import { addDays, addMilliseconds, differenceInCalendarDays, startOfDay } from "date-fns"
import { formatICSDateOnly, formatICSDateTimeUTC } from "@/lib/agenda/agenda-date"
import type { AgendaApiEvent, AgendaEvent, AgendaEventDraft } from "@/lib/agenda/agenda-types"

/** Calcule les nouvelles dates après déplacement (durée conservée). */
export function shiftedEventRange(
  event: AgendaEvent,
  targetStart: Date,
): { start: Date; end: Date } {
  if (event.allDay || isAllDaySpan(event)) {
    const spanDays = Math.max(
      1,
      differenceInCalendarDays(startOfDay(event.end), startOfDay(event.start)),
    )
    const start = startOfDay(targetStart)
    return { start, end: addDays(start, spanDays) }
  }

  const durationMs = event.end.getTime() - event.start.getTime()
  return { start: targetStart, end: addMilliseconds(targetStart, durationMs) }
}

function isAllDaySpan(event: AgendaEvent): boolean {
  return (
    event.start.getHours() === 0 &&
    event.start.getMinutes() === 0 &&
    event.end.getHours() === 0 &&
    event.end.getMinutes() === 0 &&
    event.end.getTime() - event.start.getTime() >= 24 * 3600 * 1000
  )
}

/** Payload minimal pour un déplacement — le backend merge avec l'événement existant. */
export function eventRescheduleApiPayload(
  event: AgendaEvent,
  start: Date,
  end: Date,
): Partial<AgendaApiEvent> {
  const allDay = event.allDay || isAllDaySpan(event)
  const eventStart = allDay ? startOfDay(start) : start
  return {
    uid: event.uid || event.master.uid,
    summary: event.title.trim() || "(Sans titre)",
    start: allDay ? formatICSDateOnly(eventStart) : formatICSDateTimeUTC(eventStart),
    end: allDay ? formatICSDateOnly(end) : formatICSDateTimeUTC(end),
    all_day: allDay,
  }
}

/** Brouillon UI (legacy — préférer eventRescheduleApiPayload pour l'API). */
export function eventMoveDraft(
  event: AgendaEvent,
  start: Date,
  end: Date,
): AgendaEventDraft {
  return {
    title: event.title === "(Sans titre)" ? "" : event.title,
    start,
    end,
    allDay: event.allDay,
    calendarId: event.calendarId,
    description: event.description,
    location: event.location,
    attendees: event.attendees,
    rrule: event.rrule,
    color: event.master.color,
  }
}