package paychmgr

import (
	"bytes"
	"context"
	"fmt"

	"github.com/filecoin-project/lotus/api"

	"github.com/filecoin-project/specs-actors/actors/abi/big"

	"github.com/filecoin-project/specs-actors/actors/builtin"
	init_ "github.com/filecoin-project/specs-actors/actors/builtin/init"
	"github.com/filecoin-project/specs-actors/actors/builtin/paych"
	"github.com/ipfs/go-cid"
	"golang.org/x/xerrors"

	"github.com/filecoin-project/go-address"

	"github.com/filecoin-project/lotus/build"
	"github.com/filecoin-project/lotus/chain/actors"
	"github.com/filecoin-project/lotus/chain/types"
)

type paychApi interface {
	StateWaitMsg(ctx context.Context, msg cid.Cid, confidence uint64) (*api.MsgLookup, error)
	MpoolPushMessage(ctx context.Context, msg *types.Message) (*types.SignedMessage, error)
}

// paychFundsRes is the response to a create channel or add funds request
type paychFundsRes struct {
	channel address.Address
	mcid    cid.Cid
	err     error
}

type onCompleteFn func(*paychFundsRes)

// fundsReq is a request to create a channel or add funds to a channel
type fundsReq struct {
	ctx        context.Context
	from       address.Address
	to         address.Address
	amt        types.BigInt
	onComplete onCompleteFn
}

// getPaych ensures that a channel exists between the from and to addresses,
// and adds the given amount of funds.
// If the channel does not exist a create channel message is sent and the
// message CID is returned.
// If the channel does exist an add funds message is sent and both the channel
// address and message CID are returned.
// If there is an in progress operation (create channel / add funds), getPaych
// blocks until the previous operation completes, then returns both the channel
// address and the CID of the new add funds message.
// If an operation returns an error, subsequent waiting operations will still
// be attempted.
func (ca *channelAccessor) getPaych(ctx context.Context, from, to address.Address, amt types.BigInt) (address.Address, cid.Cid, error) {
	// Add the request to add funds to a queue and wait for the result
	promise := ca.enqueue(&fundsReq{ctx: ctx, from: from, to: to, amt: amt})
	select {
	case res := <-promise:
		return res.channel, res.mcid, res.err
	case <-ctx.Done():
		return address.Undef, cid.Undef, ctx.Err()
	}
}

// Queue up an add funds operation
func (ca *channelAccessor) enqueue(task *fundsReq) chan *paychFundsRes {
	promise := make(chan *paychFundsRes)
	task.onComplete = func(res *paychFundsRes) {
		select {
		case <-task.ctx.Done():
		case promise <- res:
		}
	}

	ca.lk.Lock()
	defer ca.lk.Unlock()

	ca.fundsReqQueue = append(ca.fundsReqQueue, task)
	go ca.processNextQueueItem()

	return promise
}

// Run the operation at the head of the queue
func (ca *channelAccessor) processNextQueueItem() {
	ca.lk.Lock()
	defer ca.lk.Unlock()

	if len(ca.fundsReqQueue) == 0 {
		return
	}

	head := ca.fundsReqQueue[0]
	res := ca.processTask(head.ctx, head.from, head.to, head.amt, head.onComplete)

	// If the task is waiting on an external event (eg something to appear on
	// chain) it will return nil
	if res == nil {
		// Stop processing the fundsReqQueue and wait. When the event occurs it will
		// call processNextQueueItem() again
		return
	}

	// The task has finished processing so clean it up
	ca.fundsReqQueue[0] = nil // allow GC of element
	ca.fundsReqQueue = ca.fundsReqQueue[1:]

	// Call the task callback with its results
	head.onComplete(res)

	// Process the next task
	if len(ca.fundsReqQueue) > 0 {
		go ca.processNextQueueItem()
	}
}

// msgWaitComplete is called when the message for a previous task is confirmed
// or there is an error.
func (ca *channelAccessor) msgWaitComplete(mcid cid.Cid, err error, cb onCompleteFn) {
	ca.lk.Lock()
	defer ca.lk.Unlock()

	// Save the message result to the store
	dserr := ca.store.SaveMessageResult(mcid, err)
	if dserr != nil {
		log.Errorf("saving message result: %s", dserr)
	}

	// Call the onComplete callback
	ca.callOnComplete(mcid, err, cb)

	// Inform listeners that the message has completed
	ca.msgListeners.fireMsgComplete(mcid, err)

	// The queue may have been waiting for msg completion to proceed, so
	// process the next queue item
	if len(ca.fundsReqQueue) > 0 {
		go ca.processNextQueueItem()
	}
}

// callOnComplete calls the onComplete callback for a task
func (ca *channelAccessor) callOnComplete(mcid cid.Cid, err error, cb onCompleteFn) {
	if cb == nil {
		return
	}

	if err != nil {
		go cb(&paychFundsRes{err: err})
		return
	}

	// Get the channel address
	ci, storeErr := ca.store.ByMessageCid(mcid)
	if storeErr != nil {
		log.Errorf("getting channel by message cid: %s", err)
		go cb(&paychFundsRes{err: storeErr})
		return
	}

	if ci.Channel == nil {
		panic("channel address is nil when calling onComplete callback")
	}

	go cb(&paychFundsRes{channel: *ci.Channel, mcid: mcid, err: err})
}

// processTask checks the state of the channel and takes appropriate action
// (see description of getPaych).
// Note that processTask may be called repeatedly in the same state, and should
// return nil if there is no state change to be made (eg when waiting for a
// message to be confirmed on chain)
func (ca *channelAccessor) processTask(
	ctx context.Context,
	from address.Address,
	to address.Address,
	amt types.BigInt,
	onComplete onCompleteFn,
) *paychFundsRes {
	// Get the payment channel for the from/to addresses.
	// Note: It's ok if we get ErrChannelNotTracked. It just means we need to
	// create a channel.
	channelInfo, err := ca.store.OutboundActiveByFromTo(from, to)
	if err != nil && err != ErrChannelNotTracked {
		return &paychFundsRes{err: err}
	}

	// If a channel has not yet been created, create one.
	// Note that if the previous attempt to create the channel failed because of a VM error
	// (eg not enough gas), both channelInfo.Channel and channelInfo.CreateMsg will be nil.
	if channelInfo == nil || channelInfo.Channel == nil && channelInfo.CreateMsg == nil {
		mcid, err := ca.createPaych(ctx, from, to, amt, onComplete)
		if err != nil {
			return &paychFundsRes{err: err}
		}

		return &paychFundsRes{mcid: mcid}
	}

	// If the create channel message has been sent but the channel hasn't
	// been created on chain yet
	if channelInfo.CreateMsg != nil {
		// Wait for the channel to be created before trying again
		return nil
	}

	// If an add funds message was sent to the chain but hasn't been confirmed
	// on chain yet
	if channelInfo.AddFundsMsg != nil {
		// Wait for the add funds message to be confirmed before trying again
		return nil
	}

	// We need to add more funds, so send an add funds message to
	// cover the amount for this request
	mcid, err := ca.addFunds(ctx, from, to, amt, onComplete)
	if err != nil {
		return &paychFundsRes{err: err}
	}
	return &paychFundsRes{channel: *channelInfo.Channel, mcid: *mcid}
}

// createPaych sends a message to create the channel and returns the message cid
func (ca *channelAccessor) createPaych(ctx context.Context, from, to address.Address, amt types.BigInt, cb onCompleteFn) (cid.Cid, error) {
	params, aerr := actors.SerializeParams(&paych.ConstructorParams{From: from, To: to})
	if aerr != nil {
		return cid.Undef, aerr
	}

	enc, aerr := actors.SerializeParams(&init_.ExecParams{
		CodeCID:           builtin.PaymentChannelActorCodeID,
		ConstructorParams: params,
	})
	if aerr != nil {
		return cid.Undef, aerr
	}

	msg := &types.Message{
		To:       builtin.InitActorAddr,
		From:     from,
		Value:    amt,
		Method:   builtin.MethodsInit.Exec,
		Params:   enc,
		GasLimit: 0,
		GasPrice: types.NewInt(0),
	}

	smsg, err := ca.api.MpoolPushMessage(ctx, msg)
	if err != nil {
		return cid.Undef, xerrors.Errorf("initializing paych actor: %w", err)
	}
	mcid := smsg.Cid()

	// Create a new channel in the store
	if _, err := ca.store.createChannel(from, to, mcid, amt); err != nil {
		log.Errorf("creating channel: %s", err)
		return cid.Undef, err
	}

	// Wait for the channel to be created on chain
	go ca.waitForPaychCreateMsg(from, to, mcid, cb)

	return mcid, nil
}

// waitForPaychCreateMsg waits for mcid to appear on chain and stores the robust address of the
// created payment channel
func (ca *channelAccessor) waitForPaychCreateMsg(from address.Address, to address.Address, mcid cid.Cid, cb onCompleteFn) {
	err := ca.waitPaychCreateMsg(from, to, mcid)
	ca.msgWaitComplete(mcid, err, cb)
}

func (ca *channelAccessor) waitPaychCreateMsg(from address.Address, to address.Address, mcid cid.Cid) error {
	mwait, err := ca.api.StateWaitMsg(ca.waitCtx, mcid, build.MessageConfidence)
	if err != nil {
		log.Errorf("wait msg: %w", err)
		return err
	}

	if mwait.Receipt.ExitCode != 0 {
		err := xerrors.Errorf("payment channel creation failed (exit code %d)", mwait.Receipt.ExitCode)
		log.Error(err)

		ca.lk.Lock()
		defer ca.lk.Unlock()

		ca.mutateChannelInfo(from, to, func(channelInfo *ChannelInfo) {
			channelInfo.PendingAmount = big.NewInt(0)
			channelInfo.CreateMsg = nil
		})

		return err
	}

	var decodedReturn init_.ExecReturn
	err = decodedReturn.UnmarshalCBOR(bytes.NewReader(mwait.Receipt.Return))
	if err != nil {
		log.Error(err)
		return err
	}

	ca.lk.Lock()
	defer ca.lk.Unlock()

	// Store robust address of channel
	ca.mutateChannelInfo(from, to, func(channelInfo *ChannelInfo) {
		channelInfo.Channel = &decodedReturn.RobustAddress
		channelInfo.Amount = channelInfo.PendingAmount
		channelInfo.PendingAmount = big.NewInt(0)
		channelInfo.CreateMsg = nil
	})

	return nil
}

// addFunds sends a message to add funds to the channel and returns the message cid
func (ca *channelAccessor) addFunds(ctx context.Context, from address.Address, to address.Address, amt types.BigInt, cb onCompleteFn) (*cid.Cid, error) {
	channelInfo, err := ca.store.OutboundActiveByFromTo(from, to)
	if err != nil {
		return nil, err
	}

	msg := &types.Message{
		To:       *channelInfo.Channel,
		From:     channelInfo.Control,
		Value:    amt,
		Method:   0,
		GasLimit: 0,
		GasPrice: types.NewInt(0),
	}

	smsg, err := ca.api.MpoolPushMessage(ctx, msg)
	if err != nil {
		return nil, err
	}
	mcid := smsg.Cid()

	// Store the add funds message CID on the channel
	ca.mutateChannelInfo(from, to, func(ci *ChannelInfo) {
		ci.PendingAmount = amt
		ci.AddFundsMsg = &mcid
	})

	// Store a reference from the message CID to the channel, so that we can
	// look up the channel from the message CID
	err = ca.store.SaveNewMessage(channelInfo.ChannelID, mcid)
	if err != nil {
		log.Errorf("saving add funds message CID %s: %s", mcid, err)
	}

	go ca.waitForAddFundsMsg(from, to, mcid, cb)

	return &mcid, nil
}

// waitForAddFundsMsg waits for mcid to appear on chain and returns error, if any
func (ca *channelAccessor) waitForAddFundsMsg(from address.Address, to address.Address, mcid cid.Cid, cb onCompleteFn) {
	err := ca.waitAddFundsMsg(from, to, mcid)
	ca.msgWaitComplete(mcid, err, cb)
}

func (ca *channelAccessor) waitAddFundsMsg(from address.Address, to address.Address, mcid cid.Cid) error {
	mwait, err := ca.api.StateWaitMsg(ca.waitCtx, mcid, build.MessageConfidence)
	if err != nil {
		log.Error(err)
		return err
	}

	if mwait.Receipt.ExitCode != 0 {
		err := xerrors.Errorf("voucher channel creation failed: adding funds (exit code %d)", mwait.Receipt.ExitCode)
		log.Error(err)

		ca.lk.Lock()
		defer ca.lk.Unlock()

		ca.mutateChannelInfo(from, to, func(channelInfo *ChannelInfo) {
			channelInfo.PendingAmount = big.NewInt(0)
			channelInfo.AddFundsMsg = nil
		})

		return err
	}

	ca.lk.Lock()
	defer ca.lk.Unlock()

	// Store updated amount
	ca.mutateChannelInfo(from, to, func(channelInfo *ChannelInfo) {
		channelInfo.Amount = types.BigAdd(channelInfo.Amount, channelInfo.PendingAmount)
		channelInfo.PendingAmount = big.NewInt(0)
		channelInfo.AddFundsMsg = nil
	})

	return nil
}

// Change the state of the channel in the store
func (ca *channelAccessor) mutateChannelInfo(from address.Address, to address.Address, mutate func(*ChannelInfo)) {
	channelInfo, err := ca.store.OutboundActiveByFromTo(from, to)

	// If there's an error reading or writing to the store just log an error.
	// For now we're assuming it's unlikely to happen in practice.
	// Later we may want to implement a transactional approach, whereby
	// we record to the store that we're going to send a message, send
	// the message, and then record that the message was sent.
	if err != nil {
		log.Errorf("Error reading channel info from store: %s", err)
	}

	mutate(channelInfo)

	err = ca.store.putChannelInfo(channelInfo)
	if err != nil {
		log.Errorf("Error writing channel info to store: %s", err)
	}
}

// getPaychWaitReady waits for a the response to the message with the given cid
func (ca *channelAccessor) getPaychWaitReady(ctx context.Context, mcid cid.Cid) (address.Address, error) {
	ca.lk.Lock()

	// First check if the message has completed
	msgInfo, err := ca.store.GetMessage(mcid)
	if err != nil {
		ca.lk.Unlock()

		return address.Undef, err
	}

	// If the create channel / add funds message failed, return an error
	if len(msgInfo.Err) > 0 {
		ca.lk.Unlock()

		return address.Undef, xerrors.New(msgInfo.Err)
	}

	// If the message has completed successfully
	if msgInfo.Received {
		ca.lk.Unlock()

		// Get the channel address
		ci, err := ca.store.ByMessageCid(mcid)
		if err != nil {
			return address.Undef, err
		}

		if ci.Channel == nil {
			panic(fmt.Sprintf("create / add funds message %s succeeded but channelInfo.Channel is nil", mcid))
		}
		return *ci.Channel, nil
	}

	// The message hasn't completed yet so wait for it to complete
	promise := ca.msgPromise(ctx, mcid)

	// Unlock while waiting
	ca.lk.Unlock()

	select {
	case res := <-promise:
		return res.channel, res.err
	case <-ctx.Done():
		return address.Undef, ctx.Err()
	}
}

type onMsgRes struct {
	channel address.Address
	err     error
}

// msgPromise returns a channel that receives the result of the message with
// the given CID
func (ca *channelAccessor) msgPromise(ctx context.Context, mcid cid.Cid) chan onMsgRes {
	promise := make(chan onMsgRes)
	triggerUnsub := make(chan struct{})
	sub := ca.msgListeners.onMsg(mcid, func(err error) {
		close(triggerUnsub)

		// Use a go-routine so as not to block the event handler loop
		go func() {
			res := onMsgRes{err: err}
			if res.err == nil {
				// Get the channel associated with the message cid
				ci, err := ca.store.ByMessageCid(mcid)
				if err != nil {
					res.err = err
				} else {
					res.channel = *ci.Channel
				}
			}

			// Pass the result to the caller
			select {
			case promise <- res:
			case <-ctx.Done():
			}
		}()
	})

	// Unsubscribe when the message is received or the context is done
	go func() {
		select {
		case <-ctx.Done():
		case <-triggerUnsub:
		}

		ca.msgListeners.unsubscribe(sub)
	}()

	return promise
}