package usecase

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"sync"
	"time"

	"golang.org/x/sync/errgroup"

	"cryptoHermes/internal/entity"
)

var supportedSymbols = map[string]bool{
	"BTCUSDT": true,
	"ETHUSDT": true,
}

var supportedIntervals = []string{"15m", "1h", "4h", "1d", "1w"}

const (
	klineWindowSize    = 300
	klineMinForOK      = 200
	derivativePeriod   = "1h"
	fundingHistoryLen  = 100
	oiHistoryLen       = 200
	longShortLen       = 200
	takerHistoryLen    = 200
)

type MarketContextUsecase struct {
	marketData  MarketDataProvider
	derivatives DerivativesProvider

	klineRepo   KlineRepository
	fundingRepo FundingRepository
	oiRepo      OpenInterestRepository
	lsRepo      LongShortRatioRepository

	log *slog.Logger
}

func NewMarketContextUsecase(
	marketData MarketDataProvider,
	derivatives DerivativesProvider,
	klineRepo KlineRepository,
	fundingRepo FundingRepository,
	oiRepo OpenInterestRepository,
	lsRepo LongShortRatioRepository,
	log *slog.Logger,
) *MarketContextUsecase {
	return &MarketContextUsecase{
		marketData:  marketData,
		derivatives: derivatives,
		klineRepo:   klineRepo,
		fundingRepo: fundingRepo,
		oiRepo:      oiRepo,
		lsRepo:      lsRepo,
		log:         log,
	}
}

func (u *MarketContextUsecase) Build(ctx context.Context, symbol string) (*entity.MarketContext, error) {
	if !supportedSymbols[symbol] {
		return nil, fmt.Errorf("unsupported symbol: %s", symbol)
	}

	var (
		snapshot      *entity.Ticker24h
		currentFund   *entity.FundingRate
		currentOI     *entity.OpenInterest
		warnMu        sync.Mutex
		warnings      []string
	)
	addWarn := func(w string) {
		warnMu.Lock()
		warnings = append(warnings, w)
		warnMu.Unlock()
	}

	g, gctx := errgroup.WithContext(ctx)

	g.Go(func() error {
		s, err := u.marketData.GetTicker24h(gctx, symbol)
		if err != nil {
			addWarn("snapshot fetch failed: " + err.Error())
			return nil
		}
		snapshot = s
		return nil
	})
	g.Go(func() error {
		f, err := u.derivatives.GetCurrentFunding(gctx, symbol)
		if err != nil {
			addWarn("current funding fetch failed: " + err.Error())
			return nil
		}
		currentFund = f
		return nil
	})
	g.Go(func() error {
		oi, err := u.derivatives.GetCurrentOpenInterest(gctx, symbol)
		if err != nil {
			addWarn("current OI fetch failed: " + err.Error())
			return nil
		}
		currentOI = oi
		return nil
	})

	_ = g.Wait()

	klines := make(map[string][]entity.Kline, len(supportedIntervals))
	for _, iv := range supportedIntervals {
		rows, err := u.klineRepo.FindRecent(ctx, symbol, iv, klineWindowSize)
		if err != nil {
			addWarn(fmt.Sprintf("klines DB query failed for %s: %v", iv, err))
			rows = nil
		}
		if len(rows) < klineMinForOK {
			addWarn(fmt.Sprintf("klines %s only %d in DB, falling back to Binance", iv, len(rows)))
			fresh, ferr := u.marketData.GetKlines(ctx, symbol, iv, klineWindowSize)
			if ferr != nil {
				addWarn(fmt.Sprintf("klines fallback %s failed: %v", iv, ferr))
			} else {
				closed := make([]entity.Kline, 0, len(fresh))
				for _, k := range fresh {
					if k.IsClosed {
						closed = append(closed, k)
					}
				}
				go func(items []entity.Kline) {
					bgCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
					defer cancel()
					if err := u.klineRepo.UpsertMany(bgCtx, items); err != nil {
						u.log.Error("background_kline_upsert_failed", "err", err)
					}
				}(closed)
				rows = closed
			}
		}
		klines[iv] = rows
	}

	fundingHist, err := u.fundingRepo.FindRecent(ctx, symbol, fundingHistoryLen)
	if err != nil {
		addWarn("funding history query failed: " + err.Error())
	}

	oiHist, err := u.oiRepo.FindRecent(ctx, symbol, derivativePeriod, oiHistoryLen)
	if err != nil {
		addWarn("OI history query failed: " + err.Error())
	}

	globalLS, err := u.lsRepo.FindRecent(ctx, symbol, derivativePeriod, entity.RatioTypeGlobalAccount, longShortLen)
	if err != nil {
		addWarn("global long/short query failed: " + err.Error())
	}
	topLS, err := u.lsRepo.FindRecent(ctx, symbol, derivativePeriod, entity.RatioTypeTopTraderPosition, longShortLen)
	if err != nil {
		addWarn("top trader position long/short query failed: " + err.Error())
	}

	out := &entity.MarketContext{
		Symbol:      symbol,
		GeneratedAt: time.Now().UnixMilli(),
		Snapshot:    snapshot,
		Klines:      klines,
		Derivatives: entity.DerivativesBundle{
			Funding: entity.FundingBundle{
				Current: currentFund,
				History: fundingHist,
			},
			OpenInterest: entity.OpenInterestBundle{
				Current: currentOI,
				History: oiHist,
			},
			LongShortRatio: entity.LongShortBundle{
				Global:            globalLS,
				TopTraderPosition: topLS,
			},
			TakerBuySellVolume: nil,
		},
		Technical: entity.TechnicalStructure{
			Support:    []entity.TechnicalLevel{},
			Resistance: []entity.TechnicalLevel{},
		},
		DataQuality: entity.DataQuality{
			Source:   "binance",
			Warnings: warnings,
		},
	}

	if out.DataQuality.Warnings == nil {
		out.DataQuality.Warnings = []string{}
	}

	if snapshot == nil {
		return out, errors.New("market snapshot unavailable")
	}
	return out, nil
}