from tclint.format import Formatter as BaseFormatter
from typing import List


class NxFormatter(BaseFormatter):
    """
    Custom formatter that inherits from tclint's Formatter but preserves explicit
    line continuations (\\) inside braced expressions when they span multiple lines.

    This avoids generating syntax errors in environments that require a trailing
    backslash for multi-line expressions (e.g., certain NX Post interpreters),
    while leaving all other formatting behavior unchanged.
    """

    def format_braced_expression(self, expr) -> List[str]:  # type: ignore[override]
        # This method mirrors BaseFormatter.format_braced_expression but inserts
        # a line continuation (" \") between continuation lines similar to
        # BaseFormatter.format_expression.
        formatted = [""]
        for child in expr.children:
            lines = self.format(child)
            formatted[-1] += lines[0]
            for line in lines[1:]:
                # add continuation on the previous line; keep next line at the same level
                formatted[-1] += " \\"  # keep explicit continuation
                formatted += [line]

        if expr.pos[0] == expr.end_pos[0]:
            space_before = expr.children[0].pos[1] - expr.pos[1] - 1
            space_after = expr.end_pos[1] - expr.children[-1].end_pos[1] - 1
            return self._brace(formatted, (space_before, space_after))

        return ["{"] + self._indent(formatted, self.opts.indent) + ["}"]