//! A module for communicating with the [bitFlyer API](https://lightning.bitflyer.com/docs).
//! For example usages, see files in the examples/ directory.

use std::{
    marker::PhantomData,
    time::SystemTime,
};
use hmac::{Hmac, Mac};
use sha2::Sha256;
use rand::{Rng, distributions::Alphanumeric};
use serde::{de::DeserializeOwned, Deserialize, Serialize};
use serde_json::json;
use generic_api_client::{http::{*, header::HeaderValue}, websocket::*};
use crate::traits::*;

/// The type returned by [Client::request()].
pub type BitFlyerRequestResult<T> = Result<T, BitFlyerRequestError>;
pub type BitFlyerRequestError = RequestError<&'static str, BitFlyerHandlerError>;

/// Options that can be set when creating handlers
pub enum BitFlyerOption {
    /// [Default] variant, does nothing
    Default,
    /// API key
    Key(String),
    /// Api secret
    Secret(String),
    /// Base url for HTTP requests
    HttpUrl(BitFlyerHttpUrl),
    /// Whether [BitFlyerRequestHandler] should perform authentication
    HttpAuth(bool),
    /// [RequestConfig] used when sending requests.
    /// `url_prefix` will be overridden by [HttpUrl](Self::HttpUrl) unless `HttpUrl` is [BitFlyerHttpUrl::None].
    RequestConfig(RequestConfig),
    /// Base url for WebSocket connections
    WebSocketUrl(BitFlyerWebSocketUrl),
    /// Whether [BitFlyerWebSocketHandler] should perform authentication
    WebSocketAuth(bool),
    /// The channels to be subscribed by [BitFlyerWebSocketHandler].
    WebSocketChannels(Vec<String>),
    /// [WebSocketConfig] used for creating [WebSocketConnection]s
    /// `url_prefix` will be overridden by [WebSocketUrl](Self::WebSocketUrl) unless `WebSocketUrl` is [BitFlyerWebSocketUrl::None].
    /// By default, ignore_duplicate_during_reconnection` is set to `true`.
    WebSocketConfig(WebSocketConfig),
}

/// A `struct` that represents a set of [BitFlyerOption] s.
#[derive(Clone, Debug)]
pub struct BitFlyerOptions {
    /// see [BitFlyerOption::Key]
    pub key: Option<String>,
    /// see [BitFlyerOption::Secret]
    pub secret: Option<String>,
    /// see [BitFlyerOption::HttpUrl]
    pub http_url: BitFlyerHttpUrl,
    /// see [BitFlyerOption::HttpAuth]
    pub http_auth: bool,
    /// see [BitFlyerOption::RequestConfig]
    pub request_config: RequestConfig,
    /// see [BitFlyerOption::WebSocketUrl]
    pub websocket_url: BitFlyerWebSocketUrl,
    /// see [BitFlyerOption::WebSocketAuth]
    pub websocket_auth: bool,
    /// see [BitFlyerOption::WebSocketChannels]
    pub websocket_channels: Vec<String>,
    /// see [BitFlyerOption::WebSocketConfig]
    pub websocket_config: WebSocketConfig,
}

/// A `enum` that represents the base url of the BitFlyer HTTP API.
#[derive(Debug, Eq, PartialEq, Copy, Clone)]
pub enum BitFlyerHttpUrl {
    /// `https://api.bitflyer.com`
    Default,
    /// The url will not be modified by [BitFlyerRequestHandler]
    None,
}

/// A `enum` that represents the base url of the BitFlyer Realtime API
#[derive(Debug, Eq, PartialEq, Copy, Clone)]
#[non_exhaustive]
pub enum BitFlyerWebSocketUrl {
    /// `wss://ws.lightstream.bitflyer.com`
    Default,
    /// The url will not be modified by [BitFlyerWebSocketHandler]
    None,
}

#[derive(Deserialize, Debug)]
pub struct BitFlyerChannelMessage {
    pub channel: String,
    pub message: serde_json::Value,
}

#[derive(Debug)]
pub enum BitFlyerHandlerError {
    ApiError(serde_json::Value),
    ParseError,
}

/// A `struct` that implements [RequestHandler]
pub struct BitFlyerRequestHandler<'a, R: DeserializeOwned> {
    options: BitFlyerOptions,
    _phantom: PhantomData<&'a R>,
}

/// A `struct` that implements [WebSocketHandler]
pub struct BitFlyerWebSocketHandler {
    message_handler: Box<dyn FnMut(BitFlyerChannelMessage) + Send>,
    auth_id: Option<String>,
    options: BitFlyerOptions,
}

impl<'a, B, R> RequestHandler<B> for BitFlyerRequestHandler<'a, R>
where
    B: Serialize,
    R: DeserializeOwned,
{
    type Successful = R;
    type Unsuccessful = BitFlyerHandlerError;
    type BuildError = &'static str;

    fn request_config(&self) -> RequestConfig {
        let mut config = self.options.request_config.clone();
        if self.options.http_url != BitFlyerHttpUrl::None {
            config.url_prefix = self.options.http_url.as_str().to_owned();
        }
        config
    }

    fn build_request(&self, mut builder: RequestBuilder, request_body: &Option<B>, _: u8) -> Result<Request, Self::BuildError> {
        if let Some(body) = request_body {
            let json = serde_json::to_vec(body).or(Err("could not serialize body as application/json"))?;
            builder = builder
                .header(header::CONTENT_TYPE, "application/json")
                .body(json);
        }

        let mut request = builder.build().or(Err("failed to build request"))?;

        if self.options.http_auth {
            // https://lightning.bitflyer.com/docs?lang=en#authentication
            let time = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap(); // always after the epoch
            let timestamp = time.as_millis() as u64;

            let mut path = request.url().path().to_owned();
            if let Some(query) = request.url().query() {
                path.push('?');
                path.push_str(query)
            }
            let body = request.body()
                .and_then(|body| body.as_bytes())
                .map(String::from_utf8_lossy)
                .unwrap_or_default();

            let sign_contents = format!("{}{}{}{}", timestamp, request.method(), path, body);

            let secret = self.options.secret.as_deref().ok_or("API secret not set")?;
            let mut hmac = Hmac::<Sha256>::new_from_slice(secret.as_bytes()).unwrap(); // hmac accepts key of any length

            hmac.update(sign_contents.as_bytes());
            let signature = hex::encode(hmac.finalize().into_bytes());

            let key = HeaderValue::from_str(self.options.key.as_deref().ok_or("API key not set")?).or(
                Err("invalid character in API key")
            )?;
            let headers = request.headers_mut();
            headers.insert("ACCESS-KEY", key);
            headers.insert("ACCESS-TIMESTAMP", HeaderValue::from(timestamp));
            headers.insert("ACCESS-SIGN", HeaderValue::from_str(&signature).unwrap()); // hex digits are valid
            headers.insert(header::CONTENT_TYPE, HeaderValue::from_str("application/json").unwrap()); // only contains valid letters
        }

        Ok(request)
    }

    fn handle_response(&self, status: StatusCode, _: HeaderMap, response_body: Bytes) -> Result<Self::Successful, Self::Unsuccessful> {
        if status.is_success() {
            serde_json::from_slice(&response_body).map_err(|error| {
                log::debug!("Failed to parse response due to an error: {}", error);
                BitFlyerHandlerError::ParseError
            })
        } else {
            let error = match serde_json::from_slice(&response_body) {
                Ok(parsed_error) => BitFlyerHandlerError::ApiError(parsed_error),
                Err(error) => {
                    log::debug!("Failed to parse error response due to an error: {}", error);
                    BitFlyerHandlerError::ParseError
                }
            };
            Err(error)
        }
    }
}

impl WebSocketHandler for BitFlyerWebSocketHandler {
    fn websocket_config(&self) -> WebSocketConfig {
        let mut config = self.options.websocket_config.clone();
        if self.options.websocket_url != BitFlyerWebSocketUrl::None {
            config.url_prefix = self.options.websocket_url.as_str().to_owned();
        }
        config
    }

    fn handle_start(&mut self) -> Vec<WebSocketMessage> {
        if self.options.websocket_auth {
            // https://bf-lightning-api.readme.io/docs/realtime-api-auth
            if let Some(key) = self.options.key.as_deref() {
                if let Some(secret) = self.options.secret.as_deref() {
                    let time = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap(); // always after the epoch
                    let timestamp = time.as_millis() as u64;
                    let nonce: String = rand::thread_rng()
                        .sample_iter(&Alphanumeric)
                        .take(16)
                        .map(char::from)
                        .collect();

                    let mut hmac = Hmac::<Sha256>::new_from_slice(secret.as_bytes()).unwrap(); // hmac accepts key of any length

                    hmac.update(format!("{timestamp}{nonce}").as_bytes());
                    let signature = hex::encode(hmac.finalize().into_bytes());

                    let id = format!("_auth{}", time.as_nanos());
                    self.auth_id = Some(id.clone());

                    return vec![WebSocketMessage::Text(json!({
                        "method": "auth",
                        "params": {
                            "api_key": key,
                            "timestamp": timestamp,
                            "nonce": nonce,
                            "signature": signature,
                        },
                        "id": id,
                    }).to_string())];
                } else {
                    log::debug!("API secret not set.");
                };
            } else {
                log::debug!("API key not set.");
            };
        }
        self.message_subscribe()
    }

    fn handle_message(&mut self, message: WebSocketMessage) -> Vec<WebSocketMessage> {
        #[derive(Deserialize)]
        struct Message {
            #[allow(dead_code)]
            jsonrpc: String, // 2.0
            method: Option<String>,
            result: Option<serde_json::Value>,
            params: Option<BitFlyerChannelMessage>,
            id: Option<String>,
        }

        match message {
            WebSocketMessage::Text(message) => {
                let message: Message = match serde_json::from_str(&message) {
                    Ok(message) => message,
                    Err(_) => {
                        log::debug!("Invalid JSON-RPC message received");
                        return vec![];
                    },
                };
                if self.options.websocket_auth && self.auth_id == message.id {
                    // result of auth
                    if message.result == Some(serde_json::Value::Bool(true)) {
                        log::debug!("WebSocket authentication successful");
                        return self.message_subscribe();
                    } else {
                        log::debug!("WebSocket authentication unsuccessful");
                    }
                    self.auth_id = None;
                } else if message.method.as_deref() == Some("channelMessage") {
                    if let Some(channel_message) = message.params {
                        (self.message_handler)(channel_message);
                    }
                }
            },
            WebSocketMessage::Binary(_) => log::debug!("Unexpected binary message received"),
            WebSocketMessage::Ping(_) | WebSocketMessage::Pong(_) => (),
        }
        vec![]
    }
}

impl BitFlyerWebSocketHandler {
    #[inline]
    fn message_subscribe(&self) -> Vec<WebSocketMessage> {
        self.options.websocket_channels.clone().into_iter().map(|channel| {
            WebSocketMessage::Text(json!({ "method": "subscribe", "params": { "channel": channel } }).to_string())
        }).collect()
    }
}

impl BitFlyerHttpUrl {
    /// The base URL that this variant represents.
    #[inline(always)]
    fn as_str(&self) -> &'static str {
        match self {
            Self::Default => "https://api.bitflyer.com",
            Self::None => "",
        }
    }
}

impl BitFlyerWebSocketUrl {
    /// The base URL that this variant represents.
    #[inline(always)]
    fn as_str(&self) -> &'static str {
        match self {
            Self::Default => "wss://ws.lightstream.bitflyer.com",
            Self::None => "",
        }
    }
}

impl HandlerOptions for BitFlyerOptions {
    type OptionItem = BitFlyerOption;

    fn update(&mut self, option: Self::OptionItem) {
        match option {
            BitFlyerOption::Default => (),
            BitFlyerOption::Key(v) => self.key = Some(v),
            BitFlyerOption::Secret(v) => self.secret = Some(v),
            BitFlyerOption::HttpUrl(v) => self.http_url = v,
            BitFlyerOption::HttpAuth(v) => self.http_auth = v,
            BitFlyerOption::RequestConfig(v) => self.request_config = v,
            BitFlyerOption::WebSocketUrl(v) => self.websocket_url = v,
            BitFlyerOption::WebSocketAuth(v) => self.websocket_auth = v,
            BitFlyerOption::WebSocketChannels(v) => self.websocket_channels = v,
            BitFlyerOption::WebSocketConfig(v) => self.websocket_config = v,
        }
    }
}

impl Default for BitFlyerOptions {
    fn default() -> Self {
        let mut websocket_config = WebSocketConfig::new();
        websocket_config.ignore_duplicate_during_reconnection = true;
        Self {
            key: None,
            secret: None,
            http_url: BitFlyerHttpUrl::Default,
            http_auth: false,
            request_config: RequestConfig::default(),
            websocket_url: BitFlyerWebSocketUrl::Default,
            websocket_auth: false,
            websocket_channels: vec![],
            websocket_config,
        }
    }
}

impl<'a, R, B> HttpOption<'a, R, B> for BitFlyerOption
where
    R: DeserializeOwned + 'a,
    B: Serialize,
{
    type RequestHandler = BitFlyerRequestHandler<'a, R>;

    #[inline(always)]
    fn request_handler(options: Self::Options) -> Self::RequestHandler {
        BitFlyerRequestHandler::<'a, R> {
            options,
            _phantom: PhantomData,
        }
    }
}

impl<H: FnMut(BitFlyerChannelMessage) + Send + 'static> WebSocketOption<H> for BitFlyerOption {
    type WebSocketHandler = BitFlyerWebSocketHandler;

    #[inline(always)]
    fn websocket_handler(handler: H, options: Self::Options) -> Self::WebSocketHandler {
        BitFlyerWebSocketHandler {
            message_handler: Box::new(handler),
            auth_id: None,
            options,
        }
    }
}

impl HandlerOption for BitFlyerOption {
    type Options = BitFlyerOptions;
}

impl Default for BitFlyerOption {
    fn default() -> Self {
        Self::Default
    }
}