/** @category Validation Rules */

import { GraphQLError } from '../../error/GraphQLError.ts';

import type {
  FieldDefinitionNode,
  InputValueDefinitionNode,
  NameNode,
} from '../../language/ast.ts';
import type { ASTVisitor } from '../../language/visitor.ts';

import type { GraphQLNamedType } from '../../type/definition.ts';
import {
  isInputObjectType,
  isInterfaceType,
  isObjectType,
} from '../../type/definition.ts';

import type { SDLValidationContext } from '../ValidationContext.ts';

/**
 * Unique field definition names
 *
 * A GraphQL complex type is only valid if all its fields are uniquely named.
 * @param context - The validation context used while checking the document.
 * @returns A visitor that reports validation errors for this rule.
 * @example
 * ```ts
 * import { buildSchema } from 'graphql';
 * import { UniqueFieldDefinitionNamesRule } from 'graphql/validation';
 *
 * const invalidSDL = `
 *   type Query { name: String name: String }
 * `;
 *
 * UniqueFieldDefinitionNamesRule.name; // => 'UniqueFieldDefinitionNamesRule'
 * buildSchema(invalidSDL); // throws an error
 *
 * const validSDL = `
 *   type Query { name: String other: String }
 * `;
 *
 * buildSchema(validSDL); // does not throw
 * ```
 */
export function UniqueFieldDefinitionNamesRule(
  context: SDLValidationContext,
): ASTVisitor {
  const schema = context.getSchema();
  const existingTypeMap = schema ? schema.getTypeMap() : Object.create(null);
  const knownFieldNames = new Map<string, Map<string, NameNode>>();

  return {
    InputObjectTypeDefinition: checkFieldUniqueness,
    InputObjectTypeExtension: checkFieldUniqueness,
    InterfaceTypeDefinition: checkFieldUniqueness,
    InterfaceTypeExtension: checkFieldUniqueness,
    ObjectTypeDefinition: checkFieldUniqueness,
    ObjectTypeExtension: checkFieldUniqueness,
  };

  function checkFieldUniqueness(node: {
    readonly name: NameNode;
    readonly fields?:
      | ReadonlyArray<InputValueDefinitionNode | FieldDefinitionNode>
      | undefined;
  }) {
    const typeName = node.name.value;

    let fieldNames = knownFieldNames.get(typeName);
    if (fieldNames == null) {
      fieldNames = new Map();
      knownFieldNames.set(typeName, fieldNames);
    }

    const fieldNodes = node.fields ?? [];

    for (const fieldDef of fieldNodes) {
      const fieldName = fieldDef.name.value;

      if (hasField(existingTypeMap[typeName], fieldName)) {
        context.reportError(
          new GraphQLError(
            `Field "${typeName}.${fieldName}" already exists in the schema. It cannot also be defined in this type extension.`,
            { nodes: fieldDef.name },
          ),
        );
        continue;
      }

      const knownFieldName = fieldNames.get(fieldName);
      if (knownFieldName != null) {
        context.reportError(
          new GraphQLError(
            `Field "${typeName}.${fieldName}" can only be defined once.`,
            { nodes: [knownFieldName, fieldDef.name] },
          ),
        );
      } else {
        fieldNames.set(fieldName, fieldDef.name);
      }
    }

    return false;
  }
}

function hasField(type: GraphQLNamedType, fieldName: string): boolean {
  if (isObjectType(type) || isInterfaceType(type) || isInputObjectType(type)) {
    return type.getFields()[fieldName] != null;
  }
  return false;
}