// SPDX-FileCopyrightText: 2026 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
// SPDX-License-Identifier: GPL-3.0-only

#include "ViewerTheme.h"

#include <QApplication>
#include <QChart>
#include <QPalette>
#include <QSettings>
#include <QStyle>
#include <QStyleHints>
#include <QWidget>

namespace {
    bool dark_theme = false;

    const QColor DARK_WINDOW(0x1A, 0x1D, 0x3A);   // a deep indigo
    const QColor DARK_TEXT(0xE3, 0xE7, 0xEC);

    bool SystemIsDark() {
#if QT_VERSION >= QT_VERSION_CHECK(6, 5, 0)
        return QGuiApplication::styleHints()->colorScheme() == Qt::ColorScheme::Dark;
#else
        return false;
#endif
    }

    // Text roles are set for the active and inactive groups only, so disabled text keeps the greyed
    // colour the palette derived for it.
    void SetTextColor(QPalette &pal, const QColor &color) {
        for (auto group: {QPalette::Active, QPalette::Inactive})
            for (auto role: {QPalette::WindowText, QPalette::Text, QPalette::ButtonText, QPalette::ToolTipText})
                pal.setColor(group, role, color);
    }

    // Salmon panels, white entry fields that fall back to salmon when disabled, and a navy accent for
    // selections and progress-bar chunks. It starts from Fusion's own (light) palette, not the system
    // one, which is dark under a dark OS theme; the text is set to black because on macOS the palette's
    // text colours come from the platform theme and are grey.
    QPalette LightPalette() {
        QPalette pal = QApplication::style()->standardPalette();
        pal.setColor(QPalette::Window, QColor(255, 235, 230));
        pal.setColor(QPalette::Base, Qt::white);
        pal.setColor(QPalette::AlternateBase, QColor(255, 245, 242));
        pal.setColor(QPalette::Button, QColor(255, 235, 230));
        pal.setColor(QPalette::Disabled, QPalette::Base, QColor(255, 235, 230));
        pal.setColor(QPalette::Highlight, QColor(0x1f, 0x3a, 0x5f));
        pal.setColor(QPalette::HighlightedText, Qt::white);
        SetTextColor(pal, Qt::black);
        return pal;
    }

    // The same layout in the dark: indigo panels, entry fields darker still, and a lighter navy for
    // selections so they stand out from the panels. QPalette(button) derives the bevel shades and the
    // disabled text from the one colour.
    QPalette DarkPalette() {
        QPalette pal(DARK_WINDOW);
        pal.setColor(QPalette::Window, DARK_WINDOW);
        pal.setColor(QPalette::Base, QColor(0x12, 0x14, 0x2B));
        pal.setColor(QPalette::AlternateBase, QColor(0x24, 0x28, 0x4A));
        pal.setColor(QPalette::Button, DARK_WINDOW);
        pal.setColor(QPalette::Disabled, QPalette::Base, DARK_WINDOW);
        pal.setColor(QPalette::ToolTipBase, QColor(0x2A, 0x2E, 0x55));
        pal.setColor(QPalette::Highlight, QColor(0x2F, 0x5A, 0x8F));
        pal.setColor(QPalette::HighlightedText, Qt::white);
        pal.setColor(QPalette::Link, QColor(0x8A, 0xB4, 0xF8));
        pal.setColor(QPalette::PlaceholderText, QColor(0x80, 0x84, 0xA8));
        SetTextColor(pal, DARK_TEXT);
        // The derived disabled text is nearly the panel colour, so a greyed-out field looked empty.
        // A muted lavender still reads (about 4.8:1 on the panels, against 13:1 for normal text).
        for (auto role: {QPalette::WindowText, QPalette::Text, QPalette::ButtonText})
            pal.setColor(QPalette::Disabled, role, QColor(0x85, 0x8A, 0xAE));
        return pal;
    }

    void ApplyTheme() {
        const ThemeChoice choice = LoadThemeChoice();
#if QT_VERSION >= QT_VERSION_CHECK(6, 8, 0)
        // Once the application has asked for a scheme, Qt reports that scheme instead of the desktop's,
        // so the request is withdrawn before System looks at what the desktop is using.
        if (choice == ThemeChoice::System)
            QGuiApplication::styleHints()->setColorScheme(Qt::ColorScheme::Unknown);
#endif
        dark_theme = choice == ThemeChoice::Dark || (choice == ThemeChoice::System && SystemIsDark());
#if QT_VERSION >= QT_VERSION_CHECK(6, 8, 0)
        // The window frame is drawn by the OS (macOS, Windows), not by Qt, and follows the desktop's
        // scheme unless the application asks for one - as apps with their own theme switch do, so the
        // title bar matches the window under it.
        if (choice != ThemeChoice::System)
            QGuiApplication::styleHints()->setColorScheme(dark_theme ? Qt::ColorScheme::Dark
                                                                     : Qt::ColorScheme::Light);
#endif
        QApplication::setPalette(dark_theme ? DarkPalette() : LightPalette());
        // With an application stylesheet in place, widgets take their palette when they are polished
        // and do not see a later palette change; setting the stylesheet again re-polishes them all.
        // Fusion fills QGroupBox interiors with a flat colour of its own; transparent makes them show
        // the window background like the rest of the UI (the dock resize handles are drawn by
        // SeparatorHandleStyle, not the stylesheet).
        qApp->setStyleSheet("QGroupBox { background-color: transparent; }");
        emit ThemeNotifier::Instance()->changed();
    }
}

ThemeNotifier *ThemeNotifier::Instance() {
    static ThemeNotifier notifier;
    return &notifier;
}

ThemeChoice LoadThemeChoice() {
    const QString value = QSettings("PSI", "jfjoch_viewer").value("theme", "system").toString();
    if (value == "light") return ThemeChoice::Light;
    if (value == "dark") return ThemeChoice::Dark;
    return ThemeChoice::System;
}

void SetThemeChoice(ThemeChoice choice) {
    const char *value = "system";
    if (choice == ThemeChoice::Light) value = "light";
    if (choice == ThemeChoice::Dark) value = "dark";
    QSettings("PSI", "jfjoch_viewer").setValue("theme", value);
    ApplyTheme();
}

void InitTheme() {
    ApplyTheme();
#if QT_VERSION >= QT_VERSION_CHECK(6, 5, 0)
    // Re-applied on any desktop scheme change, not only under System: the palette set here must also
    // survive the platform reacting to the change with a palette of its own.
    QObject::connect(QGuiApplication::styleHints(), &QStyleHints::colorSchemeChanged,
                     ThemeNotifier::Instance(), [] { ApplyTheme(); });
#endif
}

bool DarkTheme() {
    return dark_theme;
}

void SetThemedStyleSheet(QWidget *widget, const std::function<QString()> &style) {
    widget->setStyleSheet(style());
    QObject::connect(ThemeNotifier::Instance(), &ThemeNotifier::changed, widget,
                     [widget, style] { widget->setStyleSheet(style()); });
}

QColor AccentTextColor() {
    return dark_theme ? QColor(0x9D, 0xBB, 0xE3) : QColor(0x1F, 0x3A, 0x5F);
}

QColor IconInkColor() {
    return dark_theme ? DARK_TEXT : QColor(0x2B, 0x2B, 0x2B);
}

QString SliderStyle() {
    // On the dark panels the navy handle would vanish, so it takes the light blue of the headings.
    const QString groove = dark_theme ? "#363A66" : "#F3D9D4";
    const QString handle = dark_theme ? "#9DBBE3" : "#1F3A5F";
    const QString handle_hover = dark_theme ? "#BCD2EE" : "#16314F";
    return QString(
        "QSlider::groove:horizontal { height:6px; background:%1; border-radius:3px; }"
        "QSlider::sub-page:horizontal { background:#FA7268; border-radius:3px; }"
        "QSlider::handle:horizontal { background:%2; width:14px; margin:-5px 0; border-radius:7px; }"
        "QSlider::handle:horizontal:hover { background:%3; }").arg(groove, handle, handle_hover);
}

void StyleChart(QChart *chart) {
    chart->setTheme(dark_theme ? QChart::ChartThemeDark : QChart::ChartThemeLight);
    if (dark_theme)
        chart->setBackgroundBrush(QApplication::palette().color(QPalette::Base));
}