package engine

import (
	"errors"
	"fmt"

	"github.com/thrasher-corp/gocryptotrader/backtester/common"
	"github.com/thrasher-corp/gocryptotrader/backtester/data"
	"github.com/thrasher-corp/gocryptotrader/backtester/eventhandlers/eventholder"
	"github.com/thrasher-corp/gocryptotrader/backtester/eventhandlers/exchange"
	"github.com/thrasher-corp/gocryptotrader/backtester/eventhandlers/portfolio"
	"github.com/thrasher-corp/gocryptotrader/backtester/eventhandlers/portfolio/compliance"
	"github.com/thrasher-corp/gocryptotrader/backtester/eventhandlers/portfolio/holdings"
	"github.com/thrasher-corp/gocryptotrader/backtester/eventhandlers/statistics"
	"github.com/thrasher-corp/gocryptotrader/backtester/eventhandlers/strategies/base"
	"github.com/thrasher-corp/gocryptotrader/backtester/eventtypes/fill"
	"github.com/thrasher-corp/gocryptotrader/backtester/eventtypes/order"
	"github.com/thrasher-corp/gocryptotrader/backtester/eventtypes/signal"
	"github.com/thrasher-corp/gocryptotrader/backtester/funding"
	"github.com/thrasher-corp/gocryptotrader/currency"
	gctexchange "github.com/thrasher-corp/gocryptotrader/exchanges"
	"github.com/thrasher-corp/gocryptotrader/exchanges/asset"
	gctorder "github.com/thrasher-corp/gocryptotrader/exchanges/order"
	"github.com/thrasher-corp/gocryptotrader/log"
)

// New returns a new BackTest instance
func New() *BackTest {
	return &BackTest{
		shutdown:   make(chan struct{}),
		Datas:      &data.HandlerPerCurrency{},
		EventQueue: &eventholder.Holder{},
	}
}

// Reset BackTest values to default
func (bt *BackTest) Reset() {
	bt.EventQueue.Reset()
	bt.Datas.Reset()
	bt.Portfolio.Reset()
	bt.Statistic.Reset()
	bt.Exchange.Reset()
	bt.Funding.Reset()
	bt.exchangeManager = nil
	bt.orderManager = nil
	bt.databaseManager = nil
}

// Run will iterate over loaded data events
// save them and then handle the event based on its type
func (bt *BackTest) Run() {
	log.Info(common.Backtester, "Running backtester against pre-defined data")
dataLoadingIssue:
	for ev := bt.EventQueue.NextEvent(); ; ev = bt.EventQueue.NextEvent() {
		if ev == nil {
			dataHandlerMap := bt.Datas.GetAllData()
			var hasProcessedData bool
			for exchangeName, exchangeMap := range dataHandlerMap {
				for assetItem, assetMap := range exchangeMap {
					for currencyPair, dataHandler := range assetMap {
						d := dataHandler.Next()
						if d == nil {
							if !bt.hasHandledEvent {
								log.Errorf(common.Backtester, "Unable to perform `Next` for %v %v %v", exchangeName, assetItem, currencyPair)
							}
							break dataLoadingIssue
						}
						if bt.Strategy.UsingSimultaneousProcessing() && hasProcessedData {
							// only append one event, as simultaneous processing
							// will retrieve all relevant events to process under
							// processSimultaneousDataEvents()
							continue
						}
						bt.EventQueue.AppendEvent(d)
						hasProcessedData = true
					}
				}
			}
		} else {
			err := bt.handleEvent(ev)
			if err != nil {
				log.Error(common.Backtester, err)
			}
		}
		if !bt.hasHandledEvent {
			bt.hasHandledEvent = true
		}
	}
}

// handleEvent is the main processor of data for the backtester
// after data has been loaded and Run has appended a data event to the queue,
// handle event will process events and add further events to the queue if they
// are required
func (bt *BackTest) handleEvent(ev common.EventHandler) error {
	if ev == nil {
		return fmt.Errorf("cannot handle event %w", errNilData)
	}
	funds, err := bt.Funding.GetFundingForEvent(ev)
	if err != nil {
		return err
	}

	if bt.Funding.HasFutures() {
		err = bt.Funding.UpdateCollateral(ev)
		if err != nil {
			return err
		}
	}

	switch eType := ev.(type) {
	case common.DataEventHandler:
		if bt.Strategy.UsingSimultaneousProcessing() {
			err = bt.processSimultaneousDataEvents()
		} else {
			err = bt.processSingleDataEvent(eType, funds.FundReleaser())
		}
	case signal.Event:
		err = bt.processSignalEvent(eType, funds.FundReserver())
	case order.Event:
		err = bt.processOrderEvent(eType, funds.FundReleaser())
	case fill.Event:
		err = bt.processFillEvent(eType, funds.FundReleaser())
	default:
		return fmt.Errorf("handleEvent %w %T received, could not process",
			errUnhandledDatatype,
			ev)
	}
	if err != nil {
		return err
	}

	bt.Funding.CreateSnapshot(ev.GetTime())
	return nil
}

// processSingleDataEvent will pass the event to the strategy and determine how it should be handled
func (bt *BackTest) processSingleDataEvent(ev common.DataEventHandler, funds funding.IFundReleaser) error {
	err := bt.updateStatsForDataEvent(ev, funds)
	if err != nil {
		return err
	}
	d, err := bt.Datas.GetDataForCurrency(ev)
	if err != nil {
		return err
	}
	s, err := bt.Strategy.OnSignal(d, bt.Funding, bt.Portfolio)
	if err != nil {
		if errors.Is(err, base.ErrTooMuchBadData) {
			// too much bad data is a severe error and backtesting must cease
			return err
		}
		log.Errorf(common.Backtester, "OnSignal %v", err)
		return nil
	}
	err = bt.Statistic.SetEventForOffset(s)
	if err != nil {
		log.Errorf(common.Backtester, "SetEventForOffset %v", err)
	}
	bt.EventQueue.AppendEvent(s)

	return nil
}

// processSimultaneousDataEvents determines what signal events are generated and appended
// to the event queue. It will pass all currency events to the strategy to determine what
// currencies to act upon
func (bt *BackTest) processSimultaneousDataEvents() error {
	var dataEvents []data.Handler
	dataHandlerMap := bt.Datas.GetAllData()
	for _, exchangeMap := range dataHandlerMap {
		for _, assetMap := range exchangeMap {
			for _, dataHandler := range assetMap {
				latestData := dataHandler.Latest()
				funds, err := bt.Funding.GetFundingForEvent(latestData)
				if err != nil {
					return err
				}
				err = bt.updateStatsForDataEvent(latestData, funds.FundReleaser())
				if err != nil {
					switch {
					case errors.Is(err, statistics.ErrAlreadyProcessed):
						continue
					case errors.Is(err, gctorder.ErrPositionLiquidated):
						return nil
					default:
						log.Error(common.Backtester, err)
					}
				}
				dataEvents = append(dataEvents, dataHandler)
			}
		}
	}
	signals, err := bt.Strategy.OnSimultaneousSignals(dataEvents, bt.Funding, bt.Portfolio)
	if err != nil {
		if errors.Is(err, base.ErrTooMuchBadData) {
			// too much bad data is a severe error and backtesting must cease
			return err
		}
		log.Errorf(common.Backtester, "OnSimultaneousSignals %v", err)
		return nil
	}
	for i := range signals {
		err = bt.Statistic.SetEventForOffset(signals[i])
		if err != nil {
			log.Errorf(common.Backtester, "SetEventForOffset %v %v %v %v", signals[i].GetExchange(), signals[i].GetAssetType(), signals[i].Pair(), err)
		}
		bt.EventQueue.AppendEvent(signals[i])
	}
	return nil
}

// updateStatsForDataEvent makes various systems aware of price movements from
// data events
func (bt *BackTest) updateStatsForDataEvent(ev common.DataEventHandler, funds funding.IFundReleaser) error {
	if ev == nil {
		return common.ErrNilEvent
	}
	if funds == nil {
		return fmt.Errorf("%v %v %v %w missing fund releaser", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), common.ErrNilArguments)
	}
	// update statistics with the latest price
	err := bt.Statistic.SetupEventForTime(ev)
	if err != nil {
		if errors.Is(err, statistics.ErrAlreadyProcessed) {
			return err
		}
		log.Errorf(common.Backtester, "SetupEventForTime %v", err)
	}
	// update portfolio manager with the latest price
	err = bt.Portfolio.UpdateHoldings(ev, funds)
	if err != nil {
		log.Errorf(common.Backtester, "UpdateHoldings %v", err)
	}

	if ev.GetAssetType().IsFutures() {
		var cr funding.ICollateralReleaser
		cr, err = funds.CollateralReleaser()
		if err != nil {
			return err
		}

		err = bt.Portfolio.UpdatePNL(ev, ev.GetClosePrice())
		if err != nil {
			if errors.Is(err, gctorder.ErrPositionNotFound) {
				// if there is no position yet, there's nothing to update
				return nil
			}
			if !errors.Is(err, gctorder.ErrPositionLiquidated) {
				return fmt.Errorf("UpdatePNL %v", err)
			}
		}
		var pnl *portfolio.PNLSummary
		pnl, err = bt.Portfolio.GetLatestPNLForEvent(ev)
		if err != nil {
			return err
		}

		if pnl.Result.IsLiquidated {
			return nil
		}
		err = bt.Portfolio.CheckLiquidationStatus(ev, cr, pnl)
		if err != nil {
			if errors.Is(err, gctorder.ErrPositionLiquidated) {
				liquidErr := bt.triggerLiquidationsForExchange(ev, pnl)
				if liquidErr != nil {
					return liquidErr
				}
			}
			return err
		}

		return bt.Statistic.AddPNLForTime(pnl)
	}

	return nil
}

func (bt *BackTest) triggerLiquidationsForExchange(ev common.DataEventHandler, pnl *portfolio.PNLSummary) error {
	if ev == nil {
		return common.ErrNilEvent
	}
	if pnl == nil {
		return fmt.Errorf("%w pnl summary", common.ErrNilArguments)
	}
	orders, err := bt.Portfolio.CreateLiquidationOrdersForExchange(ev, bt.Funding)
	if err != nil {
		return err
	}
	for i := range orders {
		// these orders are raising events for event offsets
		// which may not have been processed yet
		// this will create and store stats for each order
		// then liquidate it at the funding level
		var datas data.Handler
		datas, err = bt.Datas.GetDataForCurrency(orders[i])
		if err != nil {
			return err
		}
		latest := datas.Latest()
		err = bt.Statistic.SetupEventForTime(latest)
		if err != nil && !errors.Is(err, statistics.ErrAlreadyProcessed) {
			return err
		}
		bt.EventQueue.AppendEvent(orders[i])
		err = bt.Statistic.SetEventForOffset(orders[i])
		if err != nil {
			log.Errorf(common.Backtester, "SetupEventForTime %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
		}
		bt.Funding.Liquidate(orders[i])
	}
	pnl.Result.IsLiquidated = true
	pnl.Result.Status = gctorder.Liquidated
	return bt.Statistic.AddPNLForTime(pnl)
}

// processSignalEvent receives an event from the strategy for processing under the portfolio
func (bt *BackTest) processSignalEvent(ev signal.Event, funds funding.IFundReserver) error {
	if ev == nil {
		return common.ErrNilEvent
	}
	if funds == nil {
		return fmt.Errorf("%w funds", common.ErrNilArguments)
	}
	cs, err := bt.Exchange.GetCurrencySettings(ev.GetExchange(), ev.GetAssetType(), ev.Pair())
	if err != nil {
		log.Errorf(common.Backtester, "GetCurrencySettings %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
		return fmt.Errorf("GetCurrencySettings %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
	}
	var o *order.Order
	o, err = bt.Portfolio.OnSignal(ev, &cs, funds)
	if err != nil {
		log.Errorf(common.Backtester, "OnSignal %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
		return fmt.Errorf("OnSignal %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
	}
	err = bt.Statistic.SetEventForOffset(o)
	if err != nil {
		return fmt.Errorf("SetEventForOffset %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
	}

	bt.EventQueue.AppendEvent(o)
	return nil
}

func (bt *BackTest) processOrderEvent(ev order.Event, funds funding.IFundReleaser) error {
	if ev == nil {
		return common.ErrNilEvent
	}
	if funds == nil {
		return fmt.Errorf("%w funds", common.ErrNilArguments)
	}
	d, err := bt.Datas.GetDataForCurrency(ev)
	if err != nil {
		return err
	}
	f, err := bt.Exchange.ExecuteOrder(ev, d, bt.orderManager, funds)
	if err != nil {
		if f == nil {
			log.Errorf(common.Backtester, "ExecuteOrder fill event should always be returned, please fix, %v", err)
			return fmt.Errorf("ExecuteOrder fill event should always be returned, please fix, %v", err)
		}
		if !errors.Is(err, exchange.ErrCannotTransact) {
			log.Errorf(common.Backtester, "ExecuteOrder %v %v %v %v", f.GetExchange(), f.GetAssetType(), f.Pair(), err)
		}
	}
	err = bt.Statistic.SetEventForOffset(f)
	if err != nil {
		log.Errorf(common.Backtester, "SetEventForOffset %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
	}
	bt.EventQueue.AppendEvent(f)
	return nil
}

func (bt *BackTest) processFillEvent(ev fill.Event, funds funding.IFundReleaser) error {
	t, err := bt.Portfolio.OnFill(ev, funds)
	if err != nil {
		return fmt.Errorf("OnFill %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
	}
	err = bt.Statistic.SetEventForOffset(t)
	if err != nil {
		log.Errorf(common.Backtester, "SetEventForOffset %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
	}

	var holding *holdings.Holding
	holding, err = bt.Portfolio.ViewHoldingAtTimePeriod(ev)
	if err != nil {
		log.Error(common.Backtester, err)
	}
	if holding == nil {
		log.Error(common.Backtester, "ViewHoldingAtTimePeriod why is holdings nil?")
	} else {
		err = bt.Statistic.AddHoldingsForTime(holding)
		if err != nil {
			log.Errorf(common.Backtester, "AddHoldingsForTime %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
		}
	}

	var cp *compliance.Manager
	cp, err = bt.Portfolio.GetComplianceManager(ev.GetExchange(), ev.GetAssetType(), ev.Pair())
	if err != nil {
		log.Errorf(common.Backtester, "GetComplianceManager %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
	}

	snap := cp.GetLatestSnapshot()
	err = bt.Statistic.AddComplianceSnapshotForTime(snap, ev)
	if err != nil {
		log.Errorf(common.Backtester, "AddComplianceSnapshotForTime %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
	}

	fde := ev.GetFillDependentEvent()
	if fde != nil && !fde.IsNil() {
		// some events can only be triggered on a successful fill event
		fde.SetOffset(ev.GetOffset())
		err = bt.Statistic.SetEventForOffset(fde)
		if err != nil {
			log.Errorf(common.Backtester, "SetEventForOffset %v %v %v %v", fde.GetExchange(), fde.GetAssetType(), fde.Pair(), err)
		}
		od := ev.GetOrder()
		if fde.MatchOrderAmount() && od != nil {
			fde.SetAmount(ev.GetAmount())
		}
		fde.AppendReasonf("raising event after %v %v %v fill", ev.GetExchange(), ev.GetAssetType(), ev.Pair())
		bt.EventQueue.AppendEvent(fde)
	}
	if ev.GetAssetType().IsFutures() {
		return bt.processFuturesFillEvent(ev, funds)
	}
	return nil
}

func (bt *BackTest) processFuturesFillEvent(ev fill.Event, funds funding.IFundReleaser) error {
	if ev.GetOrder() != nil {
		pnl, err := bt.Portfolio.TrackFuturesOrder(ev, funds)
		if err != nil && !errors.Is(err, gctorder.ErrSubmissionIsNil) {
			return fmt.Errorf("TrackFuturesOrder %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
		}

		var exch gctexchange.IBotExchange
		exch, err = bt.exchangeManager.GetExchangeByName(ev.GetExchange())
		if err != nil {
			return fmt.Errorf("GetExchangeByName %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
		}

		rPNL := pnl.GetRealisedPNL()
		if !rPNL.PNL.IsZero() {
			var receivingCurrency currency.Code
			var receivingAsset asset.Item
			receivingCurrency, receivingAsset, err = exch.GetCurrencyForRealisedPNL(ev.GetAssetType(), ev.Pair())
			if err != nil {
				return fmt.Errorf("GetCurrencyForRealisedPNL %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
			}
			err = bt.Funding.RealisePNL(ev.GetExchange(), receivingAsset, receivingCurrency, rPNL.PNL)
			if err != nil {
				return fmt.Errorf("RealisePNL %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
			}
		}

		err = bt.Statistic.AddPNLForTime(pnl)
		if err != nil {
			log.Errorf(common.Backtester, "AddHoldingsForTime %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
		}
	}
	err := bt.Funding.UpdateCollateral(ev)
	if err != nil {
		return fmt.Errorf("UpdateCollateral %v %v %v %v", ev.GetExchange(), ev.GetAssetType(), ev.Pair(), err)
	}
	return nil
}

// Stop shuts down the live data loop
func (bt *BackTest) Stop() {
	close(bt.shutdown)
}