Determine Date of Birth from dates/ages

This is not just a simple date method anymore :P

To make it easier I would probably start collecting some information first. You can for example determine first the average age of the given dates. Based on that you can already termine the correct year right.

To get the average date (day + month) I would probably first set the same year for all dates. Then I would start determining the difference between the days of these dates. Based on this you can also determine an average date just like the years.

I don't have any code right now, but I can help you brainstorm this idea ;)

Something in this post will point you in the right direction:

https://laracasts.com/discuss/channels/general-discussion/scope-to-get-all-records-that-have-anniversary-within-the-next-two-weeks

between June 1 and July 31, but in 2016 she had birthday between May 30th and June 5th.

After re-reading, What? She can't have multiple birthdays.

@JLRDW - Right, she only has one birthday :) you can narrow the date down by looking at the ranges in the different years, then look at the overlap. The overlap in the years 2016 and 2018 are June 1- June 5.

Thanks for the link, I will take a read through that.

Thought more about this today and think I came up with a solution. If I normalize all the dates to a common year, and adjust the ages accordingly (change 2016 dates to 2018, and add two years to the age). I will get a "snapshot" of a single year, then be able to pluck whichever date the actual age change happened.

This code is a bit of a trainwreck right now, but seems to be working.

 $collection = collect([
        [
            'date' => \Carbon\Carbon::parse('2018-07-31'),
            'age' => 42
        ],
        [
            'date' => \Carbon\Carbon::parse('2017-09-01'),
            'age' => 41
        ],
        [
            'date' => \Carbon\Carbon::parse('2016-05-30'),
            'age' => 39
        ],
        [
            'date' => \Carbon\Carbon::parse('2016-06-05'),
            'age' => 40
        ],
        [
            'date' => \Carbon\Carbon::parse('2018-06-01'),
            'age' => 41
        ],
    ]);
    $target = 2018;
    
    $normalized=$collection->transform(function ($d) use ($target) {
        $increment = $target - $d['date']->format('Y');
        $d['date']->addYear($increment);
        $d['age'] = $d['age'] + $increment;
        return $d;
    })->sortBy('age')->sortBy('date');

    $starting_age = $normalized->first()['age'];
    $birthday=$normalized->whereNotIn('age',$starting_age)->first();
    
    dd($birthday['date']->subDay(1));