//! 本机 HTTP API 入口：路由请求、限制输入大小、观察活动，并将执行工作送入串行 worker。
//! HTTP 线程不操作 VM；共享 NamespaceState 只保存最近完整发布文档和资源命令。提交序号用来拒绝已被较新 PUT/DELETE 取代的结果。
//! 关闭流程先请求运行时有界清理，再通过完成通知让原生事件循环退出。
//!
mod guide;
mod worker;

use guide::agent_guide;
use worker::{PendingRequest, RequestProgress, Worker};

use std::{
    io::Read,
    ops::{Deref, DerefMut},
    panic::{AssertUnwindSafe, catch_unwind},
    sync::{
        Arc, OnceLock, RwLock,
        mpsc::{Receiver, SyncSender, TrySendError, sync_channel},
    },
    sync::{
        Condvar, Mutex,
        atomic::{AtomicBool, Ordering},
    },
    thread,
};

use anyhow::{Context as _, Result};
use tiny_http::{Header, Method, Request, Response, Server, StatusCode};
use winit::event_loop::EventLoopProxy;

use crate::{
    activity::{Activity, ActivityLog},
    app::AppEvent,
    document::NamespaceState,
    endor_host,
};

// 只监听 IPv4 回环固定端口，接口用于本进程原生输入和本机 agent，不是对外网络服务器。
pub const API_ADDRESS: &str = "127.0.0.1:4737";
const MAX_CODE_SIZE: u64 = endor_host::MAX_SOURCE_BYTES as u64;
type Notify = Arc<dyn Fn() + Send + Sync>;

#[derive(Clone, Debug)]
/// 运行时清理的摘要与可选错误，供最终原生退出结果报告。
pub struct ShutdownOutcome {
    pub summary: String,
    pub error: Option<String>,
}
type ShutdownCompletion = Arc<(Mutex<Option<ShutdownOutcome>>, Condvar)>;
#[derive(Clone)]
/// 跨线程的退出控制句柄，使用有界通知和完成条件变量，不携带 VM。
pub struct RuntimeControl {
    sender: SyncSender<()>,
    requested: Arc<AtomicBool>,
    completion: ShutdownCompletion,
    native_sender: Arc<OnceLock<SyncSender<BuildRequest>>>,
    namespace: Arc<RwLock<NamespaceState>>,
}
impl RuntimeControl {
    /// Only the native input relay calls this blocking acknowledgement path.
    /// Window threads still use a bounded, nonblocking Input sender.
    pub(crate) fn dispatch_native(&self, input: crate::events::Input) -> Result<()> {
        anyhow::ensure!(!self.is_exiting(), "application is exiting");
        let (done, completed) = sync_channel(1);
        let job = {
            let state = self
                .namespace
                .read()
                .map_err(|_| anyhow::anyhow!("namespace lock is poisoned"))?;
            BuildRequest {
                request: RequestReply::Native(done),
                kind: RequestKind::Event,
                source: String::new(),
                namespace: state.name.clone(),
                submission: state.submission,
                native: Some(input),
            }
        };
        self.native_sender
            .get()
            .ok_or_else(|| anyhow::anyhow!("native input queue is unavailable"))?
            .send(job)
            .map_err(|_| anyhow::anyhow!("native input worker stopped"))?;
        completed
            .recv()
            .map_err(|_| anyhow::anyhow!("native input acknowledgement stopped"))?
            .map_err(anyhow::Error::msg)
    }

    /// 只发出一次退出请求，唤醒 worker 执行清理，并通过完成句柄通知原生循环。
    pub fn request_shutdown(&self) -> bool {
        // 原子标志合并重复退出请求；已请求直接返回 true，不在 GUI 线程重复排队清理。
        if self.requested.swap(true, Ordering::AcqRel) {
            return true;
        }
        if self.sender.try_send(()).is_ok() {
            true
        } else {
            // 控制队列不可用时回滚请求标志，允许调用方识别失败并再次尝试，而非永远卡在假退出状态。
            self.requested.store(false, Ordering::Release);
            false
        }
    }
    /// 读取退出标志，使窗口事件和新输入尽早停止进入运行时。
    pub fn is_exiting(&self) -> bool {
        self.requested.load(Ordering::Acquire)
    }
    /// 在明确超时内等待 worker 的清理结果，不能无限阻塞退出。
    pub fn wait_shutdown(&self, timeout: std::time::Duration) -> Option<ShutdownOutcome> {
        let (lock, ready) = &*self.completion;
        let result = lock.lock().ok()?;
        let (result, _) = ready
            // 条件变量处理虚假唤醒，直到完成槽非空或超时；返回 None 也可能来自锁中毒，不能当作清理成功。
            .wait_timeout_while(result, timeout, |result| result.is_none())
            .ok()?;
        result.clone()
    }
}
/// worker 持有的关闭接收端、控制状态和 GUI 完成通知代理。
struct Shutdown {
    receiver: Receiver<()>,
    control: RuntimeControl,
    proxy: EventLoopProxy<AppEvent>,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
/// 送入执行队列的请求类别，区分完整源码、持久输入、事件与重置。
enum RequestKind {
    Event,
    Code,
    Expression,
    Repl,
    ResetRepl,
}

/// 保留原 HTTP 请求与提交身份的执行工作，完成或失败后由 worker 回应。
struct BuildRequest {
    request: RequestReply,
    native: Option<crate::events::Input>,
    kind: RequestKind,
    source: String,
    namespace: String,
    submission: u64,
}

/// 绑定回环 API，启动请求接收与单 VM worker，返回活动日志及一次性退出控制句柄。
pub fn start(
    namespace: Arc<RwLock<NamespaceState>>,
    proxy: EventLoopProxy<AppEvent>,
) -> Result<(Activity, RuntimeControl)> {
    // 退出控制仅需一个消息槽，正常执行请求另走容量8队列，避免工作排满后无法通知关闭。
    let (sender, receiver) = sync_channel(1);
    let control = RuntimeControl {
        sender,
        requested: Arc::new(AtomicBool::new(false)),
        completion: Arc::new((Mutex::new(None), Condvar::new())),
        native_sender: Arc::new(OnceLock::new()),
        namespace: namespace.clone(),
    };
    let shutdown = Shutdown {
        receiver,
        control: control.clone(),
        proxy: proxy.clone(),
    };
    // 绑定失败在启动阶段反馈，不能假装本机 API 可用；后台通知仅发送 GUI 事件，不直接画窗口。
    let server = Server::http(API_ADDRESS)
        .map_err(|error| anyhow::anyhow!(error))
        .with_context(|| format!("bind Tessera API to {API_ADDRESS}"))?;
    let notify: Notify = Arc::new(move || {
        let _ = proxy.send_event(AppEvent::DocumentUpdated);
    });
    let activity = Arc::new(Mutex::new(ActivityLog::default()));
    start_server_observed(
        Arc::new(server),
        namespace,
        notify.clone(),
        activity.clone(),
        notify,
        Some(shutdown),
        Some(control.native_sender.clone()),
    )?;
    Ok((activity, control))
}

#[cfg(test)]
/// 为本地监听服务建立请求处理线程，并把执行请求转交有界队列。
fn start_server(
    server: Arc<Server>,
    namespace: Arc<RwLock<NamespaceState>>,
    notify: Notify,
) -> Result<thread::JoinHandle<()>> {
    start_server_observed(
        server,
        namespace,
        notify,
        Arc::new(Mutex::new(ActivityLog::default())),
        Arc::new(|| {}),
        None,
        None,
    )
}

/// 启动带活动观察的 HTTP 服务，将请求状态变化通知管理界面。
fn start_server_observed(
    server: Arc<Server>,
    namespace: Arc<RwLock<NamespaceState>>,
    notify: Notify,
    activity: Activity,
    observer_notify: Notify,
    shutdown: Option<Shutdown>,
    native_port: Option<Arc<OnceLock<SyncSender<BuildRequest>>>>,
) -> Result<thread::JoinHandle<()>> {
    // HTTP 接收与 VM 执行分离，最多8个排队请求；源代码只在单个 endor-worker 中操作 VM。
    let (sender, receiver) = sync_channel::<BuildRequest>(8);
    if let Some(native_port) = native_port {
        native_port
            .set(sender.clone())
            .map_err(|_| anyhow::anyhow!("native input queue already attached"))?;
    }
    let worker_namespace = namespace.clone();
    let worker_notify = notify.clone();
    let exiting = shutdown
        .as_ref()
        .map(|shutdown| shutdown.control.requested.clone());
    thread::Builder::new()
        .name("tessera-endor-worker".into())
        .spawn(move || {
            let mut worker = Worker::default();
            // 分片请求跨循环保留原 HTTP 请求和继续句柄；同一时刻只推进一个有未完成 VM 执行的输入。
            let mut pending: Option<(BuildRequest, PendingRequest)> = None;
            loop {
                if let Some(shutdown) = &shutdown
                    && shutdown.receiver.try_recv().is_ok()
                {
                    // 退出优先于下一量子：先撤去待响应请求，再由 shutdown_runtime 清理 VM 续体与生命周期资源。
                    if let Some((job, input)) = pending.take() {
                        drop(input);
                        let _ = job
                            .request
                            .respond(error_response(StatusCode(503), "application is exiting"));
                    }
                    let outcome = worker.shutdown_runtime();
                    // 排队请求全部明确回应503，不能留着客户端无期限等待已经停止的执行线程。
                    while let Ok(job) = receiver.try_recv() {
                        let _ = job
                            .request
                            .respond(error_response(StatusCode(503), "application is exiting"));
                    }
                    if let Ok(mut current) = worker_namespace.write() {
                        // 撤销所有帧的会话/焦点与原生命令，让 GUI 不再把旧资源当成仍可执行的活域。
                        current.runtime_session = 0;
                        current.window_commands.clear();
                        current.document.frame.session = 0;
                        current.document.frame.focus = None;
                        for view in current.document.windows.values_mut() {
                            view.frame.session = 0;
                            view.frame.focus = None;
                        }
                    }
                    eprintln!("{}", outcome.summary);
                    let (lock, ready) = &*shutdown.control.completion;
                    if let Ok(mut result) = lock.lock() {
                        *result = Some(outcome.clone());
                        // 先在锁内保存清理结果再唤醒等待者，同时用 AppEvent 通知原生事件循环退出，两条路径复用同一 outcome。
                        ready.notify_all();
                    }
                    let _ = shutdown.proxy.send_event(AppEvent::ShutdownComplete {
                        error: outcome.error,
                    });
                    break;
                }
                // 分片只让出线程，不并行执行后续输入；当前请求完成才回应并处理下一队列项。
                if let Some((job, input)) = pending.take() {
                    match worker.resume_request(&job, input, &worker_namespace, &worker_notify) {
                        RequestProgress::Pending(input) => {
                            pending = Some((job, input));
                            // A soft VM quantum is a control boundary, not a
                            // minimum-duration time slice. Yield to other ready
                            // threads without charging a timer delay per quantum.
                            thread::yield_now();
                        }
                        RequestProgress::Complete(response) => {
                            let _ = job.request.respond(response);
                        }
                    }
                    continue;
                }
                // 空闲输入边界先推进视口刷新与任务，待执行刷新/协作任务时零等待，否则最多100ms检查一次。
                worker.refresh_viewport(&worker_namespace, &worker_notify);
                let wait = if worker.repl.as_ref().is_some_and(|(_, runtime)| {
                    runtime.has_pending_refresh() || runtime.has_cooperative_tasks()
                }) {
                    std::time::Duration::ZERO
                } else {
                    std::time::Duration::from_millis(100)
                };
                match receiver.recv_timeout(wait) {
                    Ok(job) => {
                        match worker.begin_request(&job, &worker_namespace, &worker_notify) {
                            RequestProgress::Pending(input) => {
                                if job.native.is_none()
                                    && matches!(&input, PendingRequest::BeforeInput)
                                {
                                    eprintln!(
                                        "Tessera worker: submission {} waits for active refresh",
                                        job.submission
                                    );
                                }
                                pending = Some((job, input));
                            }
                            RequestProgress::Complete(response) => {
                                let _ = job.request.respond(response);
                            }
                        }
                    }
                    Err(std::sync::mpsc::RecvTimeoutError::Disconnected) => break,
                    Err(std::sync::mpsc::RecvTimeoutError::Timeout) => {
                        if worker.repl.as_ref().is_some_and(|(epoch, runtime)| {
                            worker_namespace.read().is_ok_and(|current| {
                                current.submission != *epoch
                                    && current.runtime_session != runtime.id
                            })
                        }) {
                            // 当前持久域同时失去 submission 和 runtime_session 归属时退役；不能仅因源码请求排队就误删仍权威的旧域。
                            worker.repl = None;
                        }
                        if wait.is_zero() {
                            thread::yield_now();
                        }
                    }
                }
            }
        })
        .context("start Aster execution worker")?;
    thread::Builder::new()
        .name("tessera-agent-api".to_owned())
        .spawn(move || {
            for request in server.incoming_requests() {
                if exiting
                    .as_ref()
                    .is_some_and(|flag| flag.load(Ordering::Acquire))
                    // 退出后拒绝写入/执行路由，GET 与 OPTIONS 仍可读取最近发布值或探测接口。
                    && !matches!(request.method(), Method::Get | Method::Options)
                {
                    let _ =
                        request.respond(error_response(StatusCode(503), "application is exiting"));
                    continue;
                }
                handle(
                    request,
                    &namespace,
                    &notify,
                    &sender,
                    &activity,
                    &observer_notify,
                );
            }
        })
        .context("start Tessera agent API thread")
}

// Capture only allowlisted headers: credentials and cookies never enter the inspector.
/// HTTP 请求的观察包装，在读取正文和响应时维护 Network 工具记录。
/// HTTP and in-process native jobs share one serial execution/refresh path.
/// Native envelopes cannot be created by an HTTP header or request body.
enum RequestReply {
    Http(ObservedRequest),
    Native(SyncSender<std::result::Result<(), String>>),
}
impl RequestReply {
    fn respond(self, response: Response<std::io::Cursor<Vec<u8>>>) -> std::io::Result<()> {
        match self {
            Self::Http(request) => request.respond(response),
            Self::Native(done) => {
                let status = response.status_code().0;
                let result = if status == 200 || status == 409 {
                    Ok(())
                } else {
                    Err(String::from_utf8_lossy(response.into_reader().get_ref())
                        .chars()
                        .take(2048)
                        .collect())
                };
                let _ = done.send(result);
                Ok(())
            }
        }
    }
}

struct ObservedRequest {
    inner: Request,
    activity: Activity,
    id: u64,
    notify: Notify,
}
impl ObservedRequest {
    /// 从请求提取允许观察的头部与显示来源，创建活动记录并通知工具界面。
    fn new(inner: Request, activity: Activity, notify: Notify) -> Self {
        // 活动观察只保留 Content-Type/Length；X-Tessera-Origin 仅判来源标签，不把任意认证头复制进工具日志。
        let headers = inner
            .headers()
            .iter()
            .filter(|h| h.field.equiv("Content-Type") || h.field.equiv("Content-Length"))
            .map(ToString::to_string)
            .collect::<Vec<_>>()
            .join("\n");
        // console 标记只是显示来源，不提供权限，也不改变 VM 执行语义。
        let origin = if inner
            .headers()
            .iter()
            .any(|h| h.field.equiv("X-Tessera-Origin") && h.value.as_str() == "console")
        {
            "Console"
        } else {
            "HTTP"
        }
        .to_owned();
        let id = activity.lock().unwrap().begin(
            inner.method().to_string(),
            inner.url().to_owned(),
            origin,
            headers,
        );
        notify();
        Self {
            inner,
            activity,
            id,
            notify,
        }
    }
    /// 将受限请求正文记录到活动预览，不在观察器中执行源码。
    fn record_body(&self, body: &str) {
        self.activity.lock().unwrap().body(self.id, body);
        (self.notify)();
    }
    /// 发送最终 HTTP 响应，并同步结束该条活动记录。
    fn respond(self, response: Response<std::io::Cursor<Vec<u8>>>) -> std::io::Result<()> {
        let status = response.status_code();
        let headers = response.headers().to_vec();
        let length = response.data_length();
        // 响应正文本已在内存 Cursor，记录预览后用原 status/headers/reader/length 重建响应，不消费正文内容。
        let reader = response.into_reader();
        // 记录的是已构造响应，即使后面 socket 发送失败也已结束活动记录，不能据此声称客户端成功接收。
        self.activity.lock().unwrap().finish(
            self.id,
            status.0,
            &String::from_utf8_lossy(reader.get_ref()),
            headers
                .iter()
                .map(ToString::to_string)
                .collect::<Vec<_>>()
                .join("\n"),
        );
        (self.notify)();
        self.inner
            .respond(Response::new(status, headers, reader, length, None))
    }
}
impl Deref for ObservedRequest {
    type Target = Request;
    /// 将包装类型的只读访问转交给内部当前上下文。
    fn deref(&self) -> &Request {
        &self.inner
    }
}
impl DerefMut for ObservedRequest {
    /// 将包装类型的可变访问转交给内部当前上下文。
    fn deref_mut(&mut self) -> &mut Request {
        &mut self.inner
    }
}

/// 解析 HTTP 方法和路径；只读路由读取发布值，执行路由交给 worker。
fn handle(
    request: Request,
    namespace: &Arc<RwLock<NamespaceState>>,
    notify: &Notify,
    sender: &SyncSender<BuildRequest>,
    activity: &Activity,
    observer_notify: &Notify,
) {
    let request = ObservedRequest::new(request, activity.clone(), observer_notify.clone());
    let method = request.method().clone();
    // 路由匹配去掉查询串，namespace 从固定路径提取；不把 query 当作命名空间或源代码。
    let path = request
        .url()
        .split('?')
        .next()
        .unwrap_or(request.url())
        .to_owned();

    let evaluation = namespace_from_route(&path, "/evaluate");
    let repl = namespace_from_route(&path, "/repl");
    let event = namespace_from_route(&path, "/events");
    // PUT/code 完整替换，POST 在 events/repl/evaluate 中分类，DELETE/repl 是持久会话重置；其他交给资源读取/清空路径。
    let route = if method == Method::Put {
        namespace_from_path(&path).map(|name| (name, RequestKind::Code))
    } else if method == Method::Post {
        event
            .map(|name| (name, RequestKind::Event))
            .or_else(|| repl.map(|name| (name, RequestKind::Repl)))
            .or(evaluation.map(|name| (name, RequestKind::Expression)))
    } else if method == Method::Delete {
        repl.map(|name| (name, RequestKind::ResetRepl))
    } else {
        None
    };
    if let Some((addressed, kind)) = route {
        submit(request, addressed, namespace, sender, kind);
        return;
    }
    let response = if method == Method::Get && path == "/agent" {
        match namespace.read() {
            Ok(namespace) => markdown(StatusCode(200), agent_guide(&namespace)),
            Err(_) => error_response(StatusCode(500), "namespace lock is poisoned"),
        }
    } else if let Some(addressed_namespace) = namespace_from_path(&path).map(str::to_owned) {
        code_request(method, &addressed_namespace, namespace, notify)
    } else if method == Method::Options {
        text(StatusCode(204), "", "text/plain")
    } else {
        error_response(StatusCode(404), "route not found; start with GET /agent")
    };

    let _ = request.respond(response);
}

/// 处理源码资源的 GET/DELETE 等请求，返回对应版本头或撤销运行时所有权。
fn code_request(
    method: Method,
    addressed_namespace: &str,
    namespace: &Arc<RwLock<NamespaceState>>,
    notify: &Notify,
) -> Response<std::io::Cursor<Vec<u8>>> {
    let Ok(current) = namespace.read() else {
        return error_response(StatusCode(500), "namespace lock is poisoned");
    };
    if addressed_namespace != current.name {
        return error_response(
            StatusCode(404),
            format!(
                "namespace `{addressed_namespace}` is not active; current namespace is `{}`",
                current.name
            ),
        );
    }

    // GET 返回最近成功发布的 source 而非正在排队的输入，并通过头部暴露 revision/session/window/layout 及逻辑视口。
    if method == Method::Get {
        let mut response = text(
            StatusCode(200),
            &current.document.source,
            "text/plain; charset=utf-8",
        );
        add_header(
            &mut response,
            "X-Tessera-Revision",
            &current.revision.to_string(),
        );
        add_header(
            &mut response,
            "X-Tessera-Session",
            &current.document.frame.session.to_string(),
        );
        add_header(
            &mut response,
            "X-Tessera-Window",
            &current.document.frame.window.to_string(),
        );
        add_header(
            &mut response,
            "X-Tessera-Layout-Version",
            &current.document.frame.layout_version.to_string(),
        );
        if let Some(viewport) = current.viewport {
            add_header(
                &mut response,
                "X-Tessera-Viewport-Width",
                &viewport.width.to_string(),
            );
            add_header(
                &mut response,
                "X-Tessera-Viewport-Height",
                &viewport.height.to_string(),
            );
        }
        add_header(
            &mut response,
            "X-Tessera-Source-Kind",
            if current
                .document
                .root
                .as_ref()
                .is_some_and(|root| root.kind == "repl-session")
            {
                "repl-transcript"
            } else {
                "source-snapshot"
            },
        );
        return response;
    }
    // 释放读锁后才申请写锁，避免同一线程持读锁升级为写锁死锁；修改结束也先解锁再发送 GUI 通知。
    drop(current);

    match method {
        Method::Delete => match namespace.write() {
            Ok(mut current) => {
                let revision = match current.clear() {
                    Ok(revision) => revision,
                    Err(error) => return error_response(StatusCode(500), error.to_string()),
                };
                drop(current);
                notify();
                json(
                    StatusCode(200),
                    serde_json::json!({
                        "ok": true,
                        "namespace": addressed_namespace,
                        "revision": revision
                    }),
                )
            }
            Err(_) => error_response(StatusCode(500), "namespace lock is poisoned"),
        },
        Method::Options => text(StatusCode(204), "", "text/plain"),
        _ => error_response(StatusCode(405), "code supports GET, PUT, and DELETE"),
    }
}

/// 读取并检查请求体，分配提交身份，再把工作送进有界执行队列。
fn submit(
    mut request: ObservedRequest,
    addressed: &str,
    namespace: &Arc<RwLock<NamespaceState>>,
    sender: &SyncSender<BuildRequest>,
    kind: RequestKind,
) {
    let source = match read_code(&mut request) {
        Ok(source) => source,
        Err(error) => {
            let _ = request.respond(error_response(StatusCode(400), error.to_string()));
            return;
        }
    };
    // 读取成功后才保存受限活动正文预览；超长或非法 UTF-8 请求不会进入执行队列。
    request.record_body(&source);
    let Ok(mut current) = namespace.write() else {
        let _ = request.respond(error_response(
            StatusCode(500),
            "namespace lock is poisoned",
        ));
        return;
    };
    if current.name != addressed {
        let _ = request.respond(error_response(StatusCode(404), "namespace is not active"));
        return;
    }
    // 仅完整 Code 请求分配新 submission，事件/REPL/表达式继承当前身份，保留共享域输入顺序。
    let submission = match if kind == RequestKind::Code {
        current.next_submission()
    } else {
        Ok(current.submission)
    } {
        Ok(id) => id,
        Err(error) => {
            let _ = request.respond(error_response(StatusCode(500), error.to_string()));
            return;
        }
    };
    let job = BuildRequest {
        request: RequestReply::Http(request),
        native: None,
        kind,
        source,
        namespace: addressed.into(),
        submission,
    };
    // 持 namespace 写锁完成入队和接受身份更新；worker 提交使用同一锁，保证接受与发布之间没有竞态窗口。
    match sender.try_send(job) {
        // A rejected queue entry never invalidates accepted work. The worker
        // uses this same lock when committing, so publication is atomic.
        Ok(()) => {
            if kind == RequestKind::Code {
                current.submission = submission;
            }
        }
        // 队列拒绝时不推进 submission，所以已经接受的旧工作不会因为本次失败请求而失去发布资格。
        Err(TrySendError::Full(job)) => {
            let _ = job
                .request
                .respond(error_response(StatusCode(503), "build queue is full"));
        }
        Err(TrySendError::Disconnected(job)) => {
            let _ = job.request.respond(error_response(
                StatusCode(503),
                "execution worker is unavailable",
            ));
        }
    }
}

/// 生成较旧请求已被新提交取代的响应，拒绝晚到结果覆盖当前文档。
fn superseded(submission: u64) -> Response<std::io::Cursor<Vec<u8>>> {
    json(
        StatusCode(409),
        serde_json::json!({ "ok": false, "submission": submission,
        "error": "submission superseded by a newer PUT or DELETE" }),
    )
}

/// 从固定路由格式提取命名空间，避免把不匹配的路径当作代码资源。
fn namespace_from_route<'a>(path: &'a str, suffix: &str) -> Option<&'a str> {
    // 同时检查前后缀且命名空间非空、无额外斜杠；不做模糊路径前缀匹配。
    path.strip_prefix("/v1/namespaces/")?
        .strip_suffix(suffix)
        .filter(|namespace| !namespace.is_empty() && !namespace.contains('/'))
}
/// 从固定路由格式提取命名空间，避免把不匹配的路径当作代码资源。
fn namespace_from_path(path: &str) -> Option<&str> {
    namespace_from_route(path, "/code")
}

/// 按源码字节上限读取 UTF-8 请求体，读取失败或超限时返回诊断。
fn read_code(request: &mut Request) -> Result<String> {
    if request
        .body_length()
        .is_some_and(|length| length as u64 > MAX_CODE_SIZE)
    {
        anyhow::bail!("code exceeds the 1 MiB limit");
    }
    // 已知 Content-Length 先预拒绝，再在流上最多读上限+1；防止缺失/不实长度绕过容量限制。
    // read_to_string 要求 UTF-8，不用有损替换改变用户源码。
    let mut code = String::new();
    request
        .as_reader()
        .take(MAX_CODE_SIZE + 1)
        .read_to_string(&mut code)
        .context("read code")?;
    if code.len() as u64 > MAX_CODE_SIZE {
        anyhow::bail!("code exceeds the 1 MiB limit");
    }
    Ok(code)
}

/// 将前端/编译/执行诊断编码为 API 错误响应，保留用户可理解的位置和消息。
fn compile_error(error: anyhow::Error) -> Response<std::io::Cursor<Vec<u8>>> {
    let mut diagnostic =
        serde_json::json!({ "severity": "error", "message": format!("{error:#}") });
    // 有 SourceDiagnostic 才附行/列和半开字节范围；其他运行时错误仍保留完整错误链消息，不编造源码位置。
    if let Some(source) = error.downcast_ref::<frontend::SourceDiagnostic>() {
        diagnostic["line"] = source.location.line.into();
        diagnostic["column"] = source.location.column.into();
        diagnostic["start_byte"] = source.diagnostic.span.start.into();
        diagnostic["end_byte"] = source.diagnostic.span.end.into();
    }
    json(
        StatusCode(422),
        serde_json::json!({
            "ok": false,
            "diagnostics": [diagnostic]
        }),
    )
}

/// 生成统一 JSON 错误响应，使调用方能区分协议错误与成功结果。
fn error_response(
    status: StatusCode,
    message: impl Into<String>,
) -> Response<std::io::Cursor<Vec<u8>>> {
    json(status, serde_json::json!({ "error": message.into() }))
}

/// 以明确的内容类型和状态码构造响应，并应用本机 API 的公共响应头。
fn json(status: StatusCode, value: serde_json::Value) -> Response<std::io::Cursor<Vec<u8>>> {
    text(
        status,
        &value.to_string(),
        "application/json; charset=utf-8",
    )
}

/// 以明确的内容类型和状态码构造响应，并应用本机 API 的公共响应头。
fn markdown(status: StatusCode, value: String) -> Response<std::io::Cursor<Vec<u8>>> {
    text(status, &value, "text/markdown; charset=utf-8")
}

/// 以明确的内容类型和状态码构造响应，并应用本机 API 的公共响应头。
fn text(status: StatusCode, value: &str, content_type: &str) -> Response<std::io::Cursor<Vec<u8>>> {
    // 公共响应头只允许固定本机 Origin/方法/头名，非通配任意来源；这些头不替代回环绑定与路由校验。
    let mut response = Response::from_string(value).with_status_code(status);
    add_header(&mut response, "Content-Type", content_type);
    add_header(
        &mut response,
        "Access-Control-Allow-Origin",
        "http://127.0.0.1",
    );
    add_header(
        &mut response,
        "Access-Control-Allow-Methods",
        "GET, PUT, POST, DELETE, OPTIONS",
    );
    add_header(
        &mut response,
        "Access-Control-Allow-Headers",
        "Content-Type, X-Tessera-Origin",
    );
    response
}

/// 向响应追加经过 HTTP 库检查的头字段，不直接拼接未验证的原始报文。
fn add_header(response: &mut Response<std::io::Cursor<Vec<u8>>>, name: &str, value: &str) {
    // 由 HTTP 库验证字段格式，非法头被忽略，不把未校验字符拼进原始响应报文。
    if let Ok(header) = Header::from_bytes(name, value) {
        response.add_header(header);
    }
}

#[cfg(test)]
mod tests;