feat(investment): interest schedule API for Interest Entry

Add GET /v1/investment/purchases/{id}/interest-schedule. For a holding it lists every half-yearly coupon and every 31 Mar / 30 Sep closing provision from purchase to maturity, worked out on the face value still held: provision = interest earned since the last coupon (30/360), and the coupon clears what is already booked (purchased accrued interest or the earlier provision). Lines up to the as-on date are marked due. Calculation only; nothing is posted. The day-count and interest arithmetic move into InvestmentInterestCalculator, shared with Purchase Entry, and are covered by unit tests using Jitendra Sir's worked example. Duplicate-code errors on the masters now keep the original exception as the cause. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-09 18:45:41 +05:30
parent 81b5850b62
commit 2569e0f836
7 changed files with 497 additions and 21 deletions
@@ -28,14 +28,19 @@ import jakarta.ws.rs.POST;
 import jakarta.ws.rs.Path;
 import jakarta.ws.rs.PathParam;
 import jakarta.ws.rs.Produces;
+import jakarta.ws.rs.QueryParam;
 import jakarta.ws.rs.core.MediaType;
+import java.time.LocalDate;
+import java.time.format.DateTimeFormatter;
 import java.util.List;
 import lombok.RequiredArgsConstructor;
+import org.apache.commons.lang3.StringUtils;
 import org.apache.fineract.commands.domain.CommandWrapper;
 import org.apache.fineract.commands.service.CommandWrapperBuilder;
 import org.apache.fineract.commands.service.PortfolioCommandSourceWritePlatformService;
 import org.apache.fineract.infrastructure.core.data.CommandProcessingResult;
 import org.apache.fineract.infrastructure.security.service.PlatformSecurityContext;
+import org.apache.fineract.portfolio.investment.data.InvestmentInterestScheduleData;
 import org.apache.fineract.portfolio.investment.data.InvestmentPurchaseData;
 import org.apache.fineract.portfolio.investment.service.InvestmentPurchaseReadPlatformService;
 import org.springframework.stereotype.Component;
@@ -67,6 +72,20 @@ public class InvestmentPurchaseApiResource {
        return this.readPlatformService.retrieveOne(purchaseId);
    }

+    @GET
+    @Path("{purchaseId}/interest-schedule")
+    @Produces({ MediaType.APPLICATION_JSON })
+    @Operation(summary = "Interest schedule of a holding", description = "Half-yearly coupons and 31 Mar / 30 Sep closing provisions "
+            + "from purchase to maturity. Calculated only — nothing is posted. asOnDate (dd-MM-yyyy) defaults to the business date.")
+    public InvestmentInterestScheduleData retrieveInterestSchedule(
+            @PathParam("purchaseId") @Parameter(description = "purchaseId") final Long purchaseId,
+            @QueryParam("asOnDate") @Parameter(description = "dd-MM-yyyy") final String asOnDate) {
+        this.context.authenticatedUser().validateHasReadPermission(InvestmentPurchaseApiConstants.ENTITY);
+        final LocalDate asOn = StringUtils.isBlank(asOnDate) ? null
+                : LocalDate.parse(asOnDate.trim(), DateTimeFormatter.ofPattern("dd-MM-yyyy"));
+        return this.readPlatformService.retrieveInterestSchedule(purchaseId, asOn);
+    }
+
    @POST
    @Consumes({ MediaType.APPLICATION_JSON })
    @Produces({ MediaType.APPLICATION_JSON })
@@ -0,0 +1,75 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF 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 org.apache.fineract.portfolio.investment.data;
+
+import java.math.BigDecimal;
+import java.util.List;
+import lombok.Builder;
+import lombok.Getter;
+
+/**
+ * Interest schedule of one holding: every half-yearly coupon and every 31 March / 30 September closing provision from
+ * purchase to maturity. Calculated, not yet posted.
+ */
+@Getter
+@Builder
+public class InvestmentInterestScheduleData {
+
+    private final Long purchaseId;
+    private final String dealNo;
+    private final String certNo;
+    private final String scriptCode;
+    private final String scriptDesc;
+    private final BigDecimal faceValue;
+    private final BigDecimal unitValue;
+    private final BigDecimal balanceUnits;
+    private final BigDecimal purchaseRate;
+    private final BigDecimal bookValue;
+    private final BigDecimal intRate;
+    private final String dealDate;
+    private final String lastIntDate;
+    private final String maturityDate;
+    /** Interest paid to the seller at purchase — already in Interest Receivable. */
+    private final BigDecimal purchasedAccruedInterest;
+    private final BigDecimal couponPerHalfYear;
+    private final String asOnDate;
+    private final String interestGlCode;
+    private final String interestGlName;
+    private final List<Row> rows;
+
+    @Getter
+    @Builder
+    public static class Row {
+
+        /** COUPON (cash received) or PROVISION (closing accrual). */
+        private final String type;
+        private final String intDate;
+        private final String fromDate;
+        private final String toDate;
+        private final int days;
+        /** Coupon received, or interest earned since the last coupon up to the closing. */
+        private final BigDecimal grossInterest;
+        /** Interest Receivable balance before this line (purchased accrued interest / earlier provision). */
+        private final BigDecimal alreadyBooked;
+        /** Provision to book now, or the part of the coupon that is new income. */
+        private final BigDecimal amount;
+        /** True when the date is on or before the as-on date. */
+        private final boolean due;
+    }
+}
@@ -0,0 +1,169 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF 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 org.apache.fineract.portfolio.investment.service;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+import java.time.LocalDate;
+import java.time.Month;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.TreeSet;
+
+/**
+ * Interest arithmetic for half-yearly coupon securities, as the bank's existing CBS does it (Jitendra Sir):
+ * <ul>
+ * <li>days are counted 30/360 — every month is 30 days, a half-year is 180, a year 360;</li>
+ * <li>the coupon is fixed: face value × rate ÷ 2, paid on the maturity day/month and six months either side;</li>
+ * <li>at each closing (31 March, 30 September) the interest earned since the last coupon is booked as a provision (Dr
+ * Interest Receivable / Cr Interest Income), even though the cash arrives at the next coupon;</li>
+ * <li>when the coupon arrives, the provision already booked is cleared and only the rest is new income.</li>
+ * </ul>
+ */
+public final class InvestmentInterestCalculator {
+
+    private static final BigDecimal THIRTY_SIX_THOUSAND = BigDecimal.valueOf(36000);
+    private static final BigDecimal TWO_HUNDRED = BigDecimal.valueOf(200);
+
+    public static final String TYPE_PROVISION = "PROVISION";
+    public static final String TYPE_COUPON = "COUPON";
+
+    private InvestmentInterestCalculator() {}
+
+    /** One line of the interest schedule. */
+    public record ScheduleRow(String type, LocalDate date, LocalDate fromDate, LocalDate toDate, int days, BigDecimal grossInterest,
+            BigDecimal alreadyBooked, BigDecimal amount) {
+    }
+
+    /**
+     * Days between two dates on a 30/360 basis. Counting runs from the day after {@code from} up to and including
+     * {@code to}: 10-08 → 30-09 is 50 days, 10-08 → 08-10 is 58 days, 30-06 → 30-09 is 90 days.
+     */
+    public static int days360(final LocalDate from, final LocalDate to) {
+        if (from == null || to == null || !to.isAfter(from)) {
+            return 0;
+        }
+        final int d1 = Math.min(from.getDayOfMonth(), 30);
+        final int d2 = Math.min(to.getDayOfMonth(), 30);
+        return (to.getYear() - from.getYear()) * 360 + (to.getMonthValue() - from.getMonthValue()) * 30 + (d2 - d1);
+    }
+
+    /** Interest on {@code faceValue} at {@code ratePercent} p.a. for {@code days} (30/360), rounded to the rupee. */
+    public static BigDecimal interestForDays(final BigDecimal faceValue, final BigDecimal ratePercent, final int days) {
+        return faceValue.multiply(ratePercent).multiply(BigDecimal.valueOf(days)).divide(THIRTY_SIX_THOUSAND, 0, RoundingMode.HALF_UP);
+    }
+
+    /** The fixed half-yearly coupon: face value × rate ÷ 2. */
+    public static BigDecimal halfYearCoupon(final BigDecimal faceValue, final BigDecimal ratePercent) {
+        return faceValue.multiply(ratePercent).divide(TWO_HUNDRED, 0, RoundingMode.HALF_UP);
+    }
+
+    /** k-th coupon date counting back from maturity — measured from maturity each time so month-end days survive. */
+    private static LocalDate couponBack(final LocalDate maturity, final int k) {
+        return maturity.minusMonths(6L * k);
+    }
+
+    /** The most recent coupon date on or before {@code on}. */
+    public static LocalDate lastCouponOnOrBefore(final LocalDate maturity, final LocalDate on) {
+        int k = 0;
+        LocalDate d = maturity;
+        while (d.isAfter(on)) {
+            k++;
+            d = couponBack(maturity, k);
+        }
+        return d;
+    }
+
+    /** Coupon dates strictly after {@code from}, up to and including maturity, in date order. */
+    public static List<LocalDate> couponDatesAfter(final LocalDate maturity, final LocalDate from) {
+        final List<LocalDate> dates = new ArrayList<>();
+        int k = 0;
+        LocalDate d = maturity;
+        while (d.isAfter(from)) {
+            dates.add(0, d);
+            k++;
+            d = couponBack(maturity, k);
+        }
+        return dates;
+    }
+
+    /** Closing dates (31 March, 30 September) from {@code from} up to {@code to}, inclusive. */
+    public static List<LocalDate> closingDates(final LocalDate from, final LocalDate to) {
+        final List<LocalDate> dates = new ArrayList<>();
+        for (int year = from.getYear(); year <= to.getYear(); year++) {
+            for (final LocalDate closing : List.of(LocalDate.of(year, Month.MARCH, 31), LocalDate.of(year, Month.SEPTEMBER, 30))) {
+                if (!closing.isBefore(from) && !closing.isAfter(to)) {
+                    dates.add(closing);
+                }
+            }
+        }
+        return dates;
+    }
+
+    /**
+     * The full interest schedule of a holding, from purchase to maturity.
+     *
+     * @param faceValue
+     *            face value currently held
+     * @param ratePercent
+     *            coupon rate % p.a.
+     * @param maturity
+     *            maturity date (coupons fall on its day/month and six months either side)
+     * @param lastIntDate
+     *            coupon date immediately before the purchase
+     * @param dealDate
+     *            purchase deal date — closings before it belong to the seller
+     * @param purchasedAccrued
+     *            interest paid to the seller at purchase; it already sits in Interest Receivable
+     */
+    public static List<ScheduleRow> schedule(final BigDecimal faceValue, final BigDecimal ratePercent, final LocalDate maturity,
+            final LocalDate lastIntDate, final LocalDate dealDate, final BigDecimal purchasedAccrued) {
+        final List<ScheduleRow> rows = new ArrayList<>();
+        if (faceValue == null || ratePercent == null || ratePercent.signum() <= 0 || maturity == null || lastIntDate == null
+                || dealDate == null || !maturity.isAfter(lastIntDate)) {
+            return rows;
+        }
+        final List<LocalDate> coupons = couponDatesAfter(maturity, lastIntDate);
+        final TreeSet<LocalDate> events = new TreeSet<>(coupons);
+        for (final LocalDate closing : closingDates(dealDate, maturity)) {
+            if (closing.isAfter(lastIntDate) && !events.contains(closing)) {
+                events.add(closing);
+            }
+        }
+
+        final BigDecimal coupon = halfYearCoupon(faceValue, ratePercent);
+        BigDecimal receivable = purchasedAccrued == null ? BigDecimal.ZERO : purchasedAccrued;
+        LocalDate previousCoupon = lastIntDate;
+        for (final LocalDate date : events) {
+            final int days = days360(previousCoupon, date);
+            if (coupons.contains(date)) {
+                rows.add(new ScheduleRow(TYPE_COUPON, date, previousCoupon.plusDays(1), date, days, coupon, receivable,
+                        coupon.subtract(receivable)));
+                receivable = BigDecimal.ZERO;
+                previousCoupon = date;
+            } else {
+                final BigDecimal earned = interestForDays(faceValue, ratePercent, days);
+                rows.add(new ScheduleRow(TYPE_PROVISION, date, previousCoupon.plusDays(1), date, days, earned, receivable,
+                        earned.subtract(receivable)));
+                receivable = earned;
+            }
+        }
+        return rows;
+    }
+}
@@ -157,7 +157,7 @@ public class InvestmentMasterWritePlatformServiceImpl implements InvestmentMaste
            return this.partyRepository.saveAndFlush(party);
        } catch (final DataIntegrityViolationException e) {
            throw new PlatformDataIntegrityException("error.msg.investmentparty.duplicate", "A party with this code already exists",
-                    "partyCode", party.getPartyCode());
+                    "partyCode", party.getPartyCode(), e);
        }
    }

@@ -247,7 +247,7 @@ public class InvestmentMasterWritePlatformServiceImpl implements InvestmentMaste
            return this.scriptRepository.saveAndFlush(script);
        } catch (final DataIntegrityViolationException e) {
            throw new PlatformDataIntegrityException("error.msg.investmentscript.duplicate", "A script with this code already exists",
-                    "scriptCode", script.getScriptCode());
+                    "scriptCode", script.getScriptCode(), e);
        }
    }

@@ -18,9 +18,15 @@
 */
 package org.apache.fineract.portfolio.investment.service;

+import java.math.BigDecimal;
+import java.time.LocalDate;
+import java.time.format.DateTimeFormatter;
 import java.util.List;
 import lombok.RequiredArgsConstructor;
+import org.apache.fineract.infrastructure.core.service.DateUtils;
+import org.apache.fineract.portfolio.investment.data.InvestmentInterestScheduleData;
 import org.apache.fineract.portfolio.investment.data.InvestmentPurchaseData;
+import org.apache.fineract.portfolio.investment.domain.InvestmentPurchase;
 import org.apache.fineract.portfolio.investment.domain.InvestmentPurchaseRepository;
 import org.apache.fineract.portfolio.investment.exception.InvestmentPurchaseNotFoundException;
 import org.springframework.data.domain.Sort;
@@ -32,6 +38,11 @@ import org.springframework.transaction.annotation.Transactional;
@Transactional(readOnly = true)
 public class InvestmentPurchaseReadPlatformService {

+    private static final DateTimeFormatter DATE_FORMAT = DateTimeFormatter.ofPattern("dd-MM-yyyy");
+    /** Income head for coupon and provision interest (GL 400401 under 400400 INCOME FROM INVESTMENTS). */
+    private static final String INTEREST_GL_CODE = "400401";
+    private static final String INTEREST_GL_NAME = "INTEREST ON GOVT SECURITIES";
+
    private final InvestmentPurchaseRepository purchaseRepository;

    /** All deals, newest first — the Holdings register. */
@@ -40,7 +51,41 @@ public class InvestmentPurchaseReadPlatformService {
    }

    public InvestmentPurchaseData retrieveOne(final Long purchaseId) {
-        return this.purchaseRepository.findById(purchaseId).map(InvestmentPurchaseData::from)
-                .orElseThrow(() -> new InvestmentPurchaseNotFoundException(purchaseId));
+        return InvestmentPurchaseData.from(find(purchaseId));
+    }
+
+    /**
+     * Coupon and closing-provision lines of a holding from purchase to maturity, worked out on the face value still
+     * held. Lines on or before {@code asOnDate} (default: business date) are marked due.
+     */
+    public InvestmentInterestScheduleData retrieveInterestSchedule(final Long purchaseId, final LocalDate asOnDate) {
+        final InvestmentPurchase p = find(purchaseId);
+        final LocalDate asOn = asOnDate == null ? DateUtils.getBusinessLocalDate() : asOnDate;
+        final BigDecimal unitValue = p.getScript().getFaceValuePerUnit();
+        final BigDecimal faceHeld = p.getBalanceUnits().multiply(unitValue);
+        final BigDecimal rate = p.getIntRate() == null ? BigDecimal.ZERO : p.getIntRate();
+
+        final List<InvestmentInterestScheduleData.Row> rows = InvestmentInterestCalculator
+                .schedule(faceHeld, rate, p.getMaturityDate(), p.getLastIntDate(), p.getDealDate(), p.getAccruedInterest()).stream()
+                .map(r -> InvestmentInterestScheduleData.Row.builder().type(r.type()).intDate(format(r.date()))
+                        .fromDate(format(r.fromDate())).toDate(format(r.toDate())).days(r.days()).grossInterest(r.grossInterest())
+                        .alreadyBooked(r.alreadyBooked()).amount(r.amount()).due(!r.date().isAfter(asOn)).build())
+                .toList();
+
+        return InvestmentInterestScheduleData.builder().purchaseId(p.getId()).dealNo(p.getDealNo()).certNo(p.getCertNo())
+                .scriptCode(p.getScript().getScriptCode()).scriptDesc(p.getScript().getScriptDesc()).faceValue(faceHeld)
+                .unitValue(unitValue).balanceUnits(p.getBalanceUnits()).purchaseRate(p.getPurchaseRate()).bookValue(p.getBookValue())
+                .intRate(p.getIntRate()).dealDate(format(p.getDealDate())).lastIntDate(format(p.getLastIntDate()))
+                .maturityDate(format(p.getMaturityDate())).purchasedAccruedInterest(p.getAccruedInterest())
+                .couponPerHalfYear(rate.signum() > 0 ? InvestmentInterestCalculator.halfYearCoupon(faceHeld, rate) : BigDecimal.ZERO)
+                .asOnDate(format(asOn)).interestGlCode(INTEREST_GL_CODE).interestGlName(INTEREST_GL_NAME).rows(rows).build();
+    }
+
+    private InvestmentPurchase find(final Long purchaseId) {
+        return this.purchaseRepository.findById(purchaseId).orElseThrow(() -> new InvestmentPurchaseNotFoundException(purchaseId));
+    }
+
+    private static String format(final LocalDate date) {
+        return date == null ? null : date.format(DATE_FORMAT);
    }
 }
@@ -98,7 +98,8 @@ public class InvestmentPurchaseWritePlatformServiceImpl implements InvestmentPur
            throw rule("script.inactive", "Script " + script.getScriptCode() + " is inactive");
        }
        if (!script.getBondType().equals(bondType)) {
-            throw rule("script.bondtype.mismatch", "Script " + script.getScriptCode() + " is a " + script.getBondType() + ", not " + bondType);
+            throw rule("script.bondtype.mismatch",
+                    "Script " + script.getScriptCode() + " is a " + script.getBondType() + ", not " + bondType);
        }
        if (!party.isActive()) {
            throw rule("party.inactive", "Party " + party.getPartyCode() + " is inactive");
@@ -167,11 +168,10 @@ public class InvestmentPurchaseWritePlatformServiceImpl implements InvestmentPur
        }
        final BigDecimal units = faceValue.divide(script.getFaceValuePerUnit(), 6, RoundingMode.HALF_UP);
        final BigDecimal cost = faceValue.multiply(rate).divide(HUNDRED, 2, RoundingMode.HALF_UP);
-        final int days = days360(lastIntDate, p.getDealDate());
+        final int days = InvestmentInterestCalculator.days360(lastIntDate, p.getDealDate());
        final BigDecimal intRate = zeroIfNull(script.getIntRate());
        // Interest is counted up to the deal date (the event), not the settlement date — Jitendra Sir.
-        final BigDecimal accrued = faceValue.multiply(intRate).multiply(BigDecimal.valueOf(days))
-                .divide(BigDecimal.valueOf(36000), 0, RoundingMode.HALF_UP);
+        final BigDecimal accrued = InvestmentInterestCalculator.interestForDays(faceValue, intRate, days);

        p.setFaceValue(faceValue);
        p.setPurchaseRate(rate);
@@ -204,18 +204,8 @@ public class InvestmentPurchaseWritePlatformServiceImpl implements InvestmentPur
        p.setSettlementAmount(p.getBookValue());
    }

-    /** Days between two dates on a 30/360 basis (every month 30 days), as the bank's existing CBS counts them. */
-    static int days360(final LocalDate from, final LocalDate to) {
-        if (from == null || to == null || !to.isAfter(from)) {
-            return 0;
-        }
-        final int d1 = Math.min(from.getDayOfMonth(), 30);
-        final int d2 = Math.min(to.getDayOfMonth(), 30);
-        return (to.getYear() - from.getYear()) * 360 + (to.getMonthValue() - from.getMonthValue()) * 30 + (d2 - d1);
-    }
-
    /** Approximate yield: coupon adjusted for the discount/premium spread over the security's life, over the price. */
-    private static BigDecimal approxYtm(final BigDecimal coupon, final BigDecimal price, final LocalDate issue, final LocalDate maturity) {
+    static BigDecimal approxYtm(final BigDecimal coupon, final BigDecimal price, final LocalDate issue, final LocalDate maturity) {
        if (coupon.signum() == 0 || issue == null || maturity == null || !maturity.isAfter(issue)) {
            return coupon;
        }
@@ -226,14 +216,19 @@ public class InvestmentPurchaseWritePlatformServiceImpl implements InvestmentPur

    /** Financial-year deal number: FY start year + FY end (2 digits) + 6-digit running number, e.g. 202627000001. */
    private String nextDealNo(final LocalDate dealDate) {
-        final int fyStart = dealDate.getMonthValue() >= 4 ? dealDate.getYear() : dealDate.getYear() - 1;
-        final String prefix = fyStart + String.format("%02d", (fyStart + 1) % 100);
+        final String prefix = dealNoPrefix(dealDate);
        final Integer max = this.jdbcTemplate.queryForObject(
                "SELECT MAX(CAST(SUBSTRING(deal_no FROM 7) AS INTEGER)) FROM m_investment_purchase WHERE deal_no LIKE ?", Integer.class,
                prefix + "%");
        return prefix + String.format("%06d", (max == null ? 0 : max) + 1);
    }

+    /** Financial year (April–March) of the deal date: 2026-04-01 … 2027-03-31 → "202627". */
+    static String dealNoPrefix(final LocalDate dealDate) {
+        final int fyStart = dealDate.getMonthValue() >= 4 ? dealDate.getYear() : dealDate.getYear() - 1;
+        return fyStart + String.format("%02d", (fyStart + 1) % 100);
+    }
+
    private String nextCertNo() {
        final Integer max = this.jdbcTemplate.queryForObject(
                "SELECT MAX(CAST(cert_no AS INTEGER)) FROM m_investment_purchase WHERE cert_no ~ '^[0-9]+$'", Integer.class);
@@ -0,0 +1,173 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF 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 org.apache.fineract.portfolio.investment.service;
+
+import static org.apache.fineract.portfolio.investment.service.InvestmentInterestCalculator.TYPE_COUPON;
+import static org.apache.fineract.portfolio.investment.service.InvestmentInterestCalculator.TYPE_PROVISION;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.math.BigDecimal;
+import java.time.LocalDate;
+import java.util.List;
+import org.apache.fineract.portfolio.investment.service.InvestmentInterestCalculator.ScheduleRow;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Figures from Jitendra Sir's worked example: 7.50% GOI 2034, face value 1 crore, coupons 10 Feb / 10 Aug, bought on
+ * 08-10-2026.
+ */
+class InvestmentInterestCalculatorTest {
+
+    private static final BigDecimal ONE_CRORE = new BigDecimal("10000000");
+    private static final BigDecimal RATE = new BigDecimal("7.50");
+    private static final LocalDate MATURITY = LocalDate.of(2034, 8, 10);
+    private static final LocalDate LAST_COUPON = LocalDate.of(2026, 8, 10);
+    private static final LocalDate DEAL = LocalDate.of(2026, 10, 8);
+
+    @Test
+    void days360CountsEveryMonthAsThirtyDays() {
+        assertEquals(50, InvestmentInterestCalculator.days360(LAST_COUPON, LocalDate.of(2026, 9, 30)));
+        assertEquals(58, InvestmentInterestCalculator.days360(LAST_COUPON, DEAL));
+        assertEquals(90, InvestmentInterestCalculator.days360(LocalDate.of(2026, 6, 30), LocalDate.of(2026, 9, 30)));
+        assertEquals(50, InvestmentInterestCalculator.days360(LocalDate.of(2027, 2, 10), LocalDate.of(2027, 3, 31)));
+        assertEquals(180, InvestmentInterestCalculator.days360(LAST_COUPON, LocalDate.of(2027, 2, 10)));
+        assertEquals(360, InvestmentInterestCalculator.days360(LAST_COUPON, LocalDate.of(2027, 8, 10)));
+    }
+
+    @Test
+    void days360IsZeroWhenDatesAreMissingOrReversed() {
+        assertEquals(0, InvestmentInterestCalculator.days360(null, DEAL));
+        assertEquals(0, InvestmentInterestCalculator.days360(DEAL, null));
+        assertEquals(0, InvestmentInterestCalculator.days360(DEAL, DEAL));
+        assertEquals(0, InvestmentInterestCalculator.days360(DEAL, LAST_COUPON));
+    }
+
+    @Test
+    void interestForDaysRoundsToTheRupee() {
+        assertEquals(new BigDecimal("120833"), InvestmentInterestCalculator.interestForDays(ONE_CRORE, RATE, 58));
+        assertEquals(new BigDecimal("104167"), InvestmentInterestCalculator.interestForDays(ONE_CRORE, RATE, 50));
+        assertEquals(new BigDecimal("375000"), InvestmentInterestCalculator.interestForDays(ONE_CRORE, RATE, 180));
+    }
+
+    @Test
+    void halfYearCouponIsFaceValueTimesRateOverTwo() {
+        assertEquals(new BigDecimal("375000"), InvestmentInterestCalculator.halfYearCoupon(ONE_CRORE, RATE));
+        assertEquals(new BigDecimal("362500"), InvestmentInterestCalculator.halfYearCoupon(ONE_CRORE, new BigDecimal("7.25")));
+    }
+
+    @Test
+    void couponDatesRunSixMonthlyFromMaturity() {
+        assertEquals(LAST_COUPON, InvestmentInterestCalculator.lastCouponOnOrBefore(MATURITY, DEAL));
+        assertEquals(LAST_COUPON, InvestmentInterestCalculator.lastCouponOnOrBefore(MATURITY, LAST_COUPON));
+
+        final List<LocalDate> coupons = InvestmentInterestCalculator.couponDatesAfter(MATURITY, LAST_COUPON);
+        assertEquals(16, coupons.size());
+        assertEquals(LocalDate.of(2027, 2, 10), coupons.get(0));
+        assertEquals(LocalDate.of(2027, 8, 10), coupons.get(1));
+        assertEquals(MATURITY, coupons.get(15));
+    }
+
+    @Test
+    void monthEndMaturityKeepsMonthEndCoupons() {
+        final LocalDate maturity = LocalDate.of(2030, 8, 31);
+        final List<LocalDate> coupons = InvestmentInterestCalculator.couponDatesAfter(maturity, LocalDate.of(2029, 8, 31));
+        assertEquals(List.of(LocalDate.of(2030, 2, 28), maturity), coupons);
+    }
+
+    @Test
+    void closingDatesAreMarchAndSeptemberEnds() {
+        assertEquals(List.of(LocalDate.of(2027, 3, 31), LocalDate.of(2027, 9, 30)),
+                InvestmentInterestCalculator.closingDates(DEAL, LocalDate.of(2028, 3, 30)));
+        assertEquals(List.of(LocalDate.of(2026, 9, 30)),
+                InvestmentInterestCalculator.closingDates(LocalDate.of(2026, 9, 30), LocalDate.of(2026, 9, 30)));
+    }
+
+    @Test
+    void scheduleClearsPurchasedInterestAndProvisionsAtEachClosing() {
+        final List<ScheduleRow> rows = InvestmentInterestCalculator.schedule(ONE_CRORE, RATE, MATURITY, LAST_COUPON, DEAL,
+                new BigDecimal("120833"));
+
+        // 16 coupons + 15 closings (Mar 2027 … Mar 2034); 30-09-2026 is before the deal, so it is the seller's.
+        assertEquals(31, rows.size());
+
+        // First coupon: 1,20,833 paid to the seller is recovered, only the rest is our income.
+        assertRow(rows.get(0), TYPE_COUPON, LocalDate.of(2027, 2, 10), LocalDate.of(2026, 8, 11), 180, "375000", "120833", "254167");
+        // 31 March closing: 50 days earned since 10 Feb, nothing booked yet.
+        assertRow(rows.get(1), TYPE_PROVISION, LocalDate.of(2027, 3, 31), LocalDate.of(2027, 2, 11), 50, "104167", "0", "104167");
+        // August coupon clears the March provision.
+        assertRow(rows.get(2), TYPE_COUPON, LocalDate.of(2027, 8, 10), LocalDate.of(2027, 2, 11), 180, "375000", "104167", "270833");
+        assertRow(rows.get(3), TYPE_PROVISION, LocalDate.of(2027, 9, 30), LocalDate.of(2027, 8, 11), 50, "104167", "0", "104167");
+
+        final ScheduleRow last = rows.get(rows.size() - 1);
+        assertEquals(TYPE_COUPON, last.type());
+        assertEquals(MATURITY, last.date());
+
+        // Over the life, income booked = all coupons − interest bought from the seller.
+        final BigDecimal totalIncome = rows.stream().map(ScheduleRow::amount).reduce(BigDecimal.ZERO, BigDecimal::add);
+        assertEquals(new BigDecimal("375000").multiply(BigDecimal.valueOf(16)).subtract(new BigDecimal("120833")), totalIncome);
+    }
+
+    @Test
+    void closingOnACouponDateIsNotProvisionedTwice() {
+        // Coupons on 31 Mar / 30 Sep: every closing is a coupon day, so there are no provision lines.
+        final List<ScheduleRow> rows = InvestmentInterestCalculator.schedule(ONE_CRORE, RATE, LocalDate.of(2028, 3, 31),
+                LocalDate.of(2026, 9, 30), DEAL, BigDecimal.ZERO);
+        assertEquals(3, rows.size());
+        assertTrue(rows.stream().allMatch(r -> TYPE_COUPON.equals(r.type())));
+    }
+
+    @Test
+    void scheduleIsEmptyWithoutRateOrDates() {
+        assertTrue(InvestmentInterestCalculator.schedule(ONE_CRORE, BigDecimal.ZERO, MATURITY, LAST_COUPON, DEAL, null).isEmpty());
+        assertTrue(InvestmentInterestCalculator.schedule(ONE_CRORE, RATE, null, LAST_COUPON, DEAL, null).isEmpty());
+        assertTrue(InvestmentInterestCalculator.schedule(ONE_CRORE, RATE, MATURITY, null, DEAL, null).isEmpty());
+    }
+
+    @Test
+    void dealNumberFollowsTheAprilToMarchFinancialYear() {
+        assertEquals("202627", InvestmentPurchaseWritePlatformServiceImpl.dealNoPrefix(LocalDate.of(2026, 4, 1)));
+        assertEquals("202627", InvestmentPurchaseWritePlatformServiceImpl.dealNoPrefix(DEAL));
+        assertEquals("202627", InvestmentPurchaseWritePlatformServiceImpl.dealNoPrefix(LocalDate.of(2027, 3, 31)));
+        assertEquals("202728", InvestmentPurchaseWritePlatformServiceImpl.dealNoPrefix(LocalDate.of(2027, 4, 1)));
+        assertEquals("209900", InvestmentPurchaseWritePlatformServiceImpl.dealNoPrefix(LocalDate.of(2099, 12, 1)));
+    }
+
+    @Test
+    void approxYtmRisesWhenBoughtAtADiscount() {
+        final LocalDate issue = LocalDate.of(2024, 8, 10);
+        assertEquals(new BigDecimal("7.59"),
+                InvestmentPurchaseWritePlatformServiceImpl.approxYtm(RATE, new BigDecimal("99.50"), issue, MATURITY));
+        assertEquals(new BigDecimal("7.50"),
+                InvestmentPurchaseWritePlatformServiceImpl.approxYtm(RATE, new BigDecimal("100"), issue, MATURITY));
+        assertEquals(RATE, InvestmentPurchaseWritePlatformServiceImpl.approxYtm(RATE, new BigDecimal("99.50"), null, MATURITY));
+    }
+
+    private static void assertRow(final ScheduleRow row, final String type, final LocalDate date, final LocalDate from, final int days,
+            final String gross, final String alreadyBooked, final String amount) {
+        assertEquals(type, row.type());
+        assertEquals(date, row.date());
+        assertEquals(from, row.fromDate());
+        assertEquals(date, row.toDate());
+        assertEquals(days, row.days());
+        assertEquals(new BigDecimal(gross), row.grossInterest());
+        assertEquals(new BigDecimal(alreadyBooked), row.alreadyBooked());
+        assertEquals(new BigDecimal(amount), row.amount());
+    }
+}