How to create a custom type from some properties of a complex object?

Question

I have the following type definitions as helpers:

type MapSchemaTypes = {
    string: string;
    number: number;
    integer: number;
    float: number;
    boolean: boolean;
};

type MapSchema<T extends Record<string, keyof MapSchemaTypes>> = {
    -readonly [K in keyof T]: MapSchemaTypes[T[K]]
}

With that, I can generate a type from a simple object. For example:

const TestModel1 = {
    id: "number",
    lastname: "string",
    firstname: "string",
    valid: "boolean"
} as const;
type TestRecord1 = MapSchema<typeof TestModel1>;

Result is correct:

type TestRecord1 = {
    id: number;
    lastname: string;
    firstname: string;
    valid: boolean;
}

But now, I would like to generate the exact same type but from a more complex object:

const TestModel2 = {
    id: {
        type: "number",
        mapping: "_id",
        defaultValue: 0
    },
    lastname: {
        type: "string",
        mapping: "_lastname",
        defaultValue: ""
    },
    firstname: {
        type: "string",
        mapping: "_firstname",
        defaultValue: ""
    },
    valid: {
        type: "boolean",
        mapping: "_valid",
        defaultValue: false
    }
} as const;
type TestRecord2 = MapSchema<typeof TestModel2>;

Errors:

Type '{ readonly id: { readonly type: "number"; readonly mapping: "_id"; readonly defaultValue: 0; }; readonly lastname: { readonly type: "string"; readonly mapping: "_lastname"; readonly defaultValue: ""; }; readonly firstname: { ...; }; readonly valid: { ...; }; }' does not satisfy the constraint 'Record<string, "string" | "number" | "boolean" | "integer" | "float">'.
Property 'id' is incompatible with index signature.
    Type '{ readonly type: "number"; readonly mapping: "_id"; readonly defaultValue: 0; }' is not assignable to type '"string" | "number" | "boolean" | "integer" | "float"'.
    Type '{ readonly type: "number"; readonly mapping: "_id"; readonly defaultValue: 0; }' is not assignable to type '"float"'.ts(2344)

It obviously generates the wrong type:

type TestRecord2 = {
    id: unknown;
    lastname: unknown;
    firstname: unknown;
    valid: unknown;
}

And I cannot figure how to do it correctly. I know that I have to change the MapSchema type but everything I tried failed so far.

For example I tried:

type MapSchema<T extends Record<string, keyof MapSchemaTypes>> = {
    -readonly [K in keyof T]: MapSchemaTypes[T[K]["type"]]
}

But it gives me the following error:

Type 'T[K]["type"]' cannot be used to index type 'MapSchemaTypes'.ts(2536)
Type '"type"' cannot be used to index type 'T[K]'.ts(2536)

Or again:

type MapSchema<T extends Record<string, keyof MapSchemaTypes>> = {
    -readonly [K in keyof T]: MapSchemaTypes[T[K].type]]
}

Error:

Cannot find name 'type'.ts(2304)

Is it even possible to achieve what I want to do?

Update

Following @Titian Cernicova-Dragomir very helpful answer , here are my updated type helpers:

type MapSchemaTypes = {
    string: string;
    number: number;
    integer: number;
    float: number;
    boolean: boolean;
};
type MapSchemaDefaultValues = string | number | boolean | undefined | null;
type MapSchemaSimpleField   = keyof MapSchemaTypes;
type MapSchemaComplexField  = {
    type: MapSchemaSimpleField;
    mapping: string;
    defaultValue: MapSchemaDefaultValues
};
type MapSchemaField = MapSchemaSimpleField | MapSchemaComplexField;
type MapSchemaDefinition = Record<string, MapSchemaField>;
type MapSchema<T extends MapSchemaDefinition> = {
    -readonly [K in keyof T]: T[K] extends { type: infer TypeName } ? MapSchemaTypes[TypeName & MapSchemaSimpleField] : MapSchemaTypes[T[K] & MapSchemaSimpleField]
};

This lets me do the following:

const TestModel4 = {
    id: "number",
    lastname: {
        type: "string",
        mapping: "_lastname",
        defaultValue: ""
    },
    firstname: "string",
    valid: {
        type: "boolean",
        mapping: "_valid",
        defaultValue: false
    }
} as const;
type TestRecord4 = MapSchema<typeof TestModel4>;

And the resulting type is correct:

type TestRecord4 = {
    id: number;
    lastname: string;
    firstname: string;
    valid: boolean;
}

Answer 1

The constraint you have on T is wrong if you want the properties of T to be an object with a type property, you should use Record<string, { type: keyof MapSchemaTypes }>

type MapSchema<T extends Record<string, { type: keyof MapSchemaTypes }>> = {
    -readonly [K in keyof T]: MapSchemaTypes[T[K]["type"]]
}

Playground Link

If you want it to work for both complex objects and just the type name, you can use a union in the constraint and a conditional type to discriminate between the two casses:

type MapSchema<T extends Record<string, { type: keyof MapSchemaTypes } | keyof MapSchemaTypes>> = {
    -readonly [K in keyof T]: T[K] extends { type: infer TypeName } ? MapSchemaTypes[TypeName &  keyof MapSchemaTypes] : MapSchemaTypes[T[K] & keyof MapSchemaTypes]
}

Playground Link