src/explicit_learning/executors/base.py

"""Deterministic question-program executors (``docs/02`` §8, ``docs/07`` §5 P3).

An executor turns a typed :class:`~explicit_learning.dsl.ast.Program` plus a
structured :class:`~explicit_learning.sources.base.World` into an
:class:`ExecutionResult` — a *deterministic, replayable* record of what the
program computed, which world nodes it depended on, and whether the referent
selector's cardinality precondition held.

P3 is the gold-authority layer: the executor trace (not a human label) decides
the answer and the dependency closure ``D(P,W)`` (``docs/02`` §8). Four terminal
statuses, and a hard rule: a timeout/internal error is ``ERROR`` and is **never**
silently coerced into a ``U`` label (``docs/07`` §5: "timeout/error가 U label로
변환되지 않음"):

  * ``UNIQUE`` — the program produced exactly one answer.
  * ``MISSING_INFORMATION`` — a value the program needed is absent (a redacted
    point, an x not present in a series). This is the ``U_MISSING`` precursor.
  * ``INVALID_REFERENT`` — the scalar referent selector's cardinality
    precondition broke (``required_referent_cardinality == 1`` but the selector
    resolved to ``!= 1``). This is the ``U_INVALID`` precursor. COUNT/EXIST are
    *set* selectors and declare ``None`` — a zero-cardinality referent runs to
    ``0``/``No`` and stays ``UNIQUE`` (``A_CHANGED``), never ``U_INVALID``
    (``docs/02`` §11.3).
  * ``ERROR`` — executor bug / unsupported operator / timeout.

Answers are exact (``fractions.Fraction``); serialization follows ``docs/02``
§3.3 (integer → int, number → canonical rational string, boolean → ``yes``/``no``,
year/short-text → string). Choice uniqueness is a separate, choice-aware helper
the certificate builder (P7) applies — the executor itself is choice-agnostic.
"""

from __future__ import annotations

from collections.abc import Iterable, Mapping, Sequence
from dataclasses import dataclass, field
from fractions import Fraction
from typing import Any, Literal, Protocol

from ..dsl.ast import AstNode, Program, canonical_number_str, parse_number
from ..hashing import canonical_json_hash
from ..ingest.base import Choice
from ..sources.base import World

ExecutionStatus = Literal["UNIQUE", "MISSING_INFORMATION", "INVALID_REFERENT", "ERROR"]

# The exact in-memory answer an executor computes (pre-serialization).
AnswerValue = Fraction | int | str | bool

# One step of the deterministic execution trace: the op evaluated, the resolved
# world node ids it read, and a canonical repr of its result. Hashed for replay.
type TraceStep = tuple[str, tuple[str, ...], str]


class ExecutorError(Exception):
    """An internal executor failure (unsupported op, type error, timeout).

    An :class:`ExecutorError` surfaces as ``status="ERROR"`` and is never coerced
    into a ``U`` label (``docs/07`` §5).
    """


class _MissingInformation(Exception):
    """Internal signal: the program needs a value absent from the world."""


class _InvalidReferent(Exception):
    """Internal signal: the scalar referent selector cardinality broke."""


@dataclass(frozen=True)
class ExecutionResult:
    """The deterministic outcome of executing one program over one world.

    ``answer_value`` is the exact computed answer (or ``None`` for non-``UNIQUE``
    statuses). ``answer_canonical`` is its §3.3 serialization
    (``str|int|bool|None``) — the form embedded in the certificate. ``trace_sha256``
    anchors replay: the same ``(program, world)`` must reproduce it byte-for-byte.
    ``referent_cardinality`` is the resolved size of the referent selector (the
    ``U_INVALID`` proof's ``after`` cardinality).
    """

    status: ExecutionStatus
    answer_value: AnswerValue | None
    answer_canonical: str | int | bool | None
    dependency_node_ids: tuple[str, ...]
    referent_cardinality: int | None
    trace_sha256: str
    executor_name: str
    executor_version: str

    @property
    def is_unique(self) -> bool:
        return self.status == "UNIQUE"


class Executor(Protocol):
    """One DSL's deterministic executor."""

    name: str
    version: str

    def execute(self, program: Program, *, world: World) -> ExecutionResult: ...

    def execute_selector(self, selector: AstNode, *, world: World) -> tuple[str, ...]:
        """Resolve a referent selector to the world node ids it denotes."""
        ...


# --- answer serialization (§3.3) + choice matching -------------------------


def serialize_answer(
    value: AnswerValue | None, *, return_type: str = ""
) -> str | int | bool | None:
    """Serialize an exact answer value per ``docs/02`` §3.3.

    Booleans → ``yes``/``no``; ``Fraction`` → canonical rational string;
    ``int`` → ``int``; strings (year/short-text/expression) pass through.
    ``None`` stays ``None`` (non-``UNIQUE`` statuses carry no answer).
    """
    if value is None:
        return None
    if isinstance(value, bool):
        return "yes" if value else "no"
    if isinstance(value, Fraction):
        return canonical_number_str(value)
    if isinstance(value, int):
        return value
    return str(value)


def match_choice(
    answer_value: AnswerValue | None, choices: Sequence[Choice], answer_type: str
) -> tuple[str, ...]:
    """The choice keys whose text equals ``answer_value`` (``docs/07`` §5 uniqueness).

    Type-aware: a numeric answer matches a choice by exact rational equality
    (``30`` == ``"30"`` == ``"30.0"``); a string answer matches by exact text.
    Returns zero/one/many keys — the certificate builder asserts exactly one
    (``choice_uniqueness_passed``). Choice-agnostic for non-multiple-choice items.
    """
    if answer_type != "multiple_choice" or answer_value is None:
        return ()
    if isinstance(answer_value, bool):
        target = "yes" if answer_value else "no"
        return tuple(c.key for c in choices if str(c.text).strip().lower() == target)
    if isinstance(answer_value, (Fraction, int)):
        try:
            target_frac = parse_number(answer_value)
        except (ValueError, ZeroDivisionError):
            return ()
        keys: list[str] = []
        for c in choices:
            try:
                if parse_number(str(c.text)) == target_frac:
                    keys.append(c.key)
            except (ValueError, ZeroDivisionError):
                continue
        return tuple(keys)
    target = str(answer_value).strip()
    return tuple(c.key for c in choices if str(c.text).strip() == target)


# --- trace hashing ---------------------------------------------------------


def trace_sha256(steps: Sequence[TraceStep]) -> str:
    """SHA-256 of the canonical-JSON of the execution trace (the replay anchor)."""
    return canonical_json_hash([list(s) for s in steps])


def dependency_closure(steps: Sequence[TraceStep]) -> tuple[str, ...]:
    """Sorted union of every world node id the trace read — ``D(P,W)`` (§8)."""
    ids: set[str] = set()
    for _op, nodes, _result in steps:
        ids.update(nodes)
    return tuple(sorted(ids))


@dataclass(frozen=True)
class _Trace:
    """Accumulating trace buffer shared across one evaluation."""

    steps: list[TraceStep] = field(default_factory=list)

    def record(self, op: str, nodes: Mapping[str, Any] | Iterable[Any], result: Any) -> None:
        node_ids = _node_ids(nodes)
        self.steps.append((op, tuple(sorted(node_ids)), _result_repr(result)))

    def finish(self) -> tuple[tuple[TraceStep, ...], tuple[str, ...], str]:
        frozen_steps = tuple(self.steps)
        return frozen_steps, dependency_closure(frozen_steps), trace_sha256(frozen_steps)


def _node_ids(nodes: Mapping[str, Any] | Iterable[Any]) -> set[str]:
    """Extract world node ids from a record's ``nodes`` argument.

    A single :class:`Mapping` (one world node) → its ``id``; an iterable of
    Mappings (a point-set) → each member's ``id``; an iterable of strings → the
    strings themselves. Never the dict repr — so ``D(P,W)`` holds real ids.
    """
    if isinstance(nodes, Mapping):
        return {str(nodes["id"])} if nodes.get("id") else set()
    out: set[str] = set()
    for n in nodes:
        if isinstance(n, Mapping):
            if n.get("id"):
                out.add(str(n["id"]))
        else:
            out.add(str(n))
    return out


def _result_repr(result: Any) -> str:
    if isinstance(result, bool):
        return "true" if result else "false"
    if isinstance(result, Fraction):
        return canonical_number_str(result)
    if isinstance(result, int):
        return str(result)
    if isinstance(result, str):
        return result
    if isinstance(result, tuple):
        return "[" + ",".join(_result_repr(r) for r in result) + "]"
    return str(result)


# --- shared evaluation helpers --------------------------------------------


def literal_value(node: AstNode) -> AnswerValue:
    """Extract an exact value from a ``LITERAL`` leaf (numbers as ``Fraction``)."""
    if not node.is_literal() or not node.args:
        raise ExecutorError(f"expected a literal, got {node.op!r}")
    raw = node.args[0]
    if isinstance(raw, AstNode):
        raise ExecutorError(f"literal {node.op!r} carries a nested node")
    if node.return_type in ("number", "integer"):
        if isinstance(raw, bool):  # noqa: FBT001
            raise ExecutorError("boolean where a number was expected")
        return parse_number(raw)
    if node.return_type == "boolean":
        return bool(raw)
    return str(raw)


__all__ = [
    "AnswerValue",
    "ExecutionResult",
    "ExecutionStatus",
    "Executor",
    "ExecutorError",
    "dependency_closure",
    "literal_value",
    "match_choice",
    "serialize_answer",
    "trace_sha256",
]