Module metaloaders.json

"""Metaloader for JSON documents.

Let's load a simple JSON document:

    >>> from metaloaders import load

    >>> json = load(\"""
    ... {
    ...     "test": 123
    ... }
    ... \""")

Now you can access the outer object meta-data:

    >>> json.start_line == 2
        json.end_line == 4
        json.start_column == 0
        json.end_column == 1

As well as child objects meta-data:

    >>> json.inner['test'] == Node(
            data=123,
            data_type=Type.NUMBER,
            end_column=15,
            end_line=3,
            start_column=12,
            start_line=3,
        )

Every JSON token contains all possible metadata:

    >>> json.data == {key: val}
        # Where:
        #
        # key = Node(
        #     data='test',
        #     data_type=Type.STRING,
        #     end_column=10,
        #     end_line=3,
        #     start_column=4,
        #     start_line=3,
        # )
        #
        # val = Node(
        #     data=123,
        #     data_type=Type.NUMBER,
        #     end_column=15,
        #     end_line=3,
        #     start_column=12,
        #     start_line=3,
        # )
"""
# Standard library
import ast
from typing import (
    Any,
    Optional,
)

# Third party libraries
import lark

# Local libraries
from metaloaders.exceptions import (
    MetaloaderError,
)
from metaloaders.model import (
    Node,
    Type,
)

# Constants
GRAMMAR = r"""
    ?start: value

    ?value: array
          | object
          | number
          | string
          | "false" -> false
          | "null" -> null
          | "true" -> true

    array  : "[" [value ("," value)*] "]"
    object : "{" [pair ("," pair)*] "}"
    number : SIGNED_NUMBER
    pair   : string ":" value
    string : ESCAPED_STRING

    %import common.ESCAPED_STRING
    %import common.SIGNED_NUMBER
    %import common.WS

    %ignore WS
"""


def load(stream: str) -> Node:
    """Loads a string representation of a document.

    Raises `metaloaders.exceptions.MetaloaderError` if any parsing error occur.
    """
    parser = lark.Lark(
        grammar=GRAMMAR,
        parser='lalr',
        propagate_positions=True,
    )

    try:
        obj = parser.parse(stream)
    except lark.exceptions.LarkError as exc:
        raise MetaloaderError(f'Unable to parse stream: {exc}')
    else:
        data: Node = _simplify(obj)
        return data


def _simplify(obj: Any) -> Any:
    data: Any
    data_type: Optional[Type]

    if isinstance(obj, lark.Tree):
        if obj.data == 'object':
            data = dict(map(_simplify, obj.children))
            data_type = Type.OBJECT
        elif obj.data == 'array':
            data = list(map(_simplify, obj.children))
            data_type = Type.ARRAY
        elif obj.data == 'pair':
            data = (
                _simplify(obj.children[0]),
                _simplify(obj.children[1]),
            )
            data_type = None
        elif obj.data == 'null':
            data = None
            data_type = Type.NULL
        elif obj.data == 'true':
            data = True
            data_type = Type.BOOLEAN
        elif obj.data == 'false':
            data = False
            data_type = Type.BOOLEAN
        elif obj.data == 'string':
            data = ast.literal_eval(obj.children[0].value)  # type: ignore
            data_type = Type.STRING
        elif obj.data == 'number':
            data = ast.literal_eval(obj.children[0].value)  # type: ignore
            data_type = Type.NUMBER
        else:
            raise NotImplementedError(obj)
    else:
        raise NotImplementedError(obj)

    return data if data_type is None else Node(
        data=data,
        data_type=data_type,
        end_column=obj.end_column - 1,  # type: ignore
        end_line=obj.end_line,  # type: ignore
        start_column=obj.column - 1,  # type: ignore
        start_line=obj.line,  # type: ignore
    )