feat(typescript-types): Add KeyPaths<T, F, O>

packages/typescript-types/src/key-paths.ts

@@ -0,0 +1,47 @@
+import type { If } from './if.js'
+import type { IsEmptyString } from './is-empty-string.js'
+import type { Assign } from './assign.js'
+
+interface KeyPaths_Options {
+	separator?: string
+	leavesOnly?: boolean
+}
+
+interface KeyPaths_DefaultOptions {
+	separator: '.'
+	leavesOnly: true
+}
+
+type GetPrefixedKey<
+	Parent extends string,
+	Key extends string,
+	Separator extends string
+> = `${If<IsEmptyString<Parent>, '', `${Parent}${Separator}`>}${Key}`
+
+type PrefixIfNot<Cond, Prefix, T> = If<Cond, T, Prefix | T>
+
+type KeyPathOf<
+	Obj,
+	Options extends Required<KeyPaths_Options>,
+	Parent extends string,
+	Filter = never
+> = Obj extends object
+	? PrefixIfNot<Options['leavesOnly'], Parent, KeyPathsOfStringKeys<Obj, Options, Filter, Parent>>
+	: Parent
+
+type KeyPathsOfStringKeys<
+	Obj extends object,
+	Options extends Required<KeyPaths_Options>,
+	Filter = never,
+	Parent extends string = ''
+> = {
+	[Key in keyof Obj & string]: Obj[Key] extends Filter
+		? never
+		: KeyPathOf<Obj[Key], Options, GetPrefixedKey<Parent, Key, Options['separator']>, Filter>
+}[keyof Obj & string]
+
+export type KeyPaths<
+	Obj extends object,
+	Filter = null | undefined | never,
+	Options extends KeyPaths_Options = {}
+> = KeyPathsOfStringKeys<Obj, Assign<KeyPaths_Options, KeyPaths_DefaultOptions, Options>, Filter>