parse.py

import re
import string
import logging
from string import Formatter
from typing import List, TypedDict

logger = logging.getLogger(__name__)


class PartialStringFormatter(string.Formatter):
    def get_value(self, key, args, kwds):
        if isinstance(key, str):
            try:
                return kwds[key]
            except KeyError:
                return "{" + key + "}"
        else:
            Formatter.get_value(key, args, kwds)

    def format_field(self, value, format_spec):
        try:
            return super().format_field(value, format_spec)
        except ValueError:
            # HACK: the value was an unfilled variable or not a variable at all, so the format spec should be considered part of the variable name
            if value.startswith("{") and value.endswith("}"):
                return value[:-1] + ":" + format_spec + "}"

    def _vformat(
        self, format_string, args, kwargs, used_args, recursion_depth, auto_arg_index=0
    ):
        # copied verbatim from parent class except for the # HACK
        if recursion_depth < 0:
            raise ValueError("Max string recursion exceeded")
        result = []
        for literal_text, field_name, format_spec, conversion in self.parse(
            format_string
        ):

            # output the literal text
            if literal_text:
                result.append(literal_text)

            # if there's a field, output it
            if field_name is not None:
                # this is some markup, find the object and do
                #  the formatting

                # handle arg indexing when empty field_names are given.
                if field_name == "":
                    if auto_arg_index is False:
                        raise ValueError(
                            "cannot switch from manual field "
                            "specification to automatic field "
                            "numbering"
                        )
                    field_name = str(auto_arg_index)
                    auto_arg_index += 1
                elif field_name.isdigit():
                    if auto_arg_index:
                        raise ValueError(
                            "cannot switch from manual field "
                            "specification to automatic field "
                            "numbering"
                        )
                    # disable auto arg incrementing, if it gets
                    # used later on, then an exception will be raised
                    auto_arg_index = False

                # given the field_name, find the object it references
                #  and the argument it came from
                obj, arg_used = self.get_field(field_name, args, kwargs)
                used_args.add(arg_used)

                # do any conversion on the resulting object
                obj = self.convert_field(obj, conversion)

                # expand the format spec, if needed
                format_spec, auto_arg_index = self._vformat(
                    format_spec,
                    args,
                    kwargs,
                    used_args,
                    recursion_depth - 1,
                    auto_arg_index=auto_arg_index,
                )

                # format the object and append to the result
                # HACK: if the format_spec is invalid, assume this field_name was not meant to be a variable, and don't substitute anything
                formatted_field = self.format_field(obj, format_spec)
                if formatted_field is None:
                    result.append("{" + ":".join([field_name, format_spec]) + "}")
                else:
                    result.append(formatted_field)

        return "".join(result), auto_arg_index


PartialStringFormat = PartialStringFormatter()


def partial_str_format(string, **kwargs):
    """
    Formats a string with a subset of the arguments.
    Analogous to str.format, but ignores missing arguments.
    """
    return PartialStringFormat.format(string, **kwargs)


class TemplateChunks(TypedDict):
    text: str
    start: int
    end: int
    type: str
    
    
match_fields_regex = re.compile(r"(?<!\{)\{([a-zA-Z0-9_]+)\}(?!})")


def parse_template(string, include_texts=True) -> List[TemplateChunks]:
    """
    Parses a template string to extract output fields and the text between them.

    Args:
        string (str): The template string to parse.
        include_texts (bool): Whether to include the text between the fields in the output.

    Returns:
        List[Element]: A list of dictionaries with the keys 'text', 'start', 'end', and 'type'.

    Example:
        >>> parse_template("some text {field1} some more text {field2}")
        [{"text": "some text ", "start": 0, "end": 10, "type": "text"},
         {"text": "field1", "start": 11, "end": 17, "type": "var"},
         {"text": " some more text ", "start": 18, "end": 35, "type": "text"},
         {"text": "field2", "start": 36, "end": 42, "type": "var"}]
    """

    chunks: List[TemplateChunks] = []
    last_index = 0

    for match in match_fields_regex.finditer(string):
        # for match in re.finditer(r'\{(.*?)\}', string):
        # Text before field
        if last_index < match.start() and include_texts:
            text = string[last_index : match.start()]
            chunks.append(
                {
                    "text": text,
                    "start": last_index,
                    "end": match.start(),
                    "type": "text",
                }
            )

        # Field itself
        field = match.group(1)
        start = match.start()
        end = match.end()
        chunks.append({"text": field, "start": start, "end": end, "type": "var"})

        last_index = match.end()

    # Text after the last field
    if last_index < len(string) and include_texts:
        text = string[last_index:]
        chunks.append(
            {"text": text, "start": last_index, "end": len(string), "type": "text"}
        )

    return chunks