import type { PlannedRider, SequencedStop } from '@/api/optimiser';
import type { OrderRow, RiderInfo } from '@/api/types';
import { riderName } from './assignDelivery';

/**
 * A route plan, and the rule that stops it being committed broken.
 *
 * The optimiser returns a sequence; the operator may then move a stop to
 * another rider or reorder one round. Both edits break step numbers — the rider
 * who lost a stop is left with a gap (1,2,3,5,6) and the one who gained it has
 * a step that collides or is missing — and nothing at the point of the write
 * can tell. The fix is to call `reconcile-steps` before committing, and the
 * whole point of this module is that the UI cannot forget to.
 *
 * Pure, so the gate can be tested without a network or a drag.
 */

export interface Plan {
  riders: PlannedRider[];
  /**
   * Riders edited since the last reconcile.
   *
   * Not a boolean over the whole plan: reconcile takes only the riders that
   * changed and returns those, leaving the rest alone. A single flag would
   * either re-reconcile everything or lose an edit.
   */
  dirty: ReadonlySet<string>;
}

/** Rider ids are compared as strings — they arrive as both, from both services. */
export const key = (id: string | number | undefined | null): string => String(id ?? '');

/** A plan with every stop on one rider, which is what a sequence run gives us. */
export function planFromSequence(stops: SequencedStop[], rider: RiderInfo): Plan {
  return {
    riders: [
      {
        rider_id: rider.userid,
        rider_name: riderName(rider),
        orders: [...stops].sort(byStep),
      },
    ],
    dirty: new Set(),
  };
}

/** Step order, falling back to the order the service returned. */
export function byStep(a: SequencedStop, b: SequencedStop): number {
  const sa = a.step ?? Number.MAX_SAFE_INTEGER;
  const sb = b.step ?? Number.MAX_SAFE_INTEGER;
  return sa - sb;
}

/**
 * Every stop in the plan, flattened.
 *
 * Used for the commit payload and for counting. Order within a rider is kept.
 */
export function allStops(plan: Plan): SequencedStop[] {
  return plan.riders.flatMap((rider) => rider.orders);
}

/**
 * Move one stop to another rider.
 *
 * Both riders become dirty, not just the destination. The donor is the one
 * people forget: it is left with a hole in its sequence, and a plan reconciled
 * on the recipient alone commits that hole to the database.
 */
export function moveStop(plan: Plan, orderheaderid: number, toRiderId: string | number): Plan {
  const to = key(toRiderId);
  let moved: SequencedStop | undefined;
  let fromRider = '';

  const stripped = plan.riders.map((rider) => {
    const found = rider.orders.find((order) => order.orderheaderid === orderheaderid);
    if (!found || key(rider.rider_id) === to) return rider;
    moved = found;
    fromRider = key(rider.rider_id);
    return { ...rider, orders: rider.orders.filter((o) => o.orderheaderid !== orderheaderid) };
  });

  if (!moved) return plan;

  const riders = stripped.map((rider) =>
    key(rider.rider_id) === to ? { ...rider, orders: [...rider.orders, moved as SequencedStop] } : rider,
  );

  const dirty = new Set(plan.dirty);
  if (fromRider) dirty.add(fromRider);
  dirty.add(to);

  return { riders, dirty };
}

/** Reorder one rider's stops. Only that rider is dirtied. */
export function reorderStops(plan: Plan, riderId: string | number, from: number, to: number): Plan {
  const target = key(riderId);
  const riders = plan.riders.map((rider) => {
    if (key(rider.rider_id) !== target) return rider;
    const orders = [...rider.orders];
    if (from < 0 || from >= orders.length || to < 0 || to >= orders.length) return rider;
    const [lifted] = orders.splice(from, 1);
    if (lifted) orders.splice(to, 0, lifted);
    return { ...rider, orders };
  });

  const dirty = new Set(plan.dirty);
  dirty.add(target);
  return { riders, dirty };
}

/** The riders to send to reconcile — only what changed. */
export function dirtyRiders(plan: Plan): PlannedRider[] {
  return plan.riders.filter((rider) => plan.dirty.has(key(rider.rider_id)));
}

/**
 * Merge a reconcile response back in.
 *
 * Replaces the orders of the riders the service returned and leaves every other
 * rider exactly as it was, so an edit made while the request was in flight is
 * not silently discarded. Only the reconciled riders lose their dirty mark, for
 * the same reason.
 */
export function applyReconcile(plan: Plan, response: { riders?: PlannedRider[] }): Plan {
  if (!Array.isArray(response?.riders)) return plan;

  const byId = new Map(response.riders.map((rider) => [key(rider.rider_id), rider]));

  const riders = plan.riders.map((rider) => {
    const fixed = byId.get(key(rider.rider_id));
    return fixed ? { ...rider, orders: [...fixed.orders].sort(byStep) } : rider;
  });

  const dirty = new Set(plan.dirty);
  for (const id of byId.keys()) dirty.delete(id);

  return { riders, dirty };
}

/**
 * Whether this plan may be written to the database.
 *
 * The gate. An unreconciled edit corrupts route sequences, and the corruption
 * is invisible at the point of the write — so this is enforced here rather than
 * left to whoever is looking at the screen.
 */
export function commitProblem(plan: Plan): string {
  if (plan.riders.length === 0 || allStops(plan).length === 0) {
    return 'There is nothing to assign.';
  }
  if (plan.dirty.size > 0) {
    const n = plan.dirty.size;
    return `${n} round${n === 1 ? ' has' : 's have'} unreconciled changes. Reconcile before assigning — committing now would leave gaps in the step numbers.`;
  }
  const duplicate = duplicateOrder(plan);
  if (duplicate) {
    return `Order ${duplicate} appears on two rounds. Reload the plan.`;
  }
  return '';
}

/**
 * An order on two riders at once.
 *
 * Belt and braces against a merge going wrong: the same order committed twice
 * becomes two deliveries for one order, which nothing downstream would notice.
 * The console this pattern came from carries the same guard for the same
 * reason.
 */
function duplicateOrder(plan: Plan): string | null {
  const seen = new Set<number>();
  for (const stop of allStops(plan)) {
    if (!stop.orderheaderid) continue;
    if (seen.has(stop.orderheaderid)) return stop.orderid || String(stop.orderheaderid);
    seen.add(stop.orderheaderid);
  }
  return null;
}

/** Total planned distance, for the summary line. Strings on the wire. */
export function planKms(plan: Plan): number {
  return plan.riders.reduce((sum, rider) => {
    const last = [...rider.orders].sort(byStep).at(-1);
    return sum + Number(last?.cumulativekms ?? 0);
  }, 0);
}

/**
 * Can this order be put on a route at all?
 *
 * It needs a drop coordinate. The check has to happen HERE, before the request,
 * because the optimiser does not refuse an order without one — it reads a
 * missing latitude as 0 and routes to the Gulf of Guinea. Measured against the
 * live service: one order with no coordinates turned a 17 km round into
 * **8,601 km**, with a leg of 8,584 km and an `actualkms` of 11,158.
 *
 * Nothing in the response marks that stop as different from the others, so a
 * plan built on it looks ordinary and is nonsense. Filtering on the way in is
 * the only place this can be caught.
 */
export function isRoutable(order: OrderRow): boolean {
  const lat = Number(order.deliverylat ?? order.droplat ?? '');
  const lon = Number(order.deliverylong ?? order.droplon ?? '');
  return Number.isFinite(lat) && Number.isFinite(lon) && lat !== 0 && lon !== 0;
}

/** The orders worth sending, and the ones to report instead. */
export function splitRoutable(orders: readonly OrderRow[]): {
  routable: OrderRow[];
  unroutable: OrderRow[];
} {
  return {
    routable: orders.filter(isRoutable),
    unroutable: orders.filter((order) => !isRoutable(order)),
  };
}

/**
 * Orders that went in and did not come back.
 *
 * Kept alongside `splitRoutable` rather than replaced by it: that one catches
 * what we refuse to send, this catches what the service silently drops. They
 * are different failures and both lose real work if unreported.
 */
export function unplaced(sent: readonly OrderRow[], stops: readonly SequencedStop[]): OrderRow[] {
  const placed = new Set(stops.map((stop) => stop.orderheaderid));
  return sent.filter((order) => !placed.has(order.orderheaderid));
}