/* eslint-disable prefer-named-capture-group */
export function getChangedLineNumbersFromPatch(patch: string): number[] {
  const fileLinesRegex = /^@@ -([0-9]*),?\S* \+([0-9]*),?/;
  const frontMatterRegex = /^([a-z_]+: .+)|(---)$/;
  const codeSampleRegex = /^```.*$/;
  const lineNumbersInDiff: number[] = [];

  function splitIntoParts(lines: string[], separator: string) {
    const parts: string[][] = [];
    let currentPart: undefined | string[] = undefined;

    lines.forEach((line) => {
      if (line.startsWith(separator)) {
        if (currentPart) {
          parts.push(currentPart);
        }

        currentPart = [line];
      } else if (currentPart) {
        currentPart.push(line);
      }
    });

    if (currentPart) {
      parts.push(currentPart);
    }

    return parts;
  }

  splitIntoParts(patch.split('\n'), '@@ ').forEach((lines) => {
    const fileLinesLine = lines.shift() as string;
    const matches = fileLinesLine.match(fileLinesRegex);
    if (!matches) return;

    const [, , startLineNo] = matches;

    let lineNo = parseInt(startLineNo, 10);
    let inCodeSample: boolean = false;

    lines.forEach((line: string) => {
      if (line.startsWith('+')) {
        // Don't count blank lines and front matter changes
        const newLine: string = line.substring(1);
        const codeFenceLine: boolean = Boolean(newLine.match(codeSampleRegex));
        if (newLine.length > 0 && !newLine.match(frontMatterRegex) && !codeFenceLine && !inCodeSample) {
          lineNumbersInDiff.push(lineNo);
        }
        inCodeSample = inCodeSample ? !codeFenceLine : codeFenceLine;
      } else if (line.startsWith('-')) {
        lineNo -= 1;
      }
      lineNo += 1;
    });
  });

  return lineNumbersInDiff;
}