package db

import (
	"database/sql"
	"gorm.io/gorm"
	"math"
)

// QueryBuilder 查询构造器
// TODO（hupeh）：实现 joins 和表别名
type QueryBuilder[T any] struct {
	Expr
	db       *gorm.DB
	selects  []string
	omits    []string
	orders   []string
	limit    int
	offset   int
	distinct []any
	preloads []preload
}

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

type preload struct {
	query string
	args  []any
}

type Pager[T any] struct {
	Total int  `json:"total" xml:"total"` // 数据总数
	Page  int  `json:"page"  xml:"page"`  // 当前页码
	Limit int  `json:"limit" xml:"limit"` // 数据容量
	Items []*T `json:"items" xml:"items"` // 数据列表
}

func (q *QueryBuilder[T]) Select(columns ...string) *QueryBuilder[T] {
	q.selects = append(q.selects, columns...)
	return q
}

func (q *QueryBuilder[T]) Omit(columns ...string) *QueryBuilder[T] {
	q.omits = append(q.omits, columns...)
	return q
}

func (q *QueryBuilder[T]) DescentBy(columns ...string) *QueryBuilder[T] {
	for _, col := range columns {
		q.orders = append(q.orders, col+" DESC")
	}
	return q
}

func (q *QueryBuilder[T]) AscentBy(columns ...string) *QueryBuilder[T] {
	for _, col := range columns {
		q.orders = append(q.orders, col)
	}
	return q
}

func (q *QueryBuilder[T]) Limit(limit int) *QueryBuilder[T] {
	q.limit = limit
	return q
}

func (q *QueryBuilder[T]) Offset(offset int) *QueryBuilder[T] {
	q.offset = offset
	return q
}

func (q *QueryBuilder[T]) Distinct(columns ...any) *QueryBuilder[T] {
	q.distinct = append(q.distinct, columns...)
	return q
}

func (q *QueryBuilder[T]) Preload(query string, args ...any) *QueryBuilder[T] {
	q.preloads = append(q.preloads, preload{query, args})
	return q
}

func (q *QueryBuilder[T]) Scopes(tx *gorm.DB) *gorm.DB {
	tx = q.scopesWithoutEffect(tx)
	if q.orders != nil {
		for _, order := range q.orders {
			tx = tx.Order(order)
		}
	}
	if q.limit > 0 {
		tx = tx.Limit(q.limit)
	}
	if q.offset > 0 {
		tx = tx.Offset(q.offset)
	}
	if q.preloads != nil {
		for _, pl := range q.preloads {
			tx = tx.Preload(pl.query, pl.args...)
		}
	}
	return tx
}

func (q *QueryBuilder[T]) scopesWithoutEffect(tx *gorm.DB) *gorm.DB {
	var entity T
	tx = tx.Model(&entity)
	if q.selects != nil {
		tx = tx.Select(q.selects)
	}
	if q.omits != nil {
		tx = tx.Omit(q.omits...)
	}
	if len(q.distinct) > 0 {
		tx = tx.Distinct(q.distinct...)
	}
	return q.Expr.Scopes(tx)
}

func (q *QueryBuilder[T]) Count() (int64, error) {
	var count int64
	err := q.db.Scopes(q.scopesWithoutEffect).Count(&count).Error
	return count, err
}

func (q *QueryBuilder[T]) First(entity any) error {
	return q.db.Scopes(q.Scopes).First(entity).Error
}

func (q *QueryBuilder[T]) Take(entity any) error {
	return q.db.Scopes(q.Scopes).Take(entity).Error
}

func (q *QueryBuilder[T]) Last(entity any) error {
	return q.db.Scopes(q.Scopes).Last(entity).Error
}

func (q *QueryBuilder[T]) Find(entity any) error {
	return q.db.Scopes(q.Scopes).Find(entity).Error
}

func (q *QueryBuilder[T]) Paginate() (*Pager[T], error) {
	if q.limit <= 0 {
		q.limit = 30
	}
	if q.offset < 0 {
		q.offset = 0
	}
	count, err := q.Count()
	if err != nil {
		return nil, err
	}
	var items []*T
	err = q.Find(&items)
	if err != nil {
		return nil, err
	}
	return &Pager[T]{
		Total: int(count),
		Page:  int(math.Ceil(float64(q.offset)/float64(q.limit))) + 1,
		Limit: q.limit,
		Items: items,
	}, nil
}

// Rows 返回行数据迭代器
//
// 使用示例：
//
//	rows, err := q.Eq("name", "jack").Rows()
//	if err != nil {
//	  panic(err)
//	}
//	defer rows.Close()
//	for rows.Next() {
//	  var user User
//	  db.ScanRows(rows, &user)
//	  // do something
//	}
func (q *QueryBuilder[T]) Rows() (*sql.Rows, error) {
	return q.db.Scopes(q.Scopes).Rows()
}

// Pluck 获取指定列的值
//
// 示例：
//
//	var names []string
//	q.Pluck("name", &names)
func (q *QueryBuilder[T]) Pluck(column string, dest any) error {
	return q.db.Scopes(q.Scopes).Pluck(column, dest).Error
}