1 files changed, 133 insertions, 0 deletions
diff --git a/src/calendar.cpp b/src/calendar.cpp
new file mode 100644
index 0000000..d743718
--- /dev/null
+++ b/src/calendar.cpp
@@ -0,0 +1,133 @@
+#include <GxEPD2_BW.h>
+#include <Fonts/FreeSansBold12pt7b.h>
+#include <Fonts/FreeSansBold9pt7b.h>
+#include <Fonts/FreeSans9pt7b.h>
+#include <ctime>
+
+#define CELL_SPACING 10
+
+static const char *week_days[] {
+	"Mo", "Di", "Mi", "Do", "Fr", "Sa", "So",
+};
+
+static const char *months[] {
+	"Januar", "Februar", "Maerz", "April", "Mai", "Juni", "Juli",
+	"August", "September", "Oktober", "November", "Dezember",
+};
+
+enum month_t {
+	JANUARY = 0,
+	FEBRUARY,
+	MARCH,
+	APRIL,
+	MAY,
+	JUNE,
+	JULY,
+	AUGUST,
+	SEPTEMBER,
+	OCTOBER,
+	NOVEMBER,
+	DECEMBER,
+};
+
+static int days_in_month(int month, int year) {
+	switch (month) {
+		case JANUARY:
+		case MARCH:
+		case MAY:
+		case JULY:
+		case AUGUST:
+		case OCTOBER:
+		case DECEMBER:
+			return 31;
+		case APRIL:
+		case JUNE:
+		case SEPTEMBER:
+		case NOVEMBER:
+			return 30;
+		case FEBRUARY:
+			if (year % 400 == 0) return 29;
+			if (year % 100 == 0) return 28;
+			if (year %   4 == 0) return 29;
+	}
+	assert(month >= 0 && month < 12);
+	return 0;
+}
+
+/*
+ * @display    where to draw on
+ * @x0         absolute initial X coord
+ * @y0         absolute initial Y coord
+ * @w0         width of a cell
+ * @h0         height of a cell
+ * @xoff       X pos of cell
+ * @yoff       Y pos of cell
+ * @text       text to draw
+ * @highlight  whether text should be highlighted
+ */
+static void draw_cell_content(GxEPD2_GFX_BASE_CLASS &display, int16_t x0, int16_t y0, uint16_t w0, uint16_t h0, uint8_t xoff, uint8_t yoff, String &text, bool highlight = false) {
+	int16_t x, y;
+	uint16_t w, h;
+
+	display.getTextBounds(text, 0, 0, &x, &y, &w, &h);
+
+	int16_t w_diff = w0 - w;
+	int x2 = x0 + xoff * w0 + w_diff/2 - x;
+	int y2 = y0 + yoff * h0 - y;
+
+	display.setCursor(x2, y2);
+	display.print(text);
+	if (highlight) {
+		display.drawCircle(x2 + x + w/2, y2 - h/2, (w0 - CELL_SPACING) / 2, GxEPD_BLACK);
+	}
+}
+
+void draw_calendar(GxEPD2_GFX_BASE_CLASS &display, int16_t x0, int16_t y0) {
+	struct tm now;
+	if (!getLocalTime(&now)) {
+		return;
+	}
+
+	uint8_t n_days = days_in_month(now.tm_mon, now.tm_year);
+
+	/* on which weekday is the 1st? */
+	int8_t day_of_1st = ((1 - 7 - (now.tm_mday - now.tm_wday)) % 7) + 7;
+
+	/* remap days from So-Sa = 0..6 to Mo-So = 0..6 */
+	day_of_1st = (day_of_1st - 1 + 7) % 7;
+
+	/* determine sizes */
+	int16_t x, y;
+	uint16_t w, h, cell_width, cell_height;
+	display.getTextBounds(week_days[0], 0, 0, &x, &y, &w, &h);
+	cell_width = w + CELL_SPACING;
+	cell_height = h + CELL_SPACING;
+
+	/* draw title with month and year */
+	display.setFont(&FreeSansBold12pt7b);
+	String title_text = String(months[now.tm_mon]) + " " + String(1900 + now.tm_year);
+	draw_cell_content(display, x0, y0, cell_width * 7, h, 0, 0, title_text);
+	y0 += h + 2 * CELL_SPACING;
+
+	/* draw table header with week days */
+	display.setFont(&FreeSansBold9pt7b);
+	for (int i=0; i<7; i++) {
+		String week_day = String(week_days[i]);
+		draw_cell_content(display, x0, y0, cell_width, cell_height, i, 0, week_day);
+	}
+
+	/* draw days */
+	display.setFont(&FreeSans9pt7b);
+	int8_t wday = day_of_1st;
+	uint8_t row = 1;
+	for (uint8_t day = 1; day <= n_days; day++) {
+		String day_str = String(day);
+		draw_cell_content(display, x0, y0, cell_width, cell_height, wday, row, day_str, day == now.tm_mday);
+
+		wday++;
+		if (wday > 6) {
+			wday = 0;
+			row++;
+		}
+	}
+}