import { Kind } from '../language/kinds.mjs';
import { visit } from '../language/visitor.mjs';
/**
 * separateOperations accepts a single AST document which may contain many
 * operations and fragments and returns a collection of AST documents each of
 * which contains a single operation as well the fragment definitions it
 * refers to.
 */

export function separateOperations(documentAST) {
  const operations = [];
  const depGraph = Object.create(null); // Populate metadata and build a dependency graph.

  for (const definitionNode of documentAST.definitions) {
    switch (definitionNode.kind) {
      case Kind.OPERATION_DEFINITION:
        operations.push(definitionNode);
        break;

      case Kind.FRAGMENT_DEFINITION:
        depGraph[definitionNode.name.value] = collectDependencies(
          definitionNode.selectionSet,
        );
        break;

      default: // ignore non-executable definitions
    }
  } // For each operation, produce a new synthesized AST which includes only what
  // is necessary for completing that operation.

  const separatedDocumentASTs = Object.create(null);

  for (const operation of operations) {
    const dependencies = new Set();

    for (const fragmentName of collectDependencies(operation.selectionSet)) {
      collectTransitiveDependencies(dependencies, depGraph, fragmentName);
    } // Provides the empty string for anonymous operations.

    const operationName = operation.name ? operation.name.value : ''; // The list of definition nodes to be included for this operation, sorted
    // to retain the same order as the original document.

    separatedDocumentASTs[operationName] = {
      kind: Kind.DOCUMENT,
      definitions: documentAST.definitions.filter(
        (node) =>
          node === operation ||
          (node.kind === Kind.FRAGMENT_DEFINITION &&
            dependencies.has(node.name.value)),
      ),
    };
  }

  return separatedDocumentASTs;
}

// From a dependency graph, collects a list of transitive dependencies by
// recursing through a dependency graph.
function collectTransitiveDependencies(collected, depGraph, fromName) {
  if (!collected.has(fromName)) {
    collected.add(fromName);
    const immediateDeps = depGraph[fromName];

    if (immediateDeps !== undefined) {
      for (const toName of immediateDeps) {
        collectTransitiveDependencies(collected, depGraph, toName);
      }
    }
  }
}

function collectDependencies(selectionSet) {
  const dependencies = [];
  visit(selectionSet, {
    FragmentSpread(node) {
      dependencies.push(node.name.value);
    },
  });
  return dependencies;
}