package powchain

import (
	"context"
	"fmt"
	"math/big"

	"github.com/ethereum/go-ethereum/common"
	"github.com/pkg/errors"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"go.opencensus.io/trace"
)

var cachedEth1VotingStartTime uint64
var cachedEth1DataBlockHeight *big.Int

var (
	// Metrics
	votingBlockHeightCacheMiss = promauto.NewCounter(prometheus.CounterOpts{
		Name: "powchain_voting_height_cache_miss",
		Help: "The number of voting block height requests that aren't present in the cache.",
	})
	votingBlockHeightCacheHit = promauto.NewCounter(prometheus.CounterOpts{
		Name: "powchain_voting_height_cache_hit",
		Help: "The number of voting block height requests that are present in the cache.",
	})
)

// BlockExists returns true if the block exists, it's height and any possible error encountered.
func (s *Service) BlockExists(ctx context.Context, hash common.Hash) (bool, *big.Int, error) {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.web3service.BlockExists")
	defer span.End()

	if exists, blkInfo, err := s.blockCache.BlockInfoByHash(hash); exists || err != nil {
		if err != nil {
			return false, nil, err
		}
		span.AddAttributes(trace.BoolAttribute("blockCacheHit", true))
		return true, blkInfo.Number, nil
	}
	span.AddAttributes(trace.BoolAttribute("blockCacheHit", false))
	block, err := s.blockFetcher.BlockByHash(ctx, hash)
	if err != nil {
		return false, big.NewInt(0), errors.Wrap(err, "could not query block with given hash")
	}

	if err := s.blockCache.AddBlock(block); err != nil {
		return false, big.NewInt(0), err
	}

	return true, block.Number(), nil
}

// BlockHashByHeight returns the block hash of the block at the given height.
func (s *Service) BlockHashByHeight(ctx context.Context, height *big.Int) (common.Hash, error) {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.web3service.BlockHashByHeight")
	defer span.End()

	if exists, blkInfo, err := s.blockCache.BlockInfoByHeight(height); exists || err != nil {
		if err != nil {
			return [32]byte{}, err
		}
		span.AddAttributes(trace.BoolAttribute("blockCacheHit", true))
		return blkInfo.Hash, nil
	}
	span.AddAttributes(trace.BoolAttribute("blockCacheHit", false))
	block, err := s.blockFetcher.BlockByNumber(ctx, height)
	if err != nil {
		return [32]byte{}, errors.Wrap(err, fmt.Sprintf("could not query block with height %d", height.Uint64()))
	}
	if err := s.blockCache.AddBlock(block); err != nil {
		return [32]byte{}, err
	}
	return block.Hash(), nil
}

// BlockTimeByHeight fetches an eth1.0 block timestamp by its height.
func (s *Service) BlockTimeByHeight(ctx context.Context, height *big.Int) (uint64, error) {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.web3service.BlockTimeByHeight")
	defer span.End()
	if exists, blkInfo, err := s.blockCache.BlockInfoByHeight(height); exists || err != nil {
		if err != nil {
			return 0, err
		}
		span.AddAttributes(trace.BoolAttribute("blockCacheHit", true))
		return blkInfo.Time, nil
	}
	span.AddAttributes(trace.BoolAttribute("blockCacheHit", false))
	block, err := s.blockFetcher.BlockByNumber(ctx, height)
	if err != nil {
		return 0, errors.Wrap(err, fmt.Sprintf("could not query block with height %d", height.Uint64()))
	}
	return block.Time(), nil
}

// BlockNumberByTimestamp returns the most recent block number up to a given timestamp.
// This is a naive implementation that will use O(ETH1_FOLLOW_DISTANCE) calls to cache
// or ETH1. This is called for multiple times but only changes every
// SlotsPerEth1VotingPeriod (1024 slots) so the whole method should be cached.
func (s *Service) BlockNumberByTimestamp(ctx context.Context, time uint64) (*big.Int, error) {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.web3service.BlockNumberByTimestamp")
	defer span.End()

	if time != cachedEth1VotingStartTime || cachedEth1DataBlockHeight == nil {
		votingBlockHeightCacheMiss.Inc()
		head, err := s.blockFetcher.BlockByNumber(ctx, nil)
		if err != nil {
			return nil, err
		}

		for bn := head.Number(); ; bn = big.NewInt(0).Sub(bn, big.NewInt(1)) {
			if ctx.Err() != nil {
				return nil, ctx.Err()
			}

			exists, info, err := s.blockCache.BlockInfoByHeight(bn)
			if err != nil {
				return nil, err
			}

			if !exists {
				blk, err := s.blockFetcher.BlockByNumber(ctx, bn)
				if err != nil {
					return nil, err
				}
				info = blockToBlockInfo(blk)
			}

			if info.Time <= time {
				cachedEth1VotingStartTime = time
				cachedEth1DataBlockHeight = info.Number
				return cachedEth1DataBlockHeight, nil
			}
		}
	} else {
		votingBlockHeightCacheHit.Inc()
	}
	return cachedEth1DataBlockHeight, nil
}