//! HTTP transport to a ThoughtSync server.
//!
//! Covers the compatibility handshake (M10.6) and device-token auth (M10.7a). The
//! engine that moves notes — push, pull, cursor — grows on top of the same client,
//! which is why the timeout, identity headers and error vocabulary live here rather
//! than inline at each call site.
//!
//! Nothing here runs unless the user has linked a server; the app is local-first and
//! fully usable with no network at all.

use std::time::Duration;

use reqwest::{RequestBuilder, StatusCode};
use serde::{Deserialize, Serialize};

use super::compat::{self, Compatibility, ServerInfo};

/// Timeout for the short request/response calls in this module. Kept tight because a
/// user is watching a button while they run, and the most common mistake — a wrong
/// host on a LAN — fails by hanging rather than refusing, so an unbounded wait would
/// just look frozen. The sync engine's bulk transfers will need their own, longer one.
const REQUEST_TIMEOUT: Duration = Duration::from_secs(10);

/// What the link UI needs after a handshake: where we ended up (the normalized URL,
/// which may differ from what was typed), who answered, and whether we can work
/// with them.
#[derive(Debug, Serialize)]
pub struct ProbeResult {
    pub base_url: String,
    pub server: ServerInfo,
    pub compatibility: Compatibility,
}

/// The account a device token belongs to. Surfaced after linking so the user can
/// confirm they linked the account they meant to — easy to get wrong on a server
/// hosting more than one.
#[derive(Debug, Clone, Deserialize, Serialize)]
pub struct Identity {
    pub id: String,
    pub email: String,
    #[serde(default)]
    pub display_name: String,
}

#[derive(Deserialize)]
struct DeviceLoginResponse {
    token: String,
    user: Identity,
}

fn http() -> Result<reqwest::Client, String> {
    reqwest::Client::builder()
        .timeout(REQUEST_TIMEOUT)
        .build()
        .map_err(|e| format!("Could not start the network client: {e}"))
}

/// Attach the client-identity headers every request carries, plus a bearer token
/// when we hold one.
fn prepare(builder: RequestBuilder, token: Option<&str>) -> RequestBuilder {
    let mut builder = builder;
    for (name, value) in compat::client_headers() {
        builder = builder.header(name, value);
    }
    match token {
        Some(t) => builder.bearer_auth(t),
        None => builder,
    }
}

fn unexpected_status(base_url: &str, status: StatusCode) -> String {
    format!(
        "{base_url} answered with HTTP {}. Check the address — a reverse proxy or a \
         different site may be answering there.",
        status.as_u16()
    )
}

/// Ask a server who it is and whether we can sync with it.
///
/// `Err` means we never got a usable answer (bad address, unreachable, not a
/// ThoughtSync server). A server that answers but is *incompatible* comes back `Ok`
/// with a verdict — that distinction matters, because the two need very different
/// messages: one is "check what you typed", the other is "update something".
pub async fn probe(raw_url: &str) -> Result<ProbeResult, String> {
    let base_url = compat::normalize_base_url(raw_url)
        .ok_or("Enter a server address, like https://notes.example.com")?;

    let request = prepare(http()?.get(config_url(&base_url)), None);
    let response = request
        .send()
        .await
        .map_err(|e| describe_transport_error(&base_url, &e))?;

    let status = response.status();
    if !status.is_success() {
        return Err(unexpected_status(&base_url, status));
    }

    // Something answered 200 that isn't a ThoughtSync server (a router login page, a
    // captive portal). Report the address, not the parse error, which would mean
    // nothing to the person reading it.
    let server: ServerInfo = response.json().await.map_err(|_| {
        format!(
            "{base_url} responded, but not with ThoughtSync's configuration. \
             Is that the right address?"
        )
    })?;

    let compatibility = compat::evaluate(&server);
    Ok(ProbeResult {
        base_url,
        server,
        compatibility,
    })
}

/// Exchange email + password for a device bearer token.
///
/// The fresh-install path: it needs no existing session, which is what lets a brand
/// new desktop install link without visiting the web app first.
pub async fn device_login(
    base_url: &str,
    email: &str,
    password: &str,
    device_name: &str,
) -> Result<(String, Identity), String> {
    let body = serde_json::json!({
        "email": email,
        "password": password,
        "name": device_name,
    });
    let request = prepare(http()?.post(device_login_url(base_url)), None).json(&body);
    let response = request
        .send()
        .await
        .map_err(|e| describe_transport_error(base_url, &e))?;

    let status = response.status();
    if status == StatusCode::UNAUTHORIZED {
        return Err("That email and password didn't match an account on this server.".to_string());
    }
    if !status.is_success() {
        return Err(unexpected_status(base_url, status));
    }

    let parsed: DeviceLoginResponse = response
        .json()
        .await
        .map_err(|_| format!("{base_url} signed us in but sent an unexpected reply."))?;
    Ok((parsed.token, parsed.user))
}

/// Validate a token by asking whom it belongs to.
///
/// Used when the user pastes a token issued from the web app. Storing it unverified
/// would turn a copy/paste slip into a failure that only surfaces at the next sync,
/// far from the thing that caused it.
pub async fn fetch_identity(base_url: &str, token: &str) -> Result<Identity, String> {
    let request = prepare(http()?.get(me_url(base_url)), Some(token));
    let response = request
        .send()
        .await
        .map_err(|e| describe_transport_error(base_url, &e))?;

    let status = response.status();
    if status == StatusCode::UNAUTHORIZED {
        let message = "That token isn't valid on this server — it may have been revoked. \
                       Issue a new one from the web app under Account → Linked devices.";
        return Err(message.to_string());
    }
    if !status.is_success() {
        return Err(unexpected_status(base_url, status));
    }

    response
        .json()
        .await
        .map_err(|_| format!("{base_url} accepted the token but sent an unexpected reply."))
}

/// The public, unauthenticated endpoint carrying the handshake.
fn config_url(base_url: &str) -> String {
    format!("{base_url}/api/config")
}

fn device_login_url(base_url: &str) -> String {
    format!("{base_url}/api/auth/device-login")
}

fn me_url(base_url: &str) -> String {
    format!("{base_url}/api/auth/me")
}

/// Turn a transport failure into something a person can act on. reqwest's own
/// Display is accurate but reads like a stack trace.
fn describe_transport_error(base_url: &str, err: &reqwest::Error) -> String {
    if err.is_timeout() {
        format!(
            "{base_url} didn't respond within {} seconds. It may be offline, or \
             unreachable from this network.",
            REQUEST_TIMEOUT.as_secs()
        )
    } else if err.is_connect() {
        format!(
            "Couldn't reach {base_url}. Check the address and that the server is \
             running. If it uses plain HTTP, include http:// explicitly."
        )
    } else {
        format!("Couldn't reach {base_url}: {err}")
    }
}

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

    #[test]
    fn urls_join_without_doubling_slashes() {
        // normalize_base_url has already stripped any trailing slash, so plain
        // concatenation is correct — this pins that assumption.
        assert_eq!(
            config_url("https://notes.example.com"),
            "https://notes.example.com/api/config"
        );
        assert_eq!(
            device_login_url("https://notes.example.com"),
            "https://notes.example.com/api/auth/device-login"
        );
        assert_eq!(
            me_url("https://notes.example.com"),
            "https://notes.example.com/api/auth/me"
        );
    }

    #[test]
    fn urls_preserve_a_port_and_subpath() {
        assert_eq!(
            config_url("http://192.168.1.10:8000/thoughtsync"),
            "http://192.168.1.10:8000/thoughtsync/api/config"
        );
    }
}