combination of HTML/PHP

Using a combination of HTML/PHP, implement a web page where the users can upload a text file, exclusively in .txt format, which contains a string of 400 numbers, such as:

7163626956188267042885861560789112949495657273330010533678815258490771167055601353697817977846174064839722413756570560578216637048440319989096983520312774506326125406987471585238636689664895044524452305886116467109405077164271714799244429281786645835912456652924219022671055626321071984038509624554448458015616609791913362229893423380308135731671765313306249193035890729629049156070172427121883998797

Your code should contain a PHP function that, accepting the string of 400 numbers in input, is able to find the greatest product of four adjacent numbers in all the four possible directions (up, down, left, right, or diagonally).

NOTE:

• You will need to arrange the numbers in a grid of 20×20.
• If the file doesn’t contain 400 numbers or contains some characters in between, it should change them to 0, and your application should inform the user that the file was not formatted correctly.
• You can ignore new lines and white spaces.
• Add a tester function to check the behavior of your PHP function.
• Follow the guidelines discussed and shown in class to avoid losing points.