text: // Copyright (c) 2018 The Bitcoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #ifndef BITCOIN_SCRIPT_DESCRIPTOR_H
  #define BITCOIN_SCRIPT_DESCRIPTOR_H
  
  #include <script/script.h>
  #include <script/sign.h>
  
  #include <vector>
  
  // Descriptors are strings that describe a set of scriptPubKeys, together with
  // all information necessary to solve them. By combining all information into
  // one, they avoid the need to separately import keys and scripts.
  //
  // Descriptors may be ranged, which occurs when the public keys inside are
  // specified in the form of HD chains (xpubs).
  //
  // Descriptors always represent public information - public keys and scripts -
  // but in cases where private keys need to be conveyed along with a descriptor,
  // they can be included inside by changing public keys to private keys (WIF
  // format), and changing xpubs by xprvs.
  //
  // Reference documentation about the descriptor language can be found in
  // doc/descriptors.md.
  
  /** Interface for parsed descriptor objects. */
  struct Descriptor {
      virtual ~Descriptor() = default;
  
      /** Whether the expansion of this descriptor depends on the position. */
      virtual bool IsRange() const = 0;
  
      /** Whether this descriptor has all information about signing ignoring lack of private keys.
       *  This is true for all descriptors except ones that use `raw` or `addr` constructions. */
      virtual bool IsSolvable() const = 0;
  
      /** Convert the descriptor back to a string, undoing parsing. */
      virtual std::string ToString() const = 0;
  
      /** Convert the descriptor to a private string. This fails if the provided provider does not have the relevant private keys. */
      virtual bool ToPrivateString(const SigningProvider& provider, std::string& out) const = 0;
  
      /** Expand a descriptor at a specified position.
       *
       * pos: the position at which to expand the descriptor. If IsRange() is false, this is ignored.
       * provider: the provider to query for private keys in case of hardened derivation.
       * output_script: the expanded scriptPubKeys will be put here.
       * out: scripts and public keys necessary for solving the expanded scriptPubKeys will be put here (may be equal to provider).
       * cache: vector which will be overwritten with cache data necessary to-evaluate the descriptor at this point without access to private keys.
       */
      virtual bool Expand(int pos, const SigningProvider& provider, std::vector<CScript>& output_scripts, FlatSigningProvider& out, std::vector<unsigned char>* cache = nullptr) const = 0;
  
      /** Expand a descriptor at a specified position using cached expansion data.
       *
       * pos: the position at which to expand the descriptor. If IsRange() is false, this is ignored.
       * cache: vector from which cached expansion data will be read.
       * output_script: the expanded scriptPubKeys will be put here.
       * out: scripts and public keys necessary for solving the expanded scriptPubKeys will be put here (may be equal to provider).
       */
      virtual bool ExpandFromCache(int pos, const std::vector<unsigned char>& cache, std::vector<CScript>& output_scripts, FlatSigningProvider& out) const = 0;
  };
  
  /** Parse a descriptor string. Included private keys are put in out. Returns nullptr if parsing fails. */
  std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out);
  
  /** Find a descriptor for the specified script, using information from provider where possible.
   *
   * A non-ranged descriptor which only generates the specified script will be returned in all
   * circumstances.
   *
   * For public keys with key origin information, this information will be preserved in the returned
   * descriptor.
   *
   * - If all information for solving `script` is present in `provider`, a descriptor will be returned
   *   which is `IsSolvable()` and encapsulates said information.
   * - Failing that, if `script` corresponds to a known address type, an "addr()" descriptor will be
   *   returned (which is not `IsSolvable()`).
   * - Failing that, a "raw()" descriptor is returned.
   */
  std::unique_ptr<Descriptor> InferDescriptor(const CScript& script, const SigningProvider& provider);
  
  #endif // BITCOIN_SCRIPT_DESCRIPTOR_H
  