"""Disk-usage accounting, per-user quota, and automatic eviction.

An artifact's on-disk footprint is the primary stored file plus, for markdown,
the preserved `.md` sidecar. We record it on the row (`size_bytes`) at ingest so
usage is a cheap SUM rather than a stat of every file.
"""

import shutil

from django.conf import settings
from django.db.models import Sum

from .models import Artifact, UserProfile


class QuotaExceeded(Exception):
    """Raised when a post cannot fit even after evicting every unkept artifact."""


def artifact_disk_size(relative_path, kind):
    """Bytes an artifact occupies on disk, including the markdown sidecar."""
    root = settings.ARTIFACTS_ROOT
    total = 0
    primary = root / relative_path
    if primary.exists():
        total += primary.stat().st_size
    if kind == Artifact.MARKDOWN:
        sidecar = primary.with_suffix(".md")
        if sidecar.exists():
            total += sidecar.stat().st_size
    return total


def delete_artifact_files(artifact):
    """Remove an artifact's files from disk (primary + markdown sidecar)."""
    root = settings.ARTIFACTS_ROOT
    primary = root / artifact.path
    primary.unlink(missing_ok=True)
    if artifact.kind == Artifact.MARKDOWN:
        primary.with_suffix(".md").unlink(missing_ok=True)


def user_usage_bytes(user):
    return (
        Artifact.objects.filter(owner=user).aggregate(total=Sum("size_bytes")).get("total")
        or 0
    )


def user_quota_bytes(user):
    profile, _ = UserProfile.objects.get_or_create(user=user)
    return profile.quota_bytes


def make_room_for(user, incoming_bytes):
    """Evict oldest unkept artifacts until `incoming_bytes` fits under quota.

    Returns the list of evicted artifacts (already deleted). Raises QuotaExceeded
    if even removing every unkept artifact leaves no room.
    """
    quota = user_quota_bytes(user)
    if incoming_bytes > quota:
        raise QuotaExceeded("Artifact is larger than the entire quota.")

    used = user_usage_bytes(user)
    if used + incoming_bytes <= quota:
        return []

    evicted = []
    unkept = (
        Artifact.objects.filter(owner=user, is_kept=False).order_by("created_at")
    )
    for artifact in unkept:
        if used + incoming_bytes <= quota:
            break
        used -= artifact.size_bytes
        delete_artifact_files(artifact)
        artifact.delete()
        evicted.append(artifact)

    if used + incoming_bytes > quota:
        raise QuotaExceeded("Quota is full of kept artifacts; free space to post.")
    return evicted


def disk_free_bytes():
    """Free space on the volume that holds the artifact store."""
    return shutil.disk_usage(settings.ARTIFACTS_ROOT).free


def total_allocated_bytes():
    return UserProfile.objects.aggregate(total=Sum("quota_bytes")).get("total") or 0