use crate::{
    domain::{NewSubscriber, SubscriberEmail, SubscriberName},
    email_client::EmailClient,
    startup::AppState,
};
use anyhow::Context;
use axum::{
    Form, Json,
    extract::State,
    http::StatusCode,
    response::{IntoResponse, Response},
};
use chrono::Utc;
use rand::{Rng, distr::Alphanumeric};
use serde::Deserialize;
use sqlx::{Executor, Postgres, Transaction};
use uuid::Uuid;

fn generate_subscription_token() -> String {
    let mut rng = rand::rng();
    std::iter::repeat_with(|| rng.sample(Alphanumeric))
        .map(char::from)
        .take(25)
        .collect()
}

pub fn error_chain_fmt(
    e: &impl std::error::Error,
    f: &mut std::fmt::Formatter,
) -> std::fmt::Result {
    writeln!(f, "{}", e)?;
    let mut current = e.source();
    while let Some(cause) = current {
        write!(f, "Caused by:\n\t{}", cause)?;
        current = cause.source();
        if current.is_some() {
            writeln!(f)?;
        }
    }
    Ok(())
}

#[derive(thiserror::Error)]
pub enum SubscribeError {
    #[error(transparent)]
    UnexpectedError(#[from] anyhow::Error),
    #[error("{0}")]
    ValidationError(String),
}

impl std::fmt::Debug for SubscribeError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        error_chain_fmt(self, f)
    }
}

impl IntoResponse for SubscribeError {
    fn into_response(self) -> Response {
        #[derive(serde::Serialize)]
        struct ErrorResponse<'a> {
            message: &'a str,
        }

        tracing::error!("{:?}", self);

        let status = match self {
            SubscribeError::UnexpectedError(_) => StatusCode::INTERNAL_SERVER_ERROR,
            SubscribeError::ValidationError(_) => StatusCode::BAD_REQUEST,
        };
        let message = "An internal server error occured.";
        (status, Json(ErrorResponse { message })).into_response()
    }
}

#[tracing::instrument(
    name = "Adding a new subscriber",
    skip(connection_pool, email_client, base_url, form),
    fields(
        subscriber_email = %form.email,
        subscriber_name = %form.name
    )
)]
pub async fn subscribe(
    State(AppState {
        connection_pool,
        email_client,
        base_url,
    }): State<AppState>,
    Form(form): Form<FormData>,
) -> Result<Response, SubscribeError> {
    let mut transaction = connection_pool
        .begin()
        .await
        .context("Failed to acquire a Postgres connection from the pool.")?;
    let new_subscriber = form.try_into().map_err(SubscribeError::ValidationError)?;
    let subscriber_id = insert_subscriber(&mut transaction, &new_subscriber)
        .await
        .context("Failed to insert new subscriber in the database.")?;
    let subscription_token = generate_subscription_token();
    store_token(&mut transaction, &subscription_token, &subscriber_id)
        .await
        .context("Failed to store the confirmation token for a new subscriber.")?;
    send_confirmation_email(
        &email_client,
        &new_subscriber,
        &base_url,
        &subscription_token,
    )
    .await
    .context("Failed to send a confirmation email.")?;
    transaction
        .commit()
        .await
        .context("Failed to commit the database transaction to store a new subscriber.")?;
    Ok(StatusCode::OK.into_response())
}

#[tracing::instrument(
    name = "Saving new subscriber details in the database",
    skip(transaction, new_subscriber)
)]
pub async fn insert_subscriber(
    transaction: &mut Transaction<'_, Postgres>,
    new_subscriber: &NewSubscriber,
) -> Result<Uuid, sqlx::Error> {
    let subscriber_id = Uuid::new_v4();
    let query = sqlx::query!(
        r#"
        INSERT INTO subscriptions (id, email, name, subscribed_at, status)
        VALUES ($1, $2, $3, $4, 'pending_confirmation')
        "#,
        subscriber_id,
        new_subscriber.email.as_ref(),
        new_subscriber.name.as_ref(),
        Utc::now()
    );
    transaction.execute(query).await?;
    Ok(subscriber_id)
}

#[tracing::instrument(
    name = "Store subscription token in the database",
    skip(transaction, subscription_token)
)]
async fn store_token(
    transaction: &mut Transaction<'_, Postgres>,
    subscription_token: &str,
    subscriber_id: &Uuid,
) -> Result<(), sqlx::Error> {
    let query = sqlx::query!(
        r#"
        INSERT INTO subscription_tokens (subscription_token, subscriber_id)
        VALUES ($1, $2)
        "#,
        subscription_token,
        subscriber_id,
    );
    transaction.execute(query).await?;
    Ok(())
}

#[tracing::instrument(
    name = "Send a confirmation email to a new subscriber",
    skip(email_client, new_subscriber, base_url, subscription_token)
)]
pub async fn send_confirmation_email(
    email_client: &EmailClient,
    new_subscriber: &NewSubscriber,
    base_url: &str,
    subscription_token: &str,
) -> Result<(), reqwest::Error> {
    let confirmation_link = format!(
        "{}/subscriptions/confirm?subscription_token={}",
        base_url, subscription_token
    );
    let html_content = format!(
        "Welcome to our newsletter!<br />\
Click <a href=\"{}\">here</a> to confirm your subscription.",
        confirmation_link
    );
    let text_content = format!(
        "Welcome to our newsletter!\nVisit {} to confirm your subscription.",
        confirmation_link
    );
    email_client
        .send_email(
            &new_subscriber.email,
            "Welcome!",
            &html_content,
            &text_content,
        )
        .await
}

#[derive(Debug, Deserialize)]
#[allow(dead_code)]
pub struct FormData {
    name: String,
    email: String,
}

impl TryFrom<FormData> for NewSubscriber {
    type Error = String;

    fn try_from(value: FormData) -> Result<Self, Self::Error> {
        let name = SubscriberName::parse(value.name)?;
        let email = SubscriberEmail::parse(value.email)?;
        Ok(Self { name, email })
    }
}