// Copyright (C) MongoDB, Inc. 2014-present.
//
// 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

package mongoreplay

import (
	"strconv"
	"sync"
	"time"

	"github.com/patrickmn/go-cache"
)

// cursorManager is an interface that defines how to store and retrieve
// cursorIDs that are found during live traffic playback.
type cursorManager interface {
	// GetCursor is a function that defines how to retrieve a cursor from the
	// underlying data structure.  As arguments it takes the cursorID from the
	// file and the connection number the associated op was played on.
	GetCursor(int64, int64) (int64, bool)

	// SetCursor is a function that defines how to associate a live cursor with
	// one found in the playback file.  As arguments it takes the cursorID from
	// the file and the live cursorID received during playback
	SetCursor(int64, int64)

	// MarkFailed is a function to communicate with the manager that an op has
	// failed and no longer wait for the cursorID that it may generate.  As an
	// argument, it takes the RecordedOp that failed to execute.
	MarkFailed(*RecordedOp)
}

// cursorCache is an implementation of the cursorManager that uses a ttl cache
// for storing cursorIDs during traffic playback. Inserting cursorIDs into the
// cursorCache puts them in with a timeout and retrieving a cursor does not
// block if the cursor is not immediately found in the underlying data
// structure.
type cursorCache cache.Cache

func newCursorCache() *cursorCache {
	return (*cursorCache)(cache.New(600*time.Second, 60*time.Second))
}

// GetCursor is a function that defines how to retrieve a cursor from the
// underlying data structure. As arguments it takes the cursorID from the file
// and the connection number the associated op was played on.
func (c *cursorCache) GetCursor(fileCursorID int64, connectionNum int64) (int64, bool) {
	value, ok := c.Get(strconv.FormatInt(fileCursorID, 10))
	if !ok {
		userInfoLogger.Logvf(Always, "Missing mapped cursorID for raw cursorID : %v in GetMoreOp", fileCursorID)
		return 0, false
	}
	return value.(int64), true
}
func (c *cursorCache) MarkFailed(op *RecordedOp) {}

func (c *cursorCache) SetCursor(fileCursorID int64, liveCursorID int64) {
	c.Set(strconv.FormatInt(fileCursorID, 10), liveCursorID, cache.DefaultExpiration)
}

// preprocessCursorManager is an implementation of cursorManager. The
// preprocessCursorManager holds information about the cursorIDs seen during
// preprocessing the file before playback. Setting a cursorID from live traffic
// maps the cursorID found in the preprocessing step to the live cursor.
// Retrieving a cursorID that was entered in the preprocessing step blocks until
// the live cursorID is received.
type preprocessCursorManager struct {
	cursorInfos map[int64]*preprocessCursorInfo
	opToCursors map[opKey]int64
	sync.RWMutex
}

// preprocessCursorInfo holds information about a cursor that was seen during
// the preprocessing of the traffic.
type preprocessCursorInfo struct {
	// liveCursorID is the cursorID seen during live playback.
	liveCursorID int64
	// blockChan is a channel that ensures execution of connection will halt
	// until the corresponding cursorID is seen from the live traffic. It is
	// closed in the Set function.
	successChan chan struct{}
	// failChain is a channel that communicates that the op that should have
	// created this cursor failed, so proceeding with executing of the
	// corresponding op should stop
	failChan chan struct{}
	// numUsesLeft is the number of uses the corresponding cursor has in the
	// playbackfile.
	numUsesLeft int
	// replyConn is the connection number that the reply is expected to be on
	replyConn int64
}

type cursorCounter struct {
	opOriginKey opKey
	usesConn    []int64
	replyConn   int64
	replySeen   bool
	usesSeen    int
}

type cursorsSeenMap map[int64]cursorCounter

func (c *cursorsSeenMap) trackSeen(cursorID int64, connectionNum int64) {
	val, ok := (*c)[cursorID]
	if !ok {
		(*c)[cursorID] = cursorCounter{
			usesConn:  []int64{connectionNum},
			replySeen: false,
			usesSeen:  1,
		}
		return
	}
	val.usesSeen++
	val.usesConn = append(val.usesConn, connectionNum)
	(*c)[cursorID] = val
}
func (c *cursorsSeenMap) trackReplied(cursorID int64, op *RecordedOp) {
	key := opKey{
		driverEndpoint: op.DstEndpoint,
		serverEndpoint: op.SrcEndpoint,
		opID:           op.Header.ResponseTo,
	}
	val, ok := (*c)[cursorID]
	if !ok {
		(*c)[cursorID] = cursorCounter{
			replySeen:   true,
			usesSeen:    0,
			replyConn:   op.SeenConnectionNum,
			opOriginKey: key,
		}
		return
	}
	val.replyConn = op.SeenConnectionNum
	val.replySeen = true
	(*c)[cursorID] = val

}

// MarkFailed communicates to any waiting execution sessions that the op
// associated with certain cursor has failed. It closes the failChan for that
// op so that execution for any sessions waiting on that cursor could continue.
func (p *preprocessCursorManager) MarkFailed(failedOp *RecordedOp) {
	key := opKey{
		driverEndpoint: failedOp.SrcEndpoint,
		serverEndpoint: failedOp.DstEndpoint,
		opID:           failedOp.Header.RequestID,
	}
	if cursor, ok := p.opToCursors[key]; ok {
		if cursorInfo, ok := p.cursorInfos[cursor]; ok {
			close(cursorInfo.failChan)
		}
	}
}

// newPreprocessCursorManager generates a map of cursorIDs that were found when
// preprocessing the operations. To perform this, it checks to see if a reply
// containing a given cursorID is seen and a corresponding getmore which uses
// that cursorID is also seen. It adds these such cursorIDs to the map and
// tracks how many uses they have had as well.
func newPreprocessCursorManager(opChan <-chan *RecordedOp) (*preprocessCursorManager, error) {
	userInfoLogger.Logvf(Always, "Preprocessing file")

	result := preprocessCursorManager{
		cursorInfos: make(map[int64]*preprocessCursorInfo),
		opToCursors: make(map[opKey]int64),
	}

	cursorsSeen := &cursorsSeenMap{}

	// Loop over all the ops found in the file
	for op := range opChan {

		opCode := op.RawOp.Header.OpCode
		// If they don't produce a cursor, skip them
		if opCode != OpCodeGetMore && opCode != OpCodeKillCursors &&
			opCode != OpCodeReply && opCode != OpCodeCommandReply &&
			opCode != OpCodeCommand && opCode != OpCodeMessage {
			continue
		}
		if opCode == OpCodeCommand {
			commandName, err := getCommandName(&op.RawOp)
			if err != nil {
				userInfoLogger.Logvf(DebugLow, "preprocessing op no command name: %v", err)
				continue
			}
			if commandName != "getMore" && commandName != "getmore" {
				continue
			}
		}

		parsedOp, err := op.RawOp.Parse()
		if err != nil {
			userInfoLogger.Logvf(DebugLow, "preprocessing op parse error: %v", err)
			continue
		}

		switch castOp := parsedOp.(type) {
		case cursorsRewriteable:
			// If the op makes use of a cursor, such as a getmore or a killcursors,
			// track this op and attemp to match it with the reply that contains its
			// cursor
			cursorIDs, err := castOp.getCursorIDs()
			if err != nil {
				userInfoLogger.Logvf(DebugLow, "preprocessing op no cursorId: %v", err)
				continue
			}
			for _, cursorID := range cursorIDs {
				if cursorID == 0 {
					continue
				}
				cursorsSeen.trackSeen(cursorID, op.SeenConnectionNum)
			}

		case Replyable:
			// If the op is a reply it may contain a cursorID. If so, track this
			// op and attempt to pair it with the the op that requires its
			// cursor id.
			cursorID, err := castOp.getCursorID()
			if err != nil {
				userInfoLogger.Logvf(DebugLow, "preprocessing op no cursorId: %v", err)
				continue
			}
			if cursorID == 0 {
				continue
			}
			cursorsSeen.trackReplied(cursorID, op)
		default:
			// In this case, parsing the op revealed it to not be a replyable
			// or able to be rewritten
			continue
		}
	}

	for cursorID, counter := range *cursorsSeen {
		if cursorID != 0 && counter.replySeen && counter.usesSeen > 0 {
			result.cursorInfos[cursorID] = &preprocessCursorInfo{
				failChan:    make(chan struct{}),
				successChan: make(chan struct{}),
				numUsesLeft: counter.usesSeen,
				replyConn:   counter.replyConn,
			}
			result.opToCursors[counter.opOriginKey] = cursorID
		}
	}
	userInfoLogger.Logvf(Always, "Preprocess complete")
	return &result, nil

}

// GetCursor is an implementation of the cursorManager's GetCursor by the
// preprocessCursorManager. It takes a cursorID from the recorded traffic and
// returns the corresponding cursorID found during live playback. If the reply
// that produces the corresponding cursorID has not been seen yet during
// playback, but was in the original recording file, GetCursor will block until
// it receives the cursorID. GetCursor also takes the connection number that the
// waiting operation will be played on so that it will not block if the op is
// somehow waiting for a reply that has not yet occured and is on the same
// connection.  It takes a lock to prevent prevent concurrent accesses to its
// data structues and so that it can unlock while waiting for its cursorID
// without deadlocking other attempts to access its data.
func (p *preprocessCursorManager) GetCursor(fileCursorID int64, connectionNum int64) (int64, bool) {
	p.RLock()
	cursorInfo, ok := p.cursorInfos[fileCursorID]
	p.RUnlock()
	if !ok {
		return 0, false
	}
	select {
	case <-cursorInfo.successChan:
		//the successChan is closed, so we can continue to the next section to
		//retrieve the cursor
	default:
		if connectionNum == cursorInfo.replyConn {
			// the channels are not closed, and this the same connection we are
			// supposed to be waiting on the reply for therefore, the traffic
			// was read out of order at some point, so we should not block
			toolDebugLogger.Logvf(DebugLow, "Skipping cursor rewrite of op on same connection with connection number: %v and cursorID: %v", connectionNum, fileCursorID)
			return 0, false
		}
		// otherwise, the channel is not closed, but we are not waiting on a
		// cursor form the same connection, so we should proceed to the next
		// case
	}

	select {
	case <-cursorInfo.successChan:
		// the cursor has been set after an op was completed which contained it
		p.Lock()
		cursorInfo.numUsesLeft--
		p.cursorInfos[fileCursorID] = cursorInfo
		cursor := cursorInfo.liveCursorID
		if cursorInfo.numUsesLeft <= 0 {
			delete(p.cursorInfos, fileCursorID)
		}
		p.Unlock()

		return cursor, true
	case <-cursorInfo.failChan:
		//the fail chan was closed, which means no cursor is coming for this op
		return 0, false
	}

}

func (p *preprocessCursorManager) SetCursor(fileCursorID int64, liveCursorID int64) {
	p.Lock()
	cursorInfo, ok := p.cursorInfos[fileCursorID]
	if ok {
		select {
		case <-cursorInfo.successChan:
			// if we've already closed the successChan, don't do it again
		default:
			cursorInfo.liveCursorID = liveCursorID
			close(cursorInfo.successChan)
		}
	}
	p.Unlock()
}
