from html.parser import HTMLParser
from io import BytesIO
import textwrap

from django.contrib import messages
from django.http import HttpResponse
from django.shortcuts import get_object_or_404, redirect, render
from django.utils import timezone
from django.utils.text import slugify

from reportlab.lib.pagesizes import letter
from reportlab.pdfgen import canvas

from .forms import BundleUploadForm
from .models import HtmlBundle, HtmlDocument, HtmlExport


class _HtmlTextExtractor(HTMLParser):
    block_tags = {
        "p",
        "div",
        "br",
        "li",
        "h1",
        "h2",
        "h3",
        "h4",
        "h5",
        "h6",
        "section",
        "article",
        "header",
        "footer",
    }

    def __init__(self):
        super().__init__()
        self.parts = []

    def handle_starttag(self, tag, attrs):
        if tag in self.block_tags:
            self.parts.append("\n")

    def handle_endtag(self, tag):
        if tag in self.block_tags:
            self.parts.append("\n")

    def handle_data(self, data):
        if data.strip():
            self.parts.append(data)


def _extract_text_from_html(html_bytes: bytes) -> str:
    html_text = html_bytes.decode("utf-8", errors="replace")
    parser = _HtmlTextExtractor()
    parser.feed(html_text)
    raw_text = "".join(parser.parts)
    lines = [line.strip() for line in raw_text.splitlines()]
    cleaned = "\n".join([line for line in lines if line])
    return cleaned


def _build_pdf(bundle: HtmlBundle) -> BytesIO:
    buffer = BytesIO()
    pdf = canvas.Canvas(buffer, pagesize=letter)
    width, height = letter
    margin = 72
    line_height = 14
    y = height - margin

    documents = bundle.documents.all()
    for document in documents:
        text = document.content_text or ""
        paragraphs = text.splitlines() or [""]
        for paragraph in paragraphs:
            wrapped = textwrap.wrap(paragraph, width=95) or [""]
            for line in wrapped:
                if y < margin:
                    pdf.showPage()
                    y = height - margin
                pdf.setFont("Helvetica", 11)
                pdf.drawString(margin, y, line)
                y -= line_height
            y -= 6
        y -= 12

    pdf.save()
    buffer.seek(0)
    return buffer


def home(request):
    file_errors = []
    form = BundleUploadForm()
    if request.method == "POST":
        form = BundleUploadForm(request.POST)
        files = request.FILES.getlist("files")

        if form.is_valid():
            if not files:
                file_errors.append("No files were received. Please ensure you have selected files and try again.")
            else:
                invalid_files = [f.name for f in files if not f.name.lower().endswith((".html", ".htm"))]
                if invalid_files:
                    file_errors.append(
                        f"Only .html or .htm files are supported. Invalid: {', '.join(invalid_files[:3])}"
                    )
                else:
                    title = form.cleaned_data.get("title", "").strip()
                    bundle = HtmlBundle.objects.create(title=title)
                    for index, uploaded in enumerate(files, start=1):
                        content_text = _extract_text_from_html(uploaded.read())
                        HtmlDocument.objects.create(
                            bundle=bundle,
                            original_name=uploaded.name,
                            order=index,
                            content_text=content_text,
                        )
                    messages.success(request, f"Bundle '{bundle.title or 'Untitled'}' created with {len(files)} files.")
                    return redirect("bundle_detail", bundle_id=bundle.id)

    bundles = HtmlBundle.objects.order_by("-created_at")[:5]
    exports = HtmlExport.objects.select_related("bundle").order_by("-created_at")[:5]
    context = {
        "page_title": "HTML Bundle to PDF",
        "page_description": "Upload multiple HTML files, arrange the order, and export a single PDF instantly.",
        "form": form,
        "file_errors": file_errors,
        "bundles": bundles,
        "exports": exports,
    }
    return render(request, "core/index.html", context)


def bundle_list(request):
    bundles = HtmlBundle.objects.order_by("-created_at")
    context = {
        "page_title": "All Bundles",
        "page_description": "Browse recent HTML bundles and download combined PDFs.",
        "bundles": bundles,
    }
    return render(request, "core/bundle_list.html", context)


def bundle_detail(request, bundle_id: int):
    bundle = get_object_or_404(HtmlBundle, pk=bundle_id)
    documents = bundle.documents.all()
    exports = bundle.exports.order_by("-created_at")

    if request.method == "POST" and request.POST.get("action") == "update_order":
        updates = []
        for document in documents:
            field_name = f"order_{document.id}"
            raw_value = request.POST.get(field_name)
            if raw_value is None:
                continue
            try:
                order_value = int(raw_value)
                if order_value < 1:
                    raise ValueError
            except ValueError:
                messages.error(request, "Order values must be positive numbers.")
                return redirect("bundle_detail", bundle_id=bundle.id)
            document.order = order_value
            updates.append(document)
        if updates:
            HtmlDocument.objects.bulk_update(updates, ["order"])
            messages.success(request, "Order updated.")
        return redirect("bundle_detail", bundle_id=bundle.id)

    context = {
        "page_title": bundle.title or "Untitled bundle",
        "page_description": "Review your bundle and generate a combined PDF.",
        "bundle": bundle,
        "documents": documents,
        "exports": exports,
    }
    return render(request, "core/bundle_detail.html", context)


def bundle_download(request, bundle_id: int):
    bundle = get_object_or_404(HtmlBundle, pk=bundle_id)
    slug = slugify(bundle.title) or "bundle"
    timestamp = timezone.now().strftime("%Y%m%d-%H%M")
    file_name = f"{slug}-{timestamp}.pdf"
    HtmlExport.objects.create(bundle=bundle, file_name=file_name)

    pdf_buffer = _build_pdf(bundle)
    response = HttpResponse(pdf_buffer.getvalue(), content_type="application/pdf")
    response["Content-Disposition"] = f'attachment; filename="{file_name}"'
    return response


def export_download(request, export_id: int):
    export = get_object_or_404(HtmlExport, pk=export_id)
    pdf_buffer = _build_pdf(export.bundle)
    response = HttpResponse(pdf_buffer.getvalue(), content_type="application/pdf")
    response["Content-Disposition"] = f'attachment; filename="{export.file_name}"'
    return response