package repository

import (
	"context"
	"errors"
	"fmt"
	"sort"
	"time"

	"github.com/google/uuid"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"

	"apskel-pos-be/internal/constants"
	"apskel-pos-be/internal/entities"
)

var (
	// ErrWalletTxRequired is returned by every write and lock when the context carries
	// no transaction from TxManager. Outside a transaction a lock is released as soon as
	// it is taken, and a balance could move without its ledger row.
	ErrWalletTxRequired = errors.New("wallet: operation must run inside a transaction")
	// ErrWalletNotFound means the customer does not exist, so no wallet could be made.
	ErrWalletNotFound = errors.New("wallet: customer not found")
	// ErrWalletInsufficientBalance means a conditional update matched no row because
	// the balance would have gone negative.
	ErrWalletInsufficientBalance = errors.New("wallet: insufficient balance")
	// ErrWalletLotInsufficient means a lot had less remaining than was taken from it.
	ErrWalletLotInsufficient = errors.New("wallet: lot has insufficient remaining amount")
)

// WalletRepository reads and writes the wallet tables (docs/prd-point-coin.md §7, §8).
// Only the wallet processor should call its write methods: it is the one place that
// keeps balances, ledger rows and lots in step.
//
// Unlike the gamification repositories, every method goes through DBFromContext so it
// joins the caller's transaction. Writes and locks refuse to run without one.
type WalletRepository interface {
	// LockWallet locks the customer's wallet row for the rest of the transaction,
	// creating the row first if the customer has none yet.
	LockWallet(ctx context.Context, customerID uuid.UUID) (*entities.CustomerWallet, error)
	// LockWallets locks two wallets, always in customer_id order so that two transfers
	// in opposite directions cannot deadlock. The results come back in argument order.
	LockWallets(ctx context.Context, a, b uuid.UUID) (*entities.CustomerWallet, *entities.CustomerWallet, error)
	// AddBalance moves one balance by delta and returns the new balance. A debit that
	// would make it negative changes nothing and returns ErrWalletInsufficientBalance.
	AddBalance(ctx context.Context, customerID uuid.UUID, currency string, delta int64) (int64, error)
	GetWallet(ctx context.Context, customerID uuid.UUID) (*entities.CustomerWallet, error)

	CreateTransaction(ctx context.Context, walletTx *entities.WalletTransaction) error
	// GetTransactionByIdempotencyKey returns nil, nil when no row has the key.
	GetTransactionByIdempotencyKey(ctx context.Context, key string) (*entities.WalletTransaction, error)

	CreateLot(ctx context.Context, lot *entities.WalletLot) error
	// GetLotsByIDs returns the lots with the given ids, expired or not, in no
	// particular order. Ids that match no lot are left out.
	GetLotsByIDs(ctx context.Context, ids []uuid.UUID) ([]entities.WalletLot, error)
	// ListLotsBySourceTransaction returns the lots a credit created, oldest first.
	ListLotsBySourceTransaction(ctx context.Context, transactionID uuid.UUID) ([]entities.WalletLot, error)
	// ListActiveLots returns the lots that still have balance and have not expired at
	// asOf, in the order they are spent (K9): soonest expiry first, lots without an
	// expiry last, oldest first within the same expiry.
	ListActiveLots(ctx context.Context, customerID uuid.UUID, currency string, asOf time.Time) ([]entities.WalletLot, error)
	// ConsumeLot takes amount from a lot's remaining amount. Taking more than remains
	// changes nothing and returns ErrWalletLotInsufficient.
	ConsumeLot(ctx context.Context, lotID uuid.UUID, amount int64) error

	CreateAllocations(ctx context.Context, allocations []entities.WalletLotAllocation) error
	ListAllocationsByTransaction(ctx context.Context, transactionID uuid.UUID) ([]entities.WalletLotAllocation, error)
}

type walletRepository struct {
	db *gorm.DB
}

func NewWalletRepository(db *gorm.DB) WalletRepository {
	return &walletRepository{db: db}
}

// txDB returns the caller's transaction, or ErrWalletTxRequired if there is none.
func (r *walletRepository) txDB(ctx context.Context) (*gorm.DB, error) {
	if tx, ok := ctx.Value(txKey).(*gorm.DB); ok && tx != nil {
		return tx.WithContext(ctx), nil
	}
	return nil, ErrWalletTxRequired
}

func (r *walletRepository) LockWallet(ctx context.Context, customerID uuid.UUID) (*entities.CustomerWallet, error) {
	db, err := r.txDB(ctx)
	if err != nil {
		return nil, err
	}

	// The wallet takes its organization from the customer, so the two cannot disagree.
	// ON CONFLICT covers two first operations racing to create the same wallet.
	err = db.Exec(`INSERT INTO customer_wallets (customer_id, organization_id)
		SELECT id, organization_id FROM customers WHERE id = ?
		ON CONFLICT (customer_id) DO NOTHING`, customerID).Error
	if err != nil {
		return nil, fmt.Errorf("failed to create customer wallet: %w", err)
	}

	var wallet entities.CustomerWallet
	err = db.Clauses(clause.Locking{Strength: "UPDATE"}).
		Where("customer_id = ?", customerID).
		First(&wallet).Error
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, ErrWalletNotFound
		}
		return nil, fmt.Errorf("failed to lock customer wallet: %w", err)
	}
	return &wallet, nil
}

func (r *walletRepository) LockWallets(ctx context.Context, a, b uuid.UUID) (*entities.CustomerWallet, *entities.CustomerWallet, error) {
	if a == b {
		return nil, nil, errors.New("wallet: cannot lock the same wallet twice")
	}

	ids := []uuid.UUID{a, b}
	sort.Slice(ids, func(i, j int) bool { return ids[i].String() < ids[j].String() })

	locked := make(map[uuid.UUID]*entities.CustomerWallet, 2)
	for _, id := range ids {
		wallet, err := r.LockWallet(ctx, id)
		if err != nil {
			return nil, nil, err
		}
		locked[id] = wallet
	}
	return locked[a], locked[b], nil
}

func (r *walletRepository) AddBalance(ctx context.Context, customerID uuid.UUID, currency string, delta int64) (int64, error) {
	db, err := r.txDB(ctx)
	if err != nil {
		return 0, err
	}

	var column string
	switch currency {
	case constants.WalletCurrencyPoint:
		column = "point_balance"
	case constants.WalletCurrencyCoin:
		column = "coin_balance"
	default:
		return 0, fmt.Errorf("wallet: unknown currency %q", currency)
	}

	// The WHERE clause makes an overdraft match no row instead of tripping the CHECK,
	// so the caller gets a clean error and the transaction stays usable.
	var balances []int64
	err = db.Raw(`UPDATE customer_wallets
		SET `+column+` = `+column+` + ?, updated_at = NOW()
		WHERE customer_id = ? AND `+column+` + ? >= 0
		RETURNING `+column, delta, customerID, delta).
		Scan(&balances).Error
	if err != nil {
		return 0, fmt.Errorf("failed to update wallet balance: %w", err)
	}
	if len(balances) == 0 {
		if delta >= 0 {
			return 0, ErrWalletNotFound
		}
		return 0, ErrWalletInsufficientBalance
	}
	return balances[0], nil
}

func (r *walletRepository) GetWallet(ctx context.Context, customerID uuid.UUID) (*entities.CustomerWallet, error) {
	var wallet entities.CustomerWallet
	err := DBFromContext(ctx, r.db).WithContext(ctx).
		Where("customer_id = ?", customerID).
		First(&wallet).Error
	if err != nil {
		return nil, err
	}
	return &wallet, nil
}

func (r *walletRepository) CreateTransaction(ctx context.Context, walletTx *entities.WalletTransaction) error {
	db, err := r.txDB(ctx)
	if err != nil {
		return err
	}
	return db.Create(walletTx).Error
}

func (r *walletRepository) GetTransactionByIdempotencyKey(ctx context.Context, key string) (*entities.WalletTransaction, error) {
	// Find rather than First: a new key is the normal case, and First would log every
	// one of them as a "record not found" error.
	var walletTxs []entities.WalletTransaction
	err := DBFromContext(ctx, r.db).WithContext(ctx).
		Where("idempotency_key = ?", key).
		Limit(1).
		Find(&walletTxs).Error
	if err != nil {
		return nil, fmt.Errorf("failed to get wallet transaction by idempotency key: %w", err)
	}
	if len(walletTxs) == 0 {
		return nil, nil
	}
	return &walletTxs[0], nil
}

func (r *walletRepository) CreateLot(ctx context.Context, lot *entities.WalletLot) error {
	db, err := r.txDB(ctx)
	if err != nil {
		return err
	}
	return db.Create(lot).Error
}

func (r *walletRepository) GetLotsByIDs(ctx context.Context, ids []uuid.UUID) ([]entities.WalletLot, error) {
	var lots []entities.WalletLot
	if len(ids) == 0 {
		return lots, nil
	}
	err := DBFromContext(ctx, r.db).WithContext(ctx).
		Where("id IN ?", ids).
		Find(&lots).Error
	if err != nil {
		return nil, fmt.Errorf("failed to get wallet lots: %w", err)
	}
	return lots, nil
}

func (r *walletRepository) ListLotsBySourceTransaction(ctx context.Context, transactionID uuid.UUID) ([]entities.WalletLot, error) {
	var lots []entities.WalletLot
	err := DBFromContext(ctx, r.db).WithContext(ctx).
		Where("source_transaction_id = ?", transactionID).
		Order("created_at, id").
		Find(&lots).Error
	if err != nil {
		return nil, fmt.Errorf("failed to list wallet lots by source transaction: %w", err)
	}
	return lots, nil
}

func (r *walletRepository) ListActiveLots(ctx context.Context, customerID uuid.UUID, currency string, asOf time.Time) ([]entities.WalletLot, error) {
	var lots []entities.WalletLot
	// Filter and order match idx_wallet_lots_consume.
	err := DBFromContext(ctx, r.db).WithContext(ctx).
		Where("customer_id = ? AND currency = ? AND remaining_amount > 0", customerID, currency).
		Where("(expires_at IS NULL OR expires_at > ?)", asOf).
		Order("expires_at NULLS LAST, created_at, id").
		Find(&lots).Error
	if err != nil {
		return nil, fmt.Errorf("failed to list active wallet lots: %w", err)
	}
	return lots, nil
}

func (r *walletRepository) ConsumeLot(ctx context.Context, lotID uuid.UUID, amount int64) error {
	if amount <= 0 {
		return fmt.Errorf("wallet: lot consumption must be positive, got %d", amount)
	}
	db, err := r.txDB(ctx)
	if err != nil {
		return err
	}

	result := db.Exec(`UPDATE wallet_lots SET remaining_amount = remaining_amount - ?
		WHERE id = ? AND remaining_amount >= ?`, amount, lotID, amount)
	if result.Error != nil {
		return fmt.Errorf("failed to consume wallet lot: %w", result.Error)
	}
	if result.RowsAffected == 0 {
		return ErrWalletLotInsufficient
	}
	return nil
}

func (r *walletRepository) CreateAllocations(ctx context.Context, allocations []entities.WalletLotAllocation) error {
	if len(allocations) == 0 {
		return nil
	}
	db, err := r.txDB(ctx)
	if err != nil {
		return err
	}
	return db.Create(&allocations).Error
}

func (r *walletRepository) ListAllocationsByTransaction(ctx context.Context, transactionID uuid.UUID) ([]entities.WalletLotAllocation, error) {
	var allocations []entities.WalletLotAllocation
	err := DBFromContext(ctx, r.db).WithContext(ctx).
		Where("transaction_id = ?", transactionID).
		Find(&allocations).Error
	if err != nil {
		return nil, fmt.Errorf("failed to list wallet lot allocations: %w", err)
	}
	return allocations, nil
}