import type { UnionToIntersection, UnionToTuple } from "./union.ts"

// ============================================================================
// Generation
// ============================================================================

/**
 * @description Create an intersection from a tuple of types.
 *
 * @example
 *   ```
 *   // Expect: { a: 1 } & { b: 2 }
 *   type Example1 = IntersectionAll<[{ a: 1 }, { b: 2 }]>
 *   // Expect: string & number
 *   type Example2 = IntersectionAll<[string, number]>
 *   // Expect: unknown
 *   type Example3 = IntersectionAll<[]>
 *   ```
 */
export type IntersectionAll<T extends readonly unknown[], Fallback = unknown> = [
  T[number],
] extends [never]
  ? Fallback
  : UnionToIntersection<T[number]>

// ============================================================================
// Manipulation
// ============================================================================

/**
 * @description Merge an intersection of object types into a single object type.
 *
 * @example
 *   ```
 *   // Expect: { a: 1; b: 2 }
 *   type Example1 = IntersectionMerge<{ a: 1 } & { b: 2 }>
 *   // Expect: { a: string & number }
 *   type Example2 = IntersectionMerge<{ a: string } & { a: number }>
 *   // Expect: {}
 *   type Example3 = IntersectionMerge<{}>
 *   ```
 */
export type IntersectionMerge<T extends Record<PropertyKey, unknown>> = {
  [Key in keyof T]: T[Key]
}

/**
 * @description Prettify an intersection of object types.
 *
 * @example
 *   ```
 *   // Expect: { id: string; active: boolean }
 *   type Example1 = IntersectionPrettify<{ id: string } & { active: boolean }>
 *   // Expect: { value: number }
 *   type Example2 = IntersectionPrettify<{ value: number }>
 *   // Expect: {}
 *   type Example3 = IntersectionPrettify<{}>
 *   ```
 */
export type IntersectionPrettify<T extends Record<PropertyKey, unknown>> = IntersectionMerge<T>

// ============================================================================
// Conversion
// ============================================================================

/**
 * @description Convert an intersection of object types into a union of object types.
 *
 * @example
 *   ```
 *   // Expect: { a: string } | { b: number }
 *   type Example1 = ObjectIntersectionToUnion<{ a: string } & { b: number }>
 *   // Expect: { a: never }
 *   type Example2 = ObjectIntersectionToUnion<{ a: string } & { a: number }>
 *   // Expect: never
 *   type Example3 = ObjectIntersectionToUnion<{}>
 *   ```
 */
export type ObjectIntersectionToUnion<T> = {
  [K in keyof T]: { [P in K]: T[P] }
}[keyof T]

/**
 * @description Convert an intersection of object types into a tuple of object types.
 *
 * @example
 *   ```
 *   // Expect: [{ a: string }, { b: number }]
 *   type Example1 = ObjectIntersectionToTuple<{ a: string } & { b: number }>
 *   // Expect: [{ a: never }]
 *   type Example2 = ObjectIntersectionToTuple<{ a: string } & { a: number }>
 *   // Expect: []
 *   type Example3 = ObjectIntersectionToTuple<{}>
 *   ```
 */
export type ObjectIntersectionToTuple<T> = UnionToTuple<ObjectIntersectionToUnion<T>>