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diff --git a/packages/taler-wallet-webextension/src/wallet/ExchangeSelection/state.ts b/packages/taler-wallet-webextension/src/wallet/ExchangeSelection/state.ts
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+++ b/packages/taler-wallet-webextension/src/wallet/ExchangeSelection/state.ts
@@ -0,0 +1,525 @@
+/*
+ This file is part of GNU Taler
+ (C) 2022 Taler Systems S.A.
+
+ GNU Taler is free software; you can redistribute it and/or modify it under the
+ terms of the GNU General Public License as published by the Free Software
+ Foundation; either version 3, or (at your option) any later version.
+
+ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License along with
+ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+
+import { AbsoluteTime, AmountJson, Amounts, DenominationInfo, TalerProtocolTimestamp } from "@gnu-taler/taler-util";
+import { useState } from "preact/hooks";
+import { useAsyncAsHook } from "../../hooks/useAsyncAsHook.js";
+import * as wxApi from "../../wxApi.js";
+import { FeeDescription, FeeDescriptionPair, OperationMap, Props, State } from "./index.js";
+
+export function useComponentState(
+  { onCancel, onSelection, currency }: Props,
+  api: typeof wxApi,
+): State {
+  const hook = useAsyncAsHook(api.listExchanges);
+
+  const initialValue = 0
+  const [value, setValue] = useState(String(initialValue));
+
+  if (!hook) {
+    return {
+      status: "loading",
+      error: undefined,
+    }
+  }
+  if (hook.hasError) {
+    return {
+      status: "loading-uri",
+      error: hook,
+    };
+  }
+
+  const exchanges = hook.response.exchanges;
+
+  if (exchanges.length === 0) {
+    return {
+      status: "no-exchanges",
+      error: undefined
+    }
+  }
+
+  const original = exchanges[initialValue];
+  const selected = exchanges[Number(value)];
+
+  let nextFeeUpdate = TalerProtocolTimestamp.never();
+
+  nextFeeUpdate = Object.values(selected.wireInfo.feesForType).reduce(
+    (prev, cur) => {
+      return cur.reduce((p, c) => nearestTimestamp(p, c.endStamp), prev);
+    },
+    nextFeeUpdate,
+  );
+
+  nextFeeUpdate = selected.denominations.reduce((prev, cur) => {
+    return [
+      cur.stampExpireWithdraw,
+      cur.stampExpireLegal,
+      cur.stampExpireDeposit,
+    ].reduce(nearestTimestamp, prev);
+  }, nextFeeUpdate);
+
+  const timeline: OperationMap<FeeDescription[]> = {
+    deposit: createDenominationTimeline(
+      selected.denominations,
+      "stampExpireDeposit",
+      "feeDeposit",
+    ),
+    refresh: createDenominationTimeline(
+      selected.denominations,
+      "stampExpireWithdraw",
+      "feeRefresh",
+    ),
+    refund: createDenominationTimeline(
+      selected.denominations,
+      "stampExpireWithdraw",
+      "feeRefund",
+    ),
+    withdraw: createDenominationTimeline(
+      selected.denominations,
+      "stampExpireWithdraw",
+      "feeWithdraw",
+    ),
+  };
+
+  const exchangeMap = exchanges.reduce((prev, cur, idx) => ({ ...prev, [cur.exchangeBaseUrl]: String(idx) }), {} as Record<string, string>)
+
+  if (original === selected) {
+    return {
+      status: "ready",
+      exchanges: {
+        list: exchangeMap,
+        value: value,
+        onChange: async (v) => {
+          setValue(v)
+        }
+      },
+      error: undefined,
+      nextFeeUpdate: AbsoluteTime.fromTimestamp(nextFeeUpdate),
+      onClose: {
+        onClick: onCancel
+      },
+      selected,
+      timeline
+    }
+  }
+
+  const originalTimeline: OperationMap<FeeDescription[]> = {
+    deposit: createDenominationTimeline(
+      original.denominations,
+      "stampExpireDeposit",
+      "feeDeposit",
+    ),
+    refresh: createDenominationTimeline(
+      original.denominations,
+      "stampExpireWithdraw",
+      "feeRefresh",
+    ),
+    refund: createDenominationTimeline(
+      original.denominations,
+      "stampExpireWithdraw",
+      "feeRefund",
+    ),
+    withdraw: createDenominationTimeline(
+      original.denominations,
+      "stampExpireWithdraw",
+      "feeWithdraw",
+    ),
+  };
+  const pairTimeline: OperationMap<FeeDescription[]> = {
+    deposit: createDenominationPairTimeline(timeline.deposit, originalTimeline.deposit),
+    refresh: createDenominationPairTimeline(timeline.refresh, originalTimeline.refresh),
+    refund: createDenominationPairTimeline(timeline.refund, originalTimeline.refund),
+    withdraw: createDenominationPairTimeline(timeline.withdraw, originalTimeline.withdraw),
+  }
+
+  return {
+    status: "comparing",
+    exchanges: {
+      list: exchangeMap,
+      value: value,
+      onChange: async (v) => {
+        setValue(v)
+      }
+    },
+    error: undefined,
+    nextFeeUpdate: AbsoluteTime.fromTimestamp(nextFeeUpdate),
+    onReset: {
+      onClick: async () => {
+        setValue(String(initialValue))
+      }
+    },
+    onSelect: {
+      onClick: async () => {
+        onSelection(selected.exchangeBaseUrl)
+      }
+    },
+    selected,
+    pairTimeline,
+  }
+
+}
+
+function nearestTimestamp(
+  first: TalerProtocolTimestamp,
+  second: TalerProtocolTimestamp,
+): TalerProtocolTimestamp {
+  const f = AbsoluteTime.fromTimestamp(first);
+  const s = AbsoluteTime.fromTimestamp(second);
+  const a = AbsoluteTime.min(f, s);
+  return AbsoluteTime.toTimestamp(a);
+}
+
+
+
+export interface TimePoint {
+  type: "start" | "end";
+  moment: AbsoluteTime;
+  denom: DenominationInfo;
+}
+
+/**
+ * Given a list of denominations with the same value and same period of time:
+ * return the one that will be used.
+ * The best denomination is the one that will minimize the fee cost.
+ *
+ * @param list denominations of same value
+ * @returns
+ */
+function selectBestForOverlappingDenominations(
+  list: DenominationInfo[],
+): DenominationInfo | undefined {
+  let minDeposit: DenominationInfo | undefined = undefined;
+  list.forEach((e) => {
+    if (minDeposit === undefined) {
+      minDeposit = e;
+      return;
+    }
+    if (Amounts.cmp(minDeposit.feeDeposit, e.feeDeposit) > -1) {
+      minDeposit = e;
+    }
+  });
+  return minDeposit;
+}
+
+type PropsWithReturnType<T extends object, F> = Exclude<
+  {
+    [K in keyof T]: T[K] extends F ? K : never;
+  }[keyof T],
+  undefined
+>;
+
+/**
+ * Takes two list and create one with one timeline.
+ * For any element in the position "p" on the left or right "list", then
+ * list[p].until should be equal to list[p+1].from
+ * 
+ * @see {createDenominationTimeline}
+ * 
+ * @param left list denominations @type {FeeDescription}
+ * @param right list denominations @type {FeeDescription}
+ * @returns list of pairs for the same time
+ */
+export function createDenominationPairTimeline(left: FeeDescription[], right: FeeDescription[]): FeeDescriptionPair[] {
+  //both list empty, discarded
+  if (left.length === 0 && right.length === 0) return [];
+
+  const pairList: FeeDescriptionPair[] = [];
+
+  let li = 0;
+  let ri = 0;
+
+  while (li < left.length && ri < right.length) {
+    const currentValue = Amounts.cmp(left[li].value, right[ri].value) < 0 ? left[li].value : right[ri].value;
+
+    let ll = 0 //left length (until next value)
+    while (li + ll < left.length && Amounts.cmp(left[li + ll].value, currentValue) === 0) {
+      ll++
+    }
+    let rl = 0 //right length (until next value)
+    while (ri + rl < right.length && Amounts.cmp(right[ri + rl].value, currentValue) === 0) {
+      rl++
+    }
+    const leftIsEmpty = ll === 0
+    const rightIsEmpty = rl === 0
+    //check which start after, add gap so both list starts at the same time
+    // one list may be empty
+    const leftStarts: AbsoluteTime =
+      leftIsEmpty ? { t_ms: "never" } : left[li].from;
+    const rightStarts: AbsoluteTime =
+      rightIsEmpty ? { t_ms: "never" } : right[ri].from;
+
+    //first time cut is the smallest time
+    let timeCut: AbsoluteTime = leftStarts;
+
+    if (AbsoluteTime.cmp(leftStarts, rightStarts) < 0) {
+      const ends =
+        rightIsEmpty ? left[li + ll - 1].until : right[0].from;
+
+      right.splice(ri, 0, {
+        from: leftStarts,
+        until: ends,
+        value: left[li].value,
+      });
+      rl++;
+
+      timeCut = leftStarts
+    }
+    if (AbsoluteTime.cmp(leftStarts, rightStarts) > 0) {
+      const ends =
+        leftIsEmpty ? right[ri + rl - 1].until : left[0].from;
+
+      left.splice(li, 0, {
+        from: rightStarts,
+        until: ends,
+        value: right[ri].value,
+      });
+      ll++;
+
+      timeCut = rightStarts
+    }
+
+    //check which ends sooner, add gap so both list ends at the same time
+    // here both list are non empty
+    const leftEnds: AbsoluteTime = left[li + ll - 1].until;
+    const rightEnds: AbsoluteTime = right[ri + rl - 1].until;
+
+    if (AbsoluteTime.cmp(leftEnds, rightEnds) > 0) {
+      right.splice(ri + rl, 0, {
+        from: rightEnds,
+        until: leftEnds,
+        value: left[0].value,
+      });
+      rl++;
+
+    }
+    if (AbsoluteTime.cmp(leftEnds, rightEnds) < 0) {
+      left.splice(li + ll, 0, {
+        from: leftEnds,
+        until: rightEnds,
+        value: right[0].value,
+      });
+      ll++;
+    }
+
+    //now both lists are non empty and (starts,ends) at the same time
+    while (li < left.length && ri < right.length && Amounts.cmp(left[li].value, right[ri].value) === 0) {
+      // console.log('start', li, ri, left[li], right[ri])
+
+      if (AbsoluteTime.cmp(left[li].from, timeCut) !== 0 && AbsoluteTime.cmp(right[ri].from, timeCut) !== 0) {
+        // timeCut comes from the latest "until" (expiration from the previous)
+        // and this value comes from the latest left or right
+        // it should be the same as the "from" from one of the latest left or right
+        // otherwise it means that there is missing a gap object in the middle
+        // the list is not complete and the behavior is undefined
+        console.log(li, ri, timeCut)
+        throw Error('one of the list is not completed: list[i].until !== list[i+1].from')
+      }
+
+      pairList.push({
+        left: left[li].fee,
+        right: right[ri].fee,
+        from: timeCut,
+        until: AbsoluteTime.never(),
+        value: currentValue,
+      });
+
+      if (left[li].until.t_ms === right[ri].until.t_ms) {
+        timeCut = left[li].until;
+        ri++;
+        li++;
+      } else if (left[li].until.t_ms < right[ri].until.t_ms) {
+        timeCut = left[li].until;
+        li++;
+      } else if (left[li].until.t_ms > right[ri].until.t_ms) {
+        timeCut = right[ri].until;
+        ri++;
+      }
+      pairList[pairList.length - 1].until = timeCut
+
+      if (li < left.length && Amounts.cmp(left[li].value, pairList[pairList.length - 1].value) !== 0) {
+        //value changed, should break
+        //this if will catch when both (left and right) change at the same time
+        //if just one side changed it will catch in the while condition
+        break;
+      }
+
+    }
+
+  }
+  //one of the list left or right can still have elements
+  if (li < left.length) {
+    let timeCut = pairList.length > 0 && Amounts.cmp(pairList[pairList.length - 1].value, left[li].value) === 0 ? pairList[pairList.length - 1].until : left[li].from;
+    while (li < left.length) {
+      pairList.push({
+        left: left[li].fee,
+        right: undefined,
+        from: timeCut,
+        until: left[li].until,
+        value: left[li].value,
+      })
+      timeCut = left[li].until
+      li++;
+    }
+  }
+  if (ri < right.length) {
+    let timeCut = pairList.length > 0 && Amounts.cmp(pairList[pairList.length - 1].value, right[ri].value) === 0 ? pairList[pairList.length - 1].until : right[ri].from;
+    while (ri < right.length) {
+      pairList.push({
+        right: right[ri].fee,
+        left: undefined,
+        from: timeCut,
+        until: right[ri].until,
+        value: right[ri].value,
+      })
+      timeCut = right[ri].until
+      ri++;
+    }
+  }
+  return pairList
+}
+
+/**
+ * Create a usage timeline with the denominations given.
+ *
+ * If there are multiple denominations that can be used, the list will
+ * contain the one that minimize the fee cost. @see selectBestForOverlappingDenominations
+ *
+ * @param list list of denominations
+ * @param periodProp property of element of the list that will be used as end of the usage period
+ * @param feeProp property of the element of the list that will be used as fee reference
+ * @returns  list of @type {FeeDescription} sorted by usage period
+ */
+export function createDenominationTimeline(
+  list: DenominationInfo[],
+  periodProp: PropsWithReturnType<DenominationInfo, TalerProtocolTimestamp>,
+  feeProp: PropsWithReturnType<DenominationInfo, AmountJson>,
+): FeeDescription[] {
+  const points = list
+    .reduce((ps, denom) => {
+      //exclude denoms with bad configuration
+      if (denom.stampStart.t_s >= denom[periodProp].t_s) {
+        throw Error(`denom ${denom.denomPubHash} has start after the end`);
+        // return ps;
+      }
+      ps.push({
+        type: "start",
+        moment: AbsoluteTime.fromTimestamp(denom.stampStart),
+        denom,
+      });
+      ps.push({
+        type: "end",
+        moment: AbsoluteTime.fromTimestamp(denom[periodProp]),
+        denom,
+      });
+      return ps;
+    }, [] as TimePoint[])
+    .sort((a, b) => {
+      const v = Amounts.cmp(a.denom.value, b.denom.value);
+      if (v != 0) return v;
+      const t = AbsoluteTime.cmp(a.moment, b.moment);
+      if (t != 0) return t;
+      if (a.type === b.type) return 0;
+      return a.type === "start" ? 1 : -1;
+    });
+
+  const activeAtTheSameTime: DenominationInfo[] = [];
+  return points.reduce((result, cursor, idx) => {
+    const hash = cursor.denom.denomPubHash;
+    if (!hash)
+      throw Error(
+        `denomination without hash ${JSON.stringify(
+          cursor.denom,
+          undefined,
+          2,
+        )}`,
+      );
+
+    let prev = result.length > 0 ? result[result.length - 1] : undefined;
+    const prevHasSameValue =
+      prev && Amounts.cmp(prev.value, cursor.denom.value) === 0;
+    if (prev) {
+      if (prevHasSameValue) {
+        prev.until = cursor.moment;
+
+        if (prev.from.t_ms === prev.until.t_ms) {
+          result.pop();
+          prev = result[result.length - 1];
+        }
+      } else {
+        // the last end adds a gap that we have to remove
+        result.pop();
+      }
+    }
+
+    //update the activeAtTheSameTime list
+    if (cursor.type === "end") {
+      const loc = activeAtTheSameTime.findIndex((v) => v.denomPubHash === hash);
+      if (loc === -1) {
+        throw Error(`denomination ${hash} has an end but no start`);
+      }
+      activeAtTheSameTime.splice(loc, 1);
+    } else if (cursor.type === "start") {
+      activeAtTheSameTime.push(cursor.denom);
+    } else {
+      const exhaustiveCheck: never = cursor.type;
+      throw new Error(`not TimePoint defined for type: ${exhaustiveCheck}`);
+    }
+
+    if (idx == points.length - 1) {
+      //this is the last element in the list, prevent adding
+      //a gap in the end
+      if (cursor.type !== "end") {
+        throw Error(
+          `denomination ${hash} starts after ending or doesn't have an ending`,
+        );
+      }
+      if (activeAtTheSameTime.length > 0) {
+        throw Error(
+          `there are ${activeAtTheSameTime.length} denominations without ending`,
+        );
+      }
+      return result;
+    }
+
+    const current = selectBestForOverlappingDenominations(activeAtTheSameTime);
+
+    if (current) {
+      if (
+        prev === undefined || //is the first
+        !prev.fee || //is a gap
+        Amounts.cmp(prev.fee, current[feeProp]) !== 0 // prev has the same fee
+      ) {
+        result.push({
+          value: cursor.denom.value,
+          from: cursor.moment,
+          until: AbsoluteTime.never(), //not yet known
+          fee: current[feeProp],
+        });
+      } else {
+        prev.until = cursor.moment;
+      }
+    } else {
+      result.push({
+        value: cursor.denom.value,
+        from: cursor.moment,
+        until: AbsoluteTime.never(), //not yet known
+      });
+    }
+
+    return result;
+  }, [] as FeeDescription[]);
+}