use argon2::{
    password_hash::{rand_core::OsRng, PasswordHasher, SaltString},
    Argon2,
};
use askama::Template;
use axum::{
    extract::{Form, Path, State},
    http::StatusCode,
    response::{IntoResponse, Response},
};
use sqlx::{query_as, SqlitePool};
use unicode_segmentation::UnicodeSegmentation;
use uuid::Uuid;

use crate::{templates::CreateUser, User};

pub(crate) const CREATE_QUERY: &str =
    "insert into witches (id, username, displayname, email, pwhash) values ($1, $2, $3, $4, $5)";
const ID_QUERY: &str = "select * from witches where id = $1";

//-************************************************************************
// Result types for user creation
//-************************************************************************

#[derive(Debug, Clone, Template)]
#[template(path = "signup_success.html")]
pub struct CreateUserSuccess(User);

#[Error(desc = "Could not create user.")]
#[non_exhaustive]
pub struct CreateUserError(#[from] CreateUserErrorKind);

impl IntoResponse for CreateUserError {
    fn into_response(self) -> askama_axum::Response {
        match self.0 {
            CreateUserErrorKind::UnknownDBError => {
                (StatusCode::INTERNAL_SERVER_ERROR, format!("{self}")).into_response()
            }
            _ => (StatusCode::BAD_REQUEST, format!("{self}")).into_response(),
        }
    }
}

#[Error]
#[non_exhaustive]
pub enum CreateUserErrorKind {
    AlreadyExists,
    #[error(desc = "Usernames must be between 1 and 20 non-whitespace characters long")]
    BadUsername,
    PasswordMismatch,
    #[error(desc = "Password must have at least 4 and at most 50 characters")]
    BadPassword,
    #[error(desc = "Display name must be less than 100 characters long")]
    BadDisplayname,
    BadEmail,
    MissingFields,
    UnknownDBError,
}

//-************************************************************************
// User creation route handlers
//-************************************************************************

/// Get Handler: displays the form to create a user
pub async fn get_create_user() -> CreateUser {
    CreateUser::default()
}

/// Post Handler: validates form values and calls the actual, private user
/// creation function
#[axum::debug_handler]
pub async fn post_create_user(
    State(pool): State<SqlitePool>,
    Form(signup): Form<CreateUser>,
) -> Result<impl IntoResponse, CreateUserError> {
    let username = &signup.username;
    let displayname = &signup.displayname;
    let email = &signup.email;
    let password = &signup.password;
    let verify = &signup.pw_verify;

    let username = urlencoding::decode(username)
        .map_err(|_| CreateUserErrorKind::BadUsername)?
        .to_string();
    let username = username.trim();
    let name_len = username.graphemes(true).size_hint().1.unwrap();
    // we are not ascii exclusivists around here
    if !(1..=20).contains(&name_len) {
        return Err(CreateUserErrorKind::BadUsername.into());
    }

    if password != verify {
        return Err(CreateUserErrorKind::PasswordMismatch.into());
    }

    let password = urlencoding::decode(password)
        .map_err(|_| CreateUserErrorKind::BadPassword)?
        .to_string();
    let password = password.trim();
    let password = password.as_bytes();
    if !(4..=50).contains(&password.len()) {
        return Err(CreateUserErrorKind::BadPassword.into());
    }

    let displayname = if let Some(dn) = displayname {
        let dn = urlencoding::decode(dn)
            .map_err(|_| CreateUserErrorKind::BadDisplayname)?
            .to_string()
            .trim()
            .to_string();
        if dn.graphemes(true).size_hint().1.unwrap() > 100 {
            return Err(CreateUserErrorKind::BadDisplayname.into());
        }
        Some(dn)
    } else {
        None
    };
    let displayname = &displayname;

    // TODO(2023-05-17): validate email
    let email = if let Some(email) = email {
        let email = urlencoding::decode(email)
            .map_err(|_| CreateUserErrorKind::BadEmail)?
            .to_string();
        Some(email)
    } else {
        None
    };
    let email = &email;

    let user = create_user(username, displayname, email, password, &pool).await?;
    tracing::debug!("created {user:?}");
    let id = user.id.as_simple().to_string();
    let location = format!("/signup_success/{id}");

    let resp = axum::response::Redirect::temporary(&location);

    Ok(resp)
}

/// Generic handler for successful signup
pub async fn handle_signup_success(
    Path(id): Path<String>,
    State(pool): State<SqlitePool>,
) -> Response {
    let id = id.trim();
    let user: User = {
        let id = Uuid::try_parse(id).unwrap_or_default();
        query_as(ID_QUERY)
            .bind(id)
            .fetch_one(&pool)
            .await
            .unwrap_or_default()
    };

    let mut resp = CreateUserSuccess(user.clone()).into_response();

    if user.username.is_empty() || id.is_empty() {
        // redirect to front page if we got here without a valid witch ID
        *resp.status_mut() = StatusCode::TEMPORARY_REDIRECT;
        resp.headers_mut().insert("Location", "/".parse().unwrap());
    }

    resp
}

//-************************************************************************
// private fns
//-************************************************************************

pub(crate) async fn create_user(
    username: &str,
    displayname: &Option<String>,
    email: &Option<String>,
    password: &[u8],
    pool: &SqlitePool,
) -> Result<User, CreateUserError> {
    // Argon2 with default params (Argon2id v19)
    let argon2 = Argon2::default();
    let salt = SaltString::generate(&mut OsRng);
    let pwhash = argon2
        .hash_password(password, &salt)
        .unwrap() // safe to unwrap, we know the salt is valid
        .to_string();

    let id = Uuid::new_v4();
    let query = sqlx::query(CREATE_QUERY)
        .bind(id)
        .bind(username)
        .bind(displayname)
        .bind(email)
        .bind(&pwhash);

    let res = {
        let txn = pool.begin().await.expect("Could not beign transaction");
        let r = query.execute(pool).await;
        txn.commit()
            .await
            .expect("Should be able to commit transaction");
        r
    };

    match res {
        Ok(_) => {
            let user = User {
                id,
                username: username.to_string(),
                displayname: displayname.to_owned(),
                email: email.to_owned(),
                last_seen: None,
                pwhash,
            };
            Ok(user)
        }
        Err(sqlx::Error::Database(db)) => {
            if let Some(exit) = db.code() {
                let exit = exit.parse().unwrap_or(0u32);
                // https://www.sqlite.org/rescode.html codes for unique constraint violations:
                if exit == 2067u32 || exit == 1555 {
                    Err(CreateUserErrorKind::AlreadyExists.into())
                } else {
                    Err(CreateUserErrorKind::UnknownDBError.into())
                }
            } else {
                Err(CreateUserErrorKind::UnknownDBError.into())
            }
        }
        _ => Err(CreateUserErrorKind::UnknownDBError.into()),
    }
}