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usr/apps/cal.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <termios.h>
+#include <unistd.h>
+#include <sys/cervus.h>
+#include <cervus_util.h>
+
+#define A_INVERT  "\x1b[7m"
+#define A_BOLD    "\x1b[1m"
+#define A_RESET   "\x1b[0m"
+
+static const char *MNAME[12] = {
+    "January","February","March","April","May","June",
+    "July","August","September","October","November","December"
+};
+static int MDAYS[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
+
+static int is_leap(int y)
+{
+    return (y % 4 == 0 && y % 100 != 0) || (y % 400 == 0);
+}
+
+static int days_in_month(int y, int m)
+{
+    if (m == 2 && is_leap(y)) return 29;
+    return MDAYS[m - 1];
+}
+
+static int first_dow(int y, int m)
+{
+    int64_t days = 0;
+    for (int yr = 1970; yr < y; yr++) days += is_leap(yr) ? 366 : 365;
+    int md[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
+    md[1] = is_leap(y) ? 29 : 28;
+    for (int mo = 0; mo < m - 1; mo++) days += md[mo];
+    return (int)((days + 4) % 7);
+}
+
+static void get_today(int *out_y, int *out_m, int *out_d)
+{
+    *out_y = 0; *out_m = 0; *out_d = 0;
+
+    cervus_timespec_t ts;
+    if (cervus_clock_gettime(CLOCK_REALTIME, &ts) != 0 || ts.tv_sec <= 0)
+        return;
+
+    int64_t t    = ts.tv_sec;
+    int64_t days = t / 86400;
+
+    int y = 1970;
+    while (1) {
+        int dy = is_leap(y) ? 366 : 365;
+        if (days < dy) break;
+        days -= dy;
+        y++;
+    }
+
+    int md[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
+    md[1] = is_leap(y) ? 29 : 28;
+
+    int mo = 0;
+    while (mo < 12) { if (days < md[mo]) break; days -= md[mo]; mo++; }
+
+    *out_y = y;
+    *out_m = mo + 1;
+    *out_d = (int)(days + 1);
+}
+
+static void print_header(int y, int m, int today_y, int today_m)
+{
+    char title[64];
+    snprintf(title, sizeof(title), "%s %d", MNAME[m - 1], y);
+    int tlen = (int)strlen(title);
+    int pad  = (20 - tlen) / 2;
+
+    for (int i = 0; i < pad; i++) putchar(' ');
+
+    if (y == today_y && m == today_m) {
+        fputs(A_INVERT A_BOLD, stdout);
+        fputs(title, stdout);
+        fputs(A_RESET, stdout);
+    } else {
+        fputs(A_BOLD, stdout);
+        fputs(title, stdout);
+        fputs(A_RESET, stdout);
+    }
+    putchar('\n');
+    fputs(C_GRAY " Su Mo Tu We Th Fr Sa" A_RESET "\n", stdout);
+}
+
+static void print_month(int y, int m, int today_y, int today_m, int today_d)
+{
+    print_header(y, m, today_y, today_m);
+
+    int mdays = days_in_month(y, m);
+    int dow   = first_dow(y, m);
+
+    for (int i = 0; i < dow; i++) fputs("   ", stdout);
+
+    for (int d = 1; d <= mdays; d++) {
+        int is_today = (y == today_y && m == today_m && d == today_d);
+
+        if (is_today) {
+            fprintf(stdout, " " A_INVERT A_BOLD "%2d" A_RESET, d);
+        } else {
+            fprintf(stdout, " %2d", d);
+        }
+
+        if (++dow == 7) {
+            putchar('\n');
+            dow = 0;
+        }
+    }
+    if (dow != 0) putchar('\n');
+}
+
+static void print_help(void)
+{
+    fputs(
+        "Usage: cal [OPTION] [[MONTH] YEAR]\n"
+        "Display a calendar.\n"
+        "\n"
+        "  (no args)       current month\n"
+        "  YEAR            all 12 months of YEAR\n"
+        "  MONTH YEAR      specific month (MONTH = 1-12)\n"
+        "  --help          display this help and exit\n"
+        "\n"
+        "Today's day is highlighted with " A_INVERT "inverted colours" A_RESET ".\n"
+        "The current month header is also " A_INVERT "inverted" A_RESET ".\n",
+        stdout
+    );
+}
+
+int main(int argc, char **argv)
+{
+    int today_y, today_m, today_d;
+    get_today(&today_y, &today_m, &today_d);
+
+    int year  = today_y  ? today_y  : 2025;
+    int month = today_m  ? today_m  : 1;
+
+    const char *args[2] = {NULL, NULL};
+    int real_argc = 0;
+    int flag_help = 0;
+
+    for (int i = 1; i < argc; i++) {
+        if (is_shell_flag(argv[i])) continue;
+        if (strcmp(argv[i], "--help") == 0) { flag_help = 1; continue; }
+        if (real_argc < 2) args[real_argc] = argv[i];
+        real_argc++;
+    }
+
+    if (flag_help) { print_help(); return 0; }
+
+    if (real_argc == 2) {
+        month = atoi(args[0]);
+        year  = atoi(args[1]);
+    } else if (real_argc == 1) {
+        year = atoi(args[0]);
+        putchar('\n');
+        fprintf(stdout, "          " A_BOLD "%d" A_RESET "\n\n", year);
+        for (int m = 1; m <= 12; m++) {
+            print_month(year, m, today_y, today_m, today_d);
+            putchar('\n');
+        }
+        return 0;
+    }
+
+    if (month < 1 || month > 12) {
+        fputs("cal: invalid month (must be 1-12)\n", stderr);
+        return 1;
+    }
+
+    putchar('\n');
+    print_month(year, month, today_y, today_m, today_d);
+    putchar('\n');
+    return 0;
+}