// Copyright (c) 2014-2016 The btcsuite developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package chaincfg

import (
	"errors"
	"math"
	"math/big"
	"strings"
	"time"

	"github.com/btcsuite/btcd/chaincfg/chainhash"
	"github.com/btcsuite/btcd/wire"
)

// These variables are the chain proof-of-work limit parameters for each default
// network.
var (
	// bigOne is 1 represented as a big.Int.  It is defined here to avoid
	// the overhead of creating it multiple times.
	bigOne = big.NewInt(1)

	// mainPowLimit is the highest proof of work value a Bitcoin block can
	// have for the main network.  It is the value 2^224 - 1.
	mainPowLimit = new(big.Int).Sub(new(big.Int).Lsh(bigOne, 224), bigOne)

	// regressionPowLimit is the highest proof of work value a Bitcoin block
	// can have for the regression test network.  It is the value 2^255 - 1.
	regressionPowLimit = new(big.Int).Sub(new(big.Int).Lsh(bigOne, 255), bigOne)

	// testNet3PowLimit is the highest proof of work value a Bitcoin block
	// can have for the test network (version 3).  It is the value
	// 2^224 - 1.
	testNet3PowLimit = new(big.Int).Sub(new(big.Int).Lsh(bigOne, 224), bigOne)

	// simNetPowLimit is the highest proof of work value a Bitcoin block
	// can have for the simulation test network.  It is the value 2^255 - 1.
	simNetPowLimit = new(big.Int).Sub(new(big.Int).Lsh(bigOne, 255), bigOne)
)

// Checkpoint identifies a known good point in the block chain.  Using
// checkpoints allows a few optimizations for old blocks during initial download
// and also prevents forks from old blocks.
//
// Each checkpoint is selected based upon several factors.  See the
// documentation for blockchain.IsCheckpointCandidate for details on the
// selection criteria.
type Checkpoint struct {
	Height int32
	Hash   *chainhash.Hash
}

// DNSSeed identifies a DNS seed.
type DNSSeed struct {
	// Host defines the hostname of the seed.
	Host string

	// HasFiltering defines whether the seed supports filtering
	// by service flags (wire.ServiceFlag).
	HasFiltering bool
}

// ConsensusDeployment defines details related to a specific consensus rule
// change that is voted in.  This is part of BIP0009.
type ConsensusDeployment struct {
	// BitNumber defines the specific bit number within the block version
	// this particular soft-fork deployment refers to.
	BitNumber uint8

	// StartTime is the median block time after which voting on the
	// deployment starts.
	StartTime uint64

	// ExpireTime is the median block time after which the attempted
	// deployment expires.
	ExpireTime uint64
}

// Constants that define the deployment offset in the deployments field of the
// parameters for each deployment.  This is useful to be able to get the details
// of a specific deployment by name.
const (
	// DeploymentTestDummy defines the rule change deployment ID for testing
	// purposes.
	DeploymentTestDummy = iota

	// DeploymentCSV defines the rule change deployment ID for the CSV
	// soft-fork package. The CSV package includes the depolyment of BIPS
	// 68, 112, and 113.
	DeploymentCSV

	// DeploymentSegwit defines the rule change deployment ID for the
	// Segragated Witness (segwit) soft-fork package. The segwit package
	// includes the deployment of BIPS 141, 142, 144, 145, 147 and 173.
	DeploymentSegwit

	// NOTE: DefinedDeployments must always come last since it is used to
	// determine how many defined deployments there currently are.

	// DefinedDeployments is the number of currently defined deployments.
	DefinedDeployments
)

// Params defines a Bitcoin network by its parameters.  These parameters may be
// used by Bitcoin applications to differentiate networks as well as addresses
// and keys for one network from those intended for use on another network.
type Params struct {
	// Name defines a human-readable identifier for the network.
	Name string

	// Net defines the magic bytes used to identify the network.
	Net wire.BitcoinNet

	// DefaultPort defines the default peer-to-peer port for the network.
	DefaultPort string

	// DNSSeeds defines a list of DNS seeds for the network that are used
	// as one method to discover peers.
	DNSSeeds []DNSSeed

	// GenesisBlock defines the first block of the chain.
	GenesisBlock *wire.MsgBlock

	// GenesisHash is the starting block hash.
	GenesisHash *chainhash.Hash

	// PowLimit defines the highest allowed proof of work value for a block
	// as a uint256.
	PowLimit *big.Int

	// PowLimitBits defines the highest allowed proof of work value for a
	// block in compact form.
	PowLimitBits uint32

	// These fields define the block heights at which the specified softfork
	// BIP became active.
	BIP0034Height int32
	BIP0065Height int32
	BIP0066Height int32

	// CoinbaseMaturity is the number of blocks required before newly mined
	// coins (coinbase transactions) can be spent.
	CoinbaseMaturity uint16

	// SubsidyReductionInterval is the interval of blocks before the subsidy
	// is reduced.
	SubsidyReductionInterval int32

	// TargetTimespan is the desired amount of time that should elapse
	// before the block difficulty requirement is examined to determine how
	// it should be changed in order to maintain the desired block
	// generation rate.
	TargetTimespan time.Duration

	// TargetTimePerBlock is the desired amount of time to generate each
	// block.
	TargetTimePerBlock time.Duration

	// RetargetAdjustmentFactor is the adjustment factor used to limit
	// the minimum and maximum amount of adjustment that can occur between
	// difficulty retargets.
	RetargetAdjustmentFactor int64

	// ReduceMinDifficulty defines whether the network should reduce the
	// minimum required difficulty after a long enough period of time has
	// passed without finding a block.  This is really only useful for test
	// networks and should not be set on a main network.
	ReduceMinDifficulty bool

	// MinDiffReductionTime is the amount of time after which the minimum
	// required difficulty should be reduced when a block hasn't been found.
	//
	// NOTE: This only applies if ReduceMinDifficulty is true.
	MinDiffReductionTime time.Duration

	// GenerateSupported specifies whether or not CPU mining is allowed.
	GenerateSupported bool

	// Checkpoints ordered from oldest to newest.
	Checkpoints []Checkpoint

	// These fields are related to voting on consensus rule changes as
	// defined by BIP0009.
	//
	// RuleChangeActivationThreshold is the number of blocks in a threshold
	// state retarget window for which a positive vote for a rule change
	// must be cast in order to lock in a rule change. It should typically
	// be 95% for the main network and 75% for test networks.
	//
	// MinerConfirmationWindow is the number of blocks in each threshold
	// state retarget window.
	//
	// Deployments define the specific consensus rule changes to be voted
	// on.
	RuleChangeActivationThreshold uint32
	MinerConfirmationWindow       uint32
	Deployments                   [DefinedDeployments]ConsensusDeployment

	// Mempool parameters
	RelayNonStdTxs bool

	// Human-readable part for Bech32 encoded segwit addresses, as defined
	// in BIP 173.
	Bech32HRPSegwit string

	// Address encoding magics
	PubKeyHashAddrID        byte // First byte of a P2PKH address
	ScriptHashAddrID        byte // First byte of a P2SH address
	PrivateKeyID            byte // First byte of a WIF private key
	WitnessPubKeyHashAddrID byte // First byte of a P2WPKH address
	WitnessScriptHashAddrID byte // First byte of a P2WSH address

	// BIP32 hierarchical deterministic extended key magics
	HDPrivateKeyID [4]byte
	HDPublicKeyID  [4]byte

	// BIP44 coin type used in the hierarchical deterministic path for
	// address generation.
	HDCoinType uint32
}

// MainNetParams defines the network parameters for the main Bitcoin network.
var MainNetParams = Params{
	Name:        "mainnet",
	Net:         wire.MainNet,
	DefaultPort: "8333",
	DNSSeeds: []DNSSeed{
		{"seed.bitcoin.sipa.be", true},
		{"dnsseed.bluematt.me", true},
		{"dnsseed.bitcoin.dashjr.org", false},
		{"seed.bitcoinstats.com", true},
		{"seed.bitnodes.io", false},
		{"seed.bitcoin.jonasschnelli.ch", true},
	},

	// Chain parameters
	GenesisBlock:             &genesisBlock,
	GenesisHash:              &genesisHash,
	PowLimit:                 mainPowLimit,
	PowLimitBits:             0x1d00ffff,
	BIP0034Height:            227931, // 000000000000024b89b42a942fe0d9fea3bb44ab7bd1b19115dd6a759c0808b8
	BIP0065Height:            388381, // 000000000000000004c2b624ed5d7756c508d90fd0da2c7c679febfa6c4735f0
	BIP0066Height:            363725, // 00000000000000000379eaa19dce8c9b722d46ae6a57c2f1a988119488b50931
	CoinbaseMaturity:         100,
	SubsidyReductionInterval: 210000,
	TargetTimespan:           time.Hour * 24 * 14, // 14 days
	TargetTimePerBlock:       time.Minute * 10,    // 10 minutes
	RetargetAdjustmentFactor: 4,                   // 25% less, 400% more
	ReduceMinDifficulty:      false,
	MinDiffReductionTime:     0,
	GenerateSupported:        false,

	// Checkpoints ordered from oldest to newest.
	Checkpoints: []Checkpoint{
		{11111, newHashFromStr("0000000069e244f73d78e8fd29ba2fd2ed618bd6fa2ee92559f542fdb26e7c1d")},
		{33333, newHashFromStr("000000002dd5588a74784eaa7ab0507a18ad16a236e7b1ce69f00d7ddfb5d0a6")},
		{74000, newHashFromStr("0000000000573993a3c9e41ce34471c079dcf5f52a0e824a81e7f953b8661a20")},
		{105000, newHashFromStr("00000000000291ce28027faea320c8d2b054b2e0fe44a773f3eefb151d6bdc97")},
		{134444, newHashFromStr("00000000000005b12ffd4cd315cd34ffd4a594f430ac814c91184a0d42d2b0fe")},
		{168000, newHashFromStr("000000000000099e61ea72015e79632f216fe6cb33d7899acb35b75c8303b763")},
		{193000, newHashFromStr("000000000000059f452a5f7340de6682a977387c17010ff6e6c3bd83ca8b1317")},
		{210000, newHashFromStr("000000000000048b95347e83192f69cf0366076336c639f9b7228e9ba171342e")},
		{216116, newHashFromStr("00000000000001b4f4b433e81ee46494af945cf96014816a4e2370f11b23df4e")},
		{225430, newHashFromStr("00000000000001c108384350f74090433e7fcf79a606b8e797f065b130575932")},
		{250000, newHashFromStr("000000000000003887df1f29024b06fc2200b55f8af8f35453d7be294df2d214")},
		{267300, newHashFromStr("000000000000000a83fbd660e918f218bf37edd92b748ad940483c7c116179ac")},
		{279000, newHashFromStr("0000000000000001ae8c72a0b0c301f67e3afca10e819efa9041e458e9bd7e40")},
		{300255, newHashFromStr("0000000000000000162804527c6e9b9f0563a280525f9d08c12041def0a0f3b2")},
		{319400, newHashFromStr("000000000000000021c6052e9becade189495d1c539aa37c58917305fd15f13b")},
		{343185, newHashFromStr("0000000000000000072b8bf361d01a6ba7d445dd024203fafc78768ed4368554")},
		{352940, newHashFromStr("000000000000000010755df42dba556bb72be6a32f3ce0b6941ce4430152c9ff")},
		{382320, newHashFromStr("00000000000000000a8dc6ed5b133d0eb2fd6af56203e4159789b092defd8ab2")},
	},

	// Consensus rule change deployments.
	//
	// The miner confirmation window is defined as:
	//   target proof of work timespan / target proof of work spacing
	RuleChangeActivationThreshold: 1916, // 95% of MinerConfirmationWindow
	MinerConfirmationWindow:       2016, //
	Deployments: [DefinedDeployments]ConsensusDeployment{
		DeploymentTestDummy: {
			BitNumber:  28,
			StartTime:  1199145601, // January 1, 2008 UTC
			ExpireTime: 1230767999, // December 31, 2008 UTC
		},
		DeploymentCSV: {
			BitNumber:  0,
			StartTime:  1462060800, // May 1st, 2016
			ExpireTime: 1493596800, // May 1st, 2017
		},
		DeploymentSegwit: {
			BitNumber:  1,
			StartTime:  1479168000, // November 15, 2016 UTC
			ExpireTime: 1510704000, // November 15, 2017 UTC.
		},
	},

	// Mempool parameters
	RelayNonStdTxs: false,

	// Human-readable part for Bech32 encoded segwit addresses, as defined in
	// BIP 173.
	Bech32HRPSegwit: "bc", // always bc for main net

	// Address encoding magics
	PubKeyHashAddrID:        0x00, // starts with 1
	ScriptHashAddrID:        0x05, // starts with 3
	PrivateKeyID:            0x80, // starts with 5 (uncompressed) or K (compressed)
	WitnessPubKeyHashAddrID: 0x06, // starts with p2
	WitnessScriptHashAddrID: 0x0A, // starts with 7Xh

	// BIP32 hierarchical deterministic extended key magics
	HDPrivateKeyID: [4]byte{0x04, 0x88, 0xad, 0xe4}, // starts with xprv
	HDPublicKeyID:  [4]byte{0x04, 0x88, 0xb2, 0x1e}, // starts with xpub

	// BIP44 coin type used in the hierarchical deterministic path for
	// address generation.
	HDCoinType: 0,
}

// RegressionNetParams defines the network parameters for the regression test
// Bitcoin network.  Not to be confused with the test Bitcoin network (version
// 3), this network is sometimes simply called "testnet".
var RegressionNetParams = Params{
	Name:        "regtest",
	Net:         wire.TestNet,
	DefaultPort: "18444",
	DNSSeeds:    []DNSSeed{},

	// Chain parameters
	GenesisBlock:             &regTestGenesisBlock,
	GenesisHash:              &regTestGenesisHash,
	PowLimit:                 regressionPowLimit,
	PowLimitBits:             0x207fffff,
	CoinbaseMaturity:         100,
	BIP0034Height:            100000000, // Not active - Permit ver 1 blocks
	BIP0065Height:            1351,      // Used by regression tests
	BIP0066Height:            1251,      // Used by regression tests
	SubsidyReductionInterval: 150,
	TargetTimespan:           time.Hour * 24 * 14, // 14 days
	TargetTimePerBlock:       time.Minute * 10,    // 10 minutes
	RetargetAdjustmentFactor: 4,                   // 25% less, 400% more
	ReduceMinDifficulty:      true,
	MinDiffReductionTime:     time.Minute * 20, // TargetTimePerBlock * 2
	GenerateSupported:        true,

	// Checkpoints ordered from oldest to newest.
	Checkpoints: nil,

	// Consensus rule change deployments.
	//
	// The miner confirmation window is defined as:
	//   target proof of work timespan / target proof of work spacing
	RuleChangeActivationThreshold: 108, // 75%  of MinerConfirmationWindow
	MinerConfirmationWindow:       144,
	Deployments: [DefinedDeployments]ConsensusDeployment{
		DeploymentTestDummy: {
			BitNumber:  28,
			StartTime:  0,             // Always available for vote
			ExpireTime: math.MaxInt64, // Never expires
		},
		DeploymentCSV: {
			BitNumber:  0,
			StartTime:  0,             // Always available for vote
			ExpireTime: math.MaxInt64, // Never expires
		},
		DeploymentSegwit: {
			BitNumber:  1,
			StartTime:  0,             // Always available for vote
			ExpireTime: math.MaxInt64, // Never expires.
		},
	},

	// Mempool parameters
	RelayNonStdTxs: true,

	// Human-readable part for Bech32 encoded segwit addresses, as defined in
	// BIP 173.
	Bech32HRPSegwit: "tb", // always tb for test net

	// Address encoding magics
	PubKeyHashAddrID: 0x6f, // starts with m or n
	ScriptHashAddrID: 0xc4, // starts with 2
	PrivateKeyID:     0xef, // starts with 9 (uncompressed) or c (compressed)

	// BIP32 hierarchical deterministic extended key magics
	HDPrivateKeyID: [4]byte{0x04, 0x35, 0x83, 0x94}, // starts with tprv
	HDPublicKeyID:  [4]byte{0x04, 0x35, 0x87, 0xcf}, // starts with tpub

	// BIP44 coin type used in the hierarchical deterministic path for
	// address generation.
	HDCoinType: 1,
}

// TestNet3Params defines the network parameters for the test Bitcoin network
// (version 3).  Not to be confused with the regression test network, this
// network is sometimes simply called "testnet".
var TestNet3Params = Params{
	Name:        "testnet3",
	Net:         wire.TestNet3,
	DefaultPort: "18333",
	DNSSeeds: []DNSSeed{
		{"testnet-seed.bitcoin.jonasschnelli.ch", true},
		{"testnet-seed.bitcoin.schildbach.de", false},
		{"seed.tbtc.petertodd.org", true},
		{"testnet-seed.bluematt.me", false},
	},

	// Chain parameters
	GenesisBlock:             &testNet3GenesisBlock,
	GenesisHash:              &testNet3GenesisHash,
	PowLimit:                 testNet3PowLimit,
	PowLimitBits:             0x1d00ffff,
	BIP0034Height:            21111,  // 0000000023b3a96d3484e5abb3755c413e7d41500f8e2a5c3f0dd01299cd8ef8
	BIP0065Height:            581885, // 00000000007f6655f22f98e72ed80d8b06dc761d5da09df0fa1dc4be4f861eb6
	BIP0066Height:            330776, // 000000002104c8c45e99a8853285a3b592602a3ccde2b832481da85e9e4ba182
	CoinbaseMaturity:         100,
	SubsidyReductionInterval: 210000,
	TargetTimespan:           time.Hour * 24 * 14, // 14 days
	TargetTimePerBlock:       time.Minute * 10,    // 10 minutes
	RetargetAdjustmentFactor: 4,                   // 25% less, 400% more
	ReduceMinDifficulty:      true,
	MinDiffReductionTime:     time.Minute * 20, // TargetTimePerBlock * 2
	GenerateSupported:        false,

	// Checkpoints ordered from oldest to newest.
	Checkpoints: []Checkpoint{
		{546, newHashFromStr("000000002a936ca763904c3c35fce2f3556c559c0214345d31b1bcebf76acb70")},
		{100000, newHashFromStr("00000000009e2958c15ff9290d571bf9459e93b19765c6801ddeccadbb160a1e")},
		{200000, newHashFromStr("0000000000287bffd321963ef05feab753ebe274e1d78b2fd4e2bfe9ad3aa6f2")},
		{300001, newHashFromStr("0000000000004829474748f3d1bc8fcf893c88be255e6d7f571c548aff57abf4")},
		{400002, newHashFromStr("0000000005e2c73b8ecb82ae2dbc2e8274614ebad7172b53528aba7501f5a089")},
		{500011, newHashFromStr("00000000000929f63977fbac92ff570a9bd9e7715401ee96f2848f7b07750b02")},
		{600002, newHashFromStr("000000000001f471389afd6ee94dcace5ccc44adc18e8bff402443f034b07240")},
		{700000, newHashFromStr("000000000000406178b12a4dea3b27e13b3c4fe4510994fd667d7c1e6a3f4dc1")},
		{800010, newHashFromStr("000000000017ed35296433190b6829db01e657d80631d43f5983fa403bfdb4c1")},
		{900000, newHashFromStr("0000000000356f8d8924556e765b7a94aaebc6b5c8685dcfa2b1ee8b41acd89b")},
		{1000007, newHashFromStr("00000000001ccb893d8a1f25b70ad173ce955e5f50124261bbbc50379a612ddf")},
	},

	// Consensus rule change deployments.
	//
	// The miner confirmation window is defined as:
	//   target proof of work timespan / target proof of work spacing
	RuleChangeActivationThreshold: 1512, // 75% of MinerConfirmationWindow
	MinerConfirmationWindow:       2016,
	Deployments: [DefinedDeployments]ConsensusDeployment{
		DeploymentTestDummy: {
			BitNumber:  28,
			StartTime:  1199145601, // January 1, 2008 UTC
			ExpireTime: 1230767999, // December 31, 2008 UTC
		},
		DeploymentCSV: {
			BitNumber:  0,
			StartTime:  1456790400, // March 1st, 2016
			ExpireTime: 1493596800, // May 1st, 2017
		},
		DeploymentSegwit: {
			BitNumber:  1,
			StartTime:  1462060800, // May 1, 2016 UTC
			ExpireTime: 1493596800, // May 1, 2017 UTC.
		},
	},

	// Mempool parameters
	RelayNonStdTxs: true,

	// Human-readable part for Bech32 encoded segwit addresses, as defined in
	// BIP 173.
	Bech32HRPSegwit: "tb", // always tb for test net

	// Address encoding magics
	PubKeyHashAddrID:        0x6f, // starts with m or n
	ScriptHashAddrID:        0xc4, // starts with 2
	WitnessPubKeyHashAddrID: 0x03, // starts with QW
	WitnessScriptHashAddrID: 0x28, // starts with T7n
	PrivateKeyID:            0xef, // starts with 9 (uncompressed) or c (compressed)

	// BIP32 hierarchical deterministic extended key magics
	HDPrivateKeyID: [4]byte{0x04, 0x35, 0x83, 0x94}, // starts with tprv
	HDPublicKeyID:  [4]byte{0x04, 0x35, 0x87, 0xcf}, // starts with tpub

	// BIP44 coin type used in the hierarchical deterministic path for
	// address generation.
	HDCoinType: 1,
}

// SimNetParams defines the network parameters for the simulation test Bitcoin
// network.  This network is similar to the normal test network except it is
// intended for private use within a group of individuals doing simulation
// testing.  The functionality is intended to differ in that the only nodes
// which are specifically specified are used to create the network rather than
// following normal discovery rules.  This is important as otherwise it would
// just turn into another public testnet.
var SimNetParams = Params{
	Name:        "simnet",
	Net:         wire.SimNet,
	DefaultPort: "18555",
	DNSSeeds:    []DNSSeed{}, // NOTE: There must NOT be any seeds.

	// Chain parameters
	GenesisBlock:             &simNetGenesisBlock,
	GenesisHash:              &simNetGenesisHash,
	PowLimit:                 simNetPowLimit,
	PowLimitBits:             0x207fffff,
	BIP0034Height:            0, // Always active on simnet
	BIP0065Height:            0, // Always active on simnet
	BIP0066Height:            0, // Always active on simnet
	CoinbaseMaturity:         100,
	SubsidyReductionInterval: 210000,
	TargetTimespan:           time.Hour * 24 * 14, // 14 days
	TargetTimePerBlock:       time.Minute * 10,    // 10 minutes
	RetargetAdjustmentFactor: 4,                   // 25% less, 400% more
	ReduceMinDifficulty:      true,
	MinDiffReductionTime:     time.Minute * 20, // TargetTimePerBlock * 2
	GenerateSupported:        true,

	// Checkpoints ordered from oldest to newest.
	Checkpoints: nil,

	// Consensus rule change deployments.
	//
	// The miner confirmation window is defined as:
	//   target proof of work timespan / target proof of work spacing
	RuleChangeActivationThreshold: 75, // 75% of MinerConfirmationWindow
	MinerConfirmationWindow:       100,
	Deployments: [DefinedDeployments]ConsensusDeployment{
		DeploymentTestDummy: {
			BitNumber:  28,
			StartTime:  0,             // Always available for vote
			ExpireTime: math.MaxInt64, // Never expires
		},
		DeploymentCSV: {
			BitNumber:  0,
			StartTime:  0,             // Always available for vote
			ExpireTime: math.MaxInt64, // Never expires
		},
		DeploymentSegwit: {
			BitNumber:  1,
			StartTime:  0,             // Always available for vote
			ExpireTime: math.MaxInt64, // Never expires.
		},
	},

	// Mempool parameters
	RelayNonStdTxs: true,

	// Human-readable part for Bech32 encoded segwit addresses, as defined in
	// BIP 173.
	Bech32HRPSegwit: "sb", // always sb for sim net

	// Address encoding magics
	PubKeyHashAddrID:        0x3f, // starts with S
	ScriptHashAddrID:        0x7b, // starts with s
	PrivateKeyID:            0x64, // starts with 4 (uncompressed) or F (compressed)
	WitnessPubKeyHashAddrID: 0x19, // starts with Gg
	WitnessScriptHashAddrID: 0x28, // starts with ?

	// BIP32 hierarchical deterministic extended key magics
	HDPrivateKeyID: [4]byte{0x04, 0x20, 0xb9, 0x00}, // starts with sprv
	HDPublicKeyID:  [4]byte{0x04, 0x20, 0xbd, 0x3a}, // starts with spub

	// BIP44 coin type used in the hierarchical deterministic path for
	// address generation.
	HDCoinType: 115, // ASCII for s
}

var (
	// ErrDuplicateNet describes an error where the parameters for a Bitcoin
	// network could not be set due to the network already being a standard
	// network or previously-registered into this package.
	ErrDuplicateNet = errors.New("duplicate Bitcoin network")

	// ErrUnknownHDKeyID describes an error where the provided id which
	// is intended to identify the network for a hierarchical deterministic
	// private extended key is not registered.
	ErrUnknownHDKeyID = errors.New("unknown hd private extended key bytes")
)

var (
	registeredNets       = make(map[wire.BitcoinNet]struct{})
	pubKeyHashAddrIDs    = make(map[byte]struct{})
	scriptHashAddrIDs    = make(map[byte]struct{})
	bech32SegwitPrefixes = make(map[string]struct{})
	hdPrivToPubKeyIDs    = make(map[[4]byte][]byte)
)

// String returns the hostname of the DNS seed in human-readable form.
func (d DNSSeed) String() string {
	return d.Host
}

// Register registers the network parameters for a Bitcoin network.  This may
// error with ErrDuplicateNet if the network is already registered (either
// due to a previous Register call, or the network being one of the default
// networks).
//
// Network parameters should be registered into this package by a main package
// as early as possible.  Then, library packages may lookup networks or network
// parameters based on inputs and work regardless of the network being standard
// or not.
func Register(params *Params) error {
	if _, ok := registeredNets[params.Net]; ok {
		return ErrDuplicateNet
	}
	registeredNets[params.Net] = struct{}{}
	pubKeyHashAddrIDs[params.PubKeyHashAddrID] = struct{}{}
	scriptHashAddrIDs[params.ScriptHashAddrID] = struct{}{}
	hdPrivToPubKeyIDs[params.HDPrivateKeyID] = params.HDPublicKeyID[:]

	// A valid Bech32 encoded segwit address always has as prefix the
	// human-readable part for the given net followed by '1'.
	bech32SegwitPrefixes[params.Bech32HRPSegwit+"1"] = struct{}{}
	return nil
}

// mustRegister performs the same function as Register except it panics if there
// is an error.  This should only be called from package init functions.
func mustRegister(params *Params) {
	if err := Register(params); err != nil {
		panic("failed to register network: " + err.Error())
	}
}

// IsPubKeyHashAddrID returns whether the id is an identifier known to prefix a
// pay-to-pubkey-hash address on any default or registered network.  This is
// used when decoding an address string into a specific address type.  It is up
// to the caller to check both this and IsScriptHashAddrID and decide whether an
// address is a pubkey hash address, script hash address, neither, or
// undeterminable (if both return true).
func IsPubKeyHashAddrID(id byte) bool {
	_, ok := pubKeyHashAddrIDs[id]
	return ok
}

// IsScriptHashAddrID returns whether the id is an identifier known to prefix a
// pay-to-script-hash address on any default or registered network.  This is
// used when decoding an address string into a specific address type.  It is up
// to the caller to check both this and IsPubKeyHashAddrID and decide whether an
// address is a pubkey hash address, script hash address, neither, or
// undeterminable (if both return true).
func IsScriptHashAddrID(id byte) bool {
	_, ok := scriptHashAddrIDs[id]
	return ok
}

// IsBech32SegwitPrefix returns whether the prefix is a known prefix for segwit
// addresses on any default or registered network.  This is used when decoding
// an address string into a specific address type.
func IsBech32SegwitPrefix(prefix string) bool {
	prefix = strings.ToLower(prefix)
	_, ok := bech32SegwitPrefixes[prefix]
	return ok
}

// HDPrivateKeyToPublicKeyID accepts a private hierarchical deterministic
// extended key id and returns the associated public key id.  When the provided
// id is not registered, the ErrUnknownHDKeyID error will be returned.
func HDPrivateKeyToPublicKeyID(id []byte) ([]byte, error) {
	if len(id) != 4 {
		return nil, ErrUnknownHDKeyID
	}

	var key [4]byte
	copy(key[:], id)
	pubBytes, ok := hdPrivToPubKeyIDs[key]
	if !ok {
		return nil, ErrUnknownHDKeyID
	}

	return pubBytes, nil
}

// newHashFromStr converts the passed big-endian hex string into a
// chainhash.Hash.  It only differs from the one available in chainhash in that
// it panics on an error since it will only (and must only) be called with
// hard-coded, and therefore known good, hashes.
func newHashFromStr(hexStr string) *chainhash.Hash {
	hash, err := chainhash.NewHashFromStr(hexStr)
	if err != nil {
		// Ordinarily I don't like panics in library code since it
		// can take applications down without them having a chance to
		// recover which is extremely annoying, however an exception is
		// being made in this case because the only way this can panic
		// is if there is an error in the hard-coded hashes.  Thus it
		// will only ever potentially panic on init and therefore is
		// 100% predictable.
		panic(err)
	}
	return hash
}

func init() {
	// Register all default networks when the package is initialized.
	mustRegister(&MainNetParams)
	mustRegister(&TestNet3Params)
	mustRegister(&RegressionNetParams)
	mustRegister(&SimNetParams)
}