```ts
/**
 * Parse a semantic version string.
 *
 * @param version - The semantic version string to parse.
 * @returns The parsed version object.
 */
export function parseSemver(version: string): {
  major: number;
  minor: number;
  patch: number;
  prerelease: string | null;
  build: string | null;
} {
  const match = /^(\d+)\.(\d+)(?:\.(\d+))?(-[a-zA-Z0-9_-]+)?\+([a-zA-Z0-9_-]+)?$/u.exec(version);
  
  if (!match) {
    throw new Error(`Invalid version string: ${version}`);
  }
  
  return {
    major: parseInt(match[1], 10),
    minor: parseInt(match[2], 10),
    patch: match[3] ? parseInt(match[3], 10) : 0,
    prerelease: match[4],
    build: match[5],
  };
}
```