"""``SUBSTITUTE_V1`` — sample a new typed value for a node (§10.4).

The substitute is drawn from the node's typed domain, deterministically seeded:

  * **numeric** (a plot point's ``y``, a table cell, a geometry measure) — a
    value within the source range and at the source precision, distinct from the
    current value.
  * **category** (a series / entity label) — a label that does not collide with
    any existing label.
  * **geometry** — after the substitute, the constraint graph must stay feasible
    (no contradiction); :mod:`feasibility` guards this.
  * **multiple choice** — when the problem is multiple-choice, the *new* answer
    the executor computes on the substituted world must match **exactly one** of
    the unchanged choices. A substitute that drives the answer out of the choice
    set (zero or >1 matches) is rejected (P5 gate: "objective choice outside
    unchanged choices reject").

The operator never labels the resulting state — it only validates that the
substitute is *admissible*; P7 derives ``A_SAME`` / ``A_CHANGED`` by execution.
"""

from __future__ import annotations

import hashlib
import math
from collections.abc import Iterator, Sequence
from fractions import Fraction
from typing import Any

from ..dsl.ast import Dsl, Program, canonical_number_str, parse_number
from ..executors.base import Executor, match_choice
from ..ingest.base import Choice
from ..sources.base import World
from ..sources.world_ops import (
    clone_world,
    find_point,
    find_row,
    find_series,
    find_stating_constraint,
    is_geometry,
    looks_numeric,
    node_kind,
    world_sha256,
)
from .base import (
    InterventionError,
    OperatorName,
    TransformedWorld,
    _set_value,
    transformed_hash,
)
from .feasibility import FeasibilityError, is_feasible

_NAME: OperatorName = "SUBSTITUTE_V1"


class SubstituteOperator:
    """Substitute a seeded, typed, admissible new value onto ``target_node``."""

    name = _NAME

    def apply(
        self,
        world: World,
        target_node: str,
        *,
        seed: int,
        dsl: Dsl,
        executor: Executor | None = None,
        program: Program | None = None,
        choices: Sequence[Choice] = (),
        answer_type: str = "",
        **_kwargs: Any,
    ) -> TransformedWorld:
        kind = node_kind(world, target_node)
        if kind is None:
            raise InterventionError(f"SUBSTITUTE_V1: target {target_node!r} is not a world node")
        value, desc = _sample_value(world, target_node, kind, seed)
        new = clone_world(world)
        if not _set_value(new, target_node, value):
            raise InterventionError(
                f"SUBSTITUTE_V1: target {target_node!r} has no mutable value site"
            )
        if is_geometry(new):
            try:
                is_feasible(new, dsl=dsl)
            except FeasibilityError as exc:
                raise InterventionError(
                    f"SUBSTITUTE_V1: infeasible substitute on {target_node!r}: {exc}"
                ) from exc
        # Multiple-choice admissibility: the new answer must be exactly one of
        # the unchanged choices (§10.4). This is a feasibility check, not a
        # state label — the operator still does not assign state.
        if answer_type == "multiple_choice":
            _assert_choice_admissible(new, executor, program, choices, target_node)
        return TransformedWorld(
            world=new,
            operator=_NAME,
            target_node=target_node,
            seed=seed,
            transformed_world_sha256=transformed_hash(
                operator=_NAME,
                target_node=target_node,
                seed=seed,
                source_world_sha256=world_sha256(world),
                transformed_world_sha256=world_sha256(new),
                hidden_nodes=frozenset(),
                substitute_value=value,
            ),
            hidden_nodes=frozenset(),
            substitute_value=value,
            description=desc,
        )


# --- admissibility ---------------------------------------------------------


def _assert_choice_admissible(
    world: World,
    executor: Executor | None,
    program: Program | None,
    choices: Sequence[Choice],
    target_node: str,
) -> None:
    if executor is None or program is None:
        raise InterventionError(
            "SUBSTITUTE_V1: multiple-choice admissibility requires an executor and program"
        )
    result = executor.execute(program, world=world)
    if result.status != "UNIQUE":
        raise InterventionError(
            f"SUBSTITUTE_V1: {target_node!r} substitute made the answer "
            f"non-unique ({result.status}); rejected"
        )
    keys = match_choice(result.answer_value, choices, "multiple_choice")
    if len(keys) != 1:
        raise InterventionError(
            f"SUBSTITUTE_V1: new answer {result.answer_canonical!r} matches "
            f"{len(keys)} unchanged choices (must be exactly one); rejected"
        )


# --- typed sampling --------------------------------------------------------


def _sample_value(world: World, node_id: str, kind: str, seed: int) -> tuple[str, str]:
    if kind == "point":
        return _sample_point_y(world, node_id, seed)
    if kind == "series":
        return _sample_series_label(world, node_id, seed)
    if kind == "row":
        return _sample_row_cell(world, node_id, seed)
    if kind == "constraint":
        return _sample_geometry_measure(world, node_id, seed)
    if kind == "entity":
        return _sample_entity_label(world, node_id, seed)
    raise InterventionError(f"SUBSTITUTE_V1: no sampler for kind {kind!r}")


def _sample_point_y(world: World, pid: str, seed: int) -> tuple[str, str]:
    point = find_point(world, pid)
    if point is None:
        raise InterventionError(f"point {pid!r} not found")
    sidx, _pidx, p = point
    siblings = world["series"][sidx].get("points", []) or []
    values = [_frac(q.get("y", "0")) for q in siblings]
    cur = _frac(p.get("y", "0"))
    lo = min(values) if values else cur
    hi = max(values) if values else cur
    new = _seeded_in_range(seed, pid, "point_y", lo, hi, {cur})
    return canonical_number_str(new), f"substitute point {pid} y → {new}"


def _sample_row_cell(world: World, rid: str, seed: int) -> tuple[str, str]:
    row = find_row(world, rid)
    if row is None:
        raise InterventionError(f"row {rid!r} not found")
    _ridx, r = row
    cells = r.get("cells", {}) or {}
    if not cells:
        raise InterventionError(f"row {rid!r} has no cells")
    key = next(iter(cells))
    cur = _frac(cells[key])
    # Range across the same column in every row, if identifiable by shared key.
    col_vals = [
        _frac(row_.get("cells", {}).get(key, cells[key]))
        for row_ in (world.get("rows", []) or [])
        if key in (row_.get("cells", {}) or {})
    ]
    lo = min(col_vals) if col_vals else cur
    hi = max(col_vals) if col_vals else cur
    new = _seeded_in_range(seed, rid, f"cell:{key}", lo, hi, {cur})
    return canonical_number_str(new), f"substitute row {rid} cell {key} → {new}"


def _sample_series_label(world: World, sid: str, seed: int) -> tuple[str, str]:
    series = find_series(world, sid)
    if series is None:
        raise InterventionError(f"series {sid!r} not found")
    _sidx, s = series
    existing = {str(t.get("label", "")) for t in world.get("series", []) or []}
    cur = str(s.get("label", sid))
    prefix = _label_prefix(cur)
    for n in _seeded_offsets(seed, sid, "label", span=1000):
        cand = f"{prefix}_{n}"
        if cand not in existing:
            return cand, f"substitute series {sid} label → {cand}"
    raise InterventionError(f"series {sid!r}: no non-colliding label found")


def _sample_geometry_measure(world: World, entity: str, seed: int) -> tuple[str, str]:
    found = find_stating_constraint(world, entity)
    if found is None:
        raise InterventionError(f"no stating constraint for {entity!r}")
    _cidx, c = found
    args = list(c.get("args") or [])
    pred = c.get("predicate")
    if pred == "MeasureOf" and len(args) >= 2:
        cur = _frac(args[1])
    elif pred == "Equals" and len(args) == 2:
        cur = _frac(args[1]) if looks_numeric(args[1]) else _frac(args[0])
    else:
        raise InterventionError(f"stating constraint for {entity!r} is not numeric")
    # Geometry measures are unbounded; sample a distinct integer near the source
    # (feasibility, not range, is the binding constraint here).
    new = cur + Fraction(next(_seeded_offsets(seed, entity, "measure", span=200)) - 100)
    return canonical_number_str(new), f"substitute measure {entity} → {new}"


def _sample_entity_label(world: World, eid: str, seed: int) -> tuple[str, str]:
    entity = next((e for e in world.get("entities", []) or [] if e.get("id") == eid), None)
    if entity is None:
        raise InterventionError(f"entity {eid!r} not found")
    cur = str(entity.get("label", entity.get("id", eid)))
    existing = {str(e.get("label", e.get("id", ""))) for e in world.get("entities", []) or []}
    prefix = _label_prefix(cur)
    for n in _seeded_offsets(seed, eid, "elabel", span=1000):
        cand = f"{prefix}_{n}"
        if cand not in existing:
            return cand, f"substitute entity {eid} label → {cand}"
    raise InterventionError(f"entity {eid!r}: no non-colliding label found")


# --- seeded helpers (deterministic, Math.random-free) ----------------------


def _seeded_in_range(
    seed: int, tag: str, kind: str, lo: Fraction, hi: Fraction, exclude: set[Fraction]
) -> Fraction:
    """A deterministic integer in ``[lo, hi]`` (extended by ±1 when degenerate),
    not in ``exclude``, at source integer precision."""
    lo_i = int(lo)
    hi_i = int(hi)
    if hi_i < lo_i:
        lo_i, hi_i = hi_i, lo_i
    if hi_i - lo_i < 1:  # degenerate range: relax by ±1 to allow a distinct value
        lo_i -= 1
        hi_i += 1
    span = hi_i - lo_i + 1
    # An affine full-cycle permutation needs at most ``len(exclude) + 1``
    # probes to find a non-excluded integer.  Never enumerate a numeric range:
    # PlotQA values can make ``span`` billions wide.
    for probe, n in enumerate(_seeded_offsets(seed, tag, kind, span=span)):
        if probe > len(exclude):
            break
        cand = Fraction(lo_i + (n % (hi_i - lo_i + 1)))
        if cand not in exclude:
            return cand
    raise InterventionError(f"no in-range substitute for {tag!r} ({kind})")


def _seeded_offsets(seed: int, tag: str, kind: str, *, span: int) -> Iterator[int]:
    """Yield a deterministic O(1)-memory permutation of ``[0, span)``."""

    span = max(span, 1)
    digest = hashlib.sha256(f"{seed}|{tag}|{kind}|affine-v1".encode()).digest()
    start = int.from_bytes(digest[:16], "big") % span
    step = int.from_bytes(digest[16:], "big") % span
    if step == 0:
        step = 1
    while math.gcd(step, span) != 1:
        step = (step + 1) % span
        if step == 0:
            step = 1
    for index in range(span):
        yield (start + index * step) % span


def _frac(value: Any) -> Fraction:
    return parse_number(value)


def _label_prefix(label: str) -> str:
    return label.rstrip("0123456789_") or label or "node"


__all__ = ["SubstituteOperator"]