#!/usr/bin/env python3
"""Compare historical and current B/S/C model behavior and gradients."""

from __future__ import annotations

import argparse
import hashlib
import importlib.util
import json
import platform
import sys
from pathlib import Path
from types import ModuleType
from typing import Any

import torch
from torch import nn


AUDIT_ROOT = Path("/nfs/ywang29/GmNet/e4_spectral_audit")
SNAPSHOT_ROOT = AUDIT_ROOT / "source_snapshots/alignment_4a62"
OLD_SOURCE = SNAPSHOT_ROOT / "gmnet/models/gmnet.py"
NEW_SOURCE = Path("/nfs/ywang29/GmNet/journal_exp/gmnet/models/gmnet.py")
SNAPSHOT_MANIFEST = SNAPSHOT_ROOT / "source_manifest.json"
EXPECTED_OLD_SHA256 = (
    "5291156084aaf72936d1f8896057e7e606f74ef05aed856df4940e4838dbe3ac"
)
EXPECTED_NEW_SHA256 = (
    "8446a0ed7d6863f81e88929f3277d363c961372210279de7d0e770f636852f3c"
)
ARMS = {
    "B": "baseline",
    "S": "stop_gradient",
    "C": "channel_derangement",
}
COMMON_METADATA_KEYS = (
    "global_block_index",
    "stage_index",
    "stage_block_index",
    "mode",
    "seed",
    "channels",
    "permutation_sha256",
    "permutation_hash_encoding",
    "fixed_points",
    "is_bijection",
)


def sha256(path: Path) -> str:
    digest = hashlib.sha256()
    with path.open("rb") as handle:
        for chunk in iter(lambda: handle.read(1024 * 1024), b""):
            digest.update(chunk)
    return digest.hexdigest()


def load_module(name: str, path: Path) -> ModuleType:
    spec = importlib.util.spec_from_file_location(name, path)
    if spec is None or spec.loader is None:
        raise RuntimeError(f"cannot create import spec for {path}")
    module = importlib.util.module_from_spec(spec)
    sys.modules[name] = module
    spec.loader.exec_module(module)
    return module


def model_kwargs(intervention: str) -> dict[str, Any]:
    return {
        "num_classes": 1000,
        "gate_type": "relu6_self",
        "stem_activation": "relu6",
        "kernel_size": 7,
        "layer_scale": 1e-6,
        "drop_path_rate": 0.02,
        "f12_bn": False,
        "projection_bn": True,
        "second_dw_bn": False,
        "gate_intervention": intervention,
        "gate_intervention_seed": 41041,
    }


def maximum_abs(left: torch.Tensor, right: torch.Tensor) -> float:
    return float((left.detach() - right.detach()).abs().max().item())


def assert_exact(left: torch.Tensor, right: torch.Tensor, label: str) -> float:
    delta = maximum_abs(left, right)
    if not torch.equal(left, right):
        raise AssertionError(f"{label} is not bitwise equal; max_abs={delta}")
    return delta


def compare_parameter_gradients(
    old_model: nn.Module, new_model: nn.Module, arm: str
) -> tuple[int, float]:
    old_parameters = dict(old_model.named_parameters())
    new_parameters = dict(new_model.named_parameters())
    if old_parameters.keys() != new_parameters.keys():
        raise AssertionError(f"{arm}: named parameter keys differ")

    maximum = 0.0
    compared = 0
    for name in old_parameters:
        old_gradient = old_parameters[name].grad
        new_gradient = new_parameters[name].grad
        if (old_gradient is None) != (new_gradient is None):
            raise AssertionError(f"{arm}:{name}: gradient None pattern differs")
        if old_gradient is None:
            continue
        maximum = max(
            maximum,
            assert_exact(old_gradient, new_gradient, f"{arm}:{name} gradient"),
        )
        compared += 1
    return compared, maximum


def project_metadata(rows: list[dict[str, object]]) -> list[dict[str, object]]:
    return [{key: row[key] for key in COMMON_METADATA_KEYS} for row in rows]


def compare_permutations(
    old_model: nn.Module, new_model: nn.Module, intervention: str
) -> dict[str, object]:
    old_buffers = {
        name: value
        for name, value in old_model.named_buffers()
        if name.endswith("gate_permutation")
    }
    new_buffers = {
        name: value
        for name, value in new_model.named_buffers()
        if name.endswith("gate_permutation")
    }
    if old_buffers.keys() != new_buffers.keys():
        raise AssertionError(f"{intervention}: gate permutation buffer keys differ")
    for name in old_buffers:
        assert_exact(old_buffers[name], new_buffers[name], f"{intervention}:{name}")

    old_metadata = old_model.gate_intervention_metadata()
    new_metadata = new_model.gate_intervention_metadata()
    if project_metadata(old_metadata) != project_metadata(new_metadata):
        raise AssertionError(f"{intervention}: common metadata projection differs")

    expected = 17 if intervention == "channel_derangement" else 0
    populated = sum(row["permutation_sha256"] is not None for row in old_metadata)
    if populated != expected:
        raise AssertionError(
            f"{intervention}: expected {expected} populated permutations, got {populated}"
        )
    if len(old_metadata) != 17:
        raise AssertionError(
            f"{intervention}: expected 17 GmNet-S3 blocks, got {len(old_metadata)}"
        )
    return {
        "block_count": len(old_metadata),
        "populated_permutation_count": populated,
        "buffer_count": len(old_buffers),
        "common_metadata_equal": True,
    }


def assert_stop_gradient_semantics(module: ModuleType) -> dict[str, object]:
    values = torch.tensor(
        [-2.0, -0.5, 0.5, 2.0, 5.5, 7.0], dtype=torch.float32
    ).reshape(1, 6, 1, 1)

    stop_input = values.clone().requires_grad_(True)
    stop_gate = module.SelfGate(
        nn.ReLU6(),
        "relu6_self",
        channels=6,
        gate_intervention="stop_gradient",
        gate_intervention_seed=41041,
    )
    stop_gate(stop_input).sum().backward()
    expected_stop = values.clamp(0.0, 6.0)
    stop_delta = assert_exact(
        stop_input.grad, expected_stop, "stop-gradient gate input derivative"
    )

    baseline_input = values.clone().requires_grad_(True)
    baseline_gate = module.SelfGate(
        nn.ReLU6(),
        "relu6_self",
        channels=6,
        gate_intervention="baseline",
        gate_intervention_seed=41041,
    )
    baseline_gate(baseline_input).sum().backward()
    expected_baseline = values.clamp(0.0, 6.0) + values * (
        (values > 0.0) & (values < 6.0)
    )
    baseline_delta = assert_exact(
        baseline_input.grad,
        expected_baseline,
        "baseline gate input derivative",
    )
    if torch.equal(stop_input.grad, baseline_input.grad):
        raise AssertionError("stop-gradient and baseline derivatives unexpectedly match")
    return {
        "stop_gradient_matches_detached_formula": True,
        "baseline_matches_full_formula": True,
        "stop_vs_baseline_derivative_differs": True,
        "maximum_abs_error": max(stop_delta, baseline_delta),
    }


def compare_arm(
    old_module: ModuleType, new_module: ModuleType, arm: str, intervention: str
) -> dict[str, object]:
    torch.manual_seed(73421)
    old_model = old_module.create_gmnet("s3", **model_kwargs(intervention))
    new_model = new_module.create_gmnet("s3", **model_kwargs(intervention))
    incompatible = new_model.load_state_dict(old_model.state_dict(), strict=True)
    if incompatible.missing_keys or incompatible.unexpected_keys:
        raise AssertionError(f"{arm}: strict state load returned incompatible keys")
    old_model.eval()
    new_model.eval()

    generator = torch.Generator(device="cpu")
    generator.manual_seed(91173)
    value = torch.randn(2, 3, 64, 64, generator=generator)
    loss_weight = torch.randn(2, 1000, generator=generator)
    old_input = value.clone().requires_grad_(True)
    new_input = value.clone().requires_grad_(True)

    old_output = old_model(old_input)
    new_output = new_model(new_input)
    output_delta = assert_exact(old_output, new_output, f"{arm} forward")
    old_loss = (old_output * loss_weight).sum()
    new_loss = (new_output * loss_weight).sum()
    assert_exact(old_loss, new_loss, f"{arm} fixed random loss")
    old_loss.backward()
    new_loss.backward()
    input_gradient_delta = assert_exact(
        old_input.grad, new_input.grad, f"{arm} input gradient"
    )
    gradient_count, parameter_gradient_delta = compare_parameter_gradients(
        old_model, new_model, arm
    )
    permutation = compare_permutations(old_model, new_model, intervention)
    return {
        "arm": arm,
        "gate_intervention": intervention,
        "parameter_count": sum(value.numel() for value in old_model.parameters()),
        "state_tensor_count": len(old_model.state_dict()),
        "compared_parameter_gradients": gradient_count,
        "forward_bitwise_equal": True,
        "input_gradient_bitwise_equal": True,
        "parameter_gradients_bitwise_equal": True,
        "maximum_abs": {
            "forward": output_delta,
            "input_gradient": input_gradient_delta,
            "parameter_gradient": parameter_gradient_delta,
        },
        "permutation_and_metadata": permutation,
    }


def main() -> int:
    parser = argparse.ArgumentParser()
    parser.add_argument("--output", type=Path)
    args = parser.parse_args()

    old_sha256 = sha256(OLD_SOURCE)
    new_sha256 = sha256(NEW_SOURCE)
    if old_sha256 != EXPECTED_OLD_SHA256:
        raise RuntimeError(f"old source SHA256 mismatch: {old_sha256}")
    if new_sha256 != EXPECTED_NEW_SHA256:
        raise RuntimeError(f"new source SHA256 mismatch: {new_sha256}")
    manifest = json.loads(SNAPSHOT_MANIFEST.read_text(encoding="utf-8"))
    manifest_hashes = {row["path"]: row["sha256"] for row in manifest["files"]}
    if manifest_hashes.get("gmnet/models/gmnet.py") != old_sha256:
        raise RuntimeError("snapshot manifest does not bind old gmnet.py")

    torch.set_num_threads(1)
    torch.use_deterministic_algorithms(True)
    old_module = load_module("gmnet_alignment_4a62", OLD_SOURCE)
    new_module = load_module("gmnet_mechanism_f6bd", NEW_SOURCE)

    results = [
        compare_arm(old_module, new_module, arm, intervention)
        for arm, intervention in ARMS.items()
    ]
    stop_old = assert_stop_gradient_semantics(old_module)
    stop_new = assert_stop_gradient_semantics(new_module)
    if stop_old != stop_new:
        raise AssertionError("old/new explicit stop-gradient assertions differ")

    payload = {
        "schema_version": 1,
        "status": "passed",
        "scope": "B/S/C full GmNet-S3 forward, input gradients, parameter gradients",
        "old_source": {"path": str(OLD_SOURCE), "sha256": old_sha256},
        "new_source": {"path": str(NEW_SOURCE), "sha256": new_sha256},
        "runtime": {
            "python": platform.python_version(),
            "torch": torch.__version__,
            "threads": torch.get_num_threads(),
            "deterministic_algorithms": torch.are_deterministic_algorithms_enabled(),
        },
        "arms": results,
        "explicit_stop_gradient_semantics": stop_old,
    }
    rendered = json.dumps(payload, indent=2, sort_keys=True) + "\n"
    if args.output is not None:
        args.output.parent.mkdir(parents=True, exist_ok=True)
        args.output.write_text(rendered, encoding="utf-8")
    print(rendered, end="")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())