use std::time::{Duration, Instant};

use axum::{
    extract::Request,
    http::{header::HeaderName, HeaderValue, Request as HttpRequest},
    middleware::Next,
    response::Response,
};
use uuid::Uuid;

pub const API_RESPONSE_ENVELOPE_HEADER: &str = "x-genarrative-response-envelope";
pub const X_REQUEST_ID_HEADER: &str = "x-request-id";

// 当前阶段先把请求级元信息统一挂到 extensions，后续响应头、envelope 与错误处理中间件继续复用。
#[derive(Clone, Debug)]
pub struct RequestContext {
    request_id: String,
    operation: String,
    request_started_at: Instant,
    wants_envelope: bool,
}

impl RequestContext {
    pub fn new(
        request_id: String,
        operation: String,
        elapsed_seed: Duration,
        wants_envelope: bool,
    ) -> Self {
        Self {
            request_id,
            operation,
            request_started_at: Instant::now()
                .checked_sub(elapsed_seed)
                .unwrap_or_else(Instant::now),
            wants_envelope,
        }
    }

    pub fn request_id(&self) -> &str {
        &self.request_id
    }

    pub fn operation(&self) -> &str {
        &self.operation
    }

    pub fn wants_envelope(&self) -> bool {
        self.wants_envelope
    }

    pub fn elapsed(&self) -> u64 {
        self.request_started_at
            .elapsed()
            .as_millis()
            .min(u64::MAX as u128) as u64
    }
}

pub async fn attach_request_context(mut request: Request, next: Next) -> Response {
    let wants_envelope = wants_api_envelope(&request);
    let request_id = request
        .headers()
        .get(X_REQUEST_ID_HEADER)
        .and_then(|value| value.to_str().ok())
        .map(str::trim)
        .filter(|value| !value.is_empty())
        .map(ToOwned::to_owned)
        .unwrap_or_else(|| Uuid::new_v4().to_string());
    let operation = format!("{} {}", request.method(), request.uri());

    request.extensions_mut().insert(RequestContext::new(
        request_id.clone(),
        operation,
        Duration::ZERO,
        wants_envelope,
    ));

    // 统一把 request_id 写回请求头，方便后续 tracing、响应头与 envelope 层读取同一来源。
    if let Ok(header_value) = HeaderValue::from_str(&request_id) {
        request
            .headers_mut()
            .insert(HeaderName::from_static(X_REQUEST_ID_HEADER), header_value);
    }

    next.run(request).await
}

pub fn resolve_request_id<B>(request: &HttpRequest<B>) -> Option<String> {
    request
        .extensions()
        .get::<RequestContext>()
        .map(|context| context.request_id().to_string())
        .or_else(|| {
            request
                .headers()
                .get(X_REQUEST_ID_HEADER)
                .and_then(|value| value.to_str().ok())
                .map(str::trim)
                .filter(|value| !value.is_empty())
                .map(ToOwned::to_owned)
        })
}

fn wants_api_envelope<B>(request: &HttpRequest<B>) -> bool {
    request
        .headers()
        .get(API_RESPONSE_ENVELOPE_HEADER)
        .and_then(|value| value.to_str().ok())
        .map(str::trim)
        .map(str::to_lowercase)
        .is_some_and(|value| matches!(value.as_str(), "1" | "true" | "v1" | "envelope"))
}