export interface ModelInfo {
  id: string;
  model: string;
  displayName: string;
  hidden: boolean;
  upgrade: string | null;
  isDefault: boolean;
}

export interface ModelCatalog {
  visibleModels: ModelInfo[];
  byId: Map<string, ModelInfo>;
  upgradeAliases: Map<string, string>;
  defaultModelId?: string | undefined;
}

export interface ModelResolution {
  requested: string;
  resolved: string;
  remappedFrom?: string | undefined;
}

export function buildModelCatalog(models: ModelInfo[]): ModelCatalog {
  const byId = new Map(models.map((model) => [model.id, model]));
  const visibleModels = models.filter((model) => !model.hidden);
  const upgradeAliases = new Map<string, string>();

  for (const model of models) {
    if (!model.upgrade) {
      continue;
    }
    if (byId.has(model.upgrade)) {
      upgradeAliases.set(model.id, model.upgrade);
    }
  }

  const defaultModelId = visibleModels.find((model) => model.isDefault)?.id ?? visibleModels[0]?.id;

  return {
    visibleModels,
    byId,
    upgradeAliases,
    defaultModelId,
  };
}

export function describeAllowedModels(catalog: ModelCatalog): string {
  return catalog.visibleModels.map((model) => model.id).sort().join(', ');
}

export function resolveModel(
  catalog: ModelCatalog,
  requestedModel?: string | undefined,
): ModelResolution {
  const requested = requestedModel ?? catalog.defaultModelId ?? 'gpt-5.4';
  if (!requested) {
    throw new Error('No models available from model/list.');
  }

  const direct = catalog.byId.get(requested);
  if (direct && !direct.hidden) {
    const upgraded = catalog.upgradeAliases.get(requested);
    if (upgraded) {
      return {
        requested,
        resolved: upgraded,
        remappedFrom: requested,
      };
    }
    return { requested, resolved: requested };
  }

  const upgraded = catalog.upgradeAliases.get(requested);
  if (upgraded) {
    return {
      requested,
      resolved: upgraded,
      remappedFrom: requested,
    };
  }

  throw new Error(
    `Unsupported model "${requested}". Allowed models: ${describeAllowedModels(catalog)}`,
  );
}