from sqlalchemy.orm import Session, joinedload
from typing import List, Optional
from . import models, schemas


# Project CRUD
def create_project(db: Session, project: schemas.ProjectCreate) -> models.Project:
    project_data = project.model_dump()
    # Ensure statuses has a default value if not provided
    if project_data.get("statuses") is None:
        project_data["statuses"] = models.DEFAULT_STATUSES

    db_project = models.Project(**project_data)
    db.add(db_project)
    db.commit()
    db.refresh(db_project)
    return db_project


def get_project(db: Session, project_id: int) -> Optional[models.Project]:
    return db.query(models.Project).filter(models.Project.id == project_id).first()


def get_projects(db: Session, skip: int = 0, limit: int = 100, archived: Optional[bool] = None) -> List[models.Project]:
    query = db.query(models.Project)

    # Filter by archive status if specified
    if archived is not None:
        query = query.filter(models.Project.is_archived == archived)

    return query.offset(skip).limit(limit).all()


def update_project(
    db: Session, project_id: int, project: schemas.ProjectUpdate
) -> Optional[models.Project]:
    db_project = get_project(db, project_id)
    if not db_project:
        return None

    update_data = project.model_dump(exclude_unset=True)
    for key, value in update_data.items():
        setattr(db_project, key, value)

    db.commit()
    db.refresh(db_project)
    return db_project


def delete_project(db: Session, project_id: int) -> bool:
    db_project = get_project(db, project_id)
    if not db_project:
        return False
    db.delete(db_project)
    db.commit()
    return True


# Task CRUD
def create_task(db: Session, task: schemas.TaskCreate) -> models.Task:
    # Validate status against project's statuses
    project = get_project(db, task.project_id)
    if project and task.status not in project.statuses:
        raise ValueError(f"Invalid status '{task.status}'. Must be one of: {', '.join(project.statuses)}")

    # Get max sort_order for siblings
    if task.parent_task_id:
        max_order = db.query(models.Task).filter(
            models.Task.parent_task_id == task.parent_task_id
        ).count()
    else:
        max_order = db.query(models.Task).filter(
            models.Task.project_id == task.project_id,
            models.Task.parent_task_id.is_(None)
        ).count()

    task_data = task.model_dump()
    if "sort_order" not in task_data or task_data["sort_order"] == 0:
        task_data["sort_order"] = max_order

    db_task = models.Task(**task_data)
    db.add(db_task)
    db.commit()
    db.refresh(db_task)
    return db_task


def get_task(db: Session, task_id: int) -> Optional[models.Task]:
    return db.query(models.Task).filter(models.Task.id == task_id).first()


def get_tasks_by_project(db: Session, project_id: int) -> List[models.Task]:
    return db.query(models.Task).filter(models.Task.project_id == project_id).all()


def get_root_tasks(db: Session, project_id: int) -> List[models.Task]:
    """Get all root-level tasks (no parent) for a project"""
    return db.query(models.Task).filter(
        models.Task.project_id == project_id,
        models.Task.parent_task_id.is_(None)
    ).order_by(models.Task.sort_order).all()


def get_task_with_subtasks(db: Session, task_id: int) -> Optional[models.Task]:
    """Recursively load a task with all its subtasks"""
    return db.query(models.Task).options(
        joinedload(models.Task.subtasks)
    ).filter(models.Task.id == task_id).first()


def check_and_update_parent_status(db: Session, parent_id: int):
    """Check if all children of a parent are done, and mark parent as done if so"""
    # Get all children of this parent
    children = db.query(models.Task).filter(
        models.Task.parent_task_id == parent_id
    ).all()

    # If no children, nothing to do
    if not children:
        return

    # Check if all children are done
    all_done = all(child.status == "done" for child in children)

    if all_done:
        # Mark parent as done
        parent = get_task(db, parent_id)
        if parent and parent.status != "done":
            parent.status = "done"
            db.commit()

            # Recursively check grandparent
            if parent.parent_task_id:
                check_and_update_parent_status(db, parent.parent_task_id)


def update_task(
    db: Session, task_id: int, task: schemas.TaskUpdate
) -> Optional[models.Task]:
    db_task = get_task(db, task_id)
    if not db_task:
        return None

    update_data = task.model_dump(exclude_unset=True)

    # Validate status against project's statuses if status is being updated
    if "status" in update_data:
        project = get_project(db, db_task.project_id)
        if project and update_data["status"] not in project.statuses:
            raise ValueError(f"Invalid status '{update_data['status']}'. Must be one of: {', '.join(project.statuses)}")
        status_changed = True
        old_status = db_task.status
    else:
        status_changed = False

    for key, value in update_data.items():
        setattr(db_task, key, value)

    db.commit()
    db.refresh(db_task)

    # If status changed to 'done' and this task has a parent, check if parent should auto-complete
    if status_changed and db_task.status == "done" and db_task.parent_task_id:
        check_and_update_parent_status(db, db_task.parent_task_id)

    return db_task


def delete_task(db: Session, task_id: int) -> bool:
    db_task = get_task(db, task_id)
    if not db_task:
        return False
    db.delete(db_task)
    db.commit()
    return True


def get_tasks_by_status(db: Session, project_id: int, status: str) -> List[models.Task]:
    """Get all tasks for a project with a specific status"""
    # Validate status against project's statuses
    project = get_project(db, project_id)
    if project and status not in project.statuses:
        raise ValueError(f"Invalid status '{status}'. Must be one of: {', '.join(project.statuses)}")

    return db.query(models.Task).filter(
        models.Task.project_id == project_id,
        models.Task.status == status
    ).all()


# ========== BLOCKER CRUD ==========

def _has_cycle(db: Session, start_id: int, target_id: int) -> bool:
    """BFS from start_id following its blockers. Returns True if target_id is reachable,
    which would mean adding target_id as a blocker of start_id creates a cycle."""
    visited = set()
    queue = [start_id]
    while queue:
        current = queue.pop(0)
        if current == target_id:
            return True
        if current in visited:
            continue
        visited.add(current)
        task = db.query(models.Task).filter(models.Task.id == current).first()
        if task:
            for b in task.blockers:
                if b.id not in visited:
                    queue.append(b.id)
    return False


def add_blocker(db: Session, task_id: int, blocker_id: int) -> models.Task:
    """Add blocker_id as a prerequisite of task_id.
    Raises ValueError on self-reference or cycle."""
    if task_id == blocker_id:
        raise ValueError("A task cannot block itself")

    task = get_task(db, task_id)
    blocker = get_task(db, blocker_id)

    if not task:
        raise ValueError("Task not found")
    if not blocker:
        raise ValueError("Blocker task not found")

    # Already linked — idempotent
    if any(b.id == blocker_id for b in task.blockers):
        return task

    # Cycle detection: would blocker_id eventually depend on task_id?
    if _has_cycle(db, blocker_id, task_id):
        raise ValueError("Adding this blocker would create a circular dependency")

    task.blockers.append(blocker)
    db.commit()
    db.refresh(task)
    return task


def remove_blocker(db: Session, task_id: int, blocker_id: int) -> bool:
    """Remove blocker_id as a prerequisite of task_id."""
    task = get_task(db, task_id)
    blocker = get_task(db, blocker_id)

    if not task or not blocker:
        return False

    if not any(b.id == blocker_id for b in task.blockers):
        return False

    task.blockers.remove(blocker)
    db.commit()
    return True


def get_task_with_blockers(db: Session, task_id: int) -> Optional[models.Task]:
    """Get a task including its blockers and blocking lists."""
    return db.query(models.Task).filter(models.Task.id == task_id).first()


def get_actionable_tasks(db: Session) -> List[dict]:
    """Return all non-done tasks that have no incomplete blockers, with project name."""
    tasks = db.query(models.Task).filter(
        models.Task.status != "done"
    ).all()

    result = []
    for task in tasks:
        incomplete_blockers = [b for b in task.blockers if b.status != "done"]
        if not incomplete_blockers:
            result.append({
                "id": task.id,
                "title": task.title,
                "project_id": task.project_id,
                "project_name": task.project.name,
                "status": task.status,
                "estimated_minutes": task.estimated_minutes,
                "tags": task.tags,
                "flag_color": task.flag_color,
            })

    return result