From 9137eca2e7809690bb4e86e9e1bd44dc00dd734f Mon Sep 17 00:00:00 2001
From: jahorton <jahorton@sil.org>
Date: Mon, 22 Jul 2019 11:53:25 +0700
Subject: [PATCH] Null-context suggestion whitespace preservation

---
 common/predictive-text/worker/model-compositor.ts | 15 +++++++++++++++
 common/predictive-text/worker/models/common.ts    |  8 ++++++++
 2 files changed, 23 insertions(+)

diff --git a/common/predictive-text/worker/model-compositor.ts b/common/predictive-text/worker/model-compositor.ts
index dbf6204c75..ab6faeb634 100644
--- a/common/predictive-text/worker/model-compositor.ts
+++ b/common/predictive-text/worker/model-compositor.ts
@@ -58,8 +58,17 @@ class ModelCompositor {
       } else if(this.isBackspace(transform) && !allowBksp) {
         continue;
       }
+
+      let preserveWhitespace: boolean = false;
+      if(this.isWhitespace(transform)) {
+        // Detect start of new word; prevent whitespace loss here.
+        let postContext = models.applyTransform(transform, context);
+        preserveWhitespace = (this.lexicalModel.wordbreak(postContext) == '');
+      }
+
       let distribution = this.lexicalModel.predict(transform, context);
 
+      let mc = this;
       distribution.forEach(function(pair: ProbabilityMass<Suggestion>) {
         // Let's not rely on the model to copy transform IDs.
         // Only bother is there IS an ID to copy.
@@ -67,6 +76,12 @@ class ModelCompositor {
           pair.sample.transformId = transform.id;
         }
 
+        // Prepends the original whitespace, ensuring it is preserved if
+        // the suggestion is accepted.
+        if(preserveWhitespace) {
+          models.prependTransform(pair.sample.transform, transform);
+        }
+
         // Combine duplicate samples.
         let displayText = pair.sample.displayAs;
 
diff --git a/common/predictive-text/worker/models/common.ts b/common/predictive-text/worker/models/common.ts
index 12c9a995ad..309c8a53e9 100644
--- a/common/predictive-text/worker/models/common.ts
+++ b/common/predictive-text/worker/models/common.ts
@@ -20,4 +20,12 @@ namespace models {
       endOfBuffer: context.endOfBuffer
     };
   }
+
+  export function prependTransform(transform: Transform, prefix: Transform) {
+    transform.insert = prefix.insert + transform.insert;
+    transform.deleteLeft += prefix.deleteLeft;
+    if(prefix.deleteRight) {
+      transform.deleteRight = (transform.deleteRight || 0) + prefix.deleteRight;
+    }
+  }
 }
\ No newline at end of file