# utils.py
# Shared helper functions and decorators

from functools import wraps
from flask import session, redirect, url_for, request, jsonify
from datetime import datetime, timezone
import random
import string


# ── AUTH DECORATORS ────────────────────────────────────────

def login_required(f):
    """Redirect to login if user is not in session. Returns 401 for API calls."""
    @wraps(f)
    def decorated(*args, **kwargs):
        if "user_id" not in session:
            if request.is_json or request.path.startswith("/api/"):
                return jsonify({"success": False, "message": "Login required."}), 401
            return redirect(url_for("auth.login_page"))
        return f(*args, **kwargs)
    return decorated


def admin_required(f):
    """Returns 403 if the current user is not an admin."""
    @wraps(f)
    def decorated(*args, **kwargs):
        if not session.get("is_admin"):
            return jsonify({"success": False, "message": "Admin access required."}), 403
        return f(*args, **kwargs)
    return decorated


# ── TIME HELPERS ───────────────────────────────────────────

def time_ago(dt: datetime) -> str:
    """Convert a datetime to a human-readable 'X ago' string."""
    now = datetime.now(timezone.utc)
    if dt.tzinfo is None:
        dt = dt.replace(tzinfo=timezone.utc)
    seconds = int((now - dt).total_seconds())

    if seconds < 60:
        return "Just now"
    elif seconds < 3600:
        m = seconds // 60
        return f"{m} minute{'s' if m > 1 else ''} ago"
    elif seconds < 86400:
        h = seconds // 3600
        return f"{h} hour{'s' if h > 1 else ''} ago"
    elif seconds < 604800:
        d = seconds // 86400
        return f"{d} day{'s' if d > 1 else ''} ago"
    else:
        return dt.strftime("%b %d, %Y")


# ── ID GENERATOR ───────────────────────────────────────────

def generate_student_id() -> str:
    """Generate a unique student ID like STU123456."""
    return "STU" + "".join(random.choices(string.digits, k=6))


# ── PAGINATION HELPER ──────────────────────────────────────

def get_pagination_args():
    """Extract page and limit from request args."""
    page  = max(1, int(request.args.get("page",  1)))
    limit = min(50, int(request.args.get("limit", 10)))
    return page, limit, (page - 1) * limit