"""Daily usage roll-up and its local store (AGENTS.md FR-7).

The client publishes ``{"day":...,"apps":[{"name":...,"seconds":N}]}`` where the
seconds are **totals for the day**, not deltas: the Control Service replaces the
row for (device, day, app) on every report (``internal/store/migrations/002``).

Windows has no per-app foreground clock like Android's Usage Access, so the
client builds its own total: every sample, the elapsed seconds are added to each
app that currently owns a visible, titled top-level window. That total is kept
on disk so a restart never loses the day, and it is republished when the link
returns (FR-14).

**Domains are not attributed.** Windows gives no cheap per-process DNS answer —
it needs a packet capture, an ETW consumer or the DNS Client event log, all of
which are either a second dependency or an administrator-only channel. The
client therefore publishes ``"domains": []`` and the gap is recorded in
``windows/README.md`` rather than filled with a guess.
"""

from __future__ import annotations

import json
import logging
import os
from dataclasses import dataclass, field
from datetime import datetime, timezone
from pathlib import Path
from typing import Iterable, Mapping

log = logging.getLogger("webrestrict.telemetry")

# Keep two weeks of daily totals on the device, matching the Android client.
MAX_DAYS = 14

# A sample longer than this is treated as this long, so a laptop that was asleep
# does not credit one app with hours of "use".
MAX_SAMPLE_SECONDS = 120.0


def day_key(moment: datetime | None = None) -> str:
    """The local ``YYYY-MM-DD`` the usage belongs to.

    An aware timestamp is converted to local time first, so a day boundary is the
    child's midnight rather than UTC's.
    """
    current = moment or datetime.now()
    if current.tzinfo is not None:
        current = current.astimezone()
    return current.strftime("%Y-%m-%d")


def to_entries(apps: Mapping[str, int]) -> list[dict[str, object]]:
    """The list form the telemetry topic accepts, sorted and positive-only."""
    return [
        {"name": name, "seconds": int(seconds)}
        for name, seconds in sorted(apps.items())
        if name and int(seconds) > 0
    ]


def build_payload(day: str, apps: Mapping[str, int]) -> dict[str, object]:
    """The Phase 3 telemetry payload (``internal/mqtt/payload.go``)."""
    return {"day": day, "apps": to_entries(apps), "domains": []}


@dataclass
class TelemetryStore:
    """day -> app -> seconds, kept on disk so a restart or outage loses nothing."""

    path: Path
    days: dict[str, dict[str, int]] = field(default_factory=dict)
    loaded: bool = False

    def load(self) -> "TelemetryStore":
        if self.loaded:
            return self
        self.loaded = True
        try:
            if not self.path.exists():
                return self
            with open(self.path, "r", encoding="utf-8") as handle:
                raw = json.load(handle)
            days = raw.get("days") if isinstance(raw, dict) else None
            if isinstance(days, dict):
                self.days = {
                    str(day): {str(name): int(seconds) for name, seconds in row.items()}
                    for day, row in days.items()
                    if isinstance(row, dict)
                }
        except (OSError, ValueError, TypeError, json.JSONDecodeError) as exc:
            log.warning("telemetry store is unreadable, starting empty: %s", exc)
            self.days = {}
        return self

    def save(self) -> None:
        self.path.parent.mkdir(parents=True, exist_ok=True)
        temp = self.path.with_suffix(self.path.suffix + ".tmp")
        with open(temp, "w", encoding="utf-8") as handle:
            json.dump({"days": self.days}, handle, sort_keys=True)
        os.replace(temp, self.path)

    def day(self, day: str) -> dict[str, int]:
        self.load()
        return dict(self.days.get(day, {}))

    def add_seconds(self, day: str, apps: Mapping[str, int]) -> dict[str, int]:
        """Add a sample to a day and return that day's new totals."""
        self.load()
        row = self.days.setdefault(day, {})
        for name, seconds in apps.items():
            if not name or seconds <= 0:
                continue
            row[name] = row.get(name, 0) + int(seconds)
        self.prune()
        self.save()
        return dict(row)

    def prune(self) -> None:
        """Keep only the [MAX_DAYS] most recent days."""
        if len(self.days) <= MAX_DAYS:
            return
        for old in sorted(self.days)[:-MAX_DAYS]:
            self.days.pop(old, None)


class UsageSampler:
    """Turns "these apps had a window" ticks into per-app daily seconds."""

    def __init__(self, store: TelemetryStore):
        self.store = store
        self.last_at: datetime | None = None

    def sample(
        self,
        apps: Iterable[str],
        now: datetime | None = None,
        day: str | None = None,
    ) -> dict[str, int]:
        """Credit the elapsed time to each app in the sample.

        Returns the day's totals. The first call only starts the clock: there is
        no way to know what ran before the client started.
        """
        moment = now or datetime.now(timezone.utc)
        self.last_at = self.last_at or moment
        elapsed = (moment - self.last_at).total_seconds()
        self.last_at = moment
        if elapsed <= 0:
            return self.store.day(day or day_key(moment))
        elapsed = min(elapsed, MAX_SAMPLE_SECONDS)

        wanted = sorted({name for name in apps if name})
        if not wanted:
            return self.store.day(day or day_key(moment))
        return self.store.add_seconds(day or day_key(moment), {name: int(elapsed) for name in wanted})