```ts
/**
 * Parses a semantic version string and returns its components.
 *
 * @param version The semantic version string to parse.
 * @returns An object containing the major, minor, patch numbers, and optional prerelease and build strings.
 */
export function parseSemver(version: string): { major: number; minor: number; patch: number; prerelease: string | null; build: string | null } {
  const semverRegex = /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})(?:-([0-9A-Za-z.-]+))?(?:\+([0-9A-Za-z.-]+))?$/;
  const match = version.match(semverRegex);

  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] || null,
    build: match[5] || null
  };
}
```