Constant MODELS 

pub const MODELS: &str = r#"use chrono::{DateTime, Utc};
use mongodb::bson::oid::ObjectId;
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};

#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct UserDocument {
    #[serde(rename = "_id")]
    pub id: ObjectId,
    pub username: String,
    pub email: String,
    pub password: String,
    #[serde(
        with = "bson::serde_helpers::chrono_datetime_as_bson_datetime",
        rename = "createdAt"
    )]
    pub created_at: DateTime<Utc>,
}

#[derive(Debug, Serialize, Deserialize, JsonSchema, Clone)]
pub struct User {
    #[serde(rename = "_id")]
    pub id: String,
    pub username: String,
    pub email: String,
    pub password: String,
    #[serde(rename = "createdAt")]
    pub created_at: String,
}

#[derive(Debug, Serialize, Deserialize, JsonSchema, Clone)]
pub struct UserInfo {
    #[serde(rename = "_id")]
    pub id: String,
    pub username: String,
    pub email: String,
    #[serde(rename = "createdAt")]
    pub created_at: String,
}

#[derive(Debug, Serialize, Deserialize, JsonSchema, Clone)]
pub struct LoginCredentials {
    pub email: String,
    pub password: String,
}

#[derive(Debug, Serialize, Deserialize, JsonSchema, Clone)]
pub struct RegistrationCredentials {
    pub username: String,
    pub email: String,
    pub password: String,
}

#[derive(Debug, Deserialize, Serialize)]
pub struct SuccessResponse {
    pub status: u16,
    pub message: String,
}

#[derive(Debug, Deserialize, Serialize)]
pub struct ErrorResponse {
    pub status: u16,
    pub message: String,
}
"#;