code refactor

src/core/file.ts

@@ -1,3 +1,39 @@
+export class KnownFileType {
+    private static readonly allInstancesByExtension: Record<string, KnownFileType> = {};
+
+    public static readonly CSV = new KnownFileType('csv', 'text/csv');
+    public static readonly TSV = new KnownFileType('tsv', 'text/tab-separated-values');
+    public static readonly MARKDOWN = new KnownFileType('md', 'text/markdown');
+
+    public readonly extension: string;
+    public readonly contentType: string;
+
+    private constructor(extension: string, contentType: string) {
+        this.extension = extension;
+        this.contentType = contentType;
+
+        KnownFileType.allInstancesByExtension[extension] = this;
+    }
+
+    public formatFileName(fileName: string): string {
+        if (fileName.endsWith(`.${this.extension}`)) {
+            return fileName;
+        }
+
+        return `${fileName}.${this.extension}`;
+    }
+
+    public createBlob(content: string): Blob {
+        return new Blob([content], {
+            type: this.contentType,
+        });
+    }
+
+    public static parse(extension: string): KnownFileType | undefined {
+        return KnownFileType.allInstancesByExtension[extension];
+    }
+}
+
 export interface ImportFileTypeAndExtensions {
     readonly type: string;
     readonly extensions?: string;