/**
 * Copyright since 2025 Mifos Initiative
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

import { Component, OnInit, inject } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { FaIconComponent } from '@fortawesome/angular-fontawesome';
import { STANDALONE_SHARED_IMPORTS } from 'app/standalone-shared.module';

import { BranchScopeService } from '../core/branch-scope.service';
import { FY_TAX_CONFIG, Quarter, QUARTER_LABEL } from '../letter-mgmt/certificates/form-15gh/tds-15gh.compute';
import { TdsDeductee, setTdsDeductees, tdsFys } from './tds-reports-data';
import { buildTdsInterestWorkbook } from './tds-interest-export';
import { TdsReportsService } from './tds-reports.service';
import {
  NEAR_THRESHOLD_BAND,
  TdsAccountLine,
  TdsInterestRow,
  TdsInterestSummary,
  TdsReportFilter,
  tdsInterestRows,
  tdsInterestSummary
} from './tds-reports.compute';

/** The three answers the register gives: TDS taken, not taken because of a declaration, none due. */
type TdsTab = 'paying' | 'declared' | 'not-paying';

@Component({
  selector: 'mifosx-tds-interest-report',
  templateUrl: './tds-interest-report.component.html',
  styleUrls: ['./tds-reports.shared.scss'],
  imports: [
    ...STANDALONE_SHARED_IMPORTS,
    FaIconComponent,
    FormsModule
  ]
})
export class TdsInterestReportComponent implements OnInit {
  private scope = inject(BranchScopeService);
  private tdsService = inject(TdsReportsService);

  /**
   * Office names the loaded customers belong to, for Head Office's branch selector. Read off the
   * data rather than a fixed list, which named branches this bank does not have and left out the
   * ones it does.
   */
  branches: string[] = [];
  /** Filled by the route resolver from Organization › TDS Configuration. */
  readonly financialYears = tdsFys();
  readonly quarterLabel = QUARTER_LABEL;
  readonly nearBand = NEAR_THRESHOLD_BAND;
  readonly quarters: Quarter[] = [
    1,
    2,
    3,
    4
  ];

  filter: TdsReportFilter = {
    fy: tdsFys()[0] ?? '',
    branchCode: '',
    quarter: 0,
    band: '',
    search: '',
    crossedOnly: false,
    nearThresholdOnly: false
  };

  /** Which customer's quarter-wise detail is open. */
  expandedId: string | null = null;
  exporting = false;
  selectedTab: TdsTab = 'paying';

  /** Rows per page; 0 shows the whole list. */
  readonly pageSizeOptions = [
    25,
    50,
    100,
    0
  ];
  pageSize = 25;
  pageIndex = 0;

  /**
   * Row and summary computation is memoised against the filter, because every getter below is
   * read many times per change-detection cycle (the KPI block alone reads `summary` a dozen
   * times) and recomputing the whole book on each read is what made this table slow enough to
   * need paging in the first place.
   */
  private rowsCacheKey = '';
  private allRows: TdsInterestRow[] = [];
  private paying: TdsInterestRow[] = [];
  private notPaying: TdsInterestRow[] = [];
  private declared: TdsInterestRow[] = [];
  private summaryCacheKey = '';
  private cachedSummary: TdsInterestSummary | null = null;

  loading = false;
  loadError = '';
  /** The "how to read this page" panel. */
  showHelp = true;

  readonly accountTypeLabel: Record<TdsAccountLine['type'], string> = {
    FD: 'Fixed deposit',
    RD: 'Recurring deposit',
    SB: 'Savings',
    OTHER: 'Other'
  };

  ngOnInit(): void {
    if (!this.financialYears.length) {
      this.loadError = 'No financial year is configured for TDS. Set one up under Organization › TDS Configuration.';
      return;
    }
    // A branch login sees only its own book and cannot widen the scope. The platform labels each
    // customer with their office's name, so the login's office name is the filter — the GL branch
    // code list does not know every office and turned a branch login into an empty report.
    if (!this.scope.isHeadOffice) {
      this.filter.branchCode = this.scope.officeName;
    }
    this.loadDeductees();
  }

  /**
   * Loads the interest the bank actually credited for the selected year.
   *
   * Everything below computes on whatever `setTdsDeductees` holds, so the load is the only place
   * that knows where the figures come from.
   */
  loadDeductees(): void {
    this.loading = true;
    this.loadError = '';
    // 'FY 2026-27' → 2026, the opening calendar year the platform filters on.
    const openingYear = Number((this.filter.fy.match(/(\d{4})/) || [])[1]) || undefined;
    this.tdsService.getDepositInterest(openingYear).subscribe({
      next: (deductees) => {
        this.loading = false;
        setTdsDeductees(deductees);
        this.branches = this.branchesOf(deductees);
        this.invalidateCaches();
      },
      error: (err: any) => {
        this.loading = false;
        setTdsDeductees([]);
        this.invalidateCaches();
        this.loadError =
          err?.error?.defaultUserMessage || 'Could not load deposit interest. The figures below cannot be shown.';
      }
    });
  }

  /**
   * Both caches are keyed on the filter alone, so a fresh load must drop them together. Clearing
   * only the summary left the KPIs counting the new data while the tables kept the empty list
   * cached on the first render, before the load returned.
   */
  private branchesOf(deductees: TdsDeductee[]): string[] {
    const names = new Set(deductees.map((d) => d.branchCode).filter((n) => !!n));
    return [...names].sort((a, b) => a.localeCompare(b));
  }

  private invalidateCaches(): void {
    this.rowsCacheKey = '';
    this.summaryCacheKey = '';
    this.cachedSummary = null;
  }

  /**
   * A different year needs a different set of interest credits, so the year re-reads from the
   * platform rather than re-filtering the set already in hand.
   */
  onYearChanged(): void {
    this.onFilterChanged();
    this.loadDeductees();
  }

  /**
   * Provision and return references for the selected year. The charge moved from
   * section 194A to section 393(1) on 01 April 2026 and the quarterly return
   * became Form 140, so the labels are read from the config rather than written
   * into the template.
   */
  get statute(): { section: string; statement: string; frequency: string } {
    const cfg = FY_TAX_CONFIG[this.filter.fy];
    return {
      section: cfg?.interestTdsSection ?? '—',
      statement: cfg?.tdsStatementForm ?? '—',
      frequency: cfg?.declarationStatementFrequency === 'MONTHLY' ? 'monthly' : 'quarterly'
    };
  }

  /** The limits and rates for the selected year, for the help panel. */
  get rules(): { general: number; senior: number; rate: number; rateNoPan: number } | null {
    const cfg = FY_TAX_CONFIG[this.filter.fy];
    if (!cfg) {
      return null;
    }
    return {
      general: cfg.thresholdGeneral,
      senior: cfg.thresholdSenior,
      rate: cfg.rate * 100,
      rateNoPan: cfg.rateNoPan * 100
    };
  }

  get canSelectBranch(): boolean {
    return this.scope.canSelectBranch;
  }

  get scopeLabel(): string {
    return this.filter.branchCode ? `${this.filter.branchCode} branch` : 'All branches';
  }

  /**
   * One plain-language status per customer, so a reader does not have to work it out from the
   * threshold, crossed and saved columns together.
   */
  statusOf(row: TdsInterestRow): { label: string; tone: 'muted' | 'warn' | 'near' | 'ok' } {
    if (!row.trackedAccounts) {
      return { label: 'Not tracked — no FD/RD', tone: 'muted' };
    }
    if (row.hasDeclaration) {
      const beforeForm = Math.round(row.schedule.totalTds - row.actualTds);
      if (beforeForm > 0) {
        return { label: `Form ${row.form} — ₹${beforeForm.toLocaleString('en-IN')} due from before the form, not yet deducted`, tone: 'warn' };
      }
      if (row.tdsSaved > 0) {
        return { label: `Form ${row.form} — TDS not deducted`, tone: 'ok' };
      }
      return { label: `Form ${row.form} on record — below the limit so far`, tone: 'ok' };
    }
    if (row.schedule.totalTds > 0) {
      const gap = Math.round(row.schedule.totalTds - row.actualTds);
      if (gap > 0) {
        return { label: `Over the limit — ₹${gap.toLocaleString('en-IN')} not yet deducted`, tone: 'warn' };
      }
      if (gap < 0) {
        return { label: `Deducted ₹${(-gap).toLocaleString('en-IN')} more than due — check`, tone: 'warn' };
      }
      return { label: 'Over the limit — TDS deducted', tone: 'ok' };
    }
    if (row.actualTds > 0) {
      return { label: `₹${Math.round(row.actualTds).toLocaleString('en-IN')} deducted but none due — check`, tone: 'warn' };
    }
    if (row.hasDeclaration && row.crossed) {
      return { label: 'Over the limit — 15G/15H, no TDS', tone: 'ok' };
    }
    if (row.nearThreshold) {
      return { label: `Near the limit — ₹${Math.round(row.headroom).toLocaleString('en-IN')} left`, tone: 'near' };
    }
    return { label: 'Below the limit', tone: 'ok' };
  }

  trackedOf(row: TdsInterestRow): TdsAccountLine[] {
    return row.accounts.filter((a) => a.tracked);
  }

  untrackedOf(row: TdsInterestRow): TdsAccountLine[] {
    return row.accounts.filter((a) => !a.tracked);
  }

  /** Recomputes the book only when the filter actually changed. Side-effect free. */
  private ensureRows(): void {
    const key = JSON.stringify(this.filter);
    if (key === this.rowsCacheKey) {
      return;
    }
    this.rowsCacheKey = key;
    this.allRows = tdsInterestRows(this.filter);
    // Three plain answers: whose TDS was taken, whose was not because they gave a declaration, and who
    // owed none. A declarant whose tax was partly taken before the form is shown with the declarants,
    // where both figures sit side by side.
    this.declared = this.allRows.filter((r) => r.hasDeclaration);
    this.paying = this.allRows.filter((r) => !r.hasDeclaration && (r.schedule.totalTds > 0 || r.actualTds > 0));
    this.notPaying = this.allRows.filter((r) => !r.hasDeclaration && r.schedule.totalTds === 0 && r.actualTds === 0);
  }

  get rows(): TdsInterestRow[] {
    this.ensureRows();
    return this.allRows;
  }

  get payingRows(): TdsInterestRow[] {
    this.ensureRows();
    return this.paying;
  }

  get notPayingRows(): TdsInterestRow[] {
    this.ensureRows();
    return this.notPaying;
  }

  get declaredRows(): TdsInterestRow[] {
    this.ensureRows();
    return this.declared;
  }

  get summary(): TdsInterestSummary {
    const key = JSON.stringify(this.filter);
    if (key !== this.summaryCacheKey || !this.cachedSummary) {
      this.summaryCacheKey = key;
      this.cachedSummary = tdsInterestSummary(this.filter);
    }
    return this.cachedSummary;
  }

  /** Every row of the tab on screen, before paging. */
  get visibleRows(): TdsInterestRow[] {
    if (this.selectedTab === 'declared') {
      return this.declaredRows;
    }
    return this.selectedTab === 'paying' ? this.payingRows : this.notPayingRows;
  }

  get pageCount(): number {
    if (!this.pageSize) {
      return 1;
    }
    return Math.max(1, Math.ceil(this.visibleRows.length / this.pageSize));
  }

  /**
   * Clamped rather than assigned, so a filter that shrinks the list can never leave the table
   * rendering an out-of-range page, and nothing mutates state during change detection.
   */
  get currentPage(): number {
    return Math.min(this.pageIndex, this.pageCount - 1);
  }

  /** The slice actually rendered. */
  get pagedRows(): TdsInterestRow[] {
    const rows = this.visibleRows;
    if (!this.pageSize) {
      return rows;
    }
    const start = this.currentPage * this.pageSize;
    return rows.slice(start, start + this.pageSize);
  }

  get rangeStart(): number {
    if (!this.visibleRows.length) {
      return 0;
    }
    return this.pageSize ? this.currentPage * this.pageSize + 1 : 1;
  }

  get rangeEnd(): number {
    const total = this.visibleRows.length;
    return this.pageSize ? Math.min(total, (this.currentPage + 1) * this.pageSize) : total;
  }

  goToPage(page: number): void {
    this.pageIndex = Math.max(0, Math.min(page, this.pageCount - 1));
    // The open quarter-wise detail belongs to a row that is no longer on screen.
    this.expandedId = null;
  }

  /** Keeps the first row currently on screen in view when the page size changes. */
  onPageSizeChange(size: number): void {
    const anchor = this.currentPage * (this.pageSize || 1);
    this.pageSize = Number(size);
    this.pageIndex = this.pageSize ? Math.floor(anchor / this.pageSize) : 0;
    this.expandedId = null;
  }

  /** A different filter is a different list, so paging starts over. */
  onFilterChanged(): void {
    this.pageIndex = 0;
    this.expandedId = null;
  }

  selectTab(tab: TdsTab): void {
    this.selectedTab = tab;
    this.onFilterChanged();
  }

  get hasFilters(): boolean {
    return !!(
      this.filter.search ||
      this.filter.quarter ||
      this.filter.band ||
      this.filter.crossedOnly ||
      this.filter.nearThresholdOnly
    );
  }

  clearFilters(): void {
    this.filter = {
      ...this.filter,
      quarter: 0,
      band: '',
      search: '',
      crossedOnly: false,
      nearThresholdOnly: false
    };
    this.onFilterChanged();
  }

  /** Jump straight to the customers worth chasing a declaration from. */
  showNearThreshold(): void {
    this.filter = { ...this.filter, crossedOnly: false, nearThresholdOnly: true };
    this.onFilterChanged();
  }

  toggleExpanded(row: TdsInterestRow): void {
    this.expandedId = this.expandedId === row.deductee.customerId ? null : row.deductee.customerId;
  }

  isExpanded(row: TdsInterestRow): boolean {
    return this.expandedId === row.deductee.customerId;
  }

  trackRow(_: number, row: TdsInterestRow): string {
    return row.deductee.customerId;
  }

  async exportWorkbook(): Promise<void> {
    this.exporting = true;
    try {
      const wb = buildTdsInterestWorkbook({
        fy: this.filter.fy,
        scopeLabel: this.scopeLabel,
        rules: this.rules,
        statement: this.statute.statement,
        // What the screen shows under the current filters, every tab included.
        rows: this.rows,
        declaredRows: this.declaredRows,
        summary: this.summary,
        statusOf: (row) => this.statusOf(row)
      });
      const buffer = await wb.xlsx.writeBuffer();
      const blob = new Blob([buffer], {
        type: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'
      });
      const url = URL.createObjectURL(blob);
      const a = document.createElement('a');
      a.href = url;
      a.download = `TDS-Register-FY${this.filter.fy}.xlsx`;
      a.click();
      URL.revokeObjectURL(url);
    } finally {
      this.exporting = false;
    }
  }
}