function createWeekCalendarImport() {
  const maxBytes=1024*1024;
  function clock(value) {
    const match=/^(\d{2}):(\d{2})$/.exec(String(value||''));
    if(!match)return null;
    const minutes=Number(match[1])*60+Number(match[2]);
    return Number(match[1])<24&&Number(match[2])<60?minutes:null;
  }
  function instant(value) {
    const match=/^(\d{4})(\d{2})(\d{2})T(\d{2})(\d{2})(\d{2})(Z?)$/.exec(value||'');
    if(!match)return null;
    const parts=match.slice(1,7).map(Number);
    const milliseconds=match[7]?Date.UTC(parts[0],parts[1]-1,parts[2],parts[3],parts[4],parts[5]):
      new Date(parts[0],parts[1]-1,parts[2],parts[3],parts[4],parts[5]).getTime();
    return Number.isFinite(milliseconds)?milliseconds:null;
  }
  function events(source) {
    if(typeof source!=='string'||!source.includes('BEGIN:VCALENDAR'))throw new Error('Choose a valid .ics calendar file.');
    if(new TextEncoder().encode(source).length>maxBytes)throw new Error('Calendar files must be 1 MB or smaller.');
    const lines=source.replace(/\r\n[ \t]/g,'').split(/\r?\n/);
    const result=[];let current=null;
    lines.forEach(line=>{
      if(line==='BEGIN:VEVENT'){current={};return;}
      if(line==='END:VEVENT'){
        if(current?.start!=null&&current?.end>current.start)result.push(current);
        current=null;return;
      }
      if(!current)return;
      const separator=line.indexOf(':');if(separator<0)return;
      const name=line.slice(0,separator).split(';')[0],value=line.slice(separator+1);
      if(name==='DTSTART')current.start=instant(value);
      if(name==='DTEND')current.end=instant(value);
    });
    return result;
  }
  function dayBoundary(date,minutes) {
    const [year,month,day]=date.split('-').map(Number);
    return new Date(year,month-1,day,Math.floor(minutes/60),minutes%60).getTime();
  }
  function review(source,{dates,workdayStart='09:00',workdayEnd='17:00'}={}) {
    if(!Array.isArray(dates)||dates.length!==7)throw new Error('Week Ahead must contain seven dates.');
    const startMinute=clock(workdayStart),endMinute=clock(workdayEnd);
    if(startMinute==null||endMinute==null||endMinute<=startMinute)throw new Error('Working hours must end after they start.');
    const calendarEvents=events(source);
    return dates.map(plan_date=>{
      const start=dayBoundary(plan_date,startMinute),end=dayBoundary(plan_date,endMinute);
      const ranges=calendarEvents.map(event=>[Math.max(start,event.start),Math.min(end,event.end)])
        .filter(range=>range[1]>range[0]).sort((left,right)=>left[0]-right[0]);
      const merged=[];
      ranges.forEach(range=>{
        const previous=merged[merged.length-1];
        if(previous&&range[0]<=previous[1])previous[1]=Math.max(previous[1],range[1]);
        else merged.push([...range]);
      });
      const busy_minutes=Math.round(merged.reduce((total,range)=>total+range[1]-range[0],0)/60000);
      return {plan_date,busy_minutes,capacity_minutes:endMinute-startMinute-busy_minutes};
    });
  }
  function createWorkflow({controller,qs,onApplied=()=>{}}={}) {
    let reviewed=null;
    const root=()=>qs('#week-capacity-import');
    function clear() {
      reviewed=null;
      qs('#week-capacity-file').value='';
      qs('#week-capacity-review').hidden=true;
      qs('#week-capacity-days').innerHTML='';
    }
    function open() {
      clear();root().hidden=false;qs('#week-capacity-status').textContent='';
      qs('#week-capacity-file').focus?.();return true;
    }
    function cancel() {clear();root().hidden=true;return true;}
    function reviewSource(source) {
      const display=controller.dates();
      reviewed=review(source,{dates:display.map(item=>item.date),workdayStart:qs('#week-capacity-start').value,
        workdayEnd:qs('#week-capacity-end').value});
      qs('#week-capacity-days').innerHTML=reviewed.map((day,index)=>'<article class="week-capacity-day"><strong>'+
        display[index].label+'</strong><span>'+day.capacity_minutes+' min available</span><small>'+day.busy_minutes+
        ' min busy during working hours</small></article>').join('');
      qs('#week-capacity-review').hidden=false;
      qs('#week-capacity-status').textContent='Review seven capacity totals. Calendar details stay on this device.';
      return reviewed.map(day=>({...day}));
    }
    async function apply() {
      if(!reviewed||!controller.stageCapacities(reviewed))return false;
      qs('#apply-week-capacities').disabled=true;
      try {await controller.flush();cancel();onApplied();return true;}
      finally {qs('#apply-week-capacities').disabled=false;}
    }
    qs('#week-capacity-file')?.addEventListener('change',async event=>{
      const file=event.currentTarget.files?.[0];if(!file)return;
      try {
        if(file.size>maxBytes)throw new Error('Calendar files must be 1 MB or smaller.');
        reviewSource(await file.text());
      } catch(error) {clear();qs('#week-capacity-status').textContent=error.message||'Calendar could not be read.';}
    });
    qs('#cancel-week-capacity-import')?.addEventListener('click',cancel);
    qs('#apply-week-capacities')?.addEventListener('click',()=>apply().catch(error=>{
      qs('#week-capacity-status').textContent=(error.message||'Week Ahead sync is unavailable.')+' Capacities remain saved on this phone.';
    }));
    return {open,cancel,review:reviewSource,apply,state:()=>reviewed?reviewed.map(day=>({...day})):null};
  }
  function mount(controller,weekWorkflow,qs) {
    const workflow=createWorkflow({controller,qs,onApplied:weekWorkflow.renderReview});
    qs('#open-week-capacity-import').addEventListener('click',workflow.open);
    return workflow;
  }
  return {review,createWorkflow,mount};
}
const weekCalendarImport=createWeekCalendarImport();
if(typeof module!=='undefined'&&module.exports)module.exports=weekCalendarImport;