"""Safe, small input helpers for harness contracts."""

from __future__ import annotations

import json
from pathlib import Path
from typing import Any, TypeVar

import yaml
from pydantic import BaseModel


MAX_INPUT_BYTES = 2 * 1024 * 1024
ModelT = TypeVar("ModelT", bound=BaseModel)


class InputError(ValueError):
    """Raised when an input file cannot be safely decoded as a model payload."""


def load_mapping(path: str | Path, *, max_bytes: int = MAX_INPUT_BYTES) -> dict[str, Any]:
    """Load one JSON/YAML mapping without constructing arbitrary Python objects."""

    input_path = Path(path)
    try:
        size = input_path.stat().st_size
    except OSError as exc:
        raise InputError(f"입력 파일을 읽을 수 없습니다: {input_path}") from exc

    if size > max_bytes:
        raise InputError(f"입력 파일이 {max_bytes}바이트 제한을 초과했습니다: {input_path}")

    try:
        text = input_path.read_text(encoding="utf-8")
    except (OSError, UnicodeDecodeError) as exc:
        raise InputError(f"입력 파일은 UTF-8 텍스트여야 합니다: {input_path}") from exc

    suffix = input_path.suffix.casefold()
    try:
        if suffix == ".json":
            value = json.loads(text)
        elif suffix in {".yaml", ".yml"}:
            value = yaml.safe_load(text)
        else:
            raise InputError("지원 형식은 .json, .yaml, .yml입니다.")
    except (json.JSONDecodeError, yaml.YAMLError) as exc:
        raise InputError(f"JSON/YAML 구문이 올바르지 않습니다: {input_path}") from exc

    if not isinstance(value, dict):
        raise InputError(f"입력 최상위 값은 객체(mapping)여야 합니다: {input_path}")
    return value


def load_model(path: str | Path, model_type: type[ModelT]) -> ModelT:
    """Load and validate a Pydantic contract from JSON/YAML."""

    return model_type.model_validate(load_mapping(path))


def dump_json(model: BaseModel) -> str:
    """Serialize a contract deterministically for audit-friendly output."""

    return json.dumps(
        model.model_dump(mode="json"),
        ensure_ascii=False,
        indent=2,
        sort_keys=True,
    )


__all__ = ["InputError", "MAX_INPUT_BYTES", "dump_json", "load_mapping", "load_model"]