package engine

import (
	"context"
	"fmt"
	"sync"
	"time"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/util/logicerr"
	"golang.org/x/sync/errgroup"
)

type EvacuateProcessState int

const (
	EvacuateProcessStateUndefined EvacuateProcessState = iota
	EvacuateProcessStateRunning
	EvacuateProcessStateCompleted
)

type EvacuationState struct {
	shardIDs     []string
	processState EvacuateProcessState
	startedAt    time.Time
	finishedAt   time.Time
	result       *EvacuateShardRes
	errMessage   string
}

func (s *EvacuationState) ShardIDs() []string {
	if s == nil {
		return nil
	}
	return s.shardIDs
}

func (s *EvacuationState) ObjectsEvacuated() uint64 {
	if s == nil {
		return 0
	}
	return s.result.ObjectsEvacuated()
}

func (s *EvacuationState) ObjectsTotal() uint64 {
	if s == nil {
		return 0
	}
	return s.result.ObjectsTotal()
}

func (s *EvacuationState) ObjectsFailed() uint64 {
	if s == nil {
		return 0
	}
	return s.result.ObjectsFailed()
}

func (s *EvacuationState) ObjectsSkipped() uint64 {
	if s == nil {
		return 0
	}
	return s.result.ObjectsSkipped()
}

func (s *EvacuationState) TreesEvacuated() uint64 {
	if s == nil {
		return 0
	}
	return s.result.TreesEvacuated()
}

func (s *EvacuationState) TreesTotal() uint64 {
	if s == nil {
		return 0
	}
	return s.result.TreesTotal()
}

func (s *EvacuationState) TreesFailed() uint64 {
	if s == nil {
		return 0
	}
	return s.result.TreesFailed()
}

func (s *EvacuationState) ProcessingStatus() EvacuateProcessState {
	if s == nil {
		return EvacuateProcessStateUndefined
	}
	return s.processState
}

func (s *EvacuationState) StartedAt() *time.Time {
	if s == nil {
		return nil
	}
	defaultTime := time.Time{}
	if s.startedAt == defaultTime {
		return nil
	}
	return &s.startedAt
}

func (s *EvacuationState) FinishedAt() *time.Time {
	if s == nil {
		return nil
	}
	defaultTime := time.Time{}
	if s.finishedAt == defaultTime {
		return nil
	}
	return &s.finishedAt
}

func (s *EvacuationState) ErrorMessage() string {
	if s == nil {
		return ""
	}
	return s.errMessage
}

func (s *EvacuationState) DeepCopy() *EvacuationState {
	if s == nil {
		return nil
	}
	shardIDs := make([]string, len(s.shardIDs))
	copy(shardIDs, s.shardIDs)

	return &EvacuationState{
		shardIDs:     shardIDs,
		processState: s.processState,
		startedAt:    s.startedAt,
		finishedAt:   s.finishedAt,
		errMessage:   s.errMessage,
		result:       s.result.DeepCopy(),
	}
}

type evacuationLimiter struct {
	state  EvacuationState
	eg     *errgroup.Group
	cancel context.CancelFunc

	guard sync.RWMutex
}

func (l *evacuationLimiter) TryStart(ctx context.Context, shardIDs []string, result *EvacuateShardRes) (*errgroup.Group, context.Context, error) {
	l.guard.Lock()
	defer l.guard.Unlock()

	select {
	case <-ctx.Done():
		return nil, nil, ctx.Err()
	default:
	}

	if l.state.processState == EvacuateProcessStateRunning {
		return nil, nil, logicerr.New(fmt.Sprintf("evacuate is already running for shard ids %v", l.state.shardIDs))
	}

	var egCtx context.Context
	egCtx, l.cancel = context.WithCancel(ctx)
	l.eg, egCtx = errgroup.WithContext(egCtx)
	l.state = EvacuationState{
		shardIDs:     shardIDs,
		processState: EvacuateProcessStateRunning,
		startedAt:    time.Now().UTC(),
		result:       result,
	}

	return l.eg, egCtx, nil
}

func (l *evacuationLimiter) Complete(err error) {
	l.guard.Lock()
	defer l.guard.Unlock()

	errMsq := ""
	if err != nil {
		errMsq = err.Error()
	}
	l.state.processState = EvacuateProcessStateCompleted
	l.state.errMessage = errMsq
	l.state.finishedAt = time.Now().UTC()

	l.eg = nil
}

func (l *evacuationLimiter) GetState() *EvacuationState {
	l.guard.RLock()
	defer l.guard.RUnlock()

	return l.state.DeepCopy()
}

func (l *evacuationLimiter) CancelIfRunning() error {
	l.guard.Lock()
	defer l.guard.Unlock()

	if l.state.processState != EvacuateProcessStateRunning {
		return logicerr.New("there is no running evacuation task")
	}

	l.cancel()
	return nil
}