Typescript Flatten Nested Interface

gistfile1.txt

// Source: https://www.typescriptlang.org/play?noErrorTruncation=true&ts=4.4.2#code/HYQwtgpgzgDiDGEAEB5ATgSwOZIN4CgkikNgAXCNAMwWQDEB7BvQ4tqpgLiSjM2Cys2RAEYg0Afm7AArmBGUhw4NAoATbgWHakHBt178sAGiU6kaiBBgAbAJ4A5VRA0tz5sZOlyFaMzoBffyIg8xlgDAZgAz5SHAAfN3ciPRijU2TRcSkkWXlFc1DiIKUyOxh6JjobEDIKFTUkAF4katr6gB5GBgA+JQB6ACokMorWqpq6iAbmpPYuHliBAG5-ACIVXhcAOj01tLjV7XDI6MWjI+E1k6jdpn3zw-9PHLzfJETwyypSF0u2DbONTbSzWexOLbAzxrV4+SgfJBfCA-Br-YjXCK3aGw-JoBFIlF-JQBQb9fBKUgUai0cYMNpTBoAWRAshANjmwlSjwEwSQL28uN5gMhdwYD0McSFm3UIKstkcQO22IFvnJ5n6-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-CHjeShjqeuJtj897Aq+tyXrIMK2X+3Fjpmwbx1mtcWTDVTPmAb5fjUSHTqVfdDwRj6Bx1FHUWmjGz0vWQIBxwL8WR5FUfR3sBsfZ8VARrcqYJolVoxj9KG-P8WYDNmacJzn6eA0DwJHKJoNglkfygBGCVponRZAsCIKlmC4LlxbthQincUFwk0eVs7VYlqDNdl6Adcw7C8LIN7GMNpWRdN8X1eAaWtethbtlI8mnaR9njdd7YxbVyXPct+CoB10aaIYOi0DsfmjGd4X0RmriIB4-jBNTuJ045zOMbm6AFepo26f6tBZMgfX3iDoXi6IE7RY2ygC4EIuQ+IGKIDi6YckVjOUnStCe7RbLcvynO9SbquiqQUlyRKvNyGT2ZcCQNKIDsYTq3PNlr24Q7qwYGBI4XPlZ5ZYzVnwNeC1sUCIA6ayelmAB9QsX8sd+kAQCLNMEsvkc5qCiPYQy7EkASDwEgNYS1uDWRYrjNixkkDIJ6A-EqP9n6YX-h-ZoShrKAOAcjA0zo3QelgfAliABpEgepd52AYNqaybEAC0UheSMKAcWA0rM4G-wIW-FB9C2Kf34SAg0pAqDwjzLQxR0iKFIHXvRWBvJ1LmBYdwAABgAElwPQgIRi8wsQAOQsIseglRoC1hrFoQ4zBCDthrFMbgcxVi942ICHojImQj42BPmoyxQTrw2ICckC+V8IqhO8XYGxZCBEIMcXA3AJk7EGhwhgeAaV37VnoZ-OBfBrwuJoDYXiLivExNOGyGxjleTSAvPCZpn4XEqE-MSFiLC2FIA4S47eujUmH2PgZay59L51LiRUqpJRH5NWgjYGoMBeIAKyWojedhP4tAABRKG3ixRRpA1FFlch6Ap8DalRGvrM5AARP48XidYtibFuBePCRAJJTkkAADIkB4T8hgNkHRDnHL1IWPgCAyCXO3tc8a3BSn3MeQaLxLy3nxM+d8voABKZJMimHyLxCgWhhzGEnN6dqFAGKUAMPQSZNpigFljGqsAd+OykBLJWWskRr92V9FXk1TM2Zcx2EhTI9Z5DQEAFVqzSvxao2M1ZYyzCIS0c8DAUJAA
// Saved here in case it ever goes away, this could be useful if you wanted to do some specific
// bindings between a react state that is flattened and a nested interface.

namespace Orig {
    interface Foo {
        foo: string
        bar?: number
        nested: {
            foo: string,
            deeplyNested: {
                bar?: number
            }
        }
        union: string | {
            foo: string,
            bar?: number
        }
    }

    type FooFlattened = Flatten<Foo>
    /* type FooFlattened = {
      foo: string;
      "nested.foo": string;
      union: string;
      "union.foo": string;
      bar?: number | undefined;
      "nested.deeplyNested.bar"?: number | undefined;
      "union.bar"?: number | undefined;
    }*/

    interface FooFlattenedManual {
        foo: string
        bar?: number
        "nested.foo": string
        "nested.deeplyNested.bar"?: number

        // if union is a string:
        union: string

        // if union is an object:
        "union.foo": string
        "union.bar"?: number
    }

    type VerifySame = MutuallyExtends<FooFlattened, FooFlattenedManual>
}

interface Foo {
    tmdb: number | {
        title: {
            original: string
            german?: string
        }
        budget?: number
        revenue?: number
        tagline?: string
        overview?: string
        productionCompanies?: {
            id?: number
            logoPath?: string
            name?: string
            originCountry?: string
        }[]
        releaseDate?: string
        genres?: string[]
        runtime?: number
        poster?: string | {
            data: { sample: any } 
            contentType: string
        }
    }
    rating: { ch: number; rt: number } | { total: number }
    dateSeen?: Date
    fsk?: number
    mm?: boolean
}

type FlattenedFoo = Flatten<Foo>
/* type FlattenedFoo = {
    tmdb: number;
    "tmdb.title.original": string;
    "tmdb.genres.0": string;
    "tmdb.poster.data.sample": any;
    "tmdb.poster.contentType": string;
    "rating.ch": number;
    "rating.rt": number;
    "rating.total": number;
    "tmdb.title.german"?: string | undefined;
    "tmdb.budget"?: number | undefined;
    "tmdb.revenue"?: number | undefined;
    "tmdb.tagline"?: string | undefined;
    "tmdb.overview"?: string | undefined;
    "tmdb.productionCompanies"?: undefined;
    "tmdb.productionCompanies.0.id"?: number | undefined;
    "tmdb.productionCompanies.0.logoPath"?: string | undefined;
    "tmdb.productionCompanies.0.name"?: string | undefined;
    "tmdb.productionCompanies.0.originCountry"?: string | undefined;
    "tmdb.releaseDate"?: string | undefined;
    "tmdb.genres"?: undefined;
    "tmdb.runtime"?: number | undefined;
    "tmdb.poster"?: string | undefined;
    dateSeen?: undefined;
    fsk?: number | undefined;
    mm?: boolean | undefined;
} */

type Entry = { key: string, value: any, optional: boolean };

type Explode<T> = _Explode<T extends readonly any[] ? { "0": T[number] } : T>;

type _Explode<T> =
    T extends object ? { [K in keyof T]-?:
        K extends string ? Explode<T[K]> extends infer E ? E extends Entry ?
        {
            key: `${K}${E['key'] extends "" ? "" : "."}${E['key']}`,
            value: E['value'],
            optional: E['key'] extends "" ? {} extends Pick<T, K> ? true : false : E['optional']
        }
        : never : never : never
    }[keyof T] : { key: "", value: T, optional: false }


type Collapse<T extends Entry> = (
    { [E in Extract<T, { optional: false }> as E['key']]: E['value'] }
    & Partial<{ [E in Extract<T, { optional: true }> as E['key']]: E['value'] }>
) extends infer O ? { [K in keyof O]: O[K] } : never

type Flatten<T> = Collapse<Explode<T>>


type MutuallyExtends<T extends U, U extends V, V = T> = void