(function(){'use strict';var PROGRESS_KEY='rsc-exercise-hub-v1:'+location.pathname;var STREAK_KEY='rsc-streak-v1';var DAILY_KEY='rsc-daily-v1';var TIME_BY_DIFF={beginner:3,intermediate:5,advanced:7};var DOTS_BY_DIFF={beginner:1,intermediate:2,advanced:3};var XP_BY_DIFF={beginner:10,intermediate:25,advanced:50};function xpWeight(difficulty){return XP_BY_DIFF[String(difficulty||'').toLowerCase()]||10;}
var COLLAPSE_DELAY=3400;var SETUP_ERR=/could not find function|object '[^']*' not found/i;var CHECK_SVG='<svg class="xh-check-svg" viewBox="0 0 24 24" aria-hidden="true">'+'<path d="M4 12.5l5 5L20 6"/></svg>';var STATUS_CONTENT={running:'<span class="xh-spinner"></span>Checking',pass:CHECK_SVG+'Success!',mismatch:'✗ Not a match',error:'⚠ Error'};var BACKFILL_FLAG_PREFIX='rsc-backfill-done-';var BACKFILL_BATCH_SIZE=200;var LOCALSTORAGE_HUB_PREFIX='rsc-exercise-hub-v1:';var authToken=null;var authedUserId=null;function pad2(n){return(n<10?'0':'')+n;}
function escapeHtml(s){return String(s).replace(/[&<>"']/g,function(c){return({'&':'&amp;','<':'&lt;','>':'&gt;','"':'&quot;',"'":'&#39;'})[c];});}
function todayStr(){return new Date().toISOString().slice(0,10);}
function normalizeOutput(text){var t=String(text||'').replace(/×/g,'x').replace(/…/g,'...').replace(/ /g,' ');var rawLines=t.split('\n');var kept=[];var inWarning=false;for(var i=0;i<rawLines.length;i++){var raw=rawLines[i];var trimmed=raw.trim();var classifyable=trimmed.replace(/^#>\s?/,'');if(/^(?:Warning message|Warning messages|Warning in\b)/i.test(classifyable)){inWarning=true;continue;}
if(inWarning){var preStripped=raw.replace(/^\s*#>\s?/,'');if(/^\s+\S/.test(preStripped)||/^\d+:\s+/.test(classifyable)||trimmed===''){continue;}
inWarning=false;}
kept.push(raw);}
return kept.map(function(l){return l.replace(/^\s*#>\s?/,'').replace(/\s+/g,' ').trim();}).filter(function(l){return l.length;}).join('\n');}
function firstDiffLine(a,b){var la=a.split('\n'),lb=b.split('\n');var n=Math.max(la.length,lb.length);for(var i=0;i<n;i++){if(la[i]!==lb[i])return i+1;}
return 0;}
var STORE={loadProgress:function(){try{var d=JSON.parse(localStorage.getItem(PROGRESS_KEY));return(d&&typeof d.solved==='object')?d:{solved:{}};}catch(e){return{solved:{}};}},saveProgress:function(d){try{localStorage.setItem(PROGRESS_KEY,JSON.stringify(d));}catch(e){}},loadStreak:function(){try{var d=JSON.parse(localStorage.getItem(STREAK_KEY));if(d&&typeof d.days==='number')return d;}catch(e){}
return{days:0,lastVisit:null};},saveStreak:function(d){try{localStorage.setItem(STREAK_KEY,JSON.stringify(d));}catch(e){}},loadDaily:function(){try{var d=JSON.parse(localStorage.getItem(DAILY_KEY));if(d&&d.date===todayStr()&&typeof d.count==='number')return d;}catch(e){}
return{date:todayStr(),count:0};},bumpDaily:function(){var d=this.loadDaily();d.count=(d.count||0)+1;d.date=todayStr();try{localStorage.setItem(DAILY_KEY,JSON.stringify(d));}catch(e){}
return d.count;}};function hubSlugFromPath(){var m=location.pathname.match(/^\/([^\/]+?)(?:\.html?)?\/?$/);return m&&m[1]?decodeURIComponent(m[1]):'';}
function getAuthToken(){return(window.__auth&&window.__auth.getAccessToken&&window.__auth.getAccessToken())||null;}
function reportSolve(card){if(!authToken)return;var hub=hubSlugFromPath();if(!hub||!card||!card.id)return;var hints=(typeof card.hintsUsed==='number')?card.hintsUsed:0;try{fetch('/api/exercise/'+encodeURIComponent(hub)+'/'+encodeURIComponent(card.id)+'/attempt',{method:'POST',headers:{'Content-Type':'application/json','Authorization':'Bearer '+authToken},body:JSON.stringify({passed:true,hints_used:hints}),keepalive:true}).then(function(r){if(r.status===402){meterFetch();return null;}
return r.ok?r.json():null;}).then(function(result){if(result&&result.meter)meterApply(result.meter,card);if(result&&typeof result.total_xp==='number'){document.dispatchEvent(new CustomEvent('exercise-progress-changed',{detail:{total_xp:result.total_xp,current_streak_days:result.current_streak_days,longest_streak_days:result.longest_streak_days}}));}}).catch(function(){});}catch(e){}}
function hydrateSolvedFromServer(){if(!authToken)return Promise.resolve();var hub=hubSlugFromPath();if(!hub)return Promise.resolve();return fetch('/api/me/exercises?hub='+encodeURIComponent(hub),{headers:{'Authorization':'Bearer '+authToken,'Accept':'application/json'}}).then(function(r){return r.ok?r.json():null;}).then(function(body){if(!body||!Array.isArray(body.solved))return;var ids=body.solved;var dirty=false;for(var i=0;i<ids.length;i++){var id=ids[i];if(!progressState.solved[id]){progressState.solved[id]=true;dirty=true;}
for(var c=0;c<cards.length;c++){var card=cards[c];if(card.id===id&&!card.solved){card.solved=true;card.section.classList.add('is-solved');}}}
if(dirty){STORE.saveProgress(progressState);updateProgress(solvedCount(),totalCount);updateXp(false);if(solvedCount()>=totalCount&&badgeEl)showBadge();}}).catch(function(){});}
function collectLocalSolves(){var items=[];try{for(var i=0;i<localStorage.length;i++){var key=localStorage.key(i);if(!key||key.indexOf(LOCALSTORAGE_HUB_PREFIX)!==0)continue;var path=key.slice(LOCALSTORAGE_HUB_PREFIX.length);var m=path.match(/^\/([^\/]+?)(?:\.html?)?\/?$/);if(!m||!m[1])continue;var hub=decodeURIComponent(m[1]);var data;try{data=JSON.parse(localStorage.getItem(key));}catch(e){continue;}
if(!data||!data.solved||typeof data.solved!=='object')continue;for(var ex in data.solved){if(data.solved[ex])items.push({hub:hub,exercise_id:ex});}}}catch(e){}
return items;}
function backfillIfNeeded(userId){if(!authToken||!userId)return Promise.resolve();var flagKey=BACKFILL_FLAG_PREFIX+userId;try{if(localStorage.getItem(flagKey)==='1')return Promise.resolve();}catch(e){}
var items=collectLocalSolves();if(!items.length){try{localStorage.setItem(flagKey,'1');}catch(e){}
return Promise.resolve();}
var batches=[];for(var i=0;i<items.length;i+=BACKFILL_BATCH_SIZE){batches.push(items.slice(i,i+BACKFILL_BATCH_SIZE));}
return batches.reduce(function(p,batch){return p.then(function(){return fetch('/api/exercise/backfill',{method:'POST',headers:{'Content-Type':'application/json','Authorization':'Bearer '+authToken},body:JSON.stringify({items:batch})}).then(function(r){return r.ok?r.json():null;});});},Promise.resolve()).then(function(lastResult){try{localStorage.setItem(flagKey,'1');}catch(e){}
if(lastResult&&typeof lastResult.total_xp==='number'){document.dispatchEvent(new CustomEvent('exercise-progress-changed',{detail:{total_xp:lastResult.total_xp,current_streak_days:lastResult.current_streak_days,longest_streak_days:lastResult.longest_streak_days}}));}}).catch(function(){});}
function onAuthHydrated(ev){var detail=ev&&ev.detail||{};var newToken=detail.token||null;var newUserId=(detail.me&&detail.me.user&&detail.me.user.id)||null;authToken=newToken;authedUserId=newUserId;if(!newToken||!newUserId)return;backfillIfNeeded(newUserId).then(hydrateSolvedFromServer).then(meterFetch);}
var TASTER_KEY='rsc-anon-taster-v1';var WIN_DISMISS_KEY='rsc-win-dismissed';var anonCardEl=null;function anonTaster(){try{return JSON.parse(localStorage.getItem(TASTER_KEY));}
catch(e){return null;}}
function anonTasterSave(rec){try{localStorage.setItem(TASTER_KEY,JSON.stringify(rec));}catch(e){}}
function gaEvent(name,params){try{if(window.gtag)window.gtag('event',name,params||{});}catch(e){}}
function anonGateCheck(card){if(authToken)return false;var hub=hubSlugFromPath();if(!hub)return false;var t=anonTaster();if(!t){anonTasterSave({hub:hub,id:card.id,xp:0});return false;}
if(t.hub===hub&&t.id===card.id)return false;anonCardShow(card,'gate',t);return true;}
function anonWinShow(card){var t=anonTaster();if(t&&t.id===card.id&&!t.xp){t.xp=card.xp;anonTasterSave(t);}
try{if(sessionStorage.getItem(WIN_DISMISS_KEY))return;}catch(e){}
anonCardShow(card,'win',t);}
function anonSigninHref(xp){return'/signin.html?next='+encodeURIComponent(location.pathname)+
(xp?'&winxp='+xp:'');}
function anonCardShow(card,variant,taster){var xp=variant==='win'?card.xp:((taster&&taster.xp)||0);if(anonCardEl&&anonCardEl.parentNode)anonCardEl.remove();var el=document.createElement('div');el.className='xh-win'+(variant==='gate'?' is-gate':'');el.setAttribute('role','status');var title,bodyText;if(variant==='win'){title='+'+xp+' XP earned';bodyText='Right now it lives only in this browser. A free account '+'keeps your XP, streak, and solved exercises on any device.';}else{title='Your first graded exercise was on the house';bodyText=xp?'That +'+xp+' XP is saved in this browser only. Create a free '+'account to keep it and to grade more exercises.':'Create a free account to keep grading exercises and earn XP for '+'every solve.';}
el.innerHTML='<div class="xh-win-title">'+title+'</div>'+'<p class="xh-win-body">'+bodyText+'</p>'+'<div class="xh-win-actions">'+'<a class="xh-win-cta" href="'+anonSigninHref(xp)+'">Create a free account</a>'+
(variant==='win'?'<button type="button" class="xh-win-later">Not now</button>':'<a class="xh-win-later" href="'+anonSigninHref(xp)+'">I already have an account</a>')+'</div>';if(variant==='win')card.section.after(el);else card.verdict.after(el);anonCardEl=el;var later=el.querySelector('button.xh-win-later');if(later){later.addEventListener('click',function(){try{sessionStorage.setItem(WIN_DISMISS_KEY,'1');}catch(e){}
el.remove();if(anonCardEl===el)anonCardEl=null;gaEvent('win_card_dismiss',{});});}
el.querySelector('.xh-win-cta').addEventListener('click',function(){gaEvent(variant==='win'?'win_card_cta':'gate_card_cta',{xp:xp});});try{localStorage.setItem('rs-signin-nudge-dismissed',String(Date.now()+864e5));}catch(e){}
if(variant==='gate'){el.scrollIntoView({behavior:'smooth',block:'center'});}
gaEvent(variant==='win'?'win_card_shown':'gate_card_shown',{xp:xp,hub:hubSlugFromPath()||''});}
var meterState=null;var meterPillEl=null,meterWallEl=null,meterIntroEl=null;var METER_INTRO_KEY='rsc-meter-intro-v1';function meterWalled(){return!!(meterState&&meterState.metered&&meterState.hub_open===false);}
function meterFetch(){if(!authToken)return;var hub=hubSlugFromPath();if(!hub)return;fetch('/api/me/meter?hub='+encodeURIComponent(hub),{headers:{'Authorization':'Bearer '+authToken,'Accept':'application/json'}}).then(function(r){return r.ok?r.json():null;}).then(function(body){if(body){meterState=body;meterRender();}}).catch(function(){});}
function meterResetLabel(){var iso=meterState&&meterState.resets;if(!iso)return'the 1st';var d=new Date(iso+'T00:00:00Z');var M=['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'];return M[d.getUTCMonth()]+' '+d.getUTCDate();}
function meterRender(){var s=meterState;if(!s||!s.metered){if(meterPillEl){meterPillEl.remove();meterPillEl=null;}
if(meterWallEl){meterWallEl.remove();meterWallEl=null;}
document.documentElement.classList.remove('xh-meter-walled');return;}
var head=document.querySelector('.xh-map-head');if(head){if(!meterPillEl){meterPillEl=document.createElement('span');head.insertBefore(meterPillEl,head.querySelector('.xh-map-count'));}
if(s.hub_started){meterPillEl.className='xh-meter is-open';meterPillEl.innerHTML='This hub stays open until '+meterResetLabel();}else{meterPillEl.className='xh-meter'+(s.left<=5?' is-low':'');var segs='';for(var i=0;i<5;i++){var fill=Math.max(0,Math.min(5,s.left-i*5))/5;segs+='<span class="xh-meter-seg"><i style="transform:scaleY('+fill+')"></i></span>';}
meterPillEl.innerHTML='<span class="xh-meter-segs" aria-hidden="true">'+segs+'</span>'+'<b>'+s.left+'</b>&nbsp;of '+s.limit+' left this month'+'<span class="xh-meter-reset">resets '+meterResetLabel()+'</span>';}}
meterIntroRender();meterWallRender();}
function meterIntroRender(){if(!meterState||!meterState.metered||meterWalled()||meterIntroEl)return;var seen=null;try{seen=localStorage.getItem(METER_INTRO_KEY);}catch(e){}
if(seen)return;var anchor=mapEl||document.querySelector('section.exercise');if(!anchor||!anchor.parentElement)return;meterIntroEl=document.createElement('div');meterIntroEl.className='xh-meter-intro';meterIntroEl.innerHTML='<div class="xh-meter-intro-body"><b>How free practice works</b>'+'<p>You get 25 graded exercises a month. Any hub you start stays open until '+'the month ends, so you can always finish what you began.</p></div>'+'<button type="button" class="xh-meter-intro-ok">Got it</button>';meterIntroEl.querySelector('.xh-meter-intro-ok').addEventListener('click',function(){try{localStorage.setItem(METER_INTRO_KEY,'1');}catch(e){}
meterIntroEl.remove();meterIntroEl=null;});anchor.parentElement.insertBefore(meterIntroEl,anchor);}
function meterWallRender(){var walled=meterWalled();document.documentElement.classList.toggle('xh-meter-walled',walled);if(!walled){if(meterWallEl){meterWallEl.remove();meterWallEl=null;}
return;}
if(meterWallEl)return;var first=document.querySelector('section.exercise');if(!first||!first.parentElement)return;var s=meterState;var open=s.open_hubs||[];var openLine=open.length?'The '+open.length+' hub'+(open.length===1?'':'s')+' you started this month, until '+meterResetLabel():'Your reading position and streak, everywhere';meterWallEl=document.createElement('div');meterWallEl.className='xh-meter-wall';meterWallEl.setAttribute('role','status');meterWallEl.innerHTML='<div class="xh-meter-wall-head">'+'<div class="xh-meter-wall-title">That&#39;s all '+s.limit+' for this month</div>'+'<div class="xh-meter-wall-sub">A full month of practice, done.</div></div>'+'<div class="xh-meter-wall-body">'+'<div class="xh-meter-wall-h">Still open right now</div>'+'<ul class="xh-meter-wall-list">'+'<li>'+openLine+'</li>'+'<li>Every lesson and every tutorial, always</li>'+'<li>A fresh '+s.limit+' on '+meterResetLabel()+'</li></ul>'+'<div class="xh-meter-wall-cta">'+'<a class="xh-meter-wall-pro" href="/pricing.html">Go Pro for unlimited practice</a>'+'<a class="xh-meter-wall-free" href="/tutorials/">Keep learning free</a></div>'+'<div class="xh-meter-wall-note">Your streak and XP are safe either way.</div>'+'</div>';first.parentElement.insertBefore(meterWallEl,first);}
function meterApply(m,card){if(!meterState)meterState={metered:true,resets:'',open_hubs:[]};meterState.metered=true;meterState.limit=m.limit;meterState.left=m.left;meterState.used=m.used;meterState.hub_started=true;meterState.hub_open=true;meterRender();if(m.left<=5&&card&&card.verdict){var vbody=card.verdict.querySelector('.xh-verdict-body');if(vbody&&!vbody.querySelector('.xh-meter-inline')){vbody.insertAdjacentHTML('beforeend','<span class="xh-meter-inline"> &middot; '+m.left+' of '+m.limit+' left this month</span>');}}}
document.addEventListener('auth-hydrated',onAuthHydrated);function updateStreak(){var s=STORE.loadStreak();var today=todayStr();if(s.lastVisit===today)return s.days||1;if(s.lastVisit){var gap=(new Date(today)-new Date(s.lastVisit))/86400000;s.days=(gap===1)?(s.days+1):1;}else{s.days=1;}
s.lastVisit=today;STORE.saveStreak(s);return s.days;}
function discoverNext(){var current=location.pathname.split('/').pop();var links=Array.prototype.slice.call(document.querySelectorAll('#nav a, .col-sm-3 a'));for(var i=0;i<links.length;i++){var href=links[i].getAttribute('href')||'';if(href&&(href===current||href.indexOf(current)>=0)){for(var j=i+1;j<links.length;j++){var nh=links[j].getAttribute('href')||'';if(nh&&nh.indexOf('.html')!==-1&&nh!==current){return{url:nh,title:links[j].textContent.trim()};}}
break;}}
return null;}
function renderMetaStrip(){var meta=document.querySelector('.engagement-header');if(!meta)return;var diff=meta.getAttribute('data-difficulty');var time=meta.getAttribute('data-time');var exc=meta.getAttribute('data-exercises');var xp=0;var exs=document.querySelectorAll('section.exercise');for(var x=0;x<exs.length;x++){xp+=xpWeight(exs[x].getAttribute('data-difficulty'));}
var parts=[];if(diff){parts.push('<span class="engagement-meta-diff engagement-meta-diff-'+
escapeHtml(diff.toLowerCase().replace(/[^a-z]/g,''))+'">'+
escapeHtml(diff)+'</span>');}
if(time)parts.push('<span class="engagement-meta-time">~ '+escapeHtml(time)+' min</span>');if(exc)parts.push('<span class="engagement-meta-count">'+escapeHtml(exc)+' exercises</span>');if(xp)parts.push('<span class="engagement-meta-xp">'+xp.toLocaleString()+' XP</span>');if(parts.length)meta.innerHTML=parts.join('<span class="engagement-meta-dot">&middot;</span>');}
var mapEl,mapCountEl,mapContinueEl,mapGoalEl;var mapLanes=[];var xpNumEl=null,xpGainEl=null;var DAILY_GOAL=3;var _painted={};var AUTO_HINT_AFTER=2;function cleanHeading(el){var raw=(el.textContent||'').replace(/^\s*#\s*/,'').trim();var m=raw.match(/^Section\s+(\d+)\s*[.:]?\s*(.+?)\s*(?:\([^)]*\))?\s*$/i);if(m)return{num:m[1],name:m[2].trim()};return{num:'',name:raw.replace(/\s*\([^)]*\)\s*$/,'')};}
function buildStatusBar(total,streakDays){var content=document.querySelector('#content')||document.body;var groups=[];var curr=null;var els=content.querySelectorAll('h2, section.exercise');Array.prototype.forEach.call(els,function(el){if(el.classList&&el.classList.contains('exercise')){var id=el.getAttribute('data-exercise-id');if(!id)return;if(!curr){curr={head:null,cards:[]};groups.push(curr);}
curr.cards.push(id);}else{curr={head:cleanHeading(el),cards:[]};groups.push(curr);}});groups=groups.filter(function(g){return g.cards.length;});if(!groups.length)return;var single=groups.length===1&&(!groups[0].head||!groups[0].head.name);mapEl=document.createElement('div');mapEl.className='xh-map'+(single?' xh-map-single':'');mapEl.setAttribute('role','group');var head=document.createElement('div');head.className='xh-map-head';head.innerHTML='<span class="xh-map-eyebrow">Your progress</span>'+'<span class="xh-map-goal" hidden></span>'+'<span class="xh-map-count"><b>0</b> of '+total+' solved</span>'+'<button type="button" class="xh-map-continue"></button>';mapEl.appendChild(head);mapCountEl=head.querySelector('.xh-map-count');mapGoalEl=head.querySelector('.xh-map-goal');mapContinueEl=head.querySelector('.xh-map-continue');mapContinueEl.addEventListener('click',continueToNext);var lanesWrap=document.createElement('div');lanesWrap.className='xh-map-lanes';mapLanes=[];groups.forEach(function(g,gi){var idxTxt=(g.head&&g.head.num)?g.head.num:String(gi+1);var name=(g.head&&g.head.name)?g.head.name:'';var lane=document.createElement('div');lane.className='xh-lane';lane.innerHTML=(single?'':'<span class="xh-lane-idx">'+escapeHtml(idxTxt)+'</span>'+'<span class="xh-lane-name">'+escapeHtml(name)+'</span>')+'<span class="xh-lane-nodes"><span class="xh-rail-bg"></span>'+'<span class="xh-rail-fill"></span></span>'+'<span class="xh-lane-count">0/'+g.cards.length+'</span>';var nodesHost=lane.querySelector('.xh-lane-nodes');var rec={el:lane,countEl:lane.querySelector('.xh-lane-count'),railFill:lane.querySelector('.xh-rail-fill'),cards:[],n:g.cards.length};g.cards.forEach(function(id,i){var node=document.createElement('button');node.type='button';node.className='xh-node';node.setAttribute('data-ex-id',id);node.setAttribute('aria-label','Go to exercise '+idxTxt+'.'+(i+1));node.addEventListener('click',function(){jumpToExercise(id);});nodesHost.appendChild(node);rec.cards.push({node:node,id:id});});mapLanes.push(rec);lanesWrap.appendChild(lane);});mapEl.appendChild(lanesWrap);var h1=content.querySelector('h1');var anchor=content.querySelector('#content h2, main h2, .exercise-hub h2')||content.querySelector('h2')||content.querySelector('section.exercise');if(anchor&&anchor.parentElement)anchor.parentElement.insertBefore(mapEl,anchor);else if(h1&&h1.parentElement)h1.parentElement.insertBefore(mapEl,h1);else content.insertBefore(mapEl,content.firstChild);}
function openAndScroll(card){setCardOpen(card.section,true);var h=card.section.querySelector('.xh-ex-head');if(h)h.setAttribute('aria-expanded','true');var y=card.section.getBoundingClientRect().top+window.scrollY-76;window.scrollTo({top:y,behavior:'smooth'});}
function cardById(id){for(var i=0;i<cards.length;i++)if(cards[i].id===id)return cards[i];return null;}
function jumpToExercise(id){var c=cardById(id);if(c){openAndScroll(c);return;}
var sec=document.querySelector('section.exercise[data-exercise-id="'+id+'"]');if(sec)sec.scrollIntoView({behavior:'smooth',block:'start'});}
function continueToNext(){for(var i=0;i<cards.length;i++){if(!cards[i].solved){openAndScroll(cards[i]);return;}}}
function isSolvedId(id){for(var i=0;i<cards.length;i++)if(cards[i].id===id)return!!cards[i].solved;return!!(progressState&&progressState.solved&&progressState.solved[id]);}
function popNode(node){node.classList.remove('xh-node-pop');void node.offsetWidth;node.classList.add('xh-node-pop');}
function updateProgress(solved,total){if(!mapEl)return;var overall=0;mapLanes.forEach(function(lane){var k=0;lane.cards.forEach(function(c){var s=isSolvedId(c.id);c.node.classList.toggle('solved',s);if(s&&!_painted[c.id]){popNode(c.node);_painted[c.id]=true;}
if(s)k++;});lane.countEl.textContent=k+'/'+lane.n;lane.el.classList.toggle('is-done',lane.n>0&&k===lane.n);var frac=lane.n>1?(k>0?(k-1)/(lane.n-1):0):(k>0?1:0);lane.railFill.style.width='calc((100% - 16px) * '+frac+')';overall+=k;});if(mapCountEl)mapCountEl.querySelector('b').textContent=overall;mapEl.setAttribute('aria-label',overall+' of '+total+' exercises solved');updateGoal();updateContinue(overall,total);}
function updateContinue(solved,total){if(!mapContinueEl)return;if(solved>=total){mapContinueEl.hidden=true;return;}
mapContinueEl.hidden=false;mapContinueEl.innerHTML=(solved===0?'Start solving':'Continue <span class="xh-cont-sep">&middot;</span> '+(total-solved)+' to go')+' <span class="xh-cont-arrow" aria-hidden="true">&rarr;</span>';}
function updateGoal(){if(!mapGoalEl)return;var n=STORE.loadDaily().count||0;if(n<=0){mapGoalEl.hidden=true;return;}
mapGoalEl.hidden=false;if(n>=DAILY_GOAL){mapGoalEl.className='xh-map-goal is-met';mapGoalEl.innerHTML='<span aria-hidden="true">&#10003;</span> Daily goal';}else{mapGoalEl.className='xh-map-goal';mapGoalEl.textContent='Today '+n+' / '+DAILY_GOAL;}}
function pulseProgress(){if(!mapCountEl)return;var b=mapCountEl.querySelector('b');if(!b)return;b.classList.remove('xh-bump');void b.offsetWidth;b.classList.add('xh-bump');}
function surgeProgressFill(){}
function xpEarned(){var n=0;for(var i=0;i<cards.length;i++){if(cards[i].solved)n+=cards[i].xp;}
return n;}
var xpShown=0;function updateXp(animate){if(!xpNumEl)return;var earned=xpEarned();var prev=xpShown;xpShown=earned;xpNumEl.textContent=earned.toLocaleString();if(!animate||earned<=prev)return;xpNumEl.classList.remove('xh-bump');void xpNumEl.offsetWidth;xpNumEl.classList.add('xh-bump');if(xpGainEl){xpGainEl.textContent='+'+(earned-prev)+' XP';xpGainEl.classList.remove('is-shown');void xpGainEl.offsetWidth;xpGainEl.classList.add('is-shown');}}
var milestoneEl;function showMilestone(text){if(!milestoneEl){milestoneEl=document.createElement('div');milestoneEl.className='xh-milestone';milestoneEl.setAttribute('role','status');document.body.appendChild(milestoneEl);}
milestoneEl.textContent=text;void milestoneEl.offsetWidth;milestoneEl.classList.add('is-shown');clearTimeout(milestoneEl._t);milestoneEl._t=setTimeout(function(){milestoneEl.classList.remove('is-shown');},2800);}
function checkMilestone(solved,total){if(!total)return;if(!progressState.milestones)progressState.milestones={};var marks=[{key:'75',at:0.75,msg:'Almost done'},{key:'50',at:0.50,msg:'Halfway there'},{key:'25',at:0.25,msg:'Quarter done'}];var pct=solved/total;for(var i=0;i<marks.length;i++){var m=marks[i];if(pct>=m.at&&!progressState.milestones[m.key]){progressState.milestones[m.key]=true;STORE.saveProgress(progressState);showMilestone(m.msg+' ('+solved+' / '+total+')');return;}}}
function difficultyPill(difficulty){var key=(difficulty||'').toLowerCase();var filled=DOTS_BY_DIFF[key]||0;if(!filled)return'';var dots='';for(var i=0;i<3;i++){dots+=(i<filled)?'<i></i>':'<i class="xh-dot-off"></i>';}
var label=key.charAt(0).toUpperCase()+key.slice(1);return'<span class="xh-diff" title="Difficulty: '+escapeHtml(label)+'">'+'<span class="xh-diff-dots" aria-hidden="true">'+dots+'</span>'+
escapeHtml(label)+'</span>';}
var cards=[];function buildZones(card,body){var problem=document.createElement('div');problem.className='xh-zone xh-zone-problem';var work=document.createElement('div');work.className='xh-zone xh-zone-work';var help=document.createElement('div');help.className='xh-zone xh-zone-help';var task=body.querySelector('.exercise-task');var expected=body.querySelector('.exercise-expected');if(task)problem.appendChild(task);if(expected)problem.appendChild(expected);if(card.yourTurn)work.appendChild(card.yourTurn);else if(card.staticTurn)work.appendChild(card.staticTurn);var checkRow=body.querySelector('.xh-check-row');if(checkRow)work.appendChild(checkRow);if(card.verdict)work.appendChild(card.verdict);var hints=body.querySelector('.xh-hints');if(hints)help.appendChild(hints);var solution=body.querySelector('details.exercise-solution');if(solution)help.appendChild(solution);var foot=body.querySelector('.xh-ex-foot');var dsrc=body.querySelector('.xh-difficulty-src');if(dsrc)dsrc.remove();var inner=document.createElement('div');inner.className='xh-ex-inner';inner.appendChild(problem);inner.appendChild(work);if(help.childNodes.length)inner.appendChild(help);if(foot)inner.appendChild(foot);body.appendChild(inner);}
function setCardOpen(section,open){var body=section.querySelector('.xh-ex-body');var isOpen=section.classList.contains('is-open');if(!body||!section.classList.contains('xh-anim')){section.classList.toggle('is-open',open);return;}
if(isOpen===open)return;var start=body.getBoundingClientRect().height;section.classList.toggle('is-open',open);var end=open?body.scrollHeight:0;body.style.height=start+'px';body.offsetHeight;body.style.height=end+'px';var timer;var settle=function(e){if(e&&e.target!==body)return;body.style.height='';body.removeEventListener('transitionend',settle);clearTimeout(timer);};body.addEventListener('transitionend',settle);timer=setTimeout(settle,480);}
function enhanceSection(section,index,total,progress){var id=section.getAttribute('data-exercise-id')||('ex-'+index);var mode=section.getAttribute('data-grade-mode')||'output-compare';var difficulty=section.getAttribute('data-difficulty')||'';var solved=!!progress.solved[id];section.classList.add('xh-card');section.classList.add(solved?'is-solved':'is-open');var h3=section.querySelector('.exercise-title');var fullTitle=h3?h3.textContent.trim():('Exercise '+(index+1));var split=fullTitle.split(/:\s*/);var exNum=(split.length>1)?split.shift():'';var exName=split.join(': ');var bodyId='xh-body-'+id;var btn=document.createElement('button');btn.type='button';btn.className='xh-ex-head';btn.setAttribute('aria-expanded',solved?'false':'true');btn.setAttribute('aria-controls',bodyId);btn.innerHTML=(exNum?'<span class="xh-ex-num">'+escapeHtml(exNum)+'</span>':'')+'<span class="xh-ex-name">'+escapeHtml(exName)+'</span>'+
difficultyPill(difficulty)+'<span class="xh-time">⏱ '+
(TIME_BY_DIFF[difficulty.toLowerCase()]||4)+' min</span>'+'<span class="xh-state" aria-hidden="true">✓</span>'+'<span class="xh-chevron" aria-hidden="true">▾</span>';if(h3){h3.textContent='';h3.appendChild(btn);}
var body=document.createElement('div');body.className='xh-ex-body';body.id=bodyId;var node=section.firstChild;while(node){var next=node.nextSibling;if(node!==h3)body.appendChild(node);node=next;}
section.appendChild(body);var ps=body.querySelectorAll('p');for(var p=0;p<ps.length;p++){if(/^\s*Difficulty:/.test(ps[p].textContent)){ps[p].classList.add('xh-difficulty-src');break;}}
var yourTurn=null;var containers=body.querySelectorAll('.webr-container');for(var c=0;c<containers.length;c++){if(!containers[c].closest('details')){yourTurn=containers[c];break;}}
var staticTurn=null;if(!yourTurn){var pres=body.querySelectorAll('pre');for(var sp=0;sp<pres.length;sp++){if(pres[sp].closest('details')||pres[sp].closest('.exercise-expected'))continue;var sc=pres[sp].querySelector('code');if(sc&&/\blanguage-r\b/.test(sc.className||'')){staticTurn=pres[sp];break;}}}
var verdict=document.createElement('div');verdict.className='xh-verdict';verdict.setAttribute('role','status');verdict.setAttribute('aria-live','polite');var checkBtn=null,checkStatus=null,doneBtn=null;if(yourTurn){var checkRow=document.createElement('div');checkRow.className='xh-check-row';checkBtn=document.createElement('button');checkBtn.type='button';checkBtn.className='xh-check-btn';checkBtn.textContent='Check answer';checkStatus=document.createElement('span');checkStatus.className='xh-check-status';checkStatus.setAttribute('role','status');checkRow.appendChild(checkBtn);checkRow.appendChild(checkStatus);yourTurn.after(checkRow);checkRow.after(verdict);}else if(staticTurn){var doneRow=document.createElement('div');doneRow.className='xh-check-row';doneBtn=document.createElement('button');doneBtn.type='button';doneBtn.className='xh-done-btn';doneBtn.textContent=solved?'✓ Marked done':'Mark as done';doneBtn.disabled=solved;doneRow.appendChild(doneBtn);staticTurn.after(doneRow);doneRow.after(verdict);}else{body.appendChild(verdict);}
buildHints(section,body,verdict);var solDetails=body.querySelector('details.exercise-solution');if(solDetails){var solSummary=solDetails.querySelector('summary');if(solSummary){solSummary.textContent='Reveal solution';solDetails.addEventListener('toggle',function(){solSummary.textContent=solDetails.open?'Hide solution':'Reveal solution';});}}
var foot=document.createElement('div');foot.className='xh-ex-foot';var nextBtn=document.createElement('button');nextBtn.type='button';nextBtn.className='xh-next';nextBtn.innerHTML='Next exercise <span class="xh-next-arrow">→</span>';foot.appendChild(nextBtn);body.appendChild(foot);var card={section:section,body:body,verdict:verdict,checkBtn:checkBtn,checkStatus:checkStatus,doneBtn:doneBtn,id:id,mode:mode,solved:solved,yourTurn:yourTurn,staticTurn:staticTurn,xp:xpWeight(difficulty)};cards.push(card);buildZones(card,body);btn.addEventListener('click',function(){var open=!section.classList.contains('is-open');setCardOpen(section,open);btn.setAttribute('aria-expanded',open?'true':'false');});nextBtn.addEventListener('click',function(){setCardOpen(section,false);btn.setAttribute('aria-expanded','false');var nextCard=cards[index+1];if(nextCard){setCardOpen(nextCard.section,true);nextCard.section.querySelector('.xh-ex-head').setAttribute('aria-expanded','true');nextCard.section.scrollIntoView({behavior:'smooth',block:'start'});}else if(badgeEl){badgeEl.scrollIntoView({behavior:'smooth'});}});return card;}
function buildHints(section,body,verdict){var src=body.querySelector('.exercise-hints');if(!src)return;var hintEls=src.querySelectorAll('p');if(!hintEls.length){src.remove();return;}
var hints=Array.prototype.map.call(hintEls,function(el){return el.innerHTML;});src.remove();var wrap=document.createElement('div');wrap.className='xh-hints';var bar=document.createElement('div');bar.className='xh-hintbar';bar.innerHTML='<span class="xh-hintbar-label">Stuck?</span>';wrap.appendChild(bar);hints.forEach(function(htmlText,h){var link=document.createElement('button');link.type='button';link.className='xh-hint-link';link.textContent='Show hint '+(h+1);if(h>0)link.disabled=true;bar.appendChild(link);var panel=document.createElement('div');panel.className='xh-hint';panel.hidden=true;panel.innerHTML='<b>Hint '+(h+1)+'</b>'+htmlText;wrap.appendChild(panel);link.addEventListener('click',function(){panel.hidden=false;link.disabled=true;link.textContent='Hint '+(h+1)+' shown';var nextLink=bar.querySelectorAll('.xh-hint-link')[h+1];if(nextLink)nextLink.disabled=false;var hostCard=null;for(var ci=0;ci<cards.length;ci++){if(cards[ci].section===section){hostCard=cards[ci];break;}}
if(hostCard){hostCard.hintsUsed=(hostCard.hintsUsed||0)+1;}});});var solution=body.querySelector('details.exercise-solution')||body.querySelector('details');if(solution)solution.parentNode.insertBefore(wrap,solution);else verdict.after(wrap);}
function setVerdict(card,state,icon,msg,detail){if(card.checkStatus){card.checkStatus.className='xh-check-status is-shown is-'+state;card.checkStatus.innerHTML=STATUS_CONTENT[state]||'';}
var v=card.verdict;if(detail){v.className='xh-verdict is-shown is-'+state;v.innerHTML='<span class="xh-verdict-icon" aria-hidden="true">'+icon+'</span>'+'<span class="xh-verdict-body">'+escapeHtml(msg)+'<span class="xh-verdict-detail">'+detail+'</span></span>';}else{v.className='xh-verdict';v.innerHTML='';}}
function hideVerdict(card){card.verdict.className='xh-verdict';card.verdict.innerHTML='';if(card.checkStatus){card.checkStatus.className='xh-check-status';card.checkStatus.innerHTML='';}}
function expectedText(card){var pre=card.section.querySelector('.exercise-expected pre');return pre?pre.textContent:'';}
function runSetupAndRetry(){var prelude=document.querySelector('.webr-container');if(!prelude)return;var runBtn=prelude.querySelector('.webr-run-btn');if(runBtn)runBtn.click();}
function grade(card){var outEl=card.yourTurn&&card.yourTurn.querySelector('.webr-output');if(!outEl)return;var cls=outEl.className||'';var text=outEl.textContent||'';if(cls.indexOf('has-error')!==-1){if(SETUP_ERR.test(text)){setVerdict(card,'error','⚠','Looks like the setup has not run yet.','Run the setup block at the top of the page, then run this again.');var btn=document.createElement('button');btn.type='button';btn.className='xh-setup-btn';btn.textContent='Run setup now';btn.addEventListener('click',runSetupAndRetry);card.verdict.querySelector('.xh-verdict-body').appendChild(btn);}else{setVerdict(card,'error','✗','Your code raised an error.','Read the message above, fix it, and run again.');registerFail(card);}
return;}
if(card.mode!=='output-compare'){setVerdict(card,'pass',CHECK_SVG,'Ran. Compare your output with the expected result above.','This exercise is self-checked: you decide if it matches.');markSolved(card);return;}
var got=normalizeOutput(text);var want=normalizeOutput(expectedText(card));if(!got){setVerdict(card,'running','…','Waiting for output…');return;}
if(got===want){setVerdict(card,'pass',CHECK_SVG,'Correct! Your output matches the expected result.');markSolved(card);}else{var ln=firstDiffLine(got,want);setVerdict(card,'mismatch','≠','Not a match yet.',(ln?'First difference around line '+ln+'. ':'')+'Compare your output with the expected result above, or open a hint.');registerFail(card);}}
function registerFail(card){card.fails=(card.fails||0)+1;if(card.fails<AUTO_HINT_AFTER||card._autoHinted)return;var link=card.section.querySelector('.xh-hint-link');if(link&&!link.disabled){card._autoHinted=true;link.click();}}
function wireGrading(card){if(card.doneBtn){card.doneBtn.addEventListener('click',function(){if(card.solved)return;if(anonGateCheck(card))return;markSolved(card);card.doneBtn.textContent='✓ Marked done';card.doneBtn.disabled=true;});}
if(!card.yourTurn)return;var outEl=card.yourTurn.querySelector('.webr-output');if(!outEl)return;if(card.checkBtn){card.checkBtn.addEventListener('click',function(){if(meterWalled()){if(meterWallEl)meterWallEl.scrollIntoView({behavior:'smooth',block:'center'});return;}
if(anonGateCheck(card))return;card.gradeNext=true;setVerdict(card,'running','<span class="xh-spinner"></span>','Checking your answer…');var runBtn=card.yourTurn.querySelector('.webr-run-btn');if(runBtn)runBtn.click();});}
card.yourTurn.addEventListener('click',function(e){if(e.target.closest&&e.target.closest('.webr-run-btn')&&!card.gradeNext){hideVerdict(card);}});var obs=new MutationObserver(function(){var cls=outEl.className||'';var ready=cls.indexOf('has-content')!==-1||cls.indexOf('has-error')!==-1||cls.indexOf('has-message')!==-1;if(ready){if(card.gradeNext){card.gradeNext=false;grade(card);}}else if(!card.gradeNext){hideVerdict(card);}});obs.observe(outEl,{attributes:true,attributeFilter:['class']});if(card.mode!=='output-compare'){var plot=card.yourTurn.querySelector('.webr-plot-output');if(plot){var plotObs=new MutationObserver(function(){if(plot.childNodes.length&&card.gradeNext&&!card.solved){card.gradeNext=false;setVerdict(card,'pass',CHECK_SVG,'Plot rendered. Compare it with the expected result.','This exercise is self-checked.');markSolved(card);}});plotObs.observe(plot,{childList:true});}}}
var progressState,totalCount,badgeEl;function solvedCount(){var n=0;for(var i=0;i<cards.length;i++)if(cards[i].solved)n++;return n;}
function markSolved(card){if(!card.solved){card.solved=true;progressState.solved[card.id]=true;STORE.saveProgress(progressState);STORE.bumpDaily();reportSolve(card);if(!authToken)anonWinShow(card);}
card.section.classList.add('is-solved');updateProgress(solvedCount(),totalCount);pulseProgress();surgeProgressFill();updateXp(true);checkMilestone(solvedCount(),totalCount);if(!card._collapseScheduled){card._collapseScheduled=true;setTimeout(function(){if(card.section.classList.contains('is-open')){setCardOpen(card.section,false);var h=card.section.querySelector('.xh-ex-head');if(h)h.setAttribute('aria-expanded','false');}
if(solvedCount()<totalCount){var y=card.section.getBoundingClientRect().top+window.scrollY-76;window.scrollTo({top:y,behavior:'smooth'});}},COLLAPSE_DELAY);}
if(solvedCount()>=totalCount&&badgeEl)showBadge();}
function buildBadge(lastSection){var h1=document.querySelector('#content h1')||document.querySelector('h1');var hubName=h1?h1.textContent.trim():'this set';badgeEl=document.createElement('div');badgeEl.className='xh-badge';badgeEl.setAttribute('role','status');var shareUrl='https://www.linkedin.com/sharing/share-offsite/?url='+
encodeURIComponent(location.href);badgeEl.innerHTML='<div class="xh-badge-medal" aria-hidden="true">🏆</div>'+'<div class="xh-badge-title">All '+totalCount+' exercises solved</div>'+'<div class="xh-badge-desc">You completed '+escapeHtml(hubName)+', a milestone on your r-statistics.co practice track.</div>'+'<div class="xh-badge-actions">'+'<a class="xh-badge-btn xh-badge-btn-primary" target="_blank" rel="noopener" href="'+
escapeHtml(shareUrl)+'">Share on LinkedIn</a>'+'</div>';lastSection.after(badgeEl);}
function showBadge(){if(!badgeEl||badgeEl.classList.contains('is-shown'))return;badgeEl.classList.add('is-shown');requestAnimationFrame(function(){badgeEl.scrollIntoView({behavior:'smooth',block:'center'});});surfaceCertClaim();}
var certClaimChecked=false;function surfaceCertClaim(){if(certClaimChecked)return;certClaimChecked=true;if(!authToken||!badgeEl)return;fetch('/api/me/tracks',{headers:{'Authorization':'Bearer '+authToken,'Accept':'application/json'},}).then(function(r){return r.ok?r.json():null;}).then(function(body){if(!body||!Array.isArray(body.tracks))return;var claimable=body.tracks.filter(function(t){return t.eligible&&!t.minted;});if(!claimable.length)return;renderClaimBlock(claimable);}).catch(function(){});}
function renderClaimBlock(tracks){var actions=badgeEl.querySelector('.xh-badge-actions')||badgeEl;var block=document.createElement('div');block.className='xh-cert-claim';block.style.cssText='margin-top:18px;padding-top:18px;border-top:1px dashed rgba(0,0,0,.12);'+'display:flex;flex-direction:column;gap:10px';var headline=document.createElement('div');headline.style.cssText='font-weight:600;color:#0a0d14';headline.textContent=tracks.length===1?'You’ve earned a certificate.':'You’ve earned '+tracks.length+' certificates.';block.appendChild(headline);tracks.forEach(function(t){var row=document.createElement('div');row.style.cssText='display:flex;align-items:center;justify-content:space-between;gap:12px;'+'background:#fff;border:1px solid #d4d9e3;border-radius:8px;padding:10px 14px';row.innerHTML='<div><div style="font-family:\'IBM Plex Serif\',Georgia,serif;font-weight:600;font-size:14.5px;color:'+t.color_primary+'">'+
escapeHtml(t.name)+'</div>'+'<div style="font-size:12px;color:#6b7280;margin-top:2px">'+t.solved+' of '+t.total_exercises+' exercises</div></div>';var btn=document.createElement('button');btn.type='button';btn.style.cssText='background:'+t.color_primary+';color:#fff;border:none;border-radius:6px;'+'padding:8px 16px;font-family:inherit;font-size:13px;font-weight:600;cursor:pointer;flex:none';btn.textContent='Claim';btn.addEventListener('click',function(){claimCert(t,btn,row);});row.appendChild(btn);block.appendChild(row);});actions.appendChild(block);}
function claimCert(track,btn,row){if(!authToken)return;btn.disabled=true;var orig=btn.textContent;btn.textContent='Minting...';fetch('/api/cert/mint',{method:'POST',headers:{'Authorization':'Bearer '+authToken,'Content-Type':'application/json',},body:JSON.stringify({track_id:track.id}),}).then(function(r){return r.json().then(function(j){return{ok:r.ok,body:j};});}).then(function(resp){if(!resp.ok)throw new Error(resp.body&&resp.body.message||'Mint failed');btn.textContent='View certificate';btn.disabled=false;btn.onclick=function(){window.open(resp.body.verify_url,'_blank','noopener');};if(typeof resp.body.total_xp==='number'){document.dispatchEvent(new CustomEvent('exercise-progress-changed',{detail:{total_xp:resp.body.total_xp,current_streak_days:resp.body.current_streak_days,longest_streak_days:resp.body.longest_streak_days,},}));}
window.open(resp.body.verify_url,'_blank','noopener');}).catch(function(e){btn.disabled=false;btn.textContent=orig;var err=document.createElement('div');err.style.cssText='font-size:12px;color:#9a1f1f;margin-top:6px';err.textContent=e.message||'Could not mint';row.appendChild(err);});}
function buildCTA(lastSection){var next=discoverNext();var cta=document.createElement('div');cta.className='xh-cta';var href=next?next.url:'index.html';var label=next?('Continue: '+next.title):'Back to all tutorials';cta.innerHTML='<div class="xh-cta-text"><strong>Finished practising?</strong>'+'<span>Keep your momentum going with the next lesson.</span></div>'+'<a class="xh-cta-btn" href="'+escapeHtml(href)+'">'+
escapeHtml(label)+' →</a>';(badgeEl||lastSection).after(cta);}
function init(){var sections=Array.prototype.slice.call(document.querySelectorAll('section.exercise'));if(!sections.length)return;totalCount=sections.length;progressState=STORE.loadProgress();var streakDays=updateStreak();renderMetaStrip();buildStatusBar(totalCount,streakDays);sections.forEach(function(section,i){enhanceSection(section,i,totalCount,progressState);});cards.forEach(wireGrading);updateProgress(solvedCount(),totalCount);updateXp(false);var lastSection=sections[sections.length-1];buildBadge(lastSection);buildCTA(lastSection);if(solvedCount()>=totalCount)showBadge();var dhash=decodeURIComponent((location.hash||'').slice(1));if(/-ex-\d+-\d+$/.test(dhash)){var dbody=document.getElementById('xh-body-'+dhash);var dcard=dbody&&dbody.closest('section.exercise');if(dcard){setCardOpen(dcard,true);setTimeout(function(){dcard.scrollIntoView();window.scrollBy(0,-84);},150);}}
var enableFold=function(){for(var i=0;i<cards.length;i++){cards[i].section.classList.add('xh-anim');}};requestAnimationFrame(function(){requestAnimationFrame(enableFold);});setTimeout(enableFold,250);}
function schedule(){if(window.requestIdleCallback)requestIdleCallback(init,{timeout:2000});else setTimeout(init,200);}
if(document.readyState==='loading'){document.addEventListener('DOMContentLoaded',schedule);}else{schedule();}})();