//! FnConnect 远程连接解析（参考 feiniu-car-music `fn-api.js`）。
//!
//! fnId → 网关 `https://5ddd.com/api/v1/fn/con`（authx md5 签名）→ 内网/公网/中继候选 →
//! 探测可达性 → 得到可用的 base_url（含 mode=relay 的中继地址）。

use md5::{Digest, Md5};
use rand::RngCore;
use serde_json::{json, Value};

/// 网关地址与签名常量（对齐 feiniu-car-music）。
const FN_CONNECT_URL: &str = "https://5ddd.com/api/v1/fn/con";
const FN_AUTHX_PREFIX: &str = "NDzZTVxnRKP8Z0jXg1VAMonaG8akvh";
const FN_API_KEY: &str = "zIGtkc3dqZnJpd29qZXJqa2w7c";

fn md5_hex(input: &str) -> String {
    let mut h = Md5::new();
    h.update(input.as_bytes());
    format!("{:x}", h.finalize())
}

/// 从输入识别 fnId：`fnos.net/<id>`、`<id>.5ddd.com`、或裸 fnId。
pub fn extract_fn_id(input: &str) -> Option<String> {
    let s = input.trim();
    if s.is_empty() {
        return None;
    }
    if let Some(id) = s.split_once("fnos.net/").map(|(_, r)| r.split('/').next().unwrap_or("")) {
        if !id.is_empty() {
            return Some(id.trim().to_string());
        }
    }
    if let Some(rest) = s.rsplit_once("/") {
        let last = rest.1;
        if last.ends_with(".5ddd.com") {
            return Some(last.trim_end_matches(".5ddd.com").to_string());
        }
    }
    if s.ends_with(".5ddd.com") {
        return Some(s.trim_end_matches(".5ddd.com").to_string());
    }
    // 裸 fnId
    if s.len() >= 3 && s.chars().all(|c| c.is_alphanumeric() || c == '-' || c == '_') && !s.starts_with("http") {
        return Some(s.to_string());
    }
    None
}

/// 计算网关 authx 签名。
fn fn_authx(method: &str, url: &str, data: &Value) -> String {
    let body = if method.eq_ignore_ascii_case("get") {
        String::new()
    } else {
        serde_json::to_string(data).unwrap_or_default()
    };
    let mut nonce = String::new();
    let mut rng = rand::thread_rng();
    for _ in 0..6 {
        nonce.push(char::from(b'0' + (rng.next_u32() % 10) as u8));
    }
    let timestamp = std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map(|d| d.as_millis().to_string())
        .unwrap_or_default();
    let raw = format!(
        "{FN_AUTHX_PREFIX}_{url}_{nonce}_{timestamp}_{}__{FN_API_KEY}",
        md5_hex(&body)
    );
    format!("nonce={nonce}&timestamp={timestamp}&sign={}", md5_hex(&raw))
}

/// 从网关查询 fnId 的连接参数。
pub async fn query_fn_connect(fn_id: &str) -> Result<Value, String> {
    let client = reqwest::Client::builder()
        .timeout(std::time::Duration::from_secs(10))
        .build()
        .map_err(|e| e.to_string())?;
    let body = json!({ "fnId": fn_id });
    let resp = client
        .post(FN_CONNECT_URL)
        .header("Content-Type", "application/json")
        .header("authx", fn_authx("post", "/api/v1/fn/con", &body))
        .json(&body)
        .send()
        .await
        .map_err(|e| format!("FnConnect 网关不可达: {e}"))?;
    let b: Value = resp.json().await.map_err(|e| e.to_string())?;
    if b["code"].as_i64().unwrap_or(-1) != 0 {
        return Err(b["msg"].as_str().unwrap_or("FnConnect 网关返回错误").to_string());
    }
    Ok(b["data"].clone())
}

/// 构建候选 base_url 列表。返回 (url, is_relay)。
pub fn build_candidates(data: &Value) -> Vec<(String, bool)> {
    let mut out: Vec<(String, bool)> = Vec::new();
    let port = &data["port"];
    let http = port["httpPort"].as_u64().unwrap_or(5666);
    let https = port["httpsPort"].as_u64().unwrap_or(5667);
    let empty = vec![];
    for ip in data["ipv4"].as_array().unwrap_or(&empty).iter().filter_map(|v| v.as_str()) {
        out.push((format!("http://{ip}:{http}"), false));
        out.push((format!("https://{ip}:{https}"), false));
    }
    for ip in data["publicIpv4"].as_array().unwrap_or(&empty).iter().filter_map(|v| v.as_str()) {
        out.push((format!("http://{ip}:{http}"), false));
        out.push((format!("https://{ip}:{https}"), false));
    }
    for ip in data["publicIpv6"].as_array().unwrap_or(&empty).iter().filter_map(|v| v.as_str()) {
        out.push((format!("http://[{ip}]:{http}"), false));
        out.push((format!("https://[{ip}]:{https}"), false));
    }
    let relays = data["fn"].as_array().unwrap_or(&empty);
    let relay_addrs: Vec<String> = if relays.is_empty() {
        vec!["5ddd.com".to_string()]
    } else {
        relays
            .iter()
            .filter_map(|v| v.as_str().map(|s| s.to_string()))
            .collect()
    };
    for addr in relay_addrs {
        let domain = addr.split(':').next().unwrap_or(&addr).to_string();
        out.push((format!("https://{domain}"), true));
    }
    out
}

/// 探测某个 base_url 是否可用。
async fn probe(url: &str) -> bool {
    let client = reqwest::Client::builder()
        .timeout(std::time::Duration::from_secs(6))
        .build()
        .unwrap_or_else(|_| reqwest::Client::new());
    let full = format!("{}/music/api/v1/track/list?page=1&size=1", url.trim_end_matches('/'));
    match client.get(&full).send().await {
        Ok(resp) => resp.status().as_u16() < 500,
        Err(_) => false,
    }
}

/// 解析 fnId → 第一个可达的 base_url；返回 (base_url, is_relay)。
pub async fn resolve_base_url(fn_id: &str) -> Result<(String, bool), String> {
    let data = query_fn_connect(fn_id).await?;
    let candidates = build_candidates(&data);
    if candidates.is_empty() {
        return Err("FnConnect 未返回可用地址".into());
    }
    for (url, relay) in &candidates {
        if probe(url).await {
            return Ok((url.clone(), *relay));
        }
    }
    Err(format!("FnConnect 候选均不可达（{} 个）", candidates.len()))
}