"""Best-effort, bounded disk usage summary for backup and restore mail reports."""

from pathlib import Path
import os
import subprocess


def human(value):
    for unit in ('B', 'KiB', 'MiB', 'GiB', 'TiB'):
        if value < 1024 or unit == 'TiB':
            return f'{value:.1f} {unit}'
        value /= 1024


def duration(seconds):
    hours, remainder = divmod(max(0, int(seconds)), 3600)
    minutes, seconds = divmod(remainder, 60)
    return f'{hours}h {minutes:02d}m {seconds:02d}s'


def allocated(path):
    """Count allocated bytes without following symlinks or crossing filesystems."""
    try:
        result = subprocess.run(['du', '-sx', '-B1', '--', str(path)],
                                capture_output=True, text=True, timeout=30, check=True)
        return int(result.stdout.split()[0])
    except (OSError, ValueError, IndexError, subprocess.SubprocessError):
        return None


def free_space(path):
    try:
        stat = os.statvfs(path)
        return stat.f_bavail * stat.f_frsize
    except OSError:
        return None


def summary(seconds, workdir, archives, staging, restore, logs):
    """Measure the final local state, after temporary-file cleanup."""
    lines = ['', 'Laufzeit und Speicher am Ende', '----------------------------',
             f'Verarbeitung: {duration(seconds)} ({max(0, int(seconds))}s)']
    paths = [('Arbeitsbereich gesamt', workdir), ('Backups (lokale Archive)', archives),
             ('Backup-Staging', staging), ('Restore-Arbeitsbereich', restore),
             ('Restore-Test', str(Path(workdir) / 'restore-test')), ('Protokolle und Berichte', logs)]
    for label, name in paths:
        if not name:
            continue
        path = Path(name)
        amount = allocated(path) if path.exists() and not path.is_symlink() else None
        lines.append(f'{label}: {human(amount) if amount is not None else "nicht verfügbar"} ({path})')
    devices = set()
    for label, name in [('Arbeitsbereich', workdir), ('Archive', archives),
                        ('Staging', staging), ('Restore', restore), ('Restore-Test', str(Path(workdir) / 'restore-test')),
                        ('Protokolle', logs)]:
        if not name:
            continue
        try:
            path = Path(name)
            if path.is_symlink():
                continue
            device = path.stat().st_dev
        except OSError:
            continue
        if device in devices:
            continue
        devices.add(device)
        amount = free_space(path)
        lines.append(f'Frei auf Datenträger {label}: '
                     f'{human(amount) if amount is not None else "nicht verfügbar"} ({path})')
    lines.append('Teilbereiche sind im Arbeitsbereich enthalten; getrennte Datenträger werden separat gemessen.')
    return lines