import type { ClockEvent } from './clock';
import { missedClockIns, workDate } from './clock-rules';

/**
 * Workforce = everyone on the Plant roster (operators + mechanics), with the time
 * the Plant Clock recorded for them. Pure functions only, so the Employees page,
 * the Attendance page and each employee's dashboard read time the same way.
 */

/** "operators:abc…" ↔ "operators-abc…" — a URL segment cannot carry the colon cleanly. */
export const employeeSlug = (id:string) => id.replace(':','-');
export function employeeIdFromSlug(slug:string):string|null {
  const m=/^(operators|mechanics)-([a-z0-9]{15})$/.exec(slug);
  return m?`${m[1]}:${m[2]}`:null;
}

export type Session = { in:ClockEvent; out:ClockEvent|null; minutes:number; day:string };
export type DayTotal = { day:string; minutes:number; firstIn:string; lastOut:string|null; open:boolean };
export type AttendanceSummary = {
  status:'in'|'out'|'away'; last:ClockEvent|null;
  todayMinutes:number; weekMinutes:number; monthMinutes:number; daysThisMonth:number;
  missed:ClockEvent[]; days:DayTotal[]; sessions:Session[];
};

const byTime=(a:ClockEvent,b:ClockEvent)=>Date.parse(a.scanned_at)-Date.parse(b.scanned_at)||a.id.localeCompare(b.id);

/**
 * Pair each IN with the same-day OUT that closed it. An IN still open TODAY counts
 * up to `now` (they are at work); an IN left open on an earlier day counts as 0 —
 * it is a missing clock-out, and inventing hours for it would overstate the time.
 */
export function sessionsOf(events:ClockEvent[], now:string):Session[] {
  const out:Session[]=[];let open:ClockEvent|null=null;
  const close=(s:ClockEvent,e:ClockEvent|null)=>{
    const day=workDate(s.scanned_at);
    const minutes=e?Math.max(0,Math.floor((Date.parse(e.scanned_at)-Date.parse(s.scanned_at))/60_000))
      :day===workDate(now)?Math.max(0,Math.floor((Date.parse(now)-Date.parse(s.scanned_at))/60_000)):0;
    out.push({in:s,out:e,minutes,day});
  };
  for(const e of [...events].sort(byTime)) {
    if(e.direction==='in'){if(open)close(open,null);open=e;}
    else if(open && workDate(open.scanned_at)===workDate(e.scanned_at)){close(open,e);open=null;}
  }
  if(open)close(open,null);
  return out;
}

/** Monday of the Africa/Johannesburg week containing `day` (YYYY-MM-DD). */
export function weekStart(day:string):string {
  const d=new Date(`${day}T12:00:00Z`);const dow=(d.getUTCDay()+6)%7;
  d.setUTCDate(d.getUTCDate()-dow);return d.toISOString().slice(0,10);
}

export function attendanceSummary(events:ClockEvent[], now:string):AttendanceSummary {
  const sorted=[...events].sort(byTime);
  const last=sorted.at(-1)??null;
  const today=workDate(now);const month=today.slice(0,7);const week=weekStart(today);
  const sessions=sessionsOf(sorted,now);
  const dayMap=new Map<string,DayTotal>();
  for(const s of sessions) {
    const d=dayMap.get(s.day)??{day:s.day,minutes:0,firstIn:s.in.scanned_at,lastOut:null,open:false};
    d.minutes+=s.minutes;
    if(s.out)d.lastOut=s.out.scanned_at;
    d.open=!s.out;
    dayMap.set(s.day,d);
  }
  const days=[...dayMap.values()].sort((a,b)=>b.day.localeCompare(a.day));
  const sum=(f:(d:DayTotal)=>boolean)=>days.filter(f).reduce((n,d)=>n+d.minutes,0);
  return {
    status:last && workDate(last.scanned_at)===today ? last.direction : 'away',
    last,
    todayMinutes:sum(d=>d.day===today),
    weekMinutes:sum(d=>d.day>=week && d.day<=today),
    monthMinutes:sum(d=>d.day.startsWith(month)),
    daysThisMonth:days.filter(d=>d.day.startsWith(month)).length,
    missed:missedClockIns(sorted,now),
    days,sessions,
  };
}

export type Period = 'day'|'week'|'month';
const addDays=(day:string,n:number)=>{const d=new Date(`${day}T12:00:00Z`);d.setUTCDate(d.getUTCDate()+n);return d.toISOString().slice(0,10);};
/** Every calendar day (YYYY-MM-DD) in the period containing `anchor`, oldest first. */
export function periodDays(period:Period, anchor:string):string[] {
  if(period==='day')return [anchor];
  if(period==='week'){const start=weekStart(anchor);return Array.from({length:7},(_,i)=>addDays(start,i));}
  const [y,m]=anchor.split('-').map(Number);
  const count=new Date(Date.UTC(y,m,0)).getUTCDate();
  return Array.from({length:count},(_,i)=>`${anchor.slice(0,7)}-${String(i+1).padStart(2,'0')}`);
}
/** The same position one period earlier (-1) or later (+1). A month step lands on the 1st. */
export function shiftPeriod(period:Period, anchor:string, step:number):string {
  if(period==='day')return addDays(anchor,step);
  if(period==='week')return addDays(weekStart(anchor),7*step);
  const [y,m]=anchor.split('-').map(Number);
  const d=new Date(Date.UTC(y,m-1+step,1));return d.toISOString().slice(0,10);
}