import type { ProjectFile } from "./project";
import type { Node, Variant, VariantGroupNode } from "./phy";

export type CascadeReference = { layer: "idx" | "elc" | "map" | "ledChains"; location: string; id: string };
type DeleteTarget =
  { kind: "node"; node: Node } | { kind: "variant"; variant: Variant; group: VariantGroupNode };

function descendants(node: Node | Variant): string[] {
  const ids = [node.id];
  if (node.type === "cluster") node.children.forEach((child) => ids.push(...descendants(child)));
  if (node.type === "variantGroup") for (const variant of node.children) ids.push(...descendants(variant));
  if (node.type === "variant") node.children.forEach((child) => ids.push(...descendants(child)));
  return ids;
}

/** Lists all saved references to a PHY node, Variant, and its descendants. T-15. */
export function listDeleteReferences(p: ProjectFile, nodeId: string): CascadeReference[] {
  const target = findTarget(p.phy.root, nodeId);
  if (!target) throw new Error(`Unknown node: ${nodeId}`);
  const ids = new Set(descendants(target.kind === "node" ? target.node : target.variant));
  const out: CascadeReference[] = [];
  p.idx.order.forEach((id) => {
    if (ids.has(id)) out.push({ layer: "idx", location: "/idx/order", id });
  });
  p.elc.keys.forEach((w, i) => {
    if (ids.has(w.key)) out.push({ layer: "elc", location: `/elc/keys/${i}`, id: w.key });
  });
  p.elc.ledChains?.forEach((chain) =>
    chain.order.forEach((id) => {
      if (ids.has(id)) out.push({ layer: "ledChains", location: `/elc/ledChains/${chain.id}`, id });
    }),
  );
  p.map.layers.forEach((layer) =>
    layer.keymap.forEach((assignment) => {
      if (ids.has(assignment.keyId))
        out.push({ layer: "map", location: `/map/layers/${layer.name}`, id: assignment.keyId });
    }),
  );
  return out;
}

/** Removes a PHY node or Variant and its references in one immutable project result. T-15. */
export function deleteNodeCascade(p: ProjectFile, nodeId: string): ProjectFile {
  const o = structuredClone(p);
  const target = findTarget(o.phy.root, nodeId);
  if (!target) throw new Error(`Unknown node: ${nodeId}`);
  const deletedIds = new Set(descendants(target.kind === "node" ? target.node : target.variant));
  removeTarget(o.phy.root, target);

  o.idx.order = o.idx.order.filter((id) => !deletedIds.has(id));
  o.elc.keys = o.elc.keys.filter((w) => !deletedIds.has(w.key));
  if (o.elc.ledChains)
    o.elc.ledChains = o.elc.ledChains.map((chain) => ({
      ...chain,
      order: chain.order.filter((id) => !deletedIds.has(id)),
    }));
  o.map.layers = o.map.layers.map((layer) => ({
    ...layer,
    keymap: layer.keymap.filter((assignment) => !deletedIds.has(assignment.keyId)),
  }));

  if (target.kind === "variant") {
    if (target.group.default === nodeId) target.group.default = target.group.children[0]!.id;
    if (o.output.variantSelection[target.group.id] === nodeId)
      o.output.variantSelection[target.group.id] = target.group.default;
  }
  pruneVariantSelection(o);
  return o;
}

function findTarget(nodes: Node[], id: string): DeleteTarget | undefined {
  for (const node of nodes) {
    if (node.id === id) return { kind: "node", node };
    if (node.type === "cluster") {
      const found = findTarget(node.children, id);
      if (found) return found;
    }
    if (node.type === "variantGroup")
      for (const variant of node.children) {
        if (variant.id === id) return { kind: "variant", variant, group: node };
        const found = findTarget(variant.children, id);
        if (found) return found;
      }
  }
  return undefined;
}

function removeTarget(nodes: Node[], target: DeleteTarget): void {
  const id = target.kind === "node" ? target.node.id : target.variant.id;
  if (target.kind === "variant") {
    const { group, variant } = target;
    if (group.children.length <= 2)
      throw new Error("Cannot delete a variant leaving fewer than two variants");
    group.children.splice(group.children.indexOf(variant), 1);
    if (group.default === id) group.default = group.children[0]!.id;
    return;
  }
  const index = nodes.findIndex((node) => node.id === id);
  if (index >= 0) {
    nodes.splice(index, 1);
    return;
  }
  for (const node of nodes) {
    if (node.type === "cluster") removeTarget(node.children, target);
    if (node.type === "variantGroup")
      for (const variant of node.children) removeTarget(variant.children, target);
  }
}

function pruneVariantSelection(project: ProjectFile): void {
  const valid = new Map<string, { ids: Set<string>; defaultId: string }>();
  const walk = (nodes: Node[]) =>
    nodes.forEach((node) => {
      if (node.type === "cluster") walk(node.children);
      if (node.type === "variantGroup") {
        valid.set(node.id, {
          ids: new Set(node.children.map((variant) => variant.id)),
          defaultId: node.default,
        });
        node.children.forEach((variant) => walk(variant.children));
      }
    });
  walk(project.phy.root);
  for (const [groupId, variantId] of Object.entries(project.output.variantSelection)) {
    const group = valid.get(groupId);
    if (!group) delete project.output.variantSelection[groupId];
    else if (!group.ids.has(variantId)) project.output.variantSelection[groupId] = group.defaultId;
  }
}