package network

import (
	"sync"
	"sync/atomic"
	"time"

	libcommon "github.com/ledgerwatch/erigon-lib/common"
	"github.com/ledgerwatch/erigon-lib/kv"
	"github.com/ledgerwatch/log/v3"
	"golang.org/x/net/context"

	"github.com/ledgerwatch/erigon/cl/cltypes"
	"github.com/ledgerwatch/erigon/cl/persistence/beacon_indicies"
	"github.com/ledgerwatch/erigon/cl/rpc"
)

// Whether the reverse downloader arrived at expected height or condition.
type OnNewBlock func(blk *cltypes.SignedBeaconBlock) (finished bool, err error)

type BackwardBeaconDownloader struct {
	ctx            context.Context
	slotToDownload uint64
	expectedRoot   libcommon.Hash
	rpc            *rpc.BeaconRpcP2P
	onNewBlock     OnNewBlock
	finished       bool
	reqInterval    *time.Ticker
	db             kv.RwDB
	neverSkip      bool

	mu sync.Mutex
}

func NewBackwardBeaconDownloader(ctx context.Context, rpc *rpc.BeaconRpcP2P, db kv.RwDB) *BackwardBeaconDownloader {
	return &BackwardBeaconDownloader{
		ctx:         ctx,
		rpc:         rpc,
		db:          db,
		reqInterval: time.NewTicker(300 * time.Millisecond),
		neverSkip:   true,
	}
}

// SetThrottle sets the throttle.
func (b *BackwardBeaconDownloader) SetThrottle(throttle time.Duration) {
	b.mu.Lock()
	defer b.mu.Unlock()
	b.reqInterval.Reset(throttle)
}

// SetSlotToDownload sets slot to download.
func (b *BackwardBeaconDownloader) SetSlotToDownload(slot uint64) {
	b.mu.Lock()
	defer b.mu.Unlock()
	b.slotToDownload = slot
}

// SetExpectedRoot sets the expected root we expect to download.
func (b *BackwardBeaconDownloader) SetExpectedRoot(root libcommon.Hash) {
	b.mu.Lock()
	defer b.mu.Unlock()
	b.expectedRoot = root
}

// SetExpectedRoot sets the expected root we expect to download.
func (b *BackwardBeaconDownloader) SetNeverSkip(neverSkip bool) {
	b.mu.Lock()
	defer b.mu.Unlock()
	b.neverSkip = neverSkip
}

// SetShouldStopAtFn sets the stop condition.
func (b *BackwardBeaconDownloader) SetOnNewBlock(onNewBlock OnNewBlock) {
	b.mu.Lock()
	defer b.mu.Unlock()
	b.onNewBlock = onNewBlock
}

// HighestProcessedRoot returns the highest processed block root so far.
func (b *BackwardBeaconDownloader) Finished() bool {
	b.mu.Lock()
	defer b.mu.Unlock()
	return b.finished
}

// Progress current progress.
func (b *BackwardBeaconDownloader) Progress() uint64 {
	// Skip if it is not downloading or limit was reached
	b.mu.Lock()
	defer b.mu.Unlock()
	return b.slotToDownload
}

// Peers returns the current number of peers connected to the BackwardBeaconDownloader.
func (b *BackwardBeaconDownloader) Peers() (uint64, error) {
	return b.rpc.Peers()
}

// RequestMore downloads a range of blocks in a backward manner.
// The function sends a request for a range of blocks starting from a given slot and ending count blocks before it.
// It then processes the response by iterating over the blocks in reverse order and calling a provided callback function onNewBlock on each block.
// If the callback returns an error or signals that the download should be finished, the function will exit.
// If the block's root hash does not match the expected root hash, it will be rejected and the function will continue to the next block.
func (b *BackwardBeaconDownloader) RequestMore(ctx context.Context) error {
	count := uint64(32)
	start := b.slotToDownload - count + 1
	// Overflow? round to 0.
	if start > b.slotToDownload {
		start = 0
	}
	var atomicResp atomic.Value
	atomicResp.Store([]*cltypes.SignedBeaconBlock{})

Loop:
	for {
		select {
		case <-b.reqInterval.C:
			go func() {
				if len(atomicResp.Load().([]*cltypes.SignedBeaconBlock)) > 0 {
					return
				}
				responses, peerId, err := b.rpc.SendBeaconBlocksByRangeReq(ctx, start, count)
				if err != nil {
					return
				}
				if responses == nil {
					return
				}
				if len(responses) == 0 {
					b.rpc.BanPeer(peerId)
					return
				}
				atomicResp.Store(responses)
			}()
		case <-ctx.Done():
			return ctx.Err()
		default:
			if len(atomicResp.Load().([]*cltypes.SignedBeaconBlock)) > 0 {
				break Loop
			}
			time.Sleep(10 * time.Millisecond)
		}
	}
	responses := atomicResp.Load().([]*cltypes.SignedBeaconBlock)
	// Import new blocks, order is forward so reverse the whole packet
	for i := len(responses) - 1; i >= 0; i-- {
		if b.finished {
			return nil
		}
		segment := responses[i]
		// is this new block root equal to the expected root?
		blockRoot, err := segment.Block.HashSSZ()
		if err != nil {
			log.Debug("Could not compute block root while processing packet", "err", err)
			continue
		}
		// No? Reject.
		if blockRoot != b.expectedRoot {
			log.Debug("Gotten unexpected root", "got", blockRoot, "expected", b.expectedRoot)
			continue
		}
		// Yes? then go for the callback.
		b.finished, err = b.onNewBlock(segment)
		if err != nil {
			log.Warn("Found error while processing packet", "err", err)
			continue
		}
		// set expected root to the segment parent root
		b.expectedRoot = segment.Block.ParentRoot
		b.slotToDownload = segment.Block.Slot - 1 // update slot (might be inexact but whatever)
	}
	if b.neverSkip {
		return nil
	}
	// try skipping if the next slot is in db
	tx, err := b.db.BeginRw(b.ctx)
	if err != nil {
		return err
	}
	defer tx.Rollback()

	// it will stop if we end finding a gap or if we reach the maxIterations
	for {
		// check if the expected root is in db
		slot, err := beacon_indicies.ReadBlockSlotByBlockRoot(tx, b.expectedRoot)
		if err != nil {
			return err
		}
		if slot == nil || *slot == 0 {
			break
		}
		b.slotToDownload = *slot - 1
		if err := beacon_indicies.MarkRootCanonical(b.ctx, tx, *slot, b.expectedRoot); err != nil {
			return err
		}
		b.expectedRoot, err = beacon_indicies.ReadParentBlockRoot(b.ctx, tx, b.expectedRoot)
		if err != nil {
			return err
		}
	}

	return tx.Commit()
}