@PatchMapping(consumes = MediaType.APPLICATION_JSON_VALUE)
    @OAuthTestable
    @AppsAllowed(property = "vg.hdc.apps.allowed.patchElections")
    @PreAuthorize("hasScope('div-cap-gains-elections-maintenance')")
    @ResponseStatus(HttpStatus.MULTI_STATUS)
    @ResponseBody
    public ChangeElectionConfirmations changeElection(
            @Valid @UserProfileInject UserProfile userProfile,
            @Valid @RequestBody ChangeElectionsRequest changeElections,
            @RequestParam(name = "validate", defaultValue = "true") boolean validate) {

        List<ChangeElectionConfirmation> confirmations = Collections.synchronizedList(new ArrayList<>());
        Map<String, List<String>> accountPositionsMap = electionService.mapAccountPositions(changeElections);
        AccountValidationDto accountValidationDto = accountRetrievalService.validateAccountAndHoldings(userProfile, accountPositionsMap);
        List<ChangeElectionDto> invalidChangeElections = electionService.buildViolations(accountValidationDto);
        List<ChangeElection> validChangeElections = electionService.filterValidChangeElections(changeElections, invalidChangeElections);
        // check if positions in validChangeElections have valid electionType
        // else throw bad request along with invalidChangeElections
        electionService.validateChangeElectionRequest(changeElections.getChangeElections(), validChangeElections, invalidChangeElections, accountValidationDto);

        if (CollectionUtils.isNotEmpty(validChangeElections)) {

            Map<ElectionLevelType, List<ChangeElection>> electionLevelTypeMap = changeElectionRequestMapper.segregateAccountAndPositionLevelElections(validChangeElections);
            if (CollectionUtils.isNotEmpty(electionLevelTypeMap.get(ElectionLevelType.ACCOUNT))) {
                confirmations.addAll(accountChangeElectionService.updateAccountElections(userProfile,
                        electionLevelTypeMap.get(ElectionLevelType.ACCOUNT), accountValidationDto, validate));
            }

            if (CollectionUtils.isNotEmpty(electionLevelTypeMap.get(ElectionLevelType.POSITION))) {
                confirmations.addAll(updatePositionsElections(electionLevelTypeMap.get(ElectionLevelType.POSITION),
                        accountValidationDto, userProfile.getPoid(), validate));
            }
        }

        confirmations.addAll(changeElectionRequestMapper.mapDtoToConfirmationResponse(invalidChangeElections));
        ChangeElectionConfirmations changeElectionConfirmations = ChangeElectionConfirmations.builder()
                .confirmations(confirmations)
                .build();
        return changeElectionConfirmations;
    }

    /**
     * Update Brokerage and TA Elections for positions
     *
     * @param positionLevelElectionRequest List&lt;ChangeElection&gt;
     * @param accountValidationDto AccountValidationDto
     * @param poId String
     * @return List&lt;ChangeElectionConfirmation&gt;
     */
    private List<ChangeElectionConfirmation> updatePositionsElections(List<ChangeElection> positionLevelElectionRequest,
                                                                      AccountValidationDto accountValidationDto, String poId, boolean validate) {
        // make call to OVV
        ClientDetails clientDetails = clientRetrievalService.getClientRestrictions();
        Map<String, List<ChangeElectionDto>> changeElectionDtoMap = electionService.validateChangeElection(positionLevelElectionRequest, accountValidationDto, clientDetails);
        List<ChangeElectionDto> validChangeElections = changeElectionDtoMap.getOrDefault(VALID_CHANGE_ELECTIONS, new ArrayList<>());

        List<ChangeElectionDto> brokerageChangeElectionDtoList = AccountUtils.getChangeElectionsByAccountType(validChangeElections, AccountType.BROKERAGE);
        List<ChangeElectionDto> taChangeElectionDtoList = AccountUtils.getChangeElectionsByAccountType(validChangeElections, AccountType.MUTUAL_FUND);
        List<ChangeElectionConfirmation> confirmations = Collections.synchronizedList(new ArrayList<>());

        if (CollectionUtils.isNotEmpty(brokerageChangeElectionDtoList) || CollectionUtils.isNotEmpty(taChangeElectionDtoList)) {
            PositionLevelElectionMapDto.PositionLevelElectionMapDtoBuilder positionLevelElectionMapDtoBuilder = electionService.
                    buildAccountDetails(accountValidationDto, poId, validChangeElections, clientDetails);

            if (CollectionUtils.isNotEmpty(brokerageChangeElectionDtoList)) {
                confirmations.addAll(brokeragePositionsElectionService.updateBrokeragePositions(accountValidationDto, poId,
                        brokerageChangeElectionDtoList, positionLevelElectionMapDtoBuilder, validate));
            }

            if (CollectionUtils.isNotEmpty(taChangeElectionDtoList)) {
                confirmations.addAll(mutualFundPositionsElectionService.updateMutualFundPositions(poId, taChangeElectionDtoList,
                        positionLevelElectionMapDtoBuilder, accountValidationDto, validate));
            }
        }

        confirmations.addAll(changeElectionRequestMapper.mapDtoToConfirmationResponse(changeElectionDtoMap
                .get(INVALID_CHANGE_ELECTIONS)));

        return confirmations;
    }

Explain each and every line of code in details