from typing import Optional, List
from datetime import datetime
from fastapi import APIRouter, Depends, HTTPException, Query
from sqlalchemy.orm import Session
import math

from app.crud import todo as todo_crud
from app.db.session import get_db
from app.models.todo import Priority
from app.schemas.todo import (
    Todo,
    TodoCreate,
    TodoUpdate,
    TodoListResponse,
    SubtaskCreate,
)
from app.utils.date_utils import (
    get_date_range_today,
)

router = APIRouter(prefix="/todos", tags=["todos"])


@router.get("/", response_model=TodoListResponse)
def read_todos(
    page: int = Query(1, ge=1, description="Page number"),
    per_page: int = Query(10, ge=1, le=100, description="Items per page"),
    completed: Optional[bool] = Query(None, description="Filter by completion status"),
    priority: Optional[Priority] = Query(None, description="Filter by priority"),
    search: Optional[str] = Query(None, description="Search in title and description"),
    category_id: Optional[int] = Query(None, description="Filter by category ID"),
    project_id: Optional[int] = Query(None, description="Filter by project ID"),
    overdue: Optional[bool] = Query(None, description="Filter by overdue status"),
    due_soon: Optional[bool] = Query(
        None, description="Filter todos due within next 7 days"
    ),
    due_date_from: Optional[datetime] = Query(
        None, description="Filter todos due after this date"
    ),
    due_date_to: Optional[datetime] = Query(
        None, description="Filter todos due before this date"
    ),
    sort_by: Optional[str] = Query(
        None,
        description="Sort by field (due_date, created_at)",
        regex="^(due_date|created_at)$",
    ),
    db: Session = Depends(get_db),
):
    """
    Retrieve todos with comprehensive filtering and sorting options.

    - **page**: Page number (starts from 1)
    - **per_page**: Number of items per page (1-100)
    - **completed**: Filter by completion status (true/false)
    - **priority**: Filter by priority level (low/medium/high)
    - **search**: Search text in title and description
    - **category_id**: Filter by category ID
    - **project_id**: Filter by project ID
    - **overdue**: Filter overdue todos (true/false)
    - **due_soon**: Filter todos due within next 7 days (true/false)
    - **due_date_from**: Show todos due after this date (ISO format)
    - **due_date_to**: Show todos due before this date (ISO format)
    - **sort_by**: Sort results by 'due_date' or 'created_at'
    """
    skip = (page - 1) * per_page

    # Determine sorting preference
    sort_by_due_date = sort_by == "due_date"

    # Handle due_soon filter by converting to overdue parameter
    if due_soon is not None:
        # For due_soon, we'll use the specialized function
        if due_soon:
            todos, total = todo_crud.get_todos_due_soon(
                db,
                days=7,
                skip=skip,
                limit=per_page,
                completed=completed,
                priority=priority,
                category_id=category_id,
                project_id=project_id,
            )
        else:
            # Get all todos that are NOT due soon
            todos, total = todo_crud.get_todos(
                db,
                skip=skip,
                limit=per_page,
                completed=completed,
                priority=priority,
                search=search,
                category_id=category_id,
                project_id=project_id,
                overdue=False,
                sort_by_due_date=sort_by_due_date,
                due_date_start=due_date_from,
                due_date_end=due_date_to,
            )
    elif overdue is not None and overdue:
        # Use specialized overdue function
        todos, total = todo_crud.get_overdue_todos(
            db,
            skip=skip,
            limit=per_page,
            completed=completed,
            priority=priority,
            category_id=category_id,
            project_id=project_id,
        )
    else:
        # Standard query with all filters
        todos, total = todo_crud.get_todos(
            db,
            skip=skip,
            limit=per_page,
            completed=completed,
            priority=priority,
            search=search,
            category_id=category_id,
            project_id=project_id,
            overdue=overdue,
            sort_by_due_date=sort_by_due_date,
            due_date_start=due_date_from,
            due_date_end=due_date_to,
        )

    total_pages = math.ceil(total / per_page)

    return TodoListResponse(
        items=todos,
        total=total,
        page=page,
        per_page=per_page,
        has_next=page < total_pages,
        has_prev=page > 1,
    )


@router.get("/overdue", response_model=TodoListResponse)
def get_overdue_todos(
    page: int = Query(1, ge=1, description="Page number"),
    per_page: int = Query(10, ge=1, le=100, description="Items per page"),
    completed: Optional[bool] = Query(None, description="Filter by completion status"),
    priority: Optional[Priority] = Query(None, description="Filter by priority"),
    category_id: Optional[int] = Query(None, description="Filter by category ID"),
    project_id: Optional[int] = Query(None, description="Filter by project ID"),
    db: Session = Depends(get_db),
):
    """
    Get all overdue todos.

    Returns todos that have a due date in the past and are not completed.
    Results are sorted by due date (earliest first).
    """
    skip = (page - 1) * per_page
    todos, total = todo_crud.get_overdue_todos(
        db,
        skip=skip,
        limit=per_page,
        completed=completed,
        priority=priority,
        category_id=category_id,
        project_id=project_id,
    )

    total_pages = math.ceil(total / per_page)

    return TodoListResponse(
        items=todos,
        total=total,
        page=page,
        per_page=per_page,
        has_next=page < total_pages,
        has_prev=page > 1,
    )


@router.get("/due-soon", response_model=TodoListResponse)
def get_todos_due_soon(
    page: int = Query(1, ge=1, description="Page number"),
    per_page: int = Query(10, ge=1, le=100, description="Items per page"),
    days: int = Query(7, ge=1, le=30, description="Number of days to look ahead"),
    completed: Optional[bool] = Query(None, description="Filter by completion status"),
    priority: Optional[Priority] = Query(None, description="Filter by priority"),
    category_id: Optional[int] = Query(None, description="Filter by category ID"),
    project_id: Optional[int] = Query(None, description="Filter by project ID"),
    db: Session = Depends(get_db),
):
    """
    Get todos due within the next N days (default 7 days).

    Returns todos that have a due date within the specified number of days from now.
    Results are sorted by due date (earliest first).

    - **days**: Number of days to look ahead (1-30, default 7)
    """
    skip = (page - 1) * per_page
    todos, total = todo_crud.get_todos_due_soon(
        db,
        days=days,
        skip=skip,
        limit=per_page,
        completed=completed,
        priority=priority,
        category_id=category_id,
        project_id=project_id,
    )

    total_pages = math.ceil(total / per_page)

    return TodoListResponse(
        items=todos,
        total=total,
        page=page,
        per_page=per_page,
        has_next=page < total_pages,
        has_prev=page > 1,
    )


@router.get("/due-today", response_model=TodoListResponse)
def get_todos_due_today(
    page: int = Query(1, ge=1, description="Page number"),
    per_page: int = Query(10, ge=1, le=100, description="Items per page"),
    completed: Optional[bool] = Query(None, description="Filter by completion status"),
    priority: Optional[Priority] = Query(None, description="Filter by priority"),
    category_id: Optional[int] = Query(None, description="Filter by category ID"),
    project_id: Optional[int] = Query(None, description="Filter by project ID"),
    db: Session = Depends(get_db),
):
    """
    Get todos due today.

    Returns todos that have a due date within today's date range.
    Results are sorted by due date (earliest first).
    """
    skip = (page - 1) * per_page
    start_date, end_date = get_date_range_today()

    todos, total = todo_crud.get_todos_by_date_range(
        db,
        start_date=start_date,
        end_date=end_date,
        skip=skip,
        limit=per_page,
        completed=completed,
        priority=priority,
        category_id=category_id,
        project_id=project_id,
    )

    total_pages = math.ceil(total / per_page)

    return TodoListResponse(
        items=todos,
        total=total,
        page=page,
        per_page=per_page,
        has_next=page < total_pages,
        has_prev=page > 1,
    )


@router.post("/", response_model=Todo)
def create_todo(todo: TodoCreate, db: Session = Depends(get_db)):
    """
    Create a new todo.

    - **title**: Todo title (required, 1-200 characters)
    - **description**: Optional description (max 500 characters)
    - **completed**: Completion status (default: false)
    - **priority**: Priority level (low/medium/high, default: medium)
    - **category_id**: Optional category ID
    - **project_id**: Optional project ID
    - **due_date**: Optional due date with timezone
    - **tag_ids**: Optional list of tag IDs
    """
    return todo_crud.create_todo(db=db, todo=todo)


@router.get("/{todo_id}", response_model=Todo)
def read_todo(todo_id: int, db: Session = Depends(get_db)):
    """
    Get a specific todo by ID.

    Returns the todo with all its details including computed fields like
    is_overdue and days_until_due.
    """
    db_todo = todo_crud.get_todo(db, todo_id=todo_id)
    if db_todo is None:
        raise HTTPException(status_code=404, detail="Todo not found")
    return db_todo


@router.put("/{todo_id}", response_model=Todo)
def update_todo(todo_id: int, todo_update: TodoUpdate, db: Session = Depends(get_db)):
    """
    Update a specific todo.

    All fields are optional. Only provided fields will be updated.
    Use null value for due_date to clear it.
    """
    db_todo = todo_crud.update_todo(db, todo_id=todo_id, todo_update=todo_update)
    if db_todo is None:
        raise HTTPException(status_code=404, detail="Todo not found")
    return db_todo


@router.delete("/{todo_id}")
def delete_todo(todo_id: int, db: Session = Depends(get_db)):
    """
    Delete a specific todo.

    This will also delete all subtasks associated with this todo.
    """
    success = todo_crud.delete_todo(db, todo_id=todo_id)
    if not success:
        raise HTTPException(status_code=404, detail="Todo not found")
    return {"message": "Todo deleted successfully"}


@router.post("/{todo_id}/subtasks", response_model=Todo)
def create_subtask(todo_id: int, subtask: SubtaskCreate, db: Session = Depends(get_db)):
    """
    Create a subtask for a specific todo.

    - **title**: Subtask title (required, 1-200 characters)
    - **description**: Optional description (max 500 characters)
    - **priority**: Priority level (low/medium/high, default: medium)
    - **due_date**: Optional due date with timezone
    """
    db_subtask = todo_crud.create_subtask(db, parent_id=todo_id, subtask=subtask)
    if db_subtask is None:
        raise HTTPException(status_code=404, detail="Parent todo not found")
    return db_subtask


@router.get("/{todo_id}/subtasks", response_model=List[Todo])
def get_subtasks(todo_id: int, db: Session = Depends(get_db)):
    """
    Get all subtasks for a specific todo.

    Returns a list of todos that are subtasks of the specified parent todo.
    """
    # First check if parent todo exists
    parent_todo = todo_crud.get_todo(db, todo_id=todo_id)
    if parent_todo is None:
        raise HTTPException(status_code=404, detail="Todo not found")

    subtasks = todo_crud.get_subtasks(db, parent_id=todo_id)
    return subtasks


@router.put("/subtasks/{subtask_id}/move", response_model=Todo)
def move_subtask(
    subtask_id: int, new_parent_id: Optional[int] = None, db: Session = Depends(get_db)
):
    """
    Move a subtask to a different parent or make it a main todo.

    - **new_parent_id**: New parent todo ID (null to make it a main todo)

    Prevents cycles and validates that the new parent exists.
    """
    moved_subtask = todo_crud.move_subtask(
        db, subtask_id=subtask_id, new_parent_id=new_parent_id
    )
    if moved_subtask is None:
        raise HTTPException(
            status_code=400,
            detail="Cannot move subtask: subtask not found, invalid parent, or would create a cycle",
        )
    return moved_subtask