From 30349dbcb90156b98365462dcd93b6dabb540b9d Mon Sep 17 00:00:00 2001
From: Oshawk <oshawk@protonmail.com>
Date: Mon, 21 Oct 2019 20:44:57 +0100
Subject: [PATCH] Add operation

Added 'Drop nth bytes' operation.
---
 src/core/config/Categories.json      |  3 +-
 src/core/operations/DropNthBytes.mjs | 79 ++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+), 1 deletion(-)
 create mode 100644 src/core/operations/DropNthBytes.mjs

diff --git a/src/core/config/Categories.json b/src/core/config/Categories.json
index db2ab3a6..9cfeb7fe 100755
--- a/src/core/config/Categories.json
+++ b/src/core/config/Categories.json
@@ -238,7 +238,8 @@
             "Escape string",
             "Unescape string",
             "Pseudo-Random Number Generator",
-            "Sleep"
+            "Sleep",
+            "Drop nth bytes"
         ]
     },
     {
diff --git a/src/core/operations/DropNthBytes.mjs b/src/core/operations/DropNthBytes.mjs
new file mode 100644
index 00000000..e6bac1cd
--- /dev/null
+++ b/src/core/operations/DropNthBytes.mjs
@@ -0,0 +1,79 @@
+/**
+ * @author Oshawk [oshawk@protonmail.com]
+ * @copyright Crown Copyright 2019
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation.mjs";
+import OperationError from "../errors/OperationError.mjs";
+
+/**
+ * Drop nth bytes operation
+ */
+class DropNthBytes extends Operation {
+
+    /**
+     * DropNthBytes constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "Drop nth bytes";
+        this.module = "Default";
+        this.description = "Drops every nth byte starting with a given byte.";
+        this.infoURL = "";
+        this.inputType = "byteArray";
+        this.outputType = "byteArray";
+        this.args = [
+            {
+                name: "Drop every",
+                type: "number",
+                value: 4
+            },
+            {
+                name: "Starting at",
+                type: "number",
+                value: 0
+            },
+            {
+                name: "Apply to each line",
+                type: "boolean",
+                value: false
+            }
+        ];
+    }
+
+    /**
+     * @param {byteArray} input
+     * @param {Object[]} args
+     * @returns {byteArray}
+     */
+    run(input, args) {
+        const n = args[0];
+        const start = args[1];
+        const eachLine = args[2];
+
+        if (parseInt(n, 10) !== n || n <= 0) {
+            throw new OperationError("'Drop every' must be a positive integer.");
+        }
+        if (parseInt(start, 10) !== start || start < 0) {
+            throw new OperationError("'Starting at' must be a positive or zero integer.");
+        }
+
+        let offset = 0;
+        const output = [];
+        for (let i = 0; i < input.length; i++) {
+            if (eachLine && input[i] === 0x0a) {
+                output.push(0x0a);
+                offset = i + 1;
+            } else if (i - offset < start || (i - (start + offset)) % n !== 0) {
+                output.push(input[i]);
+            }
+        }
+
+        return output;
+    }
+
+}
+
+export default DropNthBytes;