Build-time Typescript-Type-safe JSON parser

build-time-typescript-type-json-parser.ts

// Base utility types
type Whitespace = '\u{9}' | '\u{A}' | '\u{20}' // tab, newline, space

type TrimLeft<V extends string> = V extends `${Whitespace}${infer R}`
    ? TrimLeft<R>
    : V

type TrimRight<V extends string> = V extends `${infer R}${Whitespace}`
    ? TrimRight<R>
    : V

type Trim<V extends string> = TrimLeft<TrimRight<V>>

type Prettify<T> = {
    [K in keyof T]: T[K]
} & {}

// Type detection helpers
type IsDate<T> = T extends string 
    ? T extends `${number}${number}${number}${number}-${number}${number}-${number}${number}` 
        ? true 
        : false
    : false

type IsNumeric<T> = T extends number 
    ? true 
    : T extends `${number}` 
        ? true 
        : false

// Custom type handling
type CustomTypes = Record<string, string | Record<string, unknown>>
type Scalar = Record<string, unknown>

// Main type extractor
type ExtractType<T> = T extends Array<infer U>
    ? ExtractType<U>[]
    : T extends object
    ? {
        [K in keyof T]: T[K] extends string
            ? IsDate<T[K]> extends true
                ? Date
                : IsNumeric<T[K]> extends true
                    ? number
                    : string
            : ExtractType<T[K]>
      }
    : T extends string
    ? IsDate<T> extends true
        ? Date
        : IsNumeric<T> extends true
            ? number
            : string
    : T extends number
    ? number
    : T extends boolean
    ? boolean
    : T extends null
    ? null
    : T extends undefined
    ? undefined
    : never

// String parsing type
type ExtractTypeFromString<T extends string> = T extends `${infer Type}\n${infer Rest}`
    ? [TrimLeft<Type>, Rest]
    : T extends `${infer Type} ${infer Rest}`
    ? [TrimLeft<Type>, Rest]
    : never

// Usage helper type
type InferredType<T> = Prettify<ExtractType<T>>

// Example usage:
const processData = <T>(data: T): InferredType<T> => {
    return data as InferredType<T>;
}