From 70a99b708003b982ca96ee2fdc1b9446d6f8e23d Mon Sep 17 00:00:00 2001
From: Roman Sivriver <roman@rsiv.net>
Date: Thu, 4 Apr 2024 11:02:46 -0400
Subject: [PATCH] Fixed weekly report week number calculation to match ISO 8601
 week definition

January 1st belongs to the last week of the previous year if it falls on Friday, Saturday or Sunday
This caused an incorrect week in the date selector and showed an empty report for the next week
---
 .../templates/weekly_report.html              | 26 ++++++++++++-------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/birdcage_frontend/templates/weekly_report.html b/birdcage_frontend/templates/weekly_report.html
index 7dae2a2..0667d04 100644
--- a/birdcage_frontend/templates/weekly_report.html
+++ b/birdcage_frontend/templates/weekly_report.html
@@ -77,8 +77,7 @@ <h3 id="report-summary">Total Detections: 0 | Unique Species: 0</h3>
         const [year, week] = weekString.split('-W');
 
         // Calculate the start of the week (Monday)
-        const start = new Date(year, 0, (week) * 7 + 1);
-        start.setDate(start.getDate() - (start.getDay() + 6) % 7);
+        const start = getMondayOfWeek(weekString);
 
         // Calculate the end of the week (Sunday)
         const end = new Date(start);
@@ -157,13 +156,19 @@ <h3 id="report-summary">Total Detections: 0 | Unique Species: 0</h3>
             });
     }
 
-
-    function getWeekNumber(date) {
-        const firstDayOfYear = new Date(date.getFullYear(), 0, 1);
-        const dayOfYear = (date - firstDayOfYear + (86400000 /* ms per day */ * (firstDayOfYear.getDay() + 1))) / 86400000;
-        return Math.ceil(dayOfYear / 7);
+    function getWeekYear(date) {
+        const thursday = new Date(date);
+        thursday.setDate(thursday.getDate() + 3 - (thursday.getDay() + 6) % 7);
+        return thursday.getFullYear();
     }
 
+    function getWeekNumber(date) {
+        const thursday = new Date(date);
+        thursday.setDate(thursday.getDate() + 3 - (thursday.getDay() + 6) % 7);
+        const firstWeek = new Date(thursday.getFullYear(), 0, 4);
+        return 1 + Math.round(((thursday.getTime() - firstWeek.getTime()) / 86400000 - 3 + (firstWeek.getDay() + 6) % 7) / 7);
+    }  
+    
     document.addEventListener('DOMContentLoaded', function () {
         flatpickr('#week-picker', {
             weekNumbers: true,
@@ -172,7 +177,7 @@ <h3 id="report-summary">Total Detections: 0 | Unique Species: 0</h3>
             onChange: function (selectedDates, dateStr, instance) {
                 if (selectedDates.length > 0) {
                     const selectedDate = selectedDates[0];
-                    const selectedWeek = selectedDate.getFullYear() + "-W" + getWeekNumber(selectedDate);
+                    const selectedWeek = getWeekYear(selectedDate) + "-W" + getWeekNumber(selectedDate);
                     instance.input.value = selectedWeek;
                     // Redirect to the new URL for the selected week
                     const newUrl = `{{ script_name }}/weekly_report/${selectedWeek}`;
@@ -185,7 +190,10 @@ <h3 id="report-summary">Total Detections: 0 | Unique Species: 0</h3>
     function getMondayOfWeek(weekString) {
         const [year, week] = weekString.split('-W');
         const date = new Date(year, 0, (week) * 7 + 1);
-        date.setDate(date.getDate() - (date.getDay() + 6) % 7);
+        if (date.getDay() <= 4) {
+            date.setDate(date.getDate() - 7);
+        }
+        date.setDate(date.getDate() - date.getDay() + 1);
         return date;
     }