import time
from typing import Any

from fastapi import APIRouter, Request
from fastapi.responses import HTMLResponse

from app.collect import disks as disk_col
from app.render import render

router = APIRouter(prefix="/api", tags=["disks"])

_prev: dict[str, Any] | None = None
_prev_t: float = 0.0


@router.get("/disks")
async def disks(_request: Request):
    """Render the Disks tab fragment: partition usage + per-disk rates.

    Per-disk read/write rates are computed from the delta between this
    request's counters and the previous request's (module-level state,
    so rates depend on poll frequency and are 0 on the first hit).

    Args:
        _request: FastAPI request (unused beyond app state access).

    Returns:
        The rendered disks.html as an HTMLResponse.
    """
    global _prev, _prev_t
    now = time.monotonic()
    cur = disk_col.counters()
    per_disk: list[dict[str, Any]] = []
    dt = (now - _prev_t) if _prev is not None and _prev_t else 0.0
    for name, c in sorted(cur.items()):
        p = (_prev or {}).get(name)
        per_disk.append(
            {
                "device": name,
                "read_rate": (c.read_bytes - p.read_bytes) / dt if p and dt > 0 else 0.0,
                "write_rate": (c.write_bytes - p.write_bytes) / dt if p and dt > 0 else 0.0,
                "reads": c.read_count,
                "writes": c.write_count,
                "read_bytes": c.read_bytes,
                "write_bytes": c.write_bytes,
            }
        )
    _prev = cur
    _prev_t = now
    return HTMLResponse(
        render("disks.html", partitions=disk_col.partitions(), per_disk=per_disk)
    )