import { parse, print, visit, type DocumentNode, type FragmentDefinitionNode } from "graphql";
import { QueryCompileError, type CheckedQuery, type QueryDeclaration, type QuerySelection } from "./types.js";

export type FragmentResolver = (packageRevisionId: string, fragmentId: string) => Promise<CheckedQuery>;
/** Expand only explicitly imported exports. Each variable mapping is checked by
 * GraphQL against the consuming operation, rather than silently inheriting names. */
export async function fragmentSources(
  declaration: QueryDeclaration,
  definitions: DocumentNode["definitions"][number][],
  resolve?: FragmentResolver,
) {
  const markers = new Map<string, NonNullable<QuerySelection["fragmentSpread"]>>();
  for (const imported of declaration.importedFragments ?? []) {
    if (!resolve)
      throw new QueryCompileError(
        "FRAGMENT_RESOLVER_REQUIRED",
        "Resolve imported fragments through package dependencies",
      );
    const checked = await resolve(imported.packageRevisionId, imported.fragmentId);
    const exported = checked.declaration.fragment;
    if (!exported || exported.admission) throw new QueryCompileError("NOT_EXPORTED_FRAGMENT", imported.fragmentId);
    const variables = checked.variables.kind === "record" ? Object.keys(checked.variables.fields) : [];
    if (JSON.stringify(Object.keys(imported.variables).sort()) !== JSON.stringify(variables.sort()))
      throw new QueryCompileError(
        "FRAGMENT_VARIABLE_MAPPING",
        `Map every variable of ${checked.declaration.displayName} explicitly`,
      );
    const source = parse(checked.document);
    const sourceOperation = source.definitions.find(
      (node) => node.kind === "OperationDefinition" && node.name?.value === checked.declaration.operation,
    );
    const consumingOperation = definitions.find(
      (node) => node.kind === "OperationDefinition" && node.name?.value === declaration.operation,
    );
    for (const variable of sourceOperation?.kind === "OperationDefinition"
      ? (sourceOperation.variableDefinitions ?? [])
      : []) {
      const name = imported.variables[variable.variable.name.value];
      const target =
        consumingOperation?.kind === "OperationDefinition"
          ? consumingOperation.variableDefinitions?.find((v) => v.variable.name.value === name)
          : undefined;
      if (!target || print(target.type) !== print(variable.type))
        throw new QueryCompileError(
          "FRAGMENT_VARIABLE_TYPE",
          `Mapped variable ${name} must have type ${print(variable.type)}`,
        );
    }
    const fragments = source.definitions.filter(
      (node): node is FragmentDefinitionNode => node.kind === "FragmentDefinition",
    );
    if (definitions.some((node) => "name" in node && node.name?.value === exported.name))
      throw new QueryCompileError("FRAGMENT_NAME_COLLISION", exported.name);
    const privateNames = new Map(
      fragments.map((node) => [
        node.name.value,
        node.name.value === exported.name ? exported.name : `${exported.name}__${node.name.value}`,
      ]),
    );
    for (const fragment of fragments) {
      definitions.push(
        visit(fragment, {
          FragmentDefinition(node) {
            return { ...node, name: { ...node.name, value: privateNames.get(node.name.value)! } };
          },
          FragmentSpread(node) {
            return { ...node, name: { ...node.name, value: privateNames.get(node.name.value) ?? node.name.value } };
          },
          Variable(node) {
            return { ...node, name: { ...node.name, value: imported.variables[node.name.value] ?? node.name.value } };
          },
        }),
      );
    }
    markers.set(exported.name, {
      package: imported.packageRevisionId,
      fragment: imported.fragmentId,
      digest: checked.definitionDigest,
      root: checked.declaration.root.interface,
      variables: imported.variables,
    });
    for (const [name, contract] of Object.entries(checked.fragmentContracts ?? {})) {
      markers.set(privateNames.get(name) ?? name, {
        ...contract,
        variables: Object.fromEntries(
          Object.entries(contract.variables).map(([inner, outer]) => [inner, imported.variables[outer] ?? outer]),
        ),
      });
    }
  }
  if (declaration.fragment) {
    const exported = declaration.fragment;
    if (!definitions.some((node) => node.kind === "FragmentDefinition" && node.name.value === exported.name))
      throw new QueryCompileError("FRAGMENT_MISSING", exported.name);
    const operations = definitions.filter((node) => node.kind === "OperationDefinition");
    if (!exported.operation) {
      if (operations.length)
        throw new QueryCompileError(
          "FRAGMENT_OPERATION_REQUIRED",
          "Name the standalone operation explicitly when a fragment document includes variables or an operation",
        );
      definitions.push(...parse(`query ${declaration.operation} { root { ...${exported.name} } }`).definitions);
    } else {
      const operation = operations.find(
        (node) => node.kind === "OperationDefinition" && node.name?.value === exported.operation,
      );
      if (!operation || operation.kind !== "OperationDefinition")
        throw new QueryCompileError("FRAGMENT_OPERATION_MISSING", exported.operation);
      // The standalone operation specifies variables only. Its result must be the
      // exact exported fragment, not additional fields or a different window.
      const expected = parse(`query ${declaration.operation} { root { ...${exported.name} } }`).definitions[0]!;
      if (expected.kind !== "OperationDefinition" || print(operation.selectionSet) !== print(expected.selectionSet))
        throw new QueryCompileError(
          "FRAGMENT_STANDALONE_SHAPE",
          "Standalone operation must select root { ...ExportedFragment }",
        );
    }
  }
  return markers;
}