// Copyright 2018 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package executor

import (
	"context"
	"encoding/json"

	"github.com/pingcap/errors"
	"github.com/pingcap/tidb/pkg/domain"
	"github.com/pingcap/tidb/pkg/executor/internal/exec"
	"github.com/pingcap/tidb/pkg/infoschema"
	"github.com/pingcap/tidb/pkg/sessionctx"
	"github.com/pingcap/tidb/pkg/statistics/handle/util"
	"github.com/pingcap/tidb/pkg/util/chunk"
)

var _ exec.Executor = &LoadStatsExec{}

// LoadStatsExec represents a load statistic executor.
type LoadStatsExec struct {
	exec.BaseExecutor
	info *LoadStatsInfo
}

// LoadStatsInfo saves the information of loading statistic operation.
type LoadStatsInfo struct {
	Path string
	Ctx  sessionctx.Context
}

// loadStatsVarKeyType is a dummy type to avoid naming collision in context.
type loadStatsVarKeyType int

// String defines a Stringer function for debugging and pretty printing.
func (loadStatsVarKeyType) String() string {
	return "load_stats_var"
}

// LoadStatsVarKey is a variable key for load statistic.
const LoadStatsVarKey loadStatsVarKeyType = 0

// Next implements the Executor Next interface.
func (e *LoadStatsExec) Next(_ context.Context, req *chunk.Chunk) error {
	req.GrowAndReset(e.MaxChunkSize())
	if len(e.info.Path) == 0 {
		return errors.New("Load Stats: file path is empty")
	}
	val := e.Ctx().Value(LoadStatsVarKey)
	if val != nil {
		e.Ctx().SetValue(LoadStatsVarKey, nil)
		return errors.New("Load Stats: previous load stats option isn't closed normally")
	}
	e.Ctx().SetValue(LoadStatsVarKey, e.info)
	return nil
}

// Close implements the Executor Close interface.
func (*LoadStatsExec) Close() error {
	return nil
}

// Open implements the Executor Open interface.
func (*LoadStatsExec) Open(context.Context) error {
	return nil
}

// Update updates the stats of the corresponding table according to the data.
func (e *LoadStatsInfo) Update(data []byte) error {
	jsonTbl := &util.JSONTable{}
	if err := json.Unmarshal(data, jsonTbl); err != nil {
		return errors.Trace(err)
	}
	// Check the `jsonTbl` in cases where the stats file with `null`.
	if jsonTbl.TableName == "" && jsonTbl.Version == 0 {
		return nil
	}
	do := domain.GetDomain(e.Ctx)
	h := do.StatsHandle()
	if h == nil {
		return errors.New("Load Stats: handle is nil")
	}
	return h.LoadStatsFromJSON(context.Background(), e.Ctx.GetInfoSchema().(infoschema.InfoSchema), jsonTbl, 0)
}