"""Jinja template filters for the frontend app."""
from datetime import datetime, timezone


def from_iso_format(s: str) -> datetime:
    """Convert ISO 8601 string to datetime object."""
    return datetime.fromisoformat(s)


def human_time(dt: datetime) -> str:
    """Format a datetime object into a human-readable relative time."""
    now = datetime.now(timezone.utc)
    if dt.tzinfo is None:
        dt = dt.replace(tzinfo=timezone.utc)

    diff = now - dt
    seconds = diff.total_seconds()

    if seconds < 60:
        return "just now"
    elif seconds < 3600:
        minutes = int(seconds / 60)
        return f"{minutes} minute{'s' if minutes > 1 else ''} ago"
    elif seconds < 86400:
        hours = int(seconds / 3600)
        return f"{hours} hour{'s' if hours > 1 else ''} ago"
    elif seconds < 2592000:
        days = int(seconds / 86400)
        return f"{days} day{'s' if days > 1 else ''} ago"
    elif seconds < 31536000:
        months = int(seconds / 2592000)
        return f"{months} month{'s' if months > 1 else ''} ago"
    else:
        years = int(seconds / 31536000)
        return f"{years} year{'s' if years > 1 else ''} ago"


def register_filters(app):
    """Register all template filters on the Flask app."""
    app.template_filter("fromisoformat")(from_iso_format)
    app.template_filter("humantime")(human_time)