text: // Copyright (c) 2018-2020 The Pexa Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include <script/descriptor.h>
  
  #include <key_io.h>
  #include <pubkey.h>
  #include <script/script.h>
  #include <script/standard.h>
  
  #include <span.h>
  #include <util/bip32.h>
  #include <util/spanparsing.h>
  #include <util/system.h>
  #include <util/strencodings.h>
  #include <util/vector.h>
  
  #include <memory>
  #include <string>
  #include <vector>
  
  namespace {
  
  ////////////////////////////////////////////////////////////////////////////
  // Checksum                                                               //
  ////////////////////////////////////////////////////////////////////////////
  
  // This section implements a checksum algorithm for descriptors with the
  // following properties:
  // * Mistakes in a descriptor string are measured in "symbol errors". The higher
  //   the number of symbol errors, the harder it is to detect:
  //   * An error substituting a character from 0123456789()[],'/*abcdefgh@:$%{} for
  //     another in that set always counts as 1 symbol error.
  //     * Note that hex encoded keys are covered by these characters. Xprvs and
  //       xpubs use other characters too, but already have their own checksum
  //       mechanism.
  //     * Function names like "multi()" use other characters, but mistakes in
  //       these would generally result in an unparsable descriptor.
  //   * A case error always counts as 1 symbol error.
  //   * Any other 1 character substitution error counts as 1 or 2 symbol errors.
  // * Any 1 symbol error is always detected.
  // * Any 2 or 3 symbol error in a descriptor of up to 49154 characters is always detected.
  // * Any 4 symbol error in a descriptor of up to 507 characters is always detected.
  // * Any 5 symbol error in a descriptor of up to 77 characters is always detected.
  // * Is optimized to minimize the chance a 5 symbol error in a descriptor up to 387 characters is undetected
  // * Random errors have a chance of 1 in 2**40 of being undetected.
  //
  // These properties are achieved by expanding every group of 3 (non checksum) characters into
  // 4 GF(32) symbols, over which a cyclic code is defined.
  
  /*
   * Interprets c as 8 groups of 5 bits which are the coefficients of a degree 8 polynomial over GF(32),
   * multiplies that polynomial by x, computes its remainder modulo a generator, and adds the constant term val.
   *
   * This generator is G(x) = x^8 + {30}x^7 + {23}x^6 + {15}x^5 + {14}x^4 + {10}x^3 + {6}x^2 + {12}x + {9}.
   * It is chosen to define an cyclic error detecting code which is selected by:
   * - Starting from all BCH codes over GF(32) of degree 8 and below, which by construction guarantee detecting
   *   3 errors in windows up to 19000 symbols.
   * - Taking all those generators, and for degree 7 ones, extend them to degree 8 by adding all degree-1 factors.
   * - Selecting just the set of generators that guarantee detecting 4 errors in a window of length 512.
   * - Selecting one of those with best worst-case behavior for 5 errors in windows of length up to 512.
   *
   * The generator and the constants to implement it can be verified using this Sage code:
   *   B = GF(2) # Binary field
   *   BP.<b> = B[] # Polynomials over the binary field
   *   F_mod = b**5 + b**3 + 1
   *   F.<f> = GF(32, modulus=F_mod, repr='int') # GF(32) definition
   *   FP.<x> = F[] # Polynomials over GF(32)
   *   E_mod = x**3 + x + F.fetch_int(8)
   *   E.<e> = F.extension(E_mod) # Extension field definition
   *   alpha = e**2743 # Choice of an element in extension field
   *   for p in divisors(E.order() - 1): # Verify alpha has order 32767.
   *       assert((alpha**p == 1) == (p % 32767 == 0))
   *   G = lcm([(alpha**i).minpoly() for i in [1056,1057,1058]] + [x + 1])
   *   print(G) # Print out the generator
   *   for i in [1,2,4,8,16]: # Print out {1,2,4,8,16}*(G mod x^8), packed in hex integers.
   *       v = 0
   *       for coef in reversed((F.fetch_int(i)*(G % x**8)).coefficients(sparse=True)):
   *           v = v*32 + coef.integer_representation()
   *       print("0x%x" % v)
   */
  uint64_t PolyMod(uint64_t c, int val)
  {
      uint8_t c0 = c >> 35;
      c = ((c & 0x7ffffffff) << 5) ^ val;
      if (c0 & 1) c ^= 0xf5dee51989;
      if (c0 & 2) c ^= 0xa9fdca3312;
      if (c0 & 4) c ^= 0x1bab10e32d;
      if (c0 & 8) c ^= 0x3706b1677a;
      if (c0 & 16) c ^= 0x644d626ffd;
      return c;
  }
  
  std::string DescriptorChecksum(const Span<const char>& span)
  {
      /** A character set designed such that:
       *  - The most common 'unprotected' descriptor characters (hex, keypaths) are in the first group of 32.
       *  - Case errors cause an offset that's a multiple of 32.
       *  - As many alphabetic characters are in the same group (while following the above restrictions).
       *
       * If p(x) gives the position of a character c in this character set, every group of 3 characters
       * (a,b,c) is encoded as the 4 symbols (p(a) & 31, p(b) & 31, p(c) & 31, (p(a) / 32) + 3 * (p(b) / 32) + 9 * (p(c) / 32).
       * This means that changes that only affect the lower 5 bits of the position, or only the higher 2 bits, will just
       * affect a single symbol.
       *
       * As a result, within-group-of-32 errors count as 1 symbol, as do cross-group errors that don't affect
       * the position within the groups.
       */
      static std::string INPUT_CHARSET =
          "0123456789()[],'/*abcdefgh@:$%{}"
          "IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~"
          "ijklmnopqrstuvwxyzABCDEFGH`#\"\\ ";
  
      /** The character set for the checksum itself (same as bech32). */
      static std::string CHECKSUM_CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";
  
      uint64_t c = 1;
      int cls = 0;
      int clscount = 0;
      for (auto ch : span) {
          auto pos = INPUT_CHARSET.find(ch);
          if (pos == std::string::npos) return "";
          c = PolyMod(c, pos & 31); // Emit a symbol for the position inside the group, for every character.
          cls = cls * 3 + (pos >> 5); // Accumulate the group numbers
          if (++clscount == 3) {
              // Emit an extra symbol representing the group numbers, for every 3 characters.
              c = PolyMod(c, cls);
              cls = 0;
              clscount = 0;
          }
      }
      if (clscount > 0) c = PolyMod(c, cls);
      for (int j = 0; j < 8; ++j) c = PolyMod(c, 0); // Shift further to determine the checksum.
      c ^= 1; // Prevent appending zeroes from not affecting the checksum.
  
      std::string ret(8, ' ');
      for (int j = 0; j < 8; ++j) ret[j] = CHECKSUM_CHARSET[(c >> (5 * (7 - j))) & 31];
      return ret;
  }
  
  std::string AddChecksum(const std::string& str) { return str + "#" + DescriptorChecksum(MakeSpan(str)); }
  
  ////////////////////////////////////////////////////////////////////////////
  // Internal representation                                                //
  ////////////////////////////////////////////////////////////////////////////
  
  typedef std::vector<uint32_t> KeyPath;
  
  /** Interface for public key objects in descriptors. */
  struct PubkeyProvider
  {
  protected:
      //! Index of this key expression in the descriptor
      //! E.g. If this PubkeyProvider is key1 in multi(2, key1, key2, key3), then m_expr_index = 0
      uint32_t m_expr_index;
  
  public:
      PubkeyProvider(uint32_t exp_index) : m_expr_index(exp_index) {}
  
      virtual ~PubkeyProvider() = default;
  
      /** Derive a public key.
       *  read_cache is the cache to read keys from (if not nullptr)
       *  write_cache is the cache to write keys to (if not nullptr)
       *  Caches are not exclusive but this is not tested. Currently we use them exclusively
       */
      virtual bool GetPubKey(int pos, const SigningProvider& arg, CPubKey& key, KeyOriginInfo& info, const DescriptorCache* read_cache = nullptr, DescriptorCache* write_cache = nullptr) = 0;
  
      /** Whether this represent multiple public keys at different positions. */
      virtual bool IsRange() const = 0;
  
      /** Get the size of the generated public key(s) in bytes (33 or 65). */
      virtual size_t GetSize() const = 0;
  
      /** Get the descriptor string form. */
      virtual std::string ToString() const = 0;
  
      /** Get the descriptor string form including private data (if available in arg). */
      virtual bool ToPrivateString(const SigningProvider& arg, std::string& out) const = 0;
  
      /** Derive a private key, if private data is available in arg. */
      virtual bool GetPrivKey(int pos, const SigningProvider& arg, CKey& key) const = 0;
  };
  
  class OriginPubkeyProvider final : public PubkeyProvider
  {
      KeyOriginInfo m_origin;
      std::unique_ptr<PubkeyProvider> m_provider;
  
      std::string OriginString() const
      {
          return HexStr(std::begin(m_origin.fingerprint), std::end(m_origin.fingerprint)) + FormatHDKeypath(m_origin.path);
      }
  
  public:
      OriginPubkeyProvider(uint32_t exp_index, KeyOriginInfo info, std::unique_ptr<PubkeyProvider> provider) : PubkeyProvider(exp_index), m_origin(std::move(info)), m_provider(std::move(provider)) {}
      bool GetPubKey(int pos, const SigningProvider& arg, CPubKey& key, KeyOriginInfo& info, const DescriptorCache* read_cache = nullptr, DescriptorCache* write_cache = nullptr) override
      {
          if (!m_provider->GetPubKey(pos, arg, key, info, read_cache, write_cache)) return false;
          std::copy(std::begin(m_origin.fingerprint), std::end(m_origin.fingerprint), info.fingerprint);
          info.path.insert(info.path.begin(), m_origin.path.begin(), m_origin.path.end());
          return true;
      }
      bool IsRange() const override { return m_provider->IsRange(); }
      size_t GetSize() const override { return m_provider->GetSize(); }
      std::string ToString() const override { return "[" + OriginString() + "]" + m_provider->ToString(); }
      bool ToPrivateString(const SigningProvider& arg, std::string& ret) const override
      {
          std::string sub;
          if (!m_provider->ToPrivateString(arg, sub)) return false;
          ret = "[" + OriginString() + "]" + std::move(sub);
          return true;
      }
      bool GetPrivKey(int pos, const SigningProvider& arg, CKey& key) const override
      {
          return m_provider->GetPrivKey(pos, arg, key);
      }
  };
  
  /** An object representing a parsed constant public key in a descriptor. */
  class ConstPubkeyProvider final : public PubkeyProvider
  {
      CPubKey m_pubkey;
  
  public:
      ConstPubkeyProvider(uint32_t exp_index, const CPubKey& pubkey) : PubkeyProvider(exp_index), m_pubkey(pubkey) {}
      bool GetPubKey(int pos, const SigningProvider& arg, CPubKey& key, KeyOriginInfo& info, const DescriptorCache* read_cache = nullptr, DescriptorCache* write_cache = nullptr) override
      {
          key = m_pubkey;
          info.path.clear();
          CKeyID keyid = m_pubkey.GetID();
          std::copy(keyid.begin(), keyid.begin() + sizeof(info.fingerprint), info.fingerprint);
          return true;
      }
      bool IsRange() const override { return false; }
      size_t GetSize() const override { return m_pubkey.size(); }
      std::string ToString() const override { return HexStr(m_pubkey.begin(), m_pubkey.end()); }
      bool ToPrivateString(const SigningProvider& arg, std::string& ret) const override
      {
          CKey key;
          if (!arg.GetKey(m_pubkey.GetID(), key)) return false;
          ret = EncodeSecret(key);
          return true;
      }
      bool GetPrivKey(int pos, const SigningProvider& arg, CKey& key) const override
      {
          return arg.GetKey(m_pubkey.GetID(), key);
      }
  };
  
  enum class DeriveType {
      NO,
      UNHARDENED,
      HARDENED,
  };
  
  /** An object representing a parsed extended public key in a descriptor. */
  class BIP32PubkeyProvider final : public PubkeyProvider
  {
      // Root xpub, path, and final derivation step type being used, if any
      CExtPubKey m_root_extkey;
      KeyPath m_path;
      DeriveType m_derive;
      // Cache of the parent of the final derived pubkeys.
      // Primarily useful for situations when no read_cache is provided
      CExtPubKey m_cached_xpub;
  
      bool GetExtKey(const SigningProvider& arg, CExtKey& ret) const
      {
          CKey key;
          if (!arg.GetKey(m_root_extkey.pubkey.GetID(), key)) return false;
          ret.nDepth = m_root_extkey.nDepth;
          std::copy(m_root_extkey.vchFingerprint, m_root_extkey.vchFingerprint + sizeof(ret.vchFingerprint), ret.vchFingerprint);
          ret.nChild = m_root_extkey.nChild;
          ret.chaincode = m_root_extkey.chaincode;
          ret.key = key;
          return true;
      }
  
      // Derives the last xprv
      bool GetDerivedExtKey(const SigningProvider& arg, CExtKey& xprv) const
      {
          if (!GetExtKey(arg, xprv)) return false;
          for (auto entry : m_path) {
              xprv.Derive(xprv, entry);
          }
          return true;
      }
  
      bool IsHardened() const
      {
          if (m_derive == DeriveType::HARDENED) return true;
          for (auto entry : m_path) {
              if (entry >> 31) return true;
          }
          return false;
      }
  
  public:
      BIP32PubkeyProvider(uint32_t exp_index, const CExtPubKey& extkey, KeyPath path, DeriveType derive) : PubkeyProvider(exp_index), m_root_extkey(extkey), m_path(std::move(path)), m_derive(derive) {}
      bool IsRange() const override { return m_derive != DeriveType::NO; }
      size_t GetSize() const override { return 33; }
      bool GetPubKey(int pos, const SigningProvider& arg, CPubKey& key_out, KeyOriginInfo& final_info_out, const DescriptorCache* read_cache = nullptr, DescriptorCache* write_cache = nullptr) override
      {
          // Info of parent of the to be derived pubkey
          KeyOriginInfo parent_info;
          CKeyID keyid = m_root_extkey.pubkey.GetID();
          std::copy(keyid.begin(), keyid.begin() + sizeof(parent_info.fingerprint), parent_info.fingerprint);
          parent_info.path = m_path;
  
          // Info of the derived key itself which is copied out upon successful completion
          KeyOriginInfo final_info_out_tmp = parent_info;
          if (m_derive == DeriveType::UNHARDENED) final_info_out_tmp.path.push_back((uint32_t)pos);
          if (m_derive == DeriveType::HARDENED) final_info_out_tmp.path.push_back(((uint32_t)pos) | 0x80000000L);
  
          // Derive keys or fetch them from cache
          CExtPubKey final_extkey = m_root_extkey;
          CExtPubKey parent_extkey = m_root_extkey;
          bool der = true;
          if (read_cache) {
              if (!read_cache->GetCachedDerivedExtPubKey(m_expr_index, pos, final_extkey)) {
                  if (m_derive == DeriveType::HARDENED) return false;
                  // Try to get the derivation parent
                  if (!read_cache->GetCachedParentExtPubKey(m_expr_index, parent_extkey)) return false;
                  final_extkey = parent_extkey;
                  if (m_derive == DeriveType::UNHARDENED) der = parent_extkey.Derive(final_extkey, pos);
              }
          } else if (m_cached_xpub.pubkey.IsValid() && m_derive != DeriveType::HARDENED) {
              parent_extkey = final_extkey = m_cached_xpub;
              if (m_derive == DeriveType::UNHARDENED) der = parent_extkey.Derive(final_extkey, pos);
          } else if (IsHardened()) {
              CExtKey xprv;
              if (!GetDerivedExtKey(arg, xprv)) return false;
              parent_extkey = xprv.Neuter();
              if (m_derive == DeriveType::UNHARDENED) der = xprv.Derive(xprv, pos);
              if (m_derive == DeriveType::HARDENED) der = xprv.Derive(xprv, pos | 0x80000000UL);
              final_extkey = xprv.Neuter();
          } else {
              for (auto entry : m_path) {
                  der = parent_extkey.Derive(parent_extkey, entry);
                  assert(der);
              }
              final_extkey = parent_extkey;
              if (m_derive == DeriveType::UNHARDENED) der = parent_extkey.Derive(final_extkey, pos);
              assert(m_derive != DeriveType::HARDENED);
          }
          assert(der);
  
          final_info_out = final_info_out_tmp;
          key_out = final_extkey.pubkey;
  
          // We rely on the consumer to check that m_derive isn't HARDENED as above
          // But we can't have already cached something in case we read something from the cache
          // and parent_extkey isn't actually the parent.
          if (!m_cached_xpub.pubkey.IsValid()) m_cached_xpub = parent_extkey;
  
          if (write_cache) {
              // Only cache parent if there is any unhardened derivation
              if (m_derive != DeriveType::HARDENED) {
                  write_cache->CacheParentExtPubKey(m_expr_index, parent_extkey);
              } else if (final_info_out.path.size() > 0) {
                  write_cache->CacheDerivedExtPubKey(m_expr_index, pos, final_extkey);
              }
          }
  
          return true;
      }
      std::string ToString() const override
      {
          std::string ret = EncodeExtPubKey(m_root_extkey) + FormatHDKeypath(m_path);
          if (IsRange()) {
              ret += "/*";
              if (m_derive == DeriveType::HARDENED) ret += '\'';
          }
          return ret;
      }
      bool ToPrivateString(const SigningProvider& arg, std::string& out) const override
      {
          CExtKey key;
          if (!GetExtKey(arg, key)) return false;
          out = EncodeExtKey(key) + FormatHDKeypath(m_path);
          if (IsRange()) {
              out += "/*";
              if (m_derive == DeriveType::HARDENED) out += '\'';
          }
          return true;
      }
      bool GetPrivKey(int pos, const SigningProvider& arg, CKey& key) const override
      {
          CExtKey extkey;
          if (!GetDerivedExtKey(arg, extkey)) return false;
          if (m_derive == DeriveType::UNHARDENED) extkey.Derive(extkey, pos);
          if (m_derive == DeriveType::HARDENED) extkey.Derive(extkey, pos | 0x80000000UL);
          key = extkey.key;
          return true;
      }
  };
  
  /** Base class for all Descriptor implementations. */
  class DescriptorImpl : public Descriptor
  {
      //! Public key arguments for this descriptor (size 1 for PK, PKH, WPKH; any size for Multisig).
      const std::vector<std::unique_ptr<PubkeyProvider>> m_pubkey_args;
      //! The string name of the descriptor function.
      const std::string m_name;
  
  protected:
      //! The sub-descriptor argument (nullptr for everything but SH and WSH).
      //! In doc/descriptors.m this is referred to as SCRIPT expressions sh(SCRIPT)
      //! and wsh(SCRIPT), and distinct from KEY expressions and ADDR expressions.
      const std::unique_ptr<DescriptorImpl> m_subdescriptor_arg;
  
      //! Return a serialization of anything except pubkey and script arguments, to be prepended to those.
      virtual std::string ToStringExtra() const { return ""; }
  
      /** A helper function to construct the scripts for this descriptor.
       *
       *  This function is invoked once for every CScript produced by evaluating
       *  m_subdescriptor_arg, or just once in case m_subdescriptor_arg is nullptr.
  
       *  @param pubkeys The evaluations of the m_pubkey_args field.
       *  @param script The evaluation of m_subdescriptor_arg (or nullptr when m_subdescriptor_arg is nullptr).
       *  @param out A FlatSigningProvider to put scripts or public keys in that are necessary to the solver.
       *             The script arguments to this function are automatically added, as is the origin info of the provided pubkeys.
       *  @return A vector with scriptPubKeys for this descriptor.
       */
      virtual std::vector<CScript> MakeScripts(const std::vector<CPubKey>& pubkeys, const CScript* script, FlatSigningProvider& out) const = 0;
  
  public:
      DescriptorImpl(std::vector<std::unique_ptr<PubkeyProvider>> pubkeys, std::unique_ptr<DescriptorImpl> script, const std::string& name) : m_pubkey_args(std::move(pubkeys)), m_name(name), m_subdescriptor_arg(std::move(script)) {}
  
      bool IsSolvable() const override
      {
          if (m_subdescriptor_arg) {
              if (!m_subdescriptor_arg->IsSolvable()) return false;
          }
          return true;
      }
  
      bool IsRange() const final
      {
          for (const auto& pubkey : m_pubkey_args) {
              if (pubkey->IsRange()) return true;
          }
          if (m_subdescriptor_arg) {
              if (m_subdescriptor_arg->IsRange()) return true;
          }
          return false;
      }
  
      bool ToStringHelper(const SigningProvider* arg, std::string& out, bool priv) const
      {
          std::string extra = ToStringExtra();
          size_t pos = extra.size() > 0 ? 1 : 0;
          std::string ret = m_name + "(" + extra;
          for (const auto& pubkey : m_pubkey_args) {
              if (pos++) ret += ",";
              std::string tmp;
              if (priv) {
                  if (!pubkey->ToPrivateString(*arg, tmp)) return false;
              } else {
                  tmp = pubkey->ToString();
              }
              ret += std::move(tmp);
          }
          if (m_subdescriptor_arg) {
              if (pos++) ret += ",";
              std::string tmp;
              if (!m_subdescriptor_arg->ToStringHelper(arg, tmp, priv)) return false;
              ret += std::move(tmp);
          }
          out = std::move(ret) + ")";
          return true;
      }
  
      std::string ToString() const final
      {
          std::string ret;
          ToStringHelper(nullptr, ret, false);
          return AddChecksum(ret);
      }
  
      bool ToPrivateString(const SigningProvider& arg, std::string& out) const final
      {
          bool ret = ToStringHelper(&arg, out, true);
          out = AddChecksum(out);
          return ret;
      }
  
      bool ExpandHelper(int pos, const SigningProvider& arg, const DescriptorCache* read_cache, std::vector<CScript>& output_scripts, FlatSigningProvider& out, DescriptorCache* write_cache) const
      {
          std::vector<std::pair<CPubKey, KeyOriginInfo>> entries;
          entries.reserve(m_pubkey_args.size());
  
          // Construct temporary data in `entries` and `subscripts`, to avoid producing output in case of failure.
          for (const auto& p : m_pubkey_args) {
              entries.emplace_back();
              if (!p->GetPubKey(pos, arg, entries.back().first, entries.back().second, read_cache, write_cache)) return false;
          }
          std::vector<CScript> subscripts;
          if (m_subdescriptor_arg) {
              FlatSigningProvider subprovider;
              if (!m_subdescriptor_arg->ExpandHelper(pos, arg, read_cache, subscripts, subprovider, write_cache)) return false;
              out = Merge(out, subprovider);
          }
  
          std::vector<CPubKey> pubkeys;
          pubkeys.reserve(entries.size());
          for (auto& entry : entries) {
              pubkeys.push_back(entry.first);
              out.origins.emplace(entry.first.GetID(), std::make_pair<CPubKey, KeyOriginInfo>(CPubKey(entry.first), std::move(entry.second)));
          }
          if (m_subdescriptor_arg) {
              for (const auto& subscript : subscripts) {
                  out.scripts.emplace(CScriptID(subscript), subscript);
                  std::vector<CScript> addscripts = MakeScripts(pubkeys, &subscript, out);
                  for (auto& addscript : addscripts) {
                      output_scripts.push_back(std::move(addscript));
                  }
              }
          } else {
              output_scripts = MakeScripts(pubkeys, nullptr, out);
          }
          return true;
      }
  
      bool Expand(int pos, const SigningProvider& provider, std::vector<CScript>& output_scripts, FlatSigningProvider& out, DescriptorCache* write_cache = nullptr) const final
      {
          return ExpandHelper(pos, provider, nullptr, output_scripts, out, write_cache);
      }
  
      bool ExpandFromCache(int pos, const DescriptorCache& read_cache, std::vector<CScript>& output_scripts, FlatSigningProvider& out) const final
      {
          return ExpandHelper(pos, DUMMY_SIGNING_PROVIDER, &read_cache, output_scripts, out, nullptr);
      }
  
      void ExpandPrivate(int pos, const SigningProvider& provider, FlatSigningProvider& out) const final
      {
          for (const auto& p : m_pubkey_args) {
              CKey key;
              if (!p->GetPrivKey(pos, provider, key)) continue;
              out.keys.emplace(key.GetPubKey().GetID(), key);
          }
          if (m_subdescriptor_arg) {
              FlatSigningProvider subprovider;
              m_subdescriptor_arg->ExpandPrivate(pos, provider, subprovider);
              out = Merge(out, subprovider);
          }
      }
  
      Optional<OutputType> GetOutputType() const override { return nullopt; }
  };
  
  /** A parsed addr(A) descriptor. */
  class AddressDescriptor final : public DescriptorImpl
  {
      const CTxDestination m_destination;
  protected:
      std::string ToStringExtra() const override { return EncodeDestination(m_destination); }
      std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, const CScript*, FlatSigningProvider&) const override { return Vector(GetScriptForDestination(m_destination)); }
  public:
      AddressDescriptor(CTxDestination destination) : DescriptorImpl({}, {}, "addr"), m_destination(std::move(destination)) {}
      bool IsSolvable() const final { return false; }
  
      Optional<OutputType> GetOutputType() const override
      {
          switch (m_destination.which()) {
              case 1 /* PKHash */:
              case 2 /* ScriptHash */: return OutputType::LEGACY;
              case 3 /* WitnessV0ScriptHash */:
              case 4 /* WitnessV0KeyHash */:
              case 5 /* WitnessUnknown */: return OutputType::BECH32;
              case 0 /* CNoDestination */:
              default: return nullopt;
          }
      }
      bool IsSingleType() const final { return true; }
  };
  
  /** A parsed raw(H) descriptor. */
  class RawDescriptor final : public DescriptorImpl
  {
      const CScript m_script;
  protected:
      std::string ToStringExtra() const override { return HexStr(m_script.begin(), m_script.end()); }
      std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, const CScript*, FlatSigningProvider&) const override { return Vector(m_script); }
  public:
      RawDescriptor(CScript script) : DescriptorImpl({}, {}, "raw"), m_script(std::move(script)) {}
      bool IsSolvable() const final { return false; }
  
      Optional<OutputType> GetOutputType() const override
      {
          CTxDestination dest;
          ExtractDestination(m_script, dest);
          switch (dest.which()) {
              case 1 /* PKHash */:
              case 2 /* ScriptHash */: return OutputType::LEGACY;
              case 3 /* WitnessV0ScriptHash */:
              case 4 /* WitnessV0KeyHash */:
              case 5 /* WitnessUnknown */: return OutputType::BECH32;
              case 0 /* CNoDestination */:
              default: return nullopt;
          }
      }
      bool IsSingleType() const final { return true; }
  };
  
  /** A parsed pk(P) descriptor. */
  class PKDescriptor final : public DescriptorImpl
  {
  protected:
      std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, const CScript*, FlatSigningProvider&) const override { return Vector(GetScriptForRawPubKey(keys[0])); }
  public:
      PKDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), {}, "pk") {}
      bool IsSingleType() const final { return true; }
  };
  
  /** A parsed pkh(P) descriptor. */
  class PKHDescriptor final : public DescriptorImpl
  {
  protected:
      std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, const CScript*, FlatSigningProvider& out) const override
      {
          CKeyID id = keys[0].GetID();
          out.pubkeys.emplace(id, keys[0]);
          return Vector(GetScriptForDestination(PKHash(id)));
      }
  public:
      PKHDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), {}, "pkh") {}
      Optional<OutputType> GetOutputType() const override { return OutputType::LEGACY; }
      bool IsSingleType() const final { return true; }
  };
  
  /** A parsed wpkh(P) descriptor. */
  class WPKHDescriptor final : public DescriptorImpl
  {
  protected:
      std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, const CScript*, FlatSigningProvider& out) const override
      {
          CKeyID id = keys[0].GetID();
          out.pubkeys.emplace(id, keys[0]);
          return Vector(GetScriptForDestination(WitnessV0KeyHash(id)));
      }
  public:
      WPKHDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), {}, "wpkh") {}
      Optional<OutputType> GetOutputType() const override { return OutputType::BECH32; }
      bool IsSingleType() const final { return true; }
  };
  
  /** A parsed combo(P) descriptor. */
  class ComboDescriptor final : public DescriptorImpl
  {
  protected:
      std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, const CScript*, FlatSigningProvider& out) const override
      {
          std::vector<CScript> ret;
          CKeyID id = keys[0].GetID();
          out.pubkeys.emplace(id, keys[0]);
          ret.emplace_back(GetScriptForRawPubKey(keys[0])); // P2PK
          ret.emplace_back(GetScriptForDestination(PKHash(id))); // P2PKH
          if (keys[0].IsCompressed()) {
              CScript p2wpkh = GetScriptForDestination(WitnessV0KeyHash(id));
              out.scripts.emplace(CScriptID(p2wpkh), p2wpkh);
              ret.emplace_back(p2wpkh);
              ret.emplace_back(GetScriptForDestination(ScriptHash(p2wpkh))); // P2SH-P2WPKH
          }
          return ret;
      }
  public:
      ComboDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), {}, "combo") {}
      bool IsSingleType() const final { return false; }
  };
  
  /** A parsed multi(...) or sortedmulti(...) descriptor */
  class MultisigDescriptor final : public DescriptorImpl
  {
      const int m_threshold;
      const bool m_sorted;
  protected:
      std::string ToStringExtra() const override { return strprintf("%i", m_threshold); }
      std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, const CScript*, FlatSigningProvider&) const override {
          if (m_sorted) {
              std::vector<CPubKey> sorted_keys(keys);
              std::sort(sorted_keys.begin(), sorted_keys.end());
              return Vector(GetScriptForMultisig(m_threshold, sorted_keys));
          }
          return Vector(GetScriptForMultisig(m_threshold, keys));
      }
  public:
      MultisigDescriptor(int threshold, std::vector<std::unique_ptr<PubkeyProvider>> providers, bool sorted = false) : DescriptorImpl(std::move(providers), {}, sorted ? "sortedmulti" : "multi"), m_threshold(threshold), m_sorted(sorted) {}
      bool IsSingleType() const final { return true; }
  };
  
  /** A parsed sh(...) descriptor. */
  class SHDescriptor final : public DescriptorImpl
  {
  protected:
      std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, const CScript* script, FlatSigningProvider&) const override { return Vector(GetScriptForDestination(ScriptHash(*script))); }
  public:
      SHDescriptor(std::unique_ptr<DescriptorImpl> desc) : DescriptorImpl({}, std::move(desc), "sh") {}
  
      Optional<OutputType> GetOutputType() const override
      {
          assert(m_subdescriptor_arg);
          if (m_subdescriptor_arg->GetOutputType() == OutputType::BECH32) return OutputType::P2SH_SEGWIT;
          return OutputType::LEGACY;
      }
      bool IsSingleType() const final { return true; }
  };
  
  /** A parsed wsh(...) descriptor. */
  class WSHDescriptor final : public DescriptorImpl
  {
  protected:
      std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, const CScript* script, FlatSigningProvider&) const override { return Vector(GetScriptForDestination(WitnessV0ScriptHash(*script))); }
  public:
      WSHDescriptor(std::unique_ptr<DescriptorImpl> desc) : DescriptorImpl({}, std::move(desc), "wsh") {}
      Optional<OutputType> GetOutputType() const override { return OutputType::BECH32; }
      bool IsSingleType() const final { return true; }
  };
  
  ////////////////////////////////////////////////////////////////////////////
  // Parser                                                                 //
  ////////////////////////////////////////////////////////////////////////////
  
  enum class ParseScriptContext {
      TOP,
      P2SH,
      P2WSH,
  };
  
  /** Parse a key path, being passed a split list of elements (the first element is ignored). */
  NODISCARD bool ParseKeyPath(const std::vector<Span<const char>>& split, KeyPath& out, std::string& error)
  {
      for (size_t i = 1; i < split.size(); ++i) {
          Span<const char> elem = split[i];
          bool hardened = false;
          if (elem.size() > 0 && (elem[elem.size() - 1] == '\'' || elem[elem.size() - 1] == 'h')) {
              elem = elem.first(elem.size() - 1);
              hardened = true;
          }
          uint32_t p;
          if (!ParseUInt32(std::string(elem.begin(), elem.end()), &p)) {
              error = strprintf("Key path value '%s' is not a valid uint32", std::string(elem.begin(), elem.end()));
              return false;
          } else if (p > 0x7FFFFFFFUL) {
              error = strprintf("Key path value %u is out of range", p);
              return false;
          }
          out.push_back(p | (((uint32_t)hardened) << 31));
      }
      return true;
  }
  
  /** Parse a public key that excludes origin information. */
  std::unique_ptr<PubkeyProvider> ParsePubkeyInner(uint32_t key_exp_index, const Span<const char>& sp, bool permit_uncompressed, FlatSigningProvider& out, std::string& error)
  {
      using namespace spanparsing;
  
      auto split = Split(sp, '/');
      std::string str(split[0].begin(), split[0].end());
      if (str.size() == 0) {
          error = "No key provided";
          return nullptr;
      }
      if (split.size() == 1) {
          if (IsHex(str)) {
              std::vector<unsigned char> data = ParseHex(str);
              CPubKey pubkey(data);
              if (pubkey.IsFullyValid()) {
                  if (permit_uncompressed || pubkey.IsCompressed()) {
                      return MakeUnique<ConstPubkeyProvider>(key_exp_index, pubkey);
                  } else {
                      error = "Uncompressed keys are not allowed";
                      return nullptr;
                  }
              }
              error = strprintf("Pubkey '%s' is invalid", str);
              return nullptr;
          }
          CKey key = DecodeSecret(str);
          if (key.IsValid()) {
              if (permit_uncompressed || key.IsCompressed()) {
                  CPubKey pubkey = key.GetPubKey();
                  out.keys.emplace(pubkey.GetID(), key);
                  return MakeUnique<ConstPubkeyProvider>(key_exp_index, pubkey);
              } else {
                  error = "Uncompressed keys are not allowed";
                  return nullptr;
              }
          }
      }
      CExtKey extkey = DecodeExtKey(str);
      CExtPubKey extpubkey = DecodeExtPubKey(str);
      if (!extkey.key.IsValid() && !extpubkey.pubkey.IsValid()) {
          error = strprintf("key '%s' is not valid", str);
          return nullptr;
      }
      KeyPath path;
      DeriveType type = DeriveType::NO;
      if (split.back() == MakeSpan("*").first(1)) {
          split.pop_back();
          type = DeriveType::UNHARDENED;
      } else if (split.back() == MakeSpan("*'").first(2) || split.back() == MakeSpan("*h").first(2)) {
          split.pop_back();
          type = DeriveType::HARDENED;
      }
      if (!ParseKeyPath(split, path, error)) return nullptr;
      if (extkey.key.IsValid()) {
          extpubkey = extkey.Neuter();
          out.keys.emplace(extpubkey.pubkey.GetID(), extkey.key);
      }
      return MakeUnique<BIP32PubkeyProvider>(key_exp_index, extpubkey, std::move(path), type);
  }
  
  /** Parse a public key including origin information (if enabled). */
  std::unique_ptr<PubkeyProvider> ParsePubkey(uint32_t key_exp_index, const Span<const char>& sp, bool permit_uncompressed, FlatSigningProvider& out, std::string& error)
  {
      using namespace spanparsing;
  
      auto origin_split = Split(sp, ']');
      if (origin_split.size() > 2) {
          error = "Multiple ']' characters found for a single pubkey";
          return nullptr;
      }
      if (origin_split.size() == 1) return ParsePubkeyInner(key_exp_index, origin_split[0], permit_uncompressed, out, error);
      if (origin_split[0].size() < 1 || origin_split[0][0] != '[') {
          error = strprintf("Key origin start '[ character expected but not found, got '%c' instead", origin_split[0][0]);
          return nullptr;
      }
      auto slash_split = Split(origin_split[0].subspan(1), '/');
      if (slash_split[0].size() != 8) {
          error = strprintf("Fingerprint is not 4 bytes (%u characters instead of 8 characters)", slash_split[0].size());
          return nullptr;
      }
      std::string fpr_hex = std::string(slash_split[0].begin(), slash_split[0].end());
      if (!IsHex(fpr_hex)) {
          error = strprintf("Fingerprint '%s' is not hex", fpr_hex);
          return nullptr;
      }
      auto fpr_bytes = ParseHex(fpr_hex);
      KeyOriginInfo info;
      static_assert(sizeof(info.fingerprint) == 4, "Fingerprint must be 4 bytes");
      assert(fpr_bytes.size() == 4);
      std::copy(fpr_bytes.begin(), fpr_bytes.end(), info.fingerprint);
      if (!ParseKeyPath(slash_split, info.path, error)) return nullptr;
      auto provider = ParsePubkeyInner(key_exp_index, origin_split[1], permit_uncompressed, out, error);
      if (!provider) return nullptr;
      return MakeUnique<OriginPubkeyProvider>(key_exp_index, std::move(info), std::move(provider));
  }
  
  /** Parse a script in a particular context. */
  std::unique_ptr<DescriptorImpl> ParseScript(uint32_t key_exp_index, Span<const char>& sp, ParseScriptContext ctx, FlatSigningProvider& out, std::string& error)
  {
      using namespace spanparsing;
  
      auto expr = Expr(sp);
      bool sorted_multi = false;
      if (Func("pk", expr)) {
          auto pubkey = ParsePubkey(key_exp_index, expr, ctx != ParseScriptContext::P2WSH, out, error);
          if (!pubkey) return nullptr;
          return MakeUnique<PKDescriptor>(std::move(pubkey));
      }
      if (Func("pkh", expr)) {
          auto pubkey = ParsePubkey(key_exp_index, expr, ctx != ParseScriptContext::P2WSH, out, error);
          if (!pubkey) return nullptr;
          return MakeUnique<PKHDescriptor>(std::move(pubkey));
      }
      if (ctx == ParseScriptContext::TOP && Func("combo", expr)) {
          auto pubkey = ParsePubkey(key_exp_index, expr, true, out, error);
          if (!pubkey) return nullptr;
          return MakeUnique<ComboDescriptor>(std::move(pubkey));
      } else if (ctx != ParseScriptContext::TOP && Func("combo", expr)) {
          error = "Cannot have combo in non-top level";
          return nullptr;
      }
      if ((sorted_multi = Func("sortedmulti", expr)) || Func("multi", expr)) {
          auto threshold = Expr(expr);
          uint32_t thres;
          std::vector<std::unique_ptr<PubkeyProvider>> providers;
          if (!ParseUInt32(std::string(threshold.begin(), threshold.end()), &thres)) {
              error = strprintf("Multi threshold '%s' is not valid", std::string(threshold.begin(), threshold.end()));
              return nullptr;
          }
          size_t script_size = 0;
          while (expr.size()) {
              if (!Const(",", expr)) {
                  error = strprintf("Multi: expected ',', got '%c'", expr[0]);
                  return nullptr;
              }
              auto arg = Expr(expr);
              auto pk = ParsePubkey(key_exp_index, arg, ctx != ParseScriptContext::P2WSH, out, error);
              if (!pk) return nullptr;
              script_size += pk->GetSize() + 1;
              providers.emplace_back(std::move(pk));
              key_exp_index++;
          }
          if (providers.size() < 1 || providers.size() > 16) {
              error = strprintf("Cannot have %u keys in multisig; must have between 1 and 16 keys, inclusive", providers.size());
              return nullptr;
          } else if (thres < 1) {
              error = strprintf("Multisig threshold cannot be %d, must be at least 1", thres);
              return nullptr;
          } else if (thres > providers.size()) {
              error = strprintf("Multisig threshold cannot be larger than the number of keys; threshold is %d but only %u keys specified", thres, providers.size());
              return nullptr;
          }
          if (ctx == ParseScriptContext::TOP) {
              if (providers.size() > 3) {
                  error = strprintf("Cannot have %u pubkeys in bare multisig; only at most 3 pubkeys", providers.size());
                  return nullptr;
              }
          }
          if (ctx == ParseScriptContext::P2SH) {
              if (script_size + 3 > MAX_SCRIPT_ELEMENT_SIZE) {
                  error = strprintf("P2SH script is too large, %d bytes is larger than %d bytes", script_size + 3, MAX_SCRIPT_ELEMENT_SIZE);
                  return nullptr;
              }
          }
          return MakeUnique<MultisigDescriptor>(thres, std::move(providers), sorted_multi);
      }
      if (ctx != ParseScriptContext::P2WSH && Func("wpkh", expr)) {
          auto pubkey = ParsePubkey(key_exp_index, expr, false, out, error);
          if (!pubkey) return nullptr;
          return MakeUnique<WPKHDescriptor>(std::move(pubkey));
      } else if (ctx == ParseScriptContext::P2WSH && Func("wpkh", expr)) {
          error = "Cannot have wpkh within wsh";
          return nullptr;
      }
      if (ctx == ParseScriptContext::TOP && Func("sh", expr)) {
          auto desc = ParseScript(key_exp_index, expr, ParseScriptContext::P2SH, out, error);
          if (!desc || expr.size()) return nullptr;
          return MakeUnique<SHDescriptor>(std::move(desc));
      } else if (ctx != ParseScriptContext::TOP && Func("sh", expr)) {
          error = "Cannot have sh in non-top level";
          return nullptr;
      }
      if (ctx != ParseScriptContext::P2WSH && Func("wsh", expr)) {
          auto desc = ParseScript(key_exp_index, expr, ParseScriptContext::P2WSH, out, error);
          if (!desc || expr.size()) return nullptr;
          return MakeUnique<WSHDescriptor>(std::move(desc));
      } else if (ctx == ParseScriptContext::P2WSH && Func("wsh", expr)) {
          error = "Cannot have wsh within wsh";
          return nullptr;
      }
      if (ctx == ParseScriptContext::TOP && Func("addr", expr)) {
          CTxDestination dest = DecodeDestination(std::string(expr.begin(), expr.end()));
          if (!IsValidDestination(dest)) {
              error = "Address is not valid";
              return nullptr;
          }
          return MakeUnique<AddressDescriptor>(std::move(dest));
      }
      if (ctx == ParseScriptContext::TOP && Func("raw", expr)) {
          std::string str(expr.begin(), expr.end());
          if (!IsHex(str)) {
              error = "Raw script is not hex";
              return nullptr;
          }
          auto bytes = ParseHex(str);
          return MakeUnique<RawDescriptor>(CScript(bytes.begin(), bytes.end()));
      }
      if (ctx == ParseScriptContext::P2SH) {
          error = "A function is needed within P2SH";
          return nullptr;
      } else if (ctx == ParseScriptContext::P2WSH) {
          error = "A function is needed within P2WSH";
          return nullptr;
      }
      error = strprintf("%s is not a valid descriptor function", std::string(expr.begin(), expr.end()));
      return nullptr;
  }
  
  std::unique_ptr<PubkeyProvider> InferPubkey(const CPubKey& pubkey, ParseScriptContext, const SigningProvider& provider)
  {
      std::unique_ptr<PubkeyProvider> key_provider = MakeUnique<ConstPubkeyProvider>(0, pubkey);
      KeyOriginInfo info;
      if (provider.GetKeyOrigin(pubkey.GetID(), info)) {
          return MakeUnique<OriginPubkeyProvider>(0, std::move(info), std::move(key_provider));
      }
      return key_provider;
  }
  
  std::unique_ptr<DescriptorImpl> InferScript(const CScript& script, ParseScriptContext ctx, const SigningProvider& provider)
  {
      std::vector<std::vector<unsigned char>> data;
      txnouttype txntype = Solver(script, data);
  
      if (txntype == TX_PUBKEY) {
          CPubKey pubkey(data[0].begin(), data[0].end());
          if (pubkey.IsValid()) {
              return MakeUnique<PKDescriptor>(InferPubkey(pubkey, ctx, provider));
          }
      }
      if (txntype == TX_PUBKEYHASH) {
          uint160 hash(data[0]);
          CKeyID keyid(hash);
          CPubKey pubkey;
          if (provider.GetPubKey(keyid, pubkey)) {
              return MakeUnique<PKHDescriptor>(InferPubkey(pubkey, ctx, provider));
          }
      }
      if (txntype == TX_WITNESS_V0_KEYHASH && ctx != ParseScriptContext::P2WSH) {
          uint160 hash(data[0]);
          CKeyID keyid(hash);
          CPubKey pubkey;
          if (provider.GetPubKey(keyid, pubkey)) {
              return MakeUnique<WPKHDescriptor>(InferPubkey(pubkey, ctx, provider));
          }
      }
      if (txntype == TX_MULTISIG) {
          std::vector<std::unique_ptr<PubkeyProvider>> providers;
          for (size_t i = 1; i + 1 < data.size(); ++i) {
              CPubKey pubkey(data[i].begin(), data[i].end());
              providers.push_back(InferPubkey(pubkey, ctx, provider));
          }
          return MakeUnique<MultisigDescriptor>((int)data[0][0], std::move(providers));
      }
      if (txntype == TX_SCRIPTHASH && ctx == ParseScriptContext::TOP) {
          uint160 hash(data[0]);
          CScriptID scriptid(hash);
          CScript subscript;
          if (provider.GetCScript(scriptid, subscript)) {
              auto sub = InferScript(subscript, ParseScriptContext::P2SH, provider);
              if (sub) return MakeUnique<SHDescriptor>(std::move(sub));
          }
      }
      if (txntype == TX_WITNESS_V0_SCRIPTHASH && ctx != ParseScriptContext::P2WSH) {
          CScriptID scriptid;
          CRIPEMD160().Write(data[0].data(), data[0].size()).Finalize(scriptid.begin());
          CScript subscript;
          if (provider.GetCScript(scriptid, subscript)) {
              auto sub = InferScript(subscript, ParseScriptContext::P2WSH, provider);
              if (sub) return MakeUnique<WSHDescriptor>(std::move(sub));
          }
      }
  
      CTxDestination dest;
      if (ExtractDestination(script, dest)) {
          if (GetScriptForDestination(dest) == script) {
              return MakeUnique<AddressDescriptor>(std::move(dest));
          }
      }
  
      return MakeUnique<RawDescriptor>(script);
  }
  
  
  } // namespace
  
  /** Check a descriptor checksum, and update desc to be the checksum-less part. */
  bool CheckChecksum(Span<const char>& sp, bool require_checksum, std::string& error, std::string* out_checksum = nullptr)
  {
      using namespace spanparsing;
  
      auto check_split = Split(sp, '#');
      if (check_split.size() > 2) {
          error = "Multiple '#' symbols";
          return false;
      }
      if (check_split.size() == 1 && require_checksum){
          error = "Missing checksum";
          return false;
      }
      if (check_split.size() == 2) {
          if (check_split[1].size() != 8) {
              error = strprintf("Expected 8 character checksum, not %u characters", check_split[1].size());
              return false;
          }
      }
      auto checksum = DescriptorChecksum(check_split[0]);
      if (checksum.empty()) {
          error = "Invalid characters in payload";
          return false;
      }
      if (check_split.size() == 2) {
          if (!std::equal(checksum.begin(), checksum.end(), check_split[1].begin())) {
              error = strprintf("Provided checksum '%s' does not match computed checksum '%s'", std::string(check_split[1].begin(), check_split[1].end()), checksum);
              return false;
          }
      }
      if (out_checksum) *out_checksum = std::move(checksum);
      sp = check_split[0];
      return true;
  }
  
  std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out, std::string& error, bool require_checksum)
  {
      Span<const char> sp(descriptor.data(), descriptor.size());
      if (!CheckChecksum(sp, require_checksum, error)) return nullptr;
      auto ret = ParseScript(0, sp, ParseScriptContext::TOP, out, error);
      if (sp.size() == 0 && ret) return std::unique_ptr<Descriptor>(std::move(ret));
      return nullptr;
  }
  
  std::string GetDescriptorChecksum(const std::string& descriptor)
  {
      std::string ret;
      std::string error;
      Span<const char> sp(descriptor.data(), descriptor.size());
      if (!CheckChecksum(sp, false, error, &ret)) return "";
      return ret;
  }
  
  std::unique_ptr<Descriptor> InferDescriptor(const CScript& script, const SigningProvider& provider)
  {
      return InferScript(script, ParseScriptContext::TOP, provider);
  }
  
  void DescriptorCache::CacheParentExtPubKey(uint32_t key_exp_pos, const CExtPubKey& xpub)
  {
      m_parent_xpubs[key_exp_pos] = xpub;
  }
  
  void DescriptorCache::CacheDerivedExtPubKey(uint32_t key_exp_pos, uint32_t der_index, const CExtPubKey& xpub)
  {
      auto& xpubs = m_derived_xpubs[key_exp_pos];
      xpubs[der_index] = xpub;
  }
  
  bool DescriptorCache::GetCachedParentExtPubKey(uint32_t key_exp_pos, CExtPubKey& xpub) const
  {
      const auto& it = m_parent_xpubs.find(key_exp_pos);
      if (it == m_parent_xpubs.end()) return false;
      xpub = it->second;
      return true;
  }
  
  bool DescriptorCache::GetCachedDerivedExtPubKey(uint32_t key_exp_pos, uint32_t der_index, CExtPubKey& xpub) const
  {
      const auto& key_exp_it = m_derived_xpubs.find(key_exp_pos);
      if (key_exp_it == m_derived_xpubs.end()) return false;
      const auto& der_it = key_exp_it->second.find(der_index);
      if (der_it == key_exp_it->second.end()) return false;
      xpub = der_it->second;
      return true;
  }
  
  const ExtPubKeyMap DescriptorCache::GetCachedParentExtPubKeys() const
  {
      return m_parent_xpubs;
  }
  
  const std::unordered_map<uint32_t, ExtPubKeyMap> DescriptorCache::GetCachedDerivedExtPubKeys() const
  {
      return m_derived_xpubs;
  }
  