How to use the diff.parsePatch function in diff

exports.applyPatch = function applyPatch(data, patch) {
    var lines = data.split('\n');
    var newLines = [];
    var dataIndex = 1;

    if (!patch.hunks) {
    //
    // patch is a textual unified diff. parse it
    //
    patch = JsDiff.parsePatch(patch)[0];
    }

    patch.hunks.forEach((hunk, hunkIndex) => {
    for (var i = dataIndex; i < hunk.oldStart; i++) {
        newLines.push(lines[i - 1]);
    }

    hunk.lines.forEach( (line, index) => {
        if (line.charAt(0) === '+') {
        // new line
        newLines.push(line.slice(1));

        } else if (line.charAt(0) === '-') {
        // removed line
        dataIndex++;

}
    }

    const fileDiffs: FileDiff[] = []
    for (const [uri, edits] of editsByUri) {
        if (edits.length === 0) {
            continue
        } else if (edits.length === 1 && edits[0].rawPatch !== undefined) {
            // Fast path: use the precomputed diff.
            const fullPatch = edits[0].rawPatch
            const patchWithoutHeader = fullPatch.slice(fullPatch.indexOf('@@'))
            const p = parseRepoURI(uri)
            fileDiffs.push({
                oldPath: uri.toString(),
                newPath: uri.toString(),
                hunks: parsePatch(fullPatch)
                    .flatMap(d => d.hunks)
                    .map(npmDiffToFileDiffHunk),
                patch: `Index: ${p.filePath!}\n--- a/${p.filePath!}\n+++ b/${p.filePath!}\n${patchWithoutHeader}`,
                patchWithFullURIs: `Index: ${uri}\n--- ${uri}\n+++ ${uri}\n${patchWithoutHeader}`,
            })
        } else {
            const oldText = await extensionsController.services.fileSystem.readFile(new URL(uri))
            const t0 = Date.now()
            const newText = applyEdits(
                oldText,
                edits.map(edit => {
                    // TODO!(sqs): doesnt account for multiple edits
                    const startOffset = positionToOffset(oldText, edit.range.start)
                    const endOffset = positionToOffset(oldText, edit.range.end)
                    return { offset: startOffset, length: endOffset - startOffset, content: edit.newText }
                })

export function getLineNumber (diffStr, fileName, hunkPosition) {
  const parsed = diff.parsePatch(diffStr)

  const file = parsed.filter(p => p.newFileName === 'b/' + fileName)[0]

  let linesParsed = 0
  for (let hunk of file.hunks) {
    if (linesParsed + hunk.lines.length >= hunkPosition) {
      const remainingLines = hunk.lines.slice(0, hunkPosition - linesParsed)
      // on the right side of the diff,
      // context and added lines increment the line number
      return remainingLines.reduce((acc, line) => {
        return line[0] === '-' ? acc : acc + 1
      }, hunk.newStart - 1)
    } else {
      // include the header for the next hunk (if any)
      linesParsed += hunk.lines.length + 1
    }

public static getEditsFromFormattedText(documentUri: string, originalText: string, formattedText: string,
		startOffset: number = 0): TextEdit[] {
		const diff = producePatch(documentUri, originalText, formattedText);
		const unifiedDiffs = parsePatch(diff);

		const edits: Edit[] = [];
		let currentEdit: Edit | null = null;

		for (const uniDiff of unifiedDiffs) {
			for (const hunk of uniDiff.hunks) {
				let startLine = hunk.oldStart + startOffset;

				for (const line of hunk.lines) {
					switch (line[0]) {
						case '-':
							if (currentEdit === null) {
								currentEdit = new Edit(EditAction.Delete, Position.create(startLine - 1, 0));
							}
							currentEdit.end = Position.create(startLine, 0);
							startLine++;

}).forEach(function (op) {
    var strPatch = fs.readFileSync(op.patch, 'utf-8')
    var strDest
    try {
      strDest = fs.readFileSync(op.dest, 'utf-8')
    } catch (err) {
      strDest = ''
    }
    fs.writeFileSync(op.dest,
      jsdiff.applyPatch(strDest, jsdiff.parsePatch(strPatch)))
    console.log('> patched', path.relative(__dirname, op.dest))
  })
  console.log()

function getEditsFromUnifiedDiffStr(diffstr) {
    const unifiedDiffs = jsDiff.parsePatch(diffstr);
    const filePatches = parseUniDiffs(unifiedDiffs);
    return filePatches;
}
exports.getEditsFromUnifiedDiffStr = getEditsFromUnifiedDiffStr;

function getChangedLines(isIgnored, diff) {
  return Diff.parsePatch(diff)
    .flatMap(file =>
      isIgnored(file.oldFileName) && isIgnored(file.newFileName)
        ? []
        : file.hunks
    )
    .flatMap(hunk => hunk.lines)
    .filter(line => line[0] === "+" || line[0] === "-").length;
}

export const DiffViewer = ( { diff } ) => (
	<div>
		{ parsePatch( diff ).map( ( file, fileIndex ) =&gt; (
			
				<div>
					{ filename( file ) }
				</div>
				<div>
					<div>
						{ file.hunks.map( ( hunk, hunkIndex ) =&gt; {
							let lineOffset = 0;
							return hunk.lines.map( ( line, index ) =&gt; (
								<div>
									{ line[ 0 ] === '+' ? '\u00a0' : hunk.oldStart + lineOffset++ }
								</div>
							) );
						} ) }
					</div>
					<div></div></div></div>

fileDiffs {
                                                            rawDiff
                                                        }
                                                    }
                                                }
                                            }
                                        `,
                                        vars: {
                                            repositoryName: base.repoName,
                                            baseRevSpec: base.rev || base.commitID,
                                            headRevSpec: head.rev || head.commitID,
                                        },
                                    })
                                )
                                const { rawDiff } = data.repository.comparison.fileDiffs
                                const fileDiffs = parsePatch(rawDiff)
                                return Promise.all(
                                    fileDiffs.map(async (fileDiff, fileDiffI) => {
                                        const uri = new URL(makeRepoURI({ ...head, filePath: fileDiff.newFileName }))
                                        const doc = await sourcegraph.workspace.openTextDocument(uri)
                                        const diagnostics = [
                                            ...markEnsureAuthz(doc),
                                            ...markSecurityReviewRequired(doc, fileDiff),
                                            ...(rootI === 0 && fileDiffI === 0 ? [suggestChangelogEntry()] : []),
                                            ...(rootI === 0 && fileDiffI === 0 ? updateDependents() : []),
                                            ...markTODO(doc, fileDiff),
                                        ].filter(isDefined)
                                        return [uri, diagnostics] as [URL, sourcegraph.Diagnostic[]]
                                    })
                                ).catch(() => [])
                            })
                            .filter(isDefined)