from datetime import datetime, timezone
from typing import Annotated, Optional
from uuid import UUID
from fastapi import APIRouter, Depends, HTTPException, status, Query
from fastapi.responses import PlainTextResponse
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import select

from app.core.database import get_db
from app.models.tree import Tree
from app.models.session import Session
from app.models.user import User
from app.schemas.session import (
    SessionCreate,
    SessionUpdate,
    SessionResponse,
    SessionExport,
    ScratchpadUpdate,
    SaveAsTreeRequest,
    SaveAsTreeResponse,
    SessionComplete,
)
from app.api.deps import get_current_active_user
from app.core.permissions import can_access_tree
from app.services.export_service import generate_markdown_export, generate_text_export, generate_html_export, generate_psa_export

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


@router.get("", response_model=list[SessionResponse])
async def list_sessions(
    db: Annotated[AsyncSession, Depends(get_db)],
    current_user: Annotated[User, Depends(get_current_active_user)],
    completed: Optional[bool] = Query(None, description="Filter by completion status"),
    ticket_number: Optional[str] = Query(None, description="Search by ticket number (partial match)"),
    client_name: Optional[str] = Query(None, description="Search by client name (partial match)"),
    tree_name: Optional[str] = Query(None, description="Filter by tree name from snapshot"),
    started_after: Optional[datetime] = Query(None, description="Filter sessions started after this datetime"),
    started_before: Optional[datetime] = Query(None, description="Filter sessions started before this datetime"),
    completed_after: Optional[datetime] = Query(None, description="Filter sessions completed after this datetime"),
    completed_before: Optional[datetime] = Query(None, description="Filter sessions completed before this datetime"),
    skip: int = Query(0, ge=0),
    limit: int = Query(50, ge=1, le=100)
):
    """List user's troubleshooting sessions with comprehensive filtering."""
    query = select(Session).where(Session.user_id == current_user.id)

    # Completion status filter
    if completed is not None:
        if completed:
            query = query.where(Session.completed_at.isnot(None))
        else:
            query = query.where(Session.completed_at.is_(None))

    # Ticket number search (case-insensitive partial match)
    if ticket_number:
        query = query.where(Session.ticket_number.ilike(f"%{ticket_number}%"))

    # Client name search (case-insensitive partial match)
    if client_name:
        query = query.where(Session.client_name.ilike(f"%{client_name}%"))

    # Tree name filter (JSONB path query)
    if tree_name:
        query = query.where(Session.tree_snapshot['name'].astext.ilike(f"%{tree_name}%"))

    # Date range filters
    if started_after:
        query = query.where(Session.started_at >= started_after)
    if started_before:
        query = query.where(Session.started_at <= started_before)
    if completed_after:
        query = query.where(Session.completed_at >= completed_after)
    if completed_before:
        query = query.where(Session.completed_at <= completed_before)

    query = query.order_by(Session.started_at.desc())
    query = query.offset(skip).limit(limit)

    result = await db.execute(query)
    sessions = result.scalars().all()
    return sessions


@router.get("/{session_id}", response_model=SessionResponse)
async def get_session(
    session_id: UUID,
    db: Annotated[AsyncSession, Depends(get_db)],
    current_user: Annotated[User, Depends(get_current_active_user)]
):
    """Get a specific session."""
    result = await db.execute(select(Session).where(Session.id == session_id))
    session = result.scalar_one_or_none()

    if not session:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Session not found"
        )

    if session.user_id != current_user.id:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="You don't have access to this session"
        )

    return session


@router.post("", response_model=SessionResponse, status_code=status.HTTP_201_CREATED)
async def start_session(
    session_data: SessionCreate,
    db: Annotated[AsyncSession, Depends(get_db)],
    current_user: Annotated[User, Depends(get_current_active_user)]
):
    """Start a new troubleshooting session."""
    # Get the tree
    result = await db.execute(select(Tree).where(Tree.id == session_data.tree_id))
    tree = result.scalar_one_or_none()

    if not tree:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Tree not found"
        )

    if not tree.is_active:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Cannot start session with inactive tree"
        )

    if not can_access_tree(current_user, tree):
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="You don't have access to this tree"
        )

    # Create session with tree snapshot (includes tree metadata for filtering/export)
    tree_snapshot = {
        **tree.tree_structure,
        "name": tree.name,
        "description": tree.description,
        "category": tree.category,
        "version": tree.version
    }

    new_session = Session(
        tree_id=tree.id,
        user_id=current_user.id,
        tree_snapshot=tree_snapshot,
        path_taken=[],
        decisions=[],
        ticket_number=session_data.ticket_number,
        client_name=session_data.client_name
    )

    # Increment tree usage count
    tree.usage_count += 1

    db.add(new_session)
    await db.commit()
    await db.refresh(new_session)
    return new_session


@router.put("/{session_id}", response_model=SessionResponse)
async def update_session(
    session_id: UUID,
    session_data: SessionUpdate,
    db: Annotated[AsyncSession, Depends(get_db)],
    current_user: Annotated[User, Depends(get_current_active_user)]
):
    """Update session (add decisions, notes, etc.)."""
    result = await db.execute(select(Session).where(Session.id == session_id))
    session = result.scalar_one_or_none()

    if not session:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Session not found"
        )

    if session.user_id != current_user.id:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="You don't have access to this session"
        )

    if session.completed_at:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Cannot update a completed session"
        )

    # Use mode='json' to ensure datetime fields are serialized as ISO strings for JSONB storage
    update_data = session_data.model_dump(exclude_unset=True, mode='json')

    for field, value in update_data.items():
        setattr(session, field, value)

    await db.commit()
    await db.refresh(session)
    return session


@router.post("/{session_id}/complete", response_model=SessionResponse)
async def complete_session(
    session_id: UUID,
    completion_data: SessionComplete,
    db: Annotated[AsyncSession, Depends(get_db)],
    current_user: Annotated[User, Depends(get_current_active_user)]
):
    """Mark session as complete."""
    result = await db.execute(select(Session).where(Session.id == session_id))
    session = result.scalar_one_or_none()

    if not session:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Session not found"
        )

    if session.user_id != current_user.id:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="You don't have access to this session"
        )

    if session.completed_at:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Session already completed"
        )

    session.completed_at = datetime.now(timezone.utc)
    session.outcome = completion_data.outcome
    session.outcome_notes = completion_data.outcome_notes
    await db.commit()
    await db.refresh(session)
    return session


@router.patch("/{session_id}/scratchpad", response_model=SessionResponse)
async def update_scratchpad(
    session_id: UUID,
    data: ScratchpadUpdate,
    db: Annotated[AsyncSession, Depends(get_db)],
    current_user: Annotated[User, Depends(get_current_active_user)]
):
    """Update session scratchpad. Accepts updates on both active and completed sessions."""
    result = await db.execute(select(Session).where(Session.id == session_id))
    session = result.scalar_one_or_none()

    if not session:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Session not found"
        )

    if session.user_id != current_user.id:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="You don't have access to this session"
        )

    session.scratchpad = data.scratchpad
    await db.commit()
    await db.refresh(session)
    return session


@router.post("/{session_id}/export")
async def export_session(
    session_id: UUID,
    export_options: SessionExport,
    db: Annotated[AsyncSession, Depends(get_db)],
    current_user: Annotated[User, Depends(get_current_active_user)]
):
    """Export session to formatted notes."""
    result = await db.execute(select(Session).where(Session.id == session_id))
    session = result.scalar_one_or_none()

    if not session:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Session not found"
        )

    if session.user_id != current_user.id:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="You don't have access to this session"
        )

    # Generate export based on format
    if export_options.format == "markdown":
        content = generate_markdown_export(session, export_options)
        media_type = "text/markdown"
    elif export_options.format == "html":
        content = generate_html_export(session, export_options)
        media_type = "text/html"
    elif export_options.format == "psa":
        content = generate_psa_export(session, export_options)
        media_type = "text/plain"
    else:  # text
        content = generate_text_export(session, export_options)
        media_type = "text/plain"

    # Resolve variables in export output
    session_vars = getattr(session, 'session_variables', None) or {}
    if session_vars:
        from app.services.variable_service import resolve_variables
        content = resolve_variables(content, session_vars)

    # Mark as exported
    session.exported = True
    await db.commit()

    return PlainTextResponse(content=content, media_type=media_type)


# --- Save Session as Tree ---


@router.post("/{session_id}/save-as-tree", response_model=SaveAsTreeResponse, status_code=status.HTTP_201_CREATED)
async def save_session_as_tree(
    session_id: UUID,
    request_data: SaveAsTreeRequest,
    db: Annotated[AsyncSession, Depends(get_db)],
    current_user: Annotated[User, Depends(get_current_active_user)]
):
    """Save a session as a new tree.

    Converts the session's path_taken and custom_steps into a linear tree structure.
    The new tree is linked to the original tree via parent_tree_id (fork relationship).

    Args:
        session_id: ID of the session to save
        request_data: Tree name, description, and status
        db: Database session
        current_user: Current authenticated user

    Returns:
        SaveAsTreeResponse with new tree ID and name
    """
    from app.core.session_to_tree import convert_session_to_tree, generate_tree_name_from_session
    from app.core.tree_validation import can_publish_tree
    from app.core.subscriptions import check_tree_limit

    # Load the session
    result = await db.execute(
        select(Session).where(
            Session.id == session_id,
            Session.user_id == current_user.id
        )
    )
    session = result.scalar_one_or_none()

    if not session:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Session not found"
        )

    # Load the original tree to get metadata
    tree_result = await db.execute(
        select(Tree).where(Tree.id == session.tree_id)
    )
    original_tree = tree_result.scalar_one_or_none()

    if not original_tree:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Original tree not found"
        )

    # Convert session to tree structure
    tree_structure = convert_session_to_tree(
        session.path_taken,
        session.tree_snapshot,
        session.custom_steps,
        session.decisions
    )

    # Generate tree name
    if request_data.tree_name:
        tree_name = request_data.tree_name
    else:
        tree_name = generate_tree_name_from_session(
            original_tree.name,
            session.ticket_number,
            session.client_name
        )

    # Validate if status is published
    if request_data.status == 'published':
        can_publish, validation_errors = can_publish_tree(
            tree_structure,
            tree_name,
            request_data.description
        )
        if not can_publish:
            raise HTTPException(
                status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
                detail={
                    "message": "Cannot save as published tree with validation errors",
                    "errors": validation_errors
                }
            )

    # Check subscription tree limit
    if current_user.account_id:
        can_create, limit, count = await check_tree_limit(current_user.account_id, db)
        if not can_create:
            raise HTTPException(
                status_code=status.HTTP_402_PAYMENT_REQUIRED,
                detail=f"Tree limit reached ({count}/{limit}). Upgrade your plan to create more trees."
            )

    # Create the new tree as a fork of the original
    new_tree = Tree(
        name=tree_name,
        description=request_data.description or f"Saved from troubleshooting session on {session.started_at.strftime('%Y-%m-%d')}",
        tree_structure=tree_structure,
        author_id=current_user.id,
        account_id=current_user.account_id,
        status=request_data.status,
        is_public=False,
        is_default=False,
        # Fork tracking - link to original tree
        parent_tree_id=original_tree.id,
        root_tree_id=original_tree.root_tree_id if original_tree.root_tree_id else original_tree.id,
        fork_depth=original_tree.fork_depth + 1,
        fork_reason=f"Saved from session: {session.ticket_number or 'No ticket'}" if session.ticket_number else "Saved from troubleshooting session",
        parent_updated_at=original_tree.updated_at
    )

    db.add(new_tree)
    await db.commit()
    await db.refresh(new_tree)

    return SaveAsTreeResponse(
        tree_id=new_tree.id,
        tree_name=new_tree.name,
        message=f"Session saved as {'published' if request_data.status == 'published' else 'draft'} tree"
    )