import {
    type Asn1Node,
    decodeAsn1,
    isConstructed,
    UNIVERSAL_TAGS,
} from "../asn1/index.js";
import { X509_CODES, X509Error } from "../errors/error-codes.js";
import type { BasicConstraints } from "./extension.types.js";

function bad(reason: string): X509Error {
    return new X509Error(
        X509_CODES.EXTENSION_MALFORMED,
        "error.x509.basic-constraints-malformed",
        { context: { reason } }
    );
}

/** OID for the basic constraints extension. */
export const OID_BASIC_CONSTRAINTS = "2.5.29.19";

export function decodeBasicConstraints(value: Uint8Array): BasicConstraints {
    const outer = decodeAsn1(value);
    if (
        !isConstructed(outer) ||
        outer.tag.tagNumber !== UNIVERSAL_TAGS.SEQUENCE
    ) {
        throw bad("not-sequence");
    }
    let cA = false;
    let pathLenConstraint: number | undefined;
    let idx = 0;
    const first = outer.children[idx];
    if (
        first !== undefined &&
        !isConstructed(first) &&
        first.tag.tagNumber === UNIVERSAL_TAGS.BOOLEAN
    ) {
        if (first.content.length !== 1) {
            throw bad("bool-len");
        }
        cA = (first.content[0] as number) !== 0x00;
        idx += 1;
    }
    const second = outer.children[idx];
    if (
        second !== undefined &&
        !isConstructed(second) &&
        second.tag.tagNumber === UNIVERSAL_TAGS.INTEGER
    ) {
        if (second.content.length === 0 || second.content.length > 4) {
            throw bad("pathlen-len");
        }
        let n = 0;
        for (let i = 0; i < second.content.length; i++) {
            n = (n << 8) | (second.content[i] as number);
        }
        if (n < 0) {
            throw bad("pathlen-negative");
        }
        pathLenConstraint = n;
        idx += 1;
    }
    if (idx !== outer.children.length) {
        throw bad("extra-fields");
    }
    return pathLenConstraint === undefined ? { cA } : { cA, pathLenConstraint };
}

// Silence unused-import warning when only types are referenced here.
export type { Asn1Node };