//! Login Flow v2 (FR-NC-1).
//!
//! The app never sees the user's password. It asks the server for a login URL,
//! opens that in the **system browser**, and polls until the server hands back
//! an app password scoped to this device.

use std::time::Duration;

use dr_sync::RemoteError;
use serde::{Deserialize, Serialize};

/// The flow's poll token is valid for 20 minutes.
const FLOW_TIMEOUT: Duration = Duration::from_secs(20 * 60);
const POLL_INTERVAL: Duration = Duration::from_secs(2);

/// What the server returns when a flow is started.
#[derive(Debug, Clone, Deserialize)]
pub struct LoginFlow {
    /// Open this in the system browser — never an embedded webview, which
    /// would defeat the point of not handling the password.
    #[serde(rename = "login")]
    pub login_url: String,
    #[serde(rename = "poll")]
    pub poll: PollInfo,
}

#[derive(Debug, Clone, Deserialize)]
pub struct PollInfo {
    pub token: String,
    pub endpoint: String,
}

/// Credentials issued at the end of the flow.
#[derive(Debug, Clone, Deserialize, Serialize)]
pub struct AppCredentials {
    pub server: String,
    #[serde(rename = "loginName")]
    pub login_name: String,
    /// Device-scoped and individually revocable — not the user's password.
    #[serde(rename = "appPassword")]
    pub app_password: String,
}

/// TRACES: FR-NC-1 | M-1
/// Begin a login flow.
///
/// The `User-Agent` names the resulting app password in the user's security
/// settings, so it should identify the device for per-device revocation.
pub async fn begin(
    client: &reqwest::Client,
    server: &str,
    user_agent: &str,
) -> Result<LoginFlow, RemoteError> {
    let url = format!("{}/index.php/login/v2", server.trim_end_matches('/'));
    let resp = client
        .post(&url)
        .header(reqwest::header::USER_AGENT, user_agent)
        .send()
        .await
        .map_err(super::map_send_error)?;

    if !resp.status().is_success() {
        return Err(RemoteError::Server {
            status: resp.status().as_u16(),
            detail: "login flow could not be started".into(),
        });
    }

    resp.json::<LoginFlow>()
        .await
        .map_err(|e| RemoteError::Protocol(e.to_string()))
}

/// Poll until the user finishes authenticating in the browser.
///
/// The server returns 404 while pending and 200 exactly once — so a dropped
/// success response means restarting the flow, and the result must be
/// persisted immediately.
pub async fn poll(
    client: &reqwest::Client,
    flow: &LoginFlow,
) -> Result<AppCredentials, RemoteError> {
    let deadline = std::time::Instant::now() + FLOW_TIMEOUT;

    while std::time::Instant::now() < deadline {
        let resp = client
            .post(&flow.poll.endpoint)
            // One field; encoding it by hand avoids pulling in reqwest's
            // form feature for a single call.
            .header(
                reqwest::header::CONTENT_TYPE,
                "application/x-www-form-urlencoded",
            )
            .body(format!("token={}", urlencode(&flow.poll.token)))
            .send()
            .await
            .map_err(super::map_send_error)?;

        match resp.status().as_u16() {
            200 => {
                return resp
                    .json::<AppCredentials>()
                    .await
                    .map_err(|e| RemoteError::Protocol(e.to_string()))
            }
            // Still waiting for the user.
            404 => tokio::time::sleep(POLL_INTERVAL).await,
            s => {
                return Err(RemoteError::Server {
                    status: s,
                    detail: "unexpected status while polling".into(),
                })
            }
        }
    }

    Err(RemoteError::AuthFailed)
}

/// Percent-encode a form value.
fn urlencode(s: &str) -> String {
    s.bytes()
        .map(|b| match b {
            b'A'..=b'Z' | b'a'..=b'z' | b'0'..=b'9' | b'-' | b'_' | b'.' | b'~' => {
                (b as char).to_string()
            }
            _ => format!("%{b:02X}"),
        })
        .collect()
}

/// TRACES: FR-NC-1 | M-4
/// Revoke the app password on logout (FR-NC-1).
pub async fn revoke(
    client: &reqwest::Client,
    server: &str,
    login: &str,
    password: &str,
) -> Result<(), RemoteError> {
    let url = format!(
        "{}/ocs/v2.php/core/apppassword",
        server.trim_end_matches('/')
    );
    client
        .delete(&url)
        .basic_auth(login, Some(password))
        .header("OCS-APIRequest", "true")
        .send()
        .await
        .map_err(super::map_send_error)?;
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn login_flow_response_deserialises() {
        // The shape Nextcloud actually returns.
        let json = r#"{
            "poll": {"token": "abc", "endpoint": "https://cloud.example/login/v2/poll"},
            "login": "https://cloud.example/login/v2/flow/xyz"
        }"#;
        let flow: LoginFlow = serde_json::from_str(json).unwrap();
        assert_eq!(flow.poll.token, "abc");
        assert!(flow.login_url.contains("/login/v2/flow/"));
    }

    #[test]
    fn form_values_are_encoded() {
        assert_eq!(urlencode("abc123"), "abc123");
        assert_eq!(urlencode("a b+c"), "a%20b%2Bc");
    }

    #[test]
    fn credentials_deserialise_with_camel_case_keys() {
        let json = r#"{
            "server": "https://cloud.example",
            "loginName": "duncan",
            "appPassword": "secret-token"
        }"#;
        let c: AppCredentials = serde_json::from_str(json).unwrap();
        assert_eq!(c.login_name, "duncan");
        assert_eq!(c.app_password, "secret-token");
    }
}