fix: project's package.json indentation is not persisted

In case project's package.json uses tabs or multiple spaces for indentation, the postinstall script of nativescript-dev-webpack overwrites it with two spaces whenever it is executed.
The problem is that the plugin tries to modify the package.json and persists it on every operation.
Fix the behavior by checking the indentation character and use it when stringifying the content.
Also compare the current content of the file with the one we will write and skip the write operation in case they match.
Add unit tests for the new methods.

Author: rosen-vladimirov

Diff for: .gitignore

@@ -32,3 +32,5 @@ jasmine-config/reporter.js.map
 
 hooks
 .DS_Store
+
+!projectHelpers.spec.js

Diff for: jasmine-config/jasmine.json

@@ -1,7 +1,8 @@
 {
   "spec_dir": ".",
   "spec_files": [
-    "./!(node_modules)/**/*.spec.js"
+	"./!(node_modules)/**/*.spec.js",
+	"./*.spec.js"
   ],
   "helpers": [
     "jasmine-config/**/*.js"

Diff for: projectHelpers.js

@@ -1,5 +1,5 @@
 const { resolve } = require("path");
-const { readFileSync, writeFileSync } = require("fs");
+const fs = require("fs");
 
 const hook = require("nativescript-hook")(__dirname);
 
@@ -38,13 +38,27 @@ const isVue = ({ projectDir, packageJson } = {}) => {
 
 const getPackageJson = projectDir => {
     const packageJsonPath = getPackageJsonPath(projectDir);
-    return JSON.parse(readFileSync(packageJsonPath, "utf8"));
+    return JSON.parse(fs.readFileSync(packageJsonPath, "utf8"));
 };
 
 const writePackageJson = (content, projectDir) => {
     const packageJsonPath = getPackageJsonPath(projectDir);
-    writeFileSync(packageJsonPath, JSON.stringify(content, null, 2))
+    const currentJsonContent = fs.readFileSync(packageJsonPath);
+    const indentation = getIndentationCharacter(currentJsonContent);
+    const stringifiedContent = JSON.stringify(content, null, indentation);
+    const currentPackageJsonContent = JSON.parse(currentJsonContent);
+
+    if (JSON.stringify(currentPackageJsonContent, null, indentation) !== stringifiedContent) {
+        fs.writeFileSync(packageJsonPath, stringifiedContent)
+    }
 }
+
+const getIndentationCharacter = (jsonContent) => {
+    const defaultIndentation = "  ";
+    const matches = jsonContent.match(/{\r*\n*(\W*)"/m);
+    return matches && matches[1];
+}
+
 const getProjectDir = hook.findProjectDir;
 
 const getPackageJsonPath = projectDir => resolve(projectDir, "package.json");
@@ -96,5 +110,6 @@ module.exports = {
     isVue,
     isTypeScript,
     writePackageJson,
-    convertSlashesInPath
+    convertSlashesInPath,
+    getIndentationCharacter
 };

Diff for: projectHelpers.spec.js

@@ -0,0 +1,105 @@
+const { getIndentationCharacter, writePackageJson } = require("./projectHelpers");
+const fs = require("fs");
+
+describe('projectHelpers', () => {
+    const originalReadFileSync = fs.readFileSync;
+    const originalWriteFileSync = fs.writeFileSync;
+    const tab = "\t";
+    const multipleSpaces = "        ";
+    const twoSpaces = "  ";
+
+    afterEach(() => {
+        fs.readFileSync = originalReadFileSync;
+        fs.writeFileSync = originalWriteFileSync;
+    });
+
+    describe('getIndentationCharacter', () => {
+        [
+            {
+                testName: 'returns two spaces when file starts with two spaces',
+                input: `{${twoSpaces}"abc": "1"${twoSpaces}}`,
+                expectedResult: twoSpaces
+            },
+            {
+                testName: 'returns empty string when file starts without any indentation',
+                input: `{"abc": "1"}`,
+                expectedResult: ''
+            },
+            {
+                testName: 'returns tab when file starts with tab',
+                input: `{${tab}"abc": "1"${tab}}`,
+                expectedResult: tab
+            },
+            {
+                testName: 'returns two spaces when file starts with two spaces and new line before them',
+                input: `{\n${twoSpaces}"abc": "1"\n}`,
+                expectedResult: twoSpaces
+            },
+            {
+                testName: 'returns tab when file starts with tab and new line before them',
+                input: `{\n${tab}"abc": "1"\n}`,
+                expectedResult: tab
+            },
+            {
+                testName: 'returns multiple spaces when file starts with multiple spaces and new line before them',
+                input: `{\n${multipleSpaces}"abc": "1"\n}`,
+                expectedResult: multipleSpaces
+            }
+        ].forEach(({ testName, input, expectedResult }) => {
+            it(testName, () => {
+                expect(getIndentationCharacter(input)).toEqual(expectedResult);
+            });
+        });
+    });
+
+    describe('writePackageJson', () => {
+        const mockFileSystemApi = () => {
+            const data = {
+                isWriteFileSyncCalled: false
+            };
+
+            fs.readFileSync = (p) => {
+                return JSON.stringify({ a: 1 });
+            };
+
+            fs.writeFileSync = (p, c) => {
+                data.isWriteFileSyncCalled = true;
+            };
+
+            return data;
+        };
+
+        it('does not write package.json when content has not changed', () => {
+            const data = mockFileSystemApi();
+            writePackageJson({ a: 1 }, "projDir");
+            expect(data.isWriteFileSyncCalled).toBe(false);
+        });
+
+        it('writes content, when the new one is different from the current one', () => {
+            const data = mockFileSystemApi();
+            writePackageJson({ b: 2 }, "projDir");
+            expect(data.isWriteFileSyncCalled).toBe(true);
+        });
+
+        it('keeps indentation of the package.json when rewriting it', () => {
+            let currentIndentSymbol = tab;
+            fs.readFileSync = (p) => {
+                return JSON.stringify({ a: 1 }, null, currentIndentSymbol);
+            };
+
+            let writtenContent = null;
+            fs.writeFileSync = (p, c) => {
+                writtenContent = c;
+            };
+
+            // Ensure tab indentation is persisted
+            writePackageJson({ b: 2 }, "projDir");
+            expect(writtenContent).toBe(`{\n${tab}"b": 2\n}`);
+
+            // Ensure spaces indentation is persisted
+            currentIndentSymbol = multipleSpaces;
+            writePackageJson({ b: 2 }, "projDir");
+            expect(writtenContent).toBe(`{\n${multipleSpaces}"b": 2\n}`);
+        });
+    });
+});