import Foundation
import Observation
import OSLog
import SwiftData

private let logger = Logger(subsystem: Bundle.main.bundleIdentifier ?? "hellbender", category: "SendViewModel")

@Observable
@MainActor
final class SendViewModel: PSBTFlowManaging {
  enum Step: Int, CaseIterable {
    case recipients
    case review
    case psbtDisplay
    case psbtScan
    case broadcast
  }

  /// Navigation
  var currentStep: Step = .recipients

  // Input
  var recipients: [Recipient] = [Recipient()]
  var amountInFiat: Bool = false
  var fiatDisplayAmount: [UUID: String] = [:] // per-recipient fiat display strings
  var feeRateSatVb: String = "" // empty until rates load
  var selectedFeePreset: FeePreset = .medium
  var showAddressScanner: Bool = false
  var scanTargetRecipientIndex: Int = 0
  var recommendedFees: BitcoinService.RecommendedFees?

  // UTXO selection
  var manualUTXOSelection: Bool = false
  var selectedUTXOIds: Set<String> = [] // "txid:vout"
  var showUTXOPicker: Bool = false

  /// Validation
  var showValidationErrors: Bool = false

  // State
  var psbtBase64: String = ""
  var psbtBytes: Data = .init()
  var signaturesCollected: Int = 0
  var requiredSignatures: Int = 2
  var totalCosigners: Int = 1
  var broadcastTxid: String = ""
  var finalizedTxBytes: Data = .init()
  var errorMessage: String?
  var isProcessing: Bool = false
  var showExportQR: Bool = false

  // Saved PSBT
  var savedPSBTId: UUID?
  var savedPSBTName: String = ""
  var showSavePSBT: Bool = false
  var showSavedConfirmation: Bool = false
  var showLoadPSBT: Bool = false

  // Import PSBT
  var showImportPSBTQR: Bool = false
  var showImportPSBTFile: Bool = false

  /// Cosigner signing status (populated from PSBT analysis)
  var signerStatus: [(label: String, fingerprint: String, hasSigned: Bool)] = []

  // Transaction details (populated after PSBT creation)
  var totalFee: UInt64 = 0
  var changeAmount: UInt64?
  var changeAddress: String?
  var inputCount: Int = 0

  /// Balance
  var availableBalance: UInt64 = 0

  private let bitcoinService: any BitcoinServiceProtocol

  // MARK: - PSBTFlowManaging

  var psbtBitcoinService: any BitcoinServiceProtocol {
    bitcoinService
  }

  func navigateAfterSign() {
    if needsMoreSignatures {
      currentStep = .psbtDisplay
    } else {
      currentStep = .broadcast
    }
  }

  init(bitcoinService: (any BitcoinServiceProtocol)? = nil) {
    self.bitcoinService = bitcoinService ?? BitcoinService.shared
  }

  var frozenOutpoints: Set<String> = []

  var allUTXOs: [UTXOItem] {
    bitcoinService.utxos
  }

  var spendableUTXOs: [UTXOItem] {
    bitcoinService.utxos.filter { !frozenOutpoints.contains($0.id) }
  }

  var frozenUTXOs: [UTXOItem] {
    bitcoinService.utxos.filter { frozenOutpoints.contains($0.id) }
  }

  func isFrozen(_ utxo: UTXOItem) -> Bool {
    frozenOutpoints.contains(utxo.id)
  }

  var selectedUTXOTotal: UInt64 {
    guard manualUTXOSelection else { return availableBalance }
    return allUTXOs
      .filter { selectedUTXOIds.contains($0.id) }
      .reduce(0) { $0 + $1.amount }
  }

  var currentNetwork: BitcoinNetwork? {
    bitcoinService.currentNetwork
  }

  var feeRateValue: Double {
    Double(feeRateSatVb) ?? 0
  }

  var isValidFeeRate: Bool {
    feeRateValue > 0
  }

  var hasAnyInput: Bool {
    recipients.contains { !$0.isAddressEmpty || !$0.isAmountEmpty || !$0.label.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty }
      || manualUTXOSelection
  }

  var hasValidRecipients: Bool {
    !recipients.isEmpty && recipients.allSatisfy { r in
      r.isValidAddress && (r.isValidAmount || (r.isSendMax && r.amountValue != nil))
    }
  }

  /// Check if a send-max recipient has zero amount (blocks review)
  var hasSendMaxZeroAmount: Bool {
    recipients.contains { $0.isSendMax && ($0.amountValue ?? 0) == 0 }
  }

  var isBalanceExceeded: Bool {
    guard !hasSendMax else { return false } // send-max self-adjusts
    let totalAmount = totalSendAmount
    let fee = estimateFee()
    return totalAmount + fee > selectedUTXOTotal
  }

  /// Attempt to proceed to review; builds a draft PSBT to get exact fee/change info
  func tryReview() {
    // If we have a loaded saved PSBT with signatures, go straight to review
    // without rebuilding (which would create a new unsigned PSBT and lose signatures)
    if savedPSBTId != nil, signaturesCollected > 0, !psbtBytes.isEmpty {
      currentStep = .review
      return
    }
    showValidationErrors = true
    guard hasValidRecipients, isValidFeeRate, !isBalanceExceeded, !hasSendMaxZeroAmount else { return }
    guard recipients.allSatisfy({ $0.isAddressFormatValid(network: currentNetwork) }) else { return }
    showValidationErrors = false
    Task { await buildDraftPSBT() }
  }

  var totalSendAmount: UInt64 {
    recipients.reduce(0) { $0 + ($1.amountValue ?? 0) }
  }

  var hasSendMax: Bool {
    recipients.contains { $0.isSendMax }
  }

  /// Build a preview TransactionItem for the send flow detail screen
  var previewTransaction: TransactionItem {
    let outputs = recipients.map { r in
      TransactionItem.TxIO(
        address: r.address.trimmingCharacters(in: .whitespacesAndNewlines),
        amount: r.amountValue ?? 0,
        prevTxid: nil,
        prevVout: nil,
        isMine: false
      )
    }
    return TransactionItem(
      id: broadcastTxid.isEmpty ? "Unsigned" : broadcastTxid,
      amount: -Int64(totalSendAmount),
      fee: nil,
      confirmations: 0,
      timestamp: nil,
      isIncoming: false,
      inputs: [],
      outputs: outputs
    )
  }

  /// Total deducted from wallet = send amount + fee
  var totalSpendAmount: UInt64 {
    totalSendAmount + totalFee
  }

  /// Total sats of all inputs = send amount + fee + change
  var inputsAmount: UInt64 {
    totalSendAmount + totalFee + (changeAmount ?? 0)
  }

  // signatureProgress and needsMoreSignatures provided by PSBTFlowManaging

  func loadBalance() {
    availableBalance = spendableUTXOs.reduce(0) { $0 + $1.amount }
    requiredSignatures = bitcoinService.requiredSignatures
    totalCosigners = bitcoinService.totalCosigners
  }

  // MARK: - Fiat Toggle

  private var fiatService: FiatPriceService {
    FiatPriceService.shared
  }

  var canToggleFiat: Bool {
    fiatService.currentRate != nil
  }

  func toggleAmountCurrency() {
    guard canToggleFiat else { return }

    if amountInFiat {
      // Switching from fiat to sats: convert fiat display amounts back to sats
      for i in recipients.indices {
        if recipients[i].isSendMax { continue }
        let fiatStr = fiatDisplayAmount[recipients[i].id] ?? ""
        if let fiatVal = Double(fiatStr), fiatVal > 0,
           let sats = fiatService.fiatToSats(fiatVal)
        {
          recipients[i].amountSats = "\(sats)"
        }
      }
    } else {
      // Switching from sats to fiat: convert sats to fiat display amounts
      for i in recipients.indices {
        if recipients[i].isSendMax {
          if let sats = recipients[i].amountValue,
             let fiatVal = fiatService.satsToFiat(sats)
          {
            fiatDisplayAmount[recipients[i].id] = String(format: "%.2f", fiatVal)
          }
          continue
        }
        if let sats = recipients[i].amountValue,
           let fiatVal = fiatService.satsToFiat(sats)
        {
          fiatDisplayAmount[recipients[i].id] = String(format: "%.2f", fiatVal)
        } else {
          fiatDisplayAmount[recipients[i].id] = ""
        }
      }
    }

    amountInFiat.toggle()
  }

  /// Called when fiat amount text changes — updates the underlying sats value
  func updateSatsFromFiat(for index: Int) {
    guard amountInFiat, !recipients[index].isSendMax else { return }
    let fiatStr = fiatDisplayAmount[recipients[index].id] ?? ""
    if let fiatVal = Double(fiatStr), fiatVal > 0,
       let sats = fiatService.fiatToSats(fiatVal)
    {
      recipients[index].amountSats = "\(sats)"
    } else {
      recipients[index].amountSats = ""
    }
  }

  // MARK: - Recipients

  var canAddRecipient: Bool {
    !hasSendMax
  }

  func addRecipient() {
    guard canAddRecipient else { return }
    recipients.append(Recipient())
  }

  func removeRecipient(at index: Int) {
    guard recipients.count > 1 else { return }
    let hadMax = recipients[index].isSendMax
    recipients.remove(at: index)
    if hadMax {
      // MAX was on the deleted recipient — clear it entirely
      for i in recipients.indices {
        recipients[i].isSendMax = false
      }
    }
  }

  func toggleUTXOSelection(_ utxoId: String) {
    if selectedUTXOIds.contains(utxoId) {
      selectedUTXOIds.remove(utxoId)
    } else {
      selectedUTXOIds.insert(utxoId)
    }
    recalculateMaxIfNeeded()
  }

  func setManualUTXOSelection(_ enabled: Bool) {
    manualUTXOSelection = enabled
    if !enabled {
      selectedUTXOIds.removeAll()
    }
    recalculateMaxIfNeeded()
  }

  /// MAX is only allowed on the last recipient
  var isMaxAllowed: Bool {
    true // Always allowed on last recipient; UI hides the button for non-last recipients
  }

  func toggleMaxAmount(for index: Int) {
    guard index == recipients.count - 1 else { return } // only last recipient

    // If already max, untoggle and clear
    if recipients[index].isSendMax {
      recipients[index].isSendMax = false
      recipients[index].amountSats = ""
      fiatDisplayAmount[recipients[index].id] = ""
      return
    }
    // Clear any other send-max flags (shouldn't exist, but be safe)
    for i in recipients.indices {
      recipients[i].isSendMax = false
    }
    recipients[index].isSendMax = true
    recalculateMax(for: index)
  }

  func fetchFeeRates() async {
    do {
      let rates = try await bitcoinService.getFeeRates()
      await MainActor.run {
        self.recommendedFees = rates
        applyPreset(selectedFeePreset)
      }
    } catch {
      logger.error("Failed to fetch fee rates: \(error)")
    }
  }

  func applyPreset(_ preset: FeePreset) {
    selectedFeePreset = preset
    if let rate = preset.rate(from: recommendedFees) {
      feeRateSatVb = formatFeeRate(rate)
    }
  }

  /// Recalculate the max amount for whichever recipient has isSendMax
  func recalculateMaxIfNeeded() {
    guard let index = recipients.firstIndex(where: { $0.isSendMax }) else { return }
    recalculateMax(for: index)
  }

  private func recalculateMax(for index: Int) {
    let spendableBalance = selectedUTXOTotal
    let otherAmounts = recipients.enumerated()
      .filter { $0.offset != index }
      .reduce(UInt64(0)) { $0 + ($1.element.amountValue ?? 0) }
    let feeEstimate = estimateFee()
    let maxAmount = spendableBalance > (otherAmounts + feeEstimate) ?
      spendableBalance - otherAmounts - feeEstimate : 0
    recipients[index].amountSats = "\(maxAmount)"
    if amountInFiat, let fiatVal = fiatService.satsToFiat(maxAmount) {
      fiatDisplayAmount[recipients[index].id] = String(format: "%.2f", fiatVal)
    }
  }

  func estimateFee() -> UInt64 {
    estimatedFee(for: feeRateValue)
  }

  func estimatedFee(for rate: Double) -> UInt64 {
    // Rough estimate: P2WSH multisig input ~200 vbytes, output ~43 vbytes each, overhead ~10
    let inputCount: Int = if manualUTXOSelection {
      max(selectedUTXOIds.count, 1)
    } else {
      max(bitcoinService.utxos.count, 1)
    }
    let outputCount = recipients.count + 1 // +1 for change
    let estimatedVbytes = UInt64(inputCount * 200 + outputCount * 43 + 10)
    return UInt64(Double(estimatedVbytes) * max(rate, 0.001))
  }

  /// Parse a BIP-21 URI or plain address string
  func parseBIP21(_ input: String, forRecipientAt index: Int) {
    recipients[index].parseBIP21(input)
  }

  // MARK: - PSBT Operations

  private var recipientList: [(address: String, amount: UInt64, isSendMax: Bool)] {
    recipients.map { r in
      (address: r.address.trimmingCharacters(in: .whitespacesAndNewlines),
       amount: r.amountValue ?? 0,
       isSendMax: r.isSendMax)
    }
  }

  private var selectedUTXOOutpoints: [(txid: String, vout: UInt32)]? {
    manualUTXOSelection
      ? allUTXOs.filter { selectedUTXOIds.contains($0.id) }.map { (txid: $0.txid, vout: $0.vout) }
      : nil
  }

  /// Apply PSBT creation result to view model state
  private func applyPSBTResult(_ result: BitcoinService.PSBTResult) {
    psbtBase64 = result.base64
    psbtBytes = result.bytes
    totalFee = result.fee
    changeAmount = result.changeAmount
    changeAddress = result.changeAddress
    inputCount = result.inputCount
    if let signerInfo = bitcoinService.psbtSignerInfo(result.bytes) {
      signerStatus = signerInfo.cosignerSignStatus
    }
  }

  /// Build a draft PSBT to populate fee/change details, then navigate to review
  private func buildDraftPSBT() async {
    isProcessing = true
    do {
      let result = try await bitcoinService.createPSBT(
        recipients: recipientList,
        feeRate: feeRateValue,
        utxos: selectedUTXOOutpoints,
        unspendable: frozenOutpoints
      )
      applyPSBTResult(result)
      currentStep = .review
    } catch {
      errorMessage = error.localizedDescription
    }
    isProcessing = false
  }

  func createPSBT() async {
    guard recipientList.allSatisfy({ !$0.address.isEmpty && ($0.amount > 0 || $0.isSendMax) }) else {
      errorMessage = "Invalid recipient or amount"
      return
    }

    // For manual selection, guard against spending a UTXO the user has frozen.
    if let validationError = validateUTXOInputs(outpoints: selectedUTXOOutpoints) {
      errorMessage = validationError
      return
    }

    isProcessing = true
    do {
      let result = try await bitcoinService.createPSBT(
        recipients: recipientList,
        feeRate: feeRateValue,
        utxos: selectedUTXOOutpoints,
        unspendable: frozenOutpoints
      )
      applyPSBTResult(result)
      signaturesCollected = 0
      currentStep = .psbtDisplay
    } catch {
      errorMessage = error.localizedDescription
    }
    isProcessing = false
  }

  // handleSignedPSBT provided by PSBTFlowManaging default implementation

  func finalizeTx() {
    guard finalizedTxBytes.isEmpty else { return }
    do {
      finalizedTxBytes = try bitcoinService.finalizePSBTBytes(psbtBytes)
    } catch {
      errorMessage = error.localizedDescription
    }
  }

  func broadcast() async {
    isProcessing = true
    do {
      let txid = try await bitcoinService.broadcastPSBT(psbtBytes)
      broadcastTxid = txid
    } catch {
      errorMessage = error.localizedDescription
    }
    isProcessing = false
  }

  /// Validate that no frozen UTXOs are in the input set. Returns an error message if any are found, nil otherwise.
  func validateUTXOInputs(outpoints: [(txid: String, vout: UInt32)]?) -> String? {
    guard let outpoints else { return nil }
    let frozenInInputs = outpoints.filter { frozenOutpoints.contains("\($0.txid):\($0.vout)") }
    if !frozenInInputs.isEmpty {
      return "Cannot create transaction: \(frozenInInputs.count) frozen UTXO(s) in inputs"
    }
    return nil
  }

  // MARK: - Saved PSBT

  func defaultPSBTName() -> String {
    let formatter = DateFormatter()
    formatter.dateFormat = "MMM d, yyyy h:mm a"
    return formatter.string(from: Date())
  }

  func savePSBT(name: String, context: ModelContext) {
    guard let walletID = BitcoinService.shared.currentProfile?.id else { return }

    let trimmedName = String(name.prefix(SavedPSBT.maxNameLength))
    let recipientData = encodeRecipients()

    let utxoIdsString = selectedUTXOIds.sorted().joined(separator: ",")
    let outpoints = bitcoinService.psbtInputOutpoints(psbtBytes).joined(separator: ",")

    if let existingId = savedPSBTId {
      let descriptor = FetchDescriptor<SavedPSBT>(predicate: #Predicate { $0.id == existingId })
      if let existing = try? context.fetch(descriptor).first {
        existing.name = trimmedName
        existing.psbtBytes = psbtBytes
        existing.psbtBase64 = psbtBase64
        existing.signaturesCollected = signaturesCollected
        existing.updatedAt = Date()
        existing.recipientsJSON = recipientData
        existing.feeRateSatVb = feeRateSatVb
        existing.totalFee = totalFee
        existing.changeAmount = changeAmount
        existing.changeAddress = changeAddress
        existing.inputCount = inputCount
        existing.manualUTXOSelection = manualUTXOSelection
        existing.selectedUTXOIds = utxoIdsString
        existing.inputOutpoints = outpoints
        do {
          try context.save()
        } catch {
          logger.error("Failed to update saved PSBT: \(error)")
          errorMessage = "Failed to save PSBT: \(error.localizedDescription)"
        }
        return
      }
    }

    let saved = SavedPSBT(
      walletID: walletID,
      name: trimmedName,
      psbtBytes: psbtBytes,
      psbtBase64: psbtBase64,
      signaturesCollected: signaturesCollected,
      requiredSignatures: requiredSignatures,
      recipientsJSON: recipientData,
      feeRateSatVb: feeRateSatVb,
      totalFee: totalFee,
      changeAmount: changeAmount,
      changeAddress: changeAddress,
      inputCount: inputCount,
      manualUTXOSelection: manualUTXOSelection,
      selectedUTXOIds: utxoIdsString,
      inputOutpoints: outpoints
    )
    context.insert(saved)
    do {
      try context.save()
      savedPSBTId = saved.id
    } catch {
      logger.error("Failed to save new PSBT: \(error)")
      errorMessage = "Failed to save PSBT: \(error.localizedDescription)"
    }
  }

  // autoSavePSBT provided by PSBTFlowManaging default implementation

  func loadSavedPSBT(_ saved: SavedPSBT) {
    if let decoded = try? JSONDecoder().decode([SavedRecipient].self, from: saved.recipientsJSON) {
      recipients = decoded.map(Recipient.init(from:))
    }

    feeRateSatVb = saved.feeRateSatVb
    totalFee = saved.totalFee
    changeAmount = saved.changeAmount
    changeAddress = saved.changeAddress
    inputCount = saved.inputCount
    psbtBytes = saved.psbtBytes
    psbtBase64 = saved.psbtBase64
    signaturesCollected = saved.signaturesCollected
    requiredSignatures = saved.requiredSignatures
    manualUTXOSelection = saved.manualUTXOSelection
    if !saved.selectedUTXOIds.isEmpty {
      selectedUTXOIds = Set(saved.selectedUTXOIds.split(separator: ",").map(String.init))
    } else {
      selectedUTXOIds = []
    }
    savedPSBTId = saved.id
    savedPSBTName = saved.name

    // Populate cosigner signing status from PSBT
    if let signerInfo = bitcoinService.psbtSignerInfo(saved.psbtBytes) {
      signaturesCollected = signerInfo.totalSignatures
      signerStatus = signerInfo.cosignerSignStatus
    }

    currentStep = .review
  }

  // deleteSavedPSBT provided by PSBTFlowManaging default implementation

  // MARK: - Import PSBT

  func importPSBT(_ psbtData: Data, source: String, context: ModelContext) {
    do {
      let result = try bitcoinService.validateAndParseImportedPSBT(psbtData, frozenOutpoints: frozenOutpoints)

      recipients = result.recipients.map(Recipient.init(from:))

      feeRateSatVb = result.feeRateSatVb
      totalFee = result.fee
      changeAmount = result.changeAmount
      changeAddress = result.changeAddress
      inputCount = result.inputCount
      psbtBytes = result.psbtBytes
      psbtBase64 = result.psbtBase64
      requiredSignatures = bitcoinService.requiredSignatures
      totalCosigners = bitcoinService.totalCosigners

      // Determine signature status
      if let signerInfo = bitcoinService.psbtSignerInfo(result.psbtBytes) {
        signaturesCollected = signerInfo.totalSignatures
        signerStatus = signerInfo.cosignerSignStatus
      } else {
        signaturesCollected = 0
        signerStatus = []
      }

      // Save immediately
      let importName = "Imported via \(source) \(defaultPSBTName())"
      savePSBT(name: importName, context: context)
      savedPSBTName = importName

      // Navigate to review
      currentStep = .review
    } catch {
      errorMessage = error.localizedDescription
    }
  }

  private func encodeRecipients() -> Data {
    let savedRecipients = recipients.map { r in
      SavedRecipient(
        address: r.address.trimmingCharacters(in: .whitespacesAndNewlines),
        amountSats: r.amountSats,
        isSendMax: r.isSendMax,
        label: r.label
      )
    }
    return (try? JSONEncoder().encode(savedRecipients)) ?? Data()
  }

  func reset() {
    currentStep = .recipients
    recipients = [Recipient()]
    amountInFiat = false
    fiatDisplayAmount.removeAll()
    feeRateSatVb = ""
    recommendedFees = nil
    selectedFeePreset = .medium
    psbtBase64 = ""
    psbtBytes = Data()
    totalFee = 0
    changeAmount = nil
    changeAddress = nil
    inputCount = 0
    signaturesCollected = 0
    signerStatus = []
    broadcastTxid = ""
    finalizedTxBytes = Data()
    errorMessage = nil
    isProcessing = false
    showValidationErrors = false
    showExportQR = false
    showAddressScanner = false
    manualUTXOSelection = false
    selectedUTXOIds.removeAll()
    showUTXOPicker = false
    savedPSBTId = nil
    savedPSBTName = ""
    showSavePSBT = false
    showSavedConfirmation = false
    showLoadPSBT = false
    showImportPSBTQR = false
    showImportPSBTFile = false
  }
}