import {
  type FieldNode,
  type DocumentNode,
  visit,
  type SelectionSetNode,
} from "graphql";

const getChildNodesField = (node: FieldNode): FieldNode | undefined => {
  return node?.selectionSet?.selections?.find(
    (node) => node.kind === "Field" && node.name.value === "nodes",
  ) as FieldNode;
};

export const getOperationFields = (documentNode: DocumentNode) => {
  const fieldLines: string[] = [];
  let isInitialEnter = true;
  let depth = 0;
  let isNestedField = false;

  visit(documentNode, {
    Field: {
      enter(node): SelectionSetNode | void {
        if (isInitialEnter) {
          isInitialEnter = false;

          const childNodesField = getChildNodesField(node);

          const nodeToReturn = childNodesField ?? node;

          if (typeof nodeToReturn.selectionSet === "undefined") {
            throw new Error("Operation must have a selection set");
          }

          return nodeToReturn.selectionSet;
        }

        fieldLines.push(
          `${depth > 0 ? "  ".repeat(isNestedField ? depth : depth - 1) : ""}${
            node.name.value
          }${node.selectionSet ? " {" : ""}`,
        );

        if (node.selectionSet) {
          depth++;
          isNestedField = true;
        }
      },
      leave(node) {
        if (node.selectionSet) {
          depth--;
          fieldLines.push(`${"  ".repeat(depth)}}`);
          isNestedField = false;
        }
      },
    },
  });

  return fieldLines.join("\n").trim();
};

export const isMutation = (documentNode: DocumentNode) => {
  let isMutation = false;

  visit(documentNode, {
    OperationDefinition: {
      enter(node) {
        if (node.operation === "mutation") {
          isMutation = true;
        }
      },
    },
  });

  return isMutation;
};