From fcccf93772ad292808c6027c3891e41d08b2e5bb Mon Sep 17 00:00:00 2001
From: ton1c <sembl1@ya.ru>
Date: Wed, 29 Jan 2025 01:50:13 +0300
Subject: [PATCH] working on validator

---
 server/src/lib/routerTree.ts |   1 +
 server/src/lib/test.ts       | 711 +++++++++++++++++++++++++++++++++++
 server/src/lib/validator.ts  | 344 +++++++++++++++++
 3 files changed, 1056 insertions(+)
 create mode 100644 server/src/lib/test.ts
 create mode 100644 server/src/lib/validator.ts

diff --git a/server/src/lib/routerTree.ts b/server/src/lib/routerTree.ts
index 2df44db..f1bd958 100644
--- a/server/src/lib/routerTree.ts
+++ b/server/src/lib/routerTree.ts
@@ -88,6 +88,7 @@ class StaticNode<T> implements Node<T> {
     }
 }
 
+// TODO: get rid of fixed param name
 class DynamicNode<T> extends StaticNode<T> implements Node<T> {
     constructor(
         public readonly paramName: string,
diff --git a/server/src/lib/test.ts b/server/src/lib/test.ts
new file mode 100644
index 0000000..c09f957
--- /dev/null
+++ b/server/src/lib/test.ts
@@ -0,0 +1,711 @@
+import { err, ok, Result } from "@shared/utils/result.ts";
+import { none, Option, some } from "@shared/utils/option.ts";
+
+class ParseError extends Error {
+    type = "ParseError";
+    constructor(
+        public readonly input: any,
+        public readonly msg: string,
+    ) {
+        super(msg);
+    }
+}
+
+function pe(input: unknown, msg: string) {
+    return new ParseError(input, msg);
+}
+
+export interface Schema<T> {
+    parse(input: unknown): Result<T, ParseError>;
+    checkIfValid(input: unknown): boolean;
+    nullable(): NullableSchema<this>;
+    option(): OptionSchema<T>;
+    or<S extends Schema<any>[]>(...schema: S): UnionSchema<[this, ...S]>;
+}
+
+type CheckFunction<T> = (input: T) => ParseError | void;
+
+export abstract class BaseSchema<T> implements Schema<T> {
+    protected checks: CheckFunction<T>[] = [];
+
+    public addCheck(check: CheckFunction<T>): this {
+        this.checks.push(check);
+        return this;
+    }
+
+    protected runChecks(input: T): Result<T, ParseError> {
+        for (const check of this.checks) {
+            const error = check(input);
+            if (error) {
+                return err(error);
+            }
+        }
+        return ok(input);
+    }
+
+    checkIfValid(input: unknown): boolean {
+        return this.parse(input).isOk();
+    }
+
+    nullable(): NullableSchema<this> {
+        return new NullableSchema(this);
+    }
+
+    or<S extends Schema<any>[]>(...schema: S): UnionSchema<[this, ...S]> {
+        return new UnionSchema(this, ...schema);
+    }
+
+    option(): OptionSchema<T> {
+        return new OptionSchema(this);
+    }
+
+    abstract parse(input: unknown): Result<T, ParseError>;
+}
+
+export abstract class PrimitiveSchema<
+    T extends
+        | string
+        | number
+        | boolean
+        | bigint
+        | undefined
+        | null
+        | object
+        | void
+        | any
+        | unknown
+        | never,
+> extends BaseSchema<T> {
+    protected abstract initialCheck(input: unknown): Result<T, ParseError>;
+
+    protected checkPrimitive<U = T>(
+        input: unknown,
+        type:
+            | "string"
+            | "number"
+            | "boolean"
+            | "bigint"
+            | "undefined"
+            | "object"
+            | "symbol"
+            | "funciton",
+    ): Result<U, ParseError> {
+        const inputType = typeof input;
+
+        if (inputType === type) {
+            return ok(input as U);
+        }
+        return err(
+            pe(input, `Expected '${type}', received '${inputType}'`),
+        );
+    }
+
+    public parse(input: unknown): Result<T, ParseError> {
+        return this.initialCheck(input).andThen((input) => {
+            for (const check of this.checks) {
+                const e = check(input);
+
+                if (e) {
+                    return err(e);
+                }
+            }
+
+            return ok(input);
+        });
+    }
+}
+
+export class StringSchema extends PrimitiveSchema<string> {
+    private static readonly emailRegex =
+        /^(([^<>()[\]\.,;:\s@\"]+(\.[^<>()[\]\.,;:\s@\"]+)*)|(\".+\"))@(([^<>()[\]\.,;:\s@\"]+\.)+[^<>()[\]\.,;:\s@\"]{2,})$/i; // https://stackoverflow.com/questions/46155/how-can-i-validate-an-email-address-in-javascript
+
+    private static readonly ipRegex =
+        /^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/; // https://stackoverflow.com/questions/4460586/javascript-regular-expression-to-check-for-ip-addresses
+
+    protected override initialCheck(
+        input: unknown,
+    ): Result<string, ParseError> {
+        return this.checkPrimitive(input, "string");
+    }
+
+    public max(
+        length: number,
+        msg: string = `String length must be at most ${length} characters long`,
+    ): this {
+        return this.addCheck((input) =>
+            input.length < length ? pe(input, msg) : undefined
+        );
+    }
+
+    public min(
+        length: number,
+        msg: string =
+            `String length must be at least ${length} characters long`,
+    ): this {
+        return this.addCheck((input) =>
+            input.length < length ? pe(input, msg) : undefined
+        );
+    }
+
+    public regex(
+        pattern: RegExp,
+        msg: string = `String must match the patter ${String(pattern)}`,
+    ): this {
+        return this.addCheck((input) =>
+            pattern.test(input) ? undefined : pe(input, msg)
+        );
+    }
+
+    public email(
+        msg: string = `String must match a valid email address`,
+    ): this {
+        return this.regex(StringSchema.emailRegex, msg);
+    }
+
+    public ip(
+        msg: string = `String must match a valid ip address`,
+    ): this {
+        return this.regex(StringSchema.ipRegex, msg);
+    }
+}
+
+export class NumberSchema extends PrimitiveSchema<number> {
+    protected override initialCheck(
+        input: unknown,
+    ): Result<number, ParseError> {
+        return this.checkPrimitive(input, "number");
+    }
+
+    gt(num: number, msg: string = `Number must be greater than ${num}`): this {
+        return this.addCheck((input) =>
+            input <= num ? pe(input, msg) : undefined
+        );
+    }
+
+    gte(
+        num: number,
+        msg: string = `Number must be greater than or equal to ${num}`,
+    ): this {
+        return this.addCheck((input) =>
+            input < num ? pe(input, msg) : undefined
+        );
+    }
+
+    lt(num: number, msg: string = `Number must be less than ${num}`): this {
+        return this.addCheck((input) =>
+            input >= num ? pe(input, msg) : undefined
+        );
+    }
+
+    lte(
+        num: number,
+        msg: string = `Number must be less than or equal to ${num}`,
+    ): this {
+        return this.addCheck((input) =>
+            input > num ? pe(input, msg) : undefined
+        );
+    }
+
+    int(msg: string = "Number must be an integer"): this {
+        return this.addCheck((input) =>
+            Number.isInteger(input) ? pe(input, msg) : undefined
+        );
+    }
+
+    positive(msg: string = "Number must be positive"): this {
+        return this.gte(0, msg);
+    }
+
+    nonnegative(msg: string = "Number must be nonnegative"): this {
+        return this.gt(0, msg);
+    }
+
+    negative(msg: string = "Number must be negative"): this {
+        return this.lt(0, msg);
+    }
+
+    nonpositive(msg: string = "Number must be nonpositive"): this {
+        return this.lte(0, msg);
+    }
+
+    finite(msg: string = "Number must be finite"): this {
+        return this.addCheck((input) =>
+            Number.isFinite(input) ? undefined : pe(input, msg)
+        );
+    }
+
+    safe(msg: string = "Number must be a safe integer"): this {
+        return this.addCheck((input) =>
+            Number.isSafeInteger(input) ? undefined : pe(input, msg)
+        );
+    }
+
+    multipleOf(
+        num: number,
+        msg: string = `Number must be a multiple of ${num}`,
+    ): this {
+        return this.addCheck((input) =>
+            input % num ? undefined : pe(input, msg)
+        );
+    }
+}
+
+export class BigintSchema extends PrimitiveSchema<bigint> {
+    protected override initialCheck(
+        input: unknown,
+    ): Result<bigint, ParseError> {
+        return this.checkPrimitive(input, "bigint");
+    }
+
+    gt(
+        num: bigint | number,
+        msg: string = `Bigint must be greater than ${num}`,
+    ): this {
+        return this.addCheck((input) =>
+            input <= num ? pe(input, msg) : undefined
+        );
+    }
+
+    gte(
+        num: bigint | number,
+        msg: string = `Bigint must be greater than or equal to ${num}`,
+    ): this {
+        return this.addCheck((input) =>
+            input < num ? pe(input, msg) : undefined
+        );
+    }
+
+    lt(
+        num: bigint | number,
+        msg: string = `Bigint must be less than ${num}`,
+    ): this {
+        return this.addCheck((input) =>
+            input >= num ? pe(input, msg) : undefined
+        );
+    }
+
+    lte(
+        num: bigint | number,
+        msg: string = `Bigint must be less than or equal to ${num}`,
+    ): this {
+        return this.addCheck((input) =>
+            input > num ? pe(input, msg) : undefined
+        );
+    }
+
+    int(msg: string = "Bigint must be an integer"): this {
+        return this.addCheck((input) =>
+            Number.isInteger(input) ? pe(input, msg) : undefined
+        );
+    }
+
+    positive(msg: string = "Bigint must be positive"): this {
+        return this.gte(0, msg);
+    }
+
+    nonnegative(msg: string = "Bigint must be nonnegative"): this {
+        return this.gt(0, msg);
+    }
+
+    negative(msg: string = "Bigint must be negative"): this {
+        return this.lt(0, msg);
+    }
+
+    nonpositive(msg: string = "Bigint must be nonpositive"): this {
+        return this.lte(0, msg);
+    }
+
+    finite(msg: string = "Bigint must be finite"): this {
+        return this.addCheck((input) =>
+            Number.isFinite(input) ? undefined : pe(input, msg)
+        );
+    }
+
+    safe(msg: string = "Bigint must be a safe integer"): this {
+        return this.addCheck((input) =>
+            Number.isSafeInteger(input) ? undefined : pe(input, msg)
+        );
+    }
+
+    multipleOf(
+        num: bigint,
+        msg: string = `Bigint must be a multiple of ${num}`,
+    ): this {
+        return this.addCheck((input) =>
+            input % num ? undefined : pe(input, msg)
+        );
+    }
+}
+
+export class BooleanSchema extends PrimitiveSchema<boolean> {
+    protected override initialCheck(
+        input: unknown,
+    ): Result<boolean, ParseError> {
+        return this.checkPrimitive(input, "boolean");
+    }
+}
+
+export class DateSchema extends PrimitiveSchema<object> {
+    protected override initialCheck(
+        input: unknown,
+    ): Result<Date, ParseError> {
+        return this.checkPrimitive(input, "object").andThen((obj) => {
+            if (obj instanceof Date) {
+                return ok(obj);
+            }
+            return err(
+                pe(
+                    input,
+                    `Expected instance of Date, received ${obj.constructor.name}`,
+                ),
+            );
+        });
+    }
+
+    min(
+        date: Date,
+        msg: string = `Date must be after ${date.toLocaleString()}`,
+    ) {
+        return this.addCheck((input) =>
+            input <= date ? pe(input, msg) : undefined
+        );
+    }
+
+    max(
+        date: Date,
+        msg: string = `Date must be before ${date.toLocaleString()}`,
+    ) {
+        return this.addCheck((input) =>
+            input >= date ? pe(input, msg) : undefined
+        );
+    }
+}
+
+class UndefinedSchema extends PrimitiveSchema<undefined> {
+    protected override initialCheck(
+        input: unknown,
+    ): Result<undefined, ParseError> {
+        return this.checkPrimitive(input, "undefined");
+    }
+}
+
+class NullSchema extends PrimitiveSchema<null> {
+    protected override initialCheck(
+        input: unknown,
+    ): Result<null, ParseError> {
+        if (input === null) {
+            return ok(input);
+        }
+        return err(pe(input, "Expected 'null', received '${typeof input}'"));
+    }
+}
+
+class VoidSchema extends PrimitiveSchema<void> {
+    protected override initialCheck(input: unknown): Result<void, ParseError> {
+        if (input !== undefined && input !== null) {
+            return err(
+                pe(input, `Expected 'void', received '${typeof input}'`),
+            );
+        }
+
+        return ok();
+    }
+}
+
+class AnySchema extends PrimitiveSchema<any> {
+    protected override initialCheck(input: unknown): Result<any, ParseError> {
+        return ok(input);
+    }
+}
+
+class UnknownSchema extends PrimitiveSchema<unknown> {
+    protected override initialCheck(
+        input: unknown,
+    ): Result<unknown, ParseError> {
+        return ok(input);
+    }
+}
+
+type InferSchema<S> = S extends Schema<infer T> ? T : never;
+
+class ObjectSchema<O extends Record<string, Schema<any>>>
+    extends PrimitiveSchema<{ [K in keyof O]: InferSchema<O[K]> }> {
+    private strict: boolean = false;
+
+    constructor(
+        private readonly schema: O,
+    ) {
+        super();
+    }
+
+    protected override initialCheck(
+        input: unknown,
+    ): Result<{ [K in keyof O]: InferSchema<O[K]> }, ParseError> {
+        return this.checkPrimitive<object>(input, "object").andThen(
+            (objPrimitive) => {
+                let obj = objPrimitive as Record<string, any>;
+                let parsedObj: Record<string, any> = {};
+
+                for (const [key, schema] of Object.entries(this.schema)) {
+                    const value = obj[key];
+
+                    const checkResult = schema.parse(value);
+
+                    if (checkResult.isErr()) {
+                        return err(
+                            pe(
+                                input,
+                                `Failed to parse '${key}' attribute: ${checkResult.error.msg}`,
+                            ),
+                        );
+                    }
+
+                    parsedObj[key] = checkResult.value;
+                }
+
+                return ok(parsedObj as { [K in keyof O]: InferSchema<O[K]> });
+            },
+        );
+    }
+}
+
+class NullableSchema<S extends Schema<any>>
+    extends PrimitiveSchema<InferSchema<S> | void> {
+    private static readonly voidSchema = new VoidSchema();
+
+    constructor(
+        private readonly schema: S,
+    ) {
+        super();
+    }
+
+    protected override initialCheck(
+        input: unknown,
+    ): Result<void | InferSchema<S>, ParseError> {
+        if (NullableSchema.voidSchema.checkIfValid(input)) {
+            return ok();
+        }
+        return this.schema.parse(input);
+    }
+}
+
+class LiteralSchema<L extends string> extends PrimitiveSchema<L> {
+    constructor(
+        private readonly literal: L,
+    ) {
+        super();
+    }
+
+    protected override initialCheck(input: unknown): Result<L, ParseError> {
+        if (input === this.literal) {
+            return ok(this.literal);
+        }
+        return err(pe(input, `Input must match literal '${this.literal}'`));
+    }
+}
+
+type InferSchemaUnion<S extends Schema<any>[]> = S[number] extends
+    Schema<infer U> ? U : never;
+
+class UnionSchema<S extends Schema<any>[]>
+    extends PrimitiveSchema<InferSchemaUnion<S>> {
+    private readonly schemas: S;
+
+    constructor(...schemas: S) {
+        super();
+        this.schemas = schemas;
+    }
+
+    protected override initialCheck(
+        input: unknown,
+    ): Result<InferSchemaUnion<S>, ParseError> {
+        const errors: string[] = [];
+
+        for (const schema of this.schemas) {
+            const checkResult = schema.parse(input);
+
+            if (checkResult.isOk()) {
+                return ok(checkResult.value);
+            }
+
+            errors.push(
+                `${schema.constructor.name} - ${checkResult.error.msg}`,
+            );
+        }
+
+        return err(
+            pe(
+                input,
+                [
+                    "No matching schema found for a union:",
+                    errors.join("\n"),
+                ].join("\n"),
+            ),
+        );
+    }
+}
+
+class ArraySchema<S extends Schema<any>>
+    extends PrimitiveSchema<InferSchema<S>[]> {
+    constructor(
+        private readonly schema: S,
+    ) {
+        super();
+    }
+
+    protected override initialCheck(
+        input: unknown[],
+    ): Result<InferSchema<S>[], ParseError> {
+        const parsed = [];
+
+        for (let i = 0; i < input.length; i++) {
+            const r = this.schema.parse(input[i]);
+
+            if (r.isErr()) {
+                return err(
+                    pe(
+                        input,
+                        `Element at index ${i} does not conform to schema:\n${r.error.msg}`,
+                    ),
+                );
+            }
+
+            parsed.push(r.value);
+        }
+
+        return ok(parsed);
+    }
+}
+
+class ResultSchema<T, E> extends PrimitiveSchema<Result<T, E>> {
+    private schema;
+
+    constructor(
+        private readonly valueSchema: Schema<T>,
+        private readonly errorSchema: Schema<E>,
+    ) {
+        super();
+
+        this.schema = new UnionSchema(
+            new ObjectSchema({
+                tag: new LiteralSchema("ok"),
+                value: valueSchema,
+            }),
+            new ObjectSchema({
+                tag: new LiteralSchema("err"),
+                error: errorSchema,
+            }),
+        );
+    }
+
+    protected override initialCheck(
+        input: unknown,
+    ): Result<Result<T, E>, ParseError> {
+        return this.schema.parse(input).map((result) => {
+            switch (result.tag) {
+                case "ok":
+                    return ok(result.value);
+                case "err":
+                    return err(result.error);
+            }
+        });
+    }
+}
+
+class OptionSchema<T> extends PrimitiveSchema<Option<T>> {
+    private schema;
+
+    constructor(private readonly valueSchema: Schema<T>) {
+        super();
+
+        this.schema = new UnionSchema(
+            new ObjectSchema({
+                tag: new LiteralSchema("some"),
+                value: valueSchema,
+            }),
+            new ObjectSchema({
+                tag: new LiteralSchema("none"),
+            }),
+        );
+    }
+
+    protected override initialCheck(
+        input: unknown,
+    ): Result<Option<T>, ParseError> {
+        return this.schema.parse(input).map((option) => {
+            switch (option.tag) {
+                case "some":
+                    return some(option.value);
+                case "none":
+                    return none;
+            }
+        });
+    }
+}
+
+class Validator {
+    string(): StringSchema {
+        return new StringSchema();
+    }
+
+    literal<L extends string>(literal: L): LiteralSchema<L> {
+        return new LiteralSchema(literal);
+    }
+
+    number(): NumberSchema {
+        return new NumberSchema();
+    }
+
+    bigint(): BigintSchema {
+        return new BigintSchema();
+    }
+
+    boolean(): BooleanSchema {
+        return new BooleanSchema();
+    }
+
+    date(): DateSchema {
+        return new DateSchema();
+    }
+
+    undefined(): UndefinedSchema {
+        return new UndefinedSchema();
+    }
+
+    null(): NullSchema {
+        return new NullSchema();
+    }
+
+    void(): VoidSchema {
+        return new VoidSchema();
+    }
+
+    any(): AnySchema {
+        return new AnySchema();
+    }
+
+    unknown(): UnknownSchema {
+        return new UnknownSchema();
+    }
+
+    union<S extends Schema<any>[]>(...schemas: S): UnionSchema<S> {
+        return new UnionSchema(...schemas);
+    }
+
+    array<S extends Schema<any>>(elementSchema: S): ArraySchema<S> {
+        return new ArraySchema(elementSchema);
+    }
+
+    result<T, E>(
+        valueSchema: Schema<T>,
+        errorSchema: Schema<E>,
+    ): ResultSchema<T, E> {
+        return new ResultSchema(valueSchema, errorSchema);
+    }
+}
+
+const v = new Validator();
+
+const r = v.array(v.union(v.string(), v.number().gt(5)));
+
+console.log(r.parse(["5", true]));
diff --git a/server/src/lib/validator.ts b/server/src/lib/validator.ts
new file mode 100644
index 0000000..6687b49
--- /dev/null
+++ b/server/src/lib/validator.ts
@@ -0,0 +1,344 @@
+import { err, ok, Result } from "@shared/utils/result.ts";
+import console from "node:console";
+
+class ParseError extends Error {
+    code = "ParseError";
+    constructor(
+        public readonly input: any,
+        public readonly msg: string,
+    ) {
+        super(msg);
+    }
+}
+
+export function pe(input: any, msg: string): ParseError {
+    return new ParseError(input, msg);
+}
+
+type CheckFunction<T> = (
+    input: T,
+    msg?: string,
+) => ParseError | void;
+
+export abstract class BaseSchema<T> {
+    private checks: CheckFunction<T>[] = [];
+    abstract initialCheck(input: unknown): Result<T, ParseError>;
+    public addCheck(check: CheckFunction<T>) {
+        this.checks.push(check);
+    }
+
+    parse(input: any): Result<T, ParseError> {
+        return this.initialCheck(input).andThen((input) => {
+            for (const check of this.checks) {
+                const e = check(input);
+                if (e) {
+                    return err(e);
+                }
+            }
+            return ok(input);
+        });
+    }
+}
+
+export class StringSchema extends BaseSchema<string> {
+    private static readonly emailRegex =
+        /^(([^<>()[\]\.,;:\s@\"]+(\.[^<>()[\]\.,;:\s@\"]+)*)|(\".+\"))@(([^<>()[\]\.,;:\s@\"]+\.)+[^<>()[\]\.,;:\s@\"]{2,})$/i; // https://stackoverflow.com/questions/46155/how-can-i-validate-an-email-address-in-javascript
+
+    private static readonly ipRegex =
+        /^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/; // https://stackoverflow.com/questions/4460586/javascript-regular-expression-to-check-for-ip-addresses
+
+    private initialCheck(input: unknown): Result<string, ParseError> {
+        if (typeof input !== "string") {
+            return err(pe(input, `Expected string, received ${typeof input}`));
+        }
+        return ok(input);
+    }
+
+    max(
+        length: number,
+        msg: string = `String length must be at most ${length} characters long`,
+    ): this {
+        this.addCheck((input) => {
+            if (input.length > length) {
+                return pe(
+                    input,
+                    msg,
+                );
+            }
+        });
+
+        return this;
+    }
+
+    min(
+        length: number,
+        msg: string =
+            `String length must be at least ${length} characters long`,
+    ): this {
+        this.addCheck((input) => {
+            if (input.length < length) {
+                return pe(
+                    input,
+                    msg,
+                );
+            }
+        });
+        return this;
+    }
+
+    regex(
+        pattern: RegExp,
+        msg: string = `String must match the pattern ${String(pattern)}`,
+    ): this {
+        this.addCheck((input) => {
+            if (!pattern.test(input)) {
+                return pe(
+                    input,
+                    msg,
+                );
+            }
+        });
+        return this;
+    }
+
+    email(msg: string = `String must be a valid email address`): this {
+        return this.regex(StringSchema.emailRegex, msg);
+    }
+    ip(msg: string = "String must be a valid ip address"): this {
+        return this.regex(StringSchema.ipRegex, msg);
+    }
+}
+
+export class NumberSchema extends BaseSchema<number> {
+    private initialCheck(input: unknown): Result<number, ParseError> {
+        if (typeof input !== "number") {
+            return err(pe(input, `Expected number, recieved ${typeof input}`));
+        }
+        return ok(input);
+    }
+
+    gt(num: number, msg: string = `Number must be greater than ${num}`): this {
+        this.addCheck((input) => {
+            if (input <= num) return pe(input, msg);
+        });
+        return this;
+    }
+
+    gte(
+        num: number,
+        msg: string = `Number must be greater than or equal to ${num}`,
+    ): this {
+        this.addCheck((input) => {
+            if (input < num) return pe(input, msg);
+        });
+        return this;
+    }
+
+    lt(num: number, msg: string = `Number must be less than ${num}`): this {
+        this.addCheck((input) => {
+            if (input >= num) return pe(input, msg);
+        });
+        return this;
+    }
+
+    lte(
+        num: number,
+        msg: string = `Number must be less than or equal to ${num}`,
+    ): this {
+        this.addCheck((input) => {
+            if (input > num) return pe(input, msg);
+        });
+        return this;
+    }
+
+    int(msg: string = "Number must be an integer"): this {
+        this.addCheck((input) => {
+            if (!Number.isInteger(input)) return pe(input, msg);
+        });
+        return this;
+    }
+
+    positive(msg: string = "Number must be positive"): this {
+        return this.gte(0, msg);
+    }
+
+    nonnegative(msg: string = "Number must be nonnegative"): this {
+        return this.gt(0, msg);
+    }
+
+    negative(msg: string = "Number must be negative"): this {
+        return this.lt(0, msg);
+    }
+
+    nonpositive(msg: string = "Number must be nonpositive"): this {
+        return this.lte(0, msg);
+    }
+}
+
+export class BooleanSchema extends BaseSchema<boolean> {
+    private initialCheck(input: unknown): Result<boolean, ParseError> {
+        if (typeof input !== "boolean") {
+            return err(pe(input, `Expected boolean, received ${typeof input}`));
+        }
+        return ok(input);
+    }
+}
+
+export class DateSchema extends BaseSchema<Date> {
+    override initialCheck(input: unknown): Result<Date, ParseError> {
+        if (typeof input === "object" && input !== null) {
+            if (input instanceof Date) {
+                return ok(input);
+            }
+            // TODO: add check for an non Date instance. Right now lsp freaks out for some reason
+        }
+
+        return err(pe(input, `Expected object, received ${typeof input}`));
+    }
+
+    min(
+        date: Date,
+        msg: string = `Date must come after ${date.toLocaleString()}`,
+    ) {
+        this.addCheck((input) => {
+            if (input < date) {
+                return pe(input, msg);
+            }
+        });
+        return this;
+    }
+
+    max(
+        date: Date,
+        msg: string = `Date must come before ${date.toLocaleString()}`,
+    ) {
+        this.addCheck((input) => {
+            if (input > date) {
+                return pe(input, msg);
+            }
+        });
+        return this;
+    }
+}
+
+const validatorsObjects = [
+    StringSchema.name,
+    NumberSchema.name,
+    BooleanSchema.name,
+    DateSchema.name,
+];
+
+class UnionSchema<U extends Schema[]> {
+    private readonly schemas: Schema[];
+
+    constructor(...schemas: Schema[]) {
+        this.schemas = schemas;
+    }
+
+    parse(input: unknown): Result<InferTypeFromSchema<U>, ParseError> {
+        for (const schema of this.schemas) {
+            const result = schema.parse(input);
+
+            if (result.isOk()) {
+                return result;
+            }
+        }
+
+        return err(
+            pe(
+                input,
+                `Failed to parse as one of the types: ${
+                    this.schemas.map((s) => s.constructor.name).join(", ")
+                }`,
+            ),
+        );
+    }
+}
+
+type Schema =
+    | NumberSchema
+    | StringSchema
+    | BooleanSchema
+    | DateSchema
+    | ObjectSchema<Record<string, Schema>>
+    | UnionSchema<Schema[]>;
+
+export class ObjectSchema<
+    S extends Record<string, Schema>,
+> {
+    // TODO: rewrite this to be a static method returning result
+    constructor(
+        private readonly schema: S,
+    ) {
+        for (const [_, value] of Object.entries(schema)) {
+            if (validatorsObjects.indexOf(schema.constructor.name) === -1) {
+                throw "Not a valid ObjectSchema >:(";
+            }
+        }
+
+        console.log("Yay! It is valid");
+    }
+
+    parse(
+        input: unknown,
+    ): Result<{ [K in keyof S]: InferTypeFromSchema<S[K]> }, ParseError> {
+        if (typeof input !== "object") {
+            return err(pe(input, `Expected object, received ${typeof input}`));
+        }
+
+        if (input === null) {
+            return err(pe(input, `Expected object, received null`));
+        }
+
+        const obj = input as Record<string, unknown>;
+        const resultObj: Partial<InferTypeFromSchema<S>> = {};
+
+        for (const [key, schema] of Object.entries(this.schema)) {
+            const inputValue = obj[key];
+
+            if (!inputValue) {
+                return err(pe(
+                    input,
+                    `Object ${input} missing the '${key}' attribute`,
+                ));
+            }
+
+            const result = schema.parse(inputValue);
+
+            if (result.isErr()) {
+                return err(result.error);
+            }
+
+            resultObj[key as keyof S] = result.value;
+        }
+
+        return ok(resultObj);
+    }
+}
+
+type InferTypeFromSchema<S extends Schema | Record<string, Schema> | Schema[]> =
+    S extends Record<string, Schema>
+        ? { [K in keyof S]: InferTypeFromSchema<S[K]> }
+        : S extends StringSchema ? string
+        : S extends NumberSchema ? number
+        : S extends DateSchema ? Date
+        : S extends BooleanSchema ? boolean
+        : S extends ObjectSchema<infer O> ? InferTypeFromSchema<O>
+        : S extends UnionSchema<infer U> ? InferTypeFromSchema<U[number]>
+        : never;
+
+export const s = {
+    string: () => new StringSchema(),
+    number: () => new NumberSchema(),
+    date: () => new DateSchema(),
+};
+
+function createObjectSchema<S extends Record<string, Schema>>(
+    schema: S,
+): ObjectSchema<S> {
+    return new ObjectSchema(schema);
+}
+
+const union = new UnionSchema(s.string(), s.number());
+
+console.log(union.parse({}));