backend/pkg/library/cassandra/query.go

package cassandra

import (
	"context"
	"fmt"

	"github.com/gocql/gocql"
	"github.com/scylladb/gocqlx/v2/qb"
)

// Condition 定義查詢條件介面
type Condition interface {
	Build() (qb.Cmp, map[string]any)
}

// Eq 等於條件
func Eq(column string, value any) Condition {
	return &eqCondition{column: column, value: value}
}

type eqCondition struct {
	column string
	value  any
}

func (c *eqCondition) Build() (qb.Cmp, map[string]any) {
	return qb.Eq(c.column), map[string]any{c.column: c.value}
}

// In IN 條件
func In(column string, values []any) Condition {
	return &inCondition{column: column, values: values}
}

type inCondition struct {
	column string
	values []any
}

func (c *inCondition) Build() (qb.Cmp, map[string]any) {
	return qb.In(c.column), map[string]any{c.column: c.values}
}

// Gt 大於條件
func Gt(column string, value any) Condition {
	return &gtCondition{column: column, value: value}
}

type gtCondition struct {
	column string
	value  any
}

func (c *gtCondition) Build() (qb.Cmp, map[string]any) {
	return qb.Gt(c.column), map[string]any{c.column: c.value}
}

// Lt 小於條件
func Lt(column string, value any) Condition {
	return &ltCondition{column: column, value: value}
}

type ltCondition struct {
	column string
	value  any
}

func (c *ltCondition) Build() (qb.Cmp, map[string]any) {
	return qb.Lt(c.column), map[string]any{c.column: c.value}
}

// QueryBuilder 定義查詢構建器介面
type QueryBuilder[T Table] interface {
	Where(condition Condition) QueryBuilder[T]
	OrderBy(column string, order Order) QueryBuilder[T]
	Limit(n int) QueryBuilder[T]
	Select(columns ...string) QueryBuilder[T]
	Scan(ctx context.Context, dest *[]T) error
	One(ctx context.Context) (T, error)
	Count(ctx context.Context) (int64, error)
}

// queryBuilder 是 QueryBuilder 的具體實作
type queryBuilder[T Table] struct {
	repo       *repository[T]
	conditions []Condition
	orders     []orderBy
	limit      int
	columns    []string
}

type orderBy struct {
	column string
	order  Order
}

// newQueryBuilder 創建新的查詢構建器
func newQueryBuilder[T Table](repo *repository[T]) QueryBuilder[T] {
	return &queryBuilder[T]{
		repo: repo,
	}
}

// Where 添加 WHERE 條件
func (q *queryBuilder[T]) Where(condition Condition) QueryBuilder[T] {
	q.conditions = append(q.conditions, condition)
	return q
}

// OrderBy 添加排序
func (q *queryBuilder[T]) OrderBy(column string, order Order) QueryBuilder[T] {
	q.orders = append(q.orders, orderBy{column: column, order: order})
	return q
}

// Limit 設置限制
func (q *queryBuilder[T]) Limit(n int) QueryBuilder[T] {
	q.limit = n
	return q
}

// Select 指定要查詢的欄位
func (q *queryBuilder[T]) Select(columns ...string) QueryBuilder[T] {
	q.columns = append(q.columns, columns...)
	return q
}

// Scan 執行查詢並將結果掃描到 dest
func (q *queryBuilder[T]) Scan(ctx context.Context, dest *[]T) error {
	if dest == nil {
		return ErrInvalidInput.WithTable(q.repo.table).WithError(
			fmt.Errorf("destination cannot be nil"),
		)
	}

	builder := qb.Select(q.repo.table)

	// 添加欄位
	if len(q.columns) > 0 {
		builder = builder.Columns(q.columns...)
	} else {
		builder = builder.Columns(q.repo.metadata.Columns...)
	}

	// 添加條件
	bindMap := make(map[string]any)
	var cmps []qb.Cmp
	for _, cond := range q.conditions {
		cmp, binds := cond.Build()
		cmps = append(cmps, cmp)
		for k, v := range binds {
			bindMap[k] = v
		}
	}
	if len(cmps) > 0 {
		builder = builder.Where(cmps...)
	}

	// 添加排序
	for _, o := range q.orders {
		order := qb.ASC
		if o.order == DESC {
			order = qb.DESC
		}

		builder = builder.OrderBy(o.column, order)
	}

	// 添加限制
	if q.limit > 0 {
		builder = builder.Limit(uint(q.limit))
	}

	stmt, names := builder.ToCql()
	query := q.repo.db.withContextAndTimestamp(ctx,
		q.repo.db.session.Query(stmt, names).BindMap(bindMap))

	return query.SelectRelease(dest)
}

// One 執行查詢並返回單筆結果
func (q *queryBuilder[T]) One(ctx context.Context) (T, error) {
	var zero T
	q.limit = 1

	var results []T
	if err := q.Scan(ctx, &results); err != nil {
		return zero, err
	}

	if len(results) == 0 {
		return zero, ErrNotFound.WithTable(q.repo.table)
	}

	return results[0], nil
}

// Count 計算符合條件的記錄數
func (q *queryBuilder[T]) Count(ctx context.Context) (int64, error) {
	builder := qb.Select(q.repo.table).Columns("COUNT(*)")

	// 添加條件
	bindMap := make(map[string]any)
	var cmps []qb.Cmp
	for _, cond := range q.conditions {
		cmp, binds := cond.Build()
		cmps = append(cmps, cmp)
		for k, v := range binds {
			bindMap[k] = v
		}
	}
	if len(cmps) > 0 {
		builder = builder.Where(cmps...)
	}

	stmt, names := builder.ToCql()
	query := q.repo.db.withContextAndTimestamp(ctx,
		q.repo.db.session.Query(stmt, names).BindMap(bindMap))

	var count int64
	err := query.GetRelease(&count)
	if err == gocql.ErrNotFound {
		return 0, nil // COUNT 查詢不會返回 ErrNotFound，但為了安全起見
	}
	return count, err
}