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-rw-r--r--mdit_py_plugins/attrs/parse.py265
1 files changed, 265 insertions, 0 deletions
diff --git a/mdit_py_plugins/attrs/parse.py b/mdit_py_plugins/attrs/parse.py
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+++ b/mdit_py_plugins/attrs/parse.py
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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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