// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

/**
 * A bit of navigation related code for handling dismissible elements.
 */
(() => {
  'use strict';

  function registerHeaderListeners() {
    const header = document.querySelector('.js-header');
    const menuButtons = document.querySelectorAll('.js-headerMenuButton');
    menuButtons.forEach(button => {
      button.addEventListener('click', e => {
        e.preventDefault();
        header.classList.toggle('is-active');
        button.setAttribute(
          'aria-expanded',
          header.classList.contains('is-active')
        );
      });
    });

    const scrim = document.querySelector('.js-scrim');
    scrim.addEventListener('click', e => {
      e.preventDefault();
      header.classList.remove('is-active');
      menuButtons.forEach(button => {
        button.setAttribute(
          'aria-expanded',
          header.classList.contains('is-active')
        );
      });
    });
  }

  function registerSolutionsTabs() {
    // Handle tab navigation on Solutions page.
    const tabList = document.querySelector('.js-solutionsTabs');

    if (tabList) {
      const tabs = tabList.querySelectorAll('[role="tab"]');
      let tabFocus = getTabFocus();

      changeTabs({ target: tabs[tabFocus] })

      tabs.forEach(tab => {
        tab.addEventListener('click', changeTabs);
      });

      // Enable arrow navigation between tabs in the tab list
      tabList.addEventListener('keydown', e => {
        // Move right
        if (e.keyCode === 39 || e.keyCode === 37) {
          tabs[tabFocus].setAttribute('tabindex', -1);
          if (e.keyCode === 39) {
            tabFocus++;
            // If we're at the end, go to the start
            if (tabFocus >= tabs.length) {
              tabFocus = 0;
            }
            // Move left
          } else if (e.keyCode === 37) {
            tabFocus--;
            // If we're at the start, move to the end
            if (tabFocus < 0) {
              tabFocus = tabs.length - 1;
            }
          }
          tabs[tabFocus].setAttribute('tabindex', 0);
          tabs[tabFocus].focus();
          setTabFocus(tabs[tabFocus].id);
        }
      });

      function getTabFocus() {
        const hash = window.location.hash;

        switch (hash) {
          case '#use-cases':
            return 1;
          case '#case-studies':
          default:
            return 0;
        }
      }

      function setTabFocus(id) {
        switch (id) {
          case 'btn-tech':
            tabFocus = 1;
            window.location.hash = '#use-cases';
            break;
          case 'btn-companies':
          default:
            window.location.hash = '#case-studies';
            tabFocus = 0;
        }
      }

      function changeTabs(e) {
        const target = e.target;
        const parent = target.parentNode;
        const grandparent = parent.parentNode;

        // Remove all current selected tabs
        parent
          .querySelectorAll('[aria-selected="true"]')
          .forEach(t => t.setAttribute('aria-selected', false));

        // Set this tab as selected
        target.setAttribute('aria-selected', true);
        setTabFocus(target.id)

        // Hide all tab panels
        grandparent
          .querySelectorAll('[role="tabpanel"]')
          .forEach(panel => panel.setAttribute('hidden', true));

        // Show the selected panel
        grandparent.parentNode
          .querySelector(`#${target.getAttribute('aria-controls')}`)
          .removeAttribute('hidden');
      }
    }
  }

  /**
   * Attempts to detect user's operating system and sets the download
   * links accordingly
   */
  async function setDownloadLinks() {
    const isMac = navigator.platform.toUpperCase().indexOf('MAC') >= 0;
    const versionElement = document.querySelector('.js-latestGoVersion');
    if (versionElement) {
      const downloadBtn = document.querySelector('.js-downloadBtn');
      const goVersionEl = document.querySelector('.js-goVersion');
      const anchorTagWindows = document.querySelector('.js-downloadWin');
      const anchorTagMac = document.querySelector('.js-downloadMac');
      const anchorTagLinux = document.querySelector('.js-downloadLinux');
      const version = await getLatestVersion();

      const macDownloadUrl = `https://dl.google.com/go/${version}.darwin-amd64.pkg`;
      const windowsDownloadUrl = `https://dl.google.com/go/${version}.windows-amd64.msi`;
      const linuxDownloadUrl = `https://dl.google.com/go/${version}.linux-amd64.tar.gz`;
      goVersionEl.textContent = `\u00a0(${version.replace('go', '')})`;

      anchorTagWindows.href = windowsDownloadUrl;
      anchorTagMac.href = macDownloadUrl;
      anchorTagLinux.href = linuxDownloadUrl;
      downloadBtn.href = isMac ? macDownloadUrl : windowsDownloadUrl;
    }
  }

  /**
   * Retrieves list of Go versions & returns the latest
   */
  async function getLatestVersion() {
    let version = 'go1.15'; // fallback version if fetch fails
    try {
      const versionData = await (
        await fetch('https://golang.org/dl/?mode=json')
      ).json();
      if (!versionData.length) {
        return version;
      }
      versionData.sort((v1, v2) => {
        return v2.version - v1.version;
      });
      version = versionData[0].version;
    } catch (err) {
      console.error(err);
    }
    return version;
  }

  window.addEventListener('DOMContentLoaded', () => {
    registerHeaderListeners();
    registerSolutionsTabs();
    setDownloadLinks();
  });
})();