将多行换成段落

Question

I would like to find paragraphs from a string, and format them, What i have kind of works, but It doesn't work 100%.

So, I have this string that looks like this:

##Chapter 1

Once upon a time there was a little girl named sally, she went to school.

One day it was awesome!

##Chapter 2

We all had a parade!

I am formatting the string, by converting ##... to <H2> 's, and it now looks like this:

<h2>Chapter 1</h2>

Once upon a time there was a little girl named sally, she went to school.

One day it was awesome!

<h2>Chapter 2</h2>

We all had a parade!

Now I want to convert everything to a paragraph, and to do so I do this:

// Converts sections to paragraphs:
$this->string = preg_replace("/(^|\n\n)(.+?)(\n\n|$)/", "<p>$2</p>", $this->string);

// To Remove paragraph tags from header tags (h1,h2,h3,h4,h5,h6,h7):
$this->string = preg_replace("/<p><h(\d)>(.+?)<\/h\d><\/p>/i", "<h$1>$2</h$1>", $this->string);

And this is the final output (New Lines added for readability):

<h2>Chapter 1</h2>
Once upon a time there was a little girl named sally, she went to school.
<p>One day it was awesome!</p>
<h2>Chapter 2</h2>
<p>We all had a parade!</p>

As I said near the beginning, this doesn't work 100%, and as you can see a paragraph was not added to the first paragraph. What Can I do to improve the regular expression?

Answer 1

you can do it in one step:

$this->string = preg_replace('~(*BSR_ANYCRLF)\R\R\K(?>[^<\r\n]++|<(?!h[1-6]\b)|\R(?!\R))+(?=\R\R|$)~u',
                             '<p>$0</p>', $this->string);

pattern details

(*BSR_ANYCRLF)       # \R can be any type of newline
\R\R                 # two newlines
\K                   # reset the match
(?>                  # open an atomic group
    [^<\r\n]++       # all characters except <, CR, LF
  |                  # OR
    <(?!h[1-6]\b)    # < not followed by a header tag
  |                  # OR
    \R(?!\R)         # single newline
)+                   # close the atomic group and repeat one or more times
(?=\R\R|$)           # followed by to newlines or the end of the string

Answer 2

Add m switch to the first regex.

// Converts sections to paragraphs:
$this->string = preg_replace("/(^|\n\n)(.+?)(\n\n|$)/m", "<p>$2</p>", $this->string);

// To Remove paragraph tags from header tags (h1,h2,h3,h4,h5,h6,h7):
$this->string = preg_replace("/<p><h(\d)>(.+?)<\/h\d><\/p>/i", "<h$1>$2</h$1>", $this->string);