#!/usr/bin/env python3
"""Create a minimal valid FAISS HNSW32 + IndexIDMap2 fixture for the test harness.

Used by the `tile-init` init service in docker-compose.test.jetson.yml.
Writes three files to /var/lib/gps-denied/tiles/:
  descriptor.index          — empty HNSW32 dim=512 binary
  descriptor.index.sha256   — sha256 sidecar (matches FaissDescriptorIndex._load)
  descriptor.index.meta.json — metadata (descriptor_dim, hnsw_params.metric, ...)

Running this twice is idempotent (overwrites the previous fixture).
"""

from __future__ import annotations

import hashlib
import json
from datetime import datetime, timezone
from pathlib import Path

import faiss  # type: ignore[import-untyped]

DESCRIPTOR_DIM = 512
HNSW_M = 32

root = Path("/var/lib/gps-denied/tiles")
root.mkdir(parents=True, exist_ok=True)

inner = faiss.IndexHNSWFlat(DESCRIPTOR_DIM, HNSW_M, faiss.METRIC_INNER_PRODUCT)
index = faiss.IndexIDMap2(inner)

idx_path = root / "descriptor.index"
faiss.write_index(index, str(idx_path))
idx_bytes = idx_path.read_bytes()
sha256 = hashlib.sha256(idx_bytes).hexdigest()

(idx_path.parent / (idx_path.name + ".sha256")).write_text(sha256, encoding="ascii")

meta = {
    "descriptor_dim": DESCRIPTOR_DIM,
    "n_vectors": 0,
    "backbone_label": "ultra_vpr",
    "backbone_sha256_hex": "0" * 64,
    "built_at": datetime.now(timezone.utc).isoformat(),
    "hnsw_params": {
        "m": HNSW_M,
        "ef_construction": 40,
        "ef_search": 16,
        "metric": "INNER_PRODUCT",
    },
    "sidecar_sha256_hex": sha256,
    "file_path": str(idx_path),
    "id_mapping": [],
}
(idx_path.parent / (idx_path.name + ".meta.json")).write_text(
    json.dumps(meta, sort_keys=True, indent=2), encoding="utf-8"
)

print(
    f"[tile-init] OK: empty HNSW32 dim={DESCRIPTOR_DIM} index "
    f"at {idx_path}  sha256={sha256[:16]}..."
)