rippled/include/xrpl/json/json_value.h

#pragma once

#include <xrpl/basics/Number.h>
#include <xrpl/json/json_forwards.h>

#include <cstring>
#include <iterator>
#include <limits>
#include <map>
#include <string>
#include <vector>

/**
 * @brief JSON (JavaScript Object Notation).
 */
namespace json {

/**
 * @brief Type of the value held by a Value object.
 */
enum class ValueType {
    Null = 0,  ///< 'null' value
    Int,       ///< signed integer value
    UInt,      ///< unsigned integer value
    Real,      ///< double value
    String,    ///< UTF-8 string value
    Boolean,   ///< bool value
    Array,     ///< array value (ordered list)
    Object     ///< object value (collection of name/value pairs).
};

/**
 * @brief Lightweight wrapper to tag static string.
 *
 * Value constructor and ValueType::Object member assignment takes advantage of the
 * StaticString and avoid the cost of string duplication when storing the
 * string or the member name.
 *
 * Example of usage:
 * @code
 * json::Value aValue( StaticString("some text") );
 * json::Value object;
 * static const StaticString code("code");
 * object[code] = 1234;
 * @endcode
 */
class StaticString
{
public:
    constexpr explicit StaticString(char const* czString) : str_(czString)
    {
    }

    constexpr
    operator char const*() const
    {
        return str_;
    }

    [[nodiscard]] constexpr char const*
    cStr() const
    {
        return str_;
    }

private:
    char const* str_;
};

inline bool
operator==(StaticString x, StaticString y)
{
    return strcmp(x.cStr(), y.cStr()) == 0;
}

inline bool
operator!=(StaticString x, StaticString y)
{
    return !(x == y);
}

inline bool
operator==(std::string const& x, StaticString y)
{
    return strcmp(x.c_str(), y.cStr()) == 0;
}

inline bool
operator!=(std::string const& x, StaticString y)
{
    return !(x == y);
}

inline bool
operator==(StaticString x, std::string const& y)
{
    return y == x;
}

inline bool
operator!=(StaticString x, std::string const& y)
{
    return !(y == x);
}

/**
 * @brief Represents a <a HREF="http://www.json.org">JSON</a> value.
 *
 * This class is a discriminated union wrapper that can represent a:
 * - signed integer [range: Value::kMinInt - Value::kMaxInt]
 * - unsigned integer (range: 0 - Value::kMaxUInt)
 * - double
 * - UTF-8 string
 * - boolean
 * - 'null'
 * - an ordered list of Value
 * - collection of name/value pairs (javascript object)
 *
 * The type of the held value is represented by a #ValueType and
 * can be obtained using type().
 *
 * values of an ValueType::Object or ValueType::Array can be accessed using operator[]()
 * methods. Non const methods will automatically create the a ValueType::Null element
 * if it does not exist.
 * The sequence of an ValueType::Array will be automatically resize and initialized
 * with ValueType::Null. resize() can be used to enlarge or truncate an ValueType::Array.
 *
 * The get() methods can be used to obtain a default value in the case the
 * required element does not exist.
 *
 * It is possible to iterate over the list of a ValueType::Object values using
 * the getMemberNames() method.
 */
class Value
{
    friend class ValueIteratorBase;

public:
    using Members = std::vector<std::string>;
    using iterator = ValueIterator;
    using const_iterator = ValueConstIterator;
    using UInt = json::UInt;
    using Int = json::Int;
    using ArrayIndex = UInt;

    static Value const kNull;
    static constexpr Int kMinInt = std::numeric_limits<Int>::min();
    static constexpr Int kMaxInt = std::numeric_limits<Int>::max();
    static constexpr UInt kMaxUInt = std::numeric_limits<UInt>::max();

private:
    class CZString
    {
    public:
        enum class DuplicationPolicy { NoDuplication = 0, Duplicate, DuplicateOnCopy };

        CZString(int index);
        CZString(char const* cstr, DuplicationPolicy allocate);
        CZString(CZString const& other);
        ~CZString();
        CZString&
        operator=(CZString const& other) = delete;
        bool
        operator<(CZString const& other) const;
        bool
        operator==(CZString const& other) const;
        [[nodiscard]] int
        index() const;
        [[nodiscard]] char const*
        cStr() const;
        [[nodiscard]] bool
        isStaticString() const;

    private:
        char const* cstr_;
        int index_;
    };

public:
    using ObjectValues = std::map<CZString, Value>;

public:
    /**
     * @brief Create a default Value of the given type.
     *
     *   This is a very useful constructor.
     *   To create an empty array, pass ValueType::Array.
     *   To create an empty object, pass ValueType::Object.
     *   Another Value can then be set to this one by assignment.
     * This is useful since clear() and resize() will not alter types.
     *
     *        Examples:
     * @code
     * json::Value null_value; // null
     * json::Value arr_value(json::ValueType::Array); // []
     * json::Value obj_value(json::ValueType::Object); // {}
     * @endcode
     */
    Value(ValueType type = ValueType::Null);
    Value(Int value);
    Value(UInt value);
    Value(double value);
    Value(char const* value);
    Value(xrpl::Number const& value);
    /**
     * @brief Constructs a value from a static string.
     *
     * Like other value string constructor but do not duplicate the string for
     * internal storage. The given string must remain alive after the call to
     * this
     * constructor.
     * Example of usage:
     * @code
     * json::Value aValue( StaticString("some text") );
     * @endcode
     */
    Value(StaticString const& value);
    Value(std::string const& value);
    Value(bool value);
    Value(Value const& other);
    ~Value();

    Value&
    operator=(Value const& other);
    Value&
    operator=(Value&& other);

    Value(Value&& other) noexcept;

    /**
     * Swap values.
     */
    void
    swap(Value& other) noexcept;

    [[nodiscard]] ValueType
    type() const;

    [[nodiscard]] char const*
    asCString() const;
    /**
     * Returns the unquoted string value.
     */
    [[nodiscard]] std::string
    asString() const;
    [[nodiscard]] Int
    asInt() const;
    [[nodiscard]] UInt
    asUInt() const;
    [[nodiscard]] double
    asDouble() const;
    [[nodiscard]] bool
    asBool() const;

    /**
     * Correct absolute value from int or unsigned int
     */
    [[nodiscard]] UInt
    asAbsUInt() const;

    // TODO: What is the "empty()" method this docstring mentions?
    /**
     * isNull() tests to see if this field is null.  Don't use this method to
     * test for emptiness: use empty().
     */
    [[nodiscard]] bool
    isNull() const;
    [[nodiscard]] bool
    isBool() const;
    [[nodiscard]] bool
    isInt() const;
    [[nodiscard]] bool
    isUInt() const;
    [[nodiscard]] bool
    isIntegral() const;
    [[nodiscard]] bool
    isDouble() const;
    [[nodiscard]] bool
    isNumeric() const;
    [[nodiscard]] bool
    isString() const;
    [[nodiscard]] bool
    isArray() const;
    [[nodiscard]] bool
    isArrayOrNull() const;
    [[nodiscard]] bool
    isObject() const;
    [[nodiscard]] bool
    isObjectOrNull() const;

    [[nodiscard]] bool
    isConvertibleTo(ValueType other) const;

    /**
     * Number of values in array or object
     */
    [[nodiscard]] UInt
    size() const;

    /**
     * Returns false if this is an empty array, empty object, empty string,
     * or null.
     */
    explicit
    operator bool() const;

    /**
     * Remove all object members and array elements.
     * @pre type() is ValueType::Array, ValueType::Object, or ValueType::Null
     * @post type() is unchanged
     */
    void
    clear();

    /**
     * Access an array element (zero based index ).
     * If the array contains less than index element, then null value are
     * inserted in the array so that its size is index+1. (You may need to say
     * 'value[0u]' to get your compiler to distinguish
     *  this from the operator[] which takes a string.)
     */
    Value&
    operator[](UInt index);
    /**
     * Access an array element (zero based index )
     * (You may need to say 'value[0u]' to get your compiler to distinguish
     *  this from the operator[] which takes a string.)
     */
    Value const&
    operator[](UInt index) const;
    /**
     * If the array contains at least index+1 elements, returns the element
     * value, otherwise returns defaultValue.
     */
    [[nodiscard]] Value
    get(UInt index, Value const& defaultValue) const;
    /**
     * Return true if index < size().
     */
    [[nodiscard]] bool
    isValidIndex(UInt index) const;
    /**
     * @brief Append value to array at the end.
     *
     * Equivalent to jsonvalue[jsonvalue.size()] = value;
     */
    Value&
    append(Value const& value);
    Value&
    append(Value&& value);

    /**
     * Access an object value by name, create a null member if it does not
     * exist.
     */
    Value&
    operator[](char const* key);
    /**
     * Access an object value by name, returns null if there is no member with
     * that name.
     */
    Value const&
    operator[](char const* key) const;
    /**
     * Access an object value by name, create a null member if it does not
     * exist.
     */
    Value&
    operator[](std::string const& key);
    /**
     * Access an object value by name, returns null if there is no member with
     * that name.
     */
    Value const&
    operator[](std::string const& key) const;
    /**
     * @brief Access an object value by name, create a null member if it does
     * not exist.
     *
     * If the object as no entry for that name, then the member name used to
     * store
     * the new entry is not duplicated.
     * Example of use:
     * @code
     * json::Value object;
     * static const StaticString code("code");
     * object[code] = 1234;
     * @endcode
     */
    Value&
    operator[](StaticString const& key);
    Value const&
    operator[](StaticString const& key) const;

    /**
     * Return the member named key if it exist, defaultValue otherwise.
     */
    Value
    get(char const* key, Value const& defaultValue) const;
    /**
     * Return the member named key if it exist, defaultValue otherwise.
     */
    [[nodiscard]] Value
    get(std::string const& key, Value const& defaultValue) const;

    /**
     * @brief Remove and return the named member.
     *
     * Do nothing if it did not exist.
     * @return the removed Value, or null.
     * @pre type() is ValueType::Object or ValueType::Null
     * @post type() is unchanged
     */
    Value
    removeMember(char const* key);
    /**
     * Same as removeMember(const char*)
     */
    Value
    removeMember(std::string const& key);

    /**
     * Return true if the object has a member named key.
     */
    bool
    isMember(char const* key) const;
    /**
     * Return true if the object has a member named key.
     */
    [[nodiscard]] bool
    isMember(std::string const& key) const;
    /**
     * Return true if the object has a member named key.
     */
    [[nodiscard]] bool
    isMember(StaticString const& key) const;

    /**
     * @brief Return a list of the member names.
     *
     * If null, return an empty list.
     * @pre type() is ValueType::Object or ValueType::Null
     * @post if type() was ValueType::Null, it remains ValueType::Null
     */
    [[nodiscard]] Members
    getMemberNames() const;

    [[nodiscard]] std::string
    toStyledString() const;

    [[nodiscard]] const_iterator
    begin() const;
    [[nodiscard]] const_iterator
    end() const;

    iterator
    begin();
    iterator
    end();

    friend bool
    operator==(Value const&, Value const&);
    friend bool
    operator<(Value const&, Value const&);

private:
    Value&
    resolveReference(char const* key, bool isStatic);

private:
    union ValueHolder
    {
        Int intVal;
        UInt uintVal;
        double realVal;
        bool boolVal;
        char* stringVal;
        ObjectValues* mapVal{nullptr};
    } value_;
    ValueType type_ : 8;
    int allocated_ : 1 {};  // Notes: if declared as bool, bitfield is useless.
};

inline Value
toJson(xrpl::Number const& number)
{
    return to_string(number);
}

bool
operator==(Value const&, Value const&);

inline bool
operator!=(Value const& x, Value const& y)
{
    return !(x == y);
}

bool
operator<(Value const&, Value const&);

inline bool
operator<=(Value const& x, Value const& y)
{
    return !(y < x);
}

inline bool
operator>(Value const& x, Value const& y)
{
    return y < x;
}

inline bool
operator>=(Value const& x, Value const& y)
{
    return !(x < y);
}

/**
 * @brief Experimental do not use: Allocator to customize member name and
 * string value memory management done by Value.
 *
 * - makeMemberName() and releaseMemberName() are called to respectively
 * duplicate and free an json::ValueType::Object member name.
 * - duplicateStringValue() and releaseStringValue() are called similarly to
 *   duplicate and free a json::ValueType::String value.
 */
class ValueAllocator
{
public:
    static constexpr auto kUnknown = (unsigned)-1;

    virtual ~ValueAllocator() = default;

    virtual char*
    makeMemberName(char const* memberName) = 0;
    virtual void
    releaseMemberName(char* memberName) = 0;
    virtual char*
    duplicateStringValue(char const* value, unsigned int length = kUnknown) = 0;
    virtual void
    releaseStringValue(char* value) = 0;
};

/**
 * @brief base class for Value iterators.
 */
class ValueIteratorBase
{
public:
    using size_t = unsigned int;
    using difference_type = int;
    using SelfType = ValueIteratorBase;

    ValueIteratorBase();

    explicit ValueIteratorBase(Value::ObjectValues::iterator const& current);

    bool
    operator==(SelfType const& other) const
    {
        return isEqual(other);
    }

    bool
    operator!=(SelfType const& other) const
    {
        return !isEqual(other);
    }

    /**
     * Return either the index or the member name of the referenced value as a
     * Value.
     */
    [[nodiscard]] Value
    key() const;

    /**
     * Return the index of the referenced Value. -1 if it is not an ValueType::Array.
     */
    [[nodiscard]] UInt
    index() const;

    /**
     * Return the member name of the referenced Value. "" if it is not an
     * ValueType::Object.
     */
    [[nodiscard]] char const*
    memberName() const;

protected:
    [[nodiscard]] Value&
    deref() const;

    void
    increment();

    void
    decrement();

    [[nodiscard]] difference_type
    computeDistance(SelfType const& other) const;

    [[nodiscard]] bool
    isEqual(SelfType const& other) const;

    void
    copy(SelfType const& other);

private:
    Value::ObjectValues::iterator current_;
    // Indicates that iterator is for a null value.
    bool isNull_;
};

/**
 * @brief const iterator for object and array value.
 */
class ValueConstIterator : public ValueIteratorBase
{
    friend class Value;

public:
    using size_t = unsigned int;
    using difference_type = int;
    using value_type = Value const;
    // std::iterator_traits needs value_type and iterator_category to classify
    // this as a Cpp17InputIterator; without them it defaults to output-only,
    // which breaks standard algorithms (e.g. std::all_of). The iterator walks a
    // map both ways via ++/--, so it is bidirectional.
    using iterator_category = std::bidirectional_iterator_tag;
    using reference = Value const&;
    using pointer = Value const*;
    using SelfType = ValueConstIterator;

    ValueConstIterator() = default;
    ValueConstIterator(ValueConstIterator const& other) = default;

private:
    /**
     * @internal Use by Value to create an iterator.
     */
    explicit ValueConstIterator(Value::ObjectValues::iterator const& current);

public:
    SelfType&
    operator=(SelfType const& other);

    SelfType
    operator++(int)
    {
        SelfType const temp(*this);
        ++*this;
        return temp;
    }

    SelfType
    operator--(int)
    {
        SelfType const temp(*this);
        --*this;
        return temp;
    }

    SelfType&
    operator--()
    {
        decrement();
        return *this;
    }

    SelfType&
    operator++()
    {
        increment();
        return *this;
    }

    reference
    operator*() const
    {
        return deref();
    }
};

/**
 * @brief Iterator for object and array value.
 */
class ValueIterator : public ValueIteratorBase
{
    friend class Value;

public:
    using size_t = unsigned int;
    using difference_type = int;
    // See ValueConstIterator: value_type and iterator_category are required for
    // std::iterator_traits to treat this as a bidirectional iterator.
    using value_type = Value;
    using iterator_category = std::bidirectional_iterator_tag;
    using reference = Value&;
    using pointer = Value*;
    using SelfType = ValueIterator;

    ValueIterator() = default;
    ValueIterator(ValueConstIterator const& other);
    ValueIterator(ValueIterator const& other);

private:
    /**
     * @internal Use by Value to create an iterator.
     */
    explicit ValueIterator(Value::ObjectValues::iterator const& current);

public:
    SelfType&
    operator=(SelfType const& other);

    SelfType
    operator++(int)
    {
        SelfType const temp(*this);
        ++*this;
        return temp;
    }

    SelfType
    operator--(int)
    {
        SelfType const temp(*this);
        --*this;
        return temp;
    }

    SelfType&
    operator--()
    {
        decrement();
        return *this;
    }

    SelfType&
    operator++()
    {
        increment();
        return *this;
    }

    reference
    operator*() const
    {
        return deref();
    }
};

}  // namespace json