// HTML5 drag-and-drop helpers, no libraries. Three flows:
//   • Calendar — drag a day chip (or a stay area band) onto another in-range
//     day to move that entry (shifts end_date by the same delta so multi-day
//     spans / stay lengths stay intact).
//   • Day editor — drag a row's handle to reorder entries within one day.
//   • Trip dashboard — drag a card's handle to reorder trips (shares the day
//     editor's row-reorder machinery, see enableReorder below).
// Touch devices don't fire HTML5 DnD events, so all flows are desktop-only and
// degrade to the existing click/edit behaviour with no polyfill.
import { api } from '../api.js';
import { toast } from '../dom.js';
import { parseYMD, ymd, addDays } from '../format.js';

const DND_MIME = 'text/plain';

function dayDelta(fromYmd, toYmd) {
  return Math.round((parseYMD(toYmd) - parseYMD(fromYmd)) / 86400000);
}

// ---------- Calendar: move an entry to another day ----------

// Mark a calendar chip as a drag source carrying its entry id.
export function makeChipDraggable(node, entry) {
  node.setAttribute('draggable', 'true');
  node.classList.add('cal-chip-draggable');
  node.addEventListener('dragstart', (e) => {
    e.dataTransfer.setData(DND_MIME, String(entry.id));
    e.dataTransfer.effectAllowed = 'move';
    node.classList.add('dragging');
  });
  node.addEventListener('dragend', () => node.classList.remove('dragging'));
}

// Mark a stay area band segment as a drag source carrying its entry id. Same
// mechanics as makeChipDraggable — dropping on an in-range day moves the
// whole stay to start there, preserving its length (end_date shifts by the
// same delta in makeDayDropTarget below).
export function makeBandDraggable(node, entry) {
  node.setAttribute('draggable', 'true');
  node.classList.add('cal-band-draggable');
  node.addEventListener('dragstart', (e) => {
    e.dataTransfer.setData(DND_MIME, String(entry.id));
    e.dataTransfer.effectAllowed = 'move';
    node.classList.add('dragging');
  });
  node.addEventListener('dragend', () => node.classList.remove('dragging'));
}

// Shared move-commit: PATCHes the dragged entry to `targetDate` with the given
// `sortOrder`, shifting `end_date` by the same day-delta in the SAME patch (the
// backend rejects date > stored end_date otherwise). No-ops when dropped back
// on its own day. Used by both the day-cell and week-bands drop targets below.
async function commitEntryMove(id, targetDate, sortOrder, entriesById, tctx) {
  const entry = entriesById.get(id);
  if (!entry || entry.date === targetDate) return; // dropped on its own day
  const patch = { date: targetDate, sort_order: sortOrder };
  if (entry.end_date) {
    const delta = dayDelta(entry.date, targetDate);
    patch.end_date = ymd(addDays(parseYMD(entry.end_date), delta));
  }
  try {
    await api.entries.update(id, patch);
    await tctx.refreshTrip();
  } catch (err) {
    toast(err.message);
  }
}

// Wire an in-range day cell as a drop target. On drop the dragged entry moves
// to `targetDate` with sort_order = `targetCount` (appended after that day's
// entries).
export function makeDayDropTarget(cell, targetDate, targetCount, entriesById, tctx) {
  cell.addEventListener('dragover', (e) => {
    e.preventDefault();
    e.dataTransfer.dropEffect = 'move';
    cell.classList.add('cal-day-drop');
  });
  cell.addEventListener('dragleave', (e) => {
    if (!cell.contains(e.relatedTarget)) cell.classList.remove('cal-day-drop');
  });
  cell.addEventListener('drop', async (e) => {
    e.preventDefault();
    cell.classList.remove('cal-day-drop');
    const id = Number(e.dataTransfer.getData(DND_MIME));
    if (!id) return;
    await commitEntryMove(id, targetDate, targetCount, entriesById, tctx);
  });
}

// Wire a week's stay-bands strip as a drop target, so dragging a chip/band
// onto a spot already covered by another stay's band still moves the entry
// (day cells sit below the bands strip and are otherwise unreachable there).
// The target day is derived from the pointer's x-position across the 7-column
// strip; the moved entry is appended (sort_order 0 — bands don't track a
// day's chip order).
export function makeWeekBandsDropTarget(strip, weekYmd, entriesById, tctx) {
  strip.addEventListener('dragover', (e) => {
    e.preventDefault();
    e.dataTransfer.dropEffect = 'move';
    strip.classList.add('cal-bands-drop');
  });
  strip.addEventListener('dragleave', (e) => {
    if (!strip.contains(e.relatedTarget)) strip.classList.remove('cal-bands-drop');
  });
  strip.addEventListener('drop', async (e) => {
    e.preventDefault();
    strip.classList.remove('cal-bands-drop');
    const id = Number(e.dataTransfer.getData(DND_MIME));
    if (!id) return;
    const rect = strip.getBoundingClientRect();
    const idx = Math.min(6, Math.max(0, Math.floor((e.clientX - rect.left) / (rect.width / 7))));
    await commitEntryMove(id, weekYmd[idx], 0, entriesById, tctx);
  });
}

// ---------- Shared reorder machinery ----------

// `rows`: [{ node, handle, item }] in current display order. Dragging a row's
// handle over another row shows a top/bottom insertion indicator; on drop the
// new order is computed and `commitPatch(id, newSortOrder)` is awaited for ONLY
// the items whose index changed, then `refresh()` re-renders. `getId`/`getSort`
// read the identifying fields off `item` (entries use id/sort_order, trips too,
// but kept generic so callers don't need matching shapes).
function enableReorder(rows, getId, getSort, commitPatch, refresh) {
  let draggingId = null;

  const clearAll = () => {
    for (const r of rows) r.node.classList.remove('drop-before', 'drop-after', 'dragging');
  };

  for (const { node, handle, item } of rows) {
    handle.setAttribute('draggable', 'true');
    handle.addEventListener('dragstart', (e) => {
      draggingId = getId(item);
      e.dataTransfer.setData(DND_MIME, String(draggingId));
      e.dataTransfer.effectAllowed = 'move';
      e.dataTransfer.setDragImage(node, 0, 0);
      node.classList.add('dragging');
    });
    handle.addEventListener('dragend', () => { draggingId = null; clearAll(); });

    node.addEventListener('dragover', (e) => {
      if (draggingId == null || getId(item) === draggingId) return;
      e.preventDefault();
      e.dataTransfer.dropEffect = 'move';
      const rect = node.getBoundingClientRect();
      const after = e.clientY - rect.top > rect.height / 2;
      node.classList.toggle('drop-after', after);
      node.classList.toggle('drop-before', !after);
    });
    node.addEventListener('dragleave', (e) => {
      if (!node.contains(e.relatedTarget)) node.classList.remove('drop-before', 'drop-after');
    });
    node.addEventListener('drop', async (e) => {
      if (draggingId == null || getId(item) === draggingId) return;
      e.preventDefault();
      const after = node.classList.contains('drop-after');
      const movedId = draggingId;
      clearAll();
      draggingId = null;
      await commitReorder(rows, movedId, getId(item), after, getId, getSort, commitPatch, refresh);
    });
  }
}

async function commitReorder(rows, movedId, targetId, after, getId, getSort, commitPatch, refresh) {
  const moved = rows.find((r) => getId(r.item) === movedId).item;
  const ordered = rows.map((r) => r.item).filter((it) => getId(it) !== movedId);
  const targetIndex = ordered.findIndex((it) => getId(it) === targetId);
  ordered.splice(after ? targetIndex + 1 : targetIndex, 0, moved);
  try {
    for (let i = 0; i < ordered.length; i++) {
      if (getSort(ordered[i]) !== i) {
        await commitPatch(getId(ordered[i]), i);
      }
    }
    await refresh();
  } catch (err) {
    toast(err.message);
  }
}

// ---------- Day editor: reorder entries within a day ----------

// `rows`: [{ node, handle, entry }] — see enableReorder above for the mechanics.
export function enableRowReorder(rows, refresh) {
  enableReorder(
    rows.map((r) => ({ node: r.node, handle: r.handle, item: r.entry })),
    (entry) => entry.id,
    (entry) => entry.sort_order,
    (id, sort_order) => api.entries.update(id, { sort_order }),
    refresh,
  );
}

// ---------- Trip dashboard: reorder trip cards ----------

// `rows`: [{ node, handle, trip }] — same mechanics as enableRowReorder, but
// PATCHes the caller's per-user `trip_members.sort_order` via api.trips.reorder.
export function enableTripReorder(rows, refresh) {
  enableReorder(
    rows.map((r) => ({ node: r.node, handle: r.handle, item: r.trip })),
    (trip) => trip.id,
    (trip) => trip.sort_order,
    (id, sort_order) => api.trips.reorder(id, sort_order),
    refresh,
  );
}

// ---------- Checklist: reorder items within a category ----------

// `rows`: [{ node, handle, item }] — same mechanics as enableRowReorder,
// scoped to one category's rows (checklist.js calls this once per category,
// so the resulting sort_order values only need to rank correctly within that
// category — category is always the primary sort key server-side).
export function enableChecklistReorder(rows, refresh) {
  enableReorder(
    rows,
    (item) => item.id,
    (item) => item.sort_order,
    (id, sort_order) => api.checklist.update(id, { sort_order }),
    refresh,
  );
}