apskel-pos-backend/internal/repository/query_builder.go

package repository

import (
	"github.com/pkg/errors"
	"gorm.io/gorm"
)

type QueryBuilder[T any] struct {
	db    *gorm.DB
	model T
}

func NewQueryBuilder[T any](db *gorm.DB) *QueryBuilder[T] {
	var model T
	return &QueryBuilder[T]{
		db:    db,
		model: model,
	}
}

type Filter struct {
	Field    string
	Operator string // "=", "!=", ">", "<", ">=", "<=", "LIKE", "IN", "NOT IN", "IS NULL", "IS NOT NULL"
	Value    interface{}
}

type QueryOptions struct {
	Filters   []Filter
	Limit     int
	Offset    int
	OrderBy   []string
	Preloads  []string
	GroupBy   []string
	Having    []Filter
	Distinct  []string
	CountOnly bool
}

func (qb *QueryBuilder[T]) BuildQuery(options QueryOptions) *gorm.DB {
	query := qb.db.Model(&qb.model)

	for _, filter := range options.Filters {
		query = qb.applyFilter(query, filter)
	}

	if len(options.Distinct) > 0 {
		for _, distinct := range options.Distinct {
			query = query.Distinct(distinct)
		}
	}

	if len(options.GroupBy) > 0 {
		for _, groupBy := range options.GroupBy {
			query = query.Group(groupBy)
		}
	}

	for _, having := range options.Having {
		query = qb.applyFilter(query, having)
	}

	return query
}

func (qb *QueryBuilder[T]) applyFilter(query *gorm.DB, filter Filter) *gorm.DB {
	switch filter.Operator {
	case "=", "":
		return query.Where(filter.Field+" = ?", filter.Value)
	case "!=":
		return query.Where(filter.Field+" != ?", filter.Value)
	case ">":
		return query.Where(filter.Field+" > ?", filter.Value)
	case "<":
		return query.Where(filter.Field+" < ?", filter.Value)
	case ">=":
		return query.Where(filter.Field+" >= ?", filter.Value)
	case "<=":
		return query.Where(filter.Field+" <= ?", filter.Value)
	case "LIKE":
		return query.Where(filter.Field+" LIKE ?", filter.Value)
	case "IN":
		return query.Where(filter.Field+" IN ?", filter.Value)
	case "NOT IN":
		return query.Where(filter.Field+" NOT IN ?", filter.Value)
	case "IS NULL":
		return query.Where(filter.Field + " IS NULL")
	case "IS NOT NULL":
		return query.Where(filter.Field + " IS NOT NULL")
	case "BETWEEN":
		if values, ok := filter.Value.([]interface{}); ok && len(values) == 2 {
			return query.Where(filter.Field+" BETWEEN ? AND ?", values[0], values[1])
		}
		return query
	default:
		return query.Where(filter.Field+" = ?", filter.Value)
	}
}

func (qb *QueryBuilder[T]) ExecuteQuery(baseQuery *gorm.DB, options QueryOptions) *gorm.DB {
	query := baseQuery.Session(&gorm.Session{})

	if len(options.OrderBy) > 0 {
		for _, orderBy := range options.OrderBy {
			query = query.Order(orderBy)
		}
	}

	for _, preload := range options.Preloads {
		query = query.Preload(preload)
	}

	if options.Limit > 0 {
		query = query.Limit(options.Limit)
	}

	if options.Offset > 0 {
		query = query.Offset(options.Offset)
	}

	return query
}

func (qb *QueryBuilder[T]) Count(baseQuery *gorm.DB) (int64, error) {
	var count int64
	if err := baseQuery.Count(&count).Error; err != nil {
		return 0, errors.Wrap(err, "failed to count records")
	}
	return count, nil
}

func (qb *QueryBuilder[T]) Find(query *gorm.DB) ([]T, error) {
	var results []T
	if err := query.Find(&results).Error; err != nil {
		return nil, errors.Wrap(err, "failed to find records")
	}
	return results, nil
}

func (qb *QueryBuilder[T]) First(query *gorm.DB) (*T, error) {
	var result T
	if err := query.First(&result).Error; err != nil {
		return nil, errors.Wrap(err, "failed to find record")
	}
	return &result, nil
}

func Equal(field string, value interface{}) Filter {
	return Filter{Field: field, Operator: "=", Value: value}
}

func NotEqual(field string, value interface{}) Filter {
	return Filter{Field: field, Operator: "!=", Value: value}
}

func GreaterThan(field string, value interface{}) Filter {
	return Filter{Field: field, Operator: ">", Value: value}
}

func LessThan(field string, value interface{}) Filter {
	return Filter{Field: field, Operator: "<", Value: value}
}

func GreaterEqual(field string, value interface{}) Filter {
	return Filter{Field: field, Operator: ">=", Value: value}
}

func LessEqual(field string, value interface{}) Filter {
	return Filter{Field: field, Operator: "<=", Value: value}
}

func Like(field string, value string) Filter {
	return Filter{Field: field, Operator: "LIKE", Value: value}
}

func In(field string, values interface{}) Filter {
	return Filter{Field: field, Operator: "IN", Value: values}
}

func NotIn(field string, values interface{}) Filter {
	return Filter{Field: field, Operator: "NOT IN", Value: values}
}

func IsNull(field string) Filter {
	return Filter{Field: field, Operator: "IS NULL"}
}

func IsNotNull(field string) Filter {
	return Filter{Field: field, Operator: "IS NOT NULL"}
}

func Between(field string, start, end interface{}) Filter {
	return Filter{Field: field, Operator: "BETWEEN", Value: []interface{}{start, end}}
}