually read or the process
// may abort for running out memory, as unread notifications are queued for
// later reads.
func (c *RPCClient) Notifications() <-chan interface{} {
	return c.dequeueNotification
}

// BlockStamp returns the latest block notified by the client, or an error
// if the client has been shut down.
func (c *RPCClient) BlockStamp() (*waddrmgr.BlockStamp, error) {
	select {
	case bs := <-c.currentBlock:
		return bs, nil
	case <-c.quit:
		return nil, errors.New("disconnected")
	}
}

// parseBlock parses a btcws definition of the block a tx is mined it to the
// Block structure of the wtxmgr package, and the block index.  This is done
// here since rpcclient doesn't parse this nicely for us.
func parseBlock(block *btcjson.BlockDetails) (*wtxmgr.BlockMeta, error) {
	if block == nil {
		return nil, nil
	}
	blkHash, err := chainhash.NewHashFromStr(block.Hash)
	if err != nil {
		return nil, err
	}
	blk := &wtxmgr.BlockMeta{
		Block: wtxmgr.Block{
			Height: block.Height,
			Hash:   *blkHash,
		},
		Time: time.Unix(block.Time, 0),
	}
	return blk, nil
}

func (c *RPCClient) onClientConnect() {
	select {
	case c.enqueueNotification <- ClientConnected{}:
	case <-c.quit:
	}
}

func (c *RPCClient) onBlockConnected(hash *chainhash.Hash, height int32, time time.Time) {
	select {
	case c.enqueueNotification <- BlockConnected{
		Block: wtxmgr.Block{
			Hash:   *hash,
			Height: height,
		},
		Time: time,
	}:
	case <-c.quit:
	}
}

func (c *RPCClient) onBlockDisconnected(hash *chainhash.Hash, height int32, time time.Time) {
	select {
	case c.enqueueNotification <- BlockDisconnected{
		Block: wtxmgr.Block{
			Hash:   *hash,
			Height: height,
		},
		Time: time,
	}:
	case <-c.quit:
	}
}

func (c *RPCClient) onRecvTx(tx *btcutil.Tx, block *btcjson.BlockDetails) {
	blk, err := parseBlock(block)
	if err != nil {
		// Log and drop improper notification.
		log.Errorf("recvtx notification bad block: %v", err)
		return
	}

	rec, err := wtxmgr.NewTxRecordFromMsgTx(tx.MsgTx(), time.Now())
	if err != nil {
		log.Errorf("Cannot create transaction record for relevant "+
			"tx: %v", err)
		return
	}
	select {
	case c.enqueueNotification <- RelevantTx{rec, blk}:
	case <-c.quit:
	}
}

func (c *RPCClient) onRedeemingTx(tx *btcutil.Tx, block *btcjson.BlockDetails) {
	// Handled exactly like recvtx notifications.
	c.onRecvTx(tx, block)
}

func (c *RPCClient) onRescanProgress(hash *chainhash.Hash, height int32, blkTime time.Time) {
	select {
	case c.enqueueNotification <- &RescanProgress{hash, height, blkTime}:
	case <-c.quit:
	}
}

func (c *RPCClient) onRescanFinished(hash *chainhash.Hash, height int32, blkTime time.Time) {
	select {
	case c.enqueueNotification <- &RescanFinished{hash, height, blkTime}:
	case <-c.quit:
	}

}

// handler maintains a queue of notifications and the current state (best
// block) of the chain.
func (c *RPCClient) handler() {
	hash, height, err := c.GetBestBlock()
	if err != nil {
		log.Errorf("Failed to receive best block from chain server: %v", err)
		c.Stop()
		c.wg.Done()
		return
	}

	bs := &waddrmgr.BlockStamp{Hash: *hash, Height: height}

	// TODO: Rather than leaving this as an unbounded queue for all types of
	// notifications, try dropping ones where a later enqueued notification
	// can fully invalidate one waiting to be processed.  For example,
	// blockconnected notifications for greater block heights can remove the
	// need to process earlier blockconnected notifications still waiting
	// here.

	var notifications []interface{}
	enqueue := c.enqueueNotification
	var dequeue chan interface{}
	var next interface{}
	pingChan := time.After(time.Minute)
	pingChanReset := make(chan (<-chan time.Time))
out:
	for {
		select {
		case n, ok := <-enqueue:
			if !ok {
				// If no notifications are queued for handling,
				// the queue is finished.
				if len(notifications) == 0 {
					break out
				}
				// nil channel so no more reads can occur.
				enqueue = nil
				continue
			}
			if len(notifications) == 0 {
				next = n
				dequeue = c.dequeueNotification
			}
			notifications = append(notifications, n)
			pingChan = time.After(time.Minute)

		case dequeue <- next:
			if n, ok := next.(BlockConnected); ok {
				bs = &waddrmgr.BlockStamp{
					Height: n.Height,
					Hash:   n.Hash,
				}
			}

			notifications[0] = nil
			notifications = notifications[1:]
			if len(notifications) != 0 {
				next = notifications[0]
			} else {
				// If no more notifications can be enqueued, the
				// queue is finished.
				if enqueue == nil {
					break out
				}
				dequeue = nil
			}

		case <-pingChan:
			// No notifications were received in the last 60s. Ensure the
			// connection is still active by making a new request to the server.
			//
			// This MUST wait for the response in a new goroutine so as to not
			// block channel sends enqueueing more notifications.  Doing so
			// would cause a deadlock and after the timeout expires, the client
			// would be shut down.
			//
			// TODO: A minute timeout is used to prevent the handler loop from
			// blocking here forever, but this is much larger than it needs to
			// be due to dcrd processing websocket requests synchronously (see
			// https://github.com/roasbeef/btcd/issues/504).  Decrease this to
			// something saner like 3s when the above issue is fixed.
			type sessionResult struct {
				err error
			}
			sessionResponse := make(chan sessionResult, 1)
			go func() {
				_, err := c.Session()
				sessionResponse <- sessionResult{err}
			}()
			go func() {
				select {
				case resp := <-sessionResponse:
					if resp.err != nil {
						log.Errorf("Failed to receive session "+
							"result: %v", resp.err)
						c.Stop()
					}
					pingChanReset <- time.After(time.Minute)

				case <-time.After(time.Minute):
					log.Errorf("Timeout waiting for session RPC")
					c.Stop()
				}
			}()

		case ch := <-pingChanReset:
			pingChan = ch

		case c.currentBlock <- bs:

		case <-c.quit:
			break out
		}
	}

	c.Stop()
	close(c.dequeueNotification)
	c.wg.Done()
}

// POSTClient creates the equivalent HTTP POST rpcclient.Client.
func (c *RPCClient) POSTClient() (*rpcclient.Client, error) {
	configCopy := *c.connConfig
	configCopy.HTTPPostMode = true
	return rpcclient.New(&configCopy, nil)
}