package fifo_stock_v2

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"hash/fnv"
	"math"
	"regexp"
	"strings"

	"github.com/sirupsen/logrus"
	entity "gitlab.com/mbugroup/lti-api.git/internal/entities"
	"gorm.io/gorm"
)

var identifierPattern = regexp.MustCompile(`^[a-zA-Z_][a-zA-Z0-9_]*$`)

type fifoStockV2Service struct {
	db                 *gorm.DB
	logger             *logrus.Logger
	defaultGatherLimit int
}

func NewService(db *gorm.DB, logger *logrus.Logger) Service {
	if logger == nil {
		logger = logrus.StandardLogger()
	}

	return &fifoStockV2Service{
		db:                 db,
		logger:             logger,
		defaultGatherLimit: 1000,
	}
}

func (s *fifoStockV2Service) withTransaction(
	ctx context.Context,
	tx *gorm.DB,
	fn func(*gorm.DB) error,
) error {
	if tx != nil {
		return fn(tx.WithContext(ctx))
	}
	return s.db.WithContext(ctx).Transaction(func(inner *gorm.DB) error {
		return fn(inner)
	})
}

func isSafeIdentifier(v string) bool {
	return identifierPattern.MatchString(strings.TrimSpace(v))
}

func mustSafeIdentifier(v string) (string, error) {
	v = strings.TrimSpace(v)
	if !isSafeIdentifier(v) {
		return "", fmt.Errorf("unsafe identifier: %s", v)
	}
	return v, nil
}

func requestHash(v any) string {
	payload, _ := json.Marshal(v)
	sum := sha256.Sum256(payload)
	return hex.EncodeToString(sum[:])
}

func shardLockKey(flagGroupCode string, productWarehouseID uint) int64 {
	h := fnv.New64a()
	_, _ = h.Write([]byte(strings.TrimSpace(strings.ToUpper(flagGroupCode))))
	_, _ = h.Write([]byte("|"))
	_, _ = h.Write([]byte(fmt.Sprintf("%d", productWarehouseID)))
	return int64(h.Sum64())
}

func (s *fifoStockV2Service) lockShard(tx *gorm.DB, flagGroupCode string, productWarehouseID uint) error {
	if strings.TrimSpace(flagGroupCode) == "" || productWarehouseID == 0 {
		return fmt.Errorf("lock shard requires flag group and product warehouse")
	}
	return tx.Exec("SELECT pg_advisory_xact_lock(?)", shardLockKey(flagGroupCode, productWarehouseID)).Error
}

type operationLogRow struct {
	ID            uint            `gorm:"column:id"`
	Status        string          `gorm:"column:status"`
	RequestHash   string          `gorm:"column:request_hash"`
	ResultPayload json.RawMessage `gorm:"column:result_payload"`
}

func (s *fifoStockV2Service) beginOperation(
	tx *gorm.DB,
	op Operation,
	idempotencyKey string,
	requestHashValue string,
	productWarehouseID uint,
	flagGroupCode string,
	usableType string,
	usableID uint,
) (*operationLogRow, bool, error) {
	if strings.TrimSpace(idempotencyKey) == "" {
		return nil, false, nil
	}

	inserted := operationLogRow{}
	insertSQL := `
		INSERT INTO fifo_stock_v2_operation_log
			(idempotency_key, operation, product_warehouse_id, flag_group_code, usable_type, usable_id, request_hash, status, created_at)
		VALUES (?, ?, ?, ?, NULLIF(?, ''), NULLIF(?, 0), ?, 'RUNNING', NOW())
		ON CONFLICT (idempotency_key, operation) DO NOTHING
		RETURNING id, status, request_hash
	`
	if err := tx.Raw(insertSQL,
		idempotencyKey,
		string(op),
		productWarehouseID,
		flagGroupCode,
		usableType,
		usableID,
		requestHashValue,
	).Scan(&inserted).Error; err != nil {
		return nil, false, err
	}
	if inserted.ID != 0 {
		return &inserted, false, nil
	}

	existing := operationLogRow{}
	if err := tx.Table("fifo_stock_v2_operation_log").
		Select("id, status, request_hash, result_payload").
		Where("idempotency_key = ? AND operation = ?", idempotencyKey, string(op)).
		Take(&existing).Error; err != nil {
		return nil, false, err
	}

	if existing.RequestHash != requestHashValue {
		return nil, false, fmt.Errorf("idempotency key %s reused with different payload", idempotencyKey)
	}

	switch strings.ToUpper(existing.Status) {
	case "DONE":
		return &existing, true, nil
	case "RUNNING":
		return nil, false, fmt.Errorf("operation %s with idempotency key %s is still running", op, idempotencyKey)
	case "FAILED":
		if err := tx.Table("fifo_stock_v2_operation_log").
			Where("id = ?", existing.ID).
			Updates(map[string]any{
				"status":      "RUNNING",
				"error_text":  nil,
				"finished_at": nil,
			}).Error; err != nil {
			return nil, false, err
		}
		existing.Status = "RUNNING"
		return &existing, false, nil
	default:
		return nil, false, fmt.Errorf("unknown operation status: %s", existing.Status)
	}
}

func (s *fifoStockV2Service) finishOperation(tx *gorm.DB, logRow *operationLogRow, payload any) error {
	if logRow == nil || logRow.ID == 0 {
		return nil
	}

	encoded, err := json.Marshal(payload)
	if err != nil {
		return err
	}

	return tx.Table("fifo_stock_v2_operation_log").
		Where("id = ?", logRow.ID).
		Updates(map[string]any{
			"status":         "DONE",
			"result_payload": encoded,
			"finished_at":    gorm.Expr("NOW()"),
		}).Error
}

func (s *fifoStockV2Service) failOperation(tx *gorm.DB, logRow *operationLogRow, failure error) {
	if logRow == nil || logRow.ID == 0 || failure == nil {
		return
	}
	_ = tx.Table("fifo_stock_v2_operation_log").
		Where("id = ?", logRow.ID).
		Updates(map[string]any{
			"status":      "FAILED",
			"error_text":  failure.Error(),
			"finished_at": gorm.Expr("NOW()"),
		}).Error
}

func (s *fifoStockV2Service) resolveOverConsume(
	tx *gorm.DB,
	flagGroupCode string,
	functionCode string,
	lane Lane,
	defaultValue bool,
) (bool, error) {
	type row struct {
		Allow bool `gorm:"column:allow_overconsume"`
	}
	selected := row{}
	err := tx.Table("fifo_stock_v2_overconsume_rules").
		Select("allow_overconsume").
		Where("is_active = TRUE").
		Where("lane = ?", string(lane)).
		Where("(flag_group_code IS NULL OR flag_group_code = ?)", flagGroupCode).
		Where("(function_code IS NULL OR function_code = ?)", functionCode).
		Order("CASE WHEN flag_group_code IS NULL THEN 1 ELSE 0 END ASC").
		Order("CASE WHEN function_code IS NULL THEN 1 ELSE 0 END ASC").
		Order("priority ASC, id ASC").
		Limit(1).
		Take(&selected).Error
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return defaultValue, nil
		}
		return false, err
	}
	return selected.Allow, nil
}

func (s *fifoStockV2Service) adjustProductWarehouseQty(tx *gorm.DB, productWarehouseID uint, delta float64) error {
	if productWarehouseID == 0 || delta == 0 {
		return nil
	}
	return tx.Table("product_warehouses").
		Where("id = ?", productWarehouseID).
		Update("qty", gorm.Expr("COALESCE(qty,0) + ?", delta)).Error
}

func nearlyZero(v float64) bool {
	return math.Abs(v) < 1e-6
}

func (s *fifoStockV2Service) ensureStockAllocationColumns(tx *gorm.DB) error {
	checkCols := []string{"engine_version", "flag_group_code", "function_code", "idempotency_key", "allocation_purpose"}
	for _, col := range checkCols {
		var count int64
		err := tx.Raw(`
			SELECT COUNT(1)
			FROM information_schema.columns
			WHERE table_schema = 'public' AND table_name = 'stock_allocations' AND column_name = ?
		`, col).Scan(&count).Error
		if err != nil {
			return err
		}
		if count == 0 {
			return fmt.Errorf("stock_allocations.%s does not exist, run fifo_stock_v2 migration first", col)
		}
	}
	return nil
}

func activeAllocationStatus() string {
	return entity.StockAllocationStatusActive
}

func releasedAllocationStatus() string {
	return entity.StockAllocationStatusReleased
}

func defaultAllocationPurpose() string {
	return entity.StockAllocationPurposeConsume
}

func normalizeAllocationPurpose(purpose string) string {
	purpose = strings.TrimSpace(strings.ToUpper(purpose))
	if purpose == "" {
		return defaultAllocationPurpose()
	}
	return purpose
}