Add some date utility functions

lib/dates.php

@@ -0,0 +1,90 @@
+<?php
+
+/**
+ * Some handy date calculations.
+ * 
+ * License exception: this code file can be used under the MIT License.
+ */
+
+/**
+ * Convert some number of seconds into hours:minutes:seconds.
+ * @param Integer $seconds Some integer number.
+ * @param Boolean $showseconds True if the returned string should show a 
+ * seconds value.
+ * @return String
+ */
+function seconds2string($seconds, $showseconds = true) {
+    // Thanks to https://stackoverflow.com/a/34681477
+    return floor($seconds / 3600) . gmdate(($showseconds ? ":i:s" : ":i"), $seconds % 3600);
+}
+
+/**
+ * Gets the timestamp of the first instant of the current week.
+ * 
+ * If $firstday = "Monday", this will return a value equal to midnight on the 
+ * previous Monday, unless it is Monday, in which case this will return the 
+ * timestamp of 00:00 (12:00am) last night.
+ * 
+ * <b>Examples:</b>
+ * 
+ * Current date is Tuesday June 3rd, $firstday is Monday, this returns
+ * a value equal to 12:00am Monday June 2nd.
+ * 
+ * Current date is Monday June 2nd, $firstday is Monday, this returns 12:00am 
+ * Monday June 2nd.
+ * 
+ * @param String $firstday "Sunday", "Monday", etc.  Default "Sunday".
+ * @return Integer UNIX timestamp of when the week started.
+ */
+function getstartofweek($firstday = "Sunday") {
+    if (date("z") - date("z", strtotime("last " . $firstday)) >= 7) {
+        // Today is the start of the week
+        $weekstart = strtotime($firstday);
+    } else {
+        // Today is not the start of the week
+        $weekstart = strtotime("last " . $firstday);
+    }
+    return $weekstart;
+}
+
+/**
+ * Formats the date string or timestamp for MySQL.
+ * @param Integer/String $time A UNIX timestamp or date/time string.
+ * @return String Y-m-d H:i:s
+ */
+function sqldatetime($time) {
+    if (is_numeric($time)) {
+        return date("Y-m-d H:i:s", $time);
+    }
+    return date("Y-m-d H:i:s", strtotime($time));
+}
+
+/**
+ * Given an array of time ranges, calculates the sum of all those ranges.
+ * @param Array $times [["2017-06-20 12:23:34","2017-06-20 15:56:00"],["Monday", "Tuesday"],...,[12345678,12345890]]
+ * @return Integer A number of seconds.
+ */
+function sumelapsedtimearray($times) {
+    $totalseconds = 0;
+    foreach ($times as $t) {
+        $curtime = time();
+        if (is_null($t[0])) {
+            $t[0] = $curtime;
+        }
+        if (is_null($t[1])) {
+            $t[1] = $curtime;
+        }
+        
+        $t0 = (is_numeric($t[0]) ? $t[0] * 1 : strtotime($t[0]));
+        $t1 = (is_numeric($t[1]) ? $t[1] * 1 : strtotime($t[1]));
+        
+        if ($t1 == $t0) {
+            // The times are equal, so we don't need to add anything
+            continue;
+        }
+
+        $diff = abs($t1 - $t0);
+        $totalseconds += $diff;
+    }
+    return $totalseconds;
+}