```ts
/**
 * Parse a semantic version string returning its numeric parts plus optional prerelease and build strings.
 */
export function parseSemver(version: string): {
  major: number;
  minor: number;
  patch: number;
  prerelease: string | null;
  build: string | null;
} {
  const regex = /^(\d+)\.(\d+)\.(\d+)(?:-(.+))?(?:\+(.+))?$/;
  const match = version.match(regex);

  if (!match) {
    throw new Error('Invalid semver format');
  }

  return {
    major: parseInt(match[1], 10),
    minor: parseInt(match[2], 10),
    patch: parseInt(match[3], 10),
    prerelease: match[4] ? match[4] : null,
    build: match[5] ? match[5] : null,
  };
}
```