import { useState, useCallback, useMemo } from "react";
import type { SelectableUTXO, VariableInput } from "../types.js";
import type { Invitation } from "../../../../services/invitation.js";
import { formatSatoshis } from "../../../theme.js";
import {
  autoSelectGreedyUtxos,
  mapUnspentOutputsToSelectable,
} from "../../../../utils/invitation-flow.js";

/**
 * Manages UTXO selection state for the wizard's inputs step.
 *
 * Only active for transaction flows that require the creator
 * to provide funding inputs.
 */
export function useUtxoSelection() {
  const [availableUtxos, setAvailableUtxos] = useState<SelectableUTXO[]>([]);
  const [selectedUtxoIndex, setSelectedUtxoIndex] = useState(0);
  const [requiredAmount, setRequiredAmount] = useState<bigint>(0n);
  const [fee, setFee] = useState<bigint>(500n);

  const selectedAmount = useMemo(
    () =>
      availableUtxos
        .filter((u) => u.selected)
        .reduce((sum, u) => sum + u.valueSatoshis, 0n),
    [availableUtxos],
  );

  const changeAmount = useMemo(
    () => selectedAmount - requiredAmount - fee,
    [selectedAmount, requiredAmount, fee],
  );

  /** Toggle the selected state of a single UTXO. */
  const toggleSelection = useCallback((index: number) => {
    setAvailableUtxos((prev) => {
      const updated = [...prev];
      const utxo = updated[index];
      if (utxo) {
        updated[index] = { ...utxo, selected: !utxo.selected };
      }
      return updated;
    });
  }, []);

  /** Select all available UTXOs. */
  const selectAll = useCallback(() => {
    setAvailableUtxos((prev) => prev.map((u) => ({ ...u, selected: true })));
  }, []);

  /** Deselect all UTXOs. */
  const deselectAll = useCallback(() => {
    setAvailableUtxos((prev) => prev.map((u) => ({ ...u, selected: false })));
  }, []);

  /**
   * Query the invitation instance for suitable UTXOs and auto-select
   * greedily to meet the required amount.
   */
  const loadUtxos = useCallback(
    async (
      invitationInstance: Invitation,
      templateIdentifier: string,
      variables: VariableInput[],
      setStatus: (msg: string) => void,
    ): Promise<void> => {
      setStatus("Finding suitable UTXOs...");

      // Derive required amount from variables that look like satoshi/amount fields.
      const requestedVar = variables.find(
        (v) =>
          v.id.toLowerCase().includes("satoshi") ||
          v.id.toLowerCase().includes("amount"),
      );
      const requested = requestedVar ? BigInt(requestedVar.value || "0") : 0n;
      setRequiredAmount(requested);

      const unspentOutputs = await invitationInstance.findSuitableResources({
        templateIdentifier,
      });

      const mapped = mapUnspentOutputsToSelectable(unspentOutputs);
      const autoSelected = autoSelectGreedyUtxos(mapped, requested + fee);
      setAvailableUtxos(autoSelected as SelectableUTXO[]);
      setStatus("Ready");
    },
    [fee],
  );

  /** Validate that the selection meets the required amounts. */
  const validate = useCallback((): string | null => {
    const selected = availableUtxos.filter((u) => u.selected);
    if (selected.length === 0) {
      return "Please select at least one UTXO";
    }
    if (selectedAmount < requiredAmount + fee) {
      return `Insufficient funds. Need ${formatSatoshis(requiredAmount + fee)}, selected ${formatSatoshis(selectedAmount)}`;
    }
    if (changeAmount < 546n) {
      return `Change amount (${changeAmount}) is below dust threshold (546 sats)`;
    }
    return null;
  }, [availableUtxos, selectedAmount, requiredAmount, fee, changeAmount]);

  return {
    availableUtxos,
    setAvailableUtxos,
    selectedUtxoIndex,
    setSelectedUtxoIndex,
    requiredAmount,
    fee,
    selectedAmount,
    changeAmount,
    toggleSelection,
    selectAll,
    deselectAll,
    loadUtxos,
    validate,
  } as const;
}

export type UtxoSelectionState = ReturnType<typeof useUtxoSelection>;