use std::{array, fmt::Display, ops::Deref};

use argon2::{
    password_hash::{rand_core::OsRng, PasswordHash, PasswordHasher, PasswordVerifier, SaltString},
    Argon2,
};
use askama::Template;
use axum::{
    extract::{Form, State},
    http::StatusCode,
    response::{IntoResponse, Response},
};
use sqlx::{sqlite::SqliteRow, Row, SqlitePool};
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)";

const ID_QUERY: &str = "select * from witches where id = $1";

const WITCH_SUCCESS_HEADER: &str = "X-Witch-Success";

#[derive(Debug, Default, Clone, PartialEq, Eq)]
pub struct User {
    id: Uuid,
    username: String,
    displayname: Option<String>,
    email: Option<String>,
    last_seen: Option<i64>,
}

impl Display for User {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let uname = &self.username;
        let dname = if let Some(ref n) = self.displayname {
            n
        } else {
            ""
        };
        let email = if let Some(ref e) = self.email { e } else { "" };
        write!(f, "Username: {uname}\nDisplayname: {dname}\nEmail: {email}")
    }
}

#[derive(Debug, Default, Clone, sqlx::Encode)]
pub(crate) struct DbUser {
    id: Uuid,
    username: String,
    displayname: Option<String>,
    email: Option<String>,
    last_seen: Option<i64>,
    pwhash: String,
}

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

impl sqlx::FromRow<'_, SqliteRow> for User {
    fn from_row(row: &SqliteRow) -> Result<Self, sqlx::Error> {
        let bytes: Vec<u8> = row.get("id");
        let bytes = bytes.as_slice();
        let bytes: [u8; 16] = bytes.try_into().unwrap();
        let id = Uuid::from_bytes_le(bytes);
        let username: String = row.get("username");
        let displayname: Option<String> = row.get("displayname");
        let last_seen: Option<i64> = row.get("last_seen");
        let email: Option<String> = row.get("email");

        Ok(Self {
            id,
            username,
            displayname,
            email,
            last_seen,
        })
    }
}

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

/// 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<Response, 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 user = create_user(username, displayname, email, password, &pool).await?;
    tracing::debug!("created {user:?}");
    let mut resp = axum::response::Redirect::temporary("/signup_success").into_response();
    resp.headers_mut().append(
        WITCH_SUCCESS_HEADER,
        user.id.simple().to_string().parse().unwrap(),
    );

    Ok(resp)
}

/// Get handler for successful signup; only meaningful
pub async fn get_signup_success(
    headers: axum::http::HeaderMap,
    State(pool): State<SqlitePool>,
) -> Response {
    let user = if let Some(id) = headers.get(WITCH_SUCCESS_HEADER) {
        let id = id.to_str().unwrap();
        let id = Uuid::try_parse(id).unwrap_or_default();
        let id_bytes = id.as_bytes();
        sqlx::query_as(ID_QUERY)
            .bind(id_bytes.as_slice())
            .fetch_one(&pool)
            .await
            .unwrap_or_default()
    } else {
        User::default()
    };

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

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

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(),
                last_seen: None,
            };
            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,
}