from __future__ import annotations

import os
import shutil
from pathlib import Path
from uuid import uuid4

from sqlalchemy import select
from sqlalchemy.orm import Session, joinedload

from app.modules.documents.models import EngagementDocument
from app.modules.documents.services import DEFAULT_STORAGE_ROOT, sanitize_segment, save_uploaded_revision
from app.modules.services.models import (
    ClientServiceSubscription,
    ClientServiceTaskInstance,
    FirmServiceTaskTemplate,
    FirmTaskDocumentRequirement,
    FirmTaskDocumentTemplate,
)

TEMPLATE_UPLOAD_ROOT = Path(os.getenv("DOCUMENT_TEMPLATE_STORAGE_ROOT", str(DEFAULT_STORAGE_ROOT.parent / "document_templates"))).resolve()


def list_task_document_requirements(db: Session, *, tenant_id: int, firm_task_template_id: int) -> list[FirmTaskDocumentRequirement]:
    return db.execute(
        select(FirmTaskDocumentRequirement)
        .where(
            FirmTaskDocumentRequirement.tenant_id == int(tenant_id),
            FirmTaskDocumentRequirement.firm_task_template_id == int(firm_task_template_id),
        )
        .order_by(FirmTaskDocumentRequirement.sort_order.asc(), FirmTaskDocumentRequirement.id.asc())
    ).scalars().all()


def get_task_document_requirement(db: Session, *, requirement_id: int, tenant_id: int | None = None) -> FirmTaskDocumentRequirement | None:
    stmt = select(FirmTaskDocumentRequirement).where(FirmTaskDocumentRequirement.id == int(requirement_id))
    if tenant_id is not None:
        stmt = stmt.where(FirmTaskDocumentRequirement.tenant_id == int(tenant_id))
    return db.execute(stmt).scalar_one_or_none()


def create_task_document_requirement(
    db: Session,
    *,
    task_template: FirmServiceTaskTemplate,
    document_name: str,
    document_type: str,
    is_mandatory: bool,
    allowed_file_types: str | None,
    instructions: str | None,
    sort_order: int,
    user,
) -> FirmTaskDocumentRequirement:
    row = FirmTaskDocumentRequirement(
        tenant_id=task_template.tenant_id,
        service_catalogue_id=task_template.service_catalogue_id,
        firm_task_template_id=task_template.id,
        document_name=document_name.strip()[:200],
        document_type=(document_type or "GENERAL").strip().upper()[:80] or "GENERAL",
        is_mandatory=bool(is_mandatory),
        allowed_file_types=(allowed_file_types or "").strip()[:255] or None,
        instructions=(instructions or "").strip() or None,
        sort_order=int(sort_order or 100),
        is_active=True,
        created_by_user_id=getattr(user, "id", None),
        updated_by_user_id=getattr(user, "id", None),
    )
    db.add(row)
    db.flush()
    return row


def update_task_document_requirement(
    db: Session,
    *,
    requirement: FirmTaskDocumentRequirement,
    document_name: str,
    document_type: str,
    is_mandatory: bool,
    allowed_file_types: str | None,
    instructions: str | None,
    sort_order: int,
    is_active: bool,
    user,
) -> FirmTaskDocumentRequirement:
    requirement.document_name = document_name.strip()[:200]
    requirement.document_type = (document_type or "GENERAL").strip().upper()[:80] or "GENERAL"
    requirement.is_mandatory = bool(is_mandatory)
    requirement.allowed_file_types = (allowed_file_types or "").strip()[:255] or None
    requirement.instructions = (instructions or "").strip() or None
    requirement.sort_order = int(sort_order or 100)
    requirement.is_active = bool(is_active)
    requirement.updated_by_user_id = getattr(user, "id", None)
    db.flush()
    return requirement


def list_task_document_templates(db: Session, *, tenant_id: int, firm_task_template_id: int) -> list[FirmTaskDocumentTemplate]:
    return db.execute(
        select(FirmTaskDocumentTemplate)
        .where(
            FirmTaskDocumentTemplate.tenant_id == int(tenant_id),
            FirmTaskDocumentTemplate.firm_task_template_id == int(firm_task_template_id),
            FirmTaskDocumentTemplate.is_active.is_(True),
        )
        .order_by(FirmTaskDocumentTemplate.uploaded_at_utc.desc(), FirmTaskDocumentTemplate.id.desc())
    ).scalars().all()


def _template_relative_path(task_template: FirmServiceTaskTemplate, original_filename: str, template_id: int) -> Path:
    suffix = Path(original_filename or "template.bin").suffix or ".bin"
    safe_name = sanitize_segment(Path(original_filename or "template.bin").stem, "template")[:80]
    return (
        Path(f"tenant_{task_template.tenant_id}")
        / f"service_{task_template.service_catalogue_id}"
        / f"task_{task_template.id}"
        / f"TPL{template_id:06d}_{safe_name}_{uuid4().hex[:8]}{suffix}"
    )


def save_task_document_template(
    db: Session,
    *,
    task_template: FirmServiceTaskTemplate,
    template_name: str,
    template_category: str | None,
    description: str | None,
    upload_file,
    user,
) -> FirmTaskDocumentTemplate:
    original_filename = Path(upload_file.filename or "template.bin").name
    row = FirmTaskDocumentTemplate(
        tenant_id=task_template.tenant_id,
        service_catalogue_id=task_template.service_catalogue_id,
        firm_task_template_id=task_template.id,
        template_name=(template_name or original_filename).strip()[:200],
        template_category=(template_category or "").strip()[:100] or None,
        description=(description or "").strip() or None,
        original_filename=original_filename,
        stored_filename="PENDING",
        content_type=getattr(upload_file, "content_type", None),
        file_size_bytes=0,
        local_relative_path="PENDING",
        uploaded_by_user_id=getattr(user, "id", None),
    )
    db.add(row)
    db.flush()

    rel_path = _template_relative_path(task_template, original_filename, row.id)
    abs_path = TEMPLATE_UPLOAD_ROOT / rel_path
    abs_path.parent.mkdir(parents=True, exist_ok=True)
    total = 0
    with abs_path.open("wb") as out:
        while True:
            chunk = upload_file.file.read(1024 * 1024)
            if not chunk:
                break
            total += len(chunk)
            out.write(chunk)
    row.stored_filename = abs_path.name
    row.file_size_bytes = total
    row.local_relative_path = str(rel_path).replace("\\", "/")
    db.flush()
    return row


def template_absolute_path(template: FirmTaskDocumentTemplate) -> Path:
    return TEMPLATE_UPLOAD_ROOT / (template.local_relative_path or "")


def get_task_with_subscription(db: Session, task_id: int) -> ClientServiceTaskInstance | None:
    return db.execute(
        select(ClientServiceTaskInstance)
        .options(
            joinedload(ClientServiceTaskInstance.subscription).joinedload(ClientServiceSubscription.client),
            joinedload(ClientServiceTaskInstance.subscription).joinedload(ClientServiceSubscription.catalogue),
            joinedload(ClientServiceTaskInstance.template),
        )
        .where(ClientServiceTaskInstance.id == int(task_id))
    ).unique().scalar_one_or_none()


def list_documents_for_task(db: Session, task_id: int) -> list[EngagementDocument]:
    return db.execute(
        select(EngagementDocument)
        .options(joinedload(EngagementDocument.versions), joinedload(EngagementDocument.document_requirement))
        .where(EngagementDocument.task_instance_id == int(task_id), EngagementDocument.is_deleted.is_(False))
        .order_by(EngagementDocument.updated_at_utc.desc(), EngagementDocument.id.desc())
    ).unique().scalars().all()


def requirement_upload_status(requirements: list[FirmTaskDocumentRequirement], documents: list[EngagementDocument]) -> list[dict]:
    by_req: dict[int, list[EngagementDocument]] = {}
    for doc in documents:
        if doc.document_requirement_id:
            by_req.setdefault(int(doc.document_requirement_id), []).append(doc)
    payload = []
    for req in requirements:
        docs = by_req.get(int(req.id), [])
        payload.append({
            "requirement": req,
            "documents": docs,
            "is_uploaded": bool(docs),
            "is_pending_mandatory": bool(req.is_mandatory and not docs),
        })
    return payload


def save_uploaded_task_document(
    db: Session,
    *,
    task: ClientServiceTaskInstance,
    requirement: FirmTaskDocumentRequirement | None,
    upload_file,
    title: str,
    document_type: str,
    description: str | None,
    remarks: str | None,
    user,
    existing_document_id: int | None = None,
) -> EngagementDocument:
    engagement = task.subscription or db.get(ClientServiceSubscription, task.subscription_id)
    if engagement is None:
        raise ValueError("Task is not linked to a valid engagement.")
    if requirement:
        title = title or requirement.document_name
        document_type = requirement.document_type or document_type
        description = description or requirement.instructions
    doc = save_uploaded_revision(
        db,
        engagement=engagement,
        upload_file=upload_file,
        title=title,
        document_type=document_type,
        description=description,
        remarks=remarks,
        user=user,
        existing_document_id=existing_document_id,
    )
    doc.task_instance_id = task.id
    doc.document_requirement_id = requirement.id if requirement else None
    db.flush()
    return doc