fix(exports): interpret PN tags as union between object and string (#364

)

* chore: format codebase

yarn run format

* fix(exports): interpret PN tags as union between object and string

the JSON standard represents PeopleNames as an object, rather than a delineated string.  this caused SRs derived
from metadata to have [object Object] for the patient name, notable in Google's Healthcare dicom store, which
seems to pick a random patient name when searching for series. much of the change is attempting to communicate
this union somewhat opaquely, and ensuring objects with additional properties aren't destroyed when being
naturalized. tested with OHIF master branch.

* fix(exports): add SR to test PN tags

Since the sample dcm has image data in it, and we don't support serializing
InlineBinary, I've added a simple SR derived from a TCIA frame for testing.

Adds test for equality between the SR dcm and the same SR recreated from the
json equivalent.

* refactor: 💡 move PersonName code into functions

for easier testing and cleanliness

* feat: 🎸 add value multiplicity to PersonName tags

And also adds the concept of tag and value accessors to
ValueRepresentation. Whenever a tag is created, it is assigned to a
Proxy which allows values to be represented differently according to
whether it's being output to JSON or being interacted with. This allows
a user to assign a string to a PN tag, and have that tag be output as a
JSON object conformant to spec.

* test: 💍 separate PersonName multiplicity test

* refactor: 💡 make proxy handler static, update comments

src/DicomDict.js

@@ -1,5 +1,6 @@
 import { WriteBufferStream } from "./BufferStream";
 import { DicomMessage } from "./DicomMessage";
+import { ValueRepresentation } from "./ValueRepresentation";
 
 const EXPLICIT_LITTLE_ENDIAN = "1.2.840.10008.1.2.1";
 
@@ -11,9 +12,11 @@ class DicomDict {
 
     upsertTag(tag, vr, values) {
         if (this.dict[tag]) {
+            // Should already have tag accessors.
             this.dict[tag].Value = values;
         } else {
-            this.dict[tag] = { vr: vr, Value: values };
+            this.dict[tag] = ValueRepresentation.addTagAccessors({ vr: vr });
+            this.dict[tag].Value = values;
         }
     }
 

src/DicomMessage.js

@@ -3,8 +3,9 @@ import {
     DEFLATED_EXPLICIT_LITTLE_ENDIAN,
     EXPLICIT_BIG_ENDIAN,
     EXPLICIT_LITTLE_ENDIAN,
-    IMPLICIT_LITTLE_ENDIAN
-} from "./constants/dicom";
+    IMPLICIT_LITTLE_ENDIAN,
+    VM_DELIMITER
+} from "./constants/dicom.js";
 import { DicomDict } from "./DicomDict.js";
 import { DicomMetaDictionary } from "./DicomMetaDictionary.js";
 import { Tag } from "./Tag.js";
@@ -147,10 +148,11 @@ class DicomMessage {
                     }
                     readInfo.values = ["ISO_IR 192"]; // change SpecificCharacterSet to UTF-8
                 }
-                dict[cleanTagString] = {
-                    vr: readInfo.vr.type,
-                    Value: readInfo.values
-                };
+
+                dict[cleanTagString] = ValueRepresentation.addTagAccessors({
+                    vr: readInfo.vr.type
+                });
+                dict[cleanTagString].Value = readInfo.values;
 
                 if (untilTag && untilTag === cleanTagString) {
                     break;
@@ -334,7 +336,7 @@ class DicomMessage {
             if (!vr.isBinary() && singleVRs.indexOf(vr.type) == -1) {
                 values = val;
                 if (typeof val === "string") {
-                    values = val.split(String.fromCharCode(0x5c));
+                    values = val.split(String.fromCharCode(VM_DELIMITER));
                 }
             } else if (vr.type == "SQ") {
                 values = val;
@@ -346,7 +348,12 @@ class DicomMessage {
         }
         stream.setEndian(oldEndian);
 
-        return { tag: tag, vr: vr, values: values };
+        const retObj = ValueRepresentation.addTagAccessors({
+            tag: tag,
+            vr: vr
+        });
+        retObj.values = values;
+        return retObj;
     }
 
     static lookupTag(tag) {

src/DicomMetaDictionary.js

@@ -2,6 +2,7 @@ import dictionary from "./dictionary";
 import log from "./log.js";
 import addAccessors from "./utilities/addAccessors";
 import { ValueRepresentation } from "./ValueRepresentation";
+import dicomJson from "./utilities/dicomJson";
 
 class DicomMetaDictionary {
     // intakes a custom dictionary that will be used to parse/denaturalize the dataset
@@ -109,9 +110,9 @@ class DicomMetaDictionary {
      * - object member names are dictionary, not group/element tag
      */
     static naturalizeDataset(dataset) {
-        const naturalDataset = {
+        const naturalDataset = ValueRepresentation.addTagAccessors({
             _vrMap: {}
-        };
+        });
 
         Object.keys(dataset).forEach(tag => {
             const data = dataset[tag];
@@ -176,6 +177,7 @@ class DicomMetaDictionary {
                 }
             }
         });
+
         return naturalDataset;
     }
 
@@ -193,9 +195,11 @@ class DicomMetaDictionary {
                 );
             }
         }
+
         value = value.map(entry =>
             entry.constructor.name == "Number" ? String(entry) : entry
         );
+
         return value;
     }
 
@@ -214,10 +218,10 @@ class DicomMetaDictionary {
                     return;
                 }
                 // process this one entry
-                var dataItem = {
-                    vr: entry.vr,
-                    Value: dataset[naturalName]
-                };
+                var dataItem = ValueRepresentation.addTagAccessors({
+                    vr: entry.vr
+                });
+                dataItem.Value = dataset[naturalName];
 
                 if (dataValue !== null) {
                     if (entry.vr == "ox") {
@@ -231,6 +235,10 @@ class DicomMetaDictionary {
                         }
                     }
 
+                    let vr = ValueRepresentation.createByTypeString(
+                        dataItem.vr
+                    );
+
                     dataItem.Value = DicomMetaDictionary.denaturalizeValue(
                         dataItem.Value
                     );
@@ -252,9 +260,7 @@ class DicomMetaDictionary {
                         }
                         dataItem.Value = unnaturalValues;
                     }
-                    let vr = ValueRepresentation.createByTypeString(
-                        dataItem.vr
-                    );
+
                     if (!vr.isBinary() && vr.maxLength) {
                         dataItem.Value = dataItem.Value.map(value => {
                             if (value.length > vr.maxLength) {