Quantity times Unit price equals total amount check

// This serverless function example can be used for annotation_content events
// (e.g. user_update action). annotation_content events provide annotation
// content tree as the input.
//
// The function below shows a warning to the operator if a row in line items
// does not fullfil the quantity*item_amount == item_amount_total equation.

// --- ROSSUM HOOK REQUEST HANDLER ---

// The rossum_hook_request_handler is an obligatory main function that accepts
// input and produces output of the rossum serverless function hook. Currently,
// the only available programming language is Javascript executed on Node.js 12 environment.
// @param {Object} annotation - see https://api.elis.rossum.ai/docs/#annotation-content-event-data-format
// @returns {Object} - the messages and operations that update the annotation content

exports.rossum_hook_request_handler = ({
  annotation: {
    content
  }
}) => {
  try {


    const quantityColumnDatapoints = findBySchemaId(
      content,
      'item_quantity',
    );

    // List of all datapoints of item_amount_base schema id
    const itemAmountColumnDatapoints = findBySchemaId(
      content,
      'item_amount',
    );
    
    // List of all datapoints of item_amount_base schema id
    const itemAmountTotalColumnDatapoints = findBySchemaId(
      content,
      'item_amount_total',
    );
    
    messages = [];
    
    for(var i = 0; i < quantityColumnDatapoints.length; i++){
      
        quantity = parseFloat(quantityColumnDatapoints[i].content.normalized_value);
        itemAmount = parseFloat(itemAmountColumnDatapoints[i].content.normalized_value); 
        itemAmountTotal = parseFloat(itemAmountTotalColumnDatapoints[i].content.normalized_value);
        
        if(quantity && itemAmount && itemAmountTotal){
        
          if(quantity*itemAmount != itemAmountTotal){
            
            const message =  `Quantity (${quantityColumnDatapoints[i].content.value}) * Item amount (${itemAmountColumnDatapoints[i].content.value}) is not equal to Item amount total (${itemAmountTotalColumnDatapoints[i].content.value})`;
            
            messages.push(
              createMessage(
                'warning',
                message,
                quantityColumnDatapoints[i].id
              )
            );
            
            messages.push(
              createMessage(
                'warning',
                message,
                itemAmountColumnDatapoints[i].id
              )
            );
            
            messages.push(
              createMessage(
                'warning',
                message,
                itemAmountTotalColumnDatapoints[i].id
              )
            );
          
          }
        }
    }

    // Return messages and operations to be used to update current annotation data
    return {
      messages
    };
  } catch (e) {
    // In case of exception, create and return error message. This may be useful for debugging.
    const messages = [
      createMessage('error', 'Serverless Function: ' + e.message)
    ];
    return {
      messages,
    };
  }
};

// --- HELPER FUNCTIONS ---

// Return datapoints matching a schema id.
// @param {Object} content - the annotation content tree (see https://api.elis.rossum.ai/docs/#annotation-data)
// @param {string} schemaId - the field's ID as defined in the extraction schema(see https://api.elis.rossum.ai/docs/#document-schema)
// @returns {Array} - the list of datapoints matching the schema ID

const findBySchemaId = (content, schemaId) =>
  content.reduce(
    (results, dp) =>
    dp.schema_id === schemaId ?
    [...results, dp] :
    dp.children ?
    [...results, ...findBySchemaId(dp.children, schemaId)] :
    results,
    [],
  );

// Create a message which will be shown to the user
// @param {number} datapointId - the id of the datapoint where the message will appear (null for "global" messages).
// @param {String} messageType - the type of the message, any of {info|warning|error}. Errors prevent confirmation in the UI.
// @param {String} messageContent - the message shown to the user
// @returns {Object} - the JSON message definition (see https://api.elis.rossum.ai/docs/#annotation-content-event-response-format)

const createMessage = (type, content, datapointId = null) => ({
  content: content,
  type: type,
  id: datapointId,
});

// Replace the value of the datapoint with a new value.
// @param {Object} datapoint - the content of the datapoint
// @param {string} - the new value of the datapoint
// @return {Object} - the JSON replace operation definition (see https://api.elis.rossum.ai/docs/#annotation-content-event-response-format)

const createReplaceOperation = (datapoint, newValue) => ({
  op: 'replace',
  id: datapoint.id,
  value: {
    content: {
      value: newValue,
    },
  },
});