Refactor PrinterDiscoverer and PrinterDetector to use a common interface.

chrome/browser/chromeos/printing/combining_printer_detector.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/chromeos/printing/combining_printer_detector.h"
+
+#include <map>
+#include <utility>
+#include <vector>
+
+#include "base/memory/ptr_util.h"
+#include "base/observer_list.h"
+#include "base/scoped_observer.h"
+#include "chrome/browser/chromeos/printing/printer_detector.h"
+#include "chromeos/printing/printer_configuration.h"
+
+namespace chromeos {
+namespace {
+
+class CombiningPrinterDetectorImpl;
+
+// We can't just implement PrinterDetector::Observer in
+// CombiningPrinterDetectorImpl because we need to be able to determing *which*
+// underlying detector is giving us new information.  Thus we use delegate
+// instantions to allow for a disambiguation about the source of a
+// PrinterDetector callback from one of the detectors being combined.
+class ObserverDelegate : public PrinterDetector::Observer {
+ public:
+  ObserverDelegate(CombiningPrinterDetectorImpl* parent,
+                   PrinterDetector* detector)
+      : parent_(parent), observer_(this) {
+    observer_.Add(detector);
+  }
+  void OnPrintersFound(const std::vector<Printer>& printers) override;
+  void OnPrinterScanComplete() override;
+
+ private:
+  CombiningPrinterDetectorImpl* parent_;
+  ScopedObserver<PrinterDetector, PrinterDetector::Observer> observer_;
+};
+
+class CombiningPrinterDetectorImpl : public CombiningPrinterDetector {
+ public:
+  ~CombiningPrinterDetectorImpl() override = default;
+
+  void AddDetector(PrinterDetector* detector) override {
+    detectors_.push_back(detector);
+    delegates_.push_back(base::MakeUnique<ObserverDelegate>(this, detector));
+    printers_.insert({delegates_.back().get(), detector->GetPrinters()});
+    scan_done_[delegates_.back().get()] = false;
+  }
+
+  void AddOwnedDetector(std::unique_ptr<PrinterDetector> detector) override {
+    AddDetector(detector.get());
+    owned_detectors_.emplace_back(std::move(detector));
+  }
+
+  // PrinterDetector implementations.
+  void AddObserver(PrinterDetector::Observer* observer) override {
+    observer_list_.AddObserver(observer);
+  }
+
+  void RemoveObserver(PrinterDetector::Observer* observer) override {
+    observer_list_.RemoveObserver(observer);
+  }
+
+  // Note this is *not* the PrinterDetectorObserver interface directly,
+  // it's the entry point for ObserverDelegates to pass along those messages
+  // into this class.
+  void OnPrintersFound(const ObserverDelegate* source,
+                       const std::vector<Printer>& printers) {
+    // If this object doesn't know about the delegate trying to update its
+    // printers, we missed delegate registration somehow, which shouldn't
+    // happen.
+    DCHECK(base::ContainsKey(printers_, source));
+    printers_[source] = printers;
+    std::vector<Printer> all_printers = GetPrinters();
+    for (PrinterDetector::Observer& observer : observer_list_) {
+      observer.OnPrintersFound(all_printers);
+    }
+  }
+
+  void OnPrinterScanComplete(const ObserverDelegate* source) {
+    DCHECK(base::ContainsKey(printers_, source));
+    bool& scan_done = scan_done_[source];
+    if (!scan_done) {
+      scan_done = true;
+      for (const auto& entry : scan_done_) {
+        if (!entry.second) {
+          // Not all done yet.
+          return;
+        }
+      }
+      // Final outstanding scan just finished, notify observers.
+      for (PrinterDetector::Observer& observer : observer_list_) {
+        observer.OnPrinterScanComplete();
+      }
+    }
+  }
+
+  // Aggregate the printers from all underlying sources and return them.
+  std::vector<Printer> GetPrinters() override {
+    std::vector<Printer> ret;
+    for (const auto& entry : printers_) {
+      ret.insert(ret.end(), entry.second.begin(), entry.second.end());
+    }
+    return ret;
+  }
+
+  void Start() override {
+    for (PrinterDetector* detector : detectors_) {
+      detector->Start();
+    }
+  }
+
+ private:
+  // Map from observer delegate to the most recent list of printers from that
+  // observer.
+  std::map<const ObserverDelegate*, std::vector<Printer>> printers_;
+
+  // Map from observer delegate to whether or not that observer has completed
+  // its scan.
+  std::map<const ObserverDelegate*, bool> scan_done_;
+
+  // Observers of this object.
+  base::ObserverList<PrinterDetector::Observer> observer_list_;
+
+  std::vector<std::unique_ptr<PrinterDetector>> owned_detectors_;
+
+  // Memory management -- this just exists to ensure that the held
+  // elements get cleaned up.
+  std::vector<std::unique_ptr<ObserverDelegate>> delegates_;
+
+  // All detectors used by the combining detector, owned or unowned.
+  std::vector<PrinterDetector*> detectors_;
+};
+
+void ObserverDelegate::OnPrintersFound(const std::vector<Printer>& printers) {
+  parent_->OnPrintersFound(this, printers);
+}
+
+void ObserverDelegate::OnPrinterScanComplete() {
+  parent_->OnPrinterScanComplete(this);
+}
+
+}  // namespace
+
+// static
+std::unique_ptr<CombiningPrinterDetector> CombiningPrinterDetector::Create() {
+  return base::MakeUnique<CombiningPrinterDetectorImpl>();
+}
+
+}  // namespace chromeos