import json
from datetime import date
from flask import (Blueprint, render_template, redirect, url_for,
                   flash, request, current_app)
from flask_login import login_required, current_user
from app.extensions import db
from app.models.assignment import Assignment
from app.models.asset import Asset
from app.models.user import User
from app.models.audit_log import AuditLog

bp = Blueprint('assignments', __name__, url_prefix='/assignments')


def _log(action, record_id, description, old=None, new=None):
    entry = AuditLog(
        table_name='assignments',
        record_id=record_id,
        action=action,
        old_values=json.dumps(old) if old else None,
        new_values=json.dumps(new) if new else None,
        performed_by_id=current_user.id,
        ip_address=request.remote_addr,
        description=description,
    )
    db.session.add(entry)


@bp.route('/')
@login_required
def index():
    page = request.args.get('page', 1, type=int)
    active_only = request.args.get('active', '1') == '1'
    q = request.args.get('q', '').strip()

    query = Assignment.query
    if active_only:
        query = query.filter_by(is_active=True)

    pagination = query.order_by(Assignment.assigned_date.desc()).paginate(
        page=page, per_page=current_app.config['ITEMS_PER_PAGE'], error_out=False
    )
    return render_template('assignments/index.html',
                           pagination=pagination, active_only=active_only, q=q)


@bp.route('/new', methods=['GET', 'POST'])
@login_required
def create():
    # Pre-fill from query params (used from asset / user detail pages)
    preselect_asset_id = request.args.get('asset_id', type=int)
    preselect_user_id = request.args.get('user_id', type=int)

    if request.method == 'POST':
        user_id = request.form.get('user_id', type=int)
        asset_id = request.form.get('asset_id', type=int)
        assigned_date_str = request.form.get('assigned_date', '')
        notes = request.form.get('notes', '').strip() or None

        user = User.query.get(user_id) if user_id else None
        asset = Asset.query.get(asset_id) if asset_id else None

        errors = []
        if not user:
            errors.append('User is required.')
        if not asset:
            errors.append('Asset is required.')
        if user and user.is_masked:
            errors.append('Cannot assign assets to a masked user.')
        if asset and asset.status == 'assigned':
            errors.append(f'Asset {asset.serial_number} is already assigned.')
        if asset and asset.status in ('retired', 'lost'):
            errors.append(f'Asset {asset.serial_number} is {asset.status} and cannot be assigned.')

        if errors:
            for e in errors:
                flash(e, 'danger')
            return render_template('assignments/form.html',
                                   preselect_asset_id=asset_id,
                                   preselect_user_id=user_id)

        try:
            assigned_date = date.fromisoformat(assigned_date_str) if assigned_date_str else date.today()
        except ValueError:
            assigned_date = date.today()

        assignment = Assignment(
            asset_id=asset.id,
            user_id=user.id,
            assigned_date=assigned_date,
            assigned_by_id=current_user.id,
            notes=notes,
            is_active=True,
        )
        asset.status = 'assigned'
        db.session.add(assignment)
        db.session.flush()
        _log('assign', assignment.id,
             f'Assigned asset SN={asset.serial_number} to WID={user.windows_id}',
             new={'asset_sn': asset.serial_number, 'user_wid': user.windows_id,
                  'date': str(assigned_date)})
        db.session.commit()
        flash(f'Asset {asset.serial_number} assigned to {user.display_name}.', 'success')
        return redirect(url_for('assignments.index'))

    return render_template('assignments/form.html',
                           preselect_asset_id=preselect_asset_id,
                           preselect_user_id=preselect_user_id)


@bp.route('/<int:assignment_id>/return', methods=['POST'])
@login_required
def return_asset(assignment_id):
    assignment = Assignment.query.get_or_404(assignment_id)

    if not assignment.is_active:
        flash('This assignment is already closed.', 'info')
        return redirect(url_for('assignments.index'))

    returned_date_str = request.form.get('returned_date', '')
    try:
        returned_date = date.fromisoformat(returned_date_str) if returned_date_str else date.today()
    except ValueError:
        returned_date = date.today()

    assignment.returned_date = returned_date
    assignment.returned_by_id = current_user.id
    assignment.is_active = False
    assignment.notes = (assignment.notes or '') + ('\n' + request.form.get('return_notes', '').strip() if request.form.get('return_notes') else '')

    # Only set asset back to available if no other active assignment (safety check)
    other_active = Assignment.query.filter(
        Assignment.asset_id == assignment.asset_id,
        Assignment.is_active == True,  # noqa: E712
        Assignment.id != assignment.id,
    ).first()
    if not other_active:
        assignment.asset.status = 'available'

    _log('return', assignment.id,
         f'Returned asset SN={assignment.asset.serial_number} from WID={assignment.user.windows_id}',
         new={'returned_date': str(returned_date)})
    db.session.commit()
    flash(f'Asset {assignment.asset.serial_number} returned.', 'success')
    return redirect(url_for('assignments.index'))