// (c) 2019-2020, Ava Labs, Inc.
//
// This file is a derived work, based on the go-ethereum library whose original
// notices appear below.
//
// It is distributed under a license compatible with the licensing terms of the
// original code from which it is derived.
//
// Much love to the original authors for their work.
// **********
// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package filters

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"math/big"
	"sync"
	"time"

	"github.com/ava-labs/subnet-evm/core/types"
	"github.com/ava-labs/subnet-evm/interfaces"
	"github.com/ava-labs/subnet-evm/rpc"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
	"github.com/ethereum/go-ethereum/event"
)

// filter is a helper struct that holds meta information over the filter type
// and associated subscription in the event system.
type filter struct {
	typ      Type
	deadline *time.Timer // filter is inactiv when deadline triggers
	hashes   []common.Hash
	crit     FilterCriteria
	logs     []*types.Log
	s        *Subscription // associated subscription in event system
}

// PublicFilterAPI offers support to create and manage filters. This will allow external clients to retrieve various
// information related to the Ethereum protocol such als blocks, transactions and logs.
type PublicFilterAPI struct {
	backend   Backend
	mux       *event.TypeMux
	quit      chan struct{}
	events    *EventSystem
	filtersMu sync.Mutex
	filters   map[rpc.ID]*filter
	timeout   time.Duration
}

// NewPublicFilterAPI returns a new PublicFilterAPI instance.
func NewPublicFilterAPI(backend Backend, lightMode bool, timeout time.Duration) *PublicFilterAPI {
	api := &PublicFilterAPI{
		backend: backend,
		events:  NewEventSystem(backend, lightMode),
		filters: make(map[rpc.ID]*filter),
		timeout: timeout,
	}
	go api.timeoutLoop(timeout)

	return api
}

// timeoutLoop runs at the interval set by 'timeout' and deletes filters
// that have not been recently used. It is started when the API is created.
func (api *PublicFilterAPI) timeoutLoop(timeout time.Duration) {
	var toUninstall []*Subscription
	ticker := time.NewTicker(timeout)
	defer ticker.Stop()
	for {
		<-ticker.C
		api.filtersMu.Lock()
		for id, f := range api.filters {
			select {
			case <-f.deadline.C:
				toUninstall = append(toUninstall, f.s)
				delete(api.filters, id)
			default:
				continue
			}
		}
		api.filtersMu.Unlock()

		// Unsubscribes are processed outside the lock to avoid the following scenario:
		// event loop attempts broadcasting events to still active filters while
		// Unsubscribe is waiting for it to process the uninstall request.
		for _, s := range toUninstall {
			s.Unsubscribe()
		}
		toUninstall = nil
	}
}

// NewPendingTransactionFilter creates a filter that fetches pending transaction hashes
// as transactions enter the pending state.
//
// It is part of the filter package because this filter can be used through the
// `eth_getFilterChanges` polling method that is also used for log filters.
//
// https://eth.wiki/json-rpc/API#eth_newpendingtransactionfilter
func (api *PublicFilterAPI) NewPendingTransactionFilter() rpc.ID {
	var (
		pendingTxs   = make(chan []common.Hash)
		pendingTxSub = api.events.SubscribePendingTxs(pendingTxs)
	)

	api.filtersMu.Lock()
	api.filters[pendingTxSub.ID] = &filter{typ: PendingTransactionsSubscription, deadline: time.NewTimer(api.timeout), hashes: make([]common.Hash, 0), s: pendingTxSub}
	api.filtersMu.Unlock()

	go func() {
		for {
			select {
			case ph := <-pendingTxs:
				api.filtersMu.Lock()
				if f, found := api.filters[pendingTxSub.ID]; found {
					f.hashes = append(f.hashes, ph...)
				}
				api.filtersMu.Unlock()
			case <-pendingTxSub.Err():
				api.filtersMu.Lock()
				delete(api.filters, pendingTxSub.ID)
				api.filtersMu.Unlock()
				return
			}
		}
	}()

	return pendingTxSub.ID
}

// NewPendingTransactions creates a subscription that is triggered each time a transaction
// enters the transaction pool and was signed from one of the transactions this nodes manages.
func (api *PublicFilterAPI) NewPendingTransactions(ctx context.Context) (*rpc.Subscription, error) {
	notifier, supported := rpc.NotifierFromContext(ctx)
	if !supported {
		return &rpc.Subscription{}, rpc.ErrNotificationsUnsupported
	}

	rpcSub := notifier.CreateSubscription()

	go func() {
		txHashes := make(chan []common.Hash, 128)
		pendingTxSub := api.events.SubscribePendingTxs(txHashes)

		for {
			select {
			case hashes := <-txHashes:
				// To keep the original behaviour, send a single tx hash in one notification.
				// TODO(rjl493456442) Send a batch of tx hashes in one notification
				for _, h := range hashes {
					notifier.Notify(rpcSub.ID, h)
				}
			case <-rpcSub.Err():
				pendingTxSub.Unsubscribe()
				return
			case <-notifier.Closed():
				pendingTxSub.Unsubscribe()
				return
			}
		}
	}()

	return rpcSub, nil
}

// NewAcceptedTransactions creates a subscription that is triggered each time a transaction is accepted.
func (api *PublicFilterAPI) NewAcceptedTransactions(ctx context.Context) (*rpc.Subscription, error) {
	notifier, supported := rpc.NotifierFromContext(ctx)
	if !supported {
		return &rpc.Subscription{}, rpc.ErrNotificationsUnsupported
	}

	rpcSub := notifier.CreateSubscription()

	go func() {
		txHashes := make(chan []common.Hash, 128)
		acceptedTxSub := api.events.SubscribeAcceptedTxs(txHashes)

		for {
			select {
			case hashes := <-txHashes:
				for _, h := range hashes {
					notifier.Notify(rpcSub.ID, h)
				}
			case <-rpcSub.Err():
				acceptedTxSub.Unsubscribe()
				return
			case <-notifier.Closed():
				acceptedTxSub.Unsubscribe()
				return
			}
		}
	}()

	return rpcSub, nil
}

// NewBlockFilter creates a filter that fetches blocks that are imported into the chain.
// It is part of the filter package since polling goes with eth_getFilterChanges.
//
// https://eth.wiki/json-rpc/API#eth_newblockfilter
func (api *PublicFilterAPI) NewBlockFilter() rpc.ID {
	var (
		headers   = make(chan *types.Header)
		headerSub *Subscription
	)

	if api.backend.GetVMConfig().AllowUnfinalizedQueries {
		headerSub = api.events.SubscribeNewHeads(headers)
	} else {
		headerSub = api.events.SubscribeAcceptedHeads(headers)
	}

	api.filtersMu.Lock()
	api.filters[headerSub.ID] = &filter{typ: BlocksSubscription, deadline: time.NewTimer(api.timeout), hashes: make([]common.Hash, 0), s: headerSub}
	api.filtersMu.Unlock()

	go func() {
		for {
			select {
			case h := <-headers:
				api.filtersMu.Lock()
				if f, found := api.filters[headerSub.ID]; found {
					f.hashes = append(f.hashes, h.Hash())
				}
				api.filtersMu.Unlock()
			case <-headerSub.Err():
				api.filtersMu.Lock()
				delete(api.filters, headerSub.ID)
				api.filtersMu.Unlock()
				return
			}
		}
	}()

	return headerSub.ID
}

// NewHeads send a notification each time a new (header) block is appended to the chain.
func (api *PublicFilterAPI) NewHeads(ctx context.Context) (*rpc.Subscription, error) {
	notifier, supported := rpc.NotifierFromContext(ctx)
	if !supported {
		return &rpc.Subscription{}, rpc.ErrNotificationsUnsupported
	}

	rpcSub := notifier.CreateSubscription()

	go func() {
		var (
			headers    = make(chan *types.Header)
			headersSub event.Subscription
		)

		if api.backend.GetVMConfig().AllowUnfinalizedQueries {
			headersSub = api.events.SubscribeNewHeads(headers)
		} else {
			headersSub = api.events.SubscribeAcceptedHeads(headers)
		}

		for {
			select {
			case h := <-headers:
				notifier.Notify(rpcSub.ID, h)
			case <-rpcSub.Err():
				headersSub.Unsubscribe()
				return
			case <-notifier.Closed():
				headersSub.Unsubscribe()
				return
			}
		}
	}()

	return rpcSub, nil
}

// Logs creates a subscription that fires for all new log that match the given filter criteria.
func (api *PublicFilterAPI) Logs(ctx context.Context, crit FilterCriteria) (*rpc.Subscription, error) {
	notifier, supported := rpc.NotifierFromContext(ctx)
	if !supported {
		return &rpc.Subscription{}, rpc.ErrNotificationsUnsupported
	}

	var (
		rpcSub      = notifier.CreateSubscription()
		matchedLogs = make(chan []*types.Log)
		logsSub     event.Subscription
		err         error
	)

	if api.backend.GetVMConfig().AllowUnfinalizedQueries {
		logsSub, err = api.events.SubscribeLogs(interfaces.FilterQuery(crit), matchedLogs)
		if err != nil {
			return nil, err
		}
	} else {
		logsSub, err = api.events.SubscribeAcceptedLogs(interfaces.FilterQuery(crit), matchedLogs)
		if err != nil {
			return nil, err
		}
	}

	go func() {
		for {
			select {
			case logs := <-matchedLogs:
				for _, log := range logs {
					notifier.Notify(rpcSub.ID, &log)
				}
			case <-rpcSub.Err(): // client send an unsubscribe request
				logsSub.Unsubscribe()
				return
			case <-notifier.Closed(): // connection dropped
				logsSub.Unsubscribe()
				return
			}
		}
	}()

	return rpcSub, nil
}

// FilterCriteria represents a request to create a new filter.
// Same as interfaces.FilterQuery but with UnmarshalJSON() method.
type FilterCriteria interfaces.FilterQuery

// NewFilter creates a new filter and returns the filter id. It can be
// used to retrieve logs when the state changes. This method cannot be
// used to fetch logs that are already stored in the state.
//
// Default criteria for the from and to block are "latest".
// Using "latest" as block number will return logs for mined blocks.
// Using "pending" as block number returns logs for not yet mined (pending) blocks.
// In case logs are removed (chain reorg) previously returned logs are returned
// again but with the removed property set to true.
//
// In case "fromBlock" > "toBlock" an error is returned.
//
// https://eth.wiki/json-rpc/API#eth_newfilter
func (api *PublicFilterAPI) NewFilter(crit FilterCriteria) (rpc.ID, error) {
	var (
		logs    = make(chan []*types.Log)
		logsSub *Subscription
		err     error
	)

	if api.backend.GetVMConfig().AllowUnfinalizedQueries {
		logsSub, err = api.events.SubscribeLogs(interfaces.FilterQuery(crit), logs)
		if err != nil {
			return rpc.ID(""), err
		}
	} else {
		logsSub, err = api.events.SubscribeAcceptedLogs(interfaces.FilterQuery(crit), logs)
		if err != nil {
			return rpc.ID(""), err
		}
	}

	api.filtersMu.Lock()
	api.filters[logsSub.ID] = &filter{typ: LogsSubscription, crit: crit, deadline: time.NewTimer(api.timeout), logs: make([]*types.Log, 0), s: logsSub}
	api.filtersMu.Unlock()

	go func() {
		for {
			select {
			case l := <-logs:
				api.filtersMu.Lock()
				if f, found := api.filters[logsSub.ID]; found {
					f.logs = append(f.logs, l...)
				}
				api.filtersMu.Unlock()
			case <-logsSub.Err():
				api.filtersMu.Lock()
				delete(api.filters, logsSub.ID)
				api.filtersMu.Unlock()
				return
			}
		}
	}()

	return logsSub.ID, nil
}

// GetLogs returns logs matching the given argument that are stored within the state.
//
// https://eth.wiki/json-rpc/API#eth_getlogs
func (api *PublicFilterAPI) GetLogs(ctx context.Context, crit FilterCriteria) ([]*types.Log, error) {
	var filter *Filter
	if crit.BlockHash != nil {
		// Block filter requested, construct a single-shot filter
		filter = NewBlockFilter(api.backend, *crit.BlockHash, crit.Addresses, crit.Topics)
	} else {
		// Convert the RPC block numbers into internal representations
		// LatestBlockNumber is left in place here to be handled
		// correctly within NewRangeFilter
		begin := rpc.LatestBlockNumber.Int64()
		if crit.FromBlock != nil {
			begin = crit.FromBlock.Int64()
		}
		end := rpc.LatestBlockNumber.Int64()
		if crit.ToBlock != nil {
			end = crit.ToBlock.Int64()
		}
		// Construct the range filter
		var err error
		filter, err = NewRangeFilter(api.backend, begin, end, crit.Addresses, crit.Topics)
		if err != nil {
			return nil, err
		}
	}
	// Run the filter and return all the logs
	logs, err := filter.Logs(ctx)
	if err != nil {
		return nil, err
	}
	return returnLogs(logs), err
}

// UninstallFilter removes the filter with the given filter id.
//
// https://eth.wiki/json-rpc/API#eth_uninstallfilter
func (api *PublicFilterAPI) UninstallFilter(id rpc.ID) bool {
	api.filtersMu.Lock()
	f, found := api.filters[id]
	if found {
		delete(api.filters, id)
	}
	api.filtersMu.Unlock()
	if found {
		f.s.Unsubscribe()
	}

	return found
}

// GetFilterLogs returns the logs for the filter with the given id.
// If the filter could not be found an empty array of logs is returned.
//
// https://eth.wiki/json-rpc/API#eth_getfilterlogs
func (api *PublicFilterAPI) GetFilterLogs(ctx context.Context, id rpc.ID) ([]*types.Log, error) {
	api.filtersMu.Lock()
	f, found := api.filters[id]
	api.filtersMu.Unlock()

	if !found || f.typ != LogsSubscription {
		return nil, fmt.Errorf("filter not found")
	}

	var filter *Filter
	if f.crit.BlockHash != nil {
		// Block filter requested, construct a single-shot filter
		filter = NewBlockFilter(api.backend, *f.crit.BlockHash, f.crit.Addresses, f.crit.Topics)
	} else {
		// Convert the RPC block numbers into internal representations
		// Leave LatestBlockNumber in place here as the defaults
		// Should be handled correctly as request for the last
		// accepted block instead throughout all APIs.
		begin := rpc.LatestBlockNumber.Int64()
		if f.crit.FromBlock != nil {
			begin = f.crit.FromBlock.Int64()
		}
		end := rpc.LatestBlockNumber.Int64()
		if f.crit.ToBlock != nil {
			end = f.crit.ToBlock.Int64()
		}
		// Construct the range filter
		var err error
		filter, err = NewRangeFilter(api.backend, begin, end, f.crit.Addresses, f.crit.Topics)
		if err != nil {
			return nil, err
		}
	}
	// Run the filter and return all the logs
	logs, err := filter.Logs(ctx)
	if err != nil {
		return nil, err
	}
	return returnLogs(logs), nil
}

// GetFilterChanges returns the logs for the filter with the given id since
// last time it was called. This can be used for polling.
//
// For pending transaction and block filters the result is []common.Hash.
// (pending)Log filters return []Log.
//
// https://eth.wiki/json-rpc/API#eth_getfilterchanges
func (api *PublicFilterAPI) GetFilterChanges(id rpc.ID) (interface{}, error) {
	api.filtersMu.Lock()
	defer api.filtersMu.Unlock()

	if f, found := api.filters[id]; found {
		if !f.deadline.Stop() {
			// timer expired but filter is not yet removed in timeout loop
			// receive timer value and reset timer
			<-f.deadline.C
		}
		f.deadline.Reset(api.timeout)

		switch f.typ {
		case PendingTransactionsSubscription, BlocksSubscription, AcceptedBlocksSubscription, AcceptedTransactionsSubscription:
			hashes := f.hashes
			f.hashes = nil
			return returnHashes(hashes), nil
		case LogsSubscription, AcceptedLogsSubscription, MinedAndPendingLogsSubscription:
			logs := f.logs
			f.logs = nil
			return returnLogs(logs), nil
		}
	}

	return []interface{}{}, fmt.Errorf("filter not found")
}

// returnHashes is a helper that will return an empty hash array case the given hash array is nil,
// otherwise the given hashes array is returned.
func returnHashes(hashes []common.Hash) []common.Hash {
	if hashes == nil {
		return []common.Hash{}
	}
	return hashes
}

// returnLogs is a helper that will return an empty log array in case the given logs array is nil,
// otherwise the given logs array is returned.
func returnLogs(logs []*types.Log) []*types.Log {
	if logs == nil {
		return []*types.Log{}
	}
	return logs
}

// UnmarshalJSON sets *args fields with given data.
func (args *FilterCriteria) UnmarshalJSON(data []byte) error {
	type input struct {
		BlockHash *common.Hash     `json:"blockHash"`
		FromBlock *rpc.BlockNumber `json:"fromBlock"`
		ToBlock   *rpc.BlockNumber `json:"toBlock"`
		Addresses interface{}      `json:"address"`
		Topics    []interface{}    `json:"topics"`
	}

	var raw input
	if err := json.Unmarshal(data, &raw); err != nil {
		return err
	}

	if raw.BlockHash != nil {
		if raw.FromBlock != nil || raw.ToBlock != nil {
			// BlockHash is mutually exclusive with FromBlock/ToBlock criteria
			return fmt.Errorf("cannot specify both BlockHash and FromBlock/ToBlock, choose one or the other")
		}
		args.BlockHash = raw.BlockHash
	} else {
		if raw.FromBlock != nil {
			args.FromBlock = big.NewInt(raw.FromBlock.Int64())
		}

		if raw.ToBlock != nil {
			args.ToBlock = big.NewInt(raw.ToBlock.Int64())
		}
	}

	args.Addresses = []common.Address{}

	if raw.Addresses != nil {
		// raw.Address can contain a single address or an array of addresses
		switch rawAddr := raw.Addresses.(type) {
		case []interface{}:
			for i, addr := range rawAddr {
				if strAddr, ok := addr.(string); ok {
					addr, err := decodeAddress(strAddr)
					if err != nil {
						return fmt.Errorf("invalid address at index %d: %v", i, err)
					}
					args.Addresses = append(args.Addresses, addr)
				} else {
					return fmt.Errorf("non-string address at index %d", i)
				}
			}
		case string:
			addr, err := decodeAddress(rawAddr)
			if err != nil {
				return fmt.Errorf("invalid address: %v", err)
			}
			args.Addresses = []common.Address{addr}
		default:
			return errors.New("invalid addresses in query")
		}
	}

	// topics is an array consisting of strings and/or arrays of strings.
	// JSON null values are converted to common.Hash{} and ignored by the filter manager.
	if len(raw.Topics) > 0 {
		args.Topics = make([][]common.Hash, len(raw.Topics))
		for i, t := range raw.Topics {
			switch topic := t.(type) {
			case nil:
				// ignore topic when matching logs

			case string:
				// match specific topic
				top, err := decodeTopic(topic)
				if err != nil {
					return err
				}
				args.Topics[i] = []common.Hash{top}

			case []interface{}:
				// or case e.g. [null, "topic0", "topic1"]
				for _, rawTopic := range topic {
					if rawTopic == nil {
						// null component, match all
						args.Topics[i] = nil
						break
					}
					if topic, ok := rawTopic.(string); ok {
						parsed, err := decodeTopic(topic)
						if err != nil {
							return err
						}
						args.Topics[i] = append(args.Topics[i], parsed)
					} else {
						return fmt.Errorf("invalid topic(s)")
					}
				}
			default:
				return fmt.Errorf("invalid topic(s)")
			}
		}
	}

	return nil
}

func decodeAddress(s string) (common.Address, error) {
	b, err := hexutil.Decode(s)
	if err == nil && len(b) != common.AddressLength {
		err = fmt.Errorf("hex has invalid length %d after decoding; expected %d for address", len(b), common.AddressLength)
	}
	return common.BytesToAddress(b), err
}

func decodeTopic(s string) (common.Hash, error) {
	b, err := hexutil.Decode(s)
	if err == nil && len(b) != common.HashLength {
		err = fmt.Errorf("hex has invalid length %d after decoding; expected %d for topic", len(b), common.HashLength)
	}
	return common.BytesToHash(b), err
}
