// Copyright (c) 2014 Conformal Systems LLC.
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package main

import (
	"fmt"
	"math/rand"
	"runtime"
	"sync"
	"time"

	"github.com/btcsuite/btcd/blockchain"
	"github.com/btcsuite/btcd/wire"
	"github.com/btcsuite/btcutil"
)

const (
	// maxNonce is the maximum value a nonce can be in a block header.
	maxNonce = ^uint32(0) // 2^32 - 1

	// maxExtraNonce is the maximum value an extra nonce used in a coinbase
	// transaction can be.
	maxExtraNonce = ^uint64(0) // 2^64 - 1

	// hpsUpdateSecs is the number of seconds to wait in between each
	// update to the hashes per second monitor.
	hpsUpdateSecs = 10

	// hashUpdateSec is the number of seconds each worker waits in between
	// notifying the speed monitor with how many hashes have been completed
	// while they are actively searching for a solution.  This is done to
	// reduce the amount of syncs between the workers that must be done to
	// keep track of the hashes per second.
	hashUpdateSecs = 15
)

var (
	// defaultNumWorkers is the default number of workers to use for mining
	// and is based on the number of processor cores.  This helps ensure the
	// system stays reasonably responsive under heavy load.
	defaultNumWorkers = uint32(runtime.NumCPU())
)

// CPUMiner provides facilities for solving blocks (mining) using the CPU in
// a concurrency-safe manner.  It consists of two main goroutines -- a speed
// monitor and a controller for worker goroutines which generate and solve
// blocks.  The number of goroutines can be set via the SetMaxGoRoutines
// function, but the default is based on the number of processor cores in the
// system which is typically sufficient.
type CPUMiner struct {
	sync.Mutex
	server            *server
	numWorkers        uint32
	started           bool
	submitBlockLock   sync.Mutex
	wg                sync.WaitGroup
	workerWg          sync.WaitGroup
	updateNumWorkers  chan struct{}
	queryHashesPerSec chan float64
	updateHashes      chan uint64
	speedMonitorQuit  chan struct{}
	quit              chan struct{}
}

// speedMonitor handles tracking the number of hashes per second the mining
// process is performing.  It must be run as a goroutine.
func (m *CPUMiner) speedMonitor() {
	minrLog.Tracef("CPU miner speed monitor started")

	var hashesPerSec float64
	var totalHashes uint64
	ticker := time.NewTicker(time.Second * hpsUpdateSecs)
	defer ticker.Stop()

out:
	for {
		select {
		// Periodic updates from the workers with how many hashes they
		// have performed.
		case numHashes := <-m.updateHashes:
			totalHashes += numHashes

		// Time to update the hashes per second.
		case <-ticker.C:
			curHashesPerSec := float64(totalHashes) / hpsUpdateSecs
			if hashesPerSec == 0 {
				hashesPerSec = curHashesPerSec
			}
			hashesPerSec = (hashesPerSec + curHashesPerSec) / 2
			totalHashes = 0
			if hashesPerSec != 0 {
				minrLog.Debugf("Hash speed: %6.0f kilohashes/s",
					hashesPerSec/1000)
			}

		// Request for the number of hashes per second.
		case m.queryHashesPerSec <- hashesPerSec:
			// Nothing to do.

		case <-m.speedMonitorQuit:
			break out
		}
	}

	m.wg.Done()
	minrLog.Tracef("CPU miner speed monitor done")
}

// submitBlock submits the passed block to network after ensuring it passes all
// of the consensus validation rules.
func (m *CPUMiner) submitBlock(block *btcutil.Block) bool {
	m.submitBlockLock.Lock()
	defer m.submitBlockLock.Unlock()

	// Ensure the block is not stale since a new block could have shown up
	// while the solution was being found.  Typically that condition is
	// detected and all work on the stale block is halted to start work on
	// a new block, but the check only happens periodically, so it is
	// possible a block was found and submitted in between.
	latestHash, _ := m.server.blockManager.chainState.Best()
	msgBlock := block.MsgBlock()
	if !msgBlock.Header.PrevBlock.IsEqual(latestHash) {
		minrLog.Debugf("Block submitted via CPU miner with previous "+
			"block %s is stale", msgBlock.Header.PrevBlock)
		return false
	}

	// Process this block using the same rules as blocks coming from other
	// nodes.  This will in turn relay it to the network like normal.
	isOrphan, err := m.server.blockManager.ProcessBlock(block, blockchain.BFNone)
	if err != nil {
		// Anything other than a rule violation is an unexpected error,
		// so log that error as an internal error.
		if _, ok := err.(blockchain.RuleError); !ok {
			minrLog.Errorf("Unexpected error while processing "+
				"block submitted via CPU miner: %v", err)
			return false
		}

		minrLog.Debugf("Block submitted via CPU miner rejected: %v", err)
		return false
	}
	if isOrphan {
		minrLog.Debugf("Block submitted via CPU miner is an orphan")
		return false
	}

	// The block was accepted.
	coinbaseTx := block.MsgBlock().Transactions[0].TxOut[0]
	minrLog.Infof("Block submitted via CPU miner accepted (hash %s, "+
		"amount %v)", block.Sha(), btcutil.Amount(coinbaseTx.Value))
	return true
}

// solveBlock attempts to find some combination of a nonce, extra nonce, and
// current timestamp which makes the passed block hash to a value less than the
// target difficulty.  The timestamp is updated periodically and the passed
// block is modified with all tweaks during this process.  This means that
// when the function returns true, the block is ready for submission.
//
// This function will return early with false when conditions that trigger a
// stale block such as a new block showing up or periodically when there are
// new transactions and enough time has elapsed without finding a solution.
func (m *CPUMiner) solveBlock(msgBlock *wire.MsgBlock, blockHeight int64,
	ticker *time.Ticker, quit chan struct{}) bool {

	// Choose a random extra nonce offset for this block template and
	// worker.
	enOffset, err := wire.RandomUint64()
	if err != nil {
		minrLog.Errorf("Unexpected error while generating random "+
			"extra nonce offset: %v", err)
		enOffset = 0
	}

	// Create a couple of convenience variables.
	header := &msgBlock.Header
	targetDifficulty := blockchain.CompactToBig(header.Bits)

	// Initial state.
	lastGenerated := time.Now()
	lastTxUpdate := m.server.txMemPool.LastUpdated()
	hashesCompleted := uint64(0)

	// Note that the entire extra nonce range is iterated and the offset is
	// added relying on the fact that overflow will wrap around 0 as
	// provided by the Go spec.
	for extraNonce := uint64(0); extraNonce < maxExtraNonce; extraNonce++ {
		// Update the extra nonce in the block template with the
		// new value by regenerating the coinbase script and
		// setting the merkle root to the new value.  The
		UpdateExtraNonce(msgBlock, blockHeight, extraNonce+enOffset)

		// Search through the entire nonce range for a solution while
		// periodically checking for early quit and stale block
		// conditions along with updates to the speed monitor.
		for i := uint32(0); i <= maxNonce; i++ {
			select {
			case <-quit:
				return false

			case <-ticker.C:
				m.updateHashes <- hashesCompleted
				hashesCompleted = 0

				// The current block is stale if the best block
				// has changed.
				bestHash, _ := m.server.blockManager.chainState.Best()
				if !header.PrevBlock.IsEqual(bestHash) {
					return false
				}

				// The current block is stale if the memory pool
				// has been updated since the block template was
				// generated and it has been at least one
				// minute.
				if lastTxUpdate != m.server.txMemPool.LastUpdated() &&
					time.Now().After(lastGenerated.Add(time.Minute)) {

					return false
				}

				UpdateBlockTime(msgBlock, m.server.blockManager)

			default:
				// Non-blocking select to fall through
			}

			// Update the nonce and hash the block header.  Each
			// hash is actually a double sha256 (two hashes), so
			// increment the number of hashes completed for each
			// attempt accordingly.
			header.Nonce = i
			hash := header.BlockSha()
			hashesCompleted += 2

			// The block is solved when the new block hash is less
			// than the target difficulty.  Yay!
			if blockchain.ShaHashToBig(&hash).Cmp(targetDifficulty) <= 0 {
				m.updateHashes <- hashesCompleted
				return true
			}
		}
	}

	return false
}

// generateBlocks is a worker that is controlled by the miningWorkerController.
// It is self contained in that it creates block templates and attempts to solve
// them while detecting when it is performing stale work and reacting
// accordingly by generating a new block template.  When a block is solved, it
// is submitted.
//
// It must be run as a goroutine.
func (m *CPUMiner) generateBlocks(quit chan struct{}) {
	minrLog.Tracef("Starting generate blocks worker")

	// Start a ticker which is used to signal checks for stale work and
	// updates to the speed monitor.
	ticker := time.NewTicker(time.Second * hashUpdateSecs)
	defer ticker.Stop()
out:
	for {
		// Quit when the miner is stopped.
		select {
		case <-quit:
			break out
		default:
			// Non-blocking select to fall through
		}

		// Wait until there is a connection to at least one other peer
		// since there is no way to relay a found block or receive
		// transactions to work on when there are no connected peers.
		if m.server.ConnectedCount() == 0 {
			time.Sleep(time.Second)
			continue
		}

		// No point in searching for a solution before the chain is
		// synced.  Also, grab the same lock as used for block
		// submission, since the current block will be changing and
		// this would otherwise end up building a new block template on
		// a block that is in the process of becoming stale.
		m.submitBlockLock.Lock()
		_, curHeight := m.server.blockManager.chainState.Best()
		if curHeight != 0 && !m.server.blockManager.IsCurrent() {
			m.submitBlockLock.Unlock()
			time.Sleep(time.Second)
			continue
		}

		// Choose a payment address at random.
		rand.Seed(time.Now().UnixNano())
		payToAddr := cfg.miningAddrs[rand.Intn(len(cfg.miningAddrs))]

		// Create a new block template using the available transactions
		// in the memory pool as a source of transactions to potentially
		// include in the block.
		template, err := NewBlockTemplate(m.server.txMemPool, payToAddr)
		m.submitBlockLock.Unlock()
		if err != nil {
			errStr := fmt.Sprintf("Failed to create new block "+
				"template: %v", err)
			minrLog.Errorf(errStr)
			continue
		}

		// Attempt to solve the block.  The function will exit early
		// with false when conditions that trigger a stale block, so
		// a new block template can be generated.  When the return is
		// true a solution was found, so submit the solved block.
		if m.solveBlock(template.block, curHeight+1, ticker, quit) {
			block := btcutil.NewBlock(template.block)
			m.submitBlock(block)
		}
	}

	m.workerWg.Done()
	minrLog.Tracef("Generate blocks worker done")
}

// miningWorkerController launches the worker goroutines that are used to
// generate block templates and solve them.  It also provides the ability to
// dynamically adjust the number of running worker goroutines.
//
// It must be run as a goroutine.
func (m *CPUMiner) miningWorkerController() {
	// launchWorkers groups common code to launch a specified number of
	// workers for generating blocks.
	var runningWorkers []chan struct{}
	launchWorkers := func(numWorkers uint32) {
		for i := uint32(0); i < numWorkers; i++ {
			quit := make(chan struct{})
			runningWorkers = append(runningWorkers, quit)

			m.workerWg.Add(1)
			go m.generateBlocks(quit)
		}
	}

	// Launch the current number of workers by default.
	runningWorkers = make([]chan struct{}, 0, m.numWorkers)
	launchWorkers(m.numWorkers)

out:
	for {
		select {
		// Update the number of running workers.
		case <-m.updateNumWorkers:
			// No change.
			numRunning := uint32(len(runningWorkers))
			if m.numWorkers == numRunning {
				continue
			}

			// Add new workers.
			if m.numWorkers > numRunning {
				launchWorkers(m.numWorkers - numRunning)
				continue
			}

			// Signal the most recently created goroutines to exit.
			for i := numRunning - 1; i >= m.numWorkers; i-- {
				close(runningWorkers[i])
				runningWorkers[i] = nil
				runningWorkers = runningWorkers[:i]
			}

		case <-m.quit:
			for _, quit := range runningWorkers {
				close(quit)
			}
			break out
		}
	}

	// Wait until all workers shut down to stop the speed monitor since
	// they rely on being able to send updates to it.
	m.workerWg.Wait()
	close(m.speedMonitorQuit)
	m.wg.Done()
}

// Start begins the CPU mining process as well as the speed monitor used to
// track hashing metrics.  Calling this function when the CPU miner has
// already been started will have no effect.
//
// This function is safe for concurrent access.
func (m *CPUMiner) Start() {
	m.Lock()
	defer m.Unlock()

	// Nothing to do if the miner is already running.
	if m.started {
		return
	}

	m.quit = make(chan struct{})
	m.speedMonitorQuit = make(chan struct{})
	m.wg.Add(2)
	go m.speedMonitor()
	go m.miningWorkerController()

	m.started = true
	minrLog.Infof("CPU miner started")
}

// Stop gracefully stops the mining process by signalling all workers, and the
// speed monitor to quit.  Calling this function when the CPU miner has not
// already been started will have no effect.
//
// This function is safe for concurrent access.
func (m *CPUMiner) Stop() {
	m.Lock()
	defer m.Unlock()

	// Nothing to do if the miner is not currently running.
	if !m.started {
		return
	}

	close(m.quit)
	m.wg.Wait()
	m.started = false
	minrLog.Infof("CPU miner stopped")
}

// IsMining returns whether or not the CPU miner has been started and is
// therefore currenting mining.
//
// This function is safe for concurrent access.
func (m *CPUMiner) IsMining() bool {
	m.Lock()
	defer m.Unlock()

	return m.started
}

// HashesPerSecond returns the number of hashes per second the mining process
// is performing.  0 is returned if the miner is not currently running.
//
// This function is safe for concurrent access.
func (m *CPUMiner) HashesPerSecond() float64 {
	m.Lock()
	defer m.Unlock()

	// Nothing to do if the miner is not currently running.
	if !m.started {
		return 0
	}

	return <-m.queryHashesPerSec
}

// SetNumWorkers sets the number of workers to create which solve blocks.  Any
// negative values will cause a default number of workers to be used which is
// based on the number of processor cores in the system.  A value of 0 will
// cause all CPU mining to be stopped.
//
// This function is safe for concurrent access.
func (m *CPUMiner) SetNumWorkers(numWorkers int32) {
	if numWorkers == 0 {
		m.Stop()
	}

	// Don't lock until after the first check since Stop does its own
	// locking.
	m.Lock()
	defer m.Unlock()

	// Use default if provided value is negative.
	if numWorkers < 0 {
		m.numWorkers = defaultNumWorkers
	} else {
		m.numWorkers = uint32(numWorkers)
	}

	// When the miner is already running, notify the controller about the
	// the change.
	if m.started {
		m.updateNumWorkers <- struct{}{}
	}
}

// NumWorkers returns the number of workers which are running to solve blocks.
//
// This function is safe for concurrent access.
func (m *CPUMiner) NumWorkers() int32 {
	m.Lock()
	defer m.Unlock()

	return int32(m.numWorkers)
}

// newCPUMiner returns a new instance of a CPU miner for the provided server.
// Use Start to begin the mining process.  See the documentation for CPUMiner
// type for more details.
func newCPUMiner(s *server) *CPUMiner {
	return &CPUMiner{
		server:            s,
		numWorkers:        defaultNumWorkers,
		updateNumWorkers:  make(chan struct{}),
		queryHashesPerSec: make(chan float64),
		updateHashes:      make(chan uint64),
	}
}
