Q33. What is function composition?

const add = (n) => n + 1;
const double = (n) => n * 2;
const square = (n) => n * n;

// তিনটা মিলিয়ে একটা ফাংশন
const complex = (n) => square(double(add(n)));

console.log(complex(3)); // 64 — কারণ 3 -> 4 -> 8 -> 64

// pipe — বাম থেকে ডানে কাজ করে
const pipe = (...fns) => (value) =>
  fns.reduce((acc, fn) => fn(acc), value);

const process = pipe(
  (n) => n + 1,   // 3 -> 4
  (n) => n * 2,   // 4 -> 8
  (n) => n * n    // 8 -> 64
);

console.log(process(3)); // 64

// compose — ডান থেকে বামে কাজ করে
const compose = (...fns) => (value) =>
  fns.reduceRight((acc, fn) => fn(acc), value);

const process = compose(
  (n) => n * n,   // 8 -> 64
  (n) => n * 2,   // 4 -> 8
  (n) => n + 1    // 3 -> 4
);

console.log(process(3)); // 64

// বাস্তব উদাহরণ — ডেটা বিশুদ্ধ করা
const trim = (s) => s.trim();
const toLower = (s) => s.toLowerCase();
const addBang = (s) => s + "!";

const clean = pipe(trim, toLower, addBang);

console.log(clean("   HELLO   ")); // "hello!"

// pipeline বানানোর pattern
const validator = (schema) => (data) => {
  const errors = {};

  for (const key in schema) {
    if (!schema[key](data[key])) {
      errors[key] = "ভুল মান";
    }
  }

  return { valid: Object.keys(errors).length === 0, errors };
};

const rules = validator({
  name: (v) => typeof v === "string" && v.length > 0,
  age: (v) => typeof v === "number" && v > 0,
});

console.log(rules({ name: "Rahim", age: 25 }));