ajv/lib/types/json-schema.ts

Another JSON Schema Validator

/* eslint-disable @typescript-eslint/no-empty-interface */
export type SomeJSONSchema = JSONSchemaType<Known, true>

export type PartialSchema<T> = Partial<JSONSchemaType<T, true>>

type JSONType<T extends string, _partial extends boolean> = _partial extends true
  ? T | undefined
  : T

export type JSONSchemaType<T, _partial extends boolean = false> = (T extends number
  ? {
      type: JSONType<"number" | "integer", _partial>
      minimum?: number
      maximum?: number
      exclusiveMinimum?: number
      exclusiveMaximum?: number
      multipleOf?: number
      format?: string
    }
  : T extends string
  ? {
      type: JSONType<"string", _partial>
      minLength?: number
      maxLength?: number
      pattern?: string
      format?: string
    }
  : T extends boolean
  ? {
      type: "boolean"
    }
  : T extends [any, ...any[]]
  ? {
      // JSON AnySchema for tuple
      type: JSONType<"array", _partial>
      items: {
        [K in keyof T]-?: JSONSchemaType<T[K]> & Nullable<T[K]>
      } & {length: T["length"]}
      minItems: T["length"]
    } & ({maxItems: T["length"]} | {additionalItems: false})
  : T extends any[]
  ? {
      type: JSONType<"array", _partial>
      items: JSONSchemaType<T[0]>
      contains?: PartialSchema<T[0]>
      minItems?: number
      maxItems?: number
      minContains?: number
      maxContains?: number
      uniqueItems?: true
      additionalItems?: never
    }
  : T extends Record<string, any>
  ? {
      // JSON AnySchema for records and dictionaries
      // "required" is not optional because it is often forgotten
      // "properties" are optional for more concise dictionary schemas
      // "patternProperties" and can be only used with interfaces that have string index
      type: JSONType<"object", _partial>
      // "required" type does not guarantee that all required properties are listed
      // it only asserts that optional cannot be listed
      required: _partial extends true ? (keyof T)[] : RequiredMembers<T>[]
      additionalProperties?: boolean | JSONSchemaType<T[string]>
      unevaluatedProperties?: boolean | JSONSchemaType<T[string]>
      properties?: _partial extends true ? Partial<PropertiesSchema<T>> : PropertiesSchema<T>
      patternProperties?: {[Pattern in string]?: JSONSchemaType<T[string]>}
      propertyNames?: JSONSchemaType<string>
      dependencies?: {[K in keyof T]?: (keyof T)[] | PartialSchema<T>}
      dependentRequired?: {[K in keyof T]?: (keyof T)[]}
      dependentSchemas?: {[K in keyof T]?: PartialSchema<T>}
      minProperties?: number
      maxProperties?: number
    }
  : T extends null
  ? {
      nullable: true
    }
  : never) & {
  [keyword: string]: any
  $id?: string
  $ref?: string
  $defs?: {
    [Key in string]?: JSONSchemaType<Known, true>
  }
  definitions?: {
    [Key in string]?: JSONSchemaType<Known, true>
  }
  allOf?: PartialSchema<T>[]
  anyOf?: PartialSchema<T>[]
  oneOf?: PartialSchema<T>[]
  if?: PartialSchema<T>
  then?: PartialSchema<T>
  else?: PartialSchema<T>
  not?: PartialSchema<T>
}

type Known = KnownRecord | [Known, ...Known[]] | Known[] | number | string | boolean | null

interface KnownRecord extends Record<string, Known> {}

type PropertiesSchema<T> = {
  [K in keyof T]-?: (JSONSchemaType<T[K]> & Nullable<T[K]>) | {$ref: string}
}

type RequiredMembers<T> = {
  [K in keyof T]-?: undefined extends T[K] ? never : K
}[keyof T]

type Nullable<T> = undefined extends T
  ? {
      nullable: true
      const?: never // any non-null value would fail `const: null`, `null` would fail any other value in const
      enum?: (T | null)[] // `null` must be explicitly included in "enum" for `null` to pass
      default?: T | null
    }
  : {
      const?: T
      enum?: T[]
      default?: T
    }