// Copyright 2023 TiKV Authors
//
// 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 resource_control

import (
	"reflect"
	"unsafe"

	"github.com/pingcap/kvproto/pkg/coprocessor"
	"github.com/pingcap/kvproto/pkg/kvrpcpb"
	"github.com/pingcap/log"
	"github.com/tikv/client-go/v2/tikvrpc"
	"go.uber.org/zap"
)

// RequestInfo contains information about a request that is able to calculate the RU cost
// before the request is sent. Specifically, the write bytes RU cost of a write request
// could be calculated by its key size to write.
type RequestInfo struct {
	// writeBytes is the actual write size if the request is a write request,
	// or -1 if it's a read request.
	writeBytes int64
}

// MakeRequestInfo extracts the relevant information from a BatchRequest.
func MakeRequestInfo(req *tikvrpc.Request) *RequestInfo {
	if !req.IsTxnWriteRequest() && !req.IsRawWriteRequest() {
		return &RequestInfo{writeBytes: -1}
	}

	var writeBytes int64
	switch r := req.Req.(type) {
	case *kvrpcpb.PrewriteRequest:
		writeBytes += int64(r.TxnSize)
	case *kvrpcpb.CommitRequest:
		writeBytes += int64(unsafe.Sizeof(r.Keys))
	}

	return &RequestInfo{writeBytes: writeBytes}
}

// IsWrite returns whether the request is a write request.
func (req *RequestInfo) IsWrite() bool {
	return req.writeBytes > -1
}

// WriteBytes returns the actual write size of the request,
// -1 will be returned if it's not a write request.
func (req *RequestInfo) WriteBytes() uint64 {
	return uint64(req.writeBytes)
}

// ResponseInfo contains information about a response that is able to calculate the RU cost
// after the response is received. Specifically, the read bytes RU cost of a read request
// could be calculated by its response size, and the KV CPU time RU cost of a request could
// be calculated by its execution details info.
type ResponseInfo struct {
	readBytes uint64
	kvCPUMs   uint64
}

// MakeResponseInfo extracts the relevant information from a BatchResponse.
func MakeResponseInfo(resp *tikvrpc.Response) *ResponseInfo {
	if resp.Resp == nil {
		return &ResponseInfo{}
	}
	// Parse the response to extract the info.
	var (
		readBytes uint64
		detailsV2 *kvrpcpb.ExecDetailsV2
		details   *kvrpcpb.ExecDetails
	)
	switch r := resp.Resp.(type) {
	case *coprocessor.Response:
		detailsV2 = r.GetExecDetailsV2()
		details = r.GetExecDetails()
		readBytes = uint64(r.Data.Size())
	case *tikvrpc.CopStreamResponse:
		// Streaming request returns `io.EOF``, so the first `CopStreamResponse.Response`` may be nil.
		if r.Response != nil {
			detailsV2 = r.Response.GetExecDetailsV2()
			details = r.Response.GetExecDetails()
		}
		readBytes = uint64(r.Data.Size())
	case *kvrpcpb.GetResponse:
		detailsV2 = r.GetExecDetailsV2()
	case *kvrpcpb.BatchGetResponse:
		detailsV2 = r.GetExecDetailsV2()
	case *kvrpcpb.ScanResponse:
		// TODO: using a more accurate size rather than using the whole response size as the read bytes.
		readBytes = uint64(r.Size())
	default:
		log.Warn("[kv resource] unknown response type to collect the info", zap.Any("type", reflect.TypeOf(r)))
		return &ResponseInfo{}
	}
	// Try to get read bytes from the `detailsV2`.
	// TODO: clarify whether we should count the underlying storage engine read bytes or not.
	if scanDetail := detailsV2.GetScanDetailV2(); scanDetail != nil {
		readBytes = scanDetail.GetProcessedVersionsSize()
	}
	// Get the KV CPU time in milliseconds from the execution time details.
	kvCPUMs := getKVCPUMs(detailsV2, details)
	return &ResponseInfo{readBytes: readBytes, kvCPUMs: kvCPUMs}
}

// TODO: find out a more accurate way to get the actual KV CPU time.
func getKVCPUMs(detailsV2 *kvrpcpb.ExecDetailsV2, details *kvrpcpb.ExecDetails) uint64 {
	if timeDetail := detailsV2.GetTimeDetail(); timeDetail != nil {
		return timeDetail.GetProcessWallTimeMs()
	}
	if timeDetail := details.GetTimeDetail(); timeDetail != nil {
		return timeDetail.GetProcessWallTimeMs()
	}
	return 0
}

// ReadBytes returns the read bytes of the response.
func (res *ResponseInfo) ReadBytes() uint64 {
	return res.readBytes
}

// KVCPUMs returns the KV CPU time in milliseconds of the response.
func (res *ResponseInfo) KVCPUMs() uint64 {
	return res.kvCPUMs
}