Address PR feedback: add Mutex for thread-safety and improve logging

Author: AndrewCheung360

app/src/main/java/com/cornellappdev/uplift/data/auth/ApolloAuthInterceptor.kt

@@ -1,5 +1,6 @@
 package com.cornellappdev.uplift.data.auth
 
+import android.util.Log
 import com.apollographql.apollo.ApolloClient
 import com.apollographql.apollo.api.ApolloRequest
 import com.apollographql.apollo.api.ApolloResponse
@@ -12,6 +13,8 @@ import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.emitAll
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.flow
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import javax.inject.Inject
 import javax.inject.Named
 import javax.inject.Singleton
@@ -35,38 +38,60 @@ class ApolloAuthInterceptor @Inject constructor(
     private val sessionManager: SessionManager,
     @Named("refresh") private val refreshClient: ApolloClient
 ) : ApolloInterceptor {
+    private val mutex = Mutex()
+
     override fun <D : Operation.Data> intercept(
         request: ApolloRequest<D>,
         chain: ApolloInterceptorChain
     ): Flow<ApolloResponse<D>> = flow {
         val response = chain.proceed(request).first()
 
         val retryCount = request.executionContext[RetryContext]?.retryCount ?: 0
+
         // TODO: replace string check with explicit error codes if backend implements
         if (response.errors?.any { it.message.contains("Signature has expired") } == true && retryCount < 1) {
             val refreshToken = tokenManager.getRefreshToken()
             if (refreshToken != null) {
-                try {
-                    val mutationResponse = refreshClient.mutation(RefreshAccessTokenMutation())
-                        .addHttpHeader("Authorization", "Bearer $refreshToken")
-                        .execute()
+                val newAccessToken = mutex.withLock {
+                    // Check if another request already refreshed the token while we were waiting for the lock
+                    val currentAccessToken = tokenManager.getAccessToken()
+                    val requestToken = request.httpHeaders?.find { it.name == "Authorization" }?.value?.substringAfter("Bearer ")
 
-                    val newAccessToken = mutationResponse.data?.refreshAccessToken?.newAccessToken
-                    if (newAccessToken != null) {
-                        tokenManager.saveTokens(newAccessToken, refreshToken)
-                        // Retry the request with the new token
-                        val newRequest = request.newBuilder()
-                            .addExecutionContext(RetryContext(retryCount + 1))
-                            .build()
-                        emitAll(chain.proceed(newRequest))
-                        return@flow
+                    if (currentAccessToken != null && currentAccessToken != requestToken) {
+                        currentAccessToken
                     } else {
-                        sessionManager.logout()
+                        try {
+                            val mutationResponse = refreshClient.mutation(RefreshAccessTokenMutation())
+                                .addHttpHeader("Authorization", "Bearer $refreshToken")
+                                .execute()
+
+                            val refreshedToken = mutationResponse.data?.refreshAccessToken?.newAccessToken
+                            if (refreshedToken != null) {
+                                tokenManager.saveTokens(refreshedToken, refreshToken)
+                                refreshedToken
+                            } else {
+                                Log.e("ApolloAuthInterceptor", "Refresh token mutation returned null access token")
+                                sessionManager.logout()
+                                null
+                            }
+                        } catch (e: Exception) {
+                            Log.e("ApolloAuthInterceptor", "Token refresh failed with exception", e)
+                            sessionManager.logout()
+                            null
+                        }
                     }
-                } catch (e: Exception) {
-                    sessionManager.logout()
+                }
+
+                if (newAccessToken != null) {
+                    // Retry the request with the new token
+                    val newRequest = request.newBuilder()
+                        .addExecutionContext(RetryContext(retryCount + 1))
+                        .build()
+                    emitAll(chain.proceed(newRequest))
+                    return@flow
                 }
             } else {
+                Log.d("ApolloAuthInterceptor", "No refresh token available, logging out")
                 sessionManager.logout()
             }
         }