import type { Payload, PayloadRequest } from "payload";
import type { LeadershipTransfer, User } from "@/payload-types";
import { isSuperuser } from "@/utils/access-control/hasPermission";
import { emitGameEvent } from "@/utils/event-log/emit";
import { EventTypes } from "@/utils/event-log/eventTypes";
import { notifyUser } from "@/lib/notifications";
import { fetchAssignment, moveMemberBetweenAssignments, notifySuperusers } from "./index";

/**
 * Notification type strings for the leadership-initiated removal flow. Defined
 * once here so the lib and any future consumers reference the same values; the
 * in-app label map in src/lib/notifications/index.ts already labels all four.
 * These deliberately bypass user mutes (removals are workflow-critical).
 */
export const LEADERSHIP_TRANSFER_NOTIFICATION_TYPES = {
  requested: "assignment:leadership-transfer-requested",
  transferred: "assignment:leadership-transfer",
  approved: "assignment:leadership-transfer-approved",
  denied: "assignment:leadership-transfer-denied",
} as const;

const LT = LEADERSHIP_TRANSFER_NOTIFICATION_TYPES;

// ---------------------------------------------------------------------------
// Internal helpers
// ---------------------------------------------------------------------------

/** Coerce a Payload relationship value (numeric id or resolved doc) to its numeric id. */
function relId(value: number | { id: number }): number {
  return typeof value === "number" ? value : value.id;
}

function userLabel(
  user: Pick<User, "displayName" | "username"> | null | undefined,
  fallback: string,
): string {
  if (!user) return fallback;
  return user.displayName || user.username || fallback;
}

async function fetchLeadershipTransfer(
  payload: Payload,
  transferId: number,
  req?: Partial<PayloadRequest>,
): Promise<LeadershipTransfer> {
  const doc = await payload.findByID({
    collection: "leadership-transfers",
    id: transferId,
    depth: 0,
    ...(req ? { req } : {}),
  });
  if (!doc) throw new Error("Removal request not found.");
  return doc;
}

/**
 * Resolve the Infantry assignment id configured on the Game Rules global.
 * Returns null when command has not configured a destination yet.
 */
async function resolveInfantryAssignmentId(payload: Payload): Promise<number | null> {
  const rules = await payload.findGlobal({ slug: "game-rules", depth: 0 });
  const configured = rules?.infantryAssignment;
  if (configured == null) return null;
  return relId(configured);
}

// ---------------------------------------------------------------------------
// Public API
// ---------------------------------------------------------------------------

/**
 * A division leader requests removing a member from their division. The
 * destination is always the Infantry assignment configured on Game Rules.
 * Every removal takes effect only after a superuser approves.
 *
 * Guards: the initiator is the CURRENT leader of a type-"division" assignment;
 * the subject is one of its members and not the initiator; the Infantry
 * destination is configured and is not the source itself (Infantry-origin
 * removals are out of scope); no other pending request exists for the same
 * subject + source.
 *
 * Nothing public happens here: no subject notification and no event-log
 * entry while the request is pending. Only the superusers are notified.
 */
export async function requestLeadershipTransfer(
  payload: Payload,
  initiator: User,
  opts: { subjectId: number; fromAssignmentId: number; reason?: string },
): Promise<LeadershipTransfer> {
  const { subjectId, fromAssignmentId } = opts;
  const reason = opts.reason?.trim();

  const fromAssignment = await fetchAssignment(payload, fromAssignmentId);

  if (fromAssignment.leader !== initiator.id) {
    throw new Error(`Only the current leader of ${fromAssignment.name} can request this removal.`);
  }
  if (fromAssignment.type !== "division") {
    throw new Error("Only divisions can remove members this way.");
  }
  if (subjectId === initiator.id) {
    throw new Error("You cannot remove yourself.");
  }
  if (!fromAssignment.members.includes(subjectId)) {
    throw new Error("That member is not a member of your division.");
  }

  const infantryId = await resolveInfantryAssignmentId(payload);
  if (infantryId == null) {
    throw new Error("Command must configure the default transfer destination first (Game Rules).");
  }
  if (infantryId === fromAssignmentId) {
    throw new Error("Infantry-origin removals are not supported yet.");
  }

  const open = await payload.find({
    collection: "leadership-transfers",
    where: {
      and: [
        { subject: { equals: subjectId } },
        { fromAssignment: { equals: fromAssignmentId } },
        { status: { equals: "pending" } },
      ],
    },
    limit: 1,
    depth: 0,
    overrideAccess: true,
  });
  if (open.docs.length > 0) {
    throw new Error("A removal request for this member is already pending.");
  }

  const [subject, infantry] = await Promise.all([
    payload.findByID({ collection: "users", id: subjectId, depth: 0 }),
    fetchAssignment(payload, infantryId),
  ]);

  const created = await payload.create({
    collection: "leadership-transfers",
    overrideAccess: true,
    depth: 0,
    data: {
      initiator: initiator.id,
      subject: subjectId,
      fromAssignment: fromAssignmentId,
      toAssignment: infantryId,
      status: "pending",
      ...(reason ? { reason } : {}),
    },
  });

  await notifySuperusers(
    payload,
    LT.requested,
    "Removal request",
    `${userLabel(initiator, `user #${initiator.id}`)} requested transferring ${userLabel(subject, `user #${subjectId}`)} from ${fromAssignment.name} to ${infantry.name}`,
  );

  return created;
}

/**
 * Superuser decision on a pending removal request.
 *
 * Approve: atomically (one transaction) stamps the request approved via a
 * compare-and-set update (status pending -> approved, with reviewedBy,
 * resolvedAt and the optional review note) and moves the member from the
 * source division into the configured Infantry assignment. Any failure rolls
 * the whole transaction back and the request stays pending. After the commit
 * the subject and the initiator are notified and a public event is emitted:
 * the user-facing attribution is always the LEADER (the initiator), never the
 * approving superuser, whose id is recorded in the event data for audit only.
 *
 * Deny: a plain terminal update; only the initiator is notified. The subject
 * learns nothing and no public event is emitted.
 */
export async function resolveLeadershipTransfer(
  payload: Payload,
  resolver: User,
  transferId: number,
  opts: { approve: boolean; note?: string },
): Promise<LeadershipTransfer> {
  if (!(await isSuperuser(payload, resolver))) {
    throw new Error("Only a superuser can resolve removal requests.");
  }

  const doc = await fetchLeadershipTransfer(payload, transferId);
  if (doc.status !== "pending") {
    throw new Error(`Only pending removal requests can be resolved (current status: ${doc.status}).`);
  }

  const note = opts.note?.trim();

  if (!opts.approve) {
    const denied = await payload.update({
      collection: "leadership-transfers",
      id: doc.id,
      data: {
        status: "denied",
        reviewedBy: resolver.id,
        resolvedAt: new Date().toISOString(),
        ...(note ? { reviewNote: note } : {}),
      },
      overrideAccess: true,
      depth: 0,
    });

    const subject = await payload.findByID({
      collection: "users",
      id: relId(doc.subject),
      depth: 0,
    });
    await notifyUser(payload, {
      userId: relId(doc.initiator),
      type: LT.denied,
      title: "Removal denied",
      message: `Your removal request for ${userLabel(subject, `user #${relId(doc.subject)}`)} was denied.${note ? ` Note: "${note}"` : ""}`,
      link: "/transfers",
      bypassMute: true,
    });

    return denied;
  }

  const txId = await payload.db.beginTransaction();
  if (txId == null) throw new Error("Failed to begin database transaction.");
  const req: Partial<PayloadRequest> = { transactionID: txId };
  let approvedDoc: LeadershipTransfer;
  try {
    const approved = await payload.update({
      collection: "leadership-transfers",
      where: {
        and: [{ id: { equals: doc.id } }, { status: { equals: "pending" } }],
      },
      data: {
        status: "approved",
        reviewedBy: resolver.id,
        resolvedAt: new Date().toISOString(),
        ...(note ? { reviewNote: note } : {}),
      },
      overrideAccess: true,
      depth: 0,
      req,
    });
    if (approved.docs.length === 0) {
      throw new Error("The removal request changed state while it was being resolved.");
    }

    await moveMemberBetweenAssignments(payload, {
      req,
      subjectId: relId(doc.subject),
      fromAssignmentId: relId(doc.fromAssignment),
      toAssignmentId: relId(doc.toAssignment),
    });

    await payload.db.commitTransaction(txId);
    approvedDoc = approved.docs[0];
  } catch (err) {
    await payload.db.rollbackTransaction(txId);
    throw err;
  }

  // Post-commit side effects. Attribution is the leader, never the resolver;
  // failures here must not roll the committed transfer back.
  const [initiator, subject, fromAssignment, toAssignment] = await Promise.all([
    payload.findByID({ collection: "users", id: relId(doc.initiator), depth: 0 }),
    payload.findByID({ collection: "users", id: relId(doc.subject), depth: 0 }),
    fetchAssignment(payload, relId(doc.fromAssignment)),
    fetchAssignment(payload, relId(doc.toAssignment)),
  ]);
  const leaderLabel = userLabel(initiator, `user #${relId(doc.initiator)}`);
  const subjectLabel = userLabel(subject, `user #${relId(doc.subject)}`);

  await notifyUser(payload, {
    userId: relId(doc.subject),
    type: LT.transferred,
    title: "Transferred",
    message: `You have been transferred from ${fromAssignment.name} to ${toAssignment.name} by ${leaderLabel}.`,
    link: "/roster",
    bypassMute: true,
  });
  await notifyUser(payload, {
    userId: relId(doc.initiator),
    type: LT.approved,
    title: "Removal approved",
    message: `Your removal request for ${subjectLabel} was approved. ${subjectLabel} has been transferred to ${toAssignment.name}.`,
    link: "/transfers",
    bypassMute: true,
  });
  await emitGameEvent(payload, {
    type: EventTypes.PersonnelTransferred,
    message: `${leaderLabel} transferred ${subjectLabel} from ${fromAssignment.name} to ${toAssignment.name}.`,
    actor: relId(doc.initiator),
    targetCollection: "leadership-transfers",
    targetId: doc.id,
    data: {
      initiatorId: relId(doc.initiator),
      approvedById: resolver.id,
      subjectId: relId(doc.subject),
      fromAssignmentId: relId(doc.fromAssignment),
      toAssignmentId: relId(doc.toAssignment),
      reason: doc.reason ?? null,
    },
  });

  return approvedDoc;
}

/**
 * Cancel a pending removal request. Only the initiator, only while pending.
 * No notifications and no public event: a cancelled removal never happened as
 * far as anyone else is concerned.
 */
export async function cancelLeadershipTransfer(
  payload: Payload,
  initiator: User,
  transferId: number,
): Promise<LeadershipTransfer> {
  const doc = await fetchLeadershipTransfer(payload, transferId);
  if (relId(doc.initiator) !== initiator.id) {
    throw new Error("Only your own pending requests can be cancelled.");
  }
  if (doc.status !== "pending") {
    throw new Error("Only your own pending requests can be cancelled.");
  }

  const updated = await payload.update({
    collection: "leadership-transfers",
    where: {
      and: [{ id: { equals: doc.id } }, { status: { equals: "pending" } }],
    },
    data: { status: "cancelled" },
    overrideAccess: true,
    depth: 0,
  });
  if (updated.docs.length === 0) {
    throw new Error("The removal request changed state while it was being cancelled.");
  }

  return updated.docs[0];
}