src/explicit_learning/schema_io.py

"""JSON Schema loading, validation, and one-shot JSON repair parsing.

The pipeline persists every model output and intermediate artifact as JSON
validated against a schema in ``schemas/``. Model JSON is parsed strictly: a
malformed response is repaired at most once, and a second failure routes the item
to the human queue (never a silent regex fallback).
"""

from __future__ import annotations

import json
from collections.abc import Callable
from pathlib import Path
from typing import Any

from jsonschema import Draft202012Validator

from .hashing import sha256_text

ParseStatus = str  # "valid_first_response" | "valid_after_one_repair" | "invalid"


class SchemaError(ValueError):
    """Raised when a schema document itself is invalid."""


def load_schema(path: str | Path) -> dict[str, Any]:
    """Load and compile-check a JSON Schema (draft 2020-12) from ``path``."""
    schema: dict[str, Any] = json.loads(Path(path).read_text(encoding="utf-8"))
    try:
        Draft202012Validator.check_schema(schema)
    except Exception as exc:  # jsonschema raises various error types
        raise SchemaError(f"invalid schema {path}: {exc}") from exc
    return schema


def validate(instance: Any, schema: dict[str, Any]) -> list[str]:
    """Return a list of human-readable validation errors (empty if valid)."""
    validator = Draft202012Validator(schema)
    return [
        _format_error(error)
        for error in sorted(validator.iter_errors(instance), key=lambda e: list(e.path))
    ]


def is_valid(instance: Any, schema: dict[str, Any]) -> bool:
    """True when ``instance`` satisfies ``schema``."""
    return not validate(instance, schema)


def _format_error(error: Any) -> str:
    path = ".".join(str(part) for part in error.path) or "$"
    return f"{path}: {error.message}"


def parse_json(raw: str) -> Any:
    """Parse a JSON document, tolerating a leading/trailing code fence.

    Raises ``json.JSONDecodeError`` on failure (no silent fallback).
    """
    text = raw.strip()
    if text.startswith("```"):
        # Strip a single surrounding fenced block (```json ... ``` or ``` ... ```).
        lines = text.splitlines()
        if lines and lines[0].startswith("```"):
            lines = lines[1:]
        if lines and lines[-1].strip().startswith("```"):
            lines = lines[:-1]
        text = "\n".join(lines).strip()
    return json.loads(text)


def parse_with_repair(
    raw: str,
    schema: dict[str, Any],
    repair: Callable[[str, list[str]], str | None],
) -> tuple[Any | None, ParseStatus, list[str]]:
    """Parse ``raw`` against ``schema``, allowing at most one repair call.

    ``repair(raw, errors)`` must return either a repaired raw string (re-parsed
    and re-validated) or ``None``/empty to give up. Returns
    ``(parsed_or_None, parse_status, final_errors)``.
    """
    try:
        candidate = parse_json(raw)
    except json.JSONDecodeError as exc:
        candidate = None
        first_errors = [f"json: {exc}"]
    else:
        first_errors = validate(candidate, schema)

    if not first_errors:
        return candidate, "valid_first_response", []

    repaired = repair(raw, first_errors)
    if not repaired:
        return None, "invalid", first_errors

    try:
        candidate = parse_json(repaired)
    except json.JSONDecodeError as exc:
        return None, "invalid", [*first_errors, f"repair-json: {exc}"]

    second_errors = validate(candidate, schema)
    if second_errors:
        return None, "invalid", [*first_errors, *second_errors]

    return candidate, "valid_after_one_repair", []


def request_hash(payload: Any) -> str:
    """Stable SHA-256 of a request payload for idempotent response caching."""
    return sha256_text(json.dumps(payload, sort_keys=True, ensure_ascii=False))