feat(investment): Interest Entry screen with coupon and provision schedule

Replace the dummy interest calculation tab with the real Interest Entry:
pick Type / Script / Deal No and Retrieve the holding's schedule from
the backend - every half-yearly coupon and every 31 Mar / 30 Sep closing
provision up to maturity, with days (30/360), gross interest, amount
already booked, net income and the Dr/Cr entry per line. Display only;
nothing is posted to GL yet.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/investment/bond-investment/bond-investment.component.ts

@@ -26,8 +26,6 @@ import {
   BOND_RATING_OPTIONS,
   INT_TYPE_OPTIONS,
   AUTHORITY_OPTIONS,
-  INTEREST_INCOME_GL_MASTER,
-  INTEREST_INCOME_GL_BY_TYPE,
   INVESTMENT_GL_BY_TYPE,
   INVESTMENT_GL_LOOKUP,
   INTEREST_RECEIVABLE_GL,
@@ -42,8 +40,6 @@ import {
   InterestFreq,
   INSTRUMENT_LABELS,
   accruedInterest,
-  accruedInterestBetween,
-  canAccrueInterest,
   daysToMaturity,
   maturityAmount,
   addPeriod,
@@ -52,7 +48,13 @@ import {
   todayDDMMYYYY
 } from '../investment-data';
 import { exportWorkbook } from '../investment-export';
-import { InvestmentPurchaseDto, InvestmentService, apiErrorMessage, toHolding } from '../investment.service';
+import {
+  InvestmentInterestScheduleDto,
+  InvestmentPurchaseDto,
+  InvestmentService,
+  apiErrorMessage,
+  toHolding
+} from '../investment.service';
 
 type BondType = 'GOVT_SECURITY' | 'NON_SLR' | 'BOND' | 'MUTUAL_FUND';
 type BondTab =
@@ -286,17 +288,16 @@ export class BondInvestmentComponent implements OnInit {
   redeemDate = this.asOnDate;
   redeemRemarks = '';
 
-  // Interest Calculation (legacy: From/To Date / Type / Script / Deal No / ALL + Process) —
-  // posts interest accrued strictly within [intCalcFromDate, intCalcToDate], same period-based
-  // basis as the Investment Interest module's Govt./Bond Interest Calculation.
-  intCalcFromDate = addPeriod(this.asOnDate, 0, -3);
-  intCalcToDate = this.asOnDate;
-  intCalcType: BondType | '' = '';
-  intCalcScript = '';
-  intCalcDealNo = '';
-  intCalcAll = false;
-  intCalcGlCode = INTEREST_INCOME_GL_BY_TYPE.GOVT_SECURITY;
-  readonly interestIncomeGlOptions = INTEREST_INCOME_GL_MASTER;
+  // 03 Interest Entry (legacy: Type / Script / Deal No + Retrieve) — the backend works out every
+  // half-yearly coupon and 31 Mar / 30 Sep closing provision of the holding. Display only:
+  // nothing is posted to GL until the posting rules are approved.
+  intType: BondType | '' = '';
+  intScript = '';
+  intPurchaseId: number | null = null;
+  intAsOnDate = this.asOnDate;
+  intSchedule: InvestmentInterestScheduleDto | null = null;
+  intLoading = false;
+  readonly interestReceivableGl = INTEREST_RECEIVABLE_GL;
 
   // Write-off
   writeoffCertNo = '';
@@ -892,78 +893,53 @@ export class BondInvestmentComponent implements OnInit {
   }
 
   // -------------------- Interest calculation --------------------
-  /** Holdings the Interest Calculation "Process" run would cover, given the filters. A
-   *  Non-Performing holding is always excluded — same accrual-basis rule as the Investment
-   *  Interest module (it's still collectible on cash basis via Interest Receive there). */
-  get intCalcTargets(): InvestmentHolding[] {
-    const base = this.holdings.filter((h) => h.status === 'ACTIVE' && canAccrueInterest(h));
-    if (this.intCalcAll) {
-      return base;
+  /** Saved holdings for the Deal No dropdown, narrowed by Type and Script. */
+  get intDealOptions(): InvestmentHolding[] {
+    return this.holdings.filter(
+      (h) =>
+        h.id != null &&
+        h.status === 'ACTIVE' &&
+        (!this.intType || h.instrumentType === this.intType) &&
+        (!this.intScript || h.scriptCode === this.intScript)
+    );
+  }
+
+  get intScriptOptions(): typeof SCRIPT_MASTER {
+    return this.scriptOptions.filter((s) => !this.intType || s.instrumentType === this.intType);
+  }
+
+  onIntFilterChange(): void {
+    if (this.intScript && !this.intScriptOptions.some((s) => s.scriptCode === this.intScript)) {
+      this.intScript = '';
     }
-    return base.filter((h) => {
-      if (this.intCalcType && h.instrumentType !== this.intCalcType) return false;
-      if (this.intCalcScript && h.scriptCode !== this.intCalcScript) return false;
-      if (this.intCalcDealNo && h.certNo !== this.intCalcDealNo.trim()) return false;
-      return true;
-    });
-  }
-
-  get intCalcExcludedNpi(): InvestmentHolding[] {
-    return this.holdings.filter((h) => h.status === 'ACTIVE' && !canAccrueInterest(h));
-  }
-
-  /** Re-suggests the Interest Income GL when the Type filter changes — still overridable. */
-  onIntCalcTypeChange(): void {
-    if (this.intCalcType) {
-      this.intCalcGlCode = INTEREST_INCOME_GL_BY_TYPE[this.intCalcType];
+    if (this.intPurchaseId != null && !this.intDealOptions.some((h) => h.id === this.intPurchaseId)) {
+      this.intPurchaseId = null;
     }
+    this.intSchedule = null;
   }
 
-  glName(glCode: string): string {
-    return this.interestIncomeGlOptions.find((g) => g.glCode === glCode)?.glName ?? glCode;
-  }
-
-  /** Interest accrued strictly within [intCalcFromDate, intCalcToDate] — a period-based
-   *  Interest Calculation & Post run, same basis as the Investment Interest module. */
-  interestAccrued(h: InvestmentHolding): number {
-    return accruedInterestBetween(h, this.intCalcFromDate || h.purchaseDate, this.intCalcToDate || this.asOnDate);
-  }
-
-  processInterest(): void {
-    const targets = this.intCalcTargets.filter((h) => this.interestAccrued(h) > 0);
-    if (targets.length === 0) {
-      this.toast('No holdings have interest due to be posted for this period.');
+  retrieveInterestSchedule(): void {
+    if (this.intPurchaseId == null) {
+      this.toast('Select a Deal No first.');
       return;
     }
-    const toDate = this.intCalcToDate || this.asOnDate;
-    const fromDate = this.intCalcFromDate || toDate;
-    const glCode = this.intCalcGlCode;
-    const glName = this.glName(glCode);
-    const newTxns: InvestmentTxn[] = targets.map((h, i) => {
-      const amt = this.interestAccrued(h);
-      h.interestPosted = (h.interestPosted ?? 0) + amt;
-      h.interestPostedTillDate = toDate;
-      return {
-        certNo: h.certNo,
-        instrumentType: h.instrumentType,
-        txnType: 'INTEREST',
-        voucherNo: `INV/INT/${h.certNo}-${this.txns.length + i + 1}`,
-        txnDate: toDate,
-        amount: amt,
-        particulars: `Interest calculated (accrual) for period ${fromDate} to ${toDate} - ${h.scriptName}`,
-        glCode,
-        glName
-      };
+    this.intLoading = true;
+    this.investmentService.getInterestSchedule(this.intPurchaseId, this.intAsOnDate || undefined).subscribe({
+      next: (schedule) => {
+        this.intSchedule = schedule;
+        this.intLoading = false;
+      },
+      error: (err) => {
+        this.intSchedule = null;
+        this.intLoading = false;
+        this.toast(apiErrorMessage(err));
+      }
     });
-    this.txns = [
-      ...newTxns,
-      ...this.txns
-    ];
-    this.intCalcFromDate = toDate;
-    const total = newTxns.reduce((s, t) => s + t.amount, 0);
-    this.toast(
-      `Interest processed for ${targets.length} holding(s) to ${glCode} - ${glName}. Total ₹${total.toLocaleString('en-IN')}.`
-    );
+  }
+
+  /** Total of the lines falling due up to the as-on date. */
+  get intDueTotal(): number {
+    return (this.intSchedule?.rows ?? []).filter((r) => r.due).reduce((sum, r) => sum + r.amount, 0);
   }
 
   // -------------------- Sell / Redeem Entry --------------------