From f4ab09a6f6051a149f7cc54d6738af3c46695b7b Mon Sep 17 00:00:00 2001
From: Christoph Hagen <christoph@spacemasters.eu>
Date: Sat, 28 May 2022 21:58:51 +0200
Subject: [PATCH] Save caps less frequently

---
 Sources/App/CapServer.swift | 51 +++++++++++++++++++++++++++++--------
 1 file changed, 40 insertions(+), 11 deletions(-)

diff --git a/Sources/App/CapServer.swift b/Sources/App/CapServer.swift
index 67df1c6..23efa5e 100644
--- a/Sources/App/CapServer.swift
+++ b/Sources/App/CapServer.swift
@@ -14,17 +14,24 @@ final class CapServer {
     
     // MARK: Caps
 
-    private var saveImmediatelly = true
-
     private var writers: Set<String>
 
+    /**
+     The time to wait for changes to be written to disk.
+
+     This delay is used to prevent file writes for each small update to the caps.
+     */
+    private let saveDelay: TimeInterval = 1
+
+    /**
+     The time when a save should occur.
+
+     No save is necessary if this property is `nil`.
+     */
+    private var nextSaveTime: Date?
+
     private var caps = [Int: Cap]() {
-        didSet {
-            guard saveImmediatelly else {
-                return
-            }
-            try? saveCaps()
-        }
+        didSet { scheduleSave() }
     }
 
     var nextClassifierVersion: Int {
@@ -54,6 +61,31 @@ final class CapServer {
         log("\(caps.count) caps loaded")
     }
 
+    private func scheduleSave() {
+        nextSaveTime = Date().addingTimeInterval(saveDelay)
+        DispatchQueue.main.asyncAfter(deadline: .now() + saveDelay) {
+            self.performScheduledSave()
+        }
+    }
+
+    private func performScheduledSave() {
+        guard let date = nextSaveTime else {
+            // No save necessary, or already saved
+            return
+        }
+        guard date < Date() else {
+            // Save pushed to future
+            return
+        }
+        do {
+            try saveCaps()
+            nextSaveTime = nil
+        } catch {
+            // Attempt save again
+            scheduleSave()
+        }
+    }
+
     private func saveCaps() throws {
         let data = try JSONEncoder().encode(caps.values.sorted())
         try data.write(to: dbFile)
@@ -83,14 +115,11 @@ final class CapServer {
     // MARK: Counts
 
     private func updateCounts() throws {
-        saveImmediatelly = false
         caps = try caps.mapValues {
             var cap = $0
             cap.count = try count(of: $0.id)
             return cap
         }
-        saveImmediatelly = true
-        try? saveCaps()
     }
 
     func countImages(in folder: URL) throws -> Int {