// DecodeAddress decodes the string encoding of an address and returns
// the Address if addr is a valid encoding for a known address type.
//
// The bitcoin network the address is associated with is extracted if possible.
// When the address does not encode the network, such as in the case of a raw
// public key, the address will be associated with the passed defaultNet.
func DecodeAddress(addr string, defaultNet *chaincfg.Params) (Address, error) {
	// Bech32 encoded segwit addresses start with a human-readable part
	// (hrp) followed by '1'. For Bitcoin mainnet the hrp is "bc", and for
	// testnet it is "tb". If the address string has a prefix that matches
	// one of the prefixes for the known networks, we try to decode it as
	// a segwit address.
	oneIndex := strings.LastIndexByte(addr, '1')
	if oneIndex > 1 {
		// The HRP is everything before the found '1'.
		hrp := strings.ToLower(addr[:oneIndex])
		if hrp == defaultNet.Bech32HRPSegwit {
			witnessVer, witnessProg, err := decodeSegWitAddress(addr)
			if err != nil {
				return nil, err
			}

			// We currently only support P2WPKH and P2WSH, which is
			// witness version 0.
			if witnessVer != 0 {
				return nil, UnsupportedWitnessVerError(witnessVer)
			}

			switch len(witnessProg) {
			case 20:
				return newAddressWitnessPubKeyHash(hrp, witnessProg)
			case 32:
				return newAddressWitnessScriptHash(hrp, witnessProg)
			default:
				return nil, UnsupportedWitnessProgLenError(len(witnessProg))
			}
		}
	}

	// Serialized public keys are either 65 bytes (130 hex chars) if
	// uncompressed/hybrid or 33 bytes (66 hex chars) if compressed.
	if len(addr) == 130 || len(addr) == 66 {
		serializedPubKey, err := hex.DecodeString(addr)
		if err != nil {
			return nil, err
		}
		return NewAddressPubKey(serializedPubKey, defaultNet)
	}

	// Switch on decoded length to determine the type.
	decoded, netID, err := base58.CheckDecode(addr)
	if err != nil {
		if err == base58.ErrChecksum {
			return nil, ErrChecksumMismatch
		}
		return nil, errors.New("decoded address is of unknown format")
	}
	switch len(decoded) {
	case ripemd160.Size: // P2PKH or P2SH
		isP2PKH := netID == defaultNet.PubKeyHashAddrID
		isP2SH := netID == defaultNet.ScriptHashAddrID
		switch hash160 := decoded; {
		case isP2PKH && isP2SH:
			return nil, ErrAddressCollision
		case isP2PKH:
			return newAddressPubKeyHash(hash160, netID)
		case isP2SH:
			return newAddressScriptHashFromHash(hash160, netID)
		default:
			return nil, ErrUnknownAddressType
		}

	default:
		return nil, errors.New("decoded address is of unknown size")
	}
}

// AddressPubKey is an Address for a pay-to-pubkey transaction.
type AddressPubKey struct {
	pubKeyFormat PubKeyFormat
	pubKey       *btcec.PublicKey
	pubKeyHashID byte
}

// AddressPubKeyHash is an Address for a pay-to-pubkey-hash (P2PKH)
// transaction.
type AddressPubKeyHash struct {
	hash  [ripemd160.Size]byte
	netID byte
}

// AddressScriptHash is an Address for a pay-to-script-hash (P2SH)
// transaction.
type AddressScriptHash struct {
	hash  [ripemd160.Size]byte
	netID byte
}

// AddressWitnessPubKeyHash is an Address for a pay-to-witness-pubkey-hash
// (P2WPKH) output. See BIP 173 for further details regarding native segregated
// witness address encoding:
// https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki
type AddressWitnessPubKeyHash struct {
	hrp            string
	witnessVersion byte
	witnessProgram [20]byte
}

// AddressWitnessScriptHash is an Address for a pay-to-witness-script-hash
// (P2WSH) output. See BIP 173 for further details regarding native segregated
// witness address encoding:
// https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki
type AddressWitnessScriptHash struct {
	hrp            string
	witnessVersion byte
	witnessProgram [32]byte
}

// isPubkeyHash returns true if the script passed is a pay-to-pubkey-hash
// transaction, false otherwise.
func isPubkeyHash(pops []parsedOpcode) bool {
	return len(pops) == 5 &&
		pops[0].opcode.value == OP_DUP &&
		pops[1].opcode.value == OP_HASH160 &&
		pops[2].opcode.value == OP_DATA_20 &&
		pops[3].opcode.value == OP_EQUALVERIFY &&
		pops[4].opcode.value == OP_CHECKSIG

}

// isPubkey returns true if the script passed is a pay-to-pubkey transaction,
// false otherwise.
func isPubkey(pops []parsedOpcode) bool {
	// Valid pubkeys are either 33 or 65 bytes.
	return len(pops) == 2 &&
		(len(pops[0].data) == 33 || len(pops[0].data) == 65) &&
		pops[1].opcode.value == OP_CHECKSIG
}

// isScriptHash returns true if the script passed is a pay-to-script-hash
// transaction, false otherwise.
func isScriptHash(pops []parsedOpcode) bool {
	return len(pops) == 3 &&
		pops[0].opcode.value == OP_HASH160 &&
		pops[1].opcode.value == OP_DATA_20 &&
		pops[2].opcode.value == OP_EQUAL
}

// isWitnessPubKeyHash returns true if the passed script is a
// pay-to-witness-pubkey-hash, and false otherwise.
func isWitnessPubKeyHash(pops []parsedOpcode) bool {
	return len(pops) == 2 &&
		pops[0].opcode.value == OP_0 &&
		pops[1].opcode.value == OP_DATA_20
}

// isWitnessScriptHash returns true if the passed script is a
// pay-to-witness-script-hash transaction, false otherwise.
func isWitnessScriptHash(pops []parsedOpcode) bool {
	return len(pops) == 2 &&
		pops[0].opcode.value == OP_0 &&
		pops[1].opcode.value == OP_DATA_32
}