import type { BaseNode } from "../node.js"
import { defineNodeKind } from "../node.js"

export interface DivisorNode extends BaseNode<number> {}

export const divisorNode = defineNodeKind<DivisorNode>(
    {
        kind: "divisor",
        parse: (input) => input,
        compile: (rule, s) =>
            s.check("divisor", rule, `${s.data} % ${rule} === 0`),
        intersect: (l, r): DivisorNode =>
            divisorNode(
                Math.abs(
                    (l.rule * r.rule) / greatestCommonDivisor(l.rule, r.rule)
                )
            )
    },
    (base) => ({ description: `a multiple of ${base.rule}` })
)

// https://en.wikipedia.org/wiki/Euclidean_algorithm
const greatestCommonDivisor = (l: number, r: number) => {
    let previous
    let greatestCommonDivisor = l
    let current = r
    while (current !== 0) {
        previous = current
        current = greatestCommonDivisor % current
        greatestCommonDivisor = previous
    }
    return greatestCommonDivisor
}