wl-webrtc/src/backend_detect.rs

use anyhow::Result;
use wayland_client::globals::registry_queue_init;
use wayland_client::globals::GlobalListContents;
use wayland_client::protocol::wl_registry::{Event, WlRegistry};
use wayland_client::{Connection, Dispatch, QueueHandle};

use crate::args::Args;

// 屏幕捕获后端类型

/// Capture backend to use for screen capture.
/// 屏幕捕获后端枚举
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum CaptureBackend {
    /// wlroots wlr-screencopy protocol (Sway, Hyprland, etc.)
    /// wlroots 合成器的 wlr-screencopy 协议（适用于 Sway、Hyprland 等）
    WlrScreencopy,
    /// xdg-desktop-portal with PipeWire (KWin/KDE, GNOME, etc.)
    /// XDG 桌面门户 + PipeWire 方式（适用于 KWin/KDE、GNOME 等）
    PortalPipeWire,
}

/// Minimal dispatch type for listing Wayland globals during backend detection.
/// 用于后端检测期间列举 Wayland 全局对象的最小化分发类型（无需实际处理事件）
struct RegistryLs;

// 为 RegistryLs 实现 Wayland 注册表事件分发（空实现，仅需类型满足 trait 约束）
impl Dispatch<WlRegistry, GlobalListContents> for RegistryLs {
    fn event(
        _state: &mut Self,
        _registry: &WlRegistry,
        _event: Event,
        _data: &GlobalListContents,
        _conn: &Connection,
        _qhandle: &QueueHandle<Self>,
    ) {
    }
}

// CAUTION: must NOT use ashpd here — ashpd caches zbus::Connection in a global
// OnceLock; if the tokio runtime owning that connection is dropped before
// setup_portal() runs, the cached connection becomes dead and hangs forever.
fn check_portal_available() -> bool {
    let rt = match tokio::runtime::Runtime::new() {
        Ok(rt) => rt,
        Err(e) => {
            tracing::warn!("Failed to create tokio runtime for portal check: {e}");
            return false;
        }
    };

    rt.block_on(async {
        let conn = match zbus::Connection::session().await {
            Ok(c) => c,
            Err(e) => {
                tracing::info!("D-Bus session bus unavailable: {e}");
                return false;
            }
        };

        let inner: zbus::Proxy = match zbus::proxy::Builder::new(&conn)
            .destination("org.freedesktop.portal.Desktop")
            .and_then(|b| b.path("/org/freedesktop/portal/desktop"))
            .and_then(|b| b.interface("org.freedesktop.portal.ScreenCast"))
        {
            Ok(b) => match b.build().await {
                Ok(p) => p,
                Err(e) => {
                    tracing::info!("Portal ScreenCast interface not available: {e}");
                    return false;
                }
            },
            Err(e) => {
                tracing::info!("Portal ScreenCast proxy build failed: {e}");
                return false;
            }
        };

        let version = match inner.get_property::<u32>("version").await {
            Ok(version) => {
                tracing::info!("Portal ScreenCast available (version: {version})");
                true
            }
            Err(e) => {
                tracing::info!("Portal ScreenCast version query failed: {e}");
                false
            }
        };
        version
    })
}

// 通过 Wayland globals 检测 wlr-screencopy 协议是否可用
fn check_screencopy_available() -> Result<bool> {
    let conn = Connection::connect_to_env()?;
    let (globals, _queue) = registry_queue_init::<RegistryLs>(&conn)?;

    let has_screencopy = globals
        .contents()
        .clone_list()
        .iter()
        .any(|g| g.interface == "zwlr_screencopy_manager_v1");

    // Drop the Wayland connection explicitly before returning.
    // The screencopy path creates its own connection. Holding two connections
    // simultaneously is wasteful and may cause issues on some compositors.
    // 显式释放检测用的 Wayland 连接，避免与后续捕获后端同时占用两个连接
    drop(conn);

    Ok(has_screencopy)
}

/// Detect which capture backend to use.
/// 检测应使用哪种屏幕捕获后端
///
/// Priority:
/// 优先级：
/// 1. Explicit `--backend` override from CLI args
///    用户通过 `--backend` 命令行参数显式指定
/// 2. Auto-detect: check wlr-screencopy (Wayland) and Portal (D-Bus) respectively
///    自动检测：分别通过 Wayland globals 和 D-Bus 检测两个后端
///
/// Both backends are checked independently. If neither is available, returns an error.
/// 两个后端独立检测，都不可用时返回错误。
pub fn detect_backend(args: &Args) -> Result<CaptureBackend> {
    // 1. Check explicit override
    // 步骤 1：检查用户是否通过命令行参数显式指定了后端
    if let Some(ref backend) = args.backend {
        return match backend.as_str() {
            "portal" => {
                tracing::info!("Backend override: Portal/PipeWire");
                Ok(CaptureBackend::PortalPipeWire)
            }
            "screencopy" => {
                tracing::info!("Backend override: wlr-screencopy");
                Ok(CaptureBackend::WlrScreencopy)
            }
            other => {
                // 未知后端名称，返回错误
                anyhow::bail!("Unknown backend '{}'. Use 'screencopy' or 'portal'.", other);
            }
        };
    }

    // 2. Auto-detect: check both backends independently
    // 步骤 2：自动检测 — 分别检测两个后端的可用性
    tracing::info!("Auto-detecting capture backend...");

    // 检测 wlr-screencopy（通过 Wayland globals）
    let has_screencopy = check_screencopy_available()?;
    // 检测 Portal（通过 D-Bus）
    let has_portal = check_portal_available();

    // 根据检测结果选择后端，screencopy 优先（性能更好、延迟更低）
    match (has_screencopy, has_portal) {
        (true, _) => {
            tracing::info!("Detected wlr-screencopy support → using WlrScreencopy backend");
            Ok(CaptureBackend::WlrScreencopy)
        }
        (false, true) => {
            tracing::info!("No wlr-screencopy, Portal available → using Portal/PipeWire backend");
            Ok(CaptureBackend::PortalPipeWire)
        }
        (false, false) => {
            anyhow::bail!(
                "No supported capture backend found. \
                 Install a wlroots compositor (for wlr-screencopy) \
                 or xdg-desktop-portal (for Portal/PipeWire)."
            );
        }
    }
}

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

    // 测试辅助函数：构造指定后端参数的 Args 实例
    fn make_args(backend: Option<&str>) -> Args {
        Args {
            output: Some("test.mp4".to_string()),
            output_name: None,
            fps: 30,
            codec: "h264".to_string(),
            hw_accel: "vaapi".to_string(),
            drm_device: None,
            bitrate: None,
            gop_size: None,
            verbose: false,
            backend: backend.map(String::from),
            port: 0,
            no_persist: false,
        }
    }

    // 测试：显式指定 portal 后端
    #[test]
    fn explicit_portal_backend() {
        let args = make_args(Some("portal"));
        let result = detect_backend(&args);
        assert!(result.is_ok());
        assert_eq!(result.unwrap(), CaptureBackend::PortalPipeWire);
    }

    // 测试：显式指定 screencopy 后端
    #[test]
    fn explicit_screencopy_backend() {
        let args = make_args(Some("screencopy"));
        let result = detect_backend(&args);
        assert!(result.is_ok());
        assert_eq!(result.unwrap(), CaptureBackend::WlrScreencopy);
    }

    // 测试：无效的后端名称应返回错误
    #[test]
    fn invalid_backend_name_returns_error() {
        let args = make_args(Some("magic"));
        let result = detect_backend(&args);
        assert!(result.is_err());
        let err = result.unwrap_err().to_string();
        assert!(
            err.contains("Unknown backend 'magic'"),
            "Expected error about unknown backend, got: {err}"
        );
    }
}