// AskForOneBlock is for testing only, so you can ask for a specific block height
// and see what goes wrong
func (s *SPVCon) AskForOneBlock(h int32) error {
	var hdr wire.BlockHeader
	var err error

	dbTip := int32(h)
	s.headerMutex.Lock() // seek to header we need
	_, err = s.headerFile.Seek(int64((dbTip)*80), os.SEEK_SET)
	if err != nil {
		return err
	}
	err = hdr.Deserialize(s.headerFile) // read header, done w/ file for now
	s.headerMutex.Unlock()              // unlock after reading 1 header
	if err != nil {
		log.Printf("header deserialize error!\n")
		return err
	}

	bHash := hdr.BlockSha()
	// create inventory we're asking for
	iv1 := wire.NewInvVect(wire.InvTypeWitnessBlock, &bHash)
	gdataMsg := wire.NewMsgGetData()
	// add inventory
	err = gdataMsg.AddInvVect(iv1)
	if err != nil {
		return err
	}
	hah := NewRootAndHeight(bHash, h)
	s.outMsgQueue <- gdataMsg
	s.blockQueue <- hah // push height and mroot of requested block on queue
	return nil
}

// checkProofOfWork ensures the block header bits which indicate the target
// difficulty is in min/max range and that the block hash is less than the
// target difficulty as claimed.
//
// The flags modify the behavior of this function as follows:
//  - BFNoPoWCheck: The check to ensure the block hash is less than the target
//    difficulty is not performed.
func checkProofOfWork(header *wire.BlockHeader, powLimit *big.Int, flags BehaviorFlags) error {
	// The target difficulty must be larger than zero.
	target := CompactToBig(header.Bits)
	if target.Sign() <= 0 {
		str := fmt.Sprintf("block target difficulty of %064x is too low",
			target)
		return ruleError(ErrUnexpectedDifficulty, str)
	}

	// The target difficulty must be less than the maximum allowed.
	if target.Cmp(powLimit) > 0 {
		str := fmt.Sprintf("block target difficulty of %064x is "+
			"higher than max of %064x", target, powLimit)
		return ruleError(ErrUnexpectedDifficulty, str)
	}

	// The block hash must be less than the claimed target unless the flag
	// to avoid proof of work checks is set.
	if flags&BFNoPoWCheck != BFNoPoWCheck {
		// The block hash must be less than the claimed target.
		hash := header.BlockHash()
		hashNum := HashToBig(&hash)
		if hashNum.Cmp(target) > 0 {
			str := fmt.Sprintf("block hash of %064x is higher than "+
				"expected max of %064x", hashNum, target)
			return ruleError(ErrHighHash, str)
		}
	}

	return nil
}

/* calcDiff returns a bool given two block headers.  This bool is
true if the correct dificulty adjustment is seen in the "next" header.
Only feed it headers n-2016 and n-1, otherwise it will calculate a difficulty
when no adjustment should take place, and return false.
Note that the epoch is actually 2015 blocks long, which is confusing. */
func calcDiffAdjust(start, end wire.BlockHeader, p *chaincfg.Params) uint32 {
	duration := end.Timestamp.UnixNano() - start.Timestamp.UnixNano()
	if duration < minRetargetTimespan {
		log.Printf("whoa there, block %s off-scale high 4X diff adjustment!",
			end.BlockSha().String())
		duration = minRetargetTimespan
	} else if duration > maxRetargetTimespan {
		log.Printf("Uh-oh! block %s off-scale low 0.25X diff adjustment!\n",
			end.BlockSha().String())
		duration = maxRetargetTimespan
	}

	// calculation of new 32-byte difficulty target
	// first turn the previous target into a big int
	prevTarget := blockchain.CompactToBig(start.Bits)
	// new target is old * duration...
	newTarget := new(big.Int).Mul(prevTarget, big.NewInt(duration))
	// divided by 2 weeks
	newTarget.Div(newTarget, big.NewInt(int64(targetTimespan)))

	// clip again if above minimum target (too easy)
	if newTarget.Cmp(p.PowLimit) > 0 {
		newTarget.Set(p.PowLimit)
	}

	// calculate and return 4-byte 'bits' difficulty from 32-byte target
	return blockchain.BigToCompact(newTarget)
}

func (s *SPVCon) AskForHeaders() error {
	var hdr wire.BlockHeader
	ghdr := wire.NewMsgGetHeaders()
	ghdr.ProtocolVersion = s.localVersion

	s.headerMutex.Lock() // start header file ops
	info, err := s.headerFile.Stat()
	if err != nil {
		return err
	}
	headerFileSize := info.Size()
	if headerFileSize == 0 || headerFileSize%80 != 0 { // header file broken
		return fmt.Errorf("Header file not a multiple of 80 bytes")
	}

	// seek to 80 bytes from end of file
	ns, err := s.headerFile.Seek(-80, os.SEEK_END)
	if err != nil {
		log.Printf("can't seek\n")
		return err
	}

	log.Printf("suk to offset %d (should be near the end\n", ns)

	// get header from last 80 bytes of file
	err = hdr.Deserialize(s.headerFile)
	if err != nil {
		log.Printf("can't Deserialize")
		return err
	}
	s.headerMutex.Unlock() // done with header file

	cHash := hdr.BlockSha()
	err = ghdr.AddBlockLocatorHash(&cHash)
	if err != nil {
		return err
	}

	fmt.Printf("get headers message has %d header hashes, first one is %s\n",
		len(ghdr.BlockLocatorHashes), ghdr.BlockLocatorHashes[0].String())

	s.outMsgQueue <- ghdr

	return nil
}

// solveBlock attempts to find a nonce which makes the passed block header hash
// to a value less than the target difficulty. When a successful solution is
// found true is returned and the nonce field of the passed header is updated
// with the solution. False is returned if no solution exists.
func solveBlock(header *wire.BlockHeader, targetDifficulty *big.Int) bool {
	// sbResult is used by the solver goroutines to send results.
	type sbResult struct {
		found bool
		nonce uint32
	}

	// solver accepts a block header and a nonce range to test. It is
	// intended to be run as a goroutine.
	quit := make(chan bool)
	results := make(chan sbResult)
	solver := func(hdr wire.BlockHeader, startNonce, stopNonce uint32) {
		// We need to modify the nonce field of the header, so make sure
		// we work with a copy of the original header.
		for i := startNonce; i >= startNonce && i <= stopNonce; i++ {
			select {
			case <-quit:
				return
			default:
				hdr.Nonce = i
				hash := hdr.BlockHash()
				if blockchain.HashToBig(&hash).Cmp(targetDifficulty) <= 0 {
					results <- sbResult{true, i}
					return
				}
			}
		}
		results <- sbResult{false, 0}
	}

	startNonce := uint32(0)
	stopNonce := uint32(math.MaxUint32)
	numCores := uint32(runtime.NumCPU())
	noncesPerCore := (stopNonce - startNonce) / numCores
	for i := uint32(0); i < numCores; i++ {
		rangeStart := startNonce + (noncesPerCore * i)
		rangeStop := startNonce + (noncesPerCore * (i + 1)) - 1
		if i == numCores-1 {
			rangeStop = stopNonce
		}
		go solver(*header, rangeStart, rangeStop)
	}
	for i := uint32(0); i < numCores; i++ {
		result := <-results
		if result.found {
			close(quit)
			header.Nonce = result.nonce
			return true
		}
	}

	return false
}

/* checkProofOfWork verifies the header hashes into something
lower than specified by the 4-byte bits field. */
func checkProofOfWork(header wire.BlockHeader, p *chaincfg.Params) bool {
	target := blockchain.CompactToBig(header.Bits)

	// The target must more than 0.  Why can you even encode negative...
	if target.Sign() <= 0 {
		log.Printf("block target %064x is neagtive(??)\n", target.Bytes())
		return false
	}
	// The target must be less than the maximum allowed (difficulty 1)
	if target.Cmp(p.PowLimit) > 0 {
		log.Printf("block target %064x is "+
			"higher than max of %064x", target, p.PowLimit.Bytes())
		return false
	}
	// The header hash must be less than the claimed target in the header.
	blockHash := header.BlockSha()
	hashNum := blockchain.ShaHashToBig(&blockHash)
	if hashNum.Cmp(target) > 0 {
		log.Printf("block hash %064x is higher than "+
			"required target of %064x", hashNum, target)
		return false
	}
	return true
}

// AskForMerkBlocks requests blocks from current to last
// right now this asks for 1 block per getData message.
// Maybe it's faster to ask for many in a each message?
func (s *SPVCon) AskForBlocks() error {
	var hdr wire.BlockHeader

	s.headerMutex.Lock() // lock just to check filesize
	stat, err := os.Stat(headerFileName)
	s.headerMutex.Unlock() // checked, unlock
	endPos := stat.Size()

	headerTip := int32(endPos/80) - 1 // move back 1 header length to read

	dbTip, err := s.TS.GetDBSyncHeight()
	if err != nil {
		return err
	}
	fmt.Printf("dbTip %d headerTip %d\n", dbTip, headerTip)
	if dbTip > headerTip {
		return fmt.Errorf("error- db longer than headers! shouldn't happen.")
	}
	if dbTip == headerTip {
		// nothing to ask for; set wait state and return
		fmt.Printf("no blocks to request, entering wait state\n")
		fmt.Printf("%d bytes received\n", s.RBytes)
		s.inWaitState <- true
		// also advertise any unconfirmed txs here
		s.Rebroadcast()
		return nil
	}

	fmt.Printf("will request blocks %d to %d\n", dbTip+1, headerTip)

	if !s.HardMode { // don't send this in hardmode! that's the whole point
		// create initial filter
		filt, err := s.TS.GimmeFilter()
		if err != nil {
			return err
		}
		// send filter
		s.SendFilter(filt)
		fmt.Printf("sent filter %x\n", filt.MsgFilterLoad().Filter)
	}
	// loop through all heights where we want merkleblocks.
	for dbTip < headerTip {
		dbTip++ // we're requesting the next header

		// load header from file
		s.headerMutex.Lock() // seek to header we need
		_, err = s.headerFile.Seek(int64((dbTip)*80), os.SEEK_SET)
		if err != nil {
			return err
		}
		err = hdr.Deserialize(s.headerFile) // read header, done w/ file for now
		s.headerMutex.Unlock()              // unlock after reading 1 header
		if err != nil {
			log.Printf("header deserialize error!\n")
			return err
		}

		bHash := hdr.BlockSha()
		// create inventory we're asking for
		iv1 := new(wire.InvVect)
		// if hardmode, ask for legit blocks, none of this ralphy stuff
		if s.HardMode {
			iv1 = wire.NewInvVect(wire.InvTypeWitnessBlock, &bHash)
		} else { // ah well
			iv1 = wire.NewInvVect(wire.InvTypeFilteredWitnessBlock, &bHash)
		}
		gdataMsg := wire.NewMsgGetData()
		// add inventory
		err = gdataMsg.AddInvVect(iv1)
		if err != nil {
			return err
		}

		hah := NewRootAndHeight(hdr.BlockSha(), dbTip)
		if dbTip == headerTip { // if this is the last block, indicate finality
			hah.final = true
		}
		// waits here most of the time for the queue to empty out
		s.blockQueue <- hah // push height and mroot of requested block on queue
		s.outMsgQueue <- gdataMsg
	}
	return nil
}

// IngestHeaders takes in a bunch of headers and appends them to the
// local header file, checking that they fit.  If there's no headers,
// it assumes we're done and returns false.  If it worked it assumes there's
// more to request and returns true.
func (s *SPVCon) IngestHeaders(m *wire.MsgHeaders) (bool, error) {
	gotNum := int64(len(m.Headers))
	if gotNum > 0 {
		fmt.Printf("got %d headers. Range:\n%s - %s\n",
			gotNum, m.Headers[0].BlockSha().String(),
			m.Headers[len(m.Headers)-1].BlockSha().String())
	} else {
		log.Printf("got 0 headers, we're probably synced up")
		return false, nil
	}

	s.headerMutex.Lock()
	defer s.headerMutex.Unlock()

	var err error
	// seek to last header
	_, err = s.headerFile.Seek(-80, os.SEEK_END)
	if err != nil {
		return false, err
	}
	var last wire.BlockHeader
	err = last.Deserialize(s.headerFile)
	if err != nil {
		return false, err
	}
	prevHash := last.BlockSha()

	endPos, err := s.headerFile.Seek(0, os.SEEK_END)
	if err != nil {
		return false, err
	}
	tip := int32(endPos/80) - 1 // move back 1 header length to read

	// check first header returned to make sure it fits on the end
	// of our header file
	if !m.Headers[0].PrevBlock.IsEqual(&prevHash) {
		// delete 100 headers if this happens!  Dumb reorg.
		log.Printf("reorg? header msg doesn't fit. points to %s, expect %s",
			m.Headers[0].PrevBlock.String(), prevHash.String())
		if endPos < 8080 {
			// jeez I give up, back to genesis
			s.headerFile.Truncate(80)
		} else {
			err = s.headerFile.Truncate(endPos - 8000)
			if err != nil {
				return false, fmt.Errorf("couldn't truncate header file")
			}
		}
		return true, fmt.Errorf("Truncated header file to try again")
	}

	for _, resphdr := range m.Headers {
		// write to end of file
		err = resphdr.Serialize(s.headerFile)
		if err != nil {
			return false, err
		}
		// advance chain tip
		tip++
		// check last header
		worked := CheckHeader(s.headerFile, tip, s.TS.Param)
		if !worked {
			if endPos < 8080 {
				// jeez I give up, back to genesis
				s.headerFile.Truncate(80)
			} else {
				err = s.headerFile.Truncate(endPos - 8000)
				if err != nil {
					return false, fmt.Errorf("couldn't truncate header file")
				}
			}
			// probably should disconnect from spv node at this point,
			// since they're giving us invalid headers.
			return true, fmt.Errorf(
				"Header %d - %s doesn't fit, dropping 100 headers.",
				resphdr.BlockSha().String(), tip)
		}
	}
	log.Printf("Headers to height %d OK.", tip)
	return true, nil
}

// checkBlockHeaderContext peforms several validation checks on the block header
// which depend on its position within the block chain.
//
// The flags modify the behavior of this function as follows:
//  - BFFastAdd: All checks except those involving comparing the header against
//    the checkpoints are not performed.
//
// This function MUST be called with the chain state lock held (for writes).
func (b *BlockChain) checkBlockHeaderContext(header *wire.BlockHeader, prevNode *blockNode, flags BehaviorFlags) error {
	// The genesis block is valid by definition.
	if prevNode == nil {
		return nil
	}

	fastAdd := flags&BFFastAdd == BFFastAdd
	if !fastAdd {
		// Ensure the difficulty specified in the block header matches
		// the calculated difficulty based on the previous block and
		// difficulty retarget rules.
		expectedDifficulty, err := b.calcNextRequiredDifficulty(prevNode,
			header.Timestamp)
		if err != nil {
			return err
		}
		blockDifficulty := header.Bits
		if blockDifficulty != expectedDifficulty {
			str := "block difficulty of %d is not the expected value of %d"
			str = fmt.Sprintf(str, blockDifficulty, expectedDifficulty)
			return ruleError(ErrUnexpectedDifficulty, str)
		}

		// Ensure the timestamp for the block header is after the
		// median time of the last several blocks (medianTimeBlocks).
		medianTime, err := b.calcPastMedianTime(prevNode)
		if err != nil {
			log.Errorf("calcPastMedianTime: %v", err)
			return err
		}
		if !header.Timestamp.After(medianTime) {
			str := "block timestamp of %v is not after expected %v"
			str = fmt.Sprintf(str, header.Timestamp, medianTime)
			return ruleError(ErrTimeTooOld, str)
		}
	}

	// The height of this block is one more than the referenced previous
	// block.
	blockHeight := prevNode.height + 1

	// Ensure chain matches up to predetermined checkpoints.
	blockHash := header.BlockHash()
	if !b.verifyCheckpoint(blockHeight, &blockHash) {
		str := fmt.Sprintf("block at height %d does not match "+
			"checkpoint hash", blockHeight)
		return ruleError(ErrBadCheckpoint, str)
	}

	// Find the previous checkpoint and prevent blocks which fork the main
	// chain before it.  This prevents storage of new, otherwise valid,
	// blocks which build off of old blocks that are likely at a much easier
	// difficulty and therefore could be used to waste cache and disk space.
	checkpointBlock, err := b.findPreviousCheckpoint()
	if err != nil {
		return err
	}
	if checkpointBlock != nil && blockHeight < checkpointBlock.Height() {
		str := fmt.Sprintf("block at height %d forks the main chain "+
			"before the previous checkpoint at height %d",
			blockHeight, checkpointBlock.Height())
		return ruleError(ErrForkTooOld, str)
	}

	// Reject outdated block versions once a majority of the network
	// has upgraded.  These were originally voted on by BIP0034,
	// BIP0065, and BIP0066.
	params := b.chainParams
	if header.Version < 2 && blockHeight >= params.BIP0034Height ||
		header.Version < 3 && blockHeight >= params.BIP0066Height ||
		header.Version < 4 && blockHeight >= params.BIP0065Height {

		str := "new blocks with version %d are no longer valid"
		str = fmt.Sprintf(str, header.Version)
		return ruleError(ErrBlockVersionTooOld, str)
	}

	return nil
}

func CheckHeader(r io.ReadSeeker, height int32, p *chaincfg.Params) bool {
	var err error
	var cur, prev, epochStart wire.BlockHeader
	// don't try to verfy the genesis block.  That way madness lies.
	if height == 0 {
		return true
	}
	// initial load of headers
	// load epochstart, previous and current.
	// get the header from the epoch start, up to 2016 blocks ago
	_, err = r.Seek(int64(80*(height-(height%epochLength))), os.SEEK_SET)
	if err != nil {
		log.Printf(err.Error())
		return false
	}
	err = epochStart.Deserialize(r)
	if err != nil {
		log.Printf(err.Error())
		return false
	}
	//	log.Printf("start epoch at height %d ", height-(height%epochLength))

	// seek to n-1 header
	_, err = r.Seek(int64(80*(height-1)), os.SEEK_SET)
	if err != nil {
		log.Printf(err.Error())
		return false
	}
	// read in n-1
	err = prev.Deserialize(r)
	if err != nil {
		log.Printf(err.Error())
		return false
	}
	// seek to curHeight header and read in
	_, err = r.Seek(int64(80*(height)), os.SEEK_SET)
	if err != nil {
		log.Printf(err.Error())
		return false
	}
	err = cur.Deserialize(r)
	if err != nil {
		log.Printf(err.Error())
		return false
	}

	// get hash of n-1 header
	prevHash := prev.BlockSha()
	// check if headers link together.  That whole 'blockchain' thing.
	if prevHash.IsEqual(&cur.PrevBlock) == false {
		log.Printf("Headers %d and %d don't link.\n",
			height-1, height)
		log.Printf("%s - %s",
			prev.BlockSha().String(), cur.BlockSha().String())
		return false
	}
	rightBits := epochStart.Bits // normal, no adjustment; Dn = Dn-1
	// see if we're on a difficulty adjustment block
	if (height)%epochLength == 0 {
		// if so, check if difficulty adjustment is valid.
		// That whole "controlled supply" thing.
		// calculate diff n based on n-2016 ... n-1
		rightBits = calcDiffAdjust(epochStart, prev, p)
		// done with adjustment, save new ephochStart header
		epochStart = cur
		log.Printf("Update epoch at height %d", height)
	} else { // not a new epoch
		// if on testnet, check for difficulty nerfing
		if p.ResetMinDifficulty && cur.Timestamp.After(
			prev.Timestamp.Add(targetSpacing*2)) {
			//	fmt.Printf("nerf %d ", curHeight)
			rightBits = p.PowLimitBits // difficulty 1
		}
		if cur.Bits != rightBits {
			log.Printf("Block %d %s incorrect difficuly.  Read %x, expect %x\n",
				height, cur.BlockSha().String(), cur.Bits, rightBits)
			return false
		}
	}

	// check if there's a valid proof of work.  That whole "Bitcoin" thing.
	if !checkProofOfWork(cur, p) {
		log.Printf("Block %d Bad proof of work.\n", height)
		return false
	}

	return true // it must have worked if there's no errors and got to the end.
}