1 files changed, 183 insertions, 0 deletions
diff --git a/app/assets/javascripts/ide/lib/diff/revert_patch.js b/app/assets/javascripts/ide/lib/diff/revert_patch.js
new file mode 100644
index 00000000000..21c90adedd8
--- /dev/null
+++ b/app/assets/javascripts/ide/lib/diff/revert_patch.js
@@ -0,0 +1,183 @@
+export function revertPatch(source, uniDiff, options = {}) {
+  if (typeof uniDiff === 'string') {
+    uniDiff = parsePatch(uniDiff);
+  }
+
+  if (Array.isArray(uniDiff)) {
+    if (uniDiff.length > 1) {
+      throw new Error('applyPatch only works with a single input.');
+    }
+
+    uniDiff = uniDiff[0];
+  }
+
+  // Apply the diff to the input
+  let lines = source.split(/\r\n|[\n\v\f\r\x85]/),
+    delimiters = source.match(/\r\n|[\n\v\f\r\x85]/g) || [],
+    hunks = uniDiff.hunks,
+    compareLine =
+      options.compareLine ||
+      ((lineNumber, line, operation, patchContent) => line === patchContent),
+    errorCount = 0,
+    fuzzFactor = options.fuzzFactor || 0,
+    minLine = 0,
+    offset = 0,
+    removeEOFNL,
+    addEOFNL;
+
+  /**
+   * Checks if the hunk exactly fits on the provided location
+   */
+  function hunkFits(hunk, toPos) {
+    for (let j = 0; j < hunk.lines.length; j++) {
+      let line = hunk.lines[j],
+        operation = line[0],
+        content = line.substr(1);
+
+      if (operation === ' ' || operation === '-') {
+        // Context sanity check
+        if (!compareLine(toPos + 1, lines[toPos], operation, content)) {
+          errorCount++;
+
+          if (errorCount > fuzzFactor) {
+            return false;
+          }
+        }
+        toPos++;
+      }
+    }
+
+    return true;
+  }
+
+  // Search best fit offsets for each hunk based on the previous ones
+  for (let i = 0; i < hunks.length; i++) {
+    let hunk = hunks[i],
+      maxLine = lines.length - hunk.oldLines,
+      localOffset = 0,
+      toPos = offset + hunk.oldStart - 1;
+
+    const iterator = distanceIterator(toPos, minLine, maxLine);
+
+    for (; localOffset !== undefined; localOffset = iterator()) {
+      if (hunkFits(hunk, toPos + localOffset)) {
+        hunk.offset = offset += localOffset;
+        break;
+      }
+    }
+
+    if (localOffset === undefined) {
+      return false;
+    }
+
+    // Set lower text limit to end of the current hunk, so next ones don't try
+    // to fit over already patched text
+    minLine = hunk.offset + hunk.oldStart + hunk.oldLines;
+  }
+
+  // Apply patch hunks
+  let diffOffset = 0;
+  for (let i = 0; i < hunks.length; i++) {
+    let hunk = hunks[i],
+      toPos = hunk.oldStart + hunk.offset + diffOffset - 1;
+    diffOffset += hunk.newLines - hunk.oldLines;
+
+    if (toPos < 0) {
+      // Creating a new file
+      toPos = 0;
+    }
+
+    for (let j = 0; j < hunk.lines.length; j++) {
+      let line = hunk.lines[j],
+        operation = line[0],
+        content = line.substr(1),
+        delimiter = hunk.linedelimiters[j];
+
+      // Turned around the commands to revert the applying
+      if (operation === ' ') {
+        toPos++;
+      } else if (operation === '+') {
+        lines.splice(toPos, 1);
+        delimiters.splice(toPos, 1);
+        /* istanbul ignore else */
+      } else if (operation === '-') {
+        lines.splice(toPos, 0, content);
+        delimiters.splice(toPos, 0, delimiter);
+        toPos++;
+      } else if (operation === '\\') {
+        const previousOperation = hunk.lines[j - 1]
+          ? hunk.lines[j - 1][0]
+          : null;
+        if (previousOperation === '+') {
+          removeEOFNL = true;
+        } else if (previousOperation === '-') {
+          addEOFNL = true;
+        }
+      }
+    }
+  }
+
+  // Handle EOFNL insertion/removal
+  if (removeEOFNL) {
+    while (!lines[lines.length - 1]) {
+      lines.pop();
+      delimiters.pop();
+    }
+  } else if (addEOFNL) {
+    lines.push('');
+    delimiters.push('\n');
+  }
+  for (let _k = 0; _k < lines.length - 1; _k++) {
+    lines[_k] = lines[_k] + delimiters[_k];
+  }
+  return lines.join('');
+}
+
+/**
+ * Utility Function
+ * @param {*} start
+ * @param {*} minLine
+ * @param {*} maxLine
+ */
+const distanceIterator = function(start, minLine, maxLine) {
+  let wantForward = true,
+    backwardExhausted = false,
+    forwardExhausted = false,
+    localOffset = 1;
+
+  return function iterator() {
+    if (wantForward && !forwardExhausted) {
+      if (backwardExhausted) {
+        localOffset++;
+      } else {
+        wantForward = false;
+      }
+
+      // Check if trying to fit beyond text length, and if not, check it fits
+      // after offset location (or desired location on first iteration)
+      if (start + localOffset <= maxLine) {
+        return localOffset;
+      }
+
+      forwardExhausted = true;
+    }
+
+    if (!backwardExhausted) {
+      if (!forwardExhausted) {
+        wantForward = true;
+      }
+
+      // Check if trying to fit before text beginning, and if not, check it fits
+      // before offset location
+      if (minLine <= start - localOffset) {
+        return -localOffset++;
+      }
+
+      backwardExhausted = true;
+      return iterator();
+    }
+
+    // We tried to fit hunk before text beginning and beyond text length, then
+    // hunk can't fit on the text. Return undefined
+  };
+};