#pragma once

/* A header-only implementation of the .ply file format.
 * https://github.com/nmwsharp/happly
 * By Nicholas Sharp - nsharp@cs.cmu.edu
 */

/*
MIT License

Copyright (c) 2018 Nick Sharp

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

#include <array>
#include <cctype>
#include <fstream>
#include <iostream>
#include <limits>
#include <memory>
#include <sstream>
#include <string>
#include <type_traits>
#include <vector>

// General namespace wrapping all Happly things.
namespace happly {

// Enum specifying binary or ASCII filetypes. Binary is always little-endian.
enum class DataFormat { ASCII, Binary };

// Type name strings
// clang-format off
template <typename T> std::string typeName()                { return "unknown"; }
template<> inline std::string typeName<int8_t>()            { return "char";    }
template<> inline std::string typeName<uint8_t>()           { return "uchar";   }
template<> inline std::string typeName<int16_t>()           { return "short";   }
template<> inline std::string typeName<uint16_t>()          { return "ushort";  }
template<> inline std::string typeName<int32_t>()           { return "int";     }
template<> inline std::string typeName<uint32_t>()          { return "uint";    }
template<> inline std::string typeName<float>()             { return "float";   }
template<> inline std::string typeName<double>()            { return "double";  }
// clang-format on

// Template hackery that makes getProperty<T>() and friends pretty while automatically picking up smaller types
namespace {

// A pointer for the equivalent/smaller equivalent of a type (eg. when a double is requested a float works too, etc)
// long int is intentionally absent to avoid platform confusion
// clang-format off
template <class T> struct TypeChain                 { bool hasChildType = false;   typedef T            type; };
template <> struct TypeChain<int64_t>               { bool hasChildType = true;    typedef int32_t      type; };
template <> struct TypeChain<int32_t>               { bool hasChildType = true;    typedef int16_t      type; };
template <> struct TypeChain<int16_t>               { bool hasChildType = true;    typedef int8_t       type; };
template <> struct TypeChain<uint64_t>              { bool hasChildType = true;    typedef uint32_t     type; };
template <> struct TypeChain<uint32_t>              { bool hasChildType = true;    typedef uint16_t     type; };
template <> struct TypeChain<uint16_t>              { bool hasChildType = true;    typedef uint8_t      type; };
template <> struct TypeChain<double>                { bool hasChildType = true;    typedef float        type; };
// clang-format on

// clang-format off
template <class T> struct CanonicalName                     { typedef T         type; };
template <> struct CanonicalName<char>                      { typedef int8_t    type; };
template <> struct CanonicalName<unsigned char>             { typedef uint8_t   type; };
template <> struct CanonicalName<size_t>                    { typedef std::conditional<std::is_same<std::make_signed<size_t>::type, int>::value, uint32_t, uint64_t>::type type; };
// clang-format on
} // namespace

/**
 * @brief A generic property, which is associated with some element. Can be plain Property or a ListProperty, of some
 * type.  Generally, the user should not need to interact with these directly, but they are exposed in case someone
 * wants to get clever.
 */
class Property {

public:
  /**
   * @brief Create a new Property with the given name.
   *
   * @param name_
   */
  Property(const std::string& name_) : name(name_){};
  virtual ~Property(){};

  std::string name;

  /**
   * @brief Reserve memory.
   * 
   * @param capacity Expected number of elements.
   */
  virtual void reserve(size_t capacity) = 0;

  /**
   * @brief (ASCII reading) Parse out the next value of this property from a list of tokens.
   *
   * @param tokens The list of property tokens for the element.
   * @param currEntry Index in to tokens, updated after this property is read.
   */
  virtual void parseNext(const std::vector<std::string>& tokens, size_t& currEntry) = 0;

  /**
   * @brief (binary reading) Copy the next value of this property from a stream of bits.
   *
   * @param stream Stream to read from.
   */
  virtual void readNext(std::ifstream& stream) = 0;

  /**
   * @brief (reading) Write a header entry for this property.
   *
   * @param outStream Stream to write to.
   */
  virtual void writeHeader(std::ofstream& outStream) = 0;

  /**
   * @brief (ASCII writing) write this property for some element to a stream in plaintext
   *
   * @param outStream Stream to write to.
   * @param iElement index of the element to write.
   */
  virtual void writeDataASCII(std::ofstream& outStream, size_t iElement) = 0;

  /**
   * @brief (binary writing) copy the bits of this property for some element to a stream
   *
   * @param outStream Stream to write to.
   * @param iElement index of the element to write.
   */
  virtual void writeDataBinary(std::ofstream& outStream, size_t iElement) = 0;

  /**
   * @brief Number of element entries for this property
   *
   * @return
   */
  virtual size_t size() = 0;

  /**
   * @brief A string naming the type of the property
   *
   * @return
   */
  virtual std::string propertyTypeName() = 0;
};

/**
 * @brief A property which takes a single value (not a list).
 */
template <class T>
class TypedProperty : public Property {

public:
  /**
   * @brief Create a new Property with the given name.
   *
   * @param name_
   */
  TypedProperty(const std::string& name_) : Property(name_) {
    if (typeName<T>() == "unknown") {
      // TODO should really be a compile-time error
      throw std::runtime_error("Attempted property type does not match any type defined by the .ply format.");
    }
  };

  /**
   * @brief Create a new property and initialize with data.
   *
   * @param name_
   * @param data_
   */
  TypedProperty(const std::string& name_, const std::vector<T>& data_) : Property(name_), data(data_) {
    if (typeName<T>() == "unknown") {
      throw std::runtime_error("Attempted property type does not match any type defined by the .ply format.");
    }
  };

  virtual ~TypedProperty() override{};

  /**
   * @brief Reserve memory.
   * 
   * @param capacity Expected number of elements.
   */
  virtual void reserve(size_t capacity) override {
    data.reserve(capacity);
  }

  /**
   * @brief (ASCII reading) Parse out the next value of this property from a list of tokens.
   *
   * @param tokens The list of property tokens for the element.
   * @param currEntry Index in to tokens, updated after this property is read.
   */
  virtual void parseNext(const std::vector<std::string>& tokens, size_t& currEntry) override {
    data.emplace_back();
    std::istringstream iss(tokens[currEntry]);
    iss >> data.back();
    currEntry++;
  };

  /**
   * @brief (binary reading) Copy the next value of this property from a stream of bits.
   *
   * @param stream Stream to read from.
   */
  virtual void readNext(std::ifstream& stream) override {
    data.emplace_back();
    stream.read((char*)&data.back(), sizeof(T));
  }

  /**
   * @brief (reading) Write a header entry for this property.
   *
   * @param outStream Stream to write to.
   */
  virtual void writeHeader(std::ofstream& outStream) override {
    outStream << "property " << typeName<T>() << " " << name << "\n";
  }

  /**
   * @brief (ASCII writing) write this property for some element to a stream in plaintext
   *
   * @param outStream Stream to write to.
   * @param iElement index of the element to write.
   */
  virtual void writeDataASCII(std::ofstream& outStream, size_t iElement) override {
    outStream.precision(std::numeric_limits<T>::max_digits10);
    outStream << data[iElement];
  }

  /**
   * @brief (binary writing) copy the bits of this property for some element to a stream
   *
   * @param outStream Stream to write to.
   * @param iElement index of the element to write.
   */
  virtual void writeDataBinary(std::ofstream& outStream, size_t iElement) override {
    outStream.write((char*)&data[iElement], sizeof(T));
  }

  /**
   * @brief Number of element entries for this property
   *
   * @return
   */
  virtual size_t size() override { return data.size(); }


  /**
   * @brief A string naming the type of the property
   *
   * @return
   */
  virtual std::string propertyTypeName() override { return typeName<T>(); }

  /**
   * @brief The actual data contained in the property
   */
  std::vector<T> data;
};

// outstream doesn't do what we want with chars, these specializations supersede the general behavior to ensure chars
// get written correctly.
template <>
inline void TypedProperty<uint8_t>::writeDataASCII(std::ofstream& outStream, size_t iElement) {
  outStream << (int)data[iElement];
}
template <>
inline void TypedProperty<int8_t>::writeDataASCII(std::ofstream& outStream, size_t iElement) {
  outStream << (int)data[iElement];
}
template <>
inline void TypedProperty<uint8_t>::parseNext(const std::vector<std::string>& tokens, size_t& currEntry) {
  std::istringstream iss(tokens[currEntry]);
  int intVal;
  iss >> intVal;
  data.push_back((uint8_t)intVal);
  currEntry++;
}
template <>
inline void TypedProperty<int8_t>::parseNext(const std::vector<std::string>& tokens, size_t& currEntry) {
  std::istringstream iss(tokens[currEntry]);
  int intVal;
  iss >> intVal;
  data.push_back((int8_t)intVal);
  currEntry++;
}


/**
 * @brief A property which is a list of value (eg, 3 doubles). Note that lists are always variable length per-element.
 */
template <class T>
class TypedListProperty : public Property {

public:
  /**
   * @brief Create a new Property with the given name.
   *
   * @param name_
   */
  TypedListProperty(const std::string& name_, int listCountBytes_) : Property(name_), listCountBytes(listCountBytes_) {
    if (typeName<T>() == "unknown") {
      throw std::runtime_error("Attempted property type does not match any type defined by the .ply format.");
    }
  };

  /**
   * @brief Create a new property and initialize with data
   *
   * @param name_
   * @param data_
   */
  TypedListProperty(const std::string& name_, const std::vector<std::vector<T>>& data_) : Property(name_), data(data_) {
    if (typeName<T>() == "unknown") {
      throw std::runtime_error("Attempted property type does not match any type defined by the .ply format.");
    }
  };

  virtual ~TypedListProperty() override{};

  /**
   * @brief Reserve memory.
   * 
   * @param capacity Expected number of elements.
   */
  virtual void reserve(size_t capacity) override {
    data.reserve(capacity);
    for (size_t i = 0; i < data.size(); i++) {
      data[i].reserve(3); // optimize for triangle meshes
    }
  }

  /**
   * @brief (ASCII reading) Parse out the next value of this property from a list of tokens.
   *
   * @param tokens The list of property tokens for the element.
   * @param currEntry Index in to tokens, updated after this property is read.
   */
  virtual void parseNext(const std::vector<std::string>& tokens, size_t& currEntry) override {

    std::istringstream iss(tokens[currEntry]);
    size_t count;
    iss >> count;
    currEntry++;

    data.emplace_back();
    data.back().resize(count);
    for (size_t iCount = 0; iCount < count; iCount++) {
      std::istringstream iss(tokens[currEntry]);
      iss >> data.back()[iCount];
      currEntry++;
    }
  }

  /**
   * @brief (binary reading) Copy the next value of this property from a stream of bits.
   *
   * @param stream Stream to read from.
   */
  virtual void readNext(std::ifstream& stream) override {

    // Read the size of the list
    size_t count = 0;
    stream.read(((char*)&count), listCountBytes);

    // Read list elements
    data.emplace_back();
    data.back().resize(count);
    stream.read((char*)&data.back().front(), count*sizeof(T));
  }

  /**
   * @brief (reading) Write a header entry for this property. Note that we already use "uchar" for the list count type.
   *
   * @param outStream Stream to write to.
   */
  virtual void writeHeader(std::ofstream& outStream) override {
    // NOTE: We ALWAYS use uchar as the list count output type
    outStream << "property list uchar " << typeName<T>() << " " << name << "\n";
  }

  /**
   * @brief (ASCII writing) write this property for some element to a stream in plaintext
   *
   * @param outStream Stream to write to.
   * @param iElement index of the element to write.
   */
  virtual void writeDataASCII(std::ofstream& outStream, size_t iElement) override {
    std::vector<T>& elemList = data[iElement];
  
    // Get the number of list elements as a uchar, and ensure the value fits
    uint8_t count = elemList.size();
    if(count != elemList.size()) {
      throw std::runtime_error("List property has an element with more entries than fit in a uchar. See note in README.");
    }

    outStream << elemList.size();
    outStream.precision(std::numeric_limits<T>::max_digits10);
    for (size_t iEntry = 0; iEntry < elemList.size(); iEntry++) {
      outStream << " " << elemList[iEntry];
    }
  }

  /**
   * @brief (binary writing) copy the bits of this property for some element to a stream
   *
   * @param outStream Stream to write to.
   * @param iElement index of the element to write.
   */
  virtual void writeDataBinary(std::ofstream& outStream, size_t iElement) override {
    std::vector<T>& elemList = data[iElement];

    // Get the number of list elements as a uchar, and ensure the value fits
    uint8_t count = elemList.size();
    if(count != elemList.size()) {
      throw std::runtime_error("List property has an element with more entries than fit in a uchar. See note in README.");
    }

    outStream.write((char*)&count, sizeof(uint8_t));
    for (size_t iEntry = 0; iEntry < elemList.size(); iEntry++) {
      outStream.write((char*)&elemList[iEntry], sizeof(T));
    }
  }

  /**
   * @brief Number of element entries for this property
   *
   * @return
   */
  virtual size_t size() override { return data.size(); }


  /**
   * @brief A string naming the type of the property
   *
   * @return
   */
  virtual std::string propertyTypeName() override { return typeName<T>(); }

  /**
   * @brief The actualy data lists for the property
   */
  std::vector<std::vector<T>> data;

  /**
   * @brief The number of bytes used to store the count for lists of data.
   */
  int listCountBytes = -1;
};

// outstream doesn't do what we want with int8_ts, these specializations supersede the general behavior to ensure
// int8_ts get written correctly.
template <>
inline void TypedListProperty<uint8_t>::writeDataASCII(std::ofstream& outStream, size_t iElement) {
  std::vector<uint8_t>& elemList = data[iElement];
  outStream << elemList.size();
  outStream.precision(std::numeric_limits<uint8_t>::max_digits10);
  for (size_t iEntry = 0; iEntry < elemList.size(); iEntry++) {
    outStream << " " << (int)elemList[iEntry];
  }
}
template <>
inline void TypedListProperty<int8_t>::writeDataASCII(std::ofstream& outStream, size_t iElement) {
  std::vector<int8_t>& elemList = data[iElement];
  outStream << elemList.size();
  outStream.precision(std::numeric_limits<int8_t>::max_digits10);
  for (size_t iEntry = 0; iEntry < elemList.size(); iEntry++) {
    outStream << " " << (int)elemList[iEntry];
  }
}
template <>
inline void TypedListProperty<uint8_t>::parseNext(const std::vector<std::string>& tokens, size_t& currEntry) {

  std::istringstream iss(tokens[currEntry]);
  size_t count;
  iss >> count;
  currEntry++;

  std::vector<uint8_t> thisVec;
  for (size_t iCount = 0; iCount < count; iCount++) {
    std::istringstream iss(tokens[currEntry]);
    int intVal;
    iss >> intVal;
    thisVec.push_back((uint8_t)intVal);
    currEntry++;
  }
  data.push_back(thisVec);
}
template <>
inline void TypedListProperty<int8_t>::parseNext(const std::vector<std::string>& tokens, size_t& currEntry) {

  std::istringstream iss(tokens[currEntry]);
  size_t count;
  iss >> count;
  currEntry++;

  std::vector<int8_t> thisVec;
  for (size_t iCount = 0; iCount < count; iCount++) {
    std::istringstream iss(tokens[currEntry]);
    int intVal;
    iss >> intVal;
    thisVec.push_back((int8_t)intVal);
    currEntry++;
  }
  data.push_back(thisVec);
}

/**
 * @brief Helper function to construct a new property of the appropriate type.
 *
 * @param name The name of the property to construct.
 * @param typeStr A string naming the type according to the format.
 * @param isList Is this a plain property, or a list property?
 * @param listCountTypeStr If a list property, the type of the count varible.
 *
 * @return A new Property with the proper type.
 */
inline std::unique_ptr<Property> createPropertyWithType(const std::string& name, const std::string& typeStr, bool isList,
                                                        const std::string& listCountTypeStr) {

  // == Figure out how many bytes the list count field has, if this is a list type
  // Note: some files seem to use signed types here, we read the width but always parse as if unsigned
  int listCountBytes = -1;
  if (isList) {
    if (listCountTypeStr == "uchar" || listCountTypeStr == "uint8" || listCountTypeStr == "char" ||
        listCountTypeStr == "int8") {
      listCountBytes = 1;
    } else if (listCountTypeStr == "ushort" || listCountTypeStr == "uint16" || listCountTypeStr == "short" ||
               listCountTypeStr == "int16") {
      listCountBytes = 2;
    } else if (listCountTypeStr == "uint" || listCountTypeStr == "uint32" || listCountTypeStr == "int" ||
               listCountTypeStr == "int32") {
      listCountBytes = 4;
    } else {
      throw std::runtime_error("Unrecognized list count type: " + listCountTypeStr);
    }
  }

  // = Unsigned int

  // 8 bit unsigned
  if (typeStr == "uchar" || typeStr == "uint8") {
    if (isList) {
      return std::unique_ptr<Property>(new TypedListProperty<uint8_t>(name, listCountBytes));
    } else {
      return std::unique_ptr<Property>(new TypedProperty<uint8_t>(name));
    }
  }

  // 16 bit unsigned
  else if (typeStr == "ushort" || typeStr == "uint16") {
    if (isList) {
      return std::unique_ptr<Property>(new TypedListProperty<uint16_t>(name, listCountBytes));
    } else {
      return std::unique_ptr<Property>(new TypedProperty<uint16_t>(name));
    }
  }

  // 32 bit unsigned
  else if (typeStr == "uint" || typeStr == "uint32") {
    if (isList) {
      return std::unique_ptr<Property>(new TypedListProperty<uint32_t>(name, listCountBytes));
    } else {
      return std::unique_ptr<Property>(new TypedProperty<uint32_t>(name));
    }
  }

  // = Signed int

  // 8 bit signed
  if (typeStr == "char" || typeStr == "int8") {
    if (isList) {
      return std::unique_ptr<Property>(new TypedListProperty<int8_t>(name, listCountBytes));
    } else {
      return std::unique_ptr<Property>(new TypedProperty<int8_t>(name));
    }
  }

  // 16 bit signed
  else if (typeStr == "short" || typeStr == "int16") {
    if (isList) {
      return std::unique_ptr<Property>(new TypedListProperty<int16_t>(name, listCountBytes));
    } else {
      return std::unique_ptr<Property>(new TypedProperty<int16_t>(name));
    }
  }

  // 32 bit signed
  else if (typeStr == "int" || typeStr == "int32") {
    if (isList) {
      return std::unique_ptr<Property>(new TypedListProperty<int32_t>(name, listCountBytes));
    } else {
      return std::unique_ptr<Property>(new TypedProperty<int32_t>(name));
    }
  }

  // = Float

  // 32 bit float
  else if (typeStr == "float" || typeStr == "float32") {
    if (isList) {
      return std::unique_ptr<Property>(new TypedListProperty<float>(name, listCountBytes));
    } else {
      return std::unique_ptr<Property>(new TypedProperty<float>(name));
    }
  }

  // 64 bit float
  else if (typeStr == "double" || typeStr == "float64") {
    if (isList) {
      return std::unique_ptr<Property>(new TypedListProperty<double>(name, listCountBytes));
    } else {
      return std::unique_ptr<Property>(new TypedProperty<double>(name));
    }
  }

  else {
    throw std::runtime_error("Data type: " + typeStr + " cannot be mapped to .ply format");
  }
}

/**
 * @brief An element (more properly an element type) in the .ply object. Tracks the name of the elemnt type (eg,
 * "vertices"), the number of elements of that type (eg, 1244), and any properties associated with that element (eg,
 * "position", "color").
 */
class Element {

public:
  /**
   * @brief Create a new element type.
   *
   * @param name_ Name of the element type (eg, "vertices")
   * @param count_ Number of instances of this element.
   */
  Element(const std::string& name_, size_t count_) : name(name_), count(count_) {}

  std::string name;
  size_t count;
  std::vector<std::unique_ptr<Property>> properties;

  /**
   * @brief Check if a property exists.
   * 
   * @param target The name of the property to get.
   *
   * @return Whether the target property exists.
   */
  bool hasProperty(const std::string& target) {
    for (std::unique_ptr<Property>& prop : properties) {
      if (prop->name == target) {
        return true;
      }
    }
    return false;
  }

  /**
   * @brief Low-level method to get a pointer to a property. Users probably don't need to call this.
   *
   * @param target The name of the property to get.
   *
   * @return A (unique_ptr) pointer to the property.
   */
  std::unique_ptr<Property>& getPropertyPtr(const std::string& target) {
    for (std::unique_ptr<Property>& prop : properties) {
      if (prop->name == target) {
        return prop;
      }
    }
    throw std::runtime_error("PLY parser: element " + name + " does not have property " + target);
  }

  /**
   * @brief Add a new (plain, not list) property for this element type.
   *
   * @tparam T The type of the property
   * @param propertyName The name of the property
   * @param data The data for the property. Must have the same length as the number of elements.
   */
  template <class T>
  void addProperty(const std::string& propertyName, const std::vector<T>& data) {

    if (data.size() != count) {
      throw std::runtime_error("PLY write: new property " + propertyName + " has size which does not match element");
    }

    // If there is already some property with this name, remove it
    for (size_t i = 0; i < properties.size(); i++) {
      if (properties[i]->name == propertyName) {
        properties.erase(properties.begin() + i);
        i--;
      }
    }

    // Copy to canonical type. Often a no-op, but takes care of standardizing widths across platforms.
    std::vector<typename CanonicalName<T>::type> canonicalVec(data.begin(), data.end());

    properties.push_back(
        std::unique_ptr<Property>(new TypedProperty<typename CanonicalName<T>::type>(propertyName, canonicalVec)));
  }

  /**
   * @brief Add a new list property for this element type.
   *
   * @tparam T The type of the property (eg, "double" for a list of doubles)
   * @param propertyName The name of the property
   * @param data The data for the property. Outer vector must have the same length as the number of elements.
   */
  template <class T>
  void addListProperty(const std::string& propertyName, const std::vector<std::vector<T>>& data) {

    if (data.size() != count) {
      throw std::runtime_error("PLY write: new property " + propertyName + " has size which does not match element");
    }

    // If there is already some property with this name, remove it
    for (size_t i = 0; i < properties.size(); i++) {
      if (properties[i]->name == propertyName) {
        properties.erase(properties.begin() + i);
        i--;
      }
    }

    // Copy to canonical type. Often a no-op, but takes care of standardizing widths across platforms.
    std::vector<std::vector<typename CanonicalName<T>::type>> canonicalListVec;
    for (const std::vector<T>& subList : data) {
      canonicalListVec.emplace_back(subList.begin(), subList.end());
    }

    properties.push_back(std::unique_ptr<Property>(
        new TypedListProperty<typename CanonicalName<T>::type>(propertyName, canonicalListVec)));
  }

  /**
   * @brief Get a vector of a data from a property for this element. Automatically promotes to larger types. Throws if
   * requested data is unavailable.
   *
   * @tparam T The type of data requested
   * @param propertyName The name of the property to get.
   *
   * @return The data.
   */
  template <class T>
  std::vector<T> getProperty(const std::string& propertyName) {

    // Find the property
    std::unique_ptr<Property>& prop = getPropertyPtr(propertyName);

    // Get a copy of the data with auto-promoting type magic
    return getDataFromPropertyRecursive<T, T>(prop.get());
  }

  /**
   * @brief Get a vector of lists of data from a property for this element. Automatically promotes to larger types.
   * Throws if requested data is unavailable.
   *
   * @tparam T The type of data requested
   * @param propertyName The name of the property to get.
   *
   * @return The data.
   */
  template <class T>
  std::vector<std::vector<T>> getListProperty(const std::string& propertyName) {

    // Find the property
    std::unique_ptr<Property>& prop = getPropertyPtr(propertyName);

    // Get a copy of the data with auto-promoting type magic
    return getDataFromListPropertyRecursive<T, T>(prop.get());
  }


  /**
   * @brief Get a vector of lists of data from a property for this element. Automatically promotes to larger types.
   * Unlike getListProperty(), this method will additionally convert between types of different sign (eg, requesting and
   * int32 would get data from a uint32); doing so naively converts between signed and unsigned types. This is typically
   * useful for data representing indices, which might be stored as signed or unsigned numbers.
   *
   * @tparam T The type of data requested
   * @param propertyName The name of the property to get.
   *
   * @return The data.
   */
  template <class T>
  std::vector<std::vector<T>> getListPropertyAnySign(const std::string& propertyName) {

    // Find the property
    std::unique_ptr<Property>& prop = getPropertyPtr(propertyName);

    // Get a copy of the data with auto-promoting type magic
    try {
      // First, try the usual approach, looking for a version of the property with the same signed-ness and possibly
      // smaller size
      return getDataFromListPropertyRecursive<T, T>(prop.get());
    } catch (std::runtime_error orig_e) {

      // If the usual approach fails, look for a version with opposite signed-ness
      try {

        // This type has the oppopsite signeness as the input type
        typedef typename CanonicalName<T>::type Tcan;
        typedef typename std::conditional<std::is_signed<Tcan>::value, typename std::make_unsigned<Tcan>::type,
                                          typename std::make_signed<Tcan>::type>::type OppsignType;

        std::vector<std::vector<OppsignType>> oppSignedResult = getListProperty<OppsignType>(propertyName);

        // Very explicitly convert while copying
        std::vector<std::vector<T>> origSignResult;
        for (std::vector<OppsignType>& l : oppSignedResult) {
          std::vector<T> newL;
          for (OppsignType& v : l) {
            newL.push_back(static_cast<T>(v));
          }
          origSignResult.push_back(newL);
        }

        return origSignResult;
      } catch (std::runtime_error new_e) {
        throw orig_e;
      }

      throw orig_e;
    }
  }


  /**
   * @brief Performs sanity checks on the element, throwing if any fail.
   */
  void validate() {

    // Make sure no properties have duplicate names, and no names have whitespace
    for (size_t iP = 0; iP < properties.size(); iP++) {
      for (char c : properties[iP]->name) {
        if (std::isspace(c)) {
          throw std::runtime_error("Ply validate: illegal whitespace in name " + properties[iP]->name);
        }
      }
      for (size_t jP = iP + 1; jP < properties.size(); jP++) {
        if (properties[iP]->name == properties[jP]->name) {
          throw std::runtime_error("Ply validate: multiple properties with name " + properties[iP]->name);
        }
      }
    }

    // Make sure all properties have right length
    for (size_t iP = 0; iP < properties.size(); iP++) {
      if (properties[iP]->size() != count) {
        throw std::runtime_error("Ply validate: property has wrong size. " + properties[iP]->name +
                                 " does not match element size.");
      }
    }
  }

  /**
   * @brief Writes out this element's information to the file header.
   *
   * @param outStream The stream to use.
   */
  void writeHeader(std::ofstream& outStream) {

    outStream << "element " << name << " " << count << "\n";

    for (std::unique_ptr<Property>& p : properties) {
      p->writeHeader(outStream);
    }
  }

  /**
   * @brief (ASCII writing) Writes out all of the data for every element of this element type to the stream, including
   * all contained properties.
   *
   * @param outStream The stream to write to.
   */
  void writeDataASCII(std::ofstream& outStream) {
    // Question: what is the proper output for an element with no properties? Here, we write a blank line, so there is
    // one line per element no matter what.
    for (size_t iE = 0; iE < count; iE++) {
      for (size_t iP = 0; iP < properties.size(); iP++) {
        properties[iP]->writeDataASCII(outStream, iE);
        if (iP < properties.size() - 1) {
          outStream << " ";
        }
      }
      outStream << "\n";
    }
  }


  /**
   * @brief (binary writing) Writes out all of the data for every element of this element type to the stream, including
   * all contained properties.
   *
   * @param outStream The stream to write to.
   */
  void writeDataBinary(std::ofstream& outStream) {
    for (size_t iE = 0; iE < count; iE++) {
      for (size_t iP = 0; iP < properties.size(); iP++) {
        properties[iP]->writeDataBinary(outStream, iE);
      }
    }
  }


  /**
   * @brief Helper function which does the hard work to implement type promotion for data getters. Throws if type
   * conversion fails.
   *
   * @tparam D The desired output type
   * @tparam T The current attempt for the actual type of the property
   * @param prop The property to get (does not delete nor share pointer)
   *
   * @return The data, with the requested type
   */
  template <class D, class T>
  std::vector<D> getDataFromPropertyRecursive(Property* prop) {

    typedef typename CanonicalName<T>::type Tcan;

    { // Try to return data of type D from a property of type T
      TypedProperty<Tcan>* castedProp = dynamic_cast<TypedProperty<Tcan>*>(prop);
      if (castedProp) {
        // Succeeded, return a buffer of the data (copy while converting type)
        std::vector<D> castedVec;
        for (Tcan& v : castedProp->data) {
          castedVec.push_back(static_cast<D>(v));
        }
        return castedVec;
      }
    }

    TypeChain<Tcan> chainType;
    if (chainType.hasChildType) {
      return getDataFromPropertyRecursive<D, typename TypeChain<Tcan>::type>(prop);
    } else {
      // No smaller type to try, failure
      throw std::runtime_error("PLY parser: property " + prop->name + " cannot be coerced to requested type " +
                               typeName<D>() + ". Has type " + prop->propertyTypeName());
    }
  }


  /**
   * @brief Helper function which does the hard work to implement type promotion for list data getters. Throws if type
   * conversion fails.
   *
   * @tparam D The desired output type
   * @tparam T The current attempt for the actual type of the property
   * @param prop The property to get (does not delete nor share pointer)
   *
   * @return The data, with the requested type
   */
  template <class D, class T>
  std::vector<std::vector<D>> getDataFromListPropertyRecursive(Property* prop) {
    typedef typename CanonicalName<T>::type Tcan;

    TypedListProperty<Tcan>* castedProp = dynamic_cast<TypedListProperty<Tcan>*>(prop);
    if (castedProp) {
      // Succeeded, return a buffer of the data (copy while converting type)
      std::vector<std::vector<D>> castedListVec;
      for (std::vector<Tcan>& l : castedProp->data) {
        std::vector<D> newL;
        for (Tcan& v : l) {
          newL.push_back(static_cast<D>(v));
        }
        castedListVec.push_back(newL);
      }
      return castedListVec;
    }

    TypeChain<Tcan> chainType;
    if (chainType.hasChildType) {
      return getDataFromListPropertyRecursive<D, typename TypeChain<Tcan>::type>(prop);
    } else {
      // No smaller type to try, failure
      throw std::runtime_error("PLY parser: list property " + prop->name +
                               " cannot be coerced to requested type list " + typeName<D>() + ". Has type list " +
                               prop->propertyTypeName());
    }
  }
};


// Some string helpers
namespace {

inline std::string trimSpaces(const std::string& input) {
  size_t start = 0;
  while (start < input.size() && input[start] == ' ') start++;
  size_t end = input.size();
  while (end > start && (input[end - 1] == ' ' || input[end - 1] == '\n' || input[end - 1] == '\r')) end--;
  return input.substr(start, end - start);
}

inline std::vector<std::string> tokenSplit(const std::string& input) {
  std::vector<std::string> result;
  size_t curr = 0;
  size_t found = 0;
  while ((found = input.find_first_of(' ', curr)) != std::string::npos) {
    std::string token = input.substr(curr, found - curr);
    token = trimSpaces(token);
    if (token.size() > 0) {
      result.push_back(token);
    }
    curr = found + 1;
  }
  std::string token = input.substr(curr);
  token = trimSpaces(token);
  if (token.size() > 0) {
    result.push_back(token);
  }

  return result;
}

inline bool startsWith(const std::string& input, const std::string& query) { return input.compare(0, query.length(), query) == 0; }
}; // namespace


/**
 * @brief Primary class; represents a set of data in the .ply format.
 */
class PLYData {

public:
  /**
   * @brief Create an empty PLYData object.
   */
  PLYData(){};

  /**
   * @brief Initialize a PLYData by reading from a file. Throws if any failures occur.
   *
   * @param filename The file to read from.
   * @param verbose If true, print useful info about the file to stdout
   */
  PLYData(const std::string& filename, bool verbose = false) {

    using std::cout;
    using std::endl;
    using std::string;
    using std::vector;

    if (verbose) cout << "PLY parser: Reading ply file: " << filename << endl;

    // Open a file in binary always, in case it turns out to have binary data.
    std::ifstream inStream(filename, std::ios::binary);
    if (inStream.fail()) {
      throw std::runtime_error("PLY parser: Could not open file " + filename);
    }


    // == Process the header
    parseHeader(inStream, verbose);


    // === Parse data from a binary file
    if (inputDataFormat == DataFormat::Binary) {
      parseBinary(inStream, verbose);
    }
    // === Parse data from an ASCII file
    else if (inputDataFormat == DataFormat::ASCII) {
      parseASCII(inStream, verbose);
    }


    if (verbose) {
      cout << "  - Finished parsing file." << endl;
    }
  }

  /**
   * @brief Perform sanity checks on the file, throwing if any fail.
   */
  void validate() {

    for (size_t iE = 0; iE < elements.size(); iE++) {
      for (char c : elements[iE].name) {
        if (std::isspace(c)) {
          throw std::runtime_error("Ply validate: illegal whitespace in element name " + elements[iE].name);
        }
      }
      for (size_t jE = iE + 1; jE < elements.size(); jE++) {
        if (elements[iE].name == elements[jE].name) {
          throw std::runtime_error("Ply validate: duplcate element name " + elements[iE].name);
        }
      }
    }

    // Do a quick validation sanity check
    for (Element& e : elements) {
      e.validate();
    }
  }

  /**
   * @brief Write this data to a .ply file.
   *
   * @param filename The file to write to.
   * @param format The format to use (binary or ascii?)
   */
  void write(const std::string& filename, DataFormat format = DataFormat::ASCII) {
    outputDataFormat = format;

    validate();

    // Open stream for writing
    std::ofstream outStream(filename, std::ios::out | std::ios::binary);
    if (!outStream.good()) {
      throw std::runtime_error("Ply writer: Could not open output file " + filename + " for writing");
    }

    writeHeader(outStream);

    // Write all elements
    for (Element& e : elements) {
      if (outputDataFormat == DataFormat::Binary) {
        e.writeDataBinary(outStream);
      } else if (outputDataFormat == DataFormat::ASCII) {
        e.writeDataASCII(outStream);
      }
    }
  }

  /**
   * @brief Get an element type by name ("vertices")
   *
   * @param target The name of the element type to get
   *
   * @return A reference to the element type.
   */
  Element& getElement(const std::string& target) {
    for (Element& e : elements) {
      if (e.name == target) return e;
    }
    throw std::runtime_error("PLY parser: no element with name: " + target);
  }


  /**
   * @brief Check if an element type exists
   *
   * @param target The name to check for.
   *
   * @return True if exists.
   */
  bool hasElement(const std::string& target) {
    for (Element& e : elements) {
      if (e.name == target) return true;
    }
    return false;
  }


  /**
   * @brief Add a new element type to the object
   *
   * @param name The name of the new element type ("vertices").
   * @param count The number of elements of this type.
   */
  void addElement(const std::string& name, size_t count) { elements.emplace_back(name, count); }

  // === Common-case helpers


  /**
   * @brief Common-case helper get mesh vertex positions
   *
   * @param vertexElementName The element name to use (default: "vertex")
   *
   * @return A vector of vertex positions.
   */
  std::vector<std::array<double, 3>> getVertexPositions(const std::string& vertexElementName = "vertex") {

    std::vector<double> xPos = getElement(vertexElementName).getProperty<double>("x");
    std::vector<double> yPos = getElement(vertexElementName).getProperty<double>("y");
    std::vector<double> zPos = getElement(vertexElementName).getProperty<double>("z");

    std::vector<std::array<double, 3>> result(xPos.size());
    for (size_t i = 0; i < result.size(); i++) {
      result[i][0] = xPos[i];
      result[i][1] = yPos[i];
      result[i][2] = zPos[i];
    }

    return result;
  }

  /**
   * @brief Common-case helper get mesh vertex colors
   *
   * @param vertexElementName The element name to use (default: "vertex")
   *
   * @return A vector of vertex colors (unsigned chars [0,255]).
   */
  std::vector<std::array<unsigned char, 3>> getVertexColors(const std::string& vertexElementName = "vertex") {

    std::vector<unsigned char> r = getElement(vertexElementName).getProperty<unsigned char>("red");
    std::vector<unsigned char> g = getElement(vertexElementName).getProperty<unsigned char>("green");
    std::vector<unsigned char> b = getElement(vertexElementName).getProperty<unsigned char>("blue");

    std::vector<std::array<unsigned char, 3>> result(r.size());
    for (size_t i = 0; i < result.size(); i++) {
      result[i][0] = r[i];
      result[i][1] = g[i];
      result[i][2] = b[i];
    }

    return result;
  }

  /**
   * @brief Common-case helper to get face indices for a mesh. If not template type is given, size_t is used. Naively
   * converts to requested signedness, which may lead to unexpected values if an unsigned type is used and file contains
   * negative values.
   *
   * @return The indices into the vertex elements for each face. Usually 0-based, though there are no formal rules.
   */
  template <typename T = size_t>
  std::vector<std::vector<T>> getFaceIndices() {

    for (const std::string& f : std::vector<std::string>{"face"}) {
      for (const std::string& p : std::vector<std::string>{"vertex_indices", "vertex_index"}) {
        try {
          return getElement(f).getListPropertyAnySign<T>(p);
        } catch (std::runtime_error e) {
          // that's fine
        }
      }
    }
    throw std::runtime_error("PLY parser: could not find face vertex indices attribute under any common name.");
  }


  /**
   * @brief Common-case helper set mesh vertex positons. Creates vertex element, if necessary.
   *
   * @param vertexPositions A vector of vertex positions
   */
  void addVertexPositions(std::vector<std::array<double, 3>>& vertexPositions) {

    std::string vertexName = "vertex";
    size_t N = vertexPositions.size();

    // Create the element
    if (!hasElement(vertexName)) {
      addElement(vertexName, N);
    }

    // De-interleave
    std::vector<double> xPos(N);
    std::vector<double> yPos(N);
    std::vector<double> zPos(N);
    for (size_t i = 0; i < vertexPositions.size(); i++) {
      xPos[i] = vertexPositions[i][0];
      yPos[i] = vertexPositions[i][1];
      zPos[i] = vertexPositions[i][2];
    }

    // Store
    getElement(vertexName).addProperty<double>("x", xPos);
    getElement(vertexName).addProperty<double>("y", yPos);
    getElement(vertexName).addProperty<double>("z", zPos);
  }

  /**
   * @brief Common-case helper set mesh vertex colors. Creates a vertex element, if necessary.
   *
   * @param colors A vector of vertex colors (unsigned chars [0,255]).
   */
  void addVertexColors(std::vector<std::array<unsigned char, 3>>& colors) {

    std::string vertexName = "vertex";
    size_t N = colors.size();

    // Create the element
    if (!hasElement(vertexName)) {
      addElement(vertexName, N);
    }

    // De-interleave
    std::vector<unsigned char> r(N);
    std::vector<unsigned char> g(N);
    std::vector<unsigned char> b(N);
    for (size_t i = 0; i < colors.size(); i++) {
      r[i] = colors[i][0];
      g[i] = colors[i][1];
      b[i] = colors[i][2];
    }

    // Store
    getElement(vertexName).addProperty<unsigned char>("red", r);
    getElement(vertexName).addProperty<unsigned char>("green", g);
    getElement(vertexName).addProperty<unsigned char>("blue", b);
  }

  /**
   * @brief Common-case helper set mesh vertex colors. Creates a vertex element, if necessary.
   *
   * @param colors A vector of vertex colors as floating point [0,1] values. Internally converted to [0,255] chars.
   */
  void addVertexColors(std::vector<std::array<double, 3>>& colors) {

    std::string vertexName = "vertex";
    size_t N = colors.size();

    // Create the element
    if (!hasElement(vertexName)) {
      addElement(vertexName, N);
    }

    auto toChar = [](double v) {
      if (v < 0.0) v = 0.0;
      if (v > 1.0) v = 1.0;
      return static_cast<unsigned char>(v * 255.);
    };

    // De-interleave
    std::vector<unsigned char> r(N);
    std::vector<unsigned char> g(N);
    std::vector<unsigned char> b(N);
    for (size_t i = 0; i < colors.size(); i++) {
      r[i] = toChar(colors[i][0]);
      g[i] = toChar(colors[i][1]);
      b[i] = toChar(colors[i][2]);
    }

    // Store
    getElement(vertexName).addProperty<unsigned char>("red", r);
    getElement(vertexName).addProperty<unsigned char>("green", g);
    getElement(vertexName).addProperty<unsigned char>("blue", b);
  }


  /**
   * @brief Common-case helper to set face indices. Creates a face element if needed. The input type will be casted to a
   * 32 bit integer of the same signedness.
   *
   * @param indices The indices into the vertex list around each face.
   */
  template <typename T>
  void addFaceIndices(std::vector<std::vector<T>>& indices) {

    std::string faceName = "face";
    size_t N = indices.size();

    // Create the element
    if (!hasElement(faceName)) {
      addElement(faceName, N);
    }

    // Cast to 32 bit
    typedef typename std::conditional<std::is_signed<T>::value, int32_t, uint32_t>::type IndType;
    std::vector<std::vector<IndType>> intInds;
    for (std::vector<T>& l : indices) {
      std::vector<IndType> thisInds;
      for (T& val : l) {
        IndType valConverted = static_cast<IndType>(val);
        if (valConverted != val) {
          throw std::runtime_error("Index value " + std::to_string(val) +
                                   " could not be converted to a .ply integer without loss of data. Note that .ply "
                                   "only supports 32-bit ints.");
        }
        thisInds.push_back(valConverted);
      }
      intInds.push_back(thisInds);
    }

    // Store
    getElement(faceName).addListProperty<IndType>("vertex_indices", intInds);
  }


  /**
   * @brief Comments for the file. When writing, each entry will be written as a sequential comment line.
   */
  std::vector<std::string> comments;

private:
  std::vector<Element> elements;
  const int majorVersion = 1; // I'll buy you a drink if these ever get bumped
  const int minorVersion = 0;

  DataFormat inputDataFormat = DataFormat::ASCII;  // set when reading from a file
  DataFormat outputDataFormat = DataFormat::ASCII; // option for writing files


  // === Reading ===

  /**
   * @brief Read the header for a file
   *
   * @param inStream
   * @param verbose
   */
  void parseHeader(std::ifstream& inStream, bool verbose) {

    using std::cout;
    using std::endl;
    using std::string;
    using std::vector;

    // First two lines are predetermined
    { // First line is magic constant
      string plyLine;
      std::getline(inStream, plyLine);
      if (trimSpaces(plyLine) != "ply") {
        throw std::runtime_error("PLY parser: File does not appear to be ply file. First line should be 'ply'");
      }
    }

    { // second line is version
      string styleLine;
      std::getline(inStream, styleLine);
      vector<string> tokens = tokenSplit(styleLine);
      if (tokens.size() != 3) throw std::runtime_error("PLY parser: bad format line");
      std::string formatStr = tokens[0];
      std::string typeStr = tokens[1];
      std::string versionStr = tokens[2];

      // "format"
      if (formatStr != "format") throw std::runtime_error("PLY parser: bad format line");

      // ascii/binary
      if (typeStr == "ascii") {
        inputDataFormat = DataFormat::ASCII;
        if (verbose) cout << "  - Type: ascii" << endl;
      } else if (typeStr == "binary_little_endian") {
        inputDataFormat = DataFormat::Binary;
        if (verbose) cout << "  - Type: binary" << endl;
      } else if (typeStr == "binary_big_endian") {
        throw std::runtime_error("PLY parser: encountered scary big endian file. Don't know how to parse that");
      } else {
        throw std::runtime_error("PLY parser: bad format line");
      }

      // version
      if (versionStr != "1.0") {
        throw std::runtime_error("PLY parser: encountered file with version != 1.0. Don't know how to parse that");
      }
      if (verbose) cout << "  - Version: " << versionStr << endl;
    }

    // Consume header line by line
    while (inStream.good()) {
      string line;
      std::getline(inStream, line);

      // Parse a comment
      if (startsWith(line, "comment")) {
        string comment = line.substr(7);
        if (verbose) cout << "  - Comment: " << comment << endl;
        comments.push_back(comment);
        continue;
      }

      // Parse an element
      else if (startsWith(line, "element")) {
        vector<string> tokens = tokenSplit(line);
        if (tokens.size() != 3) throw std::runtime_error("PLY parser: Invalid element line");
        string name = tokens[1];
        size_t count;
        std::istringstream iss(tokens[2]);
        iss >> count;
        elements.emplace_back(name, count);
        if (verbose) cout << "  - Found element: " << name << " (count = " << count << ")" << endl;
        continue;
      }

      // Parse a property list
      else if (startsWith(line, "property list")) {
        vector<string> tokens = tokenSplit(line);
        if (tokens.size() != 5) throw std::runtime_error("PLY parser: Invalid property list line");
        if (elements.size() == 0) throw std::runtime_error("PLY parser: Found property list without previous element");
        string countType = tokens[2];
        string type = tokens[3];
        string name = tokens[4];
        elements.back().properties.push_back(createPropertyWithType(name, type, true, countType));
        if (verbose)
          cout << "    - Found list property: " << name << " (count type = " << countType << ", data type = " << type
               << ")" << endl;
        continue;
      }

      // Parse a property
      else if (startsWith(line, "property")) {
        vector<string> tokens = tokenSplit(line);
        if (tokens.size() != 3) throw std::runtime_error("PLY parser: Invalid property line");
        if (elements.size() == 0) throw std::runtime_error("PLY parser: Found property without previous element");
        string type = tokens[1];
        string name = tokens[2];
        elements.back().properties.push_back(createPropertyWithType(name, type, false, ""));
        if (verbose) cout << "    - Found property: " << name << " (type = " << type << ")" << endl;
        continue;
      }

      // Parse end of header
      else if (startsWith(line, "end_header")) {
        break;
      }

      // Error!
      else {
        throw std::runtime_error("Unrecognized header line: " + line);
      }
    }
  }

  /**
   * @brief Read the actual data for a file, in ASCII
   *
   * @param inStream
   * @param verbose
   */
  void parseASCII(std::ifstream& inStream, bool verbose) {

    using std::string;
    using std::vector;

    // Read all elements
    for (Element& elem : elements) {

      if (verbose) {
        std::cout << "  - Processing element: " << elem.name << std::endl;
      }

      for (size_t iP = 0; iP < elem.properties.size(); iP++) {
        elem.properties[iP]->reserve(elem.count);
      }
      for (size_t iEntry = 0; iEntry < elem.count; iEntry++) {

        string line;
        std::getline(inStream, line);

        vector<string> tokens = tokenSplit(line);
        size_t iTok = 0;
        for (size_t iP = 0; iP < elem.properties.size(); iP++) {
          elem.properties[iP]->parseNext(tokens, iTok);
        }
      }
    }
  }

  /**
   * @brief Read the actual data for a file, in binary.
   *
   * @param inStream
   * @param verbose
   */
  void parseBinary(std::ifstream& inStream, bool verbose) {

    using std::string;
    using std::vector;

    // Read all elements
    for (Element& elem : elements) {

      if (verbose) {
        std::cout << "  - Processing element: " << elem.name << std::endl;
      }

      for (size_t iP = 0; iP < elem.properties.size(); iP++) {
        elem.properties[iP]->reserve(elem.count);
      }
      for (size_t iEntry = 0; iEntry < elem.count; iEntry++) {
        for (size_t iP = 0; iP < elem.properties.size(); iP++) {
          elem.properties[iP]->readNext(inStream);
        }
      }
    }
  }

  // === Writing ===


  /**
   * @brief Write out a header for a file
   *
   * @param outStream
   */
  void writeHeader(std::ofstream& outStream) {

    // Magic line
    outStream << "ply\n";

    // Type line
    outStream << "format ";
    if (outputDataFormat == DataFormat::Binary) {
      outStream << "binary_little_endian ";
    } else if (outputDataFormat == DataFormat::ASCII) {
      outStream << "ascii ";
    }

    // Version number
    outStream << majorVersion << "." << minorVersion << "\n";

    // Write comments
    for (const std::string& comment : comments) {
      outStream << "comment " << comment << "\n";
    }
    outStream << "comment "
              << "Written with hapPLY (https://github.com/nmwsharp/happly)"
              << "\n";

    // Write elements (and their properties)
    for (Element& e : elements) {
      e.writeHeader(outStream);
    }

    // End header
    outStream << "end_header\n";
  }
};

} // namespace happly