src/explicit_learning/dsl/ast.py

"""Immutable typed AST for the canonical question programs (``docs/02`` §7).

A question *program* is a tree of :class:`AstNode` values. The serialized form
conforms to ``schemas/compiled_program.schema.json`` ``$defs/astNode``::

    {"op": <str>, "args": [<astNode | str | number | bool>, ...], "return_type": <str>?}

Design choices pinned by the spec:

  * **Exact numerics.** Numeric literals are ``fractions.Fraction`` internally and
    serialize to a *canonical rational string* (``5`` → ``"5"``, ``3/2`` →
    ``"3/2"``, ``"1.50"`` → ``"3/2"``), never a JSON float — so ``1.5`` and
    ``3/2`` collapse to one canonical form (``docs/02`` §3.2/§3.3 "exact rational
    우선", "decimal string canonicalizer trailing-zero 제거"). A literal that would
    lose precision as a float is therefore exact.
  * **Uniform nodes.** Every meaningful operand is an :class:`AstNode`: compound
    ops (``LOOKUP``, ``MEASURE``, …) and two leaf kinds — ``REF`` (an entity
    reference with a stable id) and ``LITERAL`` (an atomic value). Bare atomic
    ``args`` are reserved for *field/key* strings (e.g. ``"value"``) that are not
    themselves typed operands. This keeps the type checker uniform: it dispatches
    on ``op`` and reads ``return_type``.
  * **Immutability.`` :class:`AstNode` and :class:`Program` are frozen; ``args`` is
    a tuple. Canonicalization returns new nodes rather than mutating.

The :class:`Program` envelope is the P2 structural record — it carries the AST,
the referent selector, the *declared* referent cardinality, the resolved
referenced node ids, and the canonical program hash. The full
``compiled_program`` record (``compile_id`` / ``compiler_role`` / ``model`` /
``request_sha256``) is the **P4 C2 model-compiler** record and is not produced
here.
"""

from __future__ import annotations

from collections.abc import Mapping
from dataclasses import dataclass
from fractions import Fraction
from functools import lru_cache
from typing import Any, Literal, Union

from ..ingest.base import IngestError
from ..paths import repo_root
from ..schema_io import load_schema, validate

Dsl = Literal["plotqa_dsl_v1", "geometry_dsl_v1", "table_dsl_v1", "clevr_dsl_v1"]
CompileStatus = Literal["compiled", "unsupported"]

# Leaf op markers. A leaf node carries exactly one atomic arg.
REF = "REF"  # entity reference: args=(id_str,), return_type = entity kind
LITERAL = "LITERAL"  # atomic value: args=(serialized_value,), return_type = value kind

# One positional operand of a node: a sub-node, or a bare atomic field/key.
Arg = Union["AstNode", str, int, Fraction, bool]


class ProgramError(IngestError):
    """Raised when an AST node or :class:`Program` is malformed or schema-invalid."""


# --- numeric canonicalization (§3.2/§3.3) ----------------------------------


def parse_number(value: str | int | Fraction) -> Fraction:
    """Parse a decimal/rational/integer into an exact reduced :class:`Fraction`.

    Accepts ``"1.5"``, ``"3/2"``, ``"5"``, ``"5.0"`` and integers. ``Fraction``
    reduces and exact-represents each so numerically-equal inputs compare equal.
    """
    if isinstance(value, Fraction):
        return value
    if isinstance(value, int) and not isinstance(value, bool):
        return Fraction(value)
    return Fraction(str(value))


def canonical_number_str(value: str | int | Fraction) -> str:
    """Canonical exact-rational string of a numeric value (``docs/02`` §3.2).

    Integers render as their decimal string (``5`` → ``"5"``); non-integer
    rationals as ``"num/den"`` in lowest terms (``3/2`` → ``"3/2"``). Trailing
    zeros are gone because the form is exact, not decimal. Two numerically-equal
    inputs always produce the same string.
    """
    frac = parse_number(value)
    if frac.denominator == 1:
        return str(frac.numerator)
    return f"{frac.numerator}/{frac.denominator}"


# --- AST node ---------------------------------------------------------------


@dataclass(frozen=True)
class AstNode:
    """One immutable node of a question program (``compiled_program.schema.json`` astNode).

    ``op`` is the operator/predicate name (``LOOKUP``, ``MeasureOf``, ``REF``,
    ``LITERAL``, …). ``args`` is an order-significant tuple of sub-nodes and bare
    atomic field keys. ``return_type`` is the typed result kind
    (``value``/``series``/``point``/``angle``/``number``/…); it is the type the
    checker and canonicalizer propagate.
    """

    op: str
    args: tuple[Arg, ...] = ()
    return_type: str = ""

    def to_ast_node_dict(self) -> dict[str, Any]:
        """Serialize to a dict conforming to ``$defs/astNode``."""
        out: dict[str, Any] = {"op": self.op, "args": [_arg_to_dict(a) for a in self.args]}
        if self.return_type:
            out["return_type"] = self.return_type
        return out

    def is_ref(self) -> bool:
        return self.op == REF

    def is_literal(self) -> bool:
        return self.op == LITERAL

    def ref_id(self) -> str:
        """The stable entity id of a ``REF`` leaf (raises otherwise)."""
        if not self.is_ref():
            raise ProgramError(f"{self.op!r} node is not an entity reference")
        if len(self.args) != 1 or not isinstance(self.args[0], str):
            raise ProgramError(f"REF node must carry one string id, got {self.args!r}")
        return self.args[0]


def _arg_to_dict(arg: Arg) -> Any:
    if isinstance(arg, AstNode):
        return arg.to_ast_node_dict()
    if isinstance(arg, bool):  # before int: bool is an int subclass
        return arg
    if isinstance(arg, int):
        return arg
    if isinstance(arg, Fraction):
        # A bare numeric arg is serialized as its canonical exact string so it
        # never degrades to a lossy float; builders normally wrap numerics in a
        # LITERAL node, but this keeps a bare Fraction exact if it appears.
        return canonical_number_str(arg)
    if isinstance(arg, str):
        return arg
    raise ProgramError(f"unsupported AST arg type {type(arg)!r}")


def _arg_from_dict(arg: Any) -> Arg:
    """Inverse of :func:`_arg_to_dict`: rebuild one AST arg from model JSON."""
    if isinstance(arg, Mapping):  # nested astNode
        return ast_node_from_dict(arg)
    if isinstance(arg, bool):  # before int: bool is an int subclass
        return arg
    if isinstance(arg, int):
        return arg
    if isinstance(arg, float):
        return parse_number(str(arg))  # exact rational, never a lossy float
    if isinstance(arg, str):
        return arg
    raise ProgramError(f"unsupported astNode arg {arg!r}")


def ast_node_from_dict(data: Mapping[str, Any]) -> AstNode:
    """Rebuild an :class:`AstNode` from a ``$defs/astNode``-shaped dict.

    The inverse of :meth:`AstNode.to_ast_node_dict`, used by the C2 compiler
    (P4) to parse a model's JSON program response into the typed AST. Numeric
    args are kept exact (a JSON float becomes a :class:`~fractions.Fraction`).
    Raises :class:`ProgramError` on a malformed node; call
    :func:`validate_ast_node` first for schema-level errors.
    """
    if not isinstance(data, Mapping):
        raise ProgramError(f"astNode must be an object, got {type(data).__name__}")
    op = data.get("op")
    if not isinstance(op, str) or not op:
        raise ProgramError("astNode requires a non-empty string 'op'")
    raw_args = data.get("args", [])
    if not isinstance(raw_args, list):
        raise ProgramError("astNode 'args' must be an array")
    args = tuple(_arg_from_dict(a) for a in raw_args)
    return_type = str(data.get("return_type", "") or "")
    return AstNode(op=op, args=args, return_type=return_type)


# --- leaf constructors ------------------------------------------------------


def ref(entity_id: str, *, return_type: str = "entity") -> AstNode:
    """Build an entity-reference leaf (``op=REF``, one string id arg)."""
    if not entity_id:
        raise ProgramError("entity reference id must be non-empty")
    return AstNode(op=REF, args=(entity_id,), return_type=return_type)


def lit(value: str | int | Fraction | bool, *, return_type: str) -> AstNode:
    """Build an atomic-literal leaf.

    Numerics (``return_type`` ``number``/``integer``) serialize via
    :func:`canonical_number_str`; booleans as JSON booleans; expressions/strings
    as their (pre-canonicalization) string form.
    """
    if return_type in ("number", "integer"):
        return AstNode(op=LITERAL, args=(canonical_number_str(value),), return_type=return_type)
    if return_type == "boolean":
        return AstNode(op=LITERAL, args=(bool(value),), return_type=return_type)
    if return_type in ("expression", "string", "field"):
        return AstNode(op=LITERAL, args=(str(value),), return_type=return_type)
    raise ProgramError(f"unsupported literal return_type {return_type!r}")


# --- program envelope -------------------------------------------------------


@dataclass(frozen=True)
class Program:
    """The P2 structural program record for one normalized item.

    ``canonical_program_sha256`` is filled by
    :func:`~explicit_learning.dsl.canonicalize.canonical_program_sha256`.
    ``constraint_channels`` carries geometry channel provenance (constraint
    node key → ``text``/``visual``/``redundant``) for the P3 intervention layer;
    it is **not** part of the schema-conforming envelope.
    """

    dsl: Dsl
    program: AstNode
    base_id: str
    question_sha256: str
    choices_sha256: str
    compile_status: CompileStatus
    referent_selector: AstNode | None = None
    required_referent_cardinality: int | None = None
    referenced_node_ids: tuple[str, ...] = ()
    canonical_program_sha256: str = ""
    reason_code: str | None = None
    constraint_channels: tuple[tuple[str, str], ...] = ()

    def to_dict(self) -> dict[str, Any]:
        """The P2 program envelope (a subset of ``compiled_program``).

        The ``program`` sub-dict conforms to ``$defs/astNode``; the envelope is
        not itself a full ``compiled_program`` record (that needs P4's
        ``compile_id``/``compiler_role``/``model``).
        """
        envelope: dict[str, Any] = {
            "dsl": self.dsl,
            "program": self.program.to_ast_node_dict(),
            "base_id": self.base_id,
            "question_sha256": self.question_sha256,
            "choices_sha256": self.choices_sha256,
            "compile_status": self.compile_status,
            "referent_selector": (
                self.referent_selector.to_ast_node_dict() if self.referent_selector else None
            ),
            "required_referent_cardinality": self.required_referent_cardinality,
            "referenced_node_ids": list(self.referenced_node_ids),
            "canonical_program_sha256": self.canonical_program_sha256 or None,
        }
        if self.reason_code is not None:
            envelope["reason_code"] = self.reason_code
        return envelope


# --- schema validation ------------------------------------------------------


@lru_cache(maxsize=1)
def _compiled_program_schema() -> dict[str, Any]:
    return load_schema(repo_root() / "schemas" / "compiled_program.schema.json")


@lru_cache(maxsize=1)
def _ast_node_schema() -> dict[str, Any]:
    """A standalone schema validating one ``astNode`` (with ``$defs`` in scope)."""
    full = _compiled_program_schema()
    return {"$schema": full.get("$schema", ""), "$defs": full["$defs"], "$ref": "#/$defs/astNode"}


def validate_ast_node(node: Mapping[str, Any] | AstNode) -> None:
    """Raise :class:`ProgramError` if ``node`` violates ``$defs/astNode``."""
    instance = node.to_ast_node_dict() if isinstance(node, AstNode) else dict(node)
    errors = validate(instance, _ast_node_schema())
    if errors:
        raise ProgramError("astNode failed schema validation: " + "; ".join(errors))


__all__ = [
    "Arg",
    "AstNode",
    "CompileStatus",
    "Dsl",
    "LITERAL",
    "Program",
    "ProgramError",
    "REF",
    "ast_node_from_dict",
    "canonical_number_str",
    "lit",
    "parse_number",
    "ref",
    "validate_ast_node",
]