import deepmerge from 'deepmerge'

/**
 * Config can be either an object or a function that receives baseConfig and data
 * and returns a partial config to be merged with the base.
 */
export type ConfigOrFn<TConfig, TData = unknown> =
  | Partial<TConfig>
  | ((baseConfig: TConfig, data: TData) => Partial<TConfig>)

/**
 * Resolves a widget config that may be either a partial object or a function receiving the computed base config and data. If it is a function, calls it with `baseConfig` and `data`; otherwise returns the value as-is.
 *
 * @param config - The config object or function to resolve.
 * @param baseConfig - The computed base configuration.
 * @param data - The widget data.
 * @returns Resolved partial config, or undefined.
 *
 * @example
 * ```tsx
 * const resolved = resolveConfig(
 *   (base, data) => ({ maxItems: base.maxItems + 5 }),
 *   baseConfig,
 *   widgetData,
 * )
 * ```
 */
export function resolveConfig<TConfig, TData>(
  config: ConfigOrFn<TConfig, TData> | undefined,
  baseConfig: TConfig,
  data: TData,
): Partial<TConfig> | undefined {
  if (typeof config === 'function') {
    return config(baseConfig, data)
  }
  return config
}

/**
 * Deep-merges two partial widget config objects using `deepmerge`, with arrays replaced rather than concatenated.
 *
 * @param options - A tuple of two partial configs to merge (base and override).
 * @returns The merged config object.
 *
 * @example
 * ```tsx
 * const finalConfig = mergeWidgetConfig(baseConfig, resolvedConfig)
 * ```
 */
export function mergeWidgetConfig<T>(
  ...options: [Partial<T> | undefined, Partial<T> | undefined]
): T {
  return deepmerge(options[0] ?? {}, options[1] ?? {}, {
    arrayMerge(_, source) {
      return source as T[keyof T][]
    },
  })
}