"""Private bounded conversation exports; no public sharing or provider execution."""
import asyncio
import json

from fastapi import APIRouter, Depends, HTTPException, Request, Response

from .app import current_user

MAX_EXPORT_BYTES = 16 * 1024 * 1024
MAX_EXPORT_MESSAGES = 10_000


def export_conversation(store, owner, identifier, format='json', byte_limit=MAX_EXPORT_BYTES):
    if format not in ('json', 'markdown'):
        raise HTTPException(422, 'Export format must be json or markdown')
    with store.lock:
        try:
            conversation = store._conversation(store._row('chat_conversations', owner, identifier))
        except (KeyError, ValueError):
            raise HTTPException(404, 'Conversation not found') from None
        count, content_bytes = store.db.execute('SELECT COUNT(*),COALESCE(SUM(length(CAST(content AS BLOB))),0) FROM chat_messages WHERE owner=? AND conversation_id=?', (owner, identifier)).fetchone()
        if count > MAX_EXPORT_MESSAGES or content_bytes > byte_limit:
            raise HTTPException(413, 'Conversation export limit exceeded')
        messages = [store._message(row) for row in store.db.execute('SELECT * FROM chat_messages WHERE owner=? AND conversation_id=? ORDER BY position', (owner, identifier))]
    if format == 'json':
        # Only public projection; no Hermes IDs, API URLs, credentials or tool events.
        encoded = json.dumps({'version': 1, 'conversation': conversation, 'messages': messages}, ensure_ascii=False, indent=2).encode('utf-8')
        mime, suffix = 'application/json', '.json'
    else:
        # Preserve original message text/citations. Always attachment+plain text:
        # user markdown/HTML is never executed or rendered by this API.
        sections = ['# ' + conversation['title'], '']
        for message in messages:
            sections += ['## ' + message['role'].capitalize() + ' — ' + message['status'], '', message['content'], '']
            if message['attachments']:
                sections += ['Attachments (IDs; private bytes not embedded): ' + ', '.join(message['attachments']), '']
        encoded = '\n'.join(sections).encode('utf-8')
        mime, suffix = 'text/plain', '.md'
    if len(encoded) > byte_limit:
        raise HTTPException(413, 'Conversation export limit exceeded')
    return encoded, mime, 'conversation-' + conversation['id'] + suffix


def create_export_router():
    router = APIRouter()

    @router.get('/api/conversations/{identifier}/export')
    async def conversation_export(identifier: str, request: Request, format: str = 'json', user=Depends(current_user)):
        data, mime, filename = await asyncio.to_thread(export_conversation, request.app.state.chat_store, user['id'], identifier, format)
        await current_user(request)  # Revocation during export denies final response.
        return Response(data, media_type=mime, headers={'Content-Disposition': 'attachment; filename="' + filename + '"',
                                                       'Cache-Control': 'no-store', 'X-Content-Type-Options': 'nosniff'})
    return router