"""FastAPI app factory. Composes all domain routers and middleware."""

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

from src.core.exceptions import (
    ChunkingError,
    BenchmarkError,
    chunking_exception_handler,
    benchmark_exception_handler,
)


def create_app() -> FastAPI:
    """Create and configure the FastAPI application.

    Mounts domain routers and registers exception handlers.
    Routers are imported lazily — domains are added in later phases.
    """
    app = FastAPI(
        title="RAG Chunking Benchmarker",
        description="Benchmark five chunking strategies on regulatory documents. "
        "Compare retrieval quality, answer faithfulness, and cost.",
        version="0.1.0",
    )

    # CORS — allow all origins for development
    app.add_middleware(
        CORSMiddleware,
        allow_origins=["*"],
        allow_credentials=True,
        allow_methods=["*"],
        allow_headers=["*"],
    )

    # Register exception handlers
    app.add_exception_handler(ChunkingError, chunking_exception_handler)
    app.add_exception_handler(BenchmarkError, benchmark_exception_handler)

    return app


app = create_app()