from pathlib import Path

from flask import Flask, flash, render_template
from werkzeug.exceptions import RequestEntityTooLarge

from app.config import Config
from app.routes import main_blueprint


def _format_size_limit(size_limit_bytes: int) -> str:
    """Render the upload limit in a friendly unit for error messages."""
    if size_limit_bytes >= 1024 * 1024:
        return f"{size_limit_bytes / (1024 * 1024):.0f} MB"
    if size_limit_bytes >= 1024:
        return f"{size_limit_bytes / 1024:.0f} KB"
    return f"{size_limit_bytes} bytes"


def create_app(config_class: type[Config] = Config) -> Flask:
    """Application factory used by Flask and Gunicorn."""
    app = Flask(__name__, instance_relative_config=True)
    app.config.from_object(config_class)

    output_dir = Path(app.config["OUTPUT_DIRECTORY"])
    if not output_dir.is_absolute():
        output_dir = Path(app.instance_path) / output_dir
    app.config["OUTPUT_DIRECTORY"] = output_dir
    output_dir.mkdir(parents=True, exist_ok=True)

    app.register_blueprint(main_blueprint)

    @app.errorhandler(RequestEntityTooLarge)
    def handle_file_too_large(_error):
        size_limit_bytes = int(app.config["MAX_CONTENT_LENGTH"])
        flash(
            f"The uploaded file is too large. Maximum allowed size is {_format_size_limit(size_limit_bytes)}.",
            "danger",
        )
        return render_template("index.html"), 413

    return app