CSSParser.py

from HTMl_Tags import TagSelector, DescendantSelector

class CSSParser:
    def __init__(self, s):
        self.s = s
        self.index = 0 # starting index of whitespace

    # add to index for all whitespaces
    def whitespace(self):
        while self.index < len(self.s) and self.s[self.index].isspace():
            self.index += 1

    # parse property names
    def word(self):
        start = self.index

        while self.index < len(self.s):
            if self.s[self.index].isalnum() or self.s[self.index] in "#-.%":
                self.index += 1

            else:
                break

        if not (self.index > start):
            raise Exception("Whitespace Parsing Error")
        
        return self.s[start:self.index]

    # check for literal punctuation
    def literal(self, literal):
        if not (self.index < len(self.s) and self.s[self.index] == literal):
            raise Exception("Parsing error")
        self.index += 1

    def pair(self):
        prop = self.word()
        self.whitespace()
        self.literal(":")
        self.whitespace()
        val = self.word()
        return prop.casefold(), val
    
    def body(self):
        pairs = {}

        while self.index < len(self.s) and self.s[self.index] != "}":
            try:
                prop, val = self.pair() 
                pairs[prop.casefold()] = val # set hash val
                self.whitespace()
                self.literal(";")
                self.whitespace()

            except Exception:
                reason = self.ignore([";", "}"])

                if reason == ";":
                    self.literal(";")
                    self.whitespace()

                else:
                    break

        return pairs
    
    # deals with error from author or non supported items
    def ignore(self, chars):
        while self.index < len(self.s):
            if self.s[self.index] in chars:
                return self.s[self.index]
            
            else:
                self.index += 1

        # no errors
        return None

    # selector
    def selector(self) -> TagSelector:
        out = TagSelector(self.word().casefold())
        self.whitespace()

        while self.index < len(self.s) and self.s[self.index] != "{":
            tag = self.word()
            descendant = TagSelector(tag.casefold())
            out = DescendantSelector(out, descendant)
            self.whitespace()
            
        return out
    
    # parses CSS files
    def parse(self):
        rules = []

        while self.index < len(self.s):
            try:
                self.whitespace()
                selector = self.selector() # get selector for CSS
                self.literal("{")
                self.whitespace()
                body = self.body() # get body for CSS from selector
                self.literal("}")
                rules.append((selector, body)) # append to rules

            except Exception:
                # parser error
                reason = self.ignore(["}"])
                if reason == "}":
                    self.literal("}")
                    self.whitespace()
                else:
                    break

        return rules