/**
 * ============================================================
 * XENEX GLASS OS
 * Boot Controller
 * ============================================================
 *
 * Responsibilities:
 * - Control boot animation timing
 * - Update boot status
 * - Respect reduced-motion preferences
 * - Transition cleanly to the login application
 *
 * This module does NOT:
 * - authenticate users
 * - contain passwords
 * - contain API secrets
 * - access Neon
 * - access S3
 * - make privileged backend decisions
 *
 * Backend authority begins when the login module is loaded.
 */

"use strict";


/* ============================================================
   CONFIGURATION
   ============================================================ */

const BOOT_CONFIG = Object.freeze({

    /*
     * Short enough to feel responsive, but long enough for
     * the visual identity to register.
     */
    minimumDuration: 3000,

    /*
     * Small transition period after the Xenex wordmark appears.
     */
    transitionDuration: 900,

    /*
     * Destination module.
     *
     * This file will be created next.
     */
    loginModule: "./login.html"

});


/* ============================================================
   BOOT STATE
   ============================================================ */

const BootState = Object.freeze({

    STARTING: "starting",
    READY: "ready",
    TRANSITIONING: "transitioning",
    COMPLETE: "complete"

});


let currentState = BootState.STARTING;


/* ============================================================
   DOM REFERENCES
   ============================================================ */

const bootRoot =
    document.getElementById("xenex-boot");

const bootStatus =
    document.getElementById("boot-status");

const transitionLayer =
    document.getElementById("boot-transition");


/* ============================================================
   VALIDATION
   ============================================================ */

function validateBootDOM() {

    if (!bootRoot) {
        throw new Error(
            "Xenex Boot: boot root was not found."
        );
    }

    if (!bootStatus) {
        throw new Error(
            "Xenex Boot: status element was not found."
        );
    }

    if (!transitionLayer) {
        throw new Error(
            "Xenex Boot: transition layer was not found."
        );
    }

}


/* ============================================================
   STATUS
   ============================================================ */

function setBootStatus(message) {

    if (!bootStatus) {
        return;
    }

    bootStatus.textContent = message;

}


/* ============================================================
   STATE
   ============================================================ */

function setState(nextState) {

    currentState = nextState;

}


/* ============================================================
   REDUCED MOTION
   ============================================================ */

function prefersReducedMotion() {

    return window.matchMedia(
        "(prefers-reduced-motion: reduce)"
    ).matches;

}


/* ============================================================
   TRANSITION
   ============================================================ */

function beginTransition() {

    if (currentState !== BootState.STARTING) {
        return;
    }

    setState(BootState.TRANSITIONING);

    setBootStatus(
        "Preparing your workspace"
    );

    transitionLayer.classList.add(
        "is-active"
    );


    /*
     * Allow the transition layer to cover the boot screen
     * before navigating to the login document.
     */
    window.setTimeout(() => {

        setState(BootState.COMPLETE);

        window.location.replace(
            BOOT_CONFIG.loginModule
        );

    }, BOOT_CONFIG.transitionDuration);

}


/* ============================================================
   NORMAL BOOT
   ============================================================ */

function startNormalBoot() {

    const startedAt = performance.now();

    setBootStatus(
        "Starting Xenex Glass OS"
    );


    /*
     * We intentionally don't use a fixed "fake loading"
     * percentage.
     *
     * This is simply the visual boot stage.
     *
     * Later, real frontend initialization can register
     * readiness tasks here.
     */
    window.setTimeout(() => {

        const elapsed =
            performance.now() - startedAt;

        const remaining =
            Math.max(
                0,
                BOOT_CONFIG.minimumDuration - elapsed
            );


        window.setTimeout(() => {

            setBootStatus(
                "Xenex Glass OS ready"
            );

            beginTransition();

        }, remaining);

    }, 100);

}


/* ============================================================
   ACCESSIBILITY BOOT
   ============================================================ */

function startReducedMotionBoot() {

    setBootStatus(
        "Xenex Glass OS ready"
    );


    /*
     * No unnecessary animation delay for users who have
     * requested reduced motion.
     */
    window.setTimeout(
        beginTransition,
        500
    );

}


/* ============================================================
   INITIALIZATION
   ============================================================ */

function initializeBoot() {

    try {

        validateBootDOM();

        setState(BootState.STARTING);

        if (prefersReducedMotion()) {

            startReducedMotionBoot();

        } else {

            startNormalBoot();

        }

    } catch (error) {

        /*
         * Do not silently fail.
         *
         * This remains a frontend boot error and does not
         * expose any backend information.
         */

        console.error(
            "Xenex Glass OS boot error:",
            error
        );

        setBootStatus(
            "Unable to start Xenex OS"
        );

    }

}


/* ============================================================
   START
   ============================================================ */

if (
    document.readyState === "loading"
) {

    document.addEventListener(
        "DOMContentLoaded",
        initializeBoot,
        {
            once: true
        }
    );

} else {

    initializeBoot();

}