src/explicit_learning/c2/mutations.py

"""Deterministic mutation suite for C2 program equivalence (``docs/02`` §7.3).

§7.3: full-source answer agreement alone cannot filter out a *coincidental*
program, so the mutation suite is mandatory. For each dependency leaf the
proposer program reads, generate ``≥8`` valid alternative mutations of the
world; execute *both* programs on each mutated world and require equal
``(status, answer)``. The suite uses the deterministic P3 executor (no model
calls) and is fully seed-determined: the same ``(world, leaves, seed)`` always
reproduces the same mutations.

Two mutation kinds, both keeping the world well-formed:

  * ``SUBSTITUTE`` — replace a leaf's numeric value with a distinct seeded
    rational (the program stays ``UNIQUE`` with a different answer).
  * ``REDACT`` — remove the leaf (point / row / series / stating constraint); the
    program may go ``MISSING_INFORMATION`` / ``INVALID_REFERENT``, but two
    equivalent programs diverge identically, so they still agree.

Per leaf the generator emits ``per_leaf`` (default 8) ``SUBSTITUTE`` variants
plus one ``REDACT`` when the leaf is cleanly removable — always ``≥8``.
"""

from __future__ import annotations

import copy
import hashlib
from dataclasses import dataclass
from fractions import Fraction
from typing import Any

from ..dsl.ast import Dsl, canonical_number_str, parse_number
from ..sources.base import World
from ..sources.world_ops import (
    find_point,
    find_row,
    find_series,
    find_stating_constraint,
    is_geometry,
    is_plot,
    is_table,
    looks_numeric,
)


@dataclass(frozen=True)
class Mutation:
    """One seeded, valid alternative world for the §7.3 suite."""

    world: World
    leaf: str
    kind: str  # "SUBSTITUTE" | "REDACT"
    description: str


def deterministic_mutations(
    world: World,
    leaves: tuple[str, ...],
    *,
    dsl: Dsl,
    seed: int,
    per_leaf: int = 8,
) -> list[Mutation]:
    """Generate ``≥per_leaf`` valid mutations per dependency leaf (seed-determined).

    Leaves with no mutable value fall back to substituting the nearest mutable
    value in the world, so every leaf still yields ``per_leaf`` distinct valid
    alternatives. The output order is deterministic: leaves in input order, then
    ``SUBSTITUTE`` (offset 0..per_leaf-1) then ``REDACT``.
    """
    out: list[Mutation] = []
    for leaf in leaves:
        for i in range(per_leaf):
            mut = _substitute(world, leaf, dsl, seed, i)
            if mut is not None:
                out.append(mut)
        redact = _redact(world, leaf, dsl, seed)
        if redact is not None:
            out.append(redact)
    # A leaf set may be empty (e.g., a pure-literal program); still emit ≥8
    # global substitutes so the suite is non-vacuous.
    if not leaves:
        for i in range(max(per_leaf, 8)):
            mut = _substitute_global(world, dsl, seed, i)
            if mut is not None:
                out.append(mut)
    return out


# --- seeded offsets ---------------------------------------------------------


def _offset(seed: int, leaf: str, kind: str, i: int) -> int:
    """A deterministic 1..99 offset (distinct per ``(leaf, kind, i)``)."""
    digest = hashlib.sha256(f"{seed}|{leaf}|{kind}|{i}".encode()).hexdigest()
    return 1 + (int(digest[:12], 16) % 99)


def _bump(value: Any, by: int) -> str:
    """Add ``by`` to a numeric world value, returning its canonical string."""
    frac = parse_number(value) + Fraction(by)
    return canonical_number_str(frac)


# --- SUBSTITUTE ------------------------------------------------------------


def _substitute(world: World, leaf: str, dsl: Dsl, seed: int, i: int) -> Mutation | None:
    by = _offset(seed, leaf, "SUBSTITUTE", i)
    new_world = copy.deepcopy(world)
    desc = _apply_substitute(new_world, leaf, by)
    if desc is None:
        # Fall back to a global mutable value so this leaf still yields a valid
        # alternative mutation.
        desc = _apply_substitute_global(new_world, by)
        if desc is None:
            return None
    return Mutation(new_world, leaf, "SUBSTITUTE", f"{desc} (+{by})")


def _apply_substitute(world: World, leaf: str, by: int) -> str | None:
    """Substitute the leaf's own value; return a description or ``None``."""
    if _is_plot(world):
        return _substitute_plot(world, leaf, by)
    if _is_table(world):
        return _substitute_table(world, leaf, by)
    if _is_geometry(world):
        return _substitute_geometry(world, leaf, by)
    return None


def _substitute_plot(world: World, leaf: str, by: int) -> str | None:
    point = _find_point(world, leaf)
    if point is not None:
        sidx, pidx, p = point
        p["y"] = _bump(p.get("y", "0"), by)
        world["series"][sidx]["points"][pidx] = p
        return f"point {leaf} y"
    series = _find_series(world, leaf)
    if series is not None:
        sidx, s = series
        pts = s.get("points", []) or []
        if pts:
            pts[0]["y"] = _bump(pts[0].get("y", "0"), by)
            world["series"][sidx]["points"] = pts
            return f"series {leaf} first-point y"
    return None


def _substitute_table(world: World, leaf: str, by: int) -> str | None:
    row = _find_row(world, leaf)
    if row is None:
        return None
    ridx, r = row
    cells = r.get("cells", {}) or {}
    if not cells:
        return None
    key = next(iter(cells))
    cells[key] = _bump(cells[key], by)
    world["rows"][ridx]["cells"] = cells
    return f"row {leaf} cell {key}"


def _substitute_geometry(world: World, leaf: str, by: int) -> str | None:
    found = _find_stating_constraint(world, leaf)
    if found is None:
        return None
    cidx, c = found
    args = list(c.get("args") or [])
    pred = c.get("predicate")
    if pred == "MeasureOf" and len(args) >= 2 and args[0] == leaf:
        args[1] = _bump(args[1], by)
    elif pred == "Equals" and len(args) == 2:
        if args[0] == leaf and _looks_numeric(args[1]):
            args[1] = _bump(args[1], by)
        elif args[1] == leaf and _looks_numeric(args[0]):
            args[0] = _bump(args[0], by)
        else:
            return None
    else:
        return None
    c["args"] = args
    world["constraints"][cidx] = c
    return f"constraint {pred}({leaf}) value"


# --- REDACT -----------------------------------------------------------------


def _redact(world: World, leaf: str, dsl: Dsl, seed: int) -> Mutation | None:
    new_world = copy.deepcopy(world)
    desc = _apply_redact(new_world, leaf)
    if desc is None:
        return None
    return Mutation(new_world, leaf, "REDACT", desc)


def _apply_redact(world: World, leaf: str) -> str | None:
    if _is_plot(world):
        point = _find_point(world, leaf)
        if point is not None:
            sidx, _pidx, p = point
            pts = world["series"][sidx].get("points", [])
            world["series"][sidx]["points"] = [q for q in pts if q.get("id") != leaf]
            return f"remove point {leaf}"
        series = _find_series(world, leaf)
        if series is not None:
            world["series"] = [s for s in world.get("series", []) if s.get("id") != leaf]
            return f"remove series {leaf}"
        return None
    if _is_table(world):
        if _find_row(world, leaf) is not None:
            world["rows"] = [r for r in world.get("rows", []) if r.get("id") != leaf]
            return f"remove row {leaf}"
        return None
    if _is_geometry(world):
        found = _find_stating_constraint(world, leaf)
        if found is not None:
            cidx, _c = found
            world["constraints"] = [
                x for k, x in enumerate(world.get("constraints", [])) if k != cidx
            ]
            return f"remove stating constraint for {leaf}"
        if any(e.get("id") == leaf for e in world.get("entities", [])):
            world["entities"] = [e for e in world.get("entities", []) if e.get("id") != leaf]
            return f"remove entity {leaf}"
        return None
    return None


# --- global fallback --------------------------------------------------------


def _substitute_global(world: World, dsl: Dsl, seed: int, i: int) -> Mutation | None:
    by = _offset(seed, "__global__", "SUBSTITUTE", i)
    new_world = copy.deepcopy(world)
    desc = _apply_substitute_global(new_world, by)
    if desc is None:
        return None
    return Mutation(new_world, "__global__", "SUBSTITUTE", f"{desc} (+{by})")


def _apply_substitute_global(world: World, by: int) -> str | None:
    if _is_plot(world):
        for s in world.get("series", []):
            pts = s.get("points", []) or []
            if pts:
                pts[0]["y"] = _bump(pts[0].get("y", "0"), by)
                s["points"] = pts
                return f"series {s.get('id')} first-point y"
        return None
    if _is_table(world):
        for r in world.get("rows", []):
            cells = r.get("cells", {}) or {}
            if cells:
                key = next(iter(cells))
                cells[key] = _bump(cells[key], by)
                r["cells"] = cells
                return f"row {r.get('id')} cell {key}"
        return None
    if _is_geometry(world):
        for c in world.get("constraints", []):
            if c.get("predicate") == "MeasureOf" and len(c.get("args") or []) >= 2:
                args = list(c["args"])
                if _looks_numeric(args[1]):
                    args[1] = _bump(args[1], by)
                    c["args"] = args
                    return f"constraint MeasureOf({args[0]}) value"
        return None
    return None


# --- world locators (shared with the P5 intervention layer) ----------------
# The locators live in :mod:`explicit_learning.sources.world_ops`; the leading
# underscore aliases keep this module's call sites unchanged.

_is_plot = is_plot
_is_table = is_table
_is_geometry = is_geometry
_find_point = find_point
_find_series = find_series
_find_row = find_row
_find_stating_constraint = find_stating_constraint
_looks_numeric = looks_numeric


__all__ = ["Mutation", "deterministic_mutations"]