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"""Parser for attributes::
attributes { id = "foo", class = "bar baz",
key1 = "val1", key2 = "val2" }
Adapted from:
https://github.com/jgm/djot/blob/fae7364b86bfce69bc6d5b5eede1f5196d845fd6/djot/attributes.lua#L1
syntax:
attributes <- '{' whitespace* attribute (whitespace attribute)* whitespace* '}'
attribute <- identifier | class | keyval
identifier <- '#' name
class <- '.' name
name <- (nonspace, nonpunctuation other than ':', '_', '-')+
keyval <- key '=' val
key <- (ASCII_ALPHANUM | ':' | '_' | '-')+
val <- bareval | quotedval
bareval <- (ASCII_ALPHANUM | ':' | '_' | '-')+
quotedval <- '"' ([^"] | '\"') '"'
"""
from __future__ import annotations
from enum import Enum
import re
from typing import Callable
class State(Enum):
START = 0
SCANNING = 1
SCANNING_ID = 2
SCANNING_CLASS = 3
SCANNING_KEY = 4
SCANNING_VALUE = 5
SCANNING_BARE_VALUE = 6
SCANNING_QUOTED_VALUE = 7
SCANNING_COMMENT = 8
SCANNING_ESCAPED = 9
DONE = 10
REGEX_SPACE = re.compile(r"\s")
REGEX_SPACE_PUNCTUATION = re.compile(r"[\s!\"#$%&'()*+,./;<=>?@[\]^`{|}~]")
REGEX_KEY_CHARACTERS = re.compile(r"[a-zA-Z\d_:-]")
class TokenState:
def __init__(self):
self._tokens = []
self.start: int = 0
def set_start(self, start: int) -> None:
self.start = start
def append(self, start: int, end: int, ttype: str):
self._tokens.append((start, end, ttype))
def compile(self, string: str) -> dict[str, str]:
"""compile the tokens into a dictionary"""
attributes = {}
classes = []
idx = 0
while idx < len(self._tokens):
start, end, ttype = self._tokens[idx]
if ttype == "id":
attributes["id"] = string[start:end]
elif ttype == "class":
classes.append(string[start:end])
elif ttype == "key":
key = string[start:end]
if idx + 1 < len(self._tokens):
start, end, ttype = self._tokens[idx + 1]
if ttype == "value":
if key == "class":
classes.append(string[start:end])
else:
attributes[key] = string[start:end]
idx += 1
idx += 1
if classes:
attributes["class"] = " ".join(classes)
return attributes
def __str__(self) -> str:
return str(self._tokens)
def __repr__(self) -> str:
return repr(self._tokens)
class ParseError(Exception):
def __init__(self, msg: str, pos: int) -> None:
self.pos = pos
super().__init__(msg + f" at position {pos}")
def parse(string: str) -> tuple[int, dict[str, str]]:
"""Parse attributes from start of string.
:returns: (length of parsed string, dict of attributes)
"""
pos = 0
state: State = State.START
tokens = TokenState()
while pos < len(string):
state = HANDLERS[state](string[pos], pos, tokens)
if state == State.DONE:
return pos, tokens.compile(string)
pos = pos + 1
return pos, tokens.compile(string)
def handle_start(char: str, pos: int, tokens: TokenState) -> State:
if char == "{":
return State.SCANNING
raise ParseError("Attributes must start with '{'", pos)
def handle_scanning(char: str, pos: int, tokens: TokenState) -> State:
if char == " " or char == "\t" or char == "\n" or char == "\r":
return State.SCANNING
if char == "}":
return State.DONE
if char == "#":
tokens.set_start(pos)
return State.SCANNING_ID
if char == "%":
tokens.set_start(pos)
return State.SCANNING_COMMENT
if char == ".":
tokens.set_start(pos)
return State.SCANNING_CLASS
if REGEX_KEY_CHARACTERS.fullmatch(char):
tokens.set_start(pos)
return State.SCANNING_KEY
raise ParseError(f"Unexpected character whilst scanning: {char}", pos)
def handle_scanning_comment(char: str, pos: int, tokens: TokenState) -> State:
if char == "%":
return State.SCANNING
return State.SCANNING_COMMENT
def handle_scanning_id(char: str, pos: int, tokens: TokenState) -> State:
if not REGEX_SPACE_PUNCTUATION.fullmatch(char):
return State.SCANNING_ID
if char == "}":
if (pos - 1) > tokens.start:
tokens.append(tokens.start + 1, pos, "id")
return State.DONE
if REGEX_SPACE.fullmatch(char):
if (pos - 1) > tokens.start:
tokens.append(tokens.start + 1, pos, "id")
return State.SCANNING
raise ParseError(f"Unexpected character whilst scanning id: {char}", pos)
def handle_scanning_class(char: str, pos: int, tokens: TokenState) -> State:
if not REGEX_SPACE_PUNCTUATION.fullmatch(char):
return State.SCANNING_CLASS
if char == "}":
if (pos - 1) > tokens.start:
tokens.append(tokens.start + 1, pos, "class")
return State.DONE
if REGEX_SPACE.fullmatch(char):
if (pos - 1) > tokens.start:
tokens.append(tokens.start + 1, pos, "class")
return State.SCANNING
raise ParseError(f"Unexpected character whilst scanning class: {char}", pos)
def handle_scanning_key(char: str, pos: int, tokens: TokenState) -> State:
if char == "=":
tokens.append(tokens.start, pos, "key")
return State.SCANNING_VALUE
if REGEX_KEY_CHARACTERS.fullmatch(char):
return State.SCANNING_KEY
raise ParseError(f"Unexpected character whilst scanning key: {char}", pos)
def handle_scanning_value(char: str, pos: int, tokens: TokenState) -> State:
if char == '"':
tokens.set_start(pos)
return State.SCANNING_QUOTED_VALUE
if REGEX_KEY_CHARACTERS.fullmatch(char):
tokens.set_start(pos)
return State.SCANNING_BARE_VALUE
raise ParseError(f"Unexpected character whilst scanning value: {char}", pos)
def handle_scanning_bare_value(char: str, pos: int, tokens: TokenState) -> State:
if REGEX_KEY_CHARACTERS.fullmatch(char):
return State.SCANNING_BARE_VALUE
if char == "}":
tokens.append(tokens.start, pos, "value")
return State.DONE
if REGEX_SPACE.fullmatch(char):
tokens.append(tokens.start, pos, "value")
return State.SCANNING
raise ParseError(f"Unexpected character whilst scanning bare value: {char}", pos)
def handle_scanning_escaped(char: str, pos: int, tokens: TokenState) -> State:
return State.SCANNING_QUOTED_VALUE
def handle_scanning_quoted_value(char: str, pos: int, tokens: TokenState) -> State:
if char == '"':
tokens.append(tokens.start + 1, pos, "value")
return State.SCANNING
if char == "\\":
return State.SCANNING_ESCAPED
if char == "{" or char == "}":
raise ParseError(
f"Unexpected character whilst scanning quoted value: {char}", pos
)
if char == "\n":
tokens.append(tokens.start + 1, pos, "value")
return State.SCANNING_QUOTED_VALUE
return State.SCANNING_QUOTED_VALUE
HANDLERS: dict[State, Callable[[str, int, TokenState], State]] = {
State.START: handle_start,
State.SCANNING: handle_scanning,
State.SCANNING_COMMENT: handle_scanning_comment,
State.SCANNING_ID: handle_scanning_id,
State.SCANNING_CLASS: handle_scanning_class,
State.SCANNING_KEY: handle_scanning_key,
State.SCANNING_VALUE: handle_scanning_value,
State.SCANNING_BARE_VALUE: handle_scanning_bare_value,
State.SCANNING_QUOTED_VALUE: handle_scanning_quoted_value,
State.SCANNING_ESCAPED: handle_scanning_escaped,
}
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