/* SPDX-FileCopyrightText: 2026 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

#pragma once

#include <atomic>
#include <string>
#include <string_view>

#ifdef WITH_WEB
/* The Web data target does not compile OpenImageIO. Keep the UString API
 * available for DNA/node data while using a deterministic local representation. */
#else
#include <OpenImageIO/ustring.h>
#endif

#include "BLI_fixed_string.hh"
#include "BLI_hash.hh"
#include "BLI_string_ref.hh"

namespace blender {

/**
 * This is a thin wrapper around OpenImageIO's ustring class. Additionally it also provides
 * conversions to our StringRef types.
 *
 * See the OpenImageIO documentation for more details:
 * https://openimageio.readthedocs.io/en/stable/imageioapi.html#efficient-unique-strings-ustring
 */
class UString {
 private:
  /**
   * Using a member instead of inheritance because it simplifies avoiding various ambiguities with
   * operator overloads (especially equality comparison between UString, StringRef, std::string,
   * std::string_view, OpenImageIO::string_view, etc.).
   */
#ifdef WITH_WEB
  std::string ustr_;
#else
  OIIO::ustring ustr_;
#endif

 public:
  UString() = default;
#ifdef WITH_WEB
  explicit UString(const char *str) : ustr_(str ? str : "") {}
  explicit UString(const StringRef str) : ustr_(std::string_view(str)) {}
#else
  explicit UString(const StringRef str) : ustr_(std::string_view(str)) {}
#endif

  /** A constructor that is meant to generate as little code as possible at the call site. */
  static UString from_ptr_noinline(const char *str);

  /**
   * Access the underlying string as a #StringRefNull.
   *
   * Note: This is not an implicit conversion to work around ambiguous function calls.
   */
  StringRefNull ref() const
  {
#ifdef WITH_WEB
    return StringRefNull(ustr_.c_str(), ustr_.length());
#else
    return StringRefNull(ustr_.c_str(), ustr_.length());
#endif
  }

  const std::string &string() const
  {
#ifdef WITH_WEB
    return ustr_;
#else
    return ustr_.string();
#endif
  }

  const char *c_str() const
  {
    return ustr_.c_str();
  }

  friend bool operator==(const UString &a, const UString &b)
  {
    return a.ustr_ == b.ustr_;
  }

  friend bool operator==(const UString &a, const StringRef b)
  {
    return a.ref() == b;
  }

  uint64_t hash() const
  {
#ifdef WITH_WEB
    /* FNV-1a is stable across native/Web builds and does not require OIIO. */
    uint64_t result = UINT64_C(14695981039346656037);
    for (const unsigned char byte : ustr_) {
      result ^= byte;
      result *= UINT64_C(1099511628211);
    }
    return result;
#else
    return ustr_.hash();
#endif
  }

  int64_t size() const
  {
    return int64_t(ustr_.size());
  }

  bool is_empty() const
  {
    return ustr_.empty();
  }

  char operator[](const int64_t i) const
  {
    /* Accessing null char at end is allowed too. */
    BLI_assert(i >= 0 && i <= this->size());
    return ustr_[i];
  }
};

/**
 * Define DefaultHash for UString keys so that it uses the cached hash on ustrings but also
 * supports hashing arbitrary (non-unique) strings in the same way.
 *
 * Note: The string hashes produced here are different from e.g. DefaultHash<StringRef>. That is
 * fine though. The only requirement is that all hashes defined in this template specialization are
 * compatible with each other.
 */
template<> struct DefaultHash<UString> {
  uint64_t operator()(const UString &value) const
  {
    return value.hash();
  }

  constexpr uint64_t operator()(const StringRef value) const
  {
#ifdef WITH_WEB
    uint64_t result = UINT64_C(14695981039346656037);
    for (const unsigned char byte : value) {
      result ^= byte;
      result *= UINT64_C(1099511628211);
    }
    return result;
#else
    /* This is the hash function used by OpenImageIO::ustring::make_unique internally. */
    return OIIO::Strutil::strhash64(value.size(), value.data());
#endif
  }
};

/**
 * Create a UString from a string literal. This is a template function so that each string is only
 * made unique once and not every time the literal is used.
 *
 * Note: OpenImageIO defines a similar `_us` string literal operator. However, it newly constructs
 * the ustring in each invocation instead of caching it in a static variable. Caching it like here
 * likely only works in C++20.
 */
template<FixedString FStr> inline UString operator""_ustr()
{
  static const UString static_ustr = UString::from_ptr_noinline(FStr.data);
  return static_ustr;
}

/**
 * Support using the `fmt` library with #UString.
 */
inline std::string_view format_as(UString str)
{
  return str.string();
}

}  // namespace blender

/**
 * Disable conflicting range formatter in fmtlib. Otherwise we will get compile errors
 * where fmtlib doesn't know if it should use the formatter from format.h or ranges.h.
 */
namespace fmt {

template<> struct is_range<blender::UString, char> : std::false_type {};

}  // namespace fmt