Add unread indicator.

// FREEBIE

Signal.xcodeproj/project.pbxproj

@@ -72,6 +72,9 @@
 		34D5CCB11EAE7E7F005515DB /* SelectRecipientViewController.m in Sources */ = {isa = PBXBuildFile; fileRef = 34D5CCB01EAE7E7F005515DB /* SelectRecipientViewController.m */; };
 		34DFCB851E8E04B500053165 /* AddToBlockListViewController.m in Sources */ = {isa = PBXBuildFile; fileRef = 34DFCB841E8E04B500053165 /* AddToBlockListViewController.m */; };
 		34E3E5681EC4B19400495BAC /* AudioProgressView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 34E3E5671EC4B19400495BAC /* AudioProgressView.swift */; };
+		34F3089C1ECA4CDB00BB7697 /* TSUnreadIndicatorInteraction.m in Sources */ = {isa = PBXBuildFile; fileRef = 34F3089B1ECA4CDB00BB7697 /* TSUnreadIndicatorInteraction.m */; };
+		34F3089F1ECA580B00BB7697 /* OWSUnreadIndicatorCell.m in Sources */ = {isa = PBXBuildFile; fileRef = 34F3089E1ECA580B00BB7697 /* OWSUnreadIndicatorCell.m */; };
+		34F308A21ECB469700BB7697 /* OWSBezierPathView.m in Sources */ = {isa = PBXBuildFile; fileRef = 34F308A11ECB469700BB7697 /* OWSBezierPathView.m */; };
 		34FD93701E3BD43A00109093 /* OWSAnyTouchGestureRecognizer.m in Sources */ = {isa = PBXBuildFile; fileRef = 34FD936F1E3BD43A00109093 /* OWSAnyTouchGestureRecognizer.m */; };
 		450573FE1E78A06D00615BB4 /* OWS103EnableVideoCalling.m in Sources */ = {isa = PBXBuildFile; fileRef = 450573FD1E78A06D00615BB4 /* OWS103EnableVideoCalling.m */; };
 		4505C2BF1E648EA300CEBF41 /* ExperienceUpgrade.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4505C2BE1E648EA300CEBF41 /* ExperienceUpgrade.swift */; };
@@ -472,6 +475,12 @@
 		34DFCB831E8E04B400053165 /* AddToBlockListViewController.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = AddToBlockListViewController.h; sourceTree = "<group>"; };
 		34DFCB841E8E04B500053165 /* AddToBlockListViewController.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = AddToBlockListViewController.m; sourceTree = "<group>"; };
 		34E3E5671EC4B19400495BAC /* AudioProgressView.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AudioProgressView.swift; sourceTree = "<group>"; };
+		34F3089A1ECA4CDB00BB7697 /* TSUnreadIndicatorInteraction.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = TSUnreadIndicatorInteraction.h; sourceTree = "<group>"; };
+		34F3089B1ECA4CDB00BB7697 /* TSUnreadIndicatorInteraction.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = TSUnreadIndicatorInteraction.m; sourceTree = "<group>"; };
+		34F3089D1ECA580B00BB7697 /* OWSUnreadIndicatorCell.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = OWSUnreadIndicatorCell.h; sourceTree = "<group>"; };
+		34F3089E1ECA580B00BB7697 /* OWSUnreadIndicatorCell.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = OWSUnreadIndicatorCell.m; sourceTree = "<group>"; };
+		34F308A01ECB469700BB7697 /* OWSBezierPathView.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = OWSBezierPathView.h; sourceTree = "<group>"; };
+		34F308A11ECB469700BB7697 /* OWSBezierPathView.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = OWSBezierPathView.m; sourceTree = "<group>"; };
 		34FD936E1E3BD43A00109093 /* OWSAnyTouchGestureRecognizer.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = OWSAnyTouchGestureRecognizer.h; path = views/OWSAnyTouchGestureRecognizer.h; sourceTree = "<group>"; };
 		34FD936F1E3BD43A00109093 /* OWSAnyTouchGestureRecognizer.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; name = OWSAnyTouchGestureRecognizer.m; path = views/OWSAnyTouchGestureRecognizer.m; sourceTree = "<group>"; };
 		450573FC1E78A06D00615BB4 /* OWS103EnableVideoCalling.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = OWS103EnableVideoCalling.h; path = Migrations/OWS103EnableVideoCalling.h; sourceTree = "<group>"; };
@@ -1307,6 +1316,8 @@
 				4531C9C21DD8E6D800F08304 /* JSQMessagesCollectionViewCell+OWS.h */,
 				4531C9C31DD8E6D800F08304 /* JSQMessagesCollectionViewCell+OWS.m */,
 				3453D8E91EC0D4ED003F9E6F /* OWSAlerts.swift */,
+				34F308A01ECB469700BB7697 /* OWSBezierPathView.h */,
+				34F308A11ECB469700BB7697 /* OWSBezierPathView.m */,
 				45C681B91D305C080050903A /* OWSCallCollectionViewCell.h */,
 				45C681BA1D305C080050903A /* OWSCallCollectionViewCell.m */,
 				45C681C01D305C9E0050903A /* OWSCallCollectionViewCell.xib */,
@@ -1327,7 +1338,11 @@
 				45F2B1961D9CA207000D2C69 /* OWSOutgoingMessageCollectionViewCell.xib */,
 				34330AA11E79686200DF2FB9 /* OWSProgressView.h */,
 				34330AA21E79686200DF2FB9 /* OWSProgressView.m */,
+				34F3089D1ECA580B00BB7697 /* OWSUnreadIndicatorCell.h */,
+				34F3089E1ECA580B00BB7697 /* OWSUnreadIndicatorCell.m */,
 				45A6DAD51EBBF85500893231 /* ReminderView.swift */,
+				34F3089A1ECA4CDB00BB7697 /* TSUnreadIndicatorInteraction.h */,
+				34F3089B1ECA4CDB00BB7697 /* TSUnreadIndicatorInteraction.m */,
 			);
 			name = Views;
 			path = views;
@@ -2045,6 +2060,7 @@
 				343D3D9B1E9283F100165CA4 /* BlockListUIUtils.m in Sources */,
 				34B3F8931E8DF1710035BE1A /* SignalsNavigationController.m in Sources */,
 				76EB063A18170B33006006FC /* FunctionalUtil.m in Sources */,
+				34F308A21ECB469700BB7697 /* OWSBezierPathView.m in Sources */,
 				76EB058A18170B33006006FC /* Release.m in Sources */,
 				45D231771DC7E8F10034FA89 /* SessionResetJob.swift in Sources */,
 				450873C71D9D867B006B54F2 /* OWSIncomingMessageCollectionViewCell.m in Sources */,
@@ -2074,6 +2090,7 @@
 				45666F561D9B2827008FE134 /* OWSScrubbingLogFormatter.m in Sources */,
 				45C0DC1E1E69011F00E04C47 /* UIStoryboard+OWS.swift in Sources */,
 				45C681C61D305C9E0050903A /* OWSDisplayedMessageCollectionViewCell.m in Sources */,
+				34F3089F1ECA580B00BB7697 /* OWSUnreadIndicatorCell.m in Sources */,
 				34B3F8861E8DF1700035BE1A /* NotificationSettingsOptionsViewController.m in Sources */,
 				452ECA4D1E087E7200E2F016 /* MessageFetcherJob.swift in Sources */,
 				452EA0971EA662330078744B /* AttachmentPointerAdapter.swift in Sources */,
@@ -2158,6 +2175,7 @@
 				34B3F87D1E8DF1700035BE1A /* FullImageViewController.m in Sources */,
 				45666F7B1D9C0533008FE134 /* OWSDatabaseMigration.m in Sources */,
 				B90418E6183E9DD40038554A /* DateUtil.m in Sources */,
+				34F3089C1ECA4CDB00BB7697 /* TSUnreadIndicatorInteraction.m in Sources */,
 				45B201761DAECBFE00C461E0 /* HighlightableLabel.swift in Sources */,
 				459311FC1D75C948008DD4F0 /* OWSDeviceTableViewCell.m in Sources */,
 			);

Signal/src/Models/TSMessageAdapaters/OWSMessageData.h

@@ -15,6 +15,7 @@ typedef NS_ENUM(NSInteger, TSMessageAdapterType) {
     TSErrorMessageAdapter,
     TSMediaAttachmentAdapter,
     TSGenericTextMessageAdapter, // Used when message direction is unknown (outgoing or incoming)
+    TSUnreadIndicatorAdapter,
 };
 
 @protocol OWSMessageData <JSQMessageData, OWSMessageEditing>

Signal/src/Models/TSMessageAdapaters/TSMessageAdapter.m

@@ -2,6 +2,7 @@
 //  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
 //
 
+#import "TSMessageAdapter.h"
 #import "AttachmentSharing.h"
 #import "OWSCall.h"
 #import "Signal-Swift.h"
@@ -16,6 +17,7 @@
 #import "TSIncomingMessage.h"
 #import "TSInfoMessage.h"
 #import "TSOutgoingMessage.h"
+#import "TSUnreadIndicatorInteraction.h"
 #import <MobileCoreServices/MobileCoreServices.h>
 
 NS_ASSUME_NONNULL_BEGIN
@@ -119,6 +121,8 @@ NS_ASSUME_NONNULL_BEGIN
             adapter.senderDisplayName = NSLocalizedString(@"ME_STRING", @"");
             adapter.messageType       = TSOutgoingMessageAdapter;
         }
+    } else {
+        OWSAssert(0);
     }
 
     if ([interaction isKindOfClass:[TSIncomingMessage class]] ||
@@ -216,11 +220,15 @@ NS_ASSUME_NONNULL_BEGIN
                                                    displayString:@""];
             return call;
         }
-    } else {
+    } else if ([interaction isKindOfClass:[TSUnreadIndicatorInteraction class]]) {
+        adapter.messageType = TSUnreadIndicatorAdapter;
+    } else if ([interaction isKindOfClass:[TSErrorMessage class]]) {
         TSErrorMessage *errorMessage = (TSErrorMessage *)interaction;
         adapter.errorMessageType = errorMessage.errorType;
         adapter.messageBody          = errorMessage.description;
         adapter.messageType          = TSErrorMessageAdapter;
+    } else {
+        OWSAssert(0);
     }
 
     if ([interaction isKindOfClass:[TSOutgoingMessage class]]) {

Signal/src/ViewControllers/MessagesViewController.m

@@ -27,6 +27,7 @@
 #import "OWSMessagesBubblesSizeCalculator.h"
 #import "OWSOutgoingMessageCollectionViewCell.h"
 #import "OWSUnknownContactBlockOfferMessage.h"
+#import "OWSUnreadIndicatorCell.h"
 #import "PropertyListPreferences.h"
 #import "Signal-Swift.h"
 #import "SignalKeyingStorage.h"
@@ -707,6 +708,8 @@ typedef enum : NSUInteger {
     _composeOnOpen = keyboardOnViewAppearing;
     _callOnOpen = callOnViewAppearing;
 
+    [ThreadUtil createUnreadMessagesIndicatorIfNecessary:thread storageManager:self.storageManager];
+
     [self markAllMessagesAsRead];
 
     [self.uiDatabaseConnection beginLongLivedReadTransaction];
@@ -813,6 +816,9 @@ typedef enum : NSUInteger {
     [self.collectionView registerNib:[OWSCallCollectionViewCell nib]
           forCellWithReuseIdentifier:[OWSCallCollectionViewCell cellReuseIdentifier]];
 
+    [self.collectionView registerClass:[OWSUnreadIndicatorCell class]
+            forCellWithReuseIdentifier:[OWSUnreadIndicatorCell cellReuseIdentifier]];
+
     [self.collectionView registerNib:[OWSDisplayedMessageCollectionViewCell nib]
           forCellWithReuseIdentifier:[OWSDisplayedMessageCollectionViewCell cellReuseIdentifier]];
 
@@ -1685,6 +1691,9 @@ typedef enum : NSUInteger {
         case TSOutgoingMessageAdapter: {
             cell = [self loadOutgoingCellForMessage:message atIndexPath:indexPath];
         } break;
+        case TSUnreadIndicatorAdapter: {
+            cell = [self loadUnreadIndicatorCell:indexPath];
+        } break;
         default: {
             DDLogWarn(@"using default cell constructor for message: %@", message);
             cell = (JSQMessagesCollectionViewCell *)[super collectionView:collectionView cellForItemAtIndexPath:indexPath];
@@ -1712,6 +1721,7 @@ typedef enum : NSUInteger {
 
     if (![cell isKindOfClass:[OWSIncomingMessageCollectionViewCell class]]) {
         DDLogError(@"%@ Unexpected cell type: %@", self.tag, cell);
+        OWSAssert(0);
         return cell;
     }
 
@@ -1732,6 +1742,7 @@ typedef enum : NSUInteger {
 
     if (![cell isKindOfClass:[OWSOutgoingMessageCollectionViewCell class]]) {
         DDLogError(@"%@ Unexpected cell type: %@", self.tag, cell);
+        OWSAssert(0);
         return cell;
     }
 
@@ -1752,6 +1763,18 @@ typedef enum : NSUInteger {
     return cell;
 }
 
+- (JSQMessagesCollectionViewCell *)loadUnreadIndicatorCell:(NSIndexPath *)indexPath
+{
+    OWSAssert(indexPath);
+
+    OWSUnreadIndicatorCell *cell =
+        [self.collectionView dequeueReusableCellWithReuseIdentifier:[OWSUnreadIndicatorCell cellReuseIdentifier]
+                                                       forIndexPath:indexPath];
+    [cell configure];
+
+    return cell;
+}
+
 - (OWSCallCollectionViewCell *)loadCallCellForCall:(OWSCall *)call atIndexPath:(NSIndexPath *)indexPath
 {
     OWSCallCollectionViewCell *callCell = [self.collectionView dequeueReusableCellWithReuseIdentifier:[OWSCallCollectionViewCell cellReuseIdentifier]
@@ -2222,6 +2245,7 @@ typedef enum : NSUInteger {
             [self handleErrorMessageTap:(TSErrorMessage *)interaction];
             break;
         case TSCallAdapter:
+        case TSUnreadIndicatorAdapter:
             break;
         default:
             DDLogDebug(@"Unhandled bubble touch for interaction: %@.", interaction);

Signal/src/util/ThreadUtil.h

@@ -27,6 +27,8 @@ NS_ASSUME_NONNULL_BEGIN
                     contactsManager:(OWSContactsManager *)contactsManager
                     blockingManager:(OWSBlockingManager *)blockingManager;
 
++ (void)createUnreadMessagesIndicatorIfNecessary:(TSThread *)thread storageManager:(TSStorageManager *)storageManager;
+
 @end
 
 NS_ASSUME_NONNULL_END

Signal/src/util/ThreadUtil.m

@@ -5,6 +5,7 @@
 #import "ThreadUtil.h"
 #import "OWSContactsManager.h"
 #import "Signal-Swift.h"
+#import "TSUnreadIndicatorInteraction.h"
 #import <SignalServiceKit/NSDate+millisecondTimeStamp.h>
 #import <SignalServiceKit/OWSBlockingManager.h>
 #import <SignalServiceKit/OWSDisappearingMessagesConfiguration.h>
@@ -178,6 +179,58 @@ NS_ASSUME_NONNULL_BEGIN
     }];
 }
 
++ (void)createUnreadMessagesIndicatorIfNecessary:(TSThread *)thread storageManager:(TSStorageManager *)storageManager
+{
+    OWSAssert(thread);
+    OWSAssert(storageManager);
+
+    [storageManager.dbConnection readWriteWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
+
+        NSMutableArray *indicators = [NSMutableArray new];
+        __block TSMessage *firstUnreadMessage = nil;
+        // TODO: Will this approach be prohibitively expensive?
+        [[transaction ext:TSMessageDatabaseViewExtensionName]
+            enumerateRowsInGroup:thread.uniqueId
+                      usingBlock:^(
+                          NSString *collection, NSString *key, id object, id metadata, NSUInteger index, BOOL *stop) {
+
+                          if ([object isKindOfClass:[TSUnreadIndicatorInteraction class]]) {
+                              [indicators addObject:object];
+                          } else if ([object isKindOfClass:[TSIncomingMessage class]]) {
+                              TSIncomingMessage *incomingMessage = (TSIncomingMessage *)object;
+                              if (!incomingMessage.wasRead) {
+                                  if (!firstUnreadMessage) {
+                                      firstUnreadMessage = incomingMessage;
+                                  } else {
+                                      OWSAssert([[firstUnreadMessage receiptDateForSorting]
+                                                    compare:[incomingMessage receiptDateForSorting]]
+                                          == NSOrderedAscending);
+                                  }
+                              }
+                          }
+                      }];
+
+        for (TSUnreadIndicatorInteraction *indicator in indicators) {
+            [indicator removeWithTransaction:transaction];
+        }
+
+        BOOL shouldHaveIndicator = firstUnreadMessage != nil;
+        if (!shouldHaveIndicator) {
+            return;
+        }
+
+        DDLogInfo(@"%@ Creating TSUnreadIndicatorInteraction", self.tag);
+
+        // We want the block offer to appear just before the first unread incoming
+        // message in the conversation timeline.
+        uint64_t indicatorTimestamp = firstUnreadMessage.timestamp - 1;
+
+        TSUnreadIndicatorInteraction *indicator =
+            [[TSUnreadIndicatorInteraction alloc] initWithTimestamp:indicatorTimestamp thread:thread];
+        [indicator saveWithTransaction:transaction];
+    }];
+}
+
 #pragma mark - Logging
 
 + (NSString *)tag

Signal/src/views/OWSBezierPathView.h

@@ -0,0 +1,22 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+typedef void (^ConfigureShapeLayerBlock)(CAShapeLayer *layer, CGRect bounds);
+
+@interface OWSBezierPathView : UIView
+
+// Configure the view with this method if it uses a single Bezier path.
+- (void)setConfigureShapeLayerBlock:(ConfigureShapeLayerBlock)configureShapeLayerBlock;
+
+// Configure the view with this method if it uses multiple Bezier paths.
+//
+// Paths will be rendered in back-to-front order.
+- (void)setConfigureShapeLayerBlocks:(NSArray<ConfigureShapeLayerBlock> *)configureShapeLayerBlocks;
+
+// This method forces the view to reconstruct its layer content.  It shouldn't
+// be necessary to call this unless the ConfigureShapeLayerBlocks depend on external
+// state which has changed.
+- (void)updateLayers;
+
+@end

Signal/src/views/OWSBezierPathView.m

@@ -0,0 +1,110 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+#import "OWSBezierPathView.h"
+
+@interface OWSBezierPathView ()
+
+@property (nonatomic) NSArray<ConfigureShapeLayerBlock> *configureShapeLayerBlocks;
+
+@end
+
+@implementation OWSBezierPathView
+
+- (id)init
+{
+    self = [super init];
+    if (self) {
+        [self initCommon];
+    }
+
+    return self;
+}
+
+- (id)initWithFrame:(CGRect)frame
+{
+    self = [super initWithFrame:frame];
+    if (self) {
+        [self initCommon];
+    }
+    return self;
+}
+
+- (void)initCommon
+{
+    self.opaque = NO;
+    self.userInteractionEnabled = NO;
+    self.backgroundColor = [UIColor clearColor];
+}
+
+- (void)setFrame:(CGRect)frame
+{
+    BOOL didChangeSize = !CGSizeEqualToSize(frame.size, self.frame.size);
+
+    [super setFrame:frame];
+
+    if (didChangeSize) {
+        [self updateLayers];
+    }
+}
+
+- (void)setBounds:(CGRect)bounds
+{
+    BOOL didChangeSize = !CGSizeEqualToSize(bounds.size, self.bounds.size);
+
+    [super setBounds:bounds];
+
+    if (didChangeSize) {
+        [self updateLayers];
+    }
+}
+
+- (void)setConfigureShapeLayerBlock:(ConfigureShapeLayerBlock)configureShapeLayerBlock
+{
+    OWSAssert(configureShapeLayerBlock);
+
+    [self setConfigureShapeLayerBlocks:@[ configureShapeLayerBlock ]];
+}
+
+- (void)setConfigureShapeLayerBlocks:(NSArray<ConfigureShapeLayerBlock> *)configureShapeLayerBlocks
+{
+    OWSAssert(configureShapeLayerBlocks.count > 0);
+
+    _configureShapeLayerBlocks = configureShapeLayerBlocks;
+
+    [self updateLayers];
+}
+
+- (void)updateLayers
+{
+    if (self.bounds.size.width <= 0.f || self.bounds.size.height <= 0.f) {
+        return;
+    }
+
+    for (CALayer *layer in self.layer.sublayers) {
+        [layer removeFromSuperlayer];
+    }
+
+    for (ConfigureShapeLayerBlock configureShapeLayerBlock in self.configureShapeLayerBlocks) {
+        CAShapeLayer *shapeLayer = [CAShapeLayer new];
+        configureShapeLayerBlock(shapeLayer, self.bounds);
+        [self.layer addSublayer:shapeLayer];
+    }
+
+    [self setNeedsDisplay];
+}
+
+#pragma mark - Logging
+
++ (NSString *)tag
+{
+    return [NSString stringWithFormat:@"[%@]", self.class];
+}
+
+- (NSString *)tag
+{
+    return self.class.tag;
+}
+
+@end

Signal/src/views/OWSUnreadIndicatorCell.h

@@ -0,0 +1,12 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+#import <JSQMessagesViewController/JSQMessagesCollectionViewCell.h>
+#import <UIKit/UIKit.h>
+
+@interface OWSUnreadIndicatorCell : JSQMessagesCollectionViewCell
+
+- (void)configure;
+
+@end

Signal/src/views/OWSUnreadIndicatorCell.m

@@ -0,0 +1,77 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+#import "OWSUnreadIndicatorCell.h"
+#import "OWSBezierPathView.h"
+#import "UIColor+OWS.h"
+#import "UIFont+OWS.h"
+#import <JSQMessagesViewController/UIView+JSQMessages.h>
+
+@interface OWSUnreadIndicatorCell ()
+
+@property (nonatomic) UILabel *label;
+@property (nonatomic) OWSBezierPathView *leftPathView;
+@property (nonatomic) OWSBezierPathView *rightPathView;
+
+@end
+
+#pragma mark -
+
+@implementation OWSUnreadIndicatorCell
+
++ (NSString *)cellReuseIdentifier
+{
+    return NSStringFromClass([self class]);
+}
+
+- (void)configure
+{
+    self.backgroundColor = [UIColor whiteColor];
+
+    if (!self.label) {
+        self.label = [UILabel new];
+        self.label.text = NSLocalizedString(
+            @"MESSAGES_VIEW_UNREAD_INDICATOR", @"Indicator that separates read from unread messages.");
+        self.label.textColor = [UIColor ows_infoMessageBorderColor];
+        self.label.font = [UIFont ows_mediumFontWithSize:12.f];
+        [self.contentView addSubview:self.label];
+
+        CGFloat kLineThickness = 0.5f;
+        CGFloat kLineMargin = 5.f;
+        ConfigureShapeLayerBlock configureShapeLayerBlock = ^(CAShapeLayer *layer, CGRect bounds) {
+            OWSCAssert(layer);
+
+            CGRect pathBounds
+                = CGRectMake(0, (bounds.size.height - kLineThickness) * 0.5f, bounds.size.width, kLineThickness);
+            pathBounds = CGRectInset(pathBounds, kLineMargin, 0);
+            UIBezierPath *path = [UIBezierPath bezierPathWithRect:pathBounds];
+            layer.path = path.CGPath;
+            layer.fillColor = [UIColor ows_infoMessageBorderColor].CGColor;
+        };
+
+        self.leftPathView = [OWSBezierPathView new];
+        self.leftPathView.configureShapeLayerBlock = configureShapeLayerBlock;
+        [self.contentView addSubview:self.leftPathView];
+
+        self.rightPathView = [OWSBezierPathView new];
+        self.rightPathView.configureShapeLayerBlock = configureShapeLayerBlock;
+        [self.contentView addSubview:self.rightPathView];
+    }
+}
+
+- (void)layoutSubviews
+{
+    CGSize labelSize = [self.label sizeThatFits:CGSizeZero];
+    self.label.frame = CGRectMake(round(self.bounds.origin.x + (self.bounds.size.width - labelSize.width) * 0.5f),
+        round(self.bounds.origin.y + (self.bounds.size.height - labelSize.height) * 0.5f),
+        labelSize.width,
+        labelSize.height);
+    self.leftPathView.frame = CGRectMake(0, 0, self.label.frame.origin.x, self.bounds.size.height);
+    self.rightPathView.frame = CGRectMake(self.label.frame.origin.x + self.label.frame.size.width,
+        0,
+        self.bounds.size.width - (self.label.frame.origin.x + self.label.frame.size.width),
+        self.bounds.size.height);
+}
+
+@end

Signal/src/views/TSUnreadIndicatorInteraction.h

@@ -0,0 +1,17 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+#import "TSMessage.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface TSUnreadIndicatorInteraction : TSMessage
+
+- (instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;
+
+- (instancetype)initWithTimestamp:(uint64_t)timestamp thread:(TSThread *)thread NS_DESIGNATED_INITIALIZER;
+
+@end
+
+NS_ASSUME_NONNULL_END

Signal/src/views/TSUnreadIndicatorInteraction.m

@@ -0,0 +1,44 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+#import "TSUnreadIndicatorInteraction.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@implementation TSUnreadIndicatorInteraction
+
+- (instancetype)initWithCoder:(NSCoder *)coder
+{
+    return [super initWithCoder:coder];
+}
+
+- (instancetype)initWithTimestamp:(uint64_t)timestamp thread:(TSThread *)thread
+{
+    self = [super initWithTimestamp:timestamp
+                           inThread:thread
+                        messageBody:nil
+                      attachmentIds:@[]
+                   expiresInSeconds:0
+                    expireStartedAt:0];
+
+    if (!self) {
+        return self;
+    }
+
+    return self;
+}
+
+- (nullable NSDate *)receiptDateForSorting
+{
+    // Always use date, since we're creating these interactions after the fact
+    // and back-dating them.
+    //
+    // By default [TSMessage receiptDateForSorting] will prefer to use receivedAtDate
+    // which is not back-dated.
+    return self.date;
+}
+
+@end
+
+NS_ASSUME_NONNULL_END

Signal/translations/en.lproj/Localizable.strings

@@ -700,6 +700,9 @@
 /* The subtitle for the messages view title indicates that the title can be tapped to access settings for this conversation. */
 "MESSAGES_VIEW_TITLE_SUBTITLE" = "Tap here for settings";
 
+/* Indicator that separates read from unread messages. */
+"MESSAGES_VIEW_UNREAD_INDICATOR" = "Unread Messages";
+
 /* {{number of minutes}} embedded in strings, e.g. 'Alice updated disappearing messages expiration to {{5 minutes}}'. See other *_TIME_AMOUNT strings */
 "MINUTES_TIME_AMOUNT" = "%u minutes";