"""Shared JSON helpers (fenced markdown, brace extraction)."""

from __future__ import annotations

import re

_MARKDOWN_JSON_FENCE_RE = re.compile(
    r"^\s*```(?:json)?\s*(.*?)\s*```\s*$",
    re.IGNORECASE | re.DOTALL,
)


def extract_json_payload(raw_response: str | None) -> str:
    """Strip optional ```json fences and return the outermost `{...}` object substring."""
    cleaned = (raw_response or "").strip()
    fenced_match = _MARKDOWN_JSON_FENCE_RE.match(cleaned)
    if fenced_match:
        cleaned = fenced_match.group(1).strip()

    if cleaned.startswith("{") and cleaned.endswith("}"):
        return cleaned

    start = cleaned.find("{")
    if start == -1:
        return cleaned
    depth = 0
    for i, ch in enumerate(cleaned[start:], start):
        if ch == "{":
            depth += 1
        elif ch == "}":
            depth -= 1
            if depth == 0:
                return cleaned[start : i + 1].strip()

    return cleaned