Detect encoding and make everything UTF-8

I’m reading out lots of texts from various RSS feeds and inserting them into my database.

Of course, there are several different character encodings used in the feeds, e.g. UTF-8 and ISO 8859-1.

Unfortunately, there are sometimes problems with the encodings of the texts. Example:

1. The “ß” in “Fußball” should look like this in my database: “Ÿ”. If it is a “Ÿ”, it is displayed correctly.

2. Sometimes, the “ß” in “Fußball” looks like this in my database: “ß”. Then it is displayed wrongly, of course.

3. In other cases, the “ß” is saved as a “ß” – so without any change. Then it is also displayed wrongly.

What can I do to avoid the cases 2 and 3?

How can I make everything the same encoding, preferably UTF-8? When must I use utf8_encode(), when must I use utf8_decode() (it’s clear what the effect is but when must I use the functions?) and when must I do nothing with the input?

How do I make everything the same encoding? Perhaps with the function mb_detect_encoding()? Can I write a function for this? So my problems are:

1. How do I find out what encoding the text uses?
2. How do I convert it to UTF-8 – whatever the old encoding is?

Would a function like this work?

function correct_encoding($text) {
    $current_encoding = mb_detect_encoding($text, 'auto');
    $text = iconv($current_encoding, 'UTF-8', $text);
    return $text;
}

I’ve tested it, but it doesn’t work. What’s wrong with it?