package common

import (
	"bufio"
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/zcash/lightwalletd/parser"
)

type darksideState struct {
	inited            bool
	startHeight       int
	saplingActivation int
	branchID          string
	chainName         string
	// Should always be nonempty. Index 0 is the block at height start_height.
	blocks               [][]byte // full blocks, binary, as from zcashd getblock rpc
	stagedBlocks         [][]byte
	incomingTransactions [][]byte // full transactions, binary, zcashd getrawtransaction txid
	stagedTransactions   [][]byte
}

var state darksideState

func DarksideIsEnabled() bool {
	return state.inited
}

func DarksideInit() {
	state = darksideState{
		inited:               true,
		startHeight:          -1,
		saplingActivation:    -1,
		branchID:             "2bb40e60", // Blossom
		chainName:            "darkside",
		blocks:               make([][]byte, 0),
		stagedBlocks:         make([][]byte, 0),
		incomingTransactions: make([][]byte, 0),
		stagedTransactions:   make([][]byte, 0),
	}
	RawRequest = darksideRawRequest
	go func() {
		time.Sleep(30 * time.Minute)
		Log.Fatal("Shutting down darksidewalletd to prevent accidental deployment in production.")
	}()
}

// DarksideAddBlock adds a single block to the blocks list.
func DarksideAddBlock(blockHex string) error {
	if blockHex == "404: Not Found" {
		// special case error (http resource not found, bad pathname)
		return errors.New(blockHex)
	}
	blockData, err := hex.DecodeString(blockHex)
	if err != nil {
		return err
	}
	block := parser.NewBlock()
	rest, err := block.ParseFromSlice(blockData)
	if err != nil {
		return err
	}
	if len(rest) != 0 {
		return errors.New("block serialization is too long")
	}
	blockHeight := block.GetHeight()
	// first block, add to existing blocks slice if possible
	if blockHeight > state.startHeight+len(state.blocks) {
		// The new block can't contiguously extend the existing
		// range, so we have to drop the existing range.
		state.blocks = state.blocks[:0]
	} else if blockHeight < state.startHeight {
		// This block will replace the entire existing range.
		state.blocks = state.blocks[:0]
	} else {
		// Drop the block that will be overwritten, and its children.
		state.blocks = state.blocks[:blockHeight-state.startHeight]
	}
	if len(state.blocks) == 0 {
		state.startHeight = blockHeight
	}
	state.blocks = append(state.blocks, blockData)
	return nil
}

func readBlocks(src io.Reader) error {
	// some blocks are too large, especially when encoded in hex, for the
	// default buffer size, so set up a larger one; 8mb should be enough.
	scan := bufio.NewScanner(src)
	var scanbuf []byte
	scan.Buffer(scanbuf, 8*1000*1000)
	for scan.Scan() { // each line (block)
		if err := DarksideAddBlock(scan.Text()); err != nil {
			return err
		}
	}
	if scan.Err() != nil {
		return scan.Err()
	}
	return nil
}

// DarksideSetMetaState allows the wallet test code to specify values
// that are returned by GetLightdInfo().
func DarksideSetMetaState(sa int32, bi, cn string) error {
	state.saplingActivation = int(sa)
	state.branchID = bi
	state.chainName = cn
	return nil
}

// DarksideGetIncomingTransactions returns all transactions we're
// received via SendTransaction().
func DarksideGetIncomingTransactions() [][]byte {
	return state.incomingTransactions
}

// DarksideStageBlocks opens and reads blocks from the given URL and
// adds them to the staging area.
func DarksideStageBlocks(url string) error {
	resp, err := http.Get(url)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	err = readBlocks(resp.Body)
	if err != nil {

		return err
	}
	return nil
}

// DarksideStageBlocksCreate creates empty blocks and adds them to the staging area.
func DarksideStageBlocksCreate(height int32, nonce int32, count int32) error {
	for i := int32(0); i < count; i++ {

		fakeCoinbase := "0400008085202f890100000000000000000000000000000000000000000000000000" +
			"00000000000000ffffffff2a03d12c0c00043855975e464b8896790758f824ceac97836" +
			"22c17ed38f1669b8a45ce1da857dbbe7950e2ffffffff02a0ebce1d000000001976a914" +
			"7ed15946ec14ae0cd8fa8991eb6084452eb3f77c88ac405973070000000017a914e445cf" +
			"a944b6f2bdacefbda904a81d5fdd26d77f8700000000000000000000000000000000000000"

		// This coinbase transaction was pulled from block 797905, whose
		// little-endian encoding is 0xD12C0C00. Replace it with the block
		// number we want.
		fakeCoinbase = strings.Replace(fakeCoinbase, "d12c0c00",
			fmt.Sprintf("%02x", height&0xFF)+
				fmt.Sprintf("%02x", (height>>8)&0xFF)+
				fmt.Sprintf("%02x", (height>>16)&0xFF)+
				fmt.Sprintf("%02x", (height>>24)&0xFF), 1)
		fakeCoinbaseBytes, err := hex.DecodeString(fakeCoinbase)
		if err != nil {
			Log.Fatal(err)
		}

		hash_of_txns_and_height := sha256.Sum256([]byte(string(nonce) + string(height)))
		blockHeader := &parser.BlockHeader{
			RawBlockHeader: &parser.RawBlockHeader{
				Version:              4,
				HashPrevBlock:        make([]byte, 32),
				HashMerkleRoot:       hash_of_txns_and_height[:],
				HashFinalSaplingRoot: make([]byte, 32),
				Time:                 1,
				NBitsBytes:           make([]byte, 4),
				Nonce:                make([]byte, 32),
				Solution:             make([]byte, 1344),
			},
		}

		headerBytes, err := blockHeader.MarshalBinary()
		if err != nil {
			Log.Fatal(err)
		}
		newBlockData := make([]byte, 0)
		newBlockData = append(newBlockData, headerBytes...)
		newBlockData = append(newBlockData, byte(1))
		newBlockData = append(newBlockData, fakeCoinbaseBytes...)
		state.stagedBlocks = append(state.stagedBlocks, newBlockData)
	}

	return nil
}

// DarksideClearIncomingTransactions empties the incoming transaction list.
func DarksideClearIncomingTransactions() {
	state.incomingTransactions = make([][]byte, 0)
}

// DarksideSendTransaction is the handler for the SendTransaction gRPC.
// Save the transaction in the incoming transactions list.
func DarksideSendTransaction(txHex []byte) ([]byte, error) {
	// Need to parse the transaction to return its hash, plus it's
	// good error checking.
	txbytes, err := hex.DecodeString(string(txHex))
	if err != nil {
		return nil, err
	}
	tx := parser.NewTransaction()
	rest, err := tx.ParseFromSlice(txbytes)
	if err != nil {
		return nil, err
	}
	if len(rest) != 0 {
		return nil, errors.New("transaction serialization is too long")
	}
	state.incomingTransactions = append(state.incomingTransactions, txbytes)
	return tx.GetDisplayHash(), nil
}

func darksideRawRequest(method string, params []json.RawMessage) (json.RawMessage, error) {
	switch method {
	case "getblockchaininfo":
		blockchaininfo := Blockchaininfo{
			Chain: state.chainName,
			Upgrades: map[string]Upgradeinfo{
				"76b809bb": {ActivationHeight: state.saplingActivation},
			},
			Headers:   state.startHeight + len(state.blocks) - 1,
			Consensus: ConsensusInfo{state.branchID, state.branchID},
		}
		return json.Marshal(blockchaininfo)

	case "getblock":
		var heightStr string
		err := json.Unmarshal(params[0], &heightStr)
		if err != nil {
			return nil, errors.New("failed to parse getblock request")
		}

		height, err := strconv.Atoi(heightStr)
		if err != nil {
			return nil, errors.New("error parsing height as integer")
		}
		index := height - state.startHeight

		const notFoundErr = "-8:"
		if state.saplingActivation < 0 || index == len(state.blocks) {
			// The current ingestor keeps going until it sees this error,
			// meaning it's up to the latest height.
			return nil, errors.New(notFoundErr)
		}

		if index < 0 || index > len(state.blocks) {
			// If an integration test can reach this, it could be a bug, so generate an error.
			Log.Errorf("getblock request made for out-of-range height %d (have %d to %d)",
				height, state.startHeight, state.startHeight+len(state.blocks)-1)
			return nil, errors.New(notFoundErr)
		}
		return []byte("\"" + hex.EncodeToString(state.blocks[index]) + "\""), nil

	case "getaddresstxids":
		// Not required for minimal reorg testing.
		return nil, errors.New("not implemented yet")

	case "getrawtransaction":
		// Not required for minimal reorg testing.
		return darksideGetRawTransaction(params)

	case "sendrawtransaction":
		var rawtx string
		err := json.Unmarshal(params[0], &rawtx)
		if err != nil {
			return nil, errors.New("failed to parse sendrawtransaction JSON")
		}
		txbytes, err := hex.DecodeString(rawtx)
		if err != nil {
			return nil, errors.New("failed to parse sendrawtransaction value as a hex string")
		}
		state.incomingTransactions = append(state.incomingTransactions, txbytes)
		return nil, nil

	default:
		return nil, errors.New("there was an attempt to call an unsupported RPC")
	}
}

func darksideGetRawTransaction(params []json.RawMessage) (json.RawMessage, error) {
	// remove the double-quotes from the beginning and end of the hex txid string
	txbytes, err := hex.DecodeString(string(params[0][1 : 1+64]))
	if err != nil {
		return nil, errors.New("-9: " + err.Error())
	}
	// Linear search for the tx, somewhat inefficient but this is test code
	// and there aren't many blocks. If this becomes a performance problem,
	// we can maintain a map of transactions indexed by txid.
	for _, b := range state.blocks {
		block := parser.NewBlock()
		rest, err := block.ParseFromSlice(b)
		if err != nil {
			// this would be strange; we've already parsed this block
			return nil, errors.New("-9: " + err.Error())
		}
		if len(rest) != 0 {
			return nil, errors.New("-9: block serialization is too long")
		}
		for _, tx := range block.Transactions() {
			if bytes.Equal(tx.GetDisplayHash(), txbytes) {
				reply := struct {
					Hex    string `json:"hex"`
					Height int    `json:"height"`
				}{hex.EncodeToString(tx.Bytes()), block.GetHeight()}
				return json.Marshal(reply)
			}
		}
	}
	return nil, errors.New("-5: No information available about transaction")
}