Implement sorted entries cache

sorted_entries cached

src/library/cache.cr

@@ -157,3 +157,90 @@ class InfoCache
     @@cached_sort_opt_previous = {} of String => Hash(String, SortOptions)
   end
 end
+
+private class SortedEntriesCacheEntry
+  getter key : String, atime : Time
+
+  def initialize(@ctime : Time, @key : String, @value : Array(String))
+    @atime = @ctime
+  end
+
+  def value
+    @atime = Time.utc
+    @value
+  end
+
+  def instance_size
+    @value.size * (instance_sizeof(String) + sizeof(String)) +
+      @value.sum(&.size) + instance_sizeof(SortedEntriesCacheEntry)
+  end
+end
+
+# LRU Cache
+class SortedEntriesCache
+  @@limit : Int128 = Int128.new 1024 * 1024 * 50 # 50MB
+  # key => entry
+  @@cache = {} of String => SortedEntriesCacheEntry
+
+  def self.gen_key(book_id : String, username : String,
+                   entries : Array(Entry), opt : SortOptions?)
+    sig = Digest::SHA1.hexdigest (entries.map &.id).to_s
+    user_context = opt && opt.method == SortMethod::Progress ? username : ""
+    Digest::SHA1.hexdigest (book_id + sig + user_context +
+                            (opt ? opt.to_tuple.to_s : "nil"))
+  end
+
+  def self.get(key : String)
+    entry = @@cache[key]?
+    Logger.debug "SortedEntries Cache Hit! #{key}" unless entry.nil?
+    Logger.debug "SortedEntries Cache Miss #{key}" if entry.nil?
+    return ids2entries entry.value unless entry.nil?
+  end
+
+  def self.set(key : String, value : Array(Entry))
+    @@cache[key] = SortedEntriesCacheEntry.new Time.utc, key, value.map &.id
+    Logger.debug "SortedEntries Cached #{key}"
+    remove_victim_cache
+  end
+
+  def self.invalidate(key : String)
+    @@cache.delete key
+  end
+
+  def self.print
+    sum = @@cache.sum { |_, entry| entry.instance_size }
+    Logger.debug "---- Sorted Entries Cache ----"
+    Logger.debug "Size: #{sum} Bytes"
+    Logger.debug "List:"
+    @@cache.each { |k, v| Logger.debug "#{k} | #{v.atime}" }
+    Logger.debug "------------------------------"
+  end
+
+  private def self.ids2entries(ids : Array(String))
+    e_map = Library.default.deep_entries.to_h { |entry| {entry.id, entry} }
+    entries = [] of Entry
+    begin
+      ids.each do |id|
+        entries << e_map[id]
+      end
+      return entries if ids.size == entries.size
+    rescue
+    end
+  end
+
+  private def self.is_cache_full
+    sum = @@cache.sum { |_, entry| entry.instance_size }
+    sum > @@limit
+  end
+
+  private def self.remove_victim_cache
+    while is_cache_full && @@cache.size > 0
+      Logger.debug "SortedEntries Cache Full! Remove LRU"
+      min = @@cache.min_by? { |_, entry| entry.atime }
+      Logger.debug "Target: #{min[0]}, Last Access Time: #{min[1].atime}" if min
+      invalidate min[0] if min
+
+      print if Logger.get_severity == Log::Severity::Debug
+    end
+  end
+end