1 files changed, 92 insertions, 0 deletions
diff --git a/ext/js/templates/template-patcher.js b/ext/js/templates/template-patcher.js
new file mode 100644
index 00000000..57178957
--- /dev/null
+++ b/ext/js/templates/template-patcher.js
@@ -0,0 +1,92 @@
+/*
+ * Copyright (C) 2021  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+class TemplatePatcher {
+    constructor() {
+        this._diffPattern1 = /\n?\{\{<<<<<<<\}\}\n/g;
+        this._diffPattern2 = /\n\{\{=======\}\}\n/g;
+        this._diffPattern3 = /\n\{\{>>>>>>>\}\}\n*/g;
+        this._lookupMarkerPattern = /[ \t]*\{\{~?>\s*\(\s*lookup\s*\.\s*"marker"\s*\)\s*~?\}\}/g;
+    }
+
+    parsePatch(content) {
+        const diffPattern1 = this._diffPattern1;
+        const diffPattern2 = this._diffPattern2;
+        const diffPattern3 = this._diffPattern3;
+        const modifications = [];
+        let index = 0;
+
+        while (true) {
+            // Find modification boundaries
+            diffPattern1.lastIndex = index;
+            const m1 = diffPattern1.exec(content);
+            if (m1 === null) { break; }
+
+            diffPattern2.lastIndex = m1.index + m1[0].length;
+            const m2 = diffPattern2.exec(content);
+            if (m2 === null) { break; }
+
+            diffPattern3.lastIndex = m2.index + m2[0].length;
+            const m3 = diffPattern3.exec(content);
+            if (m3 === null) { break; }
+
+            // Construct
+            const current = content.substring(m1.index + m1[0].length, m2.index);
+            const replacement = content.substring(m2.index + m2[0].length, m3.index);
+
+            if (current.length > 0) {
+                modifications.push({current, replacement});
+            }
+
+            // Update
+            content = content.substring(0, m1.index) + content.substring(m3.index + m3[0].length);
+            index = m1.index;
+        }
+
+        return {addition: content, modifications};
+    }
+
+    applyPatch(template, patch) {
+        for (const {current, replacement} of patch.modifications) {
+            let fromIndex = 0;
+            while (true) {
+                const index = template.indexOf(current, fromIndex);
+                if (index < 0) { break; }
+                template = template.substring(0, index) + replacement + template.substring(index + current.length);
+                fromIndex = index + replacement.length;
+            }
+        }
+        template = this._addFieldTemplatesBeforeEnd(template, patch.addition);
+        return template;
+    }
+
+    // Private
+
+    _addFieldTemplatesBeforeEnd(template, addition) {
+        const newline = '\n';
+        let replaced = false;
+        template = template.replace(this._lookupMarkerPattern, (g0) => {
+            replaced = true;
+            return `${addition}${newline}${g0}`;
+        });
+        if (!replaced) {
+            template += newline;
+            template += addition;
+        }
+        return template;
+    }
+}