"""
FastAPI application entry point for Delphi Database.

This module initializes the FastAPI application, sets up database connections,
and provides the main application instance.
"""

import os
import time
import csv
import json
import uuid
from contextlib import asynccontextmanager
from datetime import datetime
from typing import Optional, List, Dict, Any
from io import StringIO

from fastapi import FastAPI, Depends, Request, Query, HTTPException, UploadFile, File, Form
from fastapi.responses import RedirectResponse
from starlette.middleware.sessions import SessionMiddleware
from fastapi.middleware.cors import CORSMiddleware
from fastapi.staticfiles import StaticFiles
from fastapi.templating import Jinja2Templates
from sqlalchemy.orm import Session, joinedload
from sqlalchemy import or_
from dotenv import load_dotenv
from starlette.middleware.base import BaseHTTPMiddleware
import structlog
from structlog import contextvars as structlog_contextvars

from .database import create_tables, get_db, get_database_url
from .models import User, Case, Client, Phone, Transaction, Document, Payment, ImportLog
from .auth import authenticate_user, get_current_user_from_session
from .logging_config import setup_logging

# Load environment variables
load_dotenv()

# Get SECRET_KEY from environment variables
SECRET_KEY = os.getenv("SECRET_KEY")
if not SECRET_KEY:
    raise ValueError("SECRET_KEY environment variable must be set")

# Configure structured logging
setup_logging()
logger = structlog.get_logger(__name__)

# Configure Jinja2 templates
templates = Jinja2Templates(directory="app/templates")


class AuthMiddleware(BaseHTTPMiddleware):
    """
    Simple session-based authentication middleware.

    Redirects unauthenticated users to /login for protected routes.
    """

    def __init__(self, app, exempt_paths: list[str] | None = None):
        super().__init__(app)
        self.exempt_paths = exempt_paths or []

    async def dispatch(self, request, call_next):
        path = request.url.path

        # Allow exempt paths and static assets
        if (
            path in self.exempt_paths
            or path.startswith("/static")
            or path.startswith("/favicon")
        ):
            return await call_next(request)

        # Enforce authentication for other paths
        if not request.session.get("user_id"):
            return RedirectResponse(url="/login", status_code=302)

        return await call_next(request)


class RequestIdMiddleware(BaseHTTPMiddleware):
    """
    Middleware that assigns a request_id and binds request context for logging.

    Adds: request_id, http.method, http.path, user.id to the structlog context.
    Emits a JSON access log with status_code and duration_ms after response.
    """

    async def dispatch(self, request: Request, call_next):
        start_time = time.perf_counter()

        request_id = request.headers.get("X-Request-ID") or str(uuid.uuid4())
        method = request.method
        path = request.url.path

        # user id from session if available (SessionMiddleware runs first)
        user_id = request.session.get("user_id") if hasattr(request, "session") else None

        structlog_contextvars.bind_contextvars(
            request_id=request_id,
            **{"http.method": method, "http.path": path, "user.id": user_id},
        )

        try:
            response = await call_next(request)
            status_code = response.status_code
        except Exception as exc:  # noqa: BLE001 - we re-raise after logging
            status_code = 500
            duration_ms = int((time.perf_counter() - start_time) * 1000)
            logger.error(
                "request",
                status_code=status_code,
                duration_ms=duration_ms,
                exc_info=True,
            )
            structlog_contextvars.unbind_contextvars("request_id", "http.method", "http.path", "user.id")
            raise

        # Ensure response header has request id
        try:
            response.headers["X-Request-ID"] = request_id
        except Exception:
            pass

        duration_ms = int((time.perf_counter() - start_time) * 1000)
        logger.info(
            "request",
            status_code=status_code,
            duration_ms=duration_ms,
        )

        structlog_contextvars.unbind_contextvars("request_id", "http.method", "http.path", "user.id")
        return response

@asynccontextmanager
async def lifespan(app: FastAPI):
    """
    Lifespan context manager for FastAPI application.

    Handles startup and shutdown events:
    - Creates database tables on startup
    - Logs database connection info
    """
    # Startup
    logger.info("app_start")

    # Create database tables
    create_tables()
    logger.info("db_tables_verified")

    # Log database connection info
    db_url = get_database_url()
    logger.info("db_connected", database_url=db_url)

    yield

    # Shutdown
    logger.info("app_shutdown")


# Create FastAPI application with lifespan management
app = FastAPI(
    title="Delphi Database",
    description="Legal case management database application",
    version="1.0.0",
    lifespan=lifespan
)

# Add CORS middleware for cross-origin requests
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],  # In production, specify allowed origins
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

# Register request logging and authentication middleware with exempt paths
EXEMPT_PATHS = ["/", "/health", "/login", "/logout"]
app.add_middleware(RequestIdMiddleware)
app.add_middleware(AuthMiddleware, exempt_paths=EXEMPT_PATHS)

# Add SessionMiddleware for session management (must be added LAST so it runs FIRST)
app.add_middleware(SessionMiddleware, secret_key=SECRET_KEY)

# Mount static files directory
app.mount("/static", StaticFiles(directory="static"), name="static")


def get_import_type_from_filename(filename: str) -> str:
    """
    Determine import type based on filename pattern.

    Args:
        filename: Name of the uploaded CSV file

    Returns:
        Import type string (client, phone, case, transaction, document, payment)
    """
    filename_upper = filename.upper()

    if filename_upper.startswith('ROLODEX') or filename_upper.startswith('ROLEX'):
        return 'client'
    elif filename_upper.startswith('PHONE'):
        return 'phone'
    elif filename_upper.startswith('FILES'):
        return 'case'
    elif filename_upper.startswith('LEDGER'):
        return 'transaction'
    elif filename_upper.startswith('QDROS') or filename_upper.startswith('QDRO'):
        return 'document'
    elif filename_upper.startswith('PAYMENTS') or filename_upper.startswith('DEPOSITS'):
        return 'payment'
    else:
        raise ValueError(f"Unknown file type for filename: {filename}")


def validate_csv_headers(headers: List[str], expected_fields: Dict[str, str]) -> Dict[str, Any]:
    """
    Validate CSV headers against expected model fields.

    Args:
        headers: List of CSV column headers
        expected_fields: Dict mapping field names to descriptions

    Returns:
        Dict with validation results and field mapping
    """
    result = {
        'valid': True,
        'missing_fields': [],
        'field_mapping': {},
        'errors': []
    }

    # Create mapping from CSV headers to model fields (case-insensitive)
    for csv_header in headers:
        csv_header_clean = csv_header.strip().lower()
        matched = False

        for model_field, description in expected_fields.items():
            if csv_header_clean == model_field.lower():
                result['field_mapping'][model_field] = csv_header
                matched = True
                break

        if not matched:
            # Try partial matches for common variations
            for model_field, description in expected_fields.items():
                if model_field.lower() in csv_header_clean or csv_header_clean in model_field.lower():
                    result['field_mapping'][model_field] = csv_header
                    matched = True
                    break

        if not matched:
            result['errors'].append(f"Unknown header: '{csv_header}'")

    # Check for required fields (case-insensitive)
    required_fields = ['id']  # Most imports need some form of ID
    for required in required_fields:
        found = False
        for mapped_field in result['field_mapping']:
            if mapped_field.lower() == required.lower():
                found = True
                break
        if not found:
            result['missing_fields'].append(required)

    if result['missing_fields'] or result['errors']:
        result['valid'] = False

    return result


def parse_date(date_str: str) -> Optional[datetime]:
    """Parse date string into datetime object."""
    if not date_str or date_str.strip() in ('', 'NULL', 'N/A'):
        return None

    # Try common date formats
    formats = ['%Y-%m-%d', '%m/%d/%Y', '%Y/%m/%d', '%d-%m-%Y']

    for fmt in formats:
        try:
            return datetime.strptime(date_str.strip(), fmt)
        except ValueError:
            continue

    logger.warning("parse_date_failed", value=date_str)
    return None


def parse_float(value: str) -> Optional[float]:
    """Parse string value into float."""
    if not value or value.strip() in ('', 'NULL', 'N/A'):
        return None

    try:
        return float(value.strip())
    except ValueError:
        logger.warning("parse_float_failed", value=value)
        return None


def parse_int(value: str) -> Optional[int]:
    """Parse string value into int."""
    if not value or value.strip() in ('', 'NULL', 'N/A'):
        return None

    try:
        return int(value.strip())
    except ValueError:
        logger.warning("parse_int_failed", value=value)
        return None


def import_rolodex_data(db: Session, file_path: str) -> Dict[str, Any]:
    """
    Import ROLODEX CSV data into Client model.

    Expected CSV format: Id,Prefix,First,Middle,Last,Suffix,Title,A1,A2,A3,City,Abrev,St,Zip,Email,DOB,SS#,Legal_Status,Group,Memo
    """
    result = {
        'success': 0,
        'errors': [],
        'total_rows': 0
    }

    expected_fields = {
        'Id': 'Client ID',
        'Prefix': 'Name Prefix',
        'First': 'First Name',
        'Middle': 'Middle Initial',
        'Last': 'Last Name',
        'Suffix': 'Name Suffix',
        'Title': 'Company/Organization',
        'A1': 'Address Line 1',
        'A2': 'Address Line 2',
        'A3': 'Address Line 3',
        'City': 'City',
        'Abrev': 'State Abbreviation',
        'St': 'State',
        'Zip': 'ZIP Code',
        'Email': 'Email Address',
        'DOB': 'Date of Birth',
        'SS#': 'Social Security Number',
        'Legal_Status': 'Legal Status',
        'Group': 'Group',
        'Memo': 'Memo/Notes'
    }

    try:
        with open(file_path, 'r', encoding='utf-8') as file:
            reader = csv.DictReader(file)

            # Validate headers
            headers = reader.fieldnames or []
            validation = validate_csv_headers(headers, expected_fields)

            if not validation['valid']:
                result['errors'].append(f"Header validation failed: {validation['errors']}")
                return result

            for row_num, row in enumerate(reader, start=2):  # Start at 2 (header is row 1)
                result['total_rows'] += 1

                try:
                    # Extract and clean data
                    rolodex_id = row.get('Id', '').strip()
                    if not rolodex_id:
                        result['errors'].append(f"Row {row_num}: Missing client ID")
                        continue

                    # Check for existing client
                    existing = db.query(Client).filter(Client.rolodex_id == rolodex_id).first()
                    if existing:
                        result['errors'].append(f"Row {row_num}: Client with ID '{rolodex_id}' already exists")
                        continue

                    client = Client(
                        rolodex_id=rolodex_id,
                        first_name=row.get('First', '').strip() or None,
                        middle_initial=row.get('Middle', '').strip() or None,
                        last_name=row.get('Last', '').strip() or None,
                        company=row.get('Title', '').strip() or None,
                        address=row.get('A1', '').strip() or None,
                        city=row.get('City', '').strip() or None,
                        state=row.get('St', '').strip() or None,
                        zip_code=row.get('Zip', '').strip() or None
                    )

                    db.add(client)
                    result['success'] += 1

                except Exception as e:
                    result['errors'].append(f"Row {row_num}: {str(e)}")

        db.commit()

    except Exception as e:
        result['errors'].append(f"Import failed: {str(e)}")
        db.rollback()

    return result


def import_phone_data(db: Session, file_path: str) -> Dict[str, Any]:
    """
    Import PHONE CSV data into Phone model.

    Expected CSV format: Id,Phone,Location
    """
    result = {
        'success': 0,
        'errors': [],
        'total_rows': 0
    }

    try:
        with open(file_path, 'r', encoding='utf-8') as file:
            reader = csv.DictReader(file)

            headers = reader.fieldnames or []
            if len(headers) < 2:
                result['errors'].append("Invalid CSV format: expected at least 2 columns")
                return result

            for row_num, row in enumerate(reader, start=2):
                result['total_rows'] += 1

                try:
                    client_id = row.get('Id', '').strip()
                    if not client_id:
                        result['errors'].append(f"Row {row_num}: Missing client ID")
                        continue

                    # Find the client
                    client = db.query(Client).filter(Client.rolodex_id == client_id).first()
                    if not client:
                        result['errors'].append(f"Row {row_num}: Client with ID '{client_id}' not found")
                        continue

                    phone_number = row.get('Phone', '').strip()
                    if not phone_number:
                        result['errors'].append(f"Row {row_num}: Missing phone number")
                        continue

                    phone = Phone(
                        client_id=client.id,
                        phone_type=row.get('Location', '').strip() or 'primary',
                        phone_number=phone_number
                    )

                    db.add(phone)
                    result['success'] += 1

                except Exception as e:
                    result['errors'].append(f"Row {row_num}: {str(e)}")

        db.commit()

    except Exception as e:
        result['errors'].append(f"Import failed: {str(e)}")
        db.rollback()

    return result


def import_files_data(db: Session, file_path: str) -> Dict[str, Any]:
    """
    Import FILES CSV data into Case model.

    Expected CSV format: File_No,Id,File_Type,Regarding,Opened,Closed,Empl_Num,Rate_Per_Hour,Status,Footer_Code,Opposing,Hours,Hours_P,Trust_Bal,Trust_Bal_P,Hourly_Fees,Hourly_Fees_P,Flat_Fees,Flat_Fees_P,Disbursements,Disbursements_P,Credit_Bal,Credit_Bal_P,Total_Charges,Total_Charges_P,Amount_Owing,Amount_Owing_P,Transferable,Memo
    """
    result = {
        'success': 0,
        'errors': [],
        'total_rows': 0
    }

    expected_fields = {
        'File_No': 'File Number',
        'Status': 'Status',
        'File_Type': 'File Type',
        'Regarding': 'Regarding',
        'Opened': 'Opened Date',
        'Closed': 'Closed Date',
        'Id': 'Client ID',
        'Empl_Num': 'Employee Number',
        'Rate_Per_Hour': 'Rate Per Hour',
        'Footer_Code': 'Footer Code',
        'Opposing': 'Opposing Party',
        'Hours': 'Hours',
        'Hours_P': 'Hours (Previous)',
        'Trust_Bal': 'Trust Balance',
        'Trust_Bal_P': 'Trust Balance (Previous)',
        'Hourly_Fees': 'Hourly Fees',
        'Hourly_Fees_P': 'Hourly Fees (Previous)',
        'Flat_Fees': 'Flat Fees',
        'Flat_Fees_P': 'Flat Fees (Previous)',
        'Disbursements': 'Disbursements',
        'Disbursements_P': 'Disbursements (Previous)',
        'Credit_Bal': 'Credit Balance',
        'Credit_Bal_P': 'Credit Balance (Previous)',
        'Total_Charges': 'Total Charges',
        'Total_Charges_P': 'Total Charges (Previous)',
        'Amount_Owing': 'Amount Owing',
        'Amount_Owing_P': 'Amount Owing (Previous)',
        'Transferable': 'Transferable',
        'Memo': 'Memo'
    }

    try:
        with open(file_path, 'r', encoding='utf-8') as file:
            reader = csv.DictReader(file)

            headers = reader.fieldnames or []
            validation = validate_csv_headers(headers, expected_fields)

            if not validation['valid']:
                result['errors'].append(f"Header validation failed: {validation['errors']}")
                return result

            for row_num, row in enumerate(reader, start=2):
                result['total_rows'] += 1

                try:
                    file_no = row.get('File_No', '').strip()
                    if not file_no:
                        result['errors'].append(f"Row {row_num}: Missing file number")
                        continue

                    # Check for existing case
                    existing = db.query(Case).filter(Case.file_no == file_no).first()
                    if existing:
                        result['errors'].append(f"Row {row_num}: Case with file number '{file_no}' already exists")
                        continue

                    # Find client by ID
                    client_id = row.get('Id', '').strip()
                    client = None
                    if client_id:
                        client = db.query(Client).filter(Client.rolodex_id == client_id).first()
                        if not client:
                            result['errors'].append(f"Row {row_num}: Client with ID '{client_id}' not found")
                            continue

                    case = Case(
                        file_no=file_no,
                        client_id=client.id if client else None,
                        status=row.get('Status', '').strip() or 'active',
                        case_type=row.get('File_Type', '').strip() or None,
                        description=row.get('Regarding', '').strip() or None,
                        open_date=parse_date(row.get('Opened', '')),
                        close_date=parse_date(row.get('Closed', ''))
                    )

                    db.add(case)
                    result['success'] += 1

                except Exception as e:
                    result['errors'].append(f"Row {row_num}: {str(e)}")

        db.commit()

    except Exception as e:
        result['errors'].append(f"Import failed: {str(e)}")
        db.rollback()

    return result


def import_ledger_data(db: Session, file_path: str) -> Dict[str, Any]:
    """
    Import LEDGER CSV data into Transaction model.

    Expected CSV format: File_No,Date,Item_No,Empl_Num,T_Code,T_Type,T_Type_L,Quantity,Rate,Amount,Billed,Note
    """
    result = {
        'success': 0,
        'errors': [],
        'total_rows': 0
    }

    try:
        with open(file_path, 'r', encoding='utf-8') as file:
            reader = csv.DictReader(file)

            headers = reader.fieldnames or []
            if len(headers) < 3:
                result['errors'].append("Invalid CSV format: expected at least 3 columns")
                return result

            for row_num, row in enumerate(reader, start=2):
                result['total_rows'] += 1

                try:
                    file_no = row.get('File_No', '').strip()
                    if not file_no:
                        result['errors'].append(f"Row {row_num}: Missing file number")
                        continue

                    # Find the case
                    case = db.query(Case).filter(Case.file_no == file_no).first()
                    if not case:
                        result['errors'].append(f"Row {row_num}: Case with file number '{file_no}' not found")
                        continue

                    amount = parse_float(row.get('Amount', '0'))
                    if amount is None:
                        result['errors'].append(f"Row {row_num}: Invalid amount")
                        continue

                    transaction = Transaction(
                        case_id=case.id,
                        transaction_date=parse_date(row.get('Date', '')),
                        transaction_type=row.get('T_Type', '').strip() or None,
                        amount=amount,
                        description=row.get('Note', '').strip() or None,
                        reference=row.get('Item_No', '').strip() or None
                    )

                    db.add(transaction)
                    result['success'] += 1

                except Exception as e:
                    result['errors'].append(f"Row {row_num}: {str(e)}")

        db.commit()

    except Exception as e:
        result['errors'].append(f"Import failed: {str(e)}")
        db.rollback()

    return result


def import_qdros_data(db: Session, file_path: str) -> Dict[str, Any]:
    """
    Import QDROS CSV data into Document model.

    Expected CSV format: File_No,Document_Type,Description,File_Name,Date
    """
    result = {
        'success': 0,
        'errors': [],
        'total_rows': 0
    }

    try:
        with open(file_path, 'r', encoding='utf-8') as file:
            reader = csv.DictReader(file)

            headers = reader.fieldnames or []
            if len(headers) < 2:
                result['errors'].append("Invalid CSV format: expected at least 2 columns")
                return result

            for row_num, row in enumerate(reader, start=2):
                result['total_rows'] += 1

                try:
                    file_no = row.get('File_No', '').strip()
                    if not file_no:
                        result['errors'].append(f"Row {row_num}: Missing file number")
                        continue

                    # Find the case
                    case = db.query(Case).filter(Case.file_no == file_no).first()
                    if not case:
                        result['errors'].append(f"Row {row_num}: Case with file number '{file_no}' not found")
                        continue

                    document = Document(
                        case_id=case.id,
                        document_type=row.get('Document_Type', '').strip() or 'QDRO',
                        file_name=row.get('File_Name', '').strip() or None,
                        description=row.get('Description', '').strip() or None,
                        uploaded_date=parse_date(row.get('Date', ''))
                    )

                    db.add(document)
                    result['success'] += 1

                except Exception as e:
                    result['errors'].append(f"Row {row_num}: {str(e)}")

        db.commit()

    except Exception as e:
        result['errors'].append(f"Import failed: {str(e)}")
        db.rollback()

    return result


def import_payments_data(db: Session, file_path: str) -> Dict[str, Any]:
    """
    Import PAYMENTS CSV data into Payment model.

    Expected CSV format: File_No,Date,Amount,Type,Description,Check_Number
    """
    result = {
        'success': 0,
        'errors': [],
        'total_rows': 0
    }

    try:
        with open(file_path, 'r', encoding='utf-8') as file:
            reader = csv.DictReader(file)

            headers = reader.fieldnames or []
            if len(headers) < 2:
                result['errors'].append("Invalid CSV format: expected at least 2 columns")
                return result

            for row_num, row in enumerate(reader, start=2):
                result['total_rows'] += 1

                try:
                    file_no = row.get('File_No', '').strip()
                    if not file_no:
                        result['errors'].append(f"Row {row_num}: Missing file number")
                        continue

                    # Find the case
                    case = db.query(Case).filter(Case.file_no == file_no).first()
                    if not case:
                        result['errors'].append(f"Row {row_num}: Case with file number '{file_no}' not found")
                        continue

                    amount = parse_float(row.get('Amount', '0'))
                    if amount is None:
                        result['errors'].append(f"Row {row_num}: Invalid amount")
                        continue

                    payment = Payment(
                        case_id=case.id,
                        payment_date=parse_date(row.get('Date', '')),
                        payment_type=row.get('Type', '').strip() or None,
                        amount=amount,
                        description=row.get('Description', '').strip() or None,
                        check_number=row.get('Check_Number', '').strip() or None
                    )

                    db.add(payment)
                    result['success'] += 1

                except Exception as e:
                    result['errors'].append(f"Row {row_num}: {str(e)}")

        db.commit()

    except Exception as e:
        result['errors'].append(f"Import failed: {str(e)}")
        db.rollback()

    return result


def process_csv_import(db: Session, import_type: str, file_path: str) -> Dict[str, Any]:
    """
    Process CSV import based on type.

    Args:
        db: Database session
        import_type: Type of import (client, phone, case, transaction, document, payment)
        file_path: Path to CSV file

    Returns:
        Dict with import results
    """
    import_functions = {
        'client': import_rolodex_data,
        'phone': import_phone_data,
        'case': import_files_data,
        'transaction': import_ledger_data,
        'document': import_qdros_data,
        'payment': import_payments_data
    }

    import_func = import_functions.get(import_type)
    if not import_func:
        return {
            'success': 0,
            'errors': [f"Unknown import type: {import_type}"],
            'total_rows': 0
        }

    return import_func(db, file_path)


@app.get("/")
async def root():
    """
    Root endpoint - health check.
    """
    return {"message": "Delphi Database API is running"}


@app.get("/health")
async def health_check(db: Session = Depends(get_db)):
    """
    Health check endpoint that verifies database connectivity.
    """
    try:
        # Test database connection by querying user count
        user_count = db.query(User).count()
        return {
            "status": "healthy",
            "database": "connected",
            "users": user_count
        }
    except Exception as e:
        logger.error("health_check_failed", error=str(e))
        return {
            "status": "unhealthy",
            "database": "error",
            "error": str(e)
        }


@app.get("/login")
async def login_form(request: Request):
    """
    Display login form.

    If user is already logged in, redirect to dashboard.
    """
    # Check if user is already logged in
    user = get_current_user_from_session(request.session)
    if user:
        return RedirectResponse(url="/dashboard", status_code=302)

    return templates.TemplateResponse("login.html", {"request": request})


@app.post("/login")
async def login_submit(request: Request, db: Session = Depends(get_db)):
    """
    Handle login form submission.

    Authenticates user credentials and sets up session.
    """
    form = await request.form()
    username = form.get("username")
    password = form.get("password")

    if not username or not password:
        error_message = "Username and password are required"
        logger.warning("login_failed", username=username, reason="missing_credentials")
        return templates.TemplateResponse("login.html", {
            "request": request,
            "error": error_message
        })

    # Authenticate user
    user = authenticate_user(username, password)
    if not user:
        error_message = "Invalid username or password"
        logger.warning("login_failed", username=username, reason="invalid_credentials")
        return templates.TemplateResponse("login.html", {
            "request": request,
            "error": error_message
        })

    # Set up user session
    request.session["user_id"] = user.id
    request.session["user"] = {"id": user.id, "username": user.username}

    # Update bound context with authenticated user id
    structlog_contextvars.bind_contextvars(**{"user.id": user.id})
    logger.info("login_success", username=username, **{"user.id": user.id})

    # Redirect to dashboard after successful login
    return RedirectResponse(url="/dashboard", status_code=302)


@app.get("/logout")
async def logout(request: Request):
    """
    Handle user logout.

    Clears user session and redirects to home page.
    """
    username = request.session.get("user", {}).get("username", "unknown")
    request.session.clear()
    logger.info("logout", username=username)

    return RedirectResponse(url="/", status_code=302)


@app.get("/dashboard")
async def dashboard(
    request: Request,
    q: str | None = Query(None, description="Search by file number or client name"),
    page: int = Query(1, ge=1, description="Page number (1-indexed)"),
    page_size: int = Query(20, ge=1, le=100, description="Results per page"),
    db: Session = Depends(get_db),
):
    """
    Dashboard page - lists recent cases with search and pagination.

    - Optional query param `q` filters by case file number or client name/company
    - `page` and `page_size` control pagination
    """
    # Check authentication
    user = get_current_user_from_session(request.session)
    if not user:
        return RedirectResponse(url="/login", status_code=302)

    # Base query: join clients for name/company access
    query = db.query(Case).join(Client).order_by(
        Case.open_date.desc(),
        Case.created_at.desc(),
    )

    # Apply search filter if provided
    if q:
        like_term = f"%{q}%"
        query = query.filter(
            or_(
                Case.file_no.ilike(like_term),
                Client.first_name.ilike(like_term),
                Client.last_name.ilike(like_term),
                Client.company.ilike(like_term),
            )
        )

    # Total count for pagination
    total: int = query.count()

    # Clamp page to valid range when total is known
    total_pages: int = (total + page_size - 1) // page_size if total > 0 else 1
    if page > total_pages:
        page = total_pages

    # Pagination window
    offset = (page - 1) * page_size
    cases = query.offset(offset).limit(page_size).all()

    # Page number window for UI (current +/- 2)
    start_page = max(1, page - 2)
    end_page = min(total_pages, page + 2)
    page_numbers = list(range(start_page, end_page + 1))

    logger.info(
        "dashboard_render",
        query=q,
        page=page,
        page_size=page_size,
        total=total,
    )

    return templates.TemplateResponse(
        "dashboard.html",
        {
            "request": request,
            "user": user,
            "cases": cases,
            "q": q,
            "page": page,
            "page_size": page_size,
            "total": total,
            "total_pages": total_pages,
            "page_numbers": page_numbers,
            "start_index": (offset + 1) if total > 0 else 0,
            "end_index": min(offset + len(cases), total),
        },
    )


@app.post("/admin/upload")
async def admin_upload_files(
    request: Request,
    files: List[UploadFile] = File(...),
    db: Session = Depends(get_db)
):
    """
    Handle CSV file uploads for admin panel.

    Validates uploaded files are CSV format and stores them in data-import directory.
    """
    # Check authentication
    user = get_current_user_from_session(request.session)
    if not user:
        return RedirectResponse(url="/login", status_code=302)

    results = []
    errors = []

    # Ensure data-import directory exists
    import_dir = "data-import"
    os.makedirs(import_dir, exist_ok=True)

    for file in files:
        try:
            # Validate file type
            if not file.filename.lower().endswith('.csv'):
                errors.append(f"File '{file.filename}' is not a CSV file")
                continue

            # Generate unique filename to avoid conflicts
            file_id = str(uuid.uuid4())
            file_ext = os.path.splitext(file.filename)[1]
            stored_filename = f"{file_id}{file_ext}"
            file_path = os.path.join(import_dir, stored_filename)

            # Save file
            contents = await file.read()
            with open(file_path, "wb") as f:
                f.write(contents)

            # Determine import type from filename
            try:
                import_type = get_import_type_from_filename(file.filename)
            except ValueError as e:
                errors.append(f"File '{file.filename}': {str(e)}")
                # Clean up uploaded file
                os.remove(file_path)
                continue

            results.append({
                'filename': file.filename,
                'stored_filename': stored_filename,
                'import_type': import_type,
                'file_path': file_path,
                'size': len(contents)
            })

        except Exception as e:
            errors.append(f"Error processing '{file.filename}': {str(e)}")
            continue

    # Log the upload operation
    logger.info(
        "admin_upload",
        uploaded_count=len(results),
        error_count=len(errors),
        username=user.username,
    )

    return templates.TemplateResponse("admin.html", {
        "request": request,
        "user": user,
        "upload_results": results,
        "upload_errors": errors,
        "show_upload_results": True
    })


@app.post("/admin/import/{data_type}")
async def admin_import_data(
    request: Request,
    data_type: str,
    db: Session = Depends(get_db)
):
    """
    Process CSV import for specified data type.

    Creates import log entry and processes the import in the background.
    """
    # Check authentication
    user = get_current_user_from_session(request.session)
    if not user:
        return RedirectResponse(url="/login", status_code=302)

    # Validate data type
    valid_types = ['client', 'phone', 'case', 'transaction', 'document', 'payment']
    if data_type not in valid_types:
        return templates.TemplateResponse("admin.html", {
            "request": request,
            "user": user,
            "error": f"Invalid data type: {data_type}"
        })

    # Get form data for file selection
    form = await request.form()
    selected_files = form.getlist("selected_files")

    if not selected_files:
        return templates.TemplateResponse("admin.html", {
            "request": request,
            "user": user,
            "error": "No files selected for import"
        })

    import_results = []
    total_success = 0
    total_errors = 0

    for stored_filename in selected_files:
        file_path = os.path.join("data-import", stored_filename)

        if not os.path.exists(file_path):
            import_results.append({
                'filename': stored_filename,
                'status': 'error',
                'message': 'File not found'
            })
            total_errors += 1
            continue

        # Create import log entry
        import_log = ImportLog(
            import_type=data_type,
            file_name=stored_filename,
            file_path=file_path,
            status="running"
        )
        db.add(import_log)
        db.commit()

        try:
            # Process the import
            result = process_csv_import(db, data_type, file_path)

            # Update import log
            import_log.status = "completed" if result['errors'] else "failed"
            import_log.total_rows = result['total_rows']
            import_log.success_count = result['success']
            import_log.error_count = len(result['errors'])
            import_log.error_details = json.dumps(result['errors'])
            import_log.completed_at = datetime.now()

            db.commit()

            import_results.append({
                'filename': stored_filename,
                'status': 'success' if result['success'] > 0 else 'error',
                'total_rows': result['total_rows'],
                'success_count': result['success'],
                'error_count': len(result['errors']),
                'errors': result['errors'][:10]  # Show first 10 errors
            })

            total_success += result['success']
            total_errors += len(result['errors'])

        except Exception as e:
            # Update import log on error
            import_log.status = "failed"
            import_log.error_details = json.dumps([str(e)])
            import_log.completed_at = datetime.now()
            db.commit()

            import_results.append({
                'filename': stored_filename,
                'status': 'error',
                'message': str(e)
            })
            total_errors += 1

    # Log the import operation
    logger.info(
        "admin_import",
        import_type=data_type,
        success_count=total_success,
        error_count=total_errors,
        username=user.username,
    )

    return templates.TemplateResponse("admin.html", {
        "request": request,
        "user": user,
        "import_results": import_results,
        "total_success": total_success,
        "total_errors": total_errors,
        "show_import_results": True
    })


@app.get("/admin")
async def admin_panel(request: Request, db: Session = Depends(get_db)):
    """
    Admin panel - requires authentication.

    Provides administrative functions like data import and system management.
    """
    # Check authentication
    user = get_current_user_from_session(request.session)
    if not user:
        return RedirectResponse(url="/login", status_code=302)

    # Get recent import history
    recent_imports = db.query(ImportLog).order_by(ImportLog.created_at.desc()).limit(10).all()

    # Get available files for import
    import_dir = "data-import"
    available_files = []
    if os.path.exists(import_dir):
        for filename in os.listdir(import_dir):
            if filename.endswith('.csv'):
                file_path = os.path.join(import_dir, filename)
                file_size = os.path.getsize(file_path)
                try:
                    import_type = get_import_type_from_filename(filename)
                except ValueError:
                    import_type = 'unknown'

                available_files.append({
                    'filename': filename,
                    'import_type': import_type,
                    'size': file_size,
                    'modified': datetime.fromtimestamp(os.path.getmtime(file_path))
                })

    # Group files by import type
    files_by_type = {}
    for file_info in available_files:
        import_type = file_info['import_type']
        if import_type not in files_by_type:
            files_by_type[import_type] = []
        files_by_type[import_type].append(file_info)

    return templates.TemplateResponse("admin.html", {
        "request": request,
        "user": user,
        "recent_imports": recent_imports,
        "available_files": available_files,
        "files_by_type": files_by_type
    })


@app.get("/case/{case_id}")
async def case_detail(
    request: Request,
    case_id: int,
    saved: bool = Query(False, description="Whether to show success message"),
    db: Session = Depends(get_db),
):
    """
    Case detail view.

    Displays detailed information for a single case and its related client and
    associated records (transactions, documents, payments).
    """
    # Check authentication
    user = get_current_user_from_session(request.session)
    if not user:
        return RedirectResponse(url="/login", status_code=302)

    # Fetch case with related entities eagerly loaded to avoid lazy-load issues
    case_obj = (
        db.query(Case)
        .options(
            joinedload(Case.client),
            joinedload(Case.transactions),
            joinedload(Case.documents),
            joinedload(Case.payments),
        )
        .filter(Case.id == case_id)
        .first()
    )

    if not case_obj:
        logger.warning("case_not_found", case_id=case_id)
        # Get any errors from session and clear them
        errors = request.session.pop("case_update_errors", None)

        return templates.TemplateResponse(
            "case.html",
            {
                "request": request,
                "user": user,
                "case": None,
                "error": "Case not found",
                "saved": False,
                "errors": errors or [],
            },
            status_code=404,
        )

    logger.info("case_detail", case_id=case_obj.id, file_no=case_obj.file_no)

    # Get any errors from session and clear them
    errors = request.session.pop("case_update_errors", None)

    return templates.TemplateResponse(
        "case.html",
        {
            "request": request,
            "user": user,
            "case": case_obj,
            "saved": saved,
            "errors": errors or [],
        },
    )


@app.post("/case/{case_id}/update")
async def case_update(
    request: Request,
    case_id: int,
    db: Session = Depends(get_db),
) -> RedirectResponse:
    """
    Update case details.

    Updates the specified fields on a case and redirects back to the case detail view.
    """
    # Check authentication
    user = get_current_user_from_session(request.session)
    if not user:
        return RedirectResponse(url="/login", status_code=302)

    # Get form data
    form = await request.form()

    # Fetch the case
    case_obj = db.query(Case).filter(Case.id == case_id).first()
    if not case_obj:
        logger.warning("case_not_found_update", case_id=case_id)
        return RedirectResponse(url=f"/case/{case_id}", status_code=302)

    # Validate and process fields
    errors = []
    update_data = {}

    # Status validation
    status = form.get("status")
    if status is not None:
        if status not in ["active", "closed"]:
            errors.append("Status must be 'active' or 'closed'")
        else:
            update_data["status"] = status

    # Case type and description (optional)
    case_type = form.get("case_type")
    if case_type is not None:
        update_data["case_type"] = case_type.strip() if case_type.strip() else None

    description = form.get("description")
    if description is not None:
        update_data["description"] = description.strip() if description.strip() else None

    # Date validation and parsing
    open_date = form.get("open_date")
    if open_date is not None:
        if open_date.strip():
            try:
                update_data["open_date"] = datetime.strptime(open_date.strip(), "%Y-%m-%d")
            except ValueError:
                errors.append("Open date must be in YYYY-MM-DD format")
        else:
            update_data["open_date"] = None

    close_date = form.get("close_date")
    if close_date is not None:
        if close_date.strip():
            try:
                update_data["close_date"] = datetime.strptime(close_date.strip(), "%Y-%m-%d")
            except ValueError:
                errors.append("Close date must be in YYYY-MM-DD format")
        else:
            update_data["close_date"] = None

    # If there are validation errors, redirect back with errors
    if errors:
        # Store errors in session for display on the case page
        request.session["case_update_errors"] = errors
        return RedirectResponse(url=f"/case/{case_id}", status_code=302)

    # Apply updates
    try:
        changed_fields = {}
        for field, value in update_data.items():
            old_value = getattr(case_obj, field)
            if old_value != value:
                changed_fields[field] = {"old": old_value, "new": value}
            setattr(case_obj, field, value)

        db.commit()
        logger.info(
            "case_update",
            case_id=case_id,
            changed_fields=list(update_data.keys()),
            changed_details=changed_fields,
        )

        # Clear any previous errors from session
        request.session.pop("case_update_errors", None)

        return RedirectResponse(url=f"/case/{case_id}?saved=1", status_code=302)

    except Exception as e:
        db.rollback()
        logger.error("case_update_failed", case_id=case_id, error=str(e))

        # Store error in session for display
        request.session["case_update_errors"] = ["Failed to save changes. Please try again."]

        return RedirectResponse(url=f"/case/{case_id}", status_code=302)


@app.post("/case/{case_id}/close")
async def case_close(
    request: Request,
    case_id: int,
    db: Session = Depends(get_db),
) -> RedirectResponse:
    """
    Close a case.

    Sets the case status to 'closed' and sets close_date to current date if not already set.
    """
    # Check authentication
    user = get_current_user_from_session(request.session)
    if not user:
        return RedirectResponse(url="/login", status_code=302)

    # Fetch the case
    case_obj = db.query(Case).filter(Case.id == case_id).first()
    if not case_obj:
        logger.warning("case_not_found_close", case_id=case_id)
        return RedirectResponse(url=f"/case/{case_id}", status_code=302)

    # Update case
    try:
        case_obj.status = "closed"
        # Only set close_date if it's not already set
        if not case_obj.close_date:
            case_obj.close_date = datetime.now()

        db.commit()
        logger.info("case_closed", case_id=case_id, close_date=case_obj.close_date.isoformat() if case_obj.close_date else None)

        return RedirectResponse(url=f"/case/{case_id}?saved=1", status_code=302)

    except Exception as e:
        db.rollback()
        logger.error("case_close_failed", case_id=case_id, error=str(e))

        # Store error in session for display
        request.session["case_update_errors"] = ["Failed to close case. Please try again."]

        return RedirectResponse(url=f"/case/{case_id}", status_code=302)


@app.post("/case/{case_id}/reopen")
async def case_reopen(
    request: Request,
    case_id: int,
    db: Session = Depends(get_db),
) -> RedirectResponse:
    """
    Reopen a case.

    Sets the case status to 'active' and clears the close_date.
    """
    # Check authentication
    user = get_current_user_from_session(request.session)
    if not user:
        return RedirectResponse(url="/login", status_code=302)

    # Fetch the case
    case_obj = db.query(Case).filter(Case.id == case_id).first()
    if not case_obj:
        logger.warning("case_not_found_reopen", case_id=case_id)
        return RedirectResponse(url=f"/case/{case_id}", status_code=302)

    # Update case
    try:
        case_obj.status = "active"
        case_obj.close_date = None

        db.commit()
        logger.info("case_reopened", case_id=case_id)

        return RedirectResponse(url=f"/case/{case_id}?saved=1", status_code=302)

    except Exception as e:
        db.rollback()
        logger.error("case_reopen_failed", case_id=case_id, error=str(e))

        # Store error in session for display
        request.session["case_update_errors"] = ["Failed to reopen case. Please try again."]

        return RedirectResponse(url=f"/case/{case_id}", status_code=302)