From 3a44b8da250ffafec26a1c61cf41eeb5978f4549 Mon Sep 17 00:00:00 2001
From: Freya Murphy <freya@freyacat.org>
Date: Fri, 4 Apr 2025 00:10:16 -0400
Subject: real time clock

---
 lib/timetostr.c | 144 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 144 insertions(+)
 create mode 100644 lib/timetostr.c

(limited to 'lib')

diff --git a/lib/timetostr.c b/lib/timetostr.c
new file mode 100644
index 0000000..0d4e9a5
--- /dev/null
+++ b/lib/timetostr.c
@@ -0,0 +1,144 @@
+#include <lib.h>
+#include <time.h>
+
+static char* ABB_WEEKDAY[7] = {
+    "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
+};
+
+static char* FULL_WEEKDAY[7] = {
+    "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturady"
+};
+
+static char* ABB_MONTH[12] = {
+    "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
+};
+
+static char* FULL_MONTH[12] = {
+    "January", "Feburary", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"
+};
+
+static char *write_num(unsigned int num, unsigned int pad, char *buf, size_t n) {
+    size_t digits = 1;
+    unsigned int x = num;
+
+    while (x /= 10, x > 0) digits++;
+    if (pad == 0) pad = digits;
+
+    for (size_t i = 0; i < pad; i++) {
+
+        size_t digit;
+        if (i >= digits) {
+            digit = 0;
+        } else {
+            digit = num % 10;
+            num /= 10;
+        }
+
+        if (pad - i - 1 >= n) continue;
+        buf[pad - i - 1] = '0' + digit;
+
+    }
+
+    if (pad > n) pad = n;
+
+    return buf + pad;
+}
+
+void timetostr(time_t *time, char *format, char *buf, size_t n) {
+    char *index = buf;
+    char c;
+    int space;
+
+    while (
+        c = *format++,
+        space = (buf + n) - index,
+        c != '\0' && space > 0
+    ) {
+        if (c != '%') {
+            *index++ = c;
+            continue;
+        } else {
+            c = *format++;
+        }
+
+        switch (c) {
+            case '%':
+                *index++ = '%';
+                break;
+            case 'a':
+                index = strncpy(index, ABB_WEEKDAY[time->wday], space);
+                break;
+            case 'A':
+                index = strncpy(index, FULL_WEEKDAY[time->wday], space);
+                break;
+            case 'b':
+            case 'h':
+                index = strncpy(index, ABB_MONTH[time->mon], space);
+                break;
+            case 'B':
+                index = strncpy(index, FULL_MONTH[time->mon], space);
+                break;
+            case 'C':
+                index = write_num(time->cen, 0, index, space);
+                break;
+            case 'd':
+                index = write_num(time->mday, 2, index, space);
+                break;
+            case 'H':
+                index = write_num(time->hour, 2, index, space);
+                break;
+            case 'I':
+                index = write_num((time->hour + 12) % 12 + 1, 2, index, space);
+                break;
+            case 'j':
+                index = write_num(time->yday, 3, index, space);
+                break;
+            case 'm':
+                index = write_num(time->mon + 1, 2, index, space);
+                break;
+            case 'M':
+                index = write_num(time->min, 2, index, space);
+                break;
+            case 'n':
+                *index++ = '\n';
+                break;
+            case 'p':
+                index = strncpy(index, time->hour > 11 ? "PM" : "AM", space);
+                break;
+            case 'P':
+                index = strncpy(index, time->hour > 11 ? "pm" : "am", space);
+                break;
+            case 'q':
+                index = write_num((time->mon + 3) / 3, 0, index, space);
+                break;
+            case 'S':
+                index = write_num(time->sec, 2, index, space);
+                break;
+            case 't':
+                *index++ = '\t';
+                break;
+            case 'u':
+                index = write_num(((time->wday + 1 )% 7) + 1, 0, index, space);
+                break;
+            case 'w':
+                index = write_num(time->wday, 0, index, space);
+                break;
+            case 'y':
+                index = write_num(time->yn, 2, index, space);
+                break;
+            case 'Y':
+                index = write_num(time->year + 1900, 0, index, space);
+                break;
+            default: {
+                char b[3] = {'%', c, '\0'};
+                index = strncpy(index, b, space);
+                break;
+            }
+        }
+    }
+
+    if (space < 1)
+        buf[n - 1] = '\0';
+    else
+        *index = '\0';
+}
-- 
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