package snapshot

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

	"git.g3e.fr/H6N/account/internal/store"
)

type Engine struct {
	store       *store.Store
	logger      *slog.Logger
	horizonDays int
}

func New(st *store.Store, logger *slog.Logger, horizonDays int) *Engine {
	return &Engine{store: st, logger: logger, horizonDays: horizonDays}
}

func (e *Engine) Store() *store.Store { return e.store }

// RecomputeDay calcule les snapshots de tous les comptes pour une date donnée.
// Toutes les transactions (validées ou non) sont incluses.
func (e *Engine) RecomputeDay(ctx context.Context, date time.Time) error {
	date = date.Truncate(24 * time.Hour)

	accountIDs, err := e.store.ListAllAccountIDs(ctx)
	if err != nil {
		return fmt.Errorf("list accounts: %w", err)
	}

	for _, accountID := range accountIDs {
		if err := e.recomputeAccount(ctx, accountID, date); err != nil {
			e.logger.Error("snapshot: account failed", "account_id", accountID, "error", err)
		}
	}

	e.logger.Info("snapshot: day computed", "date", date.Format("2006-01-02"), "accounts", len(accountIDs))
	return nil
}

// RecomputeAccount recalcule les snapshots d'un compte depuis son invalidation
// jusqu'à aujourd'hui + horizon. Efface l'invalidation une fois terminé.
// Retourne (zero, zero, nil) si aucune invalidation n'est en attente.
func (e *Engine) RecomputeAccount(ctx context.Context, accountID int32) (from, to time.Time, err error) {
	inv, found, err := e.store.GetInvalidation(ctx, accountID)
	if err != nil {
		return time.Time{}, time.Time{}, fmt.Errorf("get invalidation: %w", err)
	}
	if !found {
		return time.Time{}, time.Time{}, nil
	}

	today := time.Now().Truncate(24 * time.Hour)
	horizon := today.AddDate(0, 0, e.horizonDays)

	if err := e.backfillAccount(ctx, accountID, inv.RecomputeFrom, horizon); err != nil {
		return time.Time{}, time.Time{}, err
	}

	if err := e.store.ClearInvalidation(ctx, accountID); err != nil {
		return time.Time{}, time.Time{}, fmt.Errorf("clear invalidation: %w", err)
	}

	return inv.RecomputeFrom, horizon, nil
}

// DailySnapshot :
//  1. Traite les invalidations en attente (jusqu'à today + horizon)
//  2. Recalcule hier (consolide les transactions de la veille)
//  3. Calcule le nouveau jour entrant dans la fenêtre (today + horizonDays)
func (e *Engine) DailySnapshot(ctx context.Context) error {
	today := time.Now().Truncate(24 * time.Hour)
	yesterday := today.AddDate(0, 0, -1)
	newHorizonDay := today.AddDate(0, 0, e.horizonDays)

	// 1. Invalidations
	if err := e.processInvalidations(ctx, newHorizonDay); err != nil {
		e.logger.Error("snapshot: invalidation processing failed", "error", err)
	}

	// 2. Hier
	if err := e.RecomputeDay(ctx, yesterday); err != nil {
		e.logger.Error("snapshot: yesterday recompute failed", "error", err)
	}

	// 3. Nouveau jour entrant dans la fenêtre
	if err := e.RecomputeDay(ctx, newHorizonDay); err != nil {
		e.logger.Error("snapshot: horizon day failed", "error", err)
	}

	return nil
}

func (e *Engine) processInvalidations(ctx context.Context, until time.Time) error {
	invalidations, err := e.store.GetInvalidations(ctx)
	if err != nil {
		return fmt.Errorf("get invalidations: %w", err)
	}
	if len(invalidations) == 0 {
		return nil
	}

	e.logger.Info("snapshot: processing invalidations", "count", len(invalidations))

	for _, inv := range invalidations {
		if err := e.backfillAccount(ctx, inv.AccountID, inv.RecomputeFrom, until); err != nil {
			e.logger.Error("snapshot: backfill failed", "account_id", inv.AccountID, "error", err)
			continue
		}
		if err := e.store.ClearInvalidation(ctx, inv.AccountID); err != nil {
			e.logger.Error("snapshot: clear invalidation failed", "account_id", inv.AccountID, "error", err)
		}
	}

	return nil
}

func (e *Engine) backfillAccount(ctx context.Context, accountID int32, from, to time.Time) error {
	from = from.Truncate(24 * time.Hour)
	to = to.Truncate(24 * time.Hour)

	if from.After(to) {
		return fmt.Errorf("from (%s) after to (%s)", from.Format("2006-01-02"), to.Format("2006-01-02"))
	}

	for d := from; !d.After(to); d = d.AddDate(0, 0, 1) {
		if err := e.recomputeAccount(ctx, accountID, d); err != nil {
			return fmt.Errorf("recompute %s: %w", d.Format("2006-01-02"), err)
		}
	}
	return nil
}

func (e *Engine) recomputeAccount(ctx context.Context, accountID int32, date time.Time) error {
	baseDate, hasBase, err := e.store.GetLatestSnapshotDate(ctx, accountID, date)
	if err != nil {
		return fmt.Errorf("get latest snapshot date: %w", err)
	}

	positions := map[int32]store.PositionRow{}
	if hasBase {
		base, err := e.store.GetBasePositions(ctx, accountID, baseDate)
		if err != nil {
			return fmt.Errorf("get base positions: %w", err)
		}
		for _, p := range base {
			positions[p.InstrumentID] = p
		}
	}

	deltas, err := e.store.ComputeDeltas(ctx, accountID, baseDate, date)
	if err != nil {
		return fmt.Errorf("compute deltas: %w", err)
	}

	for _, d := range deltas {
		p := positions[d.InstrumentID]
		p.InstrumentID = d.InstrumentID
		p.InstrumentType = d.InstrumentType
		p.Quantite += d.Quantite
		positions[d.InstrumentID] = p
	}

	var totalValeur float64

	for _, pos := range positions {
		if pos.Quantite <= 0 {
			continue
		}

		prix, found, err := e.store.GetPriceAt(ctx, pos.InstrumentID, date)
		if err != nil {
			return fmt.Errorf("get price instrument %d: %w", pos.InstrumentID, err)
		}
		if !found {
			if pos.InstrumentType == "devise" {
				prix = 1.0
			} else {
				e.logger.Warn("snapshot: no price, position skipped",
					"account_id", accountID,
					"instrument_id", pos.InstrumentID,
					"date", date.Format("2006-01-02"),
				)
				continue
			}
		}

		valeur := pos.Quantite * prix
		totalValeur += valeur

		snap := store.PositionSnapshot{
			Date:         date,
			AccountID:    accountID,
			InstrumentID: pos.InstrumentID,
			Quantite:     pos.Quantite,
			PrixCloture:  &prix,
			Valeur:       &valeur,
		}
		if err := e.store.UpsertPositionSnapshot(ctx, snap); err != nil {
			return fmt.Errorf("upsert position snapshot: %w", err)
		}
	}

	return e.store.UpsertAccountSnapshot(ctx, store.AccountSnapshot{
		Date:      date,
		AccountID: accountID,
		Valeur:    totalValeur,
	})
}