package cassandra

import (
	"context"
	"fmt"
	"reflect"

	"github.com/gocql/gocql"
	"github.com/scylladb/gocqlx/v3"
	"github.com/scylladb/gocqlx/v3/qb"
	"github.com/scylladb/gocqlx/v3/table"
)

// TODO: 只保證同一個 PK 下有一致性，中間有失敗的話可能只有失敗不會寫入，其他成功的還是會成功。
//       之後會朝兩個方向走
//       1. 最終一致性：目前的設計是直接寫入副表，然後透過 background worker 讀取 sync_task 表，補寫副表資料。
//       2. 研究 自己做 TX_ID 以及 STATUS 的方案
//       這個是已知問題，一定要解決

func (db *DB) NewBatch(ctx context.Context, keyspace string) *Batch {
	session := db.GetSession()
	return &Batch{
		ctx:      ctx,
		keyspace: keyspace,
		db:       db,
		batch: gocqlx.Batch{
			Batch: session.NewBatch(gocql.LoggedBatch).WithContext(ctx),
		},
	}
}

type Batch struct {
	ctx      context.Context
	keyspace string
	db       *DB
	batch    gocqlx.Batch
}

func (tx *Batch) Insert(doc any) error {
	metadata, err := GenerateTableMetadata(doc, tx.keyspace)
	if err != nil {
		return err
	}
	tbl := table.New(metadata)
	stmt, names := tbl.Insert()
	return tx.batch.BindStruct(tx.db.GetSession().Query(stmt, names), doc)
}

func (tx *Batch) Delete(doc any) error {
	metadata, err := GenerateTableMetadata(doc, tx.keyspace)
	if err != nil {
		return err
	}
	tbl := table.New(metadata)
	stmt, names := tbl.Delete()
	return tx.batch.BindStruct(tx.db.GetSession().Query(stmt, names), doc)
}

func (tx *Batch) Update(doc any) error {
	metadata, err := GenerateTableMetadata(doc, tx.keyspace)
	if err != nil {
		return err
	}
	v := reflect.ValueOf(doc)
	if v.Kind() == reflect.Ptr {
		v = v.Elem()
	}
	typ := v.Type()

	setCols := make([]string, 0)
	setVals := make([]any, 0)
	whereCols := make([]string, 0)
	whereVals := make([]any, 0)

	for i := 0; i < typ.NumField(); i++ {
		field := typ.Field(i)
		tag := field.Tag.Get("db")
		if tag == "" || tag == "-" {
			continue
		}
		val := v.Field(i)
		if !val.IsValid() {
			continue
		}
		if contains(metadata.PartKey, tag) || contains(metadata.SortKey, tag) {
			whereCols = append(whereCols, tag)
			whereVals = append(whereVals, val.Interface())
		} else if !isZero(val) {
			setCols = append(setCols, tag)
			setVals = append(setVals, val.Interface())
		}
	}

	if len(setCols) == 0 {
		return fmt.Errorf("update: no non-zero fields in %+v", doc)
	}

	builder := qb.Update(metadata.Name).Set(setCols...)
	for _, col := range whereCols {
		builder = builder.Where(qb.Eq(col))
	}
	stmt, names := builder.ToCql()
	args := append(setVals, whereVals...)
	return tx.batch.Bind(tx.db.GetSession().Query(stmt, names), args...)
}

func (tx *Batch) Commit() error {
	session := tx.db.GetSession()

	return session.ExecuteBatch(&tx.batch)
}