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/**
* Supported HTTP methods
*/
type HttpMethod = "get" | "post" | "put" | "delete";
/**
* Schema type for path parameter
*/
type SchemaParam = string | number | ReadonlyArray<string | number> | undefined;
/**
* Schema type for path parameters
*/
type SchemaParams = Record<string, SchemaParam>;
/**
* Schema type of query parameters (non-object values only)
*/
type SchemaQueries = Record<
string,
| boolean
| number
| string
| null
| bigint
| undefined
| ReadonlyArray<boolean | number | string | null | bigint | undefined>
>;
/**
* Schema type for URL construction parameters
*/
export type Options = { params?: SchemaParams; queries?: SchemaQueries; hash?: string };
/**
* Utility type that extracts path parameters from an endpoint string and generates object types with those as keys
*
* @example
* ExtractParams<"/users/[userId]/posts/[postId]">
* // { userId: string | number, postId: string | number }
*
* ExtractParams<"/path/[...params]">
* // { params: (string | number)[] }
*
* ExtractParams<"/path/[[...params]]">
* // { params?: (string | number)[] }
*/
type ExtractParams<Endpoint extends string> = Endpoint extends `${infer Before}[[...${infer Param}]]${infer After}`
? { [K in Param]: Extract<SchemaParam, ReadonlyArray<unknown> | undefined> } & ExtractParams<Before> &
ExtractParams<After>
: Endpoint extends `${infer Before}[...${infer Param}]${infer After}`
? { [K in Param]: Extract<SchemaParam, ReadonlyArray<unknown>> } & ExtractParams<Before> & ExtractParams<After>
: Endpoint extends `${string}[${infer Param}]${infer After}`
? { [K in Param]: Extract<SchemaParam, string | number> } & ExtractParams<After>
: unknown;
/**
* Utility type to determine if a path parameter exists from an endpoint string
*
* @example
* HasParams<"/users/[id]">
* // true
*
* HasParams<"/users">
* // false
*/
type HasParams<Endpoint extends string> = keyof ExtractParams<Endpoint> extends never ? false : true;
/**
* Utility type that defines the type of arguments the method expects, based on the endpoint string.
* - If the endpoint contains a path parameter (`[param]`): the `params` property is required
* - If the endpoint does not contain a path parameter: the `params` property is not allowed
* - `queries` are always optional.
*
* @example
* ExpectedOptions<"/users/[id]">
* // { params: { id: string | number }; queries?: SchemaQueries }
*
* ExpectedOptions<"/users">
* // { params?: never; queries?: SchemaQueries }
*/
type ExpectedOptions<Endpoint extends string> = HasParams<Endpoint> extends true
? { params: ExtractParams<Endpoint>; queries?: SchemaQueries; hash?: string }
: { params?: never; queries?: SchemaQueries; hash?: string };
/**
* Utility type to extract only nullable properties
*
* @example
* PickNullable<{ required: string; optional?: string }>
* // { optional?: string }
*/
type PickNullable<T> = {
[P in keyof T as undefined extends T[P] ? P : never]: T[P];
};
/**
* Utility type to extract only Required properties
*
* @example
* PickRequired<{ required: string; optional?: string }>
* // { required: string }
*/
type PickRequired<T> = {
[P in keyof T as undefined extends T[P] ? never : P]: T[P];
};
/**
* Utility type that recursively determines if a required property is present
*
* @example
* HasRequired<{ required: { optional?: string } }>
* // true
*
* HasRequired<{ optional?: { required: string } }>
* // true
*
* HasRequired<{ optional?: { optional?: string } }>
* // false
*/
type HasRequired<T> = (
T extends ReadonlyArray<unknown>
? false
: T extends object
? keyof PickRequired<T> extends never
? HasRequired<T[keyof T]>
: true
: false
) extends false
? false
: true;
/**
* Utility type that makes Nullable properties optional by adding `?` (optional modifier).
*
* @example
* Optional<{ required: string; optional: Nullable<string> }>
* // { required: string; optional?: string }
*/
type Optional<T> = {
[K in keyof PickNullable<T>]?: T[K];
} & {
[K in keyof PickRequired<T>]: T[K];
};
/**
* Utility type that makes all properties of an object readonly
*
* @example
* ReadonlyProperties<{ array: string[] }>
* // { readonly array: readonly string[] }
*/
type ReadonlyProperties<T> = {
[K in keyof T]: Readonly<T[K]>;
};
/**
* Converts schema definition into optional keys if it has no required fields.
* Readonly is marked to accept as const arguments.
*
* @example
* ActualOptions<{ queries: { search?: string; count?: number } }>
* // { queries?: { search?: string; count?: number } }
*
* ActualOptions<{ queries: { search: string; count?: number } }>
* // { queries: { search: string; count?: number } }
*/
type ActualOptions<Schema extends Options> = Omit<
{
[K in keyof Schema as HasRequired<Schema[K]> extends true ? K : never]: Optional<ReadonlyProperties<Schema[K]>>;
} & {
[K in keyof Schema as HasRequired<Schema[K]> extends false ? K : never]?: Optional<ReadonlyProperties<Schema[K]>>;
},
"hash"
> & {
hash?: Schema["hash"];
};
/**
* Utility type that joins an array of strings or numbers into a single string
*
* @example
* JoinParams<["123", "456"]>
* // "123/456"
*/
type JoinParams<T extends ReadonlyArray<unknown>> = T extends readonly [
infer Head extends Extract<SchemaParam, string | number>,
...infer Tail extends ReadonlyArray<unknown>,
]
? Tail["length"] extends 0
? Head
: `${Head}/${JoinParams<Tail>}`
: "";
/**
* Utility type that trims double slashes and trailing slash from a path string
*
* @example
* TrimPath<"/path//to//resource/">
* // "/path/to/resource"
*/
type TrimPath<Path extends string> = Path extends `${infer Before}//${infer After}`
? `${TrimPath<`${Before}/${After}`>}`
: Path extends `${infer Before}/`
? `${Before}`
: Path;
/**
* Replace [param] in path with actual values
*
* @example
* ReplacePathParams<"/users/[userId]/posts/[postId]", { userId: "123"; postId: "456" }>
* // "/users/123/posts/456"
*
* ReplacePathParams<"/path/[...params]", { params: ["123", "456"] }>
* // "/path/123/456"
*
* ReplacePathParams<"/path/[[...params]]", { params: ["123", "456"] }>
* // "/path/123/456"
*/
type ReplacePathParams<
Path extends string,
Params extends SchemaParams,
> = Path extends `${infer Before}[[...${infer Param}]]${infer After}`
? Param extends keyof Params
? Params[Param] extends Extract<SchemaParam, ReadonlyArray<unknown>>
? `${ReplacePathParams<Before, Params>}${JoinParams<Params[Param]>}${ReplacePathParams<After, Params>}`
: never
: `${ReplacePathParams<Before, Params>}${ReplacePathParams<After, Params>}`
: Path extends `${infer Before}[...${infer Param}]${infer After}`
? Param extends keyof Params
? Params[Param] extends Extract<SchemaParam, ReadonlyArray<unknown>>
? `${ReplacePathParams<Before, Params>}${JoinParams<Params[Param]>}${ReplacePathParams<After, Params>}`
: never
: never
: Path extends `${infer Before}[${infer Param}]${infer After}`
? Param extends keyof Params
? Params[Param] extends Extract<SchemaParam, string | number>
? `${Before}${Params[Param]}${ReplacePathParams<After, Params>}`
: never
: never
: Path;
/**
* Utility type that removes optional catch-all parameters from the path
*
* @example
* ExcludeOptionalCatchAll<"/path/[[...params]]">
* // "/path/"
*/
type ExcludeOptionalCatchAll<Path extends string> = Path extends `${infer Before}[[...${string}]]${infer After}`
? `${Before}${ExcludeOptionalCatchAll<After>}`
: Path;
/**
* Applies path parameters if they exist
*
* @example
* ApplyParams<"/users/[userId]", { userId: 123 }>
* // "/users/123"
*
* ApplyParams<"/">
* // "/"
*/
type ApplyParams<Path extends string, Params extends Nullable<Optional<ExtractParams<Path>>>> = TrimPath<
keyof Params extends never
? ExcludeOptionalCatchAll<Path>
: Params extends SchemaParams
? ReplacePathParams<Path, Params>
: never
>;
/**
* Applies query parameters if they exist
*
* @example
* ApplyQueries<"/", { required: string }>
* // `/?${string}`
*
* ApplyQueries<"/", { optional?: string }>
* // `/${string}`
*
* ApplyQueries<"/">
* // "/"
*/
type ApplyQueries<Path extends string, Queries extends Nullable<SchemaQueries>> = keyof Queries extends never
? Path
: Queries extends SchemaQueries
? `${Path}${HasRequired<Queries> extends true ? "?" : ""}${string}`
: Path;
/**
* Applies hash fragment if defined
*
* @example
* ApplyHash<"/path", "hash">
* // "/path#hash"
*
* ApplyHash<"/path">
* // "/path"
*/
type ApplyHash<Path extends string, Hash extends Nullable<string>> = Hash extends string ? `${Path}#${Hash}` : Path;
/**
* Combines path, queries, and hash into a fully typed URL string
*
* @example
* ExtractPath<"/users/[userId]", { userId: 123 }, { search: string }>
* // `/users/123?${string}`
*/
type ExpectedPath<
Path extends string,
Params extends Nullable<Optional<ExtractParams<Path>>> = undefined,
Queries extends Nullable<SchemaQueries> = undefined,
Hash extends Nullable<string> = undefined,
> = ApplyHash<ApplyQueries<ApplyParams<Path, Params>, Queries>, Hash>;
/**
* Combines endpoint and schema definition to generate a concrete return type
* Refine type according to the presence or absence of path and query parameters in the schema definition
*
* @example
* ActualReturn<"/path/[param]", { params: { param: string }, queries: { q: string } }>
* // `/path/${string}?${string}`
*
* ActualReturn<"/path/[param1]/to/[param2]", { params: { param1: string; param2: number } }>
* // `/path/${string}/to/${number}`
*
* ActualReturn<"/path", { queries: { q: string } }>
* // `/path?${string}`
*/
type ActualReturn<Path extends string, Options> = ExpectedPath<
Path,
Options extends { params: infer Params extends Optional<ExtractParams<Path>> } ? Params : undefined,
Options extends { queries?: infer Queries extends Nullable<SchemaQueries> } ? Queries : undefined,
Options extends { hash: infer Hash extends string } ? Hash : undefined
>;
/**
* Alias for methods with no parameters
*/
export type Empty = Nullable<Record<string, never>>;
/**
* Function type that returns a URL string based on the schema definition
* - Accepts parameters depending on whether required fields exist
*/
type Method<BaseUrl extends string, Endpoint extends string, OptionsSchema> = OptionsSchema extends Empty
? () => `${BaseUrl}${Endpoint}`
: OptionsSchema extends Options
? HasRequired<ActualOptions<OptionsSchema>> extends true
? <Options extends ActualOptions<OptionsSchema>>(
options: Options,
) => `${BaseUrl}${ActualReturn<Endpoint, Options>}`
: <Options extends ActualOptions<OptionsSchema>>(
options?: Options,
) => `${BaseUrl}${ActualReturn<Endpoint, Options>}`
: never;
/**
* Expected schema definition:
* - Endpoint string as key
* - Object of HTTP methods as values
* - Each method can have its own schema definition
*/
export type ExpectedSchema<Schema> = {
[EndpointKey in keyof Schema]: EndpointKey extends string
? Partial<Record<HttpMethod, ExpectedOptions<EndpointKey>>>
: never;
};
/**
* Actual schema returned from the function:
* - Each method is replaced with a typed URL generator
*/
export type ActualSchema<Schema, BaseUrl extends string> = {
[EndpointKey in keyof Schema]: EndpointKey extends string
? {
[MethodKey in keyof Schema[EndpointKey]]: Method<BaseUrl, EndpointKey, Schema[EndpointKey][MethodKey]>;
}
: never;
};
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