"""
Tests for the state_store module.

Covers:
  * round-trip snapshot/checkout
  * content-addressed dedup (same tensors -> same blob)
  * async write-behind completion (queue drains)
  * branch / log lineage walk
  * gc removes only unreachable snapshots + blobs
"""

from __future__ import annotations

import json
import os
from pathlib import Path

import pytest

torch = pytest.importorskip("torch")

from state_store import (
    StateStore,
    snapshot,
    checkout,
    log,
    diff,
    branch,
    gc,
)
from state_store.store import hash_bytes


# ---------------------------------------------------------------------------
# Tiny model + optimizer for deterministic tests
# ---------------------------------------------------------------------------
class TinyModel(torch.nn.Module):
    def __init__(self):
        super().__init__()
        self.fc1 = torch.nn.Linear(4, 8, bias=True)
        self.fc2 = torch.nn.Linear(8, 4, bias=True)

    def forward(self, x):
        return self.fc2(torch.relu(self.fc1(x)))


def _make_model_and_opt(seed: int = 0):
    torch.manual_seed(seed)
    model = TinyModel()
    opt = torch.optim.SGD(model.parameters(), lr=0.1)
    return model, opt


@pytest.fixture
def store(tmp_path):
    # Sync store simplifies assertions; async path is covered separately below.
    s = StateStore(root=tmp_path / "store", sync=True)
    yield s
    s.shutdown()


@pytest.fixture
def async_store(tmp_path):
    s = StateStore(root=tmp_path / "async_store", sync=False)
    yield s
    s.shutdown()


# ---------------------------------------------------------------------------
# Round-trip
# ---------------------------------------------------------------------------
def test_snapshot_roundtrip(store):
    m1, o1 = _make_model_and_opt(seed=1)
    metrics = {"val_bpb": 1.777, "loss": 2.5, "step": 100}
    h = snapshot(m1, o1, step=100, metrics=metrics, store=store)
    assert isinstance(h, str) and len(h) >= 32

    # Fresh model with different init -> checkout must restore weights.
    m2, o2 = _make_model_and_opt(seed=999)
    for (n1, p1), (n2, p2) in zip(m1.named_parameters(), m2.named_parameters()):
        assert not torch.equal(p1, p2), f"{n1}/{n2} should start different"

    row = checkout(h, m2, o2, store=store)
    assert row["step"] == 100
    assert row["metrics"]["val_bpb"] == 1.777

    for (n1, p1), (n2, p2) in zip(m1.named_parameters(), m2.named_parameters()):
        assert torch.equal(p1.cpu(), p2.cpu()), f"param {n1} not restored"


# ---------------------------------------------------------------------------
# Dedup: snapshotting the same model twice yields identical manifest entries
# ---------------------------------------------------------------------------
def test_content_addressed_dedup(store):
    m, o = _make_model_and_opt(seed=42)
    metrics = {"val_bpb": 2.0, "loss": 3.0}
    h1 = snapshot(m, o, step=1, metrics=metrics, store=store)
    h2 = snapshot(m, o, step=1, metrics=metrics, store=store)
    # Same step + state + metrics => identical snapshot hash.
    assert h1 == h2

    # Even if the step changes, every per-tensor blob hash must be identical
    # because the weights themselves haven't changed.
    h3 = snapshot(m, o, step=2, metrics=metrics, store=store)
    mf1 = json.loads(store.get_snapshot(h1)["manifest_json"])
    mf3 = json.loads(store.get_snapshot(h3)["manifest_json"])
    assert mf1["model"].keys() == mf3["model"].keys()
    for k in mf1["model"]:
        assert mf1["model"][k] == mf3["model"][k], f"blob hash changed for {k}"

    # Every referenced blob must be reachable via the store (works for both
    # legacy per-file layout and Phase-1 chunked/packfile layout).
    unique_blob_hashes = set(mf1["model"].values()) | set(mf3["model"].values())
    for bh in unique_blob_hashes:
        assert store.has_blob(bh), f"blob {bh} missing from store"


def test_snapshot_changes_when_weights_change(store):
    m, o = _make_model_and_opt(seed=7)
    metrics = {"val_bpb": 1.0}
    h1 = snapshot(m, o, step=1, metrics=metrics, store=store)

    with torch.no_grad():
        m.fc1.weight.add_(1.0)  # mutate
    h2 = snapshot(m, o, step=2, metrics=metrics, store=store)
    assert h1 != h2

    d = diff(h1, h2, store=store)
    assert "fc1.weight" in d["changed"]
    # fc2 weight/bias unchanged -> appears in identical_blob_count bucket.
    assert d["identical_blob_count"] >= 2


# ---------------------------------------------------------------------------
# Async write-behind
# ---------------------------------------------------------------------------
def test_async_writes_drain(async_store):
    m, o = _make_model_and_opt(seed=3)
    hashes = []
    for step in range(5):
        with torch.no_grad():
            m.fc1.weight.add_(0.01)
        hashes.append(
            snapshot(m, o, step=step, metrics={"val_bpb": float(step)}, store=async_store)
        )
    async_store.flush(timeout=15)
    # All rows visible.
    for h in hashes:
        row = async_store.get_snapshot(h)
        assert row is not None, f"snapshot {h} not persisted"
    rows = log(limit=10, store=async_store)
    assert len(rows) == 5


# ---------------------------------------------------------------------------
# Branch + log lineage
# ---------------------------------------------------------------------------
def test_branch_and_log(store):
    m, o = _make_model_and_opt(seed=2)
    h1 = snapshot(m, o, step=1, metrics={"val_bpb": 3.0}, store=store)
    with torch.no_grad():
        m.fc1.weight.add_(0.5)
    h2 = snapshot(m, o, step=2, metrics={"val_bpb": 2.5}, parent_hash=h1, store=store)
    with torch.no_grad():
        m.fc1.weight.add_(0.5)
    h3 = snapshot(m, o, step=3, metrics={"val_bpb": 2.0}, parent_hash=h2, store=store)

    branch("champ", h3, store=store)
    assert store.resolve_ref("champ") == h3

    lin = log(limit=10, branch="champ", store=store)
    assert [r["hash"] for r in lin] == [h3, h2, h1]


# ---------------------------------------------------------------------------
# GC
# ---------------------------------------------------------------------------
def test_gc_removes_only_unreachable(store):
    m, o = _make_model_and_opt(seed=5)
    hashes = []
    parent = None
    for step in range(6):
        with torch.no_grad():
            m.fc1.weight.add_(0.1)
        parent = snapshot(
            m, o, step=step, metrics={"val_bpb": 5.0 - step},
            parent_hash=parent, store=store,
        )
        hashes.append(parent)

    branch("keep_me", hashes[2], store=store)

    res = gc(keep_last=1, reachable_from="keep_me", store=store)
    # With keep_last=1, last snapshot is kept; plus lineage from keep_me (h0..h2).
    kept = res["kept_snapshots"]
    assert kept >= 3  # h0, h1, h2 are reachable from keep_me
    # keep_me head must still resolve.
    assert store.resolve_ref("keep_me") == hashes[2]
    # h3, h4 may have been removed (they're not reachable and not in keep_last=1 window).
    removed = set(res["removed_snapshots"])
    # The last (newest) snapshot is in the keep_last=1 window, so NOT removed.
    assert hashes[-1] not in removed
    # Everything kept must still be readable.
    for h in res["removed_snapshots"]:
        assert store.get_snapshot(h) is None
    # Blobs for reachable snapshots must still exist on disk.
    for h in hashes[:3]:
        row = store.get_snapshot(h)
        assert row is not None
        mf = json.loads(row["manifest_json"])
        for bh in mf["model"].values():
            assert store.has_blob(bh), f"blob {bh} gc'd but snapshot {h} still references it"


def test_gc_dry_run_does_not_delete(store):
    m, o = _make_model_and_opt(seed=8)
    parent = None
    hashes = []
    for step in range(3):
        with torch.no_grad():
            m.fc1.weight.add_(0.2)
        parent = snapshot(m, o, step=step, metrics={"loss": 1.0 * step},
                          parent_hash=parent, store=store)
        hashes.append(parent)

    res = gc(keep_last=0, dry_run=True, store=store)
    # Dry-run: snapshots still present in DB.
    for h in hashes:
        assert store.get_snapshot(h) is not None


# ---------------------------------------------------------------------------
# Hash utility sanity
# ---------------------------------------------------------------------------
def test_hash_bytes_deterministic():
    a = hash_bytes(b"hello world")
    b = hash_bytes(b"hello world")
    c = hash_bytes(b"hello worlD")
    assert a == b
    assert a != c