There are a number of ways to analyze php code to get a better feel for how complex it is and clues for what it may take to work on it. For example the following linux shell command will tell you how many lines of php code there is in a given folder.
find -type f \( -iname "*.php" -o -iname "*.html" \) -exec wc -l {} \; | awk '{lines += $1 ; files += 1 ; print }; END { print "Lines total is: ", lines ," in ", files ," files"}'
Another option is using a tool such as phploc, which makes it easy and quick to measure the size and analyze the structure of a php project. It will tell you things like number of lines of code, how many functions you have, how many classes, what percentage of your code is comments vs plain code, etc. It's also ran on the command line like this:
$ php phploc.php some/folder/
Here is what the output might look like:
Directories 3Files 8Size Lines of Code (LOC) 1858 Comment Lines of Code (CLOC) 560 (30.14%) Non-Comment Lines of Code (NCLOC) 1298 (69.86%) Logical Lines of Code (LLOC) 289 (15.55%) Classes 260 (89.97%) Average Class Length 37 Average Method Length 9 Functions 5 (1.73%) Average Function Length 5 Not in classes or functions 24 (8.30%)Complexity Cyclomatic Complexity / LLOC 0.67 Cyclomatic Complexity / Number of Methods 7.86Dependencies Global Accesses 2 Global Constants 2 (100.00%) Global Variables 0 (0.00%) Super-Global Variables 0 (0.00%) Attribute Accesses 48 Non-Static 48 (100.00%) Static 0 (0.00%) Method Calls 96 Non-Static 91 (94.79%) Static 5 (5.21%)Structure Namespaces 4 Interfaces 0 Traits 0 Classes 7 Abstract Classes 0 (0.00%) Concrete Classes 7 (100.00%) Methods 28 Scope Non-Static Methods 28 (100.00%) Static Methods 0 (0.00%) Visibility Public Method 10 (35.71%) Non-Public Methods 18 (64.29%) Functions 1 Named Functions 0 (0.00%) Anonymous Functions 1 (100.00%) Constants 1 Global Constants 1 (100.00%) Class Constants 0 (0.00%)