/*
 * Copyright 2010-2011 Ning, Inc.
 *
 * Ning licenses this file to you under the Apache License, version 2.0
 * (the "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at:
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package com.ning.billing.invoice.model;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.UUID;

import javax.annotation.Nullable;

import org.joda.time.DateTime;
import org.joda.time.Months;

import com.google.inject.Inject;
import com.ning.billing.ErrorCode;
import com.ning.billing.catalog.api.BillingPeriod;
import com.ning.billing.catalog.api.Currency;
import com.ning.billing.catalog.api.Duration;
import com.ning.billing.config.InvoiceConfig;
import com.ning.billing.entitlement.api.billing.BillingEvent;
import com.ning.billing.entitlement.api.billing.BillingModeType;
import com.ning.billing.invoice.api.Invoice;
import com.ning.billing.invoice.api.InvoiceApiException;
import com.ning.billing.invoice.api.InvoiceItem;
import com.ning.billing.junction.api.BillingEventSet;
import com.ning.billing.util.clock.Clock;

public class DefaultInvoiceGenerator implements InvoiceGenerator {
    private static final int ROUNDING_MODE = InvoicingConfiguration.getRoundingMode();
    private static final int NUMBER_OF_DECIMALS = InvoicingConfiguration.getNumberOfDecimals();

    private final Clock clock;
    private final InvoiceConfig config;

    @Inject
    public DefaultInvoiceGenerator(Clock clock, InvoiceConfig config) {
        this.clock = clock;
        this.config = config;
    }

   /*
    * adjusts target date to the maximum invoice target date, if future invoices exist
    */
    @Override
    public Invoice generateInvoice(final UUID accountId, @Nullable final BillingEventSet events,
                                         @Nullable final List<Invoice> existingInvoices,
                                         DateTime targetDate,
                                         final Currency targetCurrency) throws InvoiceApiException {
        if ((events == null) || (events.size() == 0) || events.isAccountAutoInvoiceOff()) {
            return null;
        }

        validateTargetDate(targetDate);

        List<InvoiceItem> existingItems = new ArrayList<InvoiceItem>();
        if (existingInvoices != null) {
            for (Invoice invoice : existingInvoices) {
                for(InvoiceItem item : invoice.getInvoiceItems()) {
                    if(item.getSubscriptionId() == null || // Always include migration invoices, credits etc.  
                      !events.getSubscriptionIdsWithAutoInvoiceOff()
                            .contains(item.getSubscriptionId())) { //don't add items with auto_invoice_off tag 
                        existingItems.add(item);
                    }
                }
            }

            Collections.sort(existingItems);
        }

        targetDate = adjustTargetDate(existingInvoices, targetDate);

        Invoice invoice = new DefaultInvoice(accountId, clock.getUTCNow(), targetDate, targetCurrency);
        UUID invoiceId = invoice.getId();
        List<InvoiceItem> proposedItems = generateInvoiceItems(invoiceId, accountId, events, targetDate, targetCurrency);

        removeCancellingInvoiceItems(existingItems);
        removeDuplicatedInvoiceItems(proposedItems, existingItems);

        addReversingItems(existingItems, proposedItems);
        generateCreditsForPastRepairedInvoices(accountId, existingInvoices, proposedItems, targetCurrency);
        consumeExistingCredit(invoiceId, accountId, existingItems, proposedItems, targetCurrency);

        if (proposedItems == null || proposedItems.size() == 0) {
            return null;
        } else {
            invoice.addInvoiceItems(proposedItems);

            return invoice;
        }
    }

    private void generateCreditsForPastRepairedInvoices(UUID accountId, List<Invoice> existingInvoices, List<InvoiceItem> proposedItems, Currency currency) {
        // determine most accurate invoice balances up to this point
        Map<UUID, BigDecimal> amountOwedByInvoice = new HashMap<UUID, BigDecimal>();

        if (existingInvoices != null) {
            for (Invoice invoice : existingInvoices) {
                amountOwedByInvoice.put(invoice.getId(), invoice.getBalance());
            }
        }

        for (InvoiceItem item : proposedItems) {
            UUID invoiceId = item.getInvoiceId();
            if (amountOwedByInvoice.containsKey(invoiceId)) {
                amountOwedByInvoice.put(invoiceId, amountOwedByInvoice.get(invoiceId).add(item.getAmount()));
            } else {
                amountOwedByInvoice.put(invoiceId, item.getAmount());
            }
        }

        for (UUID invoiceId : amountOwedByInvoice.keySet()) {
            BigDecimal invoiceBalance = amountOwedByInvoice.get(invoiceId);
            if (invoiceBalance.compareTo(BigDecimal.ZERO) < 0) {
                proposedItems.add(new CreditInvoiceItem(invoiceId, accountId, clock.getUTCNow(), invoiceBalance.negate(), currency));
            }
        }
    }

    private void addReversingItems(List<InvoiceItem> existingItems, List<InvoiceItem> proposedItems) {
        for (InvoiceItem existingItem : existingItems) {
            if (existingItem instanceof RecurringInvoiceItem) {
                RecurringInvoiceItem recurringItem = (RecurringInvoiceItem) existingItem;
                proposedItems.add(recurringItem.asReversingItem());
            }
        }
    }

    private void consumeExistingCredit(UUID invoiceId, UUID accountId, List<InvoiceItem> existingItems,
                                       List<InvoiceItem> proposedItems, Currency targetCurrency) {
        BigDecimal totalUnusedCreditAmount = BigDecimal.ZERO;
        BigDecimal totalAmountOwed = BigDecimal.ZERO;

        for (InvoiceItem item : existingItems) {
            if (item instanceof CreditInvoiceItem) {
                totalUnusedCreditAmount = totalUnusedCreditAmount.add(item.getAmount());
            }
        }

        for (InvoiceItem item : proposedItems) {
            if (item instanceof CreditInvoiceItem) {
                totalUnusedCreditAmount = totalUnusedCreditAmount.add(item.getAmount());
            } else {
                totalAmountOwed = totalAmountOwed.add(item.getAmount());
            }
        }

        // credits are positive when they reduce the amount owed (since they offset payment)
        // the credit balance should never be negative
        BigDecimal creditAmount = BigDecimal.ZERO;
        if (totalUnusedCreditAmount.compareTo(BigDecimal.ZERO) > 0) {
            if (totalAmountOwed.abs().compareTo(totalUnusedCreditAmount.abs()) > 0) {
                creditAmount = totalUnusedCreditAmount.negate();
            } else {
                creditAmount = totalAmountOwed;
            }
        }

        if (creditAmount.compareTo(BigDecimal.ZERO) < 0) {
            proposedItems.add(new CreditInvoiceItem(invoiceId, accountId, clock.getUTCNow(), creditAmount, targetCurrency));
        }
    }

    private void validateTargetDate(DateTime targetDate) throws InvoiceApiException {
        int maximumNumberOfMonths = config.getNumberOfMonthsInFuture();

        if (Months.monthsBetween(clock.getUTCNow(), targetDate).getMonths() > maximumNumberOfMonths) {
            throw new InvoiceApiException(ErrorCode.INVOICE_TARGET_DATE_TOO_FAR_IN_THE_FUTURE, targetDate.toString());
        }
    }

    private DateTime adjustTargetDate(final List<Invoice> existingInvoices, final DateTime targetDate) {
        if (existingInvoices == null) {return targetDate;}

        DateTime maxDate = targetDate;

        for (Invoice invoice : existingInvoices) {
            if (invoice.getTargetDate().isAfter(maxDate)) {
                maxDate = invoice.getTargetDate();
            }
        }

        return maxDate;
    }

    /*
    * removes all matching items from both submitted collections
    */
    private void removeDuplicatedInvoiceItems(final List<InvoiceItem> proposedItems,
                                              final List<InvoiceItem> existingInvoiceItems) {
        Iterator<InvoiceItem> proposedItemIterator = proposedItems.iterator();
        while (proposedItemIterator.hasNext()) {
            InvoiceItem proposedItem = proposedItemIterator.next();

            Iterator<InvoiceItem> existingItemIterator = existingInvoiceItems.iterator();
            while (existingItemIterator.hasNext()) {
                InvoiceItem existingItem = existingItemIterator.next();
                if (existingItem.equals(proposedItem)) {
                    existingItemIterator.remove();
                    proposedItemIterator.remove();
                }
            }
        }
    }

    private void removeCancellingInvoiceItems(final List<InvoiceItem> items) {
        List<UUID> itemsToRemove = new ArrayList<UUID>();

        for (InvoiceItem item1 : items) {
            if (item1 instanceof RecurringInvoiceItem) {
                RecurringInvoiceItem recurringInvoiceItem = (RecurringInvoiceItem) item1;
                if (recurringInvoiceItem.reversesItem()) {
                    itemsToRemove.add(recurringInvoiceItem.getId());
                    itemsToRemove.add(recurringInvoiceItem.getReversedItemId());
                }
            }
        }

        Iterator<InvoiceItem> iterator = items.iterator();
        while (iterator.hasNext()) {
            InvoiceItem item = iterator.next();
            if (itemsToRemove.contains(item.getId())) {
                iterator.remove();
            }
        }
    }

    private List<InvoiceItem> generateInvoiceItems(final UUID invoiceId, final UUID accountId, final BillingEventSet events,
                                                   final DateTime targetDate, final Currency currency) throws InvoiceApiException {
        List<InvoiceItem> items = new ArrayList<InvoiceItem>();
        
        if(events.size() == 0) {
            return items;
        }

        Iterator<BillingEvent> eventIt = events.iterator();

        BillingEvent nextEvent = eventIt.next();
        while(eventIt.hasNext()) {
            BillingEvent thisEvent = nextEvent;
            nextEvent = eventIt.next();
            if(!events.getSubscriptionIdsWithAutoInvoiceOff().
                    contains(thisEvent.getSubscription().getId())) { // don't consider events for subscriptions that have auto_invoice_off
                BillingEvent adjustedNextEvent = (thisEvent.getSubscription().getId() == nextEvent.getSubscription().getId()) ? nextEvent : null;
                items.addAll(processEvents(invoiceId, accountId, thisEvent, adjustedNextEvent, targetDate, currency));
            }
        }
        items.addAll(processEvents(invoiceId, accountId, nextEvent, null, targetDate, currency));
        
// The above should reproduce the semantics of the code below using iterator instead of list.
//
//        for (int i = 0; i < events.size(); i++) {
//            BillingEvent thisEvent = events.get(i);
//            BillingEvent nextEvent = events.isLast(thisEvent) ? null : events.get(i + 1);
//            if (nextEvent != null) {
//                nextEvent = (thisEvent.getSubscription().getId() == nextEvent.getSubscription().getId()) ? nextEvent : null;
//            }
//
//            items.addAll(processEvents(invoiceId, accountId, thisEvent, nextEvent, targetDate, currency));
//        }

        return items;
    }

    private List<InvoiceItem> processEvents(final UUID invoiceId, final UUID accountId, final BillingEvent thisEvent, final BillingEvent nextEvent,
                                            final DateTime targetDate, final Currency currency) throws InvoiceApiException {
        List<InvoiceItem> items = new ArrayList<InvoiceItem>();
        InvoiceItem fixedPriceInvoiceItem = generateFixedPriceItem(invoiceId, accountId, thisEvent, targetDate, currency);
        if (fixedPriceInvoiceItem != null) {
            items.add(fixedPriceInvoiceItem);
        }

        BillingPeriod billingPeriod = thisEvent.getBillingPeriod();
        if (billingPeriod != BillingPeriod.NO_BILLING_PERIOD) {
            BillingMode billingMode = instantiateBillingMode(thisEvent.getBillingMode());
            DateTime startDate = thisEvent.getEffectiveDate();
            if (!startDate.isAfter(targetDate)) {
                DateTime endDate = (nextEvent == null) ? null : nextEvent.getEffectiveDate();
                int billCycleDay = thisEvent.getBillCycleDay();

                List<RecurringInvoiceItemData> itemData;
                try {
                    itemData = billingMode.calculateInvoiceItemData(startDate, endDate, targetDate, billCycleDay, billingPeriod);
                } catch (InvalidDateSequenceException e) {
                    throw new InvoiceApiException(ErrorCode.INVOICE_INVALID_DATE_SEQUENCE, startDate, endDate, targetDate);
                }

                for (RecurringInvoiceItemData itemDatum : itemData) {
                    BigDecimal rate = thisEvent.getRecurringPrice();

                    if (rate != null) {
                        BigDecimal amount = itemDatum.getNumberOfCycles().multiply(rate).setScale(NUMBER_OF_DECIMALS, ROUNDING_MODE);

                        RecurringInvoiceItem recurringItem = new RecurringInvoiceItem(invoiceId, 
                                accountId,
                                thisEvent.getSubscription().getBundleId(), 
                                thisEvent.getSubscription().getId(),
                                thisEvent.getPlan().getName(),
                                thisEvent.getPlanPhase().getName(),
                                itemDatum.getStartDate(), itemDatum.getEndDate(),
                                amount, rate, currency);
                        items.add(recurringItem);
                    }
                }
            }
        }

        return items;
    }

    private BillingMode instantiateBillingMode(BillingModeType billingMode) {
        switch (billingMode) {
            case IN_ADVANCE:
                return new InAdvanceBillingMode();
            default:
                throw new UnsupportedOperationException();
        }
    }

    private InvoiceItem generateFixedPriceItem(final UUID invoiceId, final UUID accountId, final BillingEvent thisEvent,
                                               final DateTime targetDate, final Currency currency) throws InvoiceApiException {
        if (thisEvent.getEffectiveDate().isAfter(targetDate)) {
            return null;
        } else {
            BigDecimal fixedPrice = thisEvent.getFixedPrice();

            if (fixedPrice != null) {
                Duration duration = thisEvent.getPlanPhase().getDuration();
                DateTime endDate = duration.addToDateTime(thisEvent.getEffectiveDate());

                return new FixedPriceInvoiceItem(invoiceId, accountId, thisEvent.getSubscription().getBundleId(),
                                                 thisEvent.getSubscription().getId(),
                                                 thisEvent.getPlan().getName(), thisEvent.getPlanPhase().getName(),
                                                 thisEvent.getEffectiveDate(), endDate, fixedPrice, currency);
            } else {
                return null;
            }
        }
    }
}