index.ts

import {StrictEqualUsingBranding} from './branding'
import {
  MismatchInfo,
  Scolder,
  ExpectAny,
  ExpectUnknown,
  ExpectNever,
  ExpectFunction,
  ExpectObject,
  ExpectArray,
  ExpectNumber,
  ExpectString,
  ExpectBoolean,
  ExpectVoid,
  ExpectSymbol,
  ExpectNull,
  ExpectUndefined,
  ExpectNullable,
} from './messages'
import {
  ConstructorOverloadParameters,
  OverloadParameters,
  OverloadReturnTypes,
  OverloadsNarrowedByParameters,
} from './overloads'
import {StrictEqualUsingTSInternalIdenticalToOperator, AValue, MismatchArgs, Extends} from './utils'

export * from './branding' // backcompat, consider removing in next major version
export * from './utils' // backcompat, consider removing in next major version
export * from './messages' // backcompat, consider removing in next major version
export * from './overloads'

/**
 * Represents the positive assertion methods available for type checking in the
 * {@linkcode expectTypeOf()} utility.
 */
export interface PositiveExpectTypeOf<Actual> extends BaseExpectTypeOf<Actual, {positive: true; branded: false}> {
  toEqualTypeOf: {
    /**
     * Uses TypeScript's internal technique to check for type "identicalness".
     *
     * It will check if the types are fully equal to each other.
     * It will not fail if two objects have different values, but the same type.
     * It will fail however if an object is missing a property.
     *
     * **_Unexpected failure_**? For a more permissive but less performant
     * check that accommodates for equivalent intersection types,
     * use {@linkcode branded | .branded.toEqualTypeOf()}.
     * @see {@link https://github.com/mmkal/expect-type#why-is-my-assertion-failing | The documentation for details}.
     *
     * @example
     * <caption>Using generic type argument syntax</caption>
     * ```ts
     * expectTypeOf({ a: 1 }).toEqualTypeOf<{ a: number }>()
     *
     * expectTypeOf({ a: 1, b: 1 }).not.toEqualTypeOf<{ a: number }>()
     * ```
     *
     * @example
     * <caption>Using inferred type syntax by passing a value</caption>
     * ```ts
     * expectTypeOf({ a: 1 }).toEqualTypeOf({ a: 1 })
     *
     * expectTypeOf({ a: 1 }).toEqualTypeOf({ a: 2 })
     * ```
     *
     * @param value - The value to compare against the expected type.
     * @param MISMATCH - The mismatch arguments.
     * @returns `true`.
     */
    <
      Expected extends StrictEqualUsingTSInternalIdenticalToOperator<Actual, Expected> extends true
        ? unknown
        : MismatchInfo<Actual, Expected>,
    >(
      value: Expected & AValue, // reason for `& AValue`: make sure this is only the selected overload when the end-user passes a value for an inferred typearg. The `Mismatch` type does match `AValue`.
      ...MISMATCH: MismatchArgs<StrictEqualUsingTSInternalIdenticalToOperator<Actual, Expected>, true>
    ): true

    /**
     * Uses TypeScript's internal technique to check for type "identicalness".
     *
     * It will check if the types are fully equal to each other.
     * It will not fail if two objects have different values, but the same type.
     * It will fail however if an object is missing a property.
     *
     * **_Unexpected failure_**? For a more permissive but less performant
     * check that accommodates for equivalent intersection types,
     * use {@linkcode branded | .branded.toEqualTypeOf()}.
     * @see {@link https://github.com/mmkal/expect-type#why-is-my-assertion-failing | The documentation for details}.
     *
     * @example
     * <caption>Using generic type argument syntax</caption>
     * ```ts
     * expectTypeOf({ a: 1 }).toEqualTypeOf<{ a: number }>()
     *
     * expectTypeOf({ a: 1, b: 1 }).not.toEqualTypeOf<{ a: number }>()
     * ```
     *
     * @example
     * <caption>Using inferred type syntax by passing a value</caption>
     * ```ts
     * expectTypeOf({ a: 1 }).toEqualTypeOf({ a: 1 })
     *
     * expectTypeOf({ a: 1 }).toEqualTypeOf({ a: 2 })
     * ```
     *
     * @param MISMATCH - The mismatch arguments.
     * @returns `true`.
     */
    <
      Expected extends StrictEqualUsingTSInternalIdenticalToOperator<Actual, Expected> extends true
        ? unknown
        : MismatchInfo<Actual, Expected>,
    >(
      ...MISMATCH: MismatchArgs<StrictEqualUsingTSInternalIdenticalToOperator<Actual, Expected>, true>
    ): true
  }

  toMatchTypeOf: {
    /**
     * A less strict version of {@linkcode toEqualTypeOf | .toEqualTypeOf()}
     * that allows for extra properties.
     * This is roughly equivalent to an `extends` constraint
     * in a function type argument.
     *
     * @example
     * <caption>Using generic type argument syntax</caption>
     * ```ts
     * expectTypeOf({ a: 1, b: 1 }).toMatchTypeOf<{ a: number }>()
     * ```
     *
     * @example
     * <caption>Using inferred type syntax by passing a value</caption>
     * ```ts
     * expectTypeOf({ a: 1, b: 1 }).toMatchTypeOf({ a: 2 })
     * ```
     *
     * @param value - The value to compare against the expected type.
     * @param MISMATCH - The mismatch arguments.
     * @returns `true`.
     */
    <Expected extends Extends<Actual, Expected> extends true ? unknown : MismatchInfo<Actual, Expected>>(
      value: Expected & AValue, // reason for `& AValue`: make sure this is only the selected overload when the end-user passes a value for an inferred typearg. The `Mismatch` type does match `AValue`.
      ...MISMATCH: MismatchArgs<Extends<Actual, Expected>, true>
    ): true

    /**
     * A less strict version of {@linkcode toEqualTypeOf | .toEqualTypeOf()}
     * that allows for extra properties.
     * This is roughly equivalent to an `extends` constraint
     * in a function type argument.
     *
     * @example
     * <caption>Using generic type argument syntax</caption>
     * ```ts
     * expectTypeOf({ a: 1, b: 1 }).toMatchTypeOf<{ a: number }>()
     * ```
     *
     * @example
     * <caption>Using inferred type syntax by passing a value</caption>
     * ```ts
     * expectTypeOf({ a: 1, b: 1 }).toMatchTypeOf({ a: 2 })
     * ```
     *
     * @param MISMATCH - The mismatch arguments.
     * @returns `true`.
     */
    <Expected extends Extends<Actual, Expected> extends true ? unknown : MismatchInfo<Actual, Expected>>(
      ...MISMATCH: MismatchArgs<Extends<Actual, Expected>, true>
    ): true
  }

  /**
   * Checks whether an object has a given property.
   *
   * @example
   * <caption>check that properties exist</caption>
   * ```ts
   * const obj = { a: 1, b: '' }
   *
   * expectTypeOf(obj).toHaveProperty('a')
   *
   * expectTypeOf(obj).not.toHaveProperty('c')
   * ```
   *
   * @param key - The property key to check for.
   * @param MISMATCH - The mismatch arguments.
   * @returns `true`.
   */
  toHaveProperty: <KeyType extends keyof Actual>(
    key: KeyType,
    ...MISMATCH: MismatchArgs<Extends<KeyType, keyof Actual>, true>
  ) => KeyType extends keyof Actual ? PositiveExpectTypeOf<Actual[KeyType]> : true

  /**
   * Inverts the result of the following assertions.
   *
   * @example
   * ```ts
   * expectTypeOf({ a: 1 }).not.toMatchTypeOf({ b: 1 })
   * ```
   */
  not: NegativeExpectTypeOf<Actual>

  /**
   * Intersection types can cause issues with
   * {@linkcode toEqualTypeOf | .toEqualTypeOf()}:
   * ```ts
   * // ❌ The following line doesn't compile, even though the types are arguably the same.
   * expectTypeOf<{ a: 1 } & { b: 2 }>().toEqualTypeOf<{ a: 1; b: 2 }>()
   * ```
   * This helper works around this problem by using
   * a more permissive but less performant check.
   *
   * __Note__: This comes at a performance cost, and can cause the compiler
   * to 'give up' if used with excessively deep types, so use sparingly.
   *
   * @see {@link https://github.com/mmkal/expect-type/pull/21 | Reference}
   */
  branded: {
    /**
     * Uses TypeScript's internal technique to check for type "identicalness".
     *
     * It will check if the types are fully equal to each other.
     * It will not fail if two objects have different values, but the same type.
     * It will fail however if an object is missing a property.
     *
     * **_Unexpected failure_**? For a more permissive but less performant
     * check that accommodates for equivalent intersection types,
     * use {@linkcode PositiveExpectTypeOf.branded | .branded.toEqualTypeOf()}.
     * @see {@link https://github.com/mmkal/expect-type#why-is-my-assertion-failing | The documentation for details}.
     *
     * @example
     * <caption>Using generic type argument syntax</caption>
     * ```ts
     * expectTypeOf({ a: 1 }).toEqualTypeOf<{ a: number }>()
     *
     * expectTypeOf({ a: 1, b: 1 }).not.toEqualTypeOf<{ a: number }>()
     * ```
     *
     * @example
     * <caption>Using inferred type syntax by passing a value</caption>
     * ```ts
     * expectTypeOf({ a: 1 }).toEqualTypeOf({ a: 1 })
     *
     * expectTypeOf({ a: 1 }).toEqualTypeOf({ a: 2 })
     * ```
     *
     * @param MISMATCH - The mismatch arguments.
     * @returns `true`.
     */
    toEqualTypeOf: <
      Expected extends StrictEqualUsingBranding<Actual, Expected> extends true
        ? unknown
        : MismatchInfo<Actual, Expected>,
    >(
      ...MISMATCH: MismatchArgs<StrictEqualUsingBranding<Actual, Expected>, true>
    ) => true
  }
}

/**
 * Represents the negative expectation type for the {@linkcode Actual} type.
 */
export interface NegativeExpectTypeOf<Actual> extends BaseExpectTypeOf<Actual, {positive: false}> {
  toEqualTypeOf: {
    /**
     * Uses TypeScript's internal technique to check for type "identicalness".
     *
     * It will check if the types are fully equal to each other.
     * It will not fail if two objects have different values, but the same type.
     * It will fail however if an object is missing a property.
     *
     * **_Unexpected failure_**? For a more permissive but less performant
     * check that accommodates for equivalent intersection types,
     * use {@linkcode PositiveExpectTypeOf.branded | .branded.toEqualTypeOf()}.
     * @see {@link https://github.com/mmkal/expect-type#why-is-my-assertion-failing | The documentation for details}.
     *
     * @example
     * <caption>Using generic type argument syntax</caption>
     * ```ts
     * expectTypeOf({ a: 1 }).toEqualTypeOf<{ a: number }>()
     *
     * expectTypeOf({ a: 1, b: 1 }).not.toEqualTypeOf<{ a: number }>()
     * ```
     *
     * @example
     * <caption>Using inferred type syntax by passing a value</caption>
     * ```ts
     * expectTypeOf({ a: 1 }).toEqualTypeOf({ a: 1 })
     *
     * expectTypeOf({ a: 1 }).toEqualTypeOf({ a: 2 })
     * ```
     *
     * @param value - The value to compare against the expected type.
     * @param MISMATCH - The mismatch arguments.
     * @returns `true`.
     */
    <Expected>(
      value: Expected & AValue,
      ...MISMATCH: MismatchArgs<StrictEqualUsingTSInternalIdenticalToOperator<Actual, Expected>, false>
    ): true

    /**
     * Uses TypeScript's internal technique to check for type "identicalness".
     *
     * It will check if the types are fully equal to each other.
     * It will not fail if two objects have different values, but the same type.
     * It will fail however if an object is missing a property.
     *
     * **_Unexpected failure_**? For a more permissive but less performant
     * check that accommodates for equivalent intersection types,
     * use {@linkcode PositiveExpectTypeOf.branded | .branded.toEqualTypeOf()}.
     * @see {@link https://github.com/mmkal/expect-type#why-is-my-assertion-failing | The documentation for details}.
     *
     * @example
     * <caption>Using generic type argument syntax</caption>
     * ```ts
     * expectTypeOf({ a: 1 }).toEqualTypeOf<{ a: number }>()
     *
     * expectTypeOf({ a: 1, b: 1 }).not.toEqualTypeOf<{ a: number }>()
     * ```
     *
     * @example
     * <caption>Using inferred type syntax by passing a value</caption>
     * ```ts
     * expectTypeOf({ a: 1 }).toEqualTypeOf({ a: 1 })
     *
     * expectTypeOf({ a: 1 }).toEqualTypeOf({ a: 2 })
     * ```
     *
     * @param MISMATCH - The mismatch arguments.
     * @returns `true`.
     */
    <Expected>(...MISMATCH: MismatchArgs<StrictEqualUsingTSInternalIdenticalToOperator<Actual, Expected>, false>): true
  }

  toMatchTypeOf: {
    /**
     * A less strict version of
     * {@linkcode PositiveExpectTypeOf.toEqualTypeOf | .toEqualTypeOf()}
     * that allows for extra properties.
     * This is roughly equivalent to an `extends` constraint
     * in a function type argument.
     *
     * @example
     * <caption>Using generic type argument syntax</caption>
     * ```ts
     * expectTypeOf({ a: 1, b: 1 }).toMatchTypeOf<{ a: number }>()
     * ```
     *
     * @example
     * <caption>Using inferred type syntax by passing a value</caption>
     * ```ts
     * expectTypeOf({ a: 1, b: 1 }).toMatchTypeOf({ a: 2 })
     * ```
     *
     * @param value - The value to compare against the expected type.
     * @param MISMATCH - The mismatch arguments.
     * @returns `true`.
     */
    <Expected>(
      value: Expected & AValue, // reason for `& AValue`: make sure this is only the selected overload when the end-user passes a value for an inferred typearg. The `Mismatch` type does match `AValue`.
      ...MISMATCH: MismatchArgs<Extends<Actual, Expected>, false>
    ): true

    /**
     * A less strict version of
     * {@linkcode PositiveExpectTypeOf.toEqualTypeOf | .toEqualTypeOf()}
     * that allows for extra properties.
     * This is roughly equivalent to an `extends` constraint
     * in a function type argument.
     *
     * @example
     * <caption>Using generic type argument syntax</caption>
     * ```ts
     * expectTypeOf({ a: 1, b: 1 }).toMatchTypeOf<{ a: number }>()
     * ```
     *
     * @example
     * <caption>Using inferred type syntax by passing a value</caption>
     * ```ts
     * expectTypeOf({ a: 1, b: 1 }).toMatchTypeOf({ a: 2 })
     * ```
     *
     * @param MISMATCH - The mismatch arguments.
     * @returns `true`.
     */
    <Expected>(...MISMATCH: MismatchArgs<Extends<Actual, Expected>, false>): true
  }

  /**
   * Checks whether an object has a given property.
   *
   * @example
   * <caption>check that properties exist</caption>
   * ```ts
   * const obj = { a: 1, b: '' }
   *
   * expectTypeOf(obj).toHaveProperty('a')
   *
   * expectTypeOf(obj).not.toHaveProperty('c')
   * ```
   *
   * @param key - The property key to check for.
   * @param MISMATCH - The mismatch arguments.
   * @returns `true`.
   */
  toHaveProperty: <KeyType extends string | number | symbol>(
    key: KeyType,
    ...MISMATCH: MismatchArgs<Extends<KeyType, keyof Actual>, false>
  ) => true
}

/**
 * Represents a conditional type that selects either
 * {@linkcode PositiveExpectTypeOf} or {@linkcode NegativeExpectTypeOf} based
 * on the value of the `positive` property in the {@linkcode Options} type.
 */
export type ExpectTypeOf<Actual, Options extends {positive: boolean}> = Options['positive'] extends true
  ? PositiveExpectTypeOf<Actual>
  : NegativeExpectTypeOf<Actual>

/**
 * Represents the base interface for the
 * {@linkcode expectTypeOf()} function.
 * Provides a set of assertion methods to perform type checks on a value.
 */
export interface BaseExpectTypeOf<Actual, Options extends {positive: boolean}> {
  /**
   * Checks whether the type of the value is `any`.
   */
  toBeAny: Scolder<ExpectAny<Actual>, Options>

  /**
   * Checks whether the type of the value is `unknown`.
   */
  toBeUnknown: Scolder<ExpectUnknown<Actual>, Options>

  /**
   * Checks whether the type of the value is `never`.
   */
  toBeNever: Scolder<ExpectNever<Actual>, Options>

  /**
   * Checks whether the type of the value is `function`.
   */
  toBeFunction: Scolder<ExpectFunction<Actual>, Options>

  /**
   * Checks whether the type of the value is `object`.
   */
  toBeObject: Scolder<ExpectObject<Actual>, Options>

  /**
   * Checks whether the type of the value is an {@linkcode Array}.
   */
  toBeArray: Scolder<ExpectArray<Actual>, Options>

  /**
   * Checks whether the type of the value is `number`.
   */
  toBeNumber: Scolder<ExpectNumber<Actual>, Options>

  /**
   * Checks whether the type of the value is `string`.
   */
  toBeString: Scolder<ExpectString<Actual>, Options>

  /**
   * Checks whether the type of the value is `boolean`.
   */
  toBeBoolean: Scolder<ExpectBoolean<Actual>, Options>

  /**
   * Checks whether the type of the value is `void`.
   */
  toBeVoid: Scolder<ExpectVoid<Actual>, Options>

  /**
   * Checks whether the type of the value is `symbol`.
   */
  toBeSymbol: Scolder<ExpectSymbol<Actual>, Options>

  /**
   * Checks whether the type of the value is `null`.
   */
  toBeNull: Scolder<ExpectNull<Actual>, Options>

  /**
   * Checks whether the type of the value is `undefined`.
   */
  toBeUndefined: Scolder<ExpectUndefined<Actual>, Options>

  /**
   * Checks whether the type of the value is `null` or `undefined`.
   */
  toBeNullable: Scolder<ExpectNullable<Actual>, Options>

  /**
   * Checks whether a function is callable with the given parameters.
   *
   * __Note__: You cannot negate this assertion with
   * {@linkcode PositiveExpectTypeOf.not | .not}, you need to use
   * `ts-expect-error` instead.
   *
   * @example
   * ```ts
   * const f = (a: number) => [a, a]
   *
   * expectTypeOf(f).toBeCallableWith(1)
   * ```
   *
   * __Known Limitation__: This assertion will likely fail if you try to use it
   * with a generic function or an overload.
   * @see {@link https://github.com/mmkal/expect-type/issues/50 | This issue} for an example and a workaround.
   *
   * @param args - The arguments to check for callability.
   * @returns `true`.
   */
  toBeCallableWith: Options['positive'] extends true
    ? <Args extends OverloadParameters<Actual>>(
        ...args: Args
      ) => ExpectTypeOf<OverloadsNarrowedByParameters<Actual, Args>, Options>
    : never

  /**
   * Checks whether a class is constructible with the given parameters.
   *
   * @example
   * ```ts
   * expectTypeOf(Date).toBeConstructibleWith('1970')
   *
   * expectTypeOf(Date).toBeConstructibleWith(0)
   *
   * expectTypeOf(Date).toBeConstructibleWith(new Date())
   *
   * expectTypeOf(Date).toBeConstructibleWith()
   * ```
   *
   * @param args - The arguments to check for constructibility.
   * @returns `true`.
   */
  toBeConstructibleWith: Options['positive'] extends true
    ? <Args extends ConstructorOverloadParameters<Actual>>(...args: Args) => true
    : never

  /**
   * Equivalent to the {@linkcode Extract} utility type.
   * Helps narrow down complex union types.
   *
   * @example
   * ```ts
   * type ResponsiveProp<T> = T | T[] | { xs?: T; sm?: T; md?: T }
   *
   * interface CSSProperties {
   *   margin?: string
   *   padding?: string
   * }
   *
   * function getResponsiveProp<T>(_props: T): ResponsiveProp<T> {
   *   return {}
   * }
   *
   * const cssProperties: CSSProperties = { margin: '1px', padding: '2px' }
   *
   * expectTypeOf(getResponsiveProp(cssProperties))
   *   .extract<{ xs?: any }>() // extracts the last type from a union
   *   .toEqualTypeOf<{
   *     xs?: CSSProperties
   *     sm?: CSSProperties
   *     md?: CSSProperties
   *   }>()
   *
   * expectTypeOf(getResponsiveProp(cssProperties))
   *   .extract<unknown[]>() // extracts an array from a union
   *   .toEqualTypeOf<CSSProperties[]>()
   * ```
   *
   * __Note__: If no type is found in the union, it will return `never`.
   *
   * @param v - The type to extract from the union.
   * @returns The type after extracting the type from the union.
   */
  extract: <V>(v?: V) => ExpectTypeOf<Extract<Actual, V>, Options>

  /**
   * Equivalent to the {@linkcode Exclude} utility type.
   * Removes types from a union.
   *
   * @example
   * ```ts
   * type ResponsiveProp<T> = T | T[] | { xs?: T; sm?: T; md?: T }
   *
   * interface CSSProperties {
   *   margin?: string
   *   padding?: string
   * }
   *
   * function getResponsiveProp<T>(_props: T): ResponsiveProp<T> {
   *   return {}
   * }
   *
   * const cssProperties: CSSProperties = { margin: '1px', padding: '2px' }
   *
   * expectTypeOf(getResponsiveProp(cssProperties))
   *   .exclude<unknown[]>()
   *   .exclude<{ xs?: unknown }>() // or just `.exclude<unknown[] | { xs?: unknown }>()`
   *   .toEqualTypeOf<CSSProperties>()
   * ```
   */
  exclude: <V>(v?: V) => ExpectTypeOf<Exclude<Actual, V>, Options>

  /**
   * Equivalent to the {@linkcode Pick} utility type.
   * Helps select a subset of properties from an object type.
   *
   * @example
   * ```ts
   * interface Person {
   *   name: string
   *   age: number
   * }
   *
   * expectTypeOf<Person>()
   *   .pick<'name'>()
   *   .toEqualTypeOf<{ name: string }>()
   * ```
   *
   * @param keyToPick - The property key to pick.
   * @returns The type after picking the property.
   */
  pick: <KeyToPick extends keyof Actual>(keyToPick?: KeyToPick) => ExpectTypeOf<Pick<Actual, KeyToPick>, Options>

  /**
   * Equivalent to the {@linkcode Omit} utility type.
   * Helps remove a subset of properties from an object type.
   *
   * @example
   * ```ts
   * interface Person {
   *   name: string
   *   age: number
   * }
   *
   * expectTypeOf<Person>().omit<'name'>().toEqualTypeOf<{ age: number }>()
   * ```
   *
   * @param keyToOmit - The property key to omit.
   * @returns The type after omitting the property.
   */
  omit: <KeyToOmit extends keyof Actual | (PropertyKey & Record<never, never>)>(
    keyToOmit?: KeyToOmit,
  ) => ExpectTypeOf<Omit<Actual, KeyToOmit>, Options>

  /**
   * Extracts a certain function argument with `.parameter(number)` call to
   * perform other assertions on it.
   *
   * @example
   * ```ts
   * function foo(a: number, b: string) {
   *   return [a, b]
   * }
   *
   * expectTypeOf(foo).parameter(0).toBeNumber()
   *
   * expectTypeOf(foo).parameter(1).toBeString()
   * ```
   *
   * @param index - The index of the parameter to extract.
   * @returns The extracted parameter type.
   */
  parameter: <Index extends number>(index: Index) => ExpectTypeOf<OverloadParameters<Actual>[Index], Options>

  /**
   * Equivalent to the {@linkcode Parameters} utility type.
   * Extracts function parameters to perform assertions on its value.
   * Parameters are returned as an array.
   *
   * @example
   * ```ts
   * function noParam() {}
   *
   * function hasParam(s: string) {}
   *
   * expectTypeOf(noParam).parameters.toEqualTypeOf<[]>()
   *
   * expectTypeOf(hasParam).parameters.toEqualTypeOf<[string]>()
   * ```
   */
  parameters: ExpectTypeOf<OverloadParameters<Actual>, Options>

  /**
   * Equivalent to the {@linkcode ConstructorParameters} utility type.
   * Extracts constructor parameters as an array of values and
   * perform assertions on them with this method.
   *
   * For overloaded constructors it will return a union of all possible parameter-tuples.
   *
   * @example
   * ```ts
   * expectTypeOf(Date).constructorParameters.toEqualTypeOf<
   *   [] | [string | number | Date]
   * >()
   * ```
   */
  constructorParameters: ExpectTypeOf<ConstructorOverloadParameters<Actual>, Options>

  /**
   * Equivalent to the {@linkcode ThisParameterType} utility type.
   * Extracts the `this` parameter of a function to
   * perform assertions on its value.
   *
   * @example
   * ```ts
   * function greet(this: { name: string }, message: string) {
   *   return `Hello ${this.name}, here's your message: ${message}`
   * }
   *
   * expectTypeOf(greet).thisParameter.toEqualTypeOf<{ name: string }>()
   * ```
   */
  thisParameter: ExpectTypeOf<ThisParameterType<Actual>, Options>

  /**
   * Equivalent to the {@linkcode InstanceType} utility type.
   * Extracts the instance type of a class to perform assertions on.
   *
   * @example
   * ```ts
   * expectTypeOf(Date).instance.toHaveProperty('toISOString')
   * ```
   */
  instance: Actual extends new (...args: any[]) => infer I ? ExpectTypeOf<I, Options> : never

  /**
   * Equivalent to the {@linkcode ReturnType} utility type.
   * Extracts the return type of a function.
   *
   * @example
   * ```ts
   * expectTypeOf(() => {}).returns.toBeVoid()
   *
   * expectTypeOf((a: number) => [a, a]).returns.toEqualTypeOf([1, 2])
   * ```
   */
  returns: Actual extends Function ? ExpectTypeOf<OverloadReturnTypes<Actual>, Options> : never

  /**
   * Extracts resolved value of a Promise,
   * so you can perform other assertions on it.
   *
   * @example
   * ```ts
   * async function asyncFunc() {
   *   return 123
   * }
   *
   * expectTypeOf(asyncFunc).returns.resolves.toBeNumber()
   *
   * expectTypeOf(Promise.resolve('string')).resolves.toBeString()
   * ```
   *
   * Type Equivalent:
   * ```ts
   * type Resolves<PromiseType> = PromiseType extends PromiseLike<infer ResolvedType>
   *   ? ResolvedType
   *   : never
   * ```
   */
  resolves: Actual extends PromiseLike<infer ResolvedType> ? ExpectTypeOf<ResolvedType, Options> : never

  /**
   * Extracts array item type to perform assertions on.
   *
   * @example
   * ```ts
   * expectTypeOf([1, 2, 3]).items.toEqualTypeOf<number>()
   *
   * expectTypeOf([1, 2, 3]).items.not.toEqualTypeOf<string>()
   * ```
   *
   * __Type Equivalent__:
   * ```ts
   * type Items<ArrayType> = ArrayType extends ArrayLike<infer ItemType>
   *   ? ItemType
   *   : never
   * ```
   */
  items: Actual extends ArrayLike<infer ItemType> ? ExpectTypeOf<ItemType, Options> : never

  /**
   * Extracts the type guarded by a function to perform assertions on.
   *
   * @example
   * ```ts
   * function isString(v: any): v is string {
   *   return typeof v === 'string'
   * }
   *
   * expectTypeOf(isString).guards.toBeString()
   * ```
   */
  guards: Actual extends (v: any, ...args: any[]) => v is infer T ? ExpectTypeOf<T, Options> : never

  /**
   * Extracts the type asserted by a function to perform assertions on.
   *
   * @example
   * ```ts
   * function assertNumber(v: any): asserts v is number {
   *   if (typeof v !== 'number')
   *     throw new TypeError('Nope !')
   * }
   *
   * expectTypeOf(assertNumber).asserts.toBeNumber()
   * ```
   */
  asserts: Actual extends (v: any, ...args: any[]) => asserts v is infer T
    ? // Guard methods `(v: any) => asserts v is T` does not actually defines a return type. Thus, any function taking 1 argument matches the signature before.
      // In case the inferred assertion type `R` could not be determined (so, `unknown`), consider the function as a non-guard, and return a `never` type.
      // See https://github.com/microsoft/TypeScript/issues/34636
      unknown extends T
      ? never
      : ExpectTypeOf<T, Options>
    : never
}
const fn: any = () => true

/**
 * Represents a function that allows asserting the expected type of a value.
 */
export type _ExpectTypeOf = {
  /**
   * Asserts the expected type of a value.
   *
   * @param actual - The actual value being asserted.
   * @returns An object representing the expected type assertion.
   */
  <Actual>(actual: Actual): ExpectTypeOf<Actual, {positive: true; branded: false}>

  /**
   * Asserts the expected type of a value without providing an actual value.
   *
   * @returns An object representing the expected type assertion.
   */
  <Actual>(): ExpectTypeOf<Actual, {positive: true; branded: false}>
}

/**
 * Similar to Jest's `expect`, but with type-awareness.
 * Gives you access to a number of type-matchers that let you make assertions about the
 * form of a reference or generic type parameter.
 *
 * @example
 * ```ts
 * import { foo, bar } from '../foo'
 * import { expectTypeOf } from 'expect-type'
 *
 * test('foo types', () => {
 *   // make sure `foo` has type { a: number }
 *   expectTypeOf(foo).toMatchTypeOf({ a: 1 })
 *   expectTypeOf(foo).toHaveProperty('a').toBeNumber()
 *
 *   // make sure `bar` is a function taking a string:
 *   expectTypeOf(bar).parameter(0).toBeString()
 *   expectTypeOf(bar).returns.not.toBeAny()
 * })
 * ```
 *
 * @description
 * See the [full docs](https://npmjs.com/package/expect-type#documentation) for lots more examples.
 */
export const expectTypeOf: _ExpectTypeOf = <Actual>(
  _actual?: Actual,
): ExpectTypeOf<Actual, {positive: true; branded: false}> => {
  const nonFunctionProperties = [
    'parameters',
    'returns',
    'resolves',
    'not',
    'items',
    'constructorParameters',
    'thisParameter',
    'instance',
    'guards',
    'asserts',
    'branded',
  ] as const
  type Keys = keyof PositiveExpectTypeOf<any> | keyof NegativeExpectTypeOf<any>

  type FunctionsDict = Record<Exclude<Keys, (typeof nonFunctionProperties)[number]>, any>
  const obj: FunctionsDict = {
    /* eslint-disable @typescript-eslint/no-unsafe-assignment */
    toBeAny: fn,
    toBeUnknown: fn,
    toBeNever: fn,
    toBeFunction: fn,
    toBeObject: fn,
    toBeArray: fn,
    toBeString: fn,
    toBeNumber: fn,
    toBeBoolean: fn,
    toBeVoid: fn,
    toBeSymbol: fn,
    toBeNull: fn,
    toBeUndefined: fn,
    toBeNullable: fn,
    toMatchTypeOf: fn,
    toEqualTypeOf: fn,
    toBeConstructibleWith: fn,
    toBeCallableWith: expectTypeOf,
    extract: expectTypeOf,
    exclude: expectTypeOf,
    pick: expectTypeOf,
    omit: expectTypeOf,
    toHaveProperty: expectTypeOf,
    parameter: expectTypeOf,
  }

  const getterProperties: readonly Keys[] = nonFunctionProperties
  getterProperties.forEach((prop: Keys) => Object.defineProperty(obj, prop, {get: () => expectTypeOf({})}))

  return obj as ExpectTypeOf<Actual, {positive: true; branded: false}>
}