test2/source/blender/blenlib/BLI_serialize.hh

/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

#pragma once

/** \file
 * \ingroup bli
 *
 * An abstraction layer for serialization formats.
 *
 * Allowing to read/write data to a serialization format like JSON.
 *
 *
 *
 * # Supported data types
 *
 * The abstraction layer has a limited set of data types it supports.
 * There are specific classes that builds up the data structure that
 * can be (de)serialized.
 *
 * - StringValue: for strings
 * - IntValue: for integer values
 * - DoubleValue: for double precision floating point numbers
 * - BooleanValue: for boolean values
 * - ArrayValue: An array of any supported value.
 * - DictionaryValue: A key value pair where keys are std::string.
 * - NullValue: for null values.
 *
 * # Basic usage
 *
 * ## Serializing
 *
 * - Construct a structure that needs to be serialized using the `*Value` classes.
 * - Construct the formatter you want to use
 * - Invoke the formatter.serialize method passing an output stream and the value.
 *
 * The next example would format an integer value (42) as JSON the result will
 * be stored inside `out`.
 *
 * \code{.cc}
 * JsonFormatter json;
 * std::stringstream out;
 * IntValue test_value(42);
 * json.serialize(out, test_value);
 * \endcode
 *
 * ## Deserializing
 *
 * \code{.cc}
 * std::stringstream is("42");
 * JsonFormatter json;
 * std::unique_ptr<Value> value = json.deserialize(is);
 * \endcode
 *
 * # Adding a new formatter
 *
 * To add a new formatter a new sub-class of `Formatter` must be created and the
 * `serialize`/`deserialize` methods should be implemented.
 */

#include <iosfwd>

#include "BLI_map.hh"
#include "BLI_string_ref.hh"
#include "BLI_vector.hh"

namespace blender::io::serialize {

/**
 * Enumeration containing all sub-classes of Value. It is used as for type checking.
 *
 * \see #Value::type()
 */
enum class eValueType {
  String,
  Int,
  Array,
  Null,
  Boolean,
  Double,
  Dictionary,
  Enum,
};

class Value;
class StringValue;
class DictionaryValue;
template<typename T, eValueType V> class PrimitiveValue;
using IntValue = PrimitiveValue<int64_t, eValueType::Int>;
using DoubleValue = PrimitiveValue<double, eValueType::Double>;
using BooleanValue = PrimitiveValue<bool, eValueType::Boolean>;
using EnumValue = PrimitiveValue<int, eValueType::Enum>;
class ArrayValue;

/**
 * Class containing a (de)serializable value.
 *
 * To serialize from or to a specific format the Value will be used as an intermediate container
 * holding the values. Value class is abstract. There are concrete classes to for different data
 * types.
 *
 * - `StringValue`: contains a string.
 * - `IntValue`: contains an integer.
 * - `ArrayValue`: contains an array of elements. Elements don't need to be the same type.
 * - `NullValue`: represents nothing (null pointer or optional).
 * - `BooleanValue`: contains a boolean (true/false).
 * - `DoubleValue`: contains a double precision floating point number.
 * - `DictionaryValue`: represents an object (key value pairs where keys are strings and values can
 *   be of different types.
 */
class Value {
 private:
  eValueType type_;

 protected:
  Value() = delete;
  explicit Value(eValueType type) : type_(type) {}

 public:
  virtual ~Value() = default;
  eValueType type() const
  {
    return type_;
  }

  /**
   * Casts to a StringValue.
   * Will return nullptr when it is a different type.
   */
  const StringValue *as_string_value() const;

  /**
   * Casts to an IntValue.
   * Will return nullptr when it is a different type.
   */
  const IntValue *as_int_value() const;

  /**
   * Casts to a DoubleValue.
   * Will return nullptr when it is a different type.
   */
  const DoubleValue *as_double_value() const;

  /**
   * Casts to a BooleanValue.
   * Will return nullptr when it is a different type.
   */
  const BooleanValue *as_boolean_value() const;

  /**
   * Casts to a EnumValue.
   * Will return nullptr when it is a different type.
   */
  const EnumValue *as_enum_value() const;

  /**
   * Casts to an ArrayValue.
   * Will return nullptr when it is a different type.
   */
  const ArrayValue *as_array_value() const;

  /**
   * Casts to an DictionaryValue.
   * Will return nullptr when it is a different type.
   */
  const DictionaryValue *as_dictionary_value() const;
};

/**
 * For generating value types that represent types that are typically known processor data types.
 */
template<
    /** Wrapped c/cpp data type that is used to store the value. */
    typename T,
    /** Value type of the class. */
    eValueType V>
class PrimitiveValue : public Value {
 private:
  T inner_value_{};

 public:
  explicit PrimitiveValue(const T value) : Value(V), inner_value_(value) {}

  const T value() const
  {
    return inner_value_;
  }
};

class NullValue : public Value {
 public:
  NullValue() : Value(eValueType::Null) {}
};

class StringValue : public Value {
 private:
  std::string string_;

 public:
  StringValue(std::string string) : Value(eValueType::String), string_(std::move(string)) {}

  const std::string &value() const
  {
    return string_;
  }
};

class ArrayValue : public Value {
  Vector<std::shared_ptr<Value>> values_;

 public:
  ArrayValue() : Value(eValueType::Array) {}

  void append(std::shared_ptr<Value> value);
  void append_bool(bool value);
  void append_int(int value);
  void append_double(double value);
  void append_str(std::string value);
  void append_null();
  std::shared_ptr<DictionaryValue> append_dict();
  std::shared_ptr<ArrayValue> append_array();

  Span<std::shared_ptr<Value>> elements() const
  {
    return values_;
  }
};

/**
 * Object is a key-value container where the key must be a std::string.
 * Internally it is stored in a blender::Vector to ensure the order of keys.
 */
class DictionaryValue : public Value {
 public:
  /**
   * Elements are stored as an key value pair. The value is a shared pointer so it can be
   * shared when using `DictionaryValue::create_lookup`.
   */
  using Item = std::pair<std::string, std::shared_ptr<Value>>;
  using Lookup = Map<std::string, std::shared_ptr<Value>>;

 private:
  Vector<Item> values_;

 public:
  DictionaryValue() : Value(eValueType::Dictionary) {}

  /**
   * Return a lookup map to quickly lookup by key.
   *
   * The lookup is owned by the caller.
   */
  Lookup create_lookup() const;

  const std::shared_ptr<Value> *lookup(const StringRef key) const;
  std::optional<StringRefNull> lookup_str(const StringRef key) const;
  std::optional<int64_t> lookup_int(const StringRef key) const;
  std::optional<double> lookup_double(const StringRef key) const;
  const DictionaryValue *lookup_dict(const StringRef key) const;
  const ArrayValue *lookup_array(const StringRef key) const;
  Span<Item> elements() const
  {
    return values_;
  }

  void append(std::string key, std::shared_ptr<Value> value);
  void append_int(std::string key, int64_t value);
  void append_double(std::string key, double value);
  void append_str(std::string key, std::string value);
  std::shared_ptr<DictionaryValue> append_dict(std::string key);
  std::shared_ptr<ArrayValue> append_array(std::string key);
};

/**
 * Interface for any provided Formatter.
 */
class Formatter {
 public:
  virtual ~Formatter() = default;

  /** Serialize the value to the given stream. */
  virtual void serialize(std::ostream &os, const Value &value) = 0;

  /** Deserialize the stream. */
  virtual std::unique_ptr<Value> deserialize(std::istream &is) = 0;
};

/**
 * Formatter to (de)serialize a JSON formatted stream.
 */
class JsonFormatter : public Formatter {
 public:
  /**
   * The indentation level to use.
   * Typically number of chars. Set to 0 to not use indentation.
   */
  int8_t indentation_len = 0;

 public:
  void serialize(std::ostream &os, const Value &value) override;
  /**
   * \return The deserialized value or null on failure to parse the JSON contents. Typically this
   *         indicates a malformed file.
   */
  std::unique_ptr<Value> deserialize(std::istream &is) override;
};

void write_json_file(StringRef path, const Value &value);
std::shared_ptr<Value> read_json_file(StringRef path);

}  // namespace blender::io::serialize