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68 lines
2.1 KiB
C++
68 lines
2.1 KiB
C++
// Copyright (c) 2026 Stefan Koelle (https://stefankoelle.de) - MIT License
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#pragma once
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#include <Arduino.h>
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// No NTP/network time used, purely computed from date strings coming from
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// the calendar API itself, as specified.
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namespace DateUtils {
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inline const char *weekdayShortDE(int isoWeekday /* 0=Mon..6=Sun */) {
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static const char *names[7] = {"Mo", "Di", "Mi", "Do", "Fr", "Sa", "So"};
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if (isoWeekday < 0 || isoWeekday > 6) return "??";
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return names[isoWeekday];
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}
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// Sakamoto's algorithm, returns 0=Monday..6=Sunday
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inline int computeWeekdayMonBased(int year, int month, int day) {
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static const int t[] = {0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4};
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int y = year;
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if (month < 3) y -= 1;
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int w = (y + y / 4 - y / 100 + y / 400 + t[month - 1] + day) % 7; // 0=Sun
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return (w + 6) % 7; // convert to 0=Mon
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}
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struct ParsedDateTime {
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bool valid = false;
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int year = 0, month = 0, day = 0, hour = 0, minute = 0;
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};
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inline ParsedDateTime parseIso(const String &iso) {
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ParsedDateTime r;
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if (iso.length() < 10) return r;
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int y = iso.substring(0, 4).toInt();
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int mo = iso.substring(5, 7).toInt();
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int d = iso.substring(8, 10).toInt();
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int h = 0, mi = 0;
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int tIdx = iso.indexOf('T');
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if (tIdx > 0 && iso.length() >= tIdx + 6) {
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h = iso.substring(tIdx + 1, tIdx + 3).toInt();
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mi = iso.substring(tIdx + 4, tIdx + 6).toInt();
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}
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if (y == 0 || mo == 0 || d == 0) return r;
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r.valid = true;
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r.year = y; r.month = mo; r.day = d; r.hour = h; r.minute = mi;
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return r;
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}
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// "Mo 3.8. 14:00" for timed events, "Mo 3.8." for all-day events.
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inline String formatShortDE(const String &iso, bool allDay) {
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ParsedDateTime p = parseIso(iso);
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if (!p.valid) return iso;
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int wd = computeWeekdayMonBased(p.year, p.month, p.day);
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String out = String(weekdayShortDE(wd)) + " " + String(p.day) + "." + String(p.month) + ".";
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if (!allDay) {
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char buf[8];
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snprintf(buf, sizeof(buf), " %02d:%02d", p.hour, p.minute);
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out += buf;
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}
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return out;
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}
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} // namespace DateUtils
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