Python re.findall regex and text processing

I’m looking to find and modify some sql syntax around the convert function. I want basically any convert(A,B) or CONVERT(A,B) in all my files to be selected and converted to B::A.

So far I tried selecting them with re.findall(r"bconvertb(.*?,.*)", l, re.IGNORECASE) But it’s only returning a small selection out of what I want and I also have trouble actually manipulating the A/B I mentioned.

For example, a sample line (note the nested structure here is irrelevant, I’m only getting the outer layer working if possible)

convert(varchar, '/' || convert(nvarchar, es.Item_ID) || ':' || convert(nvarchar, o.Option_Number) || '/') as LocPath

…should become…

'/' || es.Item_ID::nvarchar || ':' || o.Option_Number::nvarchar || '/' :: varchar as LocPath

Example2:

SELECT LocationID AS ItemId, convert(bigint, -1),

…should become…

SELECT LocationID AS ItemId, -1::bigint,

I think this should be possible with some kind of re.sub with groups and currently have a code structure inside a for each loop where line is the each line in the file:

matchConvert = ["convert(", "CONVERT("]
a = next((a for a in matchConvert if a in line), False)
if a:
    print("convert() line")
    #line = re.sub(re.escape(a) + r'', '', line)

Edit: In the end I went with a non re solution and handled each line by identifying each block and manipulate them accordingly.

Answer

Here’s my solution based on @Иван-Балван‘s code. Breaking this structure into blocks makes further specification a lot easier than I previously thought and I’ll be using this method for a lot of other operations as well.

# Check for balanced brackets
def checkBracket(my_string):
    count = 0
    for c in my_string:
        if c == "(":
            count+=1
        elif c == ")":
            count-=1
    return count


# Modify the first convert in line
# Based on suggestions from stackoverflow.com/questions/73040953
def modifyConvert(l):
    # find the location of convert()
    count = l.index('convert(')

    # select the group before convert() call
    before = l[:count]

    group=""
    n1=0
    n2=0
    A=""
    B=""
    operate = False
    operators = ["|", "<", ">", "="]
    # look for A group before comma
    for n1, i in enumerate(l[count+8:], start=len(before)+8):
        # find current position in l
        checkIndex = checkBracket(l[count+8:][:n1-len(before)-8])
        if i == ',' and checkIndex == 0:
            A = group
            break
        group += i

    # look for B group after comma
    group = ""
    for n2, i in enumerate(l[n1+1:], start=n1+1):
        checkIndex = checkBracket(l[count+n1-len(before):][:n2-n1+1])
        if i == ',' and checkIndex == 0:
            return l
        elif checkIndex < 0:
            B = group
            break
        group += i
        
        # mark operators
        if i in operators:
            operate = True

    # select the group after convert() call
    after = l[n2+1:]

    # (B) if it contains operators
    if operate:
        return before + "(" + B.lstrip() + ') :: ' + A + after
    else:
        return before + B.lstrip() + '::' + A + after


# Modify cast syntax with convert(a,b). return line.
def convertCast(l):

    # Call helper for nested cases
    i = l.count('convert(')
    while i>0:
        i -= 1
        l = modifyConvert(l)

    return l