First commit, introduction message added

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Development Commands
+
+- **Build**: Compile the GTK application using the Makefile:
+  ```sh
+  make
+  ```
+  Or manually with gcc:
+  ```sh
+  gcc -o sprechen sprechen.c `pkg-config --cflags --libs gtk4`
+  ```
+
+- **Run**: Execute the built binary:
+  ```sh
+  make run
+  ```
+  or
+  ```sh
+  ./sprechen
+  ```
+
+- **Clean**: Remove compiled binaries:
+  ```sh
+  make clean
+  ```
+  or
+  ```sh
+  rm -f sprechen
+  ```
+
+- **Format**: If using clang-format, run:
+  ```sh
+  clang-format -i *.c *.h
+  ```
+
+- **Lint**: Use `clang-tidy` or `cppcheck` for static analysis:
+  ```sh
+  clang-tidy sprechen.c -- `pkg-config --cflags gtk4`
+  ```
+  or
+  ```sh
+  cppcheck --enable=all sprechen.c
+  ```
+
+- **Test**: Currently no test framework is integrated. To add unit tests, consider using a lightweight framework like `check` or `cmocka`. Tests can be compiled and run similarly.
+
+## Project Structure
+
+- **Root**: Contains the CLAUDE.md, README.md, .gitignore, LICENSE, Makefile, and source files.
+- **Source**: The main application resides in a single C file (`sprechen.c`) that uses GTK 4 for the graphical interface.
+- **Build Artifacts**: Compiled binaries are placed in the project root by default; consider using a `build/` directory for out-of-source builds.
+- **Dependencies**: Requires GTK 4 development libraries. On macOS, install via Homebrew: `brew install gtk4`. On Linux, use your package manager (e.g., `sudo apt install libgtk-4-dev`).
+
+## Architecture Overview
+
+The application is a simple GUI program written in C using GTK 4. It features:
+- A main window with a title "Sprechen.c".
+- A vertical box layout containing a centered label with welcome text.
+- Custom CSS styling for a gradient background and styled label box.
+- The text size scales dynamically with the window width to ensure readability on different screen sizes.
+- The GTK application lifecycle is managed via `GtkApplication`, with activation callback setting up the UI.
+
+Future extensions may include:
+- Additional widgets for language lessons (buttons, text entry, progress bars).
+- Separation of UI code into multiple files (e.g., `ui.c`, `ui.h`).
+- Lesson data structures and loading from external files (JSON or plain text).
+- Internationalization support using gettext.
+
+## Notes
+
+- Ensure GTK 4 is installed and accessible via pkg-config.
+- The code adheres to GTK 4 conventions and uses CSS for styling.
+- When modifying the UI, consider keeping the CSS in a separate file for maintainability, though currently it is embedded for simplicity.

sprechen.c

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+#include <gtk/gtk.h>
+#include <glib.h>
+#include <string.h>
+
+typedef struct {
+    GtkWidget *label;
+    GtkCssProvider *provider;
+} ScaleData;
+
+static void
+on_window_notify (GObject *object,
+                  GParamSpec *pspec,
+                  gpointer user_data)
+{
+    // We get the ScaleData from the window
+    ScaleData *scale_data = g_object_get_data(G_OBJECT(object), "scale-data");
+    if (!scale_data || !scale_data->label || !scale_data->provider)
+        return;
+
+    GtkWidget *window = GTK_WIDGET(object);
+    int width;
+    g_object_get(window, "width", &width, NULL);
+
+    // Calculate font size in points based on width
+    // Base: 600px width -> 18 points
+    double points_per_pixel = 18.0 / 600.0;
+    double font_size_points = width * points_per_pixel;
+    // Clamp between 10 and 24 points
+    if (font_size_points < 10.0) font_size_points = 10.0;
+    if (font_size_points > 24.0) font_size_points = 24.0;
+
+    // Update the CSS provider with the new font size
+    char *css_data = g_strdup_printf(
+        "window {"
+        "   background-color: #2E3440;"
+        "   background-image: linear-gradient(135deg, #2E3440 0%%, #3B4252 100%%);"
+        "   color: #ECEFF4;"
+        "   font-family: \"Helvetica Neue\", Helvetica, Arial, sans-serif;"
+        "}"
+        "label {"
+        "   margin: 30px;"
+        "   padding: 30px;"
+        "   background-color: rgba(59, 66, 82, 0.8);"
+        "   border-radius: 16px;"
+        "   box-shadow: 0 8px 16px rgba(0,0,0,0.4);"
+        "   font-size: %dpt;"
+        "}",
+        (int)font_size_points);
+
+    gtk_css_provider_load_from_string(scale_data->provider, css_data);
+    g_free(css_data);
+}
+
+static void activate(GtkApplication *app, gpointer user_data) {
+    GtkWidget *window;
+    GtkWidget *box;
+    GtkWidget *label;
+    GtkCssProvider *provider;
+    ScaleData *scale_data;
+
+    // Create a new application window
+    window = gtk_application_window_new(app);
+    gtk_window_set_title(GTK_WINDOW(window), "Sprechen.c");
+    gtk_window_set_default_size(GTK_WINDOW(window), 600, 400);
+
+    // Create a vertical box to hold contents
+    box = gtk_box_new(GTK_ORIENTATION_VERTICAL, 20);
+    gtk_widget_set_halign(box, GTK_ALIGN_CENTER);
+    gtk_widget_set_valign(box, GTK_ALIGN_CENTER);
+    gtk_window_set_child(GTK_WINDOW(window), box);
+
+    // Create a label with welcome message
+    label = gtk_label_new("Vítejte ve Sprechen.C!\n\nSprechen.C je vzdělávací program na procvičování Němčiny, určený pro studenty středních škol a gymnázií. Program je napsaný v Céčku studentama ze SSŠVT!");
+    gtk_label_set_justify(GTK_LABEL(label), GTK_JUSTIFY_CENTER);
+    gtk_label_set_lines(label, -1);  // Allow multiple lines
+    gtk_label_set_xalign(label, 0.5);  // Center horizontally
+    gtk_label_set_yalign(label, 0.5);  // Center vertically
+    gtk_label_set_wrap(label, TRUE);  // Enable line wrapping
+    gtk_label_set_max_width_chars(label, 40);
+    gtk_box_append(GTK_BOX(box), label);
+
+    // Create and load CSS for beautiful background with initial font size
+    provider = gtk_css_provider_new();
+    int initial_width = 600; // default width
+    double points_per_pixel = 18.0 / 600.0;
+    double initial_font_size_points = initial_width * points_per_pixel;
+    if (initial_font_size_points < 10.0) initial_font_size_points = 10.0;
+    if (initial_font_size_points > 24.0) initial_font_size_points = 24.0;
+    char *initial_css = g_strdup_printf(
+        "window {"
+        "   background-color: #2E3440;"
+        "   background-image: linear-gradient(135deg, #2E3440 0%%, #3B4252 100%%);"
+        "   color: #ECEFF4;"
+        "   font-family: \"Helvetica Neue\", Helvetica, Arial, sans-serif;"
+        "}"
+        "label {"
+        "   margin: 30px;"
+        "   padding: 30px;"
+        "   background-color: rgba(59, 66, 82, 0.8);"
+        "   border-radius: 16px;"
+        "   box-shadow: 0 8px 16px rgba(0,0,0,0.4);"
+        "   font-size: %dpt;"
+        "}",
+        (int)initial_font_size_points);
+    gtk_css_provider_load_from_string(provider, initial_css);
+    g_free(initial_css);
+
+    // Apply CSS to the window
+    gtk_style_context_add_provider_for_display(
+        gdk_display_get_default(),
+        GTK_STYLE_PROVIDER(provider),
+        GTK_STYLE_PROVIDER_PRIORITY_USER);
+
+    // We keep the provider to update it later, so we don't unreference it yet
+    // g_object_unref(provider); // We will unreference it in the cleanup? We'll store it in ScaleData and unreference when the window is destroyed.
+
+    // Set up scaling data
+    scale_data = g_new(ScaleData, 1);
+    scale_data->label = label;
+    scale_data->provider = provider;
+    g_object_set_data_full(G_OBJECT(window), "scale-data", scale_data, g_free);
+
+    // Connect to the window's notify::width and notify::height signals
+    g_signal_connect(window, "notify::width", G_CALLBACK(on_window_notify), NULL);
+    g_signal_connect(window, "notify::height", G_CALLBACK(on_window_notify), NULL);
+
+    gtk_window_present(window);
+}
+
+int main(int argc, char **argv) {
+    GtkApplication *app;
+    int status;
+
+    app = gtk_application_new("org.example.Sprechen", G_APPLICATION_DEFAULT_FLAGS);
+    g_signal_connect(app, "activate", G_CALLBACK(activate), NULL);
+    status = g_application_run(G_APPLICATION(app), argc, argv);
+    g_object_unref(app);
+
+    return status;
+}