@atomic-ehr/fhirpath/src/operations/isDistinct-function.ts

A TypeScript implementation of FHIRPath

import type { FunctionDefinition, FunctionEvaluator } from '../types';
import { Errors } from '../errors';
import { box, unbox } from '../boxing';

export const evaluate: FunctionEvaluator = async (input, context, args, evaluator) => {
  // isDistinct takes no arguments
  if (args.length !== 0) {
    throw Errors.wrongArgumentCount('isDistinct', 0, args.length);
  }

  // If input is empty, return true
  if (input.length === 0) {
    return { value: [box(true, { type: 'Boolean', singleton: true })], context };
  }

  // Check if all items are distinct by comparing each pair
  // Using the equals (=) operator logic for comparison
  for (let i = 0; i < input.length; i++) {
    for (let j = i + 1; j < input.length; j++) {
      // Two items are considered equal if they have the same value
      // Compare unboxed values
      const value1 = unbox(input[i]!);
      const value2 = unbox(input[j]!);
      
      // Use JSON.stringify for deep comparison
      if (JSON.stringify(value1) === JSON.stringify(value2)) {
        return { value: [box(false, { type: 'Boolean', singleton: true })], context };
      }
    }
  }

  // All items are distinct
  return { value: [box(true, { type: 'Boolean', singleton: true })], context };
};

export const isDistinctFunction: FunctionDefinition & { evaluate: FunctionEvaluator } = {
  name: 'isDistinct',
  category: ['existence'],
  description: 'Returns true if all the items in the input collection are distinct. To determine whether two items are distinct, the equals (=) operator is used. If the input collection is empty, the result is true.',
  examples: [
    "(1 | 2 | 3).isDistinct()",
    "(1 | 2 | 2 | 3).isDistinct()",
    "Patient.name.given.isDistinct()"
  ],
  signatures: [{

    name: 'isDistinct',
    input: { type: 'Any', singleton: false },
    parameters: [],
    result: { type: 'Boolean', singleton: true }
  }],
  evaluate
};