Attempt to use existing JSON Patch library to apply patches

lib/entity/LoadedAsset.js

@@ -1,7 +1,7 @@
 'use strict';
 
 const { config, util } = require( '..' ),
-	lodash = require( 'lodash' );
+	jsonPatch = require( 'fast-json-patch' );
 
 /**
  * Represents one asset (parsed JSON file from either vanilla or the mod). Used in AssetDatabase.
@@ -106,95 +106,26 @@ class LoadedAsset {
 	 * @param {Object} data
 	 */
 	applyPatchInstructions( patch, data ) {
-		// This is set to true if we find "test" operation that tells us to ignore the rest of this patch.
-		var patchSkipped = false;
-
-		patch.forEach( ( instruction ) => {
-			if ( patchSkipped ) {
-				// This instruction must be ignored, because preceding "test" instruction says so.
-				return;
-			}
-
+		for ( let instruction of patch ) {
 			if ( Array.isArray( instruction ) ) {
 				// This is an array of instructions, not a single instruction.
 				// Handle this recursively.
 				this.applyPatchInstructions( instruction, data );
-				return;
+				continue;
 			}
 
-			var op = instruction.op,
-				value = instruction.value;
-
-			if ( op === 'copy' || op === 'move' ) {
-				// These operations are not supported.
-				// They are also not used in the mod.
-				return;
-			}
-
-			if ( instruction.path === '/-' && op === 'add' ) {
-				// Special case: the entire data is an array, and we are adding new element to the bottom of it.
-				data.push( value );
-				return;
-			}
-
-			var objectPath = instruction.path.slice( 1 ).split( '/' );
-			if ( op === 'add' ) {
-				// Handle add operations to: 1) "/some-array/-" (add to the end of array)
-				// 2) "/some-array/123" (add the new element BEFORE what is currently element #123).
-				var possiblyIndex = objectPath.pop();
-
-				if ( possiblyIndex !== '-' && Number.isNaN( Number( possiblyIndex ) ) ) {
-					// Not an index. We don't consider this an "add to array" operation,
-					// instead this is "add new key-value" operation.
-					objectPath.push( possiblyIndex );
-				} else {
-					var currentArray = ( lodash.get( data, objectPath ) || [] );
-
-					if ( possiblyIndex === '-' ) {
-						// Pseudo-value "-" means "add after the last element of array".
-						// Here "value" is the new element that we are adding.
-						value = currentArray.concat( [ value ] );
-					} else {
-						// Add "value" to currentArray BEFORE currentArray[possiblyIndex]
-						var before = currentArray.slice( 0, possiblyIndex ),
-							after = currentArray.slice( possiblyIndex );
-
-						value = before.concat( [ value ] ).concat( after );
-					}
-
-					op = 'replace';
+			try {
+				jsonPatch.applyOperation( data, instruction );
+			} catch ( e ) {
+				if ( e.name === 'TEST_OPERATION_FAILED' ) {
+					// This "test" instruction told us to skip all instructions after it.
+					return;
 				}
-			}
 
-			if ( op === 'replace' || op === 'add' ) {
-				lodash.set( data, objectPath, value );
-			} else if ( op === 'remove' ) {
-				// Carefully delete the element from Array/Object.
-				// Note: while lodash.unset() would be enough for objects, using it to delete keys from arrays
-				// would create holes in the array, resulting in incorrect application of further patches.
-				var index = objectPath.pop();
-				var list = lodash.get( data, objectPath );
-
-				if ( Array.isArray( list ) ) {
-					// Removing numeric index from array.
-					list.splice( index, 1 );
-					lodash.set( list, objectPath );
-				} else {
-					// Unsetting property of object.
-					objectPath.push( index );
-					lodash.unset( data, objectPath );
-				}
-			} else if ( op === 'test' ) {
-				var fieldExists = lodash.has( data, objectPath );
-				if ( fieldExists && instruction.inverse ) {
-					// This patch shouldn't be applied if the field exists.
-					patchSkipped = true;
-				} else if ( !fieldExists && !instruction.inverse ) {
-					// This patch shouldn't be applied, because the field doesn't exist.
-					patchSkipped = true;
-				}
+				// FIXME: there are errors in existing assets/patches.
+				util.log( '[error] Patch error: ' + this.filename + ': ' + e.name + ': ' + JSON.stringify( instruction ) );
 			}
-		} );
+		}
 	}
 }
 

package.json

@@ -12,8 +12,8 @@
     "cli-progress": "^3.12.0",
     "deepmerge": "^4.3.1",
     "diff": "^7.0.0",
+    "fast-json-patch": "^3.1.1",
     "fs": "^0.0.2",
-    "lodash": "^4.17.21",
     "minimist": "^1.2.8",
     "mwbot": "^2.1.3",
     "picomatch": "^4.0.2",