//! Autodiscover for mobile devices (MobileSync schema) - replaces z-push/autodiscover.

use std::net::SocketAddr;
use std::sync::Arc;

use axum::body::Body;
use axum::extract::{ConnectInfo, State};
use axum::http::{HeaderMap, HeaderValue, Method, StatusCode};
use axum::response::{IntoResponse, Response};
use http_body_util::BodyExt;

use crate::app::App;
use crate::backend::AuthResult;
use crate::eas::{basic_auth, client_ip, normalize_login, user_allowed};
use crate::metrics::Event;
use crate::util::{now, xml_escape};
use crate::xmltree;

const MOBILESYNC: &str =
    "http://schemas.microsoft.com/exchange/autodiscover/mobilesync/responseschema/2006";

fn xml_response(status: StatusCode, body: String) -> Response {
    let mut r = (status, body).into_response();
    r.headers_mut().insert(
        "Content-Type",
        HeaderValue::from_static("text/xml; charset=utf-8"),
    );
    r
}

fn error_xml(code: u32, msg: &str) -> String {
    format!(
        r#"<?xml version="1.0" encoding="utf-8"?>
<Autodiscover xmlns="http://schemas.microsoft.com/exchange/autodiscover/responseschema/2006">
  <Response>
    <Error Time="{}" Id="1">
      <ErrorCode>{code}</ErrorCode>
      <Message>{}</Message>
      <DebugData />
    </Error>
  </Response>
</Autodiscover>"#,
        chrono::Utc::now().format("%H:%M:%S%.6f"),
        xml_escape(msg)
    )
}

fn unauthorized() -> Response {
    let mut r = (StatusCode::UNAUTHORIZED, "Access denied").into_response();
    r.headers_mut().insert(
        "WWW-Authenticate",
        HeaderValue::from_static("Basic realm=\"ActiveSync\""),
    );
    r
}

fn safe_host(h: &str) -> Option<&str> {
    (!h.is_empty()
        && h.len() < 256
        && h.chars()
            .all(|c| c.is_ascii_alphanumeric() || matches!(c, '.' | '-' | ':' | '[' | ']')))
    .then_some(h)
}

/// Every attempt is logged and shown in the panel (Live), including the unauthenticated
/// first request iOS sends and failures - this is what makes "my phone still asks for the
/// server" debuggable.
pub async fn handler(
    State(app): State<Arc<App>>,
    ConnectInfo(peer): ConnectInfo<SocketAddr>,
    method: Method,
    uri: axum::http::Uri,
    headers: HeaderMap,
    body: Body,
) -> Response {
    let s = app.settings();
    let started = std::time::Instant::now();
    let ip = client_ip(peer, &headers, &s).to_string();
    let hdr = |n: &str| {
        headers
            .get(n)
            .and_then(|v| v.to_str().ok())
            .unwrap_or("")
            .chars()
            .filter(|c| !c.is_control())
            .take(120)
            .collect::<String>()
    };
    let host = if hdr("x-forwarded-host").is_empty() {
        hdr("host")
    } else {
        hdr("x-forwarded-host")
    };
    let ua = hdr("user-agent");
    let user = basic_auth(&headers, &s)
        .map(|(l, _)| l)
        .unwrap_or_else(|| "-".into());
    let size = hdr("content-length").parse::<u64>().unwrap_or(0);
    // request headers for the trace (never credentials or cookies)
    let hdr_dump: Vec<String> = headers
        .iter()
        .filter(|(k, _)| {
            !matches!(
                k.as_str(),
                "authorization" | "cookie" | "proxy-authorization"
            )
        })
        .map(|(k, v)| {
            format!(
                "{}: {}",
                k.as_str(),
                String::from_utf8_lossy(v.as_bytes())
                    .chars()
                    .filter(|c| !c.is_control())
                    .take(200)
                    .collect::<String>()
            )
        })
        .collect();
    let typed_user = headers
        .get("authorization")
        .and_then(|v| v.to_str().ok())
        .and_then(|v| v.split_once(' '))
        .and_then(|(_, d)| {
            use base64::Engine;
            base64::engine::general_purpose::STANDARD
                .decode(d.trim())
                .ok()
        })
        .and_then(|b| String::from_utf8(b).ok())
        .and_then(|d| {
            d.split_once(':')
                .map(|(u, _)| u.chars().take(120).collect::<String>())
        })
        .unwrap_or_default();
    let body_bytes = match http_body_util::Limited::new(body, 64 * 1024)
        .collect()
        .await
    {
        Ok(b) => b.to_bytes(),
        Err(_) => return StatusCode::PAYLOAD_TOO_LARGE.into_response(),
    };
    let resp = inner(
        app.clone(),
        peer,
        method.clone(),
        headers,
        Body::from(body_bytes.clone()),
    )
    .await;
    let (mut parts, rbody) = resp.into_parts();
    let rbytes = rbody
        .collect()
        .await
        .map(|b| b.to_bytes())
        .unwrap_or_default();
    parts.headers.remove("content-length");
    let mut resp = Response::from_parts(parts, Body::from(rbytes.clone()));
    resp.headers_mut()
        .insert("X-ActivePush", HeaderValue::from_static("autodiscover"));
    let code = resp.status().as_u16();
    let status = match code {
        200 if String::from_utf8_lossy(&rbytes).contains("<ErrorCode>") => "invalid request",
        200 => "ok",
        401 => "auth required",
        429 => "locked out",
        503 => "backend unavailable",
        _ => "error",
    };
    tracing::info!(target: "active_push::autodiscover", ip = %ip, host = %host, path = %uri.path(), method = %method, http = code, user = %user, ua = %ua, "autodiscover {status}");
    let clip = |b: &[u8]| -> String {
        String::from_utf8_lossy(&b[..b.len().min(3000)])
            .chars()
            .filter(|c| !c.is_control() || *c == '\n')
            .collect()
    };
    app.ad_trace_push(serde_json::json!({
        "ts": now(), "ip": ip, "host": host, "method": method.as_str(), "path": uri.path(),
        "typed_user": typed_user, "http": code, "ms": started.elapsed().as_millis() as u64,
        "request_headers": hdr_dump, "request_body": clip(&body_bytes),
        "response_body": clip(&rbytes),
    }));
    app.metrics.record(Event {
        ts: now(),
        user,
        device_id: String::new(),
        device_type: "Autodiscover".into(),
        command: "Autodiscover".into(),
        ip,
        http: code,
        status: format!("{status} ({host})"),
        ms: started.elapsed().as_millis() as u64,
        bytes_in: size,
        bytes_out: 0,
        items_out: 0,
        items_in: 0,
    });
    resp
}

async fn inner(
    app: Arc<App>,
    peer: SocketAddr,
    method: Method,
    headers: HeaderMap,
    body: Body,
) -> Response {
    let s = app.settings();
    let ip = client_ip(peer, &headers, &s).to_string();
    app.metrics
        .c
        .autodiscover
        .fetch_add(1, std::sync::atomic::Ordering::Relaxed);
    if !s.autodiscover.enabled {
        return StatusCode::NOT_FOUND.into_response();
    }
    if method != Method::POST && method != Method::GET {
        return StatusCode::METHOD_NOT_ALLOWED.into_response();
    }
    let body = match http_body_util::Limited::new(body, 64 * 1024)
        .collect()
        .await
    {
        Ok(b) => b.to_bytes(),
        Err(_) => return StatusCode::PAYLOAD_TOO_LARGE.into_response(),
    };
    // requested address + schema
    let (mut email, schema) = if body.is_empty() {
        (String::new(), MOBILESYNC.to_string())
    } else {
        match xmltree::parse(&body) {
            Ok(x) => (
                x.text_of("EMailAddress").unwrap_or_default(),
                x.text_of("AcceptableResponseSchema").unwrap_or_default(),
            ),
            Err(_) => return xml_response(StatusCode::OK, error_xml(600, "Invalid Request")),
        }
    };
    if !schema.is_empty() && schema != MOBILESYNC {
        tracing::info!(ip = %ip, schema = %schema, "autodiscover: unsupported response schema (only MobileSync is served)");
        return xml_response(StatusCode::OK, error_xml(600, "Invalid Request"));
    }

    // only the configured domains (when a list is set)
    if !s.autodiscover.domains.is_empty() {
        if let Some((_, dom)) = email.rsplit_once('@') {
            let dom = crate::autodiag::normalize_domain(dom);
            if !s.autodiscover.serves(&dom) {
                tracing::info!(ip = %ip, domain = %dom, "autodiscover: domain not in the configured list");
                return xml_response(StatusCode::OK, error_xml(600, "Invalid Request"));
            }
        }
    }

    // authentication
    let creds = basic_auth(&headers, &s);
    let login = match (&creds, s.autodiscover.require_auth) {
        (None, true) => return unauthorized(),
        (Some((l, _)), _) => l.clone(),
        (None, false) => match normalize_login(&email, &s) {
            Some(l) => l,
            None => return xml_response(StatusCode::OK, error_xml(600, "Invalid Request")),
        },
    };
    let ip_key = format!("ip:{ip}");
    let user_key = format!("user:{login}");
    if app.auth.locked_until(&ip_key).is_some() || app.auth.locked_until(&user_key).is_some() {
        return (StatusCode::TOO_MANY_REQUESTS, "Too many failed logins").into_response();
    }
    if !user_allowed(&login, &s) {
        return unauthorized();
    }
    // iOS sends the same password twice: once with "user@domain" and once with the bare "user",
    // and treats a refusal of either as a failed Autodiscover. When the bare name is the local
    // part of the requested address, try the full address first (the form most IMAP servers with
    // several domains know), then the name as given.
    let mut login = login;
    if let Some((given, pass)) = &creds {
        let mut candidates: Vec<String> = Vec::new();
        if !given.contains('@') {
            if let Some((local, _)) = email.rsplit_once('@') {
                if local.eq_ignore_ascii_case(given) {
                    if let Some(full) = normalize_login(&email, &s) {
                        if user_allowed(&full, &s) {
                            candidates.push(full);
                        }
                    }
                }
            }
        }
        candidates.push(given.clone());

        let mut accepted: Option<String> = candidates
            .iter()
            .find(|c| app.auth.is_cached(&app.pool.key(c, pass)))
            .cloned();
        if accepted.is_none() {
            for cand in &candidates {
                let mut sess = app.session(cand, pass);
                match sess.authenticate().await {
                    Ok(AuthResult::Ok) => {
                        app.auth.success(&user_key);
                        app.auth
                            .cache_ok(app.pool.key(cand, pass), s.security.auth_cache_secs);
                        sess.close().await;
                        accepted = Some(cand.clone());
                        break;
                    }
                    Ok(AuthResult::Denied) => {}
                    Err(e) => {
                        tracing::error!("autodiscover: backend unavailable: {e:#}");
                        return StatusCode::SERVICE_UNAVAILABLE.into_response();
                    }
                }
            }
        }
        match accepted {
            Some(l) => login = l,
            None => {
                app.metrics.auth_failure();
                if s.security.log_auth_failures {
                    tracing::warn!(target: "active_push::auth", "authentication failed user={given} ip={ip} service=autodiscover");
                }
                let (m, w, lo) = (
                    s.security.auth_fail_max,
                    s.security.auth_fail_window_secs,
                    s.security.lockout_secs,
                );
                app.auth.fail(&ip_key, m * 3, w, lo);
                app.auth.fail(&user_key, m, w, lo);
                return unauthorized();
            }
        }
    }
    if email.is_empty() || !email.contains('@') {
        email = crate::backend::primary_email(&s, &login);
    }
    let configured = email
        .rsplit_once('@')
        .map(|(_, d)| s.autodiscover.url_for(d))
        .unwrap_or_else(|| s.autodiscover.server_url.trim().to_string());
    let url = if !configured.is_empty() {
        configured
    } else {
        let host = headers
            .get("x-forwarded-host")
            .or_else(|| headers.get("host"))
            .and_then(|h| h.to_str().ok())
            .and_then(safe_host)
            .unwrap_or("localhost");
        format!("https://{host}/Microsoft-Server-ActiveSync")
    };
    let display = email.clone();
    let xml = format!(
        r#"<?xml version="1.0" encoding="utf-8"?>
<Autodiscover xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://schemas.microsoft.com/exchange/autodiscover/responseschema/2006">
  <Response xmlns="{MOBILESYNC}">
    <Culture>en:en</Culture>
    <User>
      <DisplayName>{}</DisplayName>
      <EMailAddress>{}</EMailAddress>
    </User>
    <Action>
      <Settings>
        <Server>
          <Type>MobileSync</Type>
          <Url>{}</Url>
          <Name>{}</Name>
        </Server>
      </Settings>
    </Action>
  </Response>
</Autodiscover>"#,
        xml_escape(&display),
        xml_escape(&email),
        xml_escape(&url),
        xml_escape(&url)
    );
    xml_response(StatusCode::OK, xml)
}