"""Attachment service — unified through DMS.

All files are stored in the DMS (files table).
entity_attachments just references the DMS file with entity_type/entity_id.

This unifies: one upload path, one download path, one permission model,
one deduplication (content_hash), one storage backend.
"""

from __future__ import annotations

import hashlib
import os
import uuid
from datetime import UTC, datetime
from typing import Any

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.core.audit import log_audit
from app.core.storage import get_storage_backend
from app.core.visibility import apply_visibility_filter, check_single_entity_access
from app.models.entity_attachment import EntityAttachment

# DMS File model accessed via contract to avoid Core→Plugin dependency (P1-9 fix)

def _get_dms_file_model():
    """Get DMS File model via contract registry, or None if DMS plugin inactive."""
    from app.plugins.builtins.contracts import get_contract
    dms_contract = get_contract("dms")
    if dms_contract is not None:
        return dms_contract.dms_file
    return None


# File size limit: 50MB
MAX_FILE_SIZE = 50 * 1024 * 1024


def _generate_unique_filename(original_filename: str) -> str:
    """Generate a unique filename using UUID + original extension."""
    ext = os.path.splitext(original_filename)[1]
    return f"{uuid.uuid4().hex}{ext}"


def _entity_attachment_to_dict(ea: EntityAttachment, dms_file: Any = None) -> dict[str, Any]:
    """Serialize an EntityAttachment + DMS File to dict."""
    return {
        "id": str(ea.id),
        "entity_type": ea.entity_type,
        "entity_id": str(ea.entity_id),
        "dms_file_id": str(ea.dms_file_id),
        "category": ea.category,
        "display_name": ea.display_name,
        "filename": dms_file.name if dms_file else (ea.display_name or "unknown"),
        "mime_type": dms_file.mime_type if dms_file else "application/octet-stream",
        "file_size": dms_file.size_bytes if dms_file else 0,
        "uploaded_by": str(ea.created_by) if ea.created_by else None,
        "owner_id": str(ea.owner_id) if ea.owner_id else None,
        "created_at": ea.created_at.isoformat() if ea.created_at else None,
        "updated_at": ea.updated_at.isoformat() if ea.updated_at else None,
    }


async def save_attachment(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    user_id: uuid.UUID,
    entity_type: str,
    entity_id: uuid.UUID,
    filename: str,
    file: Any,  # UploadFile or async iterator of chunks
    mime_type: str,
    is_system_admin: bool = False,
) -> dict[str, Any]:
    """Save a file to DMS and create an entity_attachments reference.

    Streams the file in chunks to avoid loading entire file into RAM.
    """

    # Generate unique filename and storage path
    unique_filename = _generate_unique_filename(filename)
    storage_path = f"attachments/{entity_type}/{entity_id}/{unique_filename}"

    # Stream file to storage — compute hash and size during streaming
    sha256 = hashlib.sha256()
    file_size = 0
    chunk_size = 1024 * 1024  # 1MB chunks

    async def chunk_stream():
        nonlocal file_size
        if hasattr(file, 'read'):
            # UploadFile object
            while True:
                chunk = await file.read(chunk_size)
                if not chunk:
                    break
                file_size += len(chunk)
                sha256.update(chunk)
                yield chunk
        else:
            # Already bytes (backward compat)
            nonlocal_bytes = file if isinstance(file, bytes) else b''.join([c async for c in file])
            file_size = len(nonlocal_bytes)
            sha256.update(nonlocal_bytes)
            yield nonlocal_bytes

    # Check file size limit during streaming
    # (we check after streaming — for true streaming we'd need a wrapper)
    # For now, stream and check size after
    storage = get_storage_backend()
    await storage.save_stream(storage_path, chunk_stream())

    if file_size > MAX_FILE_SIZE:
        await storage.delete(storage_path)
        raise ValueError(f"File too large: {file_size} bytes (max {MAX_FILE_SIZE})")

    # Check for blocked file types
    import os as _os
    _blocked = {".exe", ".bat", ".cmd", ".sh", ".jar", ".com", ".scr", ".msi", ".dll", ".vbs", ".ps1", ".app", ".bin", ".reg", ".inf"}
    _ext = _os.path.splitext(filename)[1].lower()
    if _ext in _blocked:
        await storage.delete(storage_path)
        raise ValueError(f"File type not allowed: {_ext}")

    # Check access on parent entity
    if not is_system_admin:
        has_access = await check_single_entity_access(
            db, entity_type, entity_id, user_id, tenant_id, "write", is_system_admin
        )
        if not has_access:
            await storage.delete(storage_path)
            raise PermissionError(f"No write access to {entity_type} {entity_id}")

    content_hash = sha256.hexdigest()

    # Get DMS File model via contract (avoid Core→Plugin dependency)
    dms_file = _get_dms_file_model()
    if dms_file is None:
        await storage.delete(storage_path)
        raise RuntimeError("DMS plugin not available — cannot save attachment")

    # Check for existing DMS file with same hash in same tenant (deduplication)
    existing_file = await db.execute(
        select(dms_file).where(
            dms_file.tenant_id == tenant_id,
            dms_file.content_hash == content_hash,
            dms_file.deleted_at.is_(None),
        ).limit(1)
    )
    existing_dms_file = existing_file.scalar_one_or_none()

    if existing_dms_file:
        # Deduplicate: reuse existing DMS file, just create new reference
        dms_file = existing_dms_file
        await storage.delete(storage_path)  # Remove the duplicate we just saved
    else:
        # File already streamed to storage — create DMS File record
        dms_file = dms_file(
            tenant_id=tenant_id,
            name=filename,
            folder_id=None,  # Attachments don't go in DMS folders
            uploaded_by=user_id,
            mime_type=mime_type,
            size_bytes=file_size,
            storage_path=storage_path,
            content_hash=content_hash,
            owner_id=user_id,
        )
        db.add(dms_file)
        await db.flush()
        await db.refresh(dms_file)

    # Create entity_attachments reference
    entity_attachment = EntityAttachment(
        tenant_id=tenant_id,
        entity_type=entity_type,
        entity_id=entity_id,
        dms_file_id=dms_file.id,
        category=None,
        display_name=filename,
        owner_id=user_id,
        created_by=user_id,
    )
    db.add(entity_attachment)
    await db.flush()
    await db.refresh(entity_attachment)

    await log_audit(
        db, tenant_id, user_id, "upload", "attachment", entity_attachment.id,
        changes={"filename": filename, "entity_type": entity_type, "entity_id": str(entity_id), "dms_file_id": str(dms_file.id)},
    )
    return _entity_attachment_to_dict(entity_attachment, dms_file)


async def list_attachments(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    entity_type: str,
    entity_id: uuid.UUID,
    user_id: uuid.UUID | None = None,
    is_system_admin: bool = False,
) -> dict[str, Any]:
    """List attachments for a specific entity (via DMS files)."""
    dms_file = _get_dms_file_model()
    if dms_file is None:
        return {"items": [], "total": 0}
    q = (
        select(EntityAttachment, dms_file)
        .join(dms_file, EntityAttachment.dms_file_id == dms_file.id)
        .where(
            EntityAttachment.tenant_id == tenant_id,
            EntityAttachment.entity_type == entity_type,
            EntityAttachment.entity_id == entity_id,
            EntityAttachment.deleted_at.is_(None),
            dms_file.deleted_at.is_(None),
        )
        .order_by(EntityAttachment.created_at.desc())
    )
    if user_id and not is_system_admin:
        q = await apply_visibility_filter(
            db, q, "entity_attachment", EntityAttachment, user_id, tenant_id, is_system_admin
        )
    result = await db.execute(q)
    rows = result.all()
    return {
        "items": [_entity_attachment_to_dict(ea, df) for ea, df in rows],
        "total": len(rows),
    }


async def get_attachment(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    attachment_id: uuid.UUID,
    user_id: uuid.UUID | None = None,
    is_system_admin: bool = False,
) -> dict[str, Any] | None:
    """Get a single attachment by ID (with DMS file info)."""
    dms_file = _get_dms_file_model()
    if dms_file is None:
        return None
    q = (
        select(EntityAttachment, dms_file)
        .join(dms_file, EntityAttachment.dms_file_id == dms_file.id)
        .where(
            EntityAttachment.id == attachment_id,
            EntityAttachment.tenant_id == tenant_id,
            EntityAttachment.deleted_at.is_(None),
        )
    )
    result = await db.execute(q)
    row = result.first()
    if row is None:
        return None
    ea, dms_file = row
    if user_id and not is_system_admin:
        has_access = await check_single_entity_access(
            db, "entity_attachment", ea.id, user_id, tenant_id, "read", is_system_admin
        )
        if not has_access:
            raise PermissionError("No access")
    return _entity_attachment_to_dict(ea, dms_file)


async def get_attachment_download_path(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    attachment_id: uuid.UUID,
    user_id: uuid.UUID | None = None,
    is_system_admin: bool = False,
) -> str | None:
    """Get the storage path for downloading an attachment's DMS file."""
    dms_file = _get_dms_file_model()
    if dms_file is None:
        return None
    q = (
        select(EntityAttachment, dms_file)
        .join(dms_file, EntityAttachment.dms_file_id == dms_file.id)
        .where(
            EntityAttachment.id == attachment_id,
            EntityAttachment.tenant_id == tenant_id,
            EntityAttachment.deleted_at.is_(None),
            dms_file.deleted_at.is_(None),
        )
    )
    result = await db.execute(q)
    row = result.first()
    if row is None:
        return None
    ea, dms_file = row
    if user_id and not is_system_admin:
        has_access = await check_single_entity_access(
            db, "entity_attachment", ea.id, user_id, tenant_id, "read", is_system_admin
        )
        if not has_access:
            raise PermissionError("No access")
    return dms_file.storage_path


async def delete_attachment(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    user_id: uuid.UUID,
    attachment_id: uuid.UUID,
    is_system_admin: bool = False,
) -> bool:
    """Soft-delete an entity_attachments reference.

    The DMS file is NOT deleted because other entities may reference it.
    DMS file cleanup happens via DMS's own deletion workflow.
    """
    q = select(EntityAttachment).where(
        EntityAttachment.id == attachment_id,
        EntityAttachment.tenant_id == tenant_id,
        EntityAttachment.deleted_at.is_(None),
    )
    result = await db.execute(q)
    ea = result.scalar_one_or_none()
    if ea is None:
        return False

    if not is_system_admin:
        has_access = await check_single_entity_access(
            db, "entity_attachment", ea.id, user_id, tenant_id, "admin", is_system_admin
        )
        if not has_access:
            raise PermissionError("No access")

    ea.deleted_at = datetime.now(UTC)
    await db.flush()
    await log_audit(
        db, tenant_id, user_id, "delete", "attachment", attachment_id,
        changes={"display_name": ea.display_name, "dms_file_id": str(ea.dms_file_id)},
    )
    return True