from django.shortcuts import render, get_object_or_404, redirect
from django.contrib.auth.decorators import login_required
from django.contrib import messages
from django.http import JsonResponse
from django.urls import reverse
from django.utils import timezone

from processes.models import ProcessInstance, StepInstance
from invoices.models import Invoice
from installations.models import InstallationReport
from .models import CertificateTemplate, CertificateInstance

from _helpers.jalali import Gregorian


def _to_jalali(date_obj):
    try:
        g = Gregorian(date_obj)
        y, m, d = g.persian_tuple()
        return f"{y}/{m:02d}/{d:02d}"
    except Exception:
        return ''


def _render_template(template: CertificateTemplate, instance: ProcessInstance):
    well = instance.well
    rep = instance.representative
    latest_report = InstallationReport.objects.filter(assignment__process_instance=instance).order_by('-created').first()
    ctx = {
        'today_jalali': _to_jalali(timezone.now().date()),
        'request_code': instance.code,
        'company_name': (template.company.name if template.company else '') or '',
        'customer_full_name': rep.get_full_name() if rep else '',
        'water_subscription_number': getattr(well, 'water_subscription_number', '') or '',
        'address': getattr(well, 'address', '') or '',
        'visit_date_jalali': _to_jalali(getattr(latest_report, 'visited_date', None)) if latest_report else '',
    }
    title = (template.title or '').format(**ctx)
    body = (template.body or '')
    for k, v in ctx.items():
        body = body.replace(f"{{{{ {k} }}}}", str(v))
    return title, body


@login_required
def certificate_step(request, instance_id, step_id):
    instance = get_object_or_404(ProcessInstance, id=instance_id)

    # Ensure all previous steps are completed and invoice settled
    prior_steps = instance.process.steps.filter(order__lt=instance.current_step.order if instance.current_step else 9999)
    incomplete = StepInstance.objects.filter(process_instance=instance, step__in=prior_steps).exclude(status='completed').exists()
    if incomplete:
        messages.error(request, 'ابتدا همه مراحل قبلی را تکمیل کنید')
        return redirect('processes:request_list')
    inv = Invoice.objects.filter(process_instance=instance).first()
    if inv:
        inv.calculate_totals()
        if inv.remaining_amount != 0:
            messages.error(request, 'مانده فاکتور باید صفر باشد')
            return redirect('processes:request_list')

    template = CertificateTemplate.objects.filter(is_active=True).order_by('-created').first()
    if not template:
        return render(request, 'certificates/missing.html', {})

    title, body = _render_template(template, instance)
    cert, _ = CertificateInstance.objects.get_or_create(
        process_instance=instance,
        defaults={'template': template, 'rendered_title': title, 'rendered_body': body}
    )
    # keep rendered up-to-date
    cert.template = template
    cert.rendered_title = title
    cert.rendered_body = body
    cert.save()

    previous_step = instance.process.steps.filter(order__lt=instance.current_step.order).last() if instance.current_step else None
    next_step = instance.process.steps.filter(order__gt=instance.current_step.order).first() if instance.current_step else None

    if request.method == 'POST':
        cert.approved = True
        cert.approved_at = timezone.now()
        cert.save()
        step_instance, _ = StepInstance.objects.get_or_create(process_instance=instance, step_id=step_id)
        step_instance.status = 'completed'
        step_instance.completed_at = timezone.now()
        step_instance.save()
        if next_step:
            instance.current_step = next_step
            instance.save()
            return redirect('processes:step_detail', instance_id=instance.id, step_id=next_step.id)
        return redirect('processes:request_list')

    return render(request, 'certificates/step.html', {
        'instance': instance,
        'template': template,
        'cert': cert,
        'previous_step': previous_step,
        'next_step': next_step,
    })


@login_required
def certificate_print(request, instance_id):
    instance = get_object_or_404(ProcessInstance, id=instance_id)
    cert = CertificateInstance.objects.filter(process_instance=instance).order_by('-created').first()
    template = cert.template if cert else None
    return render(request, 'certificates/print.html', {
        'instance': instance,
        'cert': cert,
        'template': template,
    })