feat(Image): use Map for metadata member

Better interface with `has` that is more appropriate for key/value
pairs of the itk::MetaDataDictionary.

BREAKING_CHANGE: Image.metadata is now a Map instead of an Object

doc/content/api/Image.md

@@ -10,6 +10,7 @@ An `Image` is the N-dimensional image data structure for *itk-wasm*. `Image` is
 **direction**: A *dimension* by *dimension* Float64Array in column-major order, that describes the orientation of the image at its *origin*.  The orientation of each axis are the orthonormal columns.
 **size**: An Array with length *dimension* that contains the number of pixels along dimension.
 **data**: A [TypedArray](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray) containing the pixel buffer data.
+**metadata**: A [Map](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) of string keys to values that could be strings, string arrays, numbers, number arrays, or arrays of number arrays providing additional metadata for the image.
 
 For more information, see [the description](https://itk.org/ITKSoftwareGuide/html/Book1/ITKSoftwareGuide-Book1ch4.html#x38-490004.1) of an `itk::Image` in the ITK Software Guide.
 

src/core/Image.ts

@@ -1,6 +1,7 @@
 import ImageType from './ImageType.js'
 import type TypedArray from './TypedArray.js'
 import setMatrixElement from './setMatrixElement.js'
+import Metadata from './Metadata.js'
 
 class Image {
   name: string = 'image'
@@ -13,7 +14,7 @@ class Image {
 
   size: number[]
 
-  metadata: Record<string, string | string[] | number | number[] | number[][]>
+  metadata: Metadata
 
   data: null | TypedArray
 
@@ -34,7 +35,7 @@ class Image {
     this.size = new Array(dimension)
     this.size.fill(0)
 
-    this.metadata = {}
+    this.metadata = new Map()
 
     this.data = null
   }

src/core/Metadata.ts

@@ -0,0 +1,3 @@
+type Metadata = Map<string, string | string[] | number | number[] | number[][]>
+
+export default Metadata

src/core/castImage.ts

@@ -30,7 +30,8 @@ function castImage (inputImage: Image, options?: CastImageOptions): Image {
   outputImage.spacing = Array.from(inputImage.spacing)
   outputImage.direction = inputImage.direction.slice()
   outputImage.size = Array.from(inputImage.size)
-  outputImage.metadata = { ...inputImage.metadata }
+  // Deep copy the map
+  outputImage.metadata = new Map(JSON.parse(JSON.stringify(Array.from(inputImage.metadata))))
 
   if (inputImage.data !== null) {
     if (typeof options !== 'undefined' && typeof options.componentType !== 'undefined' && options.componentType !== inputImage.imageType.componentType) {

src/core/index.ts

@@ -14,6 +14,7 @@ export { default as JsonObject } from './JsonObject.js'
 export { default as TypedArray } from './TypedArray.js'
 export { default as IntTypes } from './IntTypes.js'
 export { default as FloatTypes } from './FloatTypes.js'
+export { default as Metadata } from './Metadata.js'
 
 export { default as IOTypes } from './IOTypes.js'
 

src/io/readImageDICOMArrayBufferSeries.ts

@@ -1,5 +1,6 @@
 import createWebWorkerPromise from '../core/internal/createWebWorkerPromise.js'
 import WorkerPool from '../core/WorkerPool.js'
+import Metadata from '../core/Metadata.js'
 import stackImages from '../core/stackImages.js'
 import BinaryFile from '../core/BinaryFile.js'
 import InterfaceTypes from '../core/InterfaceTypes.js'
@@ -63,12 +64,11 @@ const workerFunction = async (
   filenames?.pop()
 
   if (image.metadata === undefined) {
-    const metadata:
-    Record<string, string | string[] | number | number[] | number[][]> = {}
-    metadata.orderedFileNames = filenames
+    const metadata: Metadata = new Map()
+    metadata.set('OrderedFileNames', filenames)
     image.metadata = metadata
   } else {
-    image.metadata.orderedFileNames = filenames
+    image.metadata.set('OrderedFileNames', filenames)
   }
 
   return { image: result.outputs[0].data as Image, webWorker: worker }

src/pipeline/internal/runPipelineEmscripten.ts

@@ -123,7 +123,8 @@ function runPipelineEmscripten (pipelineModule: PipelineEmscriptenModule, args:
             spacing: image.spacing,
             direction: `data:application/vnd.itk.address,0:${directionPtr}`,
             size: image.size,
-            data: `data:application/vnd.itk.address,0:${dataPtr}`
+            data: `data:application/vnd.itk.address,0:${dataPtr}`,
+            metadata: JSON.stringify(Array.from(image.metadata.entries()))
           }
           setPipelineModuleInputJSON(pipelineModule, imageJSON, index)
           break
@@ -353,6 +354,7 @@ function runPipelineEmscripten (pipelineModule: PipelineEmscriptenModule, args:
           const image = getPipelineModuleOutputJSON(pipelineModule, index) as Image
           image.data = getPipelineModuleOutputArray(pipelineModule, index, 0, image.imageType.componentType)
           image.direction = getPipelineModuleOutputArray(pipelineModule, index, 1, FloatTypes.Float64) as Float64Array
+          image.metadata = new Map(image.metadata)
           outputData = image
           break
         }