use axum::response::{IntoResponse, Response};
use base64::{
    prelude::{BASE64_STANDARD, BASE64_URL_SAFE},
    Engine,
};
use hmac::{Hmac, Mac};
use http::{header, HeaderMap, HeaderValue, StatusCode};
use itertools::Itertools;
use serde::{Deserialize, Serialize};
use serde_json::json;
use sha1::Sha1;
use sha2::{Sha256, Sha512};
use std::{borrow::Cow, collections::HashMap};

pub type HmacSha256 = Hmac<Sha256>;
pub type HmacSha512 = Hmac<Sha512>;
pub type HmacSha1 = Hmac<Sha1>;

mod github {
    use super::*;
    pub struct Github;

    impl WebhookHandler for Github {
        fn handle_challenge_request<'header>(
            &self,
            _: &'header HeaderMap,
            _: &SignatureConfigData,
            _: &str,
        ) -> Result<Option<Response>, AuthenticationError> {
            Ok(None)
        }

        fn get_hmac_authentication_data<'payload, 'header, 'prefix>(
            &self,
            headers: &'header HeaderMap,
            raw_payload: &'payload str,
        ) -> Result<SignatureAuthenticationData<'payload, 'header, 'prefix>, AuthenticationError>
        {
            let github_secret_header = headers.try_get_webhook_header("X-Hub-Signature-256")?;

            let authentication_data = SignatureAuthenticationData::new(
                Cow::Borrowed(raw_payload),
                github_secret_header,
                Some("sha256="),
                SignatureAuthenticationDetails::new(HmacAlgorithm::Sha256, Encoding::Hex),
            );

            Ok(authentication_data)
        }
    }
}

mod slack {
    use super::*;
    pub struct Slack;

    impl WebhookHandler for Slack {
        fn handle_challenge_request<'header>(
            &self,
            _: &'header HeaderMap,
            _: &SignatureConfigData,
            _: &str,
        ) -> Result<Option<Response>, AuthenticationError> {
            Ok(None)
        }

        fn get_hmac_authentication_data<'payload, 'header, 'prefix>(
            &self,
            headers: &'header HeaderMap,
            raw_payload: &'payload str,
        ) -> Result<SignatureAuthenticationData<'payload, 'header, 'prefix>, AuthenticationError>
        {
            let slack_secret_signature = headers.try_get_webhook_header("X-Slack-Signature")?;
            let slack_timestamp_header =
                headers.try_get_webhook_header("X-Slack-Request-Timestamp")?;
            let signed_payload = format!("v0:{}:{}", slack_timestamp_header, raw_payload);

            Ok(SignatureAuthenticationData::new(
                Cow::Owned(signed_payload),
                slack_secret_signature,
                Some("v0="),
                SignatureAuthenticationDetails::new(HmacAlgorithm::Sha256, Encoding::Hex),
            ))
        }
    }
}

mod stripe {
    use super::*;

    pub struct Stripe;

    impl WebhookHandler for Stripe {
        fn handle_challenge_request<'header>(
            &self,
            _: &'header HeaderMap,
            _: &SignatureConfigData,
            _: &str,
        ) -> Result<Option<Response>, AuthenticationError> {
            Ok(None)
        }

        fn get_hmac_authentication_data<'payload, 'header, 'prefix>(
            &self,
            headers: &'header HeaderMap,
            raw_payload: &'payload str,
        ) -> Result<SignatureAuthenticationData<'payload, 'header, 'prefix>, AuthenticationError>
        {
            let stripe_signature_header = headers.try_get_webhook_header("STRIPE-SIGNATURE")?;

            let stripe_signature = parse_signature(stripe_signature_header, (",", "="));

            let timestamp = *stripe_signature
                .get("t")
                .ok_or(AuthenticationError::InvalidTimestamp)?;
            let v1 = *stripe_signature
                .get("v1")
                .ok_or(AuthenticationError::InvalidSignature)?;

            let signed_payload = format!("{}.{}", timestamp, raw_payload);

            Ok(SignatureAuthenticationData::new(
                Cow::Owned(signed_payload),
                v1,
                None,
                SignatureAuthenticationDetails::new(HmacAlgorithm::Sha256, Encoding::Hex),
            ))
        }
    }
}

mod tiktok {
    use super::*;

    pub struct TikTok;

    impl WebhookHandler for TikTok {
        fn handle_challenge_request<'header>(
            &self,
            _: &'header HeaderMap,
            _: &SignatureConfigData,
            _: &str,
        ) -> Result<Option<Response>, AuthenticationError> {
            Ok(None)
        }

        fn get_hmac_authentication_data<'payload, 'header, 'prefix>(
            &self,
            headers: &'header HeaderMap,
            raw_payload: &'payload str,
        ) -> Result<SignatureAuthenticationData<'payload, 'header, 'prefix>, AuthenticationError>
        {
            let tiktok_secret_signature = headers.try_get_webhook_header("TikTok-Signature")?;

            let stripe_signature = parse_signature(tiktok_secret_signature, (",", "="));

            let timestamp = *stripe_signature
                .get("t")
                .ok_or(AuthenticationError::InvalidTimestamp)?;
            let s = *stripe_signature
                .get("s")
                .ok_or(AuthenticationError::InvalidSignature)?;

            let signed_payload = format!("{}.{}", timestamp, raw_payload);

            Ok(SignatureAuthenticationData::new(
                Cow::Owned(signed_payload),
                s,
                None,
                SignatureAuthenticationDetails::new(HmacAlgorithm::Sha256, Encoding::Hex),
            ))
        }
    }
}

mod twitch {
    use super::*;
    use http::header;
    use serde_json::value::RawValue;
    #[derive(Debug, Deserialize)]
    struct TwitchCrcBody {
        challenge: String,
        #[allow(unused)]
        subscription: Box<RawValue>,
    }

    pub struct Twitch;

    impl WebhookHandler for Twitch {
        fn get_hmac_authentication_data<'payload, 'header, 'prefix>(
            &self,
            headers: &'header HeaderMap,
            raw_payload: &'payload str,
        ) -> Result<SignatureAuthenticationData<'payload, 'header, 'prefix>, AuthenticationError>
        {
            let twitch_secret_signature =
                headers.try_get_webhook_header("Twitch-Eventsub-Message-Signature")?;
            let twitch_message_id_header =
                headers.try_get_webhook_header("Twitch-Eventsub-Message-Id")?;
            let twitch_timestamp_header =
                headers.try_get_webhook_header("Twitch-Eventsub-Message-Timestamp")?;

            let message = format!(
                "{}{}{}",
                twitch_message_id_header, twitch_timestamp_header, raw_payload
            );

            Ok(SignatureAuthenticationData::new(
                Cow::Owned(message),
                twitch_secret_signature,
                Some("sha256="),
                SignatureAuthenticationDetails::new(HmacAlgorithm::Sha256, Encoding::Hex),
            ))
        }

        fn handle_challenge_request<'header>(
            &self,
            headers: &'header HeaderMap,
            signature_config_data: &SignatureConfigData,
            raw_payload: &str,
        ) -> Result<Option<Response>, AuthenticationError> {
            let authentication_data = self.get_hmac_authentication_data(headers, raw_payload)?;
            verify_hmac_signature(authentication_data, &signature_config_data.secret_key)?;

            let twitch_eventsub_message_type =
                headers.try_get_webhook_header("Twitch-Eventsub-Message-Type")?;

            if twitch_eventsub_message_type != "webhook_callback_verification" {
                return Ok(None);
            }
            let twitch_crc_body =
                serde_json::from_str::<TwitchCrcBody>(raw_payload).map_err(|e| {
                    AuthenticationError::InvalidChallengeResponse(format!(
                        "Twitch :{}",
                        e.to_string()
                    ))
                })?;

            let response = (
                StatusCode::OK,
                [(header::CONTENT_TYPE, "text/plain")],
                twitch_crc_body.challenge.to_string(),
            );

            Ok(Some(response.into_response()))
        }
    }
}

mod zoom {
    use axum::Json;

    use super::*;

    #[derive(Debug, Deserialize)]
    struct ZoomPayload {
        #[serde(rename = "plainToken")]
        plain_token: String,
    }

    #[derive(Debug, Deserialize)]
    #[allow(unused)]
    struct ZoomChallengeResponse {
        payload: ZoomPayload,
        event_ts: u64,
        event: String,
    }

    pub struct Zoom;

    impl WebhookHandler for Zoom {
        fn handle_challenge_request<'header>(
            &self,
            _: &'header HeaderMap,
            signature_config_data: &SignatureConfigData,
            raw_payload: &str,
        ) -> Result<Option<Response>, AuthenticationError> {
            let Ok(zoom_request_body) = serde_json::from_str::<ZoomChallengeResponse>(raw_payload)
            else {
                return Ok(None);
            };

            if zoom_request_body.event != "endpoint.url_validation" {
                return Ok(None);
            }

            let hmac_signature = calculate_hmac_signature(
                HmacAlgorithm::Sha256,
                &signature_config_data.secret_key,
                &zoom_request_body.payload.plain_token,
            );

            let encoded_hmac_signature = encode_hmac_signature(Encoding::Hex, &hmac_signature);

            let response = (
                StatusCode::OK,
                Json(json!({
                    "plainToken": zoom_request_body.payload.plain_token,
                    "encryptedToken": encoded_hmac_signature
                })),
            );

            Ok(Some(response.into_response()))
        }

        fn get_hmac_authentication_data<'payload, 'header, 'prefix>(
            &self,
            headers: &'header HeaderMap,
            raw_payload: &'payload str,
        ) -> Result<SignatureAuthenticationData<'payload, 'header, 'prefix>, AuthenticationError>
        {
            let zoom_signature_header = headers.try_get_webhook_header("x-zm-signature")?;
            let zoom_timestamp_header = headers.try_get_webhook_header("x-zm-request-timestamp")?;

            let message = format!("v0:{}:{}", zoom_timestamp_header, raw_payload);

            Ok(SignatureAuthenticationData::new(
                Cow::Owned(message),
                zoom_signature_header,
                Some("v0="),
                SignatureAuthenticationDetails::new(HmacAlgorithm::Sha256, Encoding::Hex),
            ))
        }
    }
}

use constant_time_eq::constant_time_eq;
use github::Github;
use slack::Slack;
use stripe::Stripe;
use tiktok::TikTok;
use twitch::Twitch;
use zoom::Zoom;

#[derive(Debug)]
pub struct SignatureAuthenticationDetails {
    pub algorithm_to_use: HmacAlgorithm,
    pub header_key_encoding: Encoding,
}

impl SignatureAuthenticationDetails {
    #[inline]
    fn new(algorithm_to_use: HmacAlgorithm, header_key_encoding: Encoding) -> Self {
        Self { algorithm_to_use, header_key_encoding }
    }
}

fn parse_signature<'header>(
    signature: &'header str,
    splitters: (&str, &str),
) -> HashMap<&'header str, &'header str> {
    let headers: HashMap<&str, &str> = signature
        .split(splitters.0)
        .map(|header| {
            let mut key_and_value = header.split(splitters.1);
            let key = key_and_value.next();
            let value = key_and_value.next();
            (key, value)
        })
        .filter_map(|(key, value)| match (key, value) {
            (Some(key), Some(value)) => Some((key, value)),
            _ => None,
        })
        .collect();
    headers
}

#[derive(Debug)]
pub struct SignatureAuthenticationData<'payload, 'header, 'prefix> {
    pub signed_payload: Cow<'payload, str>,
    pub header_key_value: &'header str,
    pub signature_prefix: Option<&'prefix str>,
    pub config: SignatureAuthenticationDetails,
}

impl<'payload, 'header, 'prefix> SignatureAuthenticationData<'payload, 'header, 'prefix> {
    pub fn new(
        signed_payload: Cow<'payload, str>,
        header_key_value: &'header str,
        signature_prefix: Option<&'prefix str>,
        config: SignatureAuthenticationDetails,
    ) -> Self {
        Self { signed_payload, header_key_value, signature_prefix, config }
    }
}

pub trait WebhookHandler {
    fn handle_challenge_request<'header>(
        &self,
        headers: &'header HeaderMap,
        signature_config_data: &SignatureConfigData,
        raw_payload: &str,
    ) -> Result<Option<Response>, AuthenticationError>;

    fn get_hmac_authentication_data<'payload, 'header, 'prefix>(
        &self,
        headers: &'header HeaderMap,
        raw_payload: &'payload str,
    ) -> Result<SignatureAuthenticationData<'payload, 'header, 'prefix>, AuthenticationError>;
}

#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum HmacAlgorithm {
    Sha1,
    Sha256,
    Sha512,
}

#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum Encoding {
    Base64,
    Base64Uri,
    Hex,
}
#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct SignatureAuthenticationMethod {
    algorithm: HmacAlgorithm,
    encoding: Encoding,
    signature_header_name: String,
    signature_prefix: Option<String>,
}

pub struct SignatureConfigData<'config> {
    secret_key: &'config str,
}

#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct SignatureAuthentication {
    signature_provider: WebhookType,
    secret_key: String,
    authentication_config: Option<SignatureAuthenticationMethod>,
}

#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct BasicAuthAuthentication {
    pub username: String,
    pub password: String,
}

#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct ApiKeyAuthentication {
    pub api_key_header: String,
    pub api_key_secret: String,
}

#[derive(Debug, Eq, PartialEq, Hash, Clone, Copy, Serialize, Deserialize)]
#[non_exhaustive]
pub enum WebhookType {
    Github,
    Slack,
    Stripe,
    TikTok,
    Twitch,
    Zoom,
    Custom,
}

impl WebhookType {
    pub fn get_webhook_handler(&self) -> Option<&'static dyn WebhookHandler> {
        let handler: &'static dyn WebhookHandler = match *self {
            WebhookType::Github => &Github,
            WebhookType::Slack => &Slack,
            WebhookType::Stripe => &Stripe,
            WebhookType::TikTok => &TikTok,
            WebhookType::Twitch => &Twitch,
            WebhookType::Zoom => &Zoom,
            WebhookType::Custom => return None,
        };
        Some(handler)
    }
}

trait TryGetWebhookHeader {
    fn try_get_webhook_header<'header>(
        &'header self,
        header_name: &str,
    ) -> Result<&'header str, AuthenticationError>;
}

impl TryGetWebhookHeader for HeaderMap<HeaderValue> {
    fn try_get_webhook_header<'header>(
        &'header self,
        header_name: &str,
    ) -> Result<&'header str, AuthenticationError> {
        let Some(signature_header) = self.get(header_name) else {
            return Err(AuthenticationError::MissingHeader(header_name.to_string()));
        };
        let Some(signature_header) = signature_header.to_str().ok() else {
            return Err(AuthenticationError::InvalidHeader(header_name.to_string()));
        };

        Ok(signature_header)
    }
}

pub fn calculate_hmac_signature(algorithm: HmacAlgorithm, secret: &str, payload: &str) -> Vec<u8> {
    match algorithm {
        HmacAlgorithm::Sha1 => {
            let mut mac =
                HmacSha1::new_from_slice(secret.as_bytes()).expect("HMAC can take key of any size");
            mac.update(payload.as_bytes());
            mac.finalize().into_bytes().to_vec()
        }
        HmacAlgorithm::Sha256 => {
            let mut mac = HmacSha256::new_from_slice(secret.as_bytes())
                .expect("HMAC can take key of any size");
            mac.update(payload.as_bytes());
            mac.finalize().into_bytes().to_vec()
        }
        HmacAlgorithm::Sha512 => {
            let mut mac = HmacSha512::new_from_slice(secret.as_bytes())
                .expect("HMAC can take key of any size");
            mac.update(payload.as_bytes());
            mac.finalize().into_bytes().to_vec()
        }
    }
}

pub fn encode_hmac_signature(encoding: Encoding, hmac_signature: &[u8]) -> String {
    match encoding {
        Encoding::Hex => hex::encode(hmac_signature),
        Encoding::Base64 => BASE64_STANDARD.encode(hmac_signature),
        Encoding::Base64Uri => BASE64_URL_SAFE.encode(hmac_signature),
    }
}

pub fn verify_hmac_signature(
    authentication_data: SignatureAuthenticationData,
    webhook_signing_secret: &str,
) -> Result<(), AuthenticationError> {
    let hmac_signature = calculate_hmac_signature(
        authentication_data.config.algorithm_to_use,
        &webhook_signing_secret,
        &authentication_data.signed_payload,
    );

    let encoded_signature = encode_hmac_signature(
        authentication_data.config.header_key_encoding,
        &hmac_signature,
    );

    let final_expected_signature =
        if let Some(signature_prefix) = authentication_data.signature_prefix {
            format!("{}{}", signature_prefix, encoded_signature)
        } else {
            encoded_signature
        };

    if !constant_time_eq(
        final_expected_signature.as_bytes(),
        authentication_data.header_key_value.as_bytes(),
    ) {
        return Err(AuthenticationError::InvalidSignature);
    }

    Ok(())
}

#[derive(Debug, Serialize, Deserialize, Clone)]
#[serde(untagged)]
pub enum AuthenticationMethod {
    Signature(SignatureAuthentication),
    BasicAuth(BasicAuthAuthentication),
    ApiKey(ApiKeyAuthentication),
}

impl AuthenticationMethod {
    pub fn authenticate_http_request(
        &self,
        headers: &HeaderMap,
        raw_payload: Option<&String>,
    ) -> Result<Option<Response>, AuthenticationError> {
        match self {
            AuthenticationMethod::Signature(SignatureAuthentication {
                secret_key,
                authentication_config,
                signature_provider,
            }) => {
                let raw_payload = raw_payload.ok_or(AuthenticationError::InvalidPayload)?;
                let config_data = SignatureConfigData { secret_key: &secret_key };
                let handler = signature_provider.get_webhook_handler();
                let challenge_response = handler
                    .map(|handler| {
                        handler.handle_challenge_request(headers, &config_data, raw_payload)
                    })
                    .transpose()?
                    .flatten();

                if let Some(challenge_response) = challenge_response {
                    return Ok(Some(challenge_response));
                }

                let authentication_data = match handler {
                    Some(handler) => handler.get_hmac_authentication_data(headers, raw_payload)?,
                    None => {
                        let authentication_config = authentication_config
                            .as_ref()
                            .ok_or(AuthenticationError::InvalidCustomConfig)?;
                        let signature_header_value = headers
                            .try_get_webhook_header(&authentication_config.signature_header_name)?;
                        SignatureAuthenticationData::new(
                            Cow::Borrowed(raw_payload),
                            signature_header_value,
                            authentication_config.signature_prefix.as_deref(),
                            SignatureAuthenticationDetails::new(
                                authentication_config.algorithm,
                                authentication_config.encoding,
                            ),
                        )
                    }
                };

                verify_hmac_signature(authentication_data, &secret_key)?;
            }
            AuthenticationMethod::ApiKey(ApiKeyAuthentication {
                api_key_header,
                api_key_secret,
            }) => {
                let api_key_to_cmp = headers
                    .try_get_webhook_header(&api_key_header)
                    .map_err(|_| AuthenticationError::InvalidApiKey)?;
                if api_key_to_cmp != api_key_secret {
                    return Err(AuthenticationError::InvalidApiKey);
                }
            }
            AuthenticationMethod::BasicAuth(BasicAuthAuthentication { username, password }) => {
                let mut credentials_store = headers
                    .try_get_webhook_header("Authorization")
                    .map_err(|_| AuthenticationError::UnauthorizedBasicHttpAuth)?
                    .split(' ');

                let _ = credentials_store
                    .next()
                    .filter(|r#type| *r#type == "Basic")
                    .ok_or(AuthenticationError::UnauthorizedBasicHttpAuth)?;

                let credentials_as_base64 = credentials_store
                    .next()
                    .ok_or(AuthenticationError::UnauthorizedBasicHttpAuth)?;

                let credentials_from_base64_as_bytes = BASE64_STANDARD
                    .decode(credentials_as_base64.as_bytes())
                    .map_err(|_| AuthenticationError::UnauthorizedBasicHttpAuth)?;

                let credentials_separated_with_colon =
                    String::from_utf8(credentials_from_base64_as_bytes)
                        .map_err(|_| AuthenticationError::UnauthorizedBasicHttpAuth)?;

                let credentials = credentials_separated_with_colon.split(':').collect_vec();

                if credentials.len() != 2 {
                    return Err(AuthenticationError::UnauthorizedBasicHttpAuth);
                }

                if credentials.get(0).unwrap() != username
                    || credentials.get(1).unwrap() != password
                {
                    return Err(AuthenticationError::UnauthorizedBasicHttpAuth);
                }
            }
        }

        Ok(None)
    }
}

#[derive(thiserror::Error, Debug)]
#[allow(unused)]
pub enum AuthenticationError {
    #[error("failed to parse timestamp")]
    InvalidTimestamp,

    #[error("invalid secret")]
    InvalidSecret(#[from] base64::DecodeError),

    #[error("invalid header `{0}`")]
    InvalidHeader(String),

    #[error("signature timestamp too old")]
    TimestampTooOldError,

    #[error("signature timestamp too far in future")]
    FutureTimestampError,

    #[error("missing header {0}")]
    MissingHeader(String),

    #[error("signature invalid")]
    InvalidSignature,

    #[error("payload invalid")]
    InvalidPayload,

    #[error("invalid custom config")]
    InvalidCustomConfig,

    #[error("invalid auth header: {0}")]
    InvalidAuthHeader(String),

    #[error("invalid api key")]
    InvalidApiKey,

    #[error("invalid challenge response: {0}")]
    InvalidChallengeResponse(String),

    #[error("")]
    UnauthorizedBasicHttpAuth,
}

impl IntoResponse for AuthenticationError {
    fn into_response(self) -> Response {
        let (status, error_message) = match &self {
            AuthenticationError::InvalidTimestamp
            | AuthenticationError::InvalidPayload
            | AuthenticationError::InvalidHeader(_)
            | AuthenticationError::MissingHeader(_)
            | AuthenticationError::TimestampTooOldError
            | AuthenticationError::FutureTimestampError
            | AuthenticationError::InvalidCustomConfig
            | AuthenticationError::InvalidChallengeResponse(_) => {
                (StatusCode::BAD_REQUEST, self.to_string())
            }

            AuthenticationError::InvalidSecret(_)
            | AuthenticationError::InvalidSignature
            | AuthenticationError::InvalidAuthHeader(_) => {
                (StatusCode::UNAUTHORIZED, self.to_string())
            }
            AuthenticationError::UnauthorizedBasicHttpAuth => {
                return (
                    StatusCode::UNAUTHORIZED,
                    [(header::WWW_AUTHENTICATE, r#"Basic realm="Restricted Area""#)],
                    "Unauthorized",
                )
                    .into_response()
            }
            AuthenticationError::InvalidApiKey => {
                return (StatusCode::UNAUTHORIZED, "Unauthorized").into_response()
            }
        };

        let body = json!({ "error": error_message });

        let mut headers = HeaderMap::new();
        headers.insert("Content-Type", HeaderValue::from_static("application/json"));

        (status, headers, body.to_string()).into_response()
    }
}