use argon2::{
    password_hash::{rand_core::OsRng, PasswordHash, PasswordHasher, PasswordVerifier, SaltString},
    Argon2,
};
use askama::Template;
use axum::{
    extract::{Form, Path, State},
    http::StatusCode,
    response::IntoResponse,
};
use sqlx::{error::DatabaseError, Sqlite, SqlitePool};
use tracing::log::log;
use unicode_segmentation::UnicodeSegmentation;
use uuid::Uuid;

use crate::templates::CreateUser;

const CREATE_QUERY: &str =
    "insert into witches (id, username, displayname, email, pwhash) values ($1, $2, $3, $4, $5)";

pub struct User {
    id: Uuid,
    username: String,
    displayname: Option<String>,
    email: Option<String>,
}

#[derive(Debug, Clone, sqlx::FromRow, sqlx::Encode)]
pub(crate) struct DbUser {
    id: Uuid,
    username: String,
    displayname: Option<String>,
    email: Option<String>,
    last_seen: Option<u64>,
    pwhash: String,
}

impl From<DbUser> for User {
    fn from(dbu: DbUser) -> Self {
        User {
            id: dbu.id,
            username: dbu.username,
            displayname: dbu.displayname,
            email: dbu.email,
        }
    }
}

pub async fn get_create_user() -> CreateUser {
    CreateUser::default()
}

#[axum::debug_handler]
pub async fn post_create_user(
    State(pool): State<sqlx::Pool<Sqlite>>,
    Form(signup): Form<CreateUser>,
) -> Result<(), CreateUserError> {
    let username = &signup.username;
    let displayname = &signup.displayname;
    let email = &signup.email;
    let password = &signup.password;
    let verify = &signup.pw_verify;
    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.as_bytes();

    let displayname = if let Some(dn) = displayname {
        let dn = urlencoding::decode(dn)
            .map_err(|_| CreateUserErrorKind::BadDisplayname)?
            .to_string();
        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 _ = create_user(username, displayname, email, password, &pool).await?;
    Ok(())
}

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 id_bytes = id.to_bytes_le();
    let id_bytes = id_bytes.as_slice();
    let res = sqlx::query(CREATE_QUERY)
        .bind(id_bytes)
        .bind(username)
        .bind(displayname)
        .bind(email)
        .bind(pwhash)
        .execute(pool)
        .await;

    match res {
        Ok(_) => {
            let user = User {
                id,
                username: username.to_string(),
                displayname: displayname.to_owned(),
                email: email.to_owned(),
            };
            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()),
    }
}

#[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,
    BadPassword,
    BadDisplayname,
    BadEmail,
    MissingFields,
    UnknownDBError,
}