src/explicit_learning/c2/parse.py

"""Parse a model's C2 compile response into a typed ``Program`` (``docs/02`` §7).

The model emits a JSON object with the program-envelope subset
(``dsl`` / ``program`` / ``referent_selector`` /
``required_referent_cardinality``). Parsing is strict and never guesses:

  1. JSON-parse (tolerating a surrounding code fence).
  2. Validate ``program`` and ``referent_selector`` against ``$defs/astNode``.
  3. Rebuild typed :class:`AstNode`s (numerics kept exact).
  4. Construct a :class:`Program` and run the P2 :func:`typecheck` (dangling
     selector / type mismatch / scalar-vs-set cardinality). A rejection here is a
     parse failure, not a silent accept.

The single allowed *repair* (§7) is driven by the compiler: it re-asks the model
with the first-response errors and parses the second response. This module is
pure — ``parse_program_response`` makes no model call; it reports ``ok``/invalid
and the compiler maps the attempt index to ``parse_status``.
"""

from __future__ import annotations

from dataclasses import dataclass
from typing import Any

from ..dsl.ast import (
    AstNode,
    Dsl,
    Program,
    ProgramError,
    ast_node_from_dict,
    validate_ast_node,
)
from ..dsl.canonicalize import canonical_program_sha256
from ..dsl.typecheck import TypecheckError, typecheck
from ..schema_io import parse_json
from ..sources.base import World


@dataclass(frozen=True)
class ParsedProgram:
    """The outcome of parsing one model response (one attempt).

    ``ok`` is ``True`` iff a typed, type-checked :class:`Program` was produced.
    ``canonical_program_sha256`` is filled only when ``ok`` (the §7.2 hash key).
    """

    program: Program | None
    ok: bool
    errors: tuple[str, ...]
    canonical_program_sha256: str | None


def parse_program_response(
    raw: str,
    *,
    dsl: Dsl,
    world: World,
    base_id: str,
    question_sha256: str,
    choices_sha256: str,
) -> ParsedProgram:
    """Parse one model response into a typed program or report errors.

    Never raises on a malformed response — every failure is captured in
    ``errors`` with ``ok=False`` so the compiler can drive the one repair.
    """
    errors: list[str] = []
    try:
        doc = parse_json(raw)
    except Exception as exc:  # noqa: BLE001 - any JSON failure is a parse failure
        return ParsedProgram(None, False, (f"json: {exc!r}",), None)
    if not isinstance(doc, dict):
        return ParsedProgram(None, False, ("response is not a JSON object",), None)

    resp_dsl = doc.get("dsl", dsl)
    if resp_dsl != dsl:
        errors.append(f"dsl mismatch: response {resp_dsl!r} != request {dsl!r}")

    program_node = _build_ast(doc.get("program"), "program", errors)
    referent_node = _build_ast(
        doc.get("referent_selector"), "referent_selector", errors, nullable=True
    )
    required = doc.get("required_referent_cardinality", None)

    if errors or program_node is None:
        return ParsedProgram(None, False, tuple(errors), None)

    try:
        program = Program(
            dsl=dsl,
            program=program_node,
            base_id=base_id,
            question_sha256=question_sha256,
            choices_sha256=choices_sha256,
            compile_status="compiled",
            referent_selector=referent_node,
            required_referent_cardinality=_coerce_cardinality(required, errors),
        )
    except ProgramError as exc:
        errors.append(f"program construct: {exc!r}")
        return ParsedProgram(None, False, tuple(errors), None)

    try:
        program = typecheck(program, world=world)
    except TypecheckError as exc:
        return ParsedProgram(None, False, (f"typecheck: {exc!r}",), None)
    except ProgramError as exc:
        return ParsedProgram(None, False, (f"program: {exc!r}",), None)

    canon = canonical_program_sha256(program, world=world)
    program = _replace(program, canonical_program_sha256=canon)
    return ParsedProgram(program, True, (), canon)


def _build_ast(
    value: Any, label: str, errors: list[str], *, nullable: bool = False
) -> AstNode | None:
    if value is None:
        if nullable:
            return None
        errors.append(f"{label}: missing")
        return None
    try:
        validate_ast_node(value)
    except ProgramError as exc:
        errors.append(f"{label}: {exc!r}")
        return None
    try:
        return ast_node_from_dict(value)
    except ProgramError as exc:
        errors.append(f"{label}: {exc!r}")
        return None


def _coerce_cardinality(value: Any, errors: list[str]) -> int | None:
    if value is None:
        return None
    if isinstance(value, bool) or not isinstance(value, int):
        errors.append(f"required_referent_cardinality must be int|null, got {value!r}")
        return None
    if value < 0:
        errors.append(f"required_referent_cardinality must be >= 0, got {value!r}")
        return None
    return int(value)


def _replace(program: Program, *, canonical_program_sha256: str) -> Program:
    from dataclasses import replace

    return replace(program, canonical_program_sha256=canonical_program_sha256)


__all__ = ["ParsedProgram", "parse_program_response"]