/*
    * Copyright 2016-2022 The OSHI Project Contributors
    * SPDX-License-Identifier: MIT
    */
   package oshi.hardware.platform.linux;
   
   import static oshi.util.Memoizer.defaultExpiration;
   import static oshi.util.Memoizer.memoize;
   
  import java.util.List;
  import java.util.function.Supplier;
  
  import oshi.annotation.concurrent.ThreadSafe;
  import oshi.hardware.VirtualMemory;
  import oshi.hardware.common.AbstractGlobalMemory;
  import oshi.software.os.linux.LinuxOperatingSystem;
  import oshi.util.FileUtil;
  import oshi.util.ParseUtil;
  import oshi.util.platform.linux.ProcPath;
  import oshi.util.tuples.Pair;
  
  /**
   * Memory obtained by /proc/meminfo and sysinfo.totalram
   */
  @ThreadSafe
  public final class LinuxGlobalMemory extends AbstractGlobalMemory {
  
      private static final long PAGE_SIZE = LinuxOperatingSystem.getPageSize();
  
      private final Supplier<Pair<Long, Long>> availTotal = memoize(LinuxGlobalMemory::readMemInfo, defaultExpiration());
  
      private final Supplier<VirtualMemory> vm = memoize(this::createVirtualMemory);
  
      @Override
      public long getAvailable() {
          return availTotal.get().getA();
      }
  
      @Override
      public long getTotal() {
          return availTotal.get().getB();
      }
  
      @Override
      public long getPageSize() {
          return PAGE_SIZE;
      }
  
      @Override
      public VirtualMemory getVirtualMemory() {
          return vm.get();
      }
  
      /**
       * Updates instance variables from reading /proc/meminfo. While most of the information is available in the sysinfo
       * structure, the most accurate calculation of MemAvailable is only available from reading this pseudo-file. The
       * maintainers of the Linux Kernel have indicated this location will be kept up to date if the calculation changes:
       * see https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?
       * id=34e431b0ae398fc54ea69ff85ec700722c9da773
       * <p>
       * Internally, reading /proc/meminfo is faster than sysinfo because it only spends time populating the memory
       * components of the sysinfo structure.
       *
       * @return A pair containing available and total memory in bytes
       */
      private static Pair<Long, Long> readMemInfo() {
          long memFree = 0L;
          long activeFile = 0L;
          long inactiveFile = 0L;
          long sReclaimable = 0L;
  
          long memTotal = 0L;
          long memAvailable;
  
          List<String> procMemInfo = FileUtil.readFile(ProcPath.MEMINFO);
          for (String checkLine : procMemInfo) {
              String[] memorySplit = ParseUtil.whitespaces.split(checkLine, 2);
              if (memorySplit.length > 1) {
                  switch (memorySplit[0]) {
                  case "MemTotal:":
                      memTotal = ParseUtil.parseDecimalMemorySizeToBinary(memorySplit[1]);
                      break;
                  case "MemAvailable:":
                      memAvailable = ParseUtil.parseDecimalMemorySizeToBinary(memorySplit[1]);
                      // We're done!
                      return new Pair<>(memAvailable, memTotal);
                  case "MemFree:":
                      memFree = ParseUtil.parseDecimalMemorySizeToBinary(memorySplit[1]);
                      break;
                  case "Active(file):":
                      activeFile = ParseUtil.parseDecimalMemorySizeToBinary(memorySplit[1]);
                      break;
                  case "Inactive(file):":
                      inactiveFile = ParseUtil.parseDecimalMemorySizeToBinary(memorySplit[1]);
                      break;
                  case "SReclaimable:":
                      sReclaimable = ParseUtil.parseDecimalMemorySizeToBinary(memorySplit[1]);
                      break;
                  default:
                     // do nothing with other lines
                     break;
                 }
             }
         }
         // We didn't find MemAvailable so we estimate from other fields
         return new Pair<>(memFree + activeFile + inactiveFile + sReclaimable, memTotal);
     }
 
     private VirtualMemory createVirtualMemory() {
         return new LinuxVirtualMemory(this);
     }
 }