[router] Refactor router and policy traits with dependency injection (#7987)

Co-authored-by: Jin Pan <jpan236@wisc.edu>
Co-authored-by: Keru Yang <rukeyang@gmail.com>
Co-authored-by: Yingyi Huang <yingyihuang2000@outlook.com>
Co-authored-by: Philip Zhu <phlipzhux@gmail.com>

sgl-router/src/routers/factory.rs

@@ -0,0 +1,66 @@
+//! Factory for creating router instances
+
+use super::{pd_router::PDRouter, router::Router, RouterTrait};
+use crate::config::{PolicyConfig, RouterConfig, RoutingMode};
+use crate::policies::PolicyFactory;
+
+/// Factory for creating router instances based on configuration
+pub struct RouterFactory;
+
+impl RouterFactory {
+    /// Create a router instance from configuration
+    pub fn create_router(config: &RouterConfig) -> Result<Box<dyn RouterTrait>, String> {
+        match &config.mode {
+            RoutingMode::Regular { worker_urls } => {
+                Self::create_regular_router(worker_urls, &config.policy, config)
+            }
+            RoutingMode::PrefillDecode {
+                prefill_urls,
+                decode_urls,
+            } => Self::create_pd_router(prefill_urls, decode_urls, &config.policy, config),
+        }
+    }
+
+    /// Create a regular router with injected policy
+    fn create_regular_router(
+        worker_urls: &[String],
+        policy_config: &PolicyConfig,
+        router_config: &RouterConfig,
+    ) -> Result<Box<dyn RouterTrait>, String> {
+        // Create policy
+        let policy = PolicyFactory::create_from_config(policy_config);
+
+        // Create regular router with injected policy
+        let router = Router::new(
+            worker_urls.to_vec(),
+            policy,
+            router_config.worker_startup_timeout_secs,
+            router_config.worker_startup_check_interval_secs,
+        )?;
+
+        Ok(Box::new(router))
+    }
+
+    /// Create a PD router with injected policy
+    fn create_pd_router(
+        prefill_urls: &[(String, Option<u16>)],
+        decode_urls: &[String],
+        policy_config: &PolicyConfig,
+        router_config: &RouterConfig,
+    ) -> Result<Box<dyn RouterTrait>, String> {
+        // Create policy directly from PolicyConfig
+        // All policies now support PD mode through the select_worker_pair method
+        let policy = PolicyFactory::create_from_config(policy_config);
+
+        // Create PD router with injected policy
+        let router = PDRouter::new(
+            prefill_urls.to_vec(),
+            decode_urls.to_vec(),
+            policy,
+            router_config.worker_startup_timeout_secs,
+            router_config.worker_startup_check_interval_secs,
+        )?;
+
+        Ok(Box::new(router))
+    }
+}