first commit

src/widgets/currency-converter/model/tiers.ts

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+export interface Tier {
+  min: number
+  max: number
+  pct: number
+}
+
+export const TIERS: readonly Tier[] = [
+  { min: 5_000, max: 30_000, pct: 8 },
+  { min: 30_000, max: 100_000, pct: 6 },
+  { min: 100_000, max: 600_000, pct: 4 },
+] as const
+
+export const TIER_MIN = TIERS[0].min
+export const TIER_MAX = TIERS[TIERS.length - 1].max
+
+export function findTier(amount: number): Pick<Tier, 'pct'> {
+  const match = TIERS.find((t) => amount >= t.min && amount <= t.max)
+  if (match) return match
+  if (amount > TIER_MAX) return { pct: TIERS[TIERS.length - 1].pct }
+  return { pct: TIERS[0].pct }
+}
+
+export function progressPercent(amount: number): number {
+  if (amount <= TIER_MIN) return 0
+  if (amount >= TIER_MAX) return 100
+  return ((amount - TIER_MIN) / (TIER_MAX - TIER_MIN)) * 100
+}

src/widgets/currency-converter/model/useConverter.ts

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+import { useMemo, useState } from 'react'
+import { findTier, progressPercent } from './tiers'
+
+export type ConverterMode = 'buy' | 'sell'
+
+interface UseConverterArgs {
+  usdtRate: number
+}
+
+export function useConverter({ usdtRate }: UseConverterArgs) {
+  const [mode, setMode] = useState<ConverterMode>('buy')
+  const [rubVal, setRubVal] = useState<string>('10000')
+  const [agreed, setAgreed] = useState<boolean>(false)
+
+  const numRub = Number.parseFloat(rubVal) || 0
+
+  const result = useMemo(() => {
+    const tier = findTier(numRub)
+    const commission = (numRub * tier.pct) / 100
+    const sign = mode === 'buy' ? 1 : -1
+    const effectiveRate = usdtRate * (1 + (sign * tier.pct) / 100)
+    const usdtVal = numRub > 0 ? (numRub / effectiveRate).toFixed(2) : '0.00'
+    return {
+      tierPct: tier.pct,
+      commission,
+      effectiveRate,
+      usdtVal,
+      progress: progressPercent(numRub),
+    }
+  }, [numRub, mode, usdtRate])
+
+  function updateRub(raw: string) {
+    setRubVal(raw.replace(/[^0-9.]/g, ''))
+  }
+
+  function toggleMode() {
+    setMode((m) => (m === 'buy' ? 'sell' : 'buy'))
+  }
+
+  return {
+    mode,
+    setMode,
+    rubVal,
+    updateRub,
+    numRub,
+    agreed,
+    setAgreed,
+    toggleMode,
+    ...result,
+  }
+}