From d8fccc8f1b6d840cd35f6b9f6be175fc660336db Mon Sep 17 00:00:00 2001
From: Shadowfacts <me@shadowfacts.net>
Date: Sat, 8 Jun 2024 12:23:12 -0700
Subject: [PATCH] Purge old persistent history after processing

Closes #480
---
 .../MastodonCachePersistentStore.swift        | 31 ++++++++++++++++---
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/Tusker/CoreData/MastodonCachePersistentStore.swift b/Tusker/CoreData/MastodonCachePersistentStore.swift
index a062a193..b055d119 100644
--- a/Tusker/CoreData/MastodonCachePersistentStore.swift
+++ b/Tusker/CoreData/MastodonCachePersistentStore.swift
@@ -530,11 +530,34 @@ class MastodonCachePersistentStore: NSPersistentCloudKitContainer {
                 defer {
                     PersistentHistoryTokenStore.setToken(token, for: accountInfo)
                 }
-                let req = NSPersistentHistoryChangeRequest.fetchHistory(after: lastToken)
-                if let result = try? self.remoteChangesBackgroundContext.execute(req) as? NSPersistentHistoryResult,
-                   let transactions = result.result as? [NSPersistentHistoryTransaction],
-                   !transactions.isEmpty {
+                let transactions: [NSPersistentHistoryTransaction]
+                do {
+                    let req = NSPersistentHistoryChangeRequest.fetchHistory(after: lastToken)
+                    if let result = try self.remoteChangesBackgroundContext.execute(req) as? NSPersistentHistoryResult {
+                        transactions = result.result as? [NSPersistentHistoryTransaction] ?? []
+                    } else {
+                        logger.error("Unexpectedly non-NSPersistentHistoryResult")
+                        return
+                    }
+                } catch {
+                    logger.error("Unable to fetch persistent history results: \(String(describing: error), privacy: .public)")
+                    return
+                }
+                if !transactions.isEmpty {
                     self.processPersistentHistoryTransactions(transactions)
+                    
+                    do {
+                        // delete history only before the last token, because we don't want to invalidate
+                        // the most recent token
+                        let deleteReq = NSPersistentHistoryChangeRequest.deleteHistory(before: lastToken)
+                        let result = try self.remoteChangesBackgroundContext.execute(deleteReq)
+                        if  let result = result as? NSPersistentHistoryResult,
+                            result.resultType == .statusOnly {
+                            logger.info("Delete old persistent history result status: \(result.result as! Int)")
+                        }
+                    } catch {
+                        logger.error("Unable to delete old persistent history: \(String(describing: error), privacy: .public)")
+                    }
                 }
             }
         }