/**
 * GitFlow Update Policy — Pure decisions for bringing a branch up to date with
 * its base (feature/release ← develop, hotfix ← main). No I/O, no git.
 * Shared by the `update` command and `sync --rebase`.
 */

export type BaseUpdateAction = 'none' | 'ff' | 'merge' | 'rebase';

/**
 * Pure decision: how to bring the current branch up to date with its base ref.
 * - nothing to take from the base → 'none' (ahead-only never touches the branch)
 * - behind with no own commits → 'ff' (cleanest regardless of strategy)
 * - genuinely diverged → the caller's strategy
 */
export function decideBaseUpdate(o: {
  ahead: number;
  behind: number;
  strategy: 'merge' | 'rebase';
}): BaseUpdateAction {
  if (o.behind === 0) return 'none';
  if (o.ahead === 0) return 'ff';
  return o.strategy;
}

/** EF Core artifacts in a conflict list (git paths use forward slashes). */
export function isEfCoreConflict(files: string[]): boolean {
  return files.some((f) => /ModelSnapshot\.cs$/i.test(f) || /(^|\/)Migrations\//i.test(f));
}

/**
 * Human guidance after a rolled-back merge/rebase conflict. The branch is a
 * no-op at this point (the operation was aborted) — tell the user that, then
 * how to resolve manually, and point at /efcore rebase-snapshot when the
 * conflict involves EF Core migration files (the classic snapshot collision).
 */
export function buildConflictGuidance(o: {
  operation: 'merge' | 'rebase';
  baseRef: string;
  branch: string;
  conflictFiles: string[];
}): string {
  const n = o.conflictFiles.length;
  let guidance =
    `${o.operation} of ${o.baseRef} into '${o.branch}' hit conflicts in ${n} file(s) and was aborted — ` +
    `your branch is untouched. Resolve manually (git ${o.operation === 'merge' ? `merge ${o.baseRef}` : `rebase ${o.baseRef}`}, ` +
    `fix the conflicts, then conclude), or update the branch in smaller steps.`;
  if (isEfCoreConflict(o.conflictFiles)) {
    guidance += ` EF Core migration files conflict — run /efcore rebase-snapshot after updating.`;
  }
  return guidance;
}