use crate::{
    routes::AdminError, session_state::TypedSession, telemetry::spawn_blocking_with_tracing,
};
use anyhow::Context;
use argon2::{
    Algorithm, Argon2, Params, PasswordHash, PasswordHasher, PasswordVerifier, Version,
    password_hash::{SaltString, rand_core::OsRng},
};
use axum::{extract::Request, middleware::Next, response::Response};
use secrecy::{ExposeSecret, SecretString};
use sqlx::PgPool;
use uuid::Uuid;

pub struct Credentials {
    pub username: String,
    pub password: SecretString,
}

#[derive(Debug, thiserror::Error)]
pub enum AuthError {
    #[error(transparent)]
    UnexpectedError(#[from] anyhow::Error),
    #[error("Invalid credentials.")]
    InvalidCredentials(#[source] anyhow::Error),
    #[error("Not authenticated.")]
    NotAuthenticated,
}

#[tracing::instrument(name = "Change password", skip(password, connection_pool))]
pub async fn change_password(
    user_id: Uuid,
    password: SecretString,
    connection_pool: &PgPool,
) -> Result<(), anyhow::Error> {
    let password_hash = spawn_blocking_with_tracing(move || compute_pasword_hash(password))
        .await?
        .context("Failed to hash password")?;
    sqlx::query!(
        "UPDATE users SET password_hash = $1 WHERE user_id = $2",
        password_hash.expose_secret(),
        user_id
    )
    .execute(connection_pool)
    .await
    .context("Failed to update user password in the database.")?;
    Ok(())
}

fn compute_pasword_hash(password: SecretString) -> Result<SecretString, anyhow::Error> {
    let salt = SaltString::generate(&mut OsRng);
    let password_hash = Argon2::new(
        Algorithm::Argon2id,
        Version::V0x13,
        Params::new(1500, 2, 1, None).unwrap(),
    )
    .hash_password(password.expose_secret().as_bytes(), &salt)?
    .to_string();
    Ok(SecretString::from(password_hash))
}

#[tracing::instrument(
    name = "Validate credentials",
    skip(username, password, connection_pool)
)]
pub async fn validate_credentials(
    Credentials { username, password }: Credentials,
    connection_pool: &PgPool,
) -> Result<Uuid, AuthError> {
    let mut user_id = None;
    let mut expected_password_hash = SecretString::from(
        "$argon2id$v=19$m=15000,t=2,p=1$\
gZiV/M1gPc22ElAH/Jh1Hw$\
CWOrkoo7oJBQ/iyh7uJ0LO2aLEfrHwTWllSAxT0zRno"
            .to_string(),
    );
    if let Some((stored_user_id, stored_expected_password_hash)) =
        get_stored_credentials(&username, connection_pool)
            .await
            .map_err(AuthError::UnexpectedError)?
    {
        user_id = Some(stored_user_id);
        expected_password_hash = stored_expected_password_hash;
    }

    spawn_blocking_with_tracing(|| verify_password_hash(expected_password_hash, password))
        .await
        .context("Failed to spawn blocking task.")
        .map_err(AuthError::UnexpectedError)??;

    user_id
        .ok_or_else(|| anyhow::anyhow!("Unknown username."))
        .map_err(AuthError::InvalidCredentials)
}

#[tracing::instrument(
    name = "Verify password",
    skip(expected_password_hash, password_candidate)
)]
fn verify_password_hash(
    expected_password_hash: SecretString,
    password_candidate: SecretString,
) -> Result<(), AuthError> {
    let expected_password_hash = PasswordHash::new(expected_password_hash.expose_secret())
        .context("Failed to parse hash in PHC string format.")?;
    Argon2::default()
        .verify_password(
            password_candidate.expose_secret().as_bytes(),
            &expected_password_hash,
        )
        .context("Password verification failed.")
        .map_err(AuthError::InvalidCredentials)
}

#[tracing::instrument(name = "Get stored credentials", skip(username, connection_pool))]
async fn get_stored_credentials(
    username: &str,
    connection_pool: &PgPool,
) -> Result<Option<(Uuid, SecretString)>, anyhow::Error> {
    let row = sqlx::query!(
        r#"
        SELECT user_id, password_hash
        FROM users
        WHERE username = $1
        "#,
        username,
    )
    .fetch_optional(connection_pool)
    .await
    .context("Failed to perform a query to retrieve stored credentials.")?
    .map(|row| (row.user_id, SecretString::from(row.password_hash)));
    Ok(row)
}

pub async fn require_auth(
    session: TypedSession,
    mut request: Request,
    next: Next,
) -> Result<Response, AdminError> {
    let user_id = session
        .get_user_id()
        .await
        .map_err(|e| AdminError::UnexpectedError(e.into()))?
        .ok_or(AdminError::NotAuthenticated)?;
    let username = session
        .get_username()
        .await
        .map_err(|e| AdminError::UnexpectedError(e.into()))?
        .ok_or(AdminError::UnexpectedError(anyhow::anyhow!(
            "Could not find username in session."
        )))?;

    request
        .extensions_mut()
        .insert(AuthenticatedUser { user_id, username });

    Ok(next.run(request).await)
}

#[derive(Clone)]
pub struct AuthenticatedUser {
    pub user_id: Uuid,
    pub username: String,
}