// Copyright 2025 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_NATIVE_THEME_OS_SETTINGS_PROVIDER_H_
#define UI_NATIVE_THEME_OS_SETTINGS_PROVIDER_H_

#include <optional>

#include "base/callback_list.h"
#include "base/component_export.h"
#include "base/functional/callback.h"
#include "base/time/time.h"
#include "build/build_config.h"
#include "third_party/skia/include/core/SkColor.h"
#include "ui/color/color_provider_key.h"
#include "ui/native_theme/native_theme.h"

namespace ui {

#if BUILDFLAG(IS_ANDROID)
class OsSettingsProviderAndroid;
using OsSettingsProviderImpl = OsSettingsProviderAndroid;
#elif BUILDFLAG(IS_CHROMEOS)
class OsSettingsProviderAsh;
using OsSettingsProviderImpl = OsSettingsProviderAsh;
#elif BUILDFLAG(IS_MAC)
class OsSettingsProviderMac;
using OsSettingsProviderImpl = OsSettingsProviderMac;
#elif BUILDFLAG(IS_WIN)
class OsSettingsProviderWin;
using OsSettingsProviderImpl = OsSettingsProviderWin;
#else
class OsSettingsProvider;
using OsSettingsProviderImpl = OsSettingsProvider;
#endif

// A singleton used to query the operating system for theme-related settings.
// Callers should use `Get()` to obtain the current instance.
class COMPONENT_EXPORT(NATIVE_THEME) OsSettingsProvider {
 public:
  using SettingsChangedCallbackT = void(bool force_notify);

  // Higher-numbered (i.e. higher-priority) providers override lower-priority
  // ones. Within a priority class, the most-recently-created provider wins.
  enum class PriorityLevel { kProduction = 0, kTesting, kLast = kTesting };

  enum class ColorId {
    kButtonFace,
    kButtonHighlight,
    kScrollbar,
    kWindow,
    kWindowText,
  };

  // The caret blink interval reported when the OS provides no value.
  static constexpr auto kDefaultCaretBlinkInterval = base::Milliseconds(500);

  // Creating a provider sets it as the object to be returned by `Get()`.
  //
  // NOTE: If you want to control behavior in tests, you probably want to use
  // `MockOsSettingsProvider` instead of instantiating this or some other
  // subclass.
  explicit OsSettingsProvider(
      PriorityLevel priority_level = PriorityLevel::kProduction);

  OsSettingsProvider(const OsSettingsProvider&) = delete;
  OsSettingsProvider& operator=(const OsSettingsProvider&) = delete;

  // Unhooks this provider from the list of providers checked by `Get()`.
  // Typically, this provider was the currently-active one, which means the
  // previous provider will become active.
  virtual ~OsSettingsProvider();

  // Returns the most recently-constructed `OsSettingsProvider` that has not
  // been destroyed. If there is no such provider, first creates an instance of
  // `OsSettingsProviderImpl`.
  //
  // CAUTION: On Windows, this will not create an `OsSettingsProviderWin`
  // outside the browser process, since it won't work elsewhere (due to sandbox)
  // and shouldn't be needed anyway. It will still return a non-null pointer,
  // but the default instance will be the base `OsSettingsProvider`, not the
  // platform-specific one.
  static OsSettingsProvider& Get();

  // Registers a callback to be invoked when the OS settings change. The
  // `force_notify` argument will be true if settings may have changed in a way
  // that does not affect the return values of the functions below, but
  // nevertheless should trigger theme updates. For example, a change that does
  // not affect the default `ColorProviderKey`, but affects the values of colors
  // inside that key's provider, would set this to `true`.
  static base::CallbackListSubscription RegisterOsSettingsChangedCallback(
      base::RepeatingCallback<SettingsChangedCallbackT> cb);

  // Returns whether the dark color scheme is available at an OS level.
  // NOTE: Even if this is false, it may be reasonable for Chrome to use a dark
  // theme; see comments on `PreferredColorScheme()` below.
  virtual bool DarkColorSchemeAvailable() const;

  // Returns preferred color scheme based on OS-level factors, or
  // `kNoPreference` if not set/applicable. This is not affected by e.g.
  // `switches::kForceDarkMode`; that should be handled at the `NativeTheme`
  // (i.e. caller) level.
  // NOTE: It's possible for this to be `kDark` even if
  // `DarkColorSchemeAvailable()` returns false, e.g. when the OS has no notion
  // of a native "dark scheme" but is using colors that correspond to Chrome
  // using a dark theme. A historical example would have been the "high contrast
  // black" theme in old versions of Windows.
  virtual NativeTheme::PreferredColorScheme PreferredColorScheme() const;

  // Returns the appropriate material color palette source for this OS.
  virtual ColorProviderKey::UserColorSource PreferredColorSource() const;

  // Returns OS-level preferred contrast, or `kNoPreference` if not
  // set/applicable. This is not affected by e.g.
  // `switches::kForceHighContrast`; that should be handled at the `NativeTheme`
  // (i.e. caller) level.
  virtual NativeTheme::PreferredContrast PreferredContrast() const;

  // Returns whether the OS prefers reduced transparency.
  virtual bool PrefersReducedTransparency() const;

  // Returns whether the OS prefers inverted colors.
  virtual bool PrefersInvertedColors() const;

  // Returns whether forced colors are active at the OS level. This implies that
  // various methods above should check `Color()` to decide how to behave. (They
  // do not do so by default because when forced colors are not active, system
  // colors may give an incomplete or incorrect picture of desired behavior.)
  // This is not affected by e.g. "page colors"; that should be handled at the
  // `NativeTheme` (i.e. caller) level.
  virtual bool ForcedColorsActive() const;

  // Returns OS-level accent color, if any.
  virtual std::optional<SkColor> AccentColor() const;

  // Returns OS-level colors, if available.
  virtual std::optional<SkColor> Color(ColorId color_id) const;

  // Returns OS' current scheme variant, if any.
  virtual std::optional<ColorProviderKey::SchemeVariant> SchemeVariant() const;

  // Returns the interval between caret blinks. If this is zero, the caret will
  // not blink.
  virtual base::TimeDelta CaretBlinkInterval() const;

 protected:
  // Invokes all registered callbacks.
  void NotifyOnSettingsChanged(bool force_notify = false);

 private:
  PriorityLevel priority_level_;
};

}  // namespace ui

#endif  // UI_NATIVE_THEME_OS_SETTINGS_PROVIDER_H_