src/explicit_learning/dsl/canonicalize.py

"""Six-step AST canonicalization and the canonical program hash (``docs/02`` §7.2).

Two programs are *semantically equivalent* iff their canonical ASTs hash equal.
``canonical_program_sha256`` is the integrity anchor reused by the C2 dual-compile
exact-match (``canonical_program_exact_match``) and the executor (P3):

    1. resolve entity names → stable IDs (via the world's label→id map);
    2. numeric literal normalize (exact rational; expression → SymPy canonical);
    3. commutative operand sort (per-DSL commutative ops, sorted by canonical JSON);
    4. alias operator expand (per-DSL alias → canonical op name);
    5. redundant cast/remove (per-DSL no-op identity casts collapse to their arg);
    6. topological node ordering (children canonicalized before parents, so a
       parent's commutative sort is over already-canonical operands).

Step 6 is structural in the recursion: each child is canonicalized before its
parent, and the parent's commutative sort keys on the canonical (post-alias) op.
The numbered order is the spec's conceptual order; alias-expansion is applied
before the commutative sort so sort keys on the *canonical* operator, which is
the operator commutativity is defined on.
"""

from __future__ import annotations

from collections.abc import Mapping
from dataclasses import dataclass
from fractions import Fraction
from typing import Any

from ..hashing import canonical_json, canonical_json_hash
from ..sources.base import World
from .ast import LITERAL, REF, AstNode, Dsl, Program, canonical_number_str, parse_number


# Per-DSL canonicalization profile (loaded lazily to avoid a circular import:
# the dsl modules import this module to compute the canonical hash).
@dataclass(frozen=True)
class DslProfile:
    """Per-DSL canonicalization knobs."""

    commutative_ops: frozenset[str]
    aliases: Mapping[str, str]
    identity_casts: frozenset[str]


def profile(dsl: Dsl) -> DslProfile:
    """Load the canonicalization profile for one DSL (lazy import)."""
    if dsl == "plotqa_dsl_v1":
        from . import plotdsl

        return DslProfile(plotdsl.COMMUTATIVE_OPS, plotdsl.ALIASES, plotdsl.IDENTITY_CASTS)
    if dsl == "geometry_dsl_v1":
        from . import geometrydsl

        return DslProfile(
            geometrydsl.COMMUTATIVE_OPS, geometrydsl.ALIASES, geometrydsl.IDENTITY_CASTS
        )
    if dsl == "table_dsl_v1":
        from . import tabledsl

        return DslProfile(tabledsl.COMMUTATIVE_OPS, tabledsl.ALIASES, tabledsl.IDENTITY_CASTS)
    if dsl == "clevr_dsl_v1":
        from . import clevrdsl

        return DslProfile(clevrdsl.COMMUTATIVE_OPS, clevrdsl.ALIASES, clevrdsl.IDENTITY_CASTS)
    raise ValueError(f"unknown DSL {dsl!r}")


# --- world resolution (step 1) ---------------------------------------------


def entity_ids(world: World | None) -> set[str]:
    """All stable entity ids declared by a world (``plot_world_v1`` / ``geometry_world_v1``)."""
    if not world:
        return set()
    ids: set[str] = set()
    for series in world.get("series", []) or []:
        if isinstance(series, Mapping) and series.get("id"):
            ids.add(str(series["id"]))
        for point in series.get("points", []) or [] if isinstance(series, Mapping) else []:
            if isinstance(point, Mapping) and point.get("id"):
                ids.add(str(point["id"]))
    for entity in world.get("entities", []) or []:
        if isinstance(entity, Mapping) and entity.get("id"):
            ids.add(str(entity["id"]))
    for obj in world.get("objects", []) or []:
        if isinstance(obj, Mapping) and obj.get("id"):
            ids.add(str(obj["id"]))
    return ids


def entity_aliases(world: World | None) -> dict[str, str]:
    """Label → stable-id map for entity-name resolution (``docs/02`` §7.2 step 1).

    A plot series label resolves to its ``series:`` id; a geometry entity has no
    human label separate from its id, so it maps to itself. A referent that is
    already a stable id passes through unchanged.
    """
    if not world:
        return {}
    aliases: dict[str, str] = {}
    for series in world.get("series", []) or []:
        if isinstance(series, Mapping) and series.get("id"):
            sid = str(series["id"])
            aliases[sid] = sid
            label = series.get("label")
            if isinstance(label, str) and label:
                aliases[label] = sid
    for entity in world.get("entities", []) or []:
        if isinstance(entity, Mapping) and entity.get("id"):
            eid = str(entity["id"])
            aliases[eid] = eid
    for obj in world.get("objects", []) or []:
        if isinstance(obj, Mapping) and obj.get("id"):
            oid = str(obj["id"])
            aliases[oid] = oid
    return aliases


def resolve_ref_id(node: AstNode, aliases: Mapping[str, str]) -> AstNode:
    """Step 1: replace a REF label with its stable id when a mapping exists."""
    if not node.is_ref():
        return node
    raw = node.ref_id()
    resolved = aliases.get(raw, raw)
    if resolved == raw:
        return node
    return AstNode(op=REF, args=(resolved,), return_type=node.return_type)


# --- literal normalization (step 2) ----------------------------------------


def canonical_expression(expr: str) -> str:
    """Canonical SymPy form of an expression literal (``docs/02`` §3.3).

    ``sympy.expand`` + the default printer yields a term-ordered canonical string
    so ``"1 + x"`` and ``"x + 1"`` collapse. SymPy is imported lazily; if it is
    unavailable the literal is left untouched (P2 plot programs never need it).
    """
    try:
        import sympy
    except ImportError:  # pragma: no cover - sympy is pinned in requirements
        return expr
    try:
        expanded = sympy.expand(sympy.sympify(expr))
    except Exception:  # noqa: BLE001 - sympify raises varied types on bad input
        return expr
    return str(sympy.sstr(expanded))


def normalize_literal(node: AstNode) -> AstNode:
    """Step 2: re-canonicalize a LITERAL's value (numeric exact / expression SymPy)."""
    if not node.is_literal() or not node.args:
        return node
    value = node.args[0]
    if node.return_type in ("number", "integer") and isinstance(value, str):
        return AstNode(
            op=LITERAL,
            args=(canonical_number_str(parse_number(value)),),
            return_type=node.return_type,
        )
    if node.return_type == "expression" and isinstance(value, str):
        return AstNode(
            op=LITERAL, args=(canonical_expression(value),), return_type=node.return_type
        )
    return node


# --- canonicalize ----------------------------------------------------------


def canonicalize(node: AstNode, *, dsl: Dsl, world: World | None = None) -> AstNode:
    """Apply the §7.2 six steps to ``node`` and return a new canonical :class:`AstNode`."""
    prof = profile(dsl)
    aliases = entity_aliases(world)

    def canon(n: AstNode) -> AstNode:
        # Step 1: resolve entity references.
        n = resolve_ref_id(n, aliases)
        # Leaves: step 2 only.
        if n.is_ref():
            return n
        if n.is_literal():
            return normalize_literal(n)
        # Compound: canonicalize children first (step 6 — topological ordering).
        canon_args = tuple(_canonicalize_arg(a, canon) for a in n.args)
        # Step 4: alias operator expand (before sort so sort keys on the canonical op).
        op = prof.aliases.get(n.op, n.op)
        # Step 5: redundant cast/remove — a single-arg identity cast collapses.
        if (
            op in prof.identity_casts
            and len(canon_args) == 1
            and isinstance(canon_args[0], AstNode)
        ):
            return canon_args[0]
        # Step 3: commutative operand sort over canonical child JSON.
        if op in prof.commutative_ops:
            canon_args = _sort_commutative(canon_args)
        return AstNode(op=op, args=canon_args, return_type=n.return_type)

    return canon(node)


def _canonicalize_arg(arg: Any, canon: Any) -> Any:
    """Canonicalize a sub-node; pass bare atomic field keys through untouched."""
    if isinstance(arg, AstNode):
        return canon(arg)
    return arg


def _sort_commutative(args: tuple[Any, ...]) -> tuple[Any, ...]:
    """Sort commutative operands by their canonical-JSON serialization (stable)."""
    return tuple(sorted(args, key=_arg_sort_key))


def _arg_sort_key(arg: Any) -> str:
    if isinstance(arg, AstNode):
        return canonical_json(arg.to_ast_node_dict())
    if isinstance(arg, bool):
        return canonical_json(arg)
    if isinstance(arg, int):
        return canonical_json(arg)
    if isinstance(arg, Fraction):
        return canonical_number_str(arg)
    if isinstance(arg, str):
        return canonical_json(arg)
    return canonical_json(str(arg))


# --- canonical program hash ------------------------------------------------


def canonical_program_sha256(program: Program, *, world: World | None = None) -> str:
    """SHA-256 of the canonical program AST (+ referent selector).

    The hash input is the canonical-JSON of::

        {"program": <canonical astNode>, "referent_selector": <canonical astNode | null>}

    This is the exact-match key for ``canonical_program_exact_match`` (P4) and the
    program fingerprint reused by the executor (P3). Equivalent programs hash
    equal; non-equivalent programs hash differently.
    """
    canon_program = canonicalize(program.program, dsl=program.dsl, world=world)
    referent: dict[str, Any] | None = None
    if program.referent_selector is not None:
        canon_ref = canonicalize(program.referent_selector, dsl=program.dsl, world=world)
        referent = canon_ref.to_ast_node_dict()
    return canonical_json_hash(
        {"program": canon_program.to_ast_node_dict(), "referent_selector": referent}
    )


def programs_equivalent(a: Program, b: Program, *, world: World | None = None) -> bool:
    """True iff two programs share a canonical program hash (§7.2 canonical match)."""
    return canonical_program_sha256(a, world=world) == canonical_program_sha256(b, world=world)


__all__ = [
    "DslProfile",
    "canonical_expression",
    "canonical_program_sha256",
    "canonicalize",
    "entity_aliases",
    "entity_ids",
    "profile",
    "programs_equivalent",
    "resolve_ref_id",
]