📅 Comprehensive Day of Week Analyzer

🎯 What is the Comprehensive Day of Week Analyzer?

The **Day of Week Analyzer** is more than a simple calendar tool; it is a full-spectrum utility providing deep metrics for any given date. It instantly calculates the exact day of the week, crucial calendar statistics like the ISO Week Number and Day of Year, and provides a comparative analysis by calculating the interval difference between two dates, including the count of **Business Days**.

💡 Why You Need This Tool and Its Purpose

Date analysis is critical in business, finance, and logistics, where precision scheduling is mandatory. The purpose of this tool is to:

1. **Provide Calendar Context:** Determine the Week Number (essential for fiscal reporting) and Quarter for project tracking.
2. **Simplify Scheduling:** Instantly check if a date falls on a weekend and see how many working days remain in the year.
3. **Calculate Business Time:** Accurately calculate the elapsed time between two points in terms of **Total Days** and **Business Days**, necessary for deadline management and legal agreements.

⚙️ How This Calculator Works: Date Logic and Statistical Formulas

This tool utilizes the robust JavaScript `Date` object and custom functions to perform complex date computations:

1. Day of Year and Days Left:

The **Day of Year** ($\text{D}_{\text{Y}}$) is calculated by finding the difference between the target date and January 1st of the same year. The total days in the year ($\text{D}_{\text{Total}}$) is 365 or 366 (if a Leap Year). $$ \text{Days Left} = \text{D}_{\text{Total}} - \text{D}_{\text{Y}} $$

2. Week Number (ISO Standard):

The ISO 8601 standard for week numbers states that Week 1 is the first week containing a Thursday. The calculation involves finding the Thursday of the week and seeing how many days it is from the start of the year.

3. Date Difference and Business Days:

The difference between Date 1 ($\text{D}_1$) and Date 2 ($\text{D}_2$) is found by dividing the milliseconds between them by the milliseconds in a day. The **Business Days** calculation involves iterating through each day in the interval and counting only days with an index 1 (Monday) through 5 (Friday).