/**
 * 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 {
  AmlRuleMeta,
  CTR_THRESHOLD,
  MATERIALITY,
  isNonMitigableRule,
  REVIEW_STATUS_META,
  RISK_LABEL,
  RiskAlertRow,
  RiskLevel,
  RiskTxn,
  ReviewStatus,
  amlRuleMeta,
  riskRank
} from './risk-review-data';

/** Which way the review says the rating should move. */
export type RatingDirection = 'up' | 'down' | 'same';

const RANK_TO_LEVEL: Record<number, RiskLevel> = { 1: 'LOW', 2: 'MEDIUM', 3: 'HIGH' };

export interface DateRange {
  from: string;
  to: string;
}

export interface RiskReviewFilter {
  range: DateRange;
  /** '' means every branch. */
  branchCode: string;
  /** '' means every rating. */
  currentRisk: RiskLevel | '';
  /** '' means every rule. */
  ruleCode: string;
  /** '' means every review status. */
  status: ReviewStatus | '';
  /** '' means every customer, whichever way their rating should move. */
  direction: RatingDirection | '';
  /** Free text over customer name, customer ID, account number and alert ID. */
  search: string;
  /** Only cases a reviewer still has to act on. */
  openOnly: boolean;
}

/** An alert joined to its rule catalogue entry, ready to render. */
export interface RiskAlertView extends RiskAlertRow {
  rule: AmlRuleMeta;
}

/**
 * One transaction carrying the alert and rule it belongs to.
 *
 * This is the row that answers "which AML rule did this transaction trip" —
 * the alert is flattened onto each of its entries so the same transaction can
 * be read on its own, without expanding a customer first.
 */
export interface RiskTxnView extends RiskTxn {
  alertId: string;
  alertDate: string;
  clientId: number;
  customerName: string;
  accountNo: string;
  branchCode: string;
  currentRisk: RiskLevel | null;
  status: ReviewStatus;
  remarks: string;
  rule: AmlRuleMeta;
  /** Position of this entry within its alert, e.g. "2 of 7" for a series. */
  legIndex: number;
  legCount: number;
}

/** All of one customer's alerts in the period, rolled up. */
export interface RiskCustomerRow {
  clientId: number;
  customerName: string;
  accountNo: string;
  branchCode: string;
  currentRisk: RiskLevel | null;
  alerts: RiskAlertView[];
  alertCount: number;
  /** Sum of the amounts behind the alerts — the exposure under review. */
  totalAmount: number;
  largestAmount: number;
  /** Highest risk any of the triggered rules points at, before materiality. */
  proposedRisk: RiskLevel;
  /** What the review concludes the rating should be, after materiality. */
  recommendedRisk: RiskLevel;
  /** Whether that is above, below or the same as the rating on record. */
  direction: RatingDirection;
  /** One line explaining the recommendation, shown under the verdict. */
  directionReason: string;
  /** Distinct rule labels, for the "AML Rule Triggered" cell. */
  ruleLabels: string[];
  /** Earliest and latest alert in the period. */
  firstAlertDate: string;
  lastAlertDate: string;
  openCount: number;
  /** True when any alert on the customer has gone to the Principal Officer. */
  escalated: boolean;
  /** True when the rules point above the rating currently on the KYC record. */
  needsUpgrade: boolean;
  /** True when the rating on record is higher than the activity warrants. */
  needsDowngrade: boolean;
  /** The review period the recommendation was drawn from, where the nightly job has computed one. */
  behaviourWindow?: BehaviourWindowByClient[number] | null;
}

export interface RiskReviewSummary {
  customers: number;
  alerts: number;
  /** Individual entries behind those alerts. */
  txns: number;
  /** Cash entries at or above the CTR limit on their own. */
  ctrReportable: number;
  openAlerts: number;
  escalatedCustomers: number;
  upgradeCandidates: number;
  downgradeCandidates: number;
  totalAmount: number;
  byRisk: Record<'LOW' | 'MEDIUM' | 'HIGH' | 'UNRATED', number>;
  /** Rule mix across the filtered set, most-triggered first. */
  byRule: { code: string; label: string; count: number }[];
  byStatus: { status: ReviewStatus; label: string; count: number }[];
}

function inRange(date: string, range: DateRange): boolean {
  return date >= range.from && date <= range.to;
}

function inr(n: number): string {
  return `₹${Math.round(n).toLocaleString('en-IN')}`;
}

/**
 * Works out what the rating ought to be once the size of the activity is taken
 * into account, and why.
 *
 * The rules give an upper bound — what the behaviour could mean at worst. The
 * amounts then pull that bound down: a customer sitting at High who has only put
 * a handful of small transfers through has not behaved like a High-risk customer
 * this period, and the review should say so. Two things stop the pull-down: a
 * case already referred for an STR, and rules whose seriousness has nothing to
 * do with value — a sanctions match or a structuring pattern stays grave at any
 * amount.
 */
function recommendRating(
  impliedRank: number,
  currentRisk: RiskLevel | null,
  largestAmount: number,
  totalAmount: number,
  escalated: boolean,
  ruleCodes: string[]
): { risk: RiskLevel; reason: string } {
  const implied = RANK_TO_LEVEL[impliedRank] ?? 'LOW';
  const grave = ruleCodes.find((c) => isNonMitigableRule(c));
  const material = largestAmount >= CTR_THRESHOLD || totalAmount >= MATERIALITY.highTotal;
  const small = largestAmount < MATERIALITY.smallTxn && totalAmount < MATERIALITY.smallTotal;

  // What the rating should be. Amounts only ever pull the rules' bound down, and
  // only where nothing weightier holds it up.
  let risk: RiskLevel;
  let basis: 'escalated' | 'grave' | 'material' | 'small' | 'moderate';
  if (escalated) {
    risk = 'HIGH';
    basis = 'escalated';
  } else if (grave) {
    risk = implied;
    basis = 'grave';
  } else if (material) {
    risk = implied;
    basis = 'material';
  } else {
    risk = RANK_TO_LEVEL[Math.min(impliedRank, small ? 1 : 2)] ?? 'LOW';
    basis = small ? 'small' : 'moderate';
  }

  // The wording is worked out from the conclusion, not the branch, so a customer
  // being brought down is never told the activity supports where they are.
  const sizes = `largest entry ${inr(largestAmount)}, ${inr(totalAmount)} in total`;
  const rated = currentRisk ? `Rated ${RISK_LABEL[currentRisk]} on record` : 'No rating on record';
  const delta = currentRisk ? riskRank(risk) - riskRank(currentRisk) : 0;

  if (basis === 'escalated') {
    return { risk, reason: 'Case referred to the Principal Officer — rating held at High pending the outcome.' };
  }

  if (delta < 0) {
    if (basis === 'small') {
      return { risk, reason: `Only small-value activity — ${sizes}. ${rated}; not supported by this period.` };
    }
    if (basis === 'moderate') {
      return { risk, reason: `Moderate activity — ${sizes}. ${rated}; one step down is proportionate.` };
    }
    // Material or grave, yet still below where the customer sits: the size of
    // the activity is not the reason, the rules that fired are.
    return {
      risk,
      reason:
        `Activity of ${inr(totalAmount)} is material, but the rules triggered point only at ${RISK_LABEL[risk]}. ` +
        `${rated}.`
    };
  }

  if (delta > 0) {
    return { risk, reason: `Triggered rules point at ${RISK_LABEL[risk]}, above the rating on record.` };
  }

  if (basis === 'grave') {
    return {
      risk,
      reason: `${amlRuleMeta(grave as string).label} carries its own weight — the rating does not come down on amount alone.`
    };
  }

  // The rating on file is where the activity puts it. Saying so is the verdict — leaving it blank
  // read as "not assessed yet" on screen, which is the opposite of what the review concluded.
  return {
    risk,
    reason: currentRisk
      ? `${sizes}. Consistent with ${RISK_LABEL[risk]} — the rating on file stands.`
      : `${sizes}. Activity points at ${RISK_LABEL[risk]}; no rating on record to compare against.`
  };
}

/** Applies every filter and joins each alert to its rule. */
export function riskAlertViews(alerts: RiskAlertRow[], filter: RiskReviewFilter): RiskAlertView[] {
  const needle = filter.search.trim().toLowerCase();

  return alerts
    .filter((a) => {
      if (!inRange(a.alertDate, filter.range)) {
        return false;
      }
      // A live alert carries no branch; hiding it under a branch filter would
      // silently drop real compliance data, so it stays visible.
      if (filter.branchCode && a.branchCode && a.branchCode !== filter.branchCode) {
        return false;
      }
      if (filter.currentRisk && a.currentRisk !== filter.currentRisk) {
        return false;
      }
      if (filter.ruleCode && a.ruleCode !== filter.ruleCode) {
        return false;
      }
      if (filter.status && a.status !== filter.status) {
        return false;
      }
      if (filter.openOnly && !REVIEW_STATUS_META[a.status].open) {
        return false;
      }
      if (needle) {
        const hay = `${a.customerName} ${a.clientId} ${a.accountNo} ${a.alertId} ${a.ruleCode}`.toLowerCase();
        if (!hay.includes(needle)) {
          return false;
        }
      }
      return true;
    })
    .map((a) => ({ ...a, rule: amlRuleMeta(a.ruleCode, a.ruleDescription) }))
    .sort((a, b) => b.alertDate.localeCompare(a.alertDate) || a.customerName.localeCompare(b.customerName));
}

/**
 * Rolls the alerts up per customer. Sorted so the cases needing attention —
 * escalated, then rated below what the rules point at, then most alerts —
 * come to the top of the worklist.
 */
/**
 * The behaviour window the nightly job computed for one customer, where there is one.
 *
 * Keyed on client id. A customer with no window - one the job has not seen yet, or a tenant where the job has never
 * run - falls back to the per-alert reckoning below, so the report renders either way.
 */
export interface BehaviourWindowByClient {
  [clientId: number]: {
    clientId: number;
    clientName: string | null;
    accountNo: string | null;
    officeName: string | null;
    riskCategoryAtReview: number | null;
    txnCount: number | null;
    distinctMonths: number | null;
    windowFrom: any;
    windowTo: any;
    creditTotal: number | null;
    debitTotal: number | null;
    largestTxn: number | null;
    cashTotal: number | null;
    alertCount: number | null;
    strCaseCount: number | null;
    suggestedDirection: string | null;
    suggestedCategory: number | null;
    suggestionReason: string | null;
  };
}

export function riskCustomerRows(views: RiskAlertView[], windows: BehaviourWindowByClient = {}): RiskCustomerRow[] {
  const byClient = new Map<number, RiskAlertView[]>();
  for (const v of views) {
    const list = byClient.get(v.clientId);
    if (list) {
      list.push(v);
    } else {
      byClient.set(v.clientId, [v]);
    }
  }

  const rows: RiskCustomerRow[] = [];
  for (const [
    clientId,
    alerts
  ] of byClient) {
    const dates = alerts.map((a) => a.alertDate).sort();
    const proposedRank = Math.max(...alerts.map((a) => riskRank(a.rule.impliedRisk)));
    const proposedRisk: RiskLevel = RANK_TO_LEVEL[proposedRank] ?? 'LOW';
    const head = alerts[0];

    const currentRisk = alerts.find((a) => a.currentRisk)?.currentRisk ?? null;
    const totalAmount = alerts.reduce((s, a) => s + a.amount, 0);
    const largestAmount = Math.max(...alerts.map((a) => a.amount));
    const escalated = alerts.some((a) => a.status === 'ESCALATED_STR' || a.status === 'STR_FILED');

    // The server's own reckoning, where the nightly job has produced one.
    //
    // It is the better answer, and not because it is newer: it is drawn from a review period rather than from the
    // alerts on this screen. A customer appears here only once a rule has fired, so judging them on those alerts
    // alone describes the exceptions and never the ordinary months around them - which is exactly what a rating is
    // supposed to reflect. The job also tests the things this screen cannot see at all: how many separate months the
    // activity falls in, how long the customer has held the rating, whether an STR inside the block window forbids
    // lowering it.
    //
    // Without a window - a tenant where the job has not run, or a customer it has not reached - the per-alert
    // reckoning below still stands, so the report never renders blank while the two are in step.
    // A window is only good for as long as the rating it was computed against. The job takes a snapshot each night
    // and records the rating the customer held at the time; once an officer moves that rating the snapshot describes
    // a customer who no longer exists, and the screen would go on asking for a change that has already been applied
    // and approved. Dropping it here falls back to the per-alert reckoning until tonight's job catches up.
    const raw = windows[clientId];
    const staleWindow =
      raw?.riskCategoryAtReview != null && currentRisk != null && RANK_TO_LEVEL[raw.riskCategoryAtReview] !== currentRisk;
    const window = staleWindow ? undefined : raw;
    const recommendation = window?.suggestedDirection
      ? {
          risk: RANK_TO_LEVEL[window.suggestedCategory ?? 0] ?? currentRisk ?? 'LOW',
          reason: window.suggestionReason ?? ''
        }
      : recommendRating(
          proposedRank,
          currentRisk,
          largestAmount,
          totalAmount,
          escalated,
          alerts.map((a) => a.ruleCode)
        );

    // Where the customer carries no rating there is nothing to move, so an
    // unrated customer is never counted as an upgrade or a downgrade.
    const delta = currentRisk ? riskRank(recommendation.risk) - riskRank(currentRisk) : 0;
    const direction: RatingDirection = window?.suggestedDirection
      ? window.suggestedDirection === 'UP'
        ? 'up'
        : window.suggestedDirection === 'DOWN'
          ? 'down'
          : 'same'
      : delta > 0
        ? 'up'
        : delta < 0
          ? 'down'
          : 'same';

    rows.push({
      clientId,
      customerName: head.customerName,
      // Take the first non-blank — live alerts leave these empty.
      accountNo: alerts.find((a) => a.accountNo)?.accountNo || '',
      branchCode: alerts.find((a) => a.branchCode)?.branchCode || '',
      currentRisk,
      alerts,
      alertCount: alerts.length,
      totalAmount,
      largestAmount,
      proposedRisk,
      recommendedRisk: recommendation.risk,
      direction,
      directionReason: recommendation.reason,
      ruleLabels: [...new Set(alerts.map((a) => a.rule.label))],
      firstAlertDate: dates[0],
      lastAlertDate: dates[dates.length - 1],
      openCount: alerts.filter((a) => REVIEW_STATUS_META[a.status].open).length,
      escalated,
      needsUpgrade: direction === 'up',
      needsDowngrade: direction === 'down',
      // Carried through so the screen can show the period a recommendation was drawn from. A rating an officer is
      // asked to approve has to show its working, and the alerts on this row are not it.
      behaviourWindow: window ?? null
    });
  }

  // Escalations first, then ratings that need moving up, then down, then volume.
  return rows.sort(
    (a, b) =>
      Number(b.escalated) - Number(a.escalated) ||
      Number(b.needsUpgrade) - Number(a.needsUpgrade) ||
      Number(b.needsDowngrade) - Number(a.needsDowngrade) ||
      b.alertCount - a.alertCount ||
      b.totalAmount - a.totalAmount
  );
}

/**
 * Restricts the alerts to customers whose rating should move a given way.
 *
 * Direction is a property of the customer, not of a single alert, so it can only
 * be applied once the rollup has run — the alert and transaction views are then
 * narrowed to the same customers so all three views agree.
 */
export function applyDirectionFilter(
  views: RiskAlertView[],
  customers: RiskCustomerRow[],
  direction: RatingDirection | ''
): { views: RiskAlertView[]; customers: RiskCustomerRow[] } {
  if (!direction) {
    return { views, customers };
  }
  const keep = customers.filter((c) => c.direction === direction);
  const ids = new Set(keep.map((c) => c.clientId));
  return { views: views.filter((v) => ids.has(v.clientId)), customers: keep };
}

/**
 * Flattens every alert onto its transactions, newest entry first, so each row
 * names the rule that transaction tripped.
 */
export function riskTxnRows(views: RiskAlertView[]): RiskTxnView[] {
  const rows: RiskTxnView[] = [];

  for (const v of views) {
    v.txns.forEach((t, i) => {
      rows.push({
        ...t,
        alertId: v.alertId,
        alertDate: v.alertDate,
        clientId: v.clientId,
        customerName: v.customerName,
        accountNo: v.accountNo,
        branchCode: v.branchCode,
        currentRisk: v.currentRisk,
        status: v.status,
        remarks: v.remarks,
        rule: v.rule,
        legIndex: i + 1,
        legCount: v.txns.length
      });
    });
  }

  return rows.sort((a, b) => b.date.localeCompare(a.date) || a.txnId.localeCompare(b.txnId));
}

export function riskReviewSummary(views: RiskAlertView[], customers: RiskCustomerRow[]): RiskReviewSummary {
  const byRisk: RiskReviewSummary['byRisk'] = { LOW: 0, MEDIUM: 0, HIGH: 0, UNRATED: 0 };
  for (const c of customers) {
    byRisk[c.currentRisk ?? 'UNRATED']++;
  }

  const ruleCounts = new Map<string, { label: string; count: number }>();
  for (const v of views) {
    const entry = ruleCounts.get(v.ruleCode);
    if (entry) {
      entry.count++;
    } else {
      ruleCounts.set(v.ruleCode, { label: v.rule.label, count: 1 });
    }
  }

  const statusCounts = new Map<ReviewStatus, number>();
  for (const v of views) {
    statusCounts.set(v.status, (statusCounts.get(v.status) || 0) + 1);
  }

  return {
    customers: customers.length,
    alerts: views.length,
    txns: views.reduce((s, v) => s + v.txns.length, 0),
    ctrReportable: views.reduce((s, v) => s + v.txns.filter((t) => t.ctrReportable).length, 0),
    openAlerts: views.filter((v) => REVIEW_STATUS_META[v.status].open).length,
    escalatedCustomers: customers.filter((c) => c.escalated).length,
    upgradeCandidates: customers.filter((c) => c.needsUpgrade).length,
    downgradeCandidates: customers.filter((c) => c.needsDowngrade).length,
    totalAmount: views.reduce((s, v) => s + v.amount, 0),
    byRisk,
    byRule: [...ruleCounts.entries()]
      .map(
        ([
          code,
          v
        ]) => ({ code, label: v.label, count: v.count })
      )
      .sort((a, b) => b.count - a.count),
    byStatus: [...statusCounts.entries()]
      .map(
        ([
          status,
          count
        ]) => ({ status, label: REVIEW_STATUS_META[status].label, count })
      )
      .sort((a, b) => b.count - a.count)
  };
}

/** Everything the screen renders, computed in one pass. */
export interface RiskReviewModel {
  alerts: RiskAlertView[];
  customers: RiskCustomerRow[];
  txns: RiskTxnView[];
  summary: RiskReviewSummary;
}

/**
 * Single entry point for the screen. Filtering, rollup, direction narrowing and
 * the summary all run once per filter change rather than once per template
 * binding, which matters because every view reads from the same result.
 */
export function buildRiskReview(
  alerts: RiskAlertRow[],
  filter: RiskReviewFilter,
  windows: BehaviourWindowByClient = {}
): RiskReviewModel {
  const base = riskAlertViews(alerts, filter);
  const narrowed = applyDirectionFilter(base, riskCustomerRows(base, windows), filter.direction);

  return {
    alerts: narrowed.views,
    customers: narrowed.customers,
    txns: riskTxnRows(narrowed.views),
    summary: riskReviewSummary(narrowed.views, narrowed.customers)
  };
}

// ── Period helpers (shared with the other period-filtered reports) ───────────

/** Monday to Saturday containing the given date. */
export function weekRange(anyDateInWeek: string): DateRange {
  const d = new Date(`${anyDateInWeek}T00:00:00Z`);
  const dow = d.getUTCDay();
  const backToMonday = dow === 0 ? 6 : dow - 1;
  const monday = new Date(d.getTime() - backToMonday * 86400000);
  const saturday = new Date(monday.getTime() + 5 * 86400000);
  return { from: monday.toISOString().slice(0, 10), to: saturday.toISOString().slice(0, 10) };
}

/** First to last day of the given yyyy-MM. */
export function monthRange(month: string): DateRange {
  const [
    y,
    m
  ] = month.split('-').map(Number);
  const last = new Date(Date.UTC(y, m, 0)).getUTCDate();
  return { from: `${month}-01`, to: `${month}-${String(last).padStart(2, '0')}` };
}