```ts
function parseSemver(version: string): { major: number; minor: number; patch: number; prerelease: string | null; build: string | null } {
  const regex = /^v?(\d+)\.(\d+)\.(\d+)(-[a-zA-Z0-9-]*)?(\+[a-zA-Z0-9-]*)?$/;
  const match = version.match(regex);

  if (!match) {
    throw new Error(`Invalid semantic version string: ${version}`);
  }

  let major = parseInt(match[1], 10);
  let minor = parseInt(match[2], 10);
  let patch = parseInt(match[3], 10);

  const prereleaseParts = match[4] ? match[4].split('-') : [];
  const buildParts = match[5] ? match[5].split('+') : [];

  return {
    major,
    minor,
    patch,
    prerelease:
      prereleaseParts.length > 1
        ? `${prereleaseParts.slice(0, -1).join('-')}-${prereleaseParts.pop()!}`
        : prereleaseParts.length === 1
          ? prereleaseParts[0]
          : null,
    build: buildParts.length > 1 ? `${buildParts.slice(0, -1).join('+')}+${buildParts.pop()!}` : buildParts.length === 1 ? buildParts[0] : null
  };
}
```