from __future__ import annotations

from datetime import datetime, timezone
from pathlib import Path
from typing import Any

from pobsync.snapshot_meta import iter_snapshot_dirs, read_snapshot_meta, resolve_host_root

from .models import GlobalConfig, HostConfig, SnapshotRecord


def parse_snapshot_datetime(dirname: str, meta: dict[str, Any], key: str) -> datetime | None:
    value = meta.get(key)
    if isinstance(value, str):
        parsed = _parse_iso_z(value)
        if parsed is not None:
            return parsed

    if key == "started_at":
        try:
            prefix = dirname.split("__", 1)[0]
            return datetime.strptime(prefix, "%Y%m%d-%H%M%SZ").replace(tzinfo=timezone.utc)
        except ValueError:
            return None
    return None


def discover_snapshots(
    *,
    host: HostConfig | None = None,
    global_config: GlobalConfig | None = None,
    kinds: list[str] | None = None,
) -> dict[str, Any]:
    global_config = global_config or GlobalConfig.objects.get(name="default")
    host_qs = HostConfig.objects.filter(enabled=True).order_by("host")
    if host is not None:
        host_qs = host_qs.filter(pk=host.pk)

    kinds = kinds or ["scheduled", "manual", "incomplete"]
    scanned = 0
    created = 0
    updated = 0

    for host_config in host_qs:
        host_root = resolve_host_root(global_config.backup_root, host_config.host)
        for kind in kinds:
            for snapshot_dir in iter_snapshot_dirs(host_root, kind):
                _record, was_created = upsert_snapshot_record(
                    host=host_config,
                    kind=kind,
                    snapshot_dir=snapshot_dir,
                )
                scanned += 1
                if was_created:
                    created += 1
                else:
                    updated += 1
        resolve_base_links(host=host_config)

    return {
        "ok": True,
        "scanned": scanned,
        "created": created,
        "updated": updated,
    }


def upsert_snapshot_record(*, host: HostConfig, kind: str, snapshot_dir: Path) -> tuple[SnapshotRecord, bool]:
    meta = read_snapshot_meta(snapshot_dir)
    base_defaults = _base_defaults_from_meta(meta)
    defaults = {
        "path": str(snapshot_dir),
        **base_defaults,
        "base": _resolve_base_record(
            host=host,
            kind=base_defaults["base_kind"],
            dirname=base_defaults["base_dirname"],
        ),
        "status": str(meta.get("status") or ""),
        "started_at": parse_snapshot_datetime(snapshot_dir.name, meta, "started_at"),
        "ended_at": parse_snapshot_datetime(snapshot_dir.name, meta, "ended_at"),
        "metadata": meta,
    }
    return SnapshotRecord.objects.update_or_create(
        host=host,
        kind=kind,
        dirname=snapshot_dir.name,
        defaults=defaults,
    )


def resolve_base_links(*, host: HostConfig | None = None) -> int:
    snapshot_qs = SnapshotRecord.objects.exclude(base_dirname="").filter(base__isnull=True)
    if host is not None:
        snapshot_qs = snapshot_qs.filter(host=host)

    updated = 0
    for snapshot in snapshot_qs.select_related("host"):
        base = _resolve_base_record(
            host=snapshot.host,
            kind=snapshot.base_kind,
            dirname=snapshot.base_dirname,
        )
        if base is None:
            continue
        snapshot.base = base
        snapshot.save(update_fields=["base"])
        updated += 1
    return updated


def infer_snapshot_kind(snapshot_path: Path) -> str:
    parent = snapshot_path.parent.name
    if parent == "scheduled":
        return "scheduled"
    if parent == "manual":
        return "manual"
    if parent == ".incomplete":
        return "incomplete"
    raise ValueError(f"Cannot infer snapshot kind from path: {snapshot_path}")


def _base_defaults_from_meta(meta: dict[str, Any]) -> dict[str, Any]:
    base = meta.get("base")
    if not isinstance(base, dict):
        base = {}

    return {
        "base_kind": _base_value(base.get("kind")),
        "base_dirname": _base_value(base.get("dirname")),
        "base_path": _base_value(base.get("path")),
        "base_snapshot_id": _base_value(base.get("id")),
    }


def _base_value(value: Any) -> str:
    return value if isinstance(value, str) else ""


def _resolve_base_record(*, host: HostConfig, kind: str, dirname: str) -> SnapshotRecord | None:
    if not kind or not dirname:
        return None
    return SnapshotRecord.objects.filter(host=host, kind=kind, dirname=dirname).first()


def _parse_iso_z(value: str) -> datetime | None:
    try:
        if value.endswith("Z"):
            return datetime.fromisoformat(value.removesuffix("Z") + "+00:00")
        parsed = datetime.fromisoformat(value)
        if parsed.tzinfo is None:
            return parsed.replace(tzinfo=timezone.utc)
        return parsed
    except ValueError:
        return None