use reqwest::header::{ACCEPT, AUTHORIZATION, HeaderMap, HeaderValue, USER_AGENT};
use reqwest::{Client, Response};
use serde::Serialize;
use std::sync::Arc;
use tokio::sync::{OwnedSemaphorePermit, Semaphore};

fn build_user_agent() -> String {
    let info = os_info::get();
    let mut parts = vec![info.os_type().to_string()];
    if *info.version() != os_info::Version::Unknown {
        parts.push(info.version().to_string());
    }
    if let Some(codename) = info.codename() {
        parts.push(codename.to_string());
    }
    if let Some(edition) = info.edition() {
        parts.push(edition.to_string());
    }
    let arch = info
        .architecture()
        .unwrap_or(std::env::consts::ARCH)
        .to_string();
    parts.push(arch);
    format!(
        "MdrsClient/{} (Rust {} - {})",
        env!("CARGO_PKG_VERSION"),
        env!("RUSTC_VERSION"),
        parts.join(" ")
    )
}

#[derive(Clone)]
/// HTTP transport layer for MDRS API calls.
pub struct MDRSConnection {
    pub remote: Option<String>,
    pub url: String,
    pub client: Client,
    pub token: Option<String>,
}

#[derive(Clone)]
pub struct ApiRequestLimiter {
    semaphore: Arc<Semaphore>,
}

impl ApiRequestLimiter {
    pub fn new(limit: usize) -> Self {
        Self {
            semaphore: Arc::new(Semaphore::new(limit.max(1))),
        }
    }

    pub async fn acquire(&self) -> Result<OwnedSemaphorePermit, anyhow::Error> {
        self.semaphore
            .clone()
            .acquire_owned()
            .await
            .map_err(|_| anyhow::anyhow!("API request limiter was closed."))
    }
}

impl MDRSConnection {
    pub fn new(url: &str) -> Self {
        MDRSConnection {
            remote: None,
            url: url.to_string(),
            client: Client::new(),
            token: None,
        }
    }

    pub fn with_remote(mut self, remote: &str) -> Self {
        self.remote = Some(remote.to_string());
        self
    }

    /// Create a new connection that shares the HTTP client (and its connection
    /// pool) with the receiver but uses a fresh access token.  Useful for
    /// spawning per-task connections without allocating a new connection pool
    /// for every concurrent task.
    ///
    /// `reqwest::Client` wraps an internal `Arc`; cloning it is cheap and
    /// keeps the shared pool intact.
    pub fn with_token(&self, access_token: String) -> Self {
        MDRSConnection {
            remote: self.remote.clone(),
            url: self.url.clone(),
            client: self.client.clone(),
            token: Some(access_token),
        }
    }

    async fn connection_with_fresh_token(&self) -> Result<Self, anyhow::Error> {
        match (&self.remote, &self.token) {
            (Some(remote), Some(_)) => {
                let cache = crate::cache::load_cache_with_token_refresh(remote).await?;
                Ok(self.with_token(cache.token.access))
            }
            _ => Ok(self.clone()),
        }
    }

    pub fn build_url(&self, path: &str) -> String {
        format!("{}/{}", self.url.trim_end_matches('/'), path)
    }

    pub fn prepare_headers(&self) -> HeaderMap {
        let mut headers = HeaderMap::new();
        headers.insert(
            USER_AGENT,
            HeaderValue::from_str(&build_user_agent())
                .expect("user-agent string contains invalid header characters"),
        );
        headers.insert(ACCEPT, HeaderValue::from_static("application/json"));
        if let Some(token) = &self.token {
            headers.insert(
                AUTHORIZATION,
                HeaderValue::from_str(&format!("Bearer {}", token))
                    .expect("token contains invalid header characters"),
            );
        }
        headers
    }

    pub async fn get(&self, path: &str) -> Result<Response, anyhow::Error> {
        let conn = self.connection_with_fresh_token().await?;
        Ok(conn
            .client
            .get(conn.build_url(path))
            .headers(conn.prepare_headers())
            .send()
            .await?)
    }

    pub async fn get_with_query<Q>(&self, path: &str, query: &Q) -> Result<Response, anyhow::Error>
    where
        Q: Serialize + ?Sized,
    {
        let conn = self.connection_with_fresh_token().await?;
        Ok(conn
            .client
            .get(conn.build_url(path))
            .headers(conn.prepare_headers())
            .query(query)
            .send()
            .await?)
    }

    pub async fn get_url(&self, url: &str) -> Result<Response, anyhow::Error> {
        let conn = self.connection_with_fresh_token().await?;
        Ok(conn
            .client
            .get(if url.starts_with("http") {
                url.to_string()
            } else {
                conn.build_url(url)
            })
            .headers(conn.prepare_headers())
            .send()
            .await?)
    }

    pub async fn post_json<B>(&self, path: &str, body: &B) -> Result<Response, anyhow::Error>
    where
        B: Serialize + ?Sized,
    {
        let conn = self.connection_with_fresh_token().await?;
        Ok(conn
            .client
            .post(conn.build_url(path))
            .headers(conn.prepare_headers())
            .json(body)
            .send()
            .await?)
    }

    pub async fn post_multipart(
        &self,
        path: &str,
        form: reqwest::multipart::Form,
    ) -> Result<Response, anyhow::Error> {
        let conn = self.connection_with_fresh_token().await?;
        Ok(conn
            .client
            .post(conn.build_url(path))
            .headers(conn.prepare_headers())
            .multipart(form)
            .send()
            .await?)
    }

    pub async fn delete(&self, path: &str) -> Result<Response, anyhow::Error> {
        let conn = self.connection_with_fresh_token().await?;
        Ok(conn
            .client
            .delete(conn.build_url(path))
            .headers(conn.prepare_headers())
            .send()
            .await?)
    }

    pub async fn delete_with_query<Q>(
        &self,
        path: &str,
        query: &Q,
    ) -> Result<Response, anyhow::Error>
    where
        Q: Serialize + ?Sized,
    {
        let conn = self.connection_with_fresh_token().await?;
        Ok(conn
            .client
            .delete(conn.build_url(path))
            .headers(conn.prepare_headers())
            .query(query)
            .send()
            .await?)
    }
}