import type { SupabaseClient } from '@supabase/supabase-js'
import type { Transaction, ReconciliationMethod } from '@/types'
import { eventBus } from '@/lib/events/bus'

// ============================================================
// Types
// ============================================================

/** A posted journal entry line on account 1930 not yet linked to any transaction */
export interface UnlinkedGLLine {
  line_id: string
  journal_entry_id: string
  debit_amount: number
  credit_amount: number
  line_description: string | null
  entry_date: string
  voucher_number: number
  voucher_series: string
  entry_description: string
  source_type: string
}

export interface ReconciliationMatch {
  transaction: Transaction
  glLine: UnlinkedGLLine
  method: ReconciliationMethod
  confidence: number
}

export interface ReconciliationRunResult {
  matches: ReconciliationMatch[]
  applied: number
  errors: number
}

export interface ReconciliationStatus {
  bank_transaction_total: number
  gl_1930_balance: number
  difference: number
  is_reconciled: boolean
  matched_count: number
  unmatched_transaction_count: number
  unmatched_gl_line_count: number
}

export interface ReconciliationOptions {
  dateFrom?: string
  dateTo?: string
  dryRun?: boolean
}

// ============================================================
// In-memory matching: single transaction against GL line pool
// ============================================================

/**
 * Try to reconcile a single transaction against a pool of unlinked GL lines.
 * Returns the best match or null. Purely in-memory, no DB calls.
 *
 * Only reconciles SEK transactions.
 */
export function tryReconcileTransaction(
  transaction: Transaction,
  glLines: UnlinkedGLLine[]
): ReconciliationMatch | null {
  if (transaction.currency !== 'SEK') return null
  if (glLines.length === 0) return null

  const txAmount = transaction.amount
  const txDate = transaction.date
  const txDescription = (transaction.description || '').toLowerCase()
  const txReference = (transaction.reference || '').toLowerCase()

  let bestMatch: ReconciliationMatch | null = null

  for (const line of glLines) {
    const lineAmount = getDirectionalAmount(line)
    if (!isDirectionCompatible(txAmount, line)) continue

    const amountMatches = Math.abs(Math.abs(txAmount) - Math.abs(lineAmount)) < 0.005
    const fuzzyAmountMatches = Math.abs(Math.abs(txAmount) - Math.abs(lineAmount)) <= 0.01
    const exactDateMatch = txDate === line.entry_date
    const dateWithinRange = isDateWithinRange(txDate, line.entry_date, 3)
    const referenceMatch = hasReferenceMatch(txDescription, txReference, line)

    let method: ReconciliationMethod | null = null
    let confidence = 0

    // Pass 1: Exact amount + exact date
    if (amountMatches && exactDateMatch) {
      method = 'auto_exact'
      confidence = 0.95
    }
    // Pass 2: Exact amount + reference match
    else if (amountMatches && referenceMatch) {
      method = 'auto_reference'
      confidence = 0.90
    }
    // Pass 3: Exact amount + date within ±3 days
    else if (amountMatches && dateWithinRange) {
      method = 'auto_date_range'
      confidence = 0.85
    }
    // Pass 4: Fuzzy amount (±0.01) + exact date
    else if (fuzzyAmountMatches && exactDateMatch) {
      method = 'auto_fuzzy'
      confidence = 0.75
    }

    if (method && confidence > (bestMatch?.confidence ?? 0)) {
      bestMatch = { transaction, glLine: line, method, confidence }
    }
  }

  return bestMatch
}

// ============================================================
// Batch reconciliation
// ============================================================

/**
 * Run auto-reconciliation for all unmatched transactions.
 * Fetches data, runs 4-pass matching, optionally applies matches.
 */
export async function runReconciliation(
  supabase: SupabaseClient,
  userId: string,
  options: ReconciliationOptions = {}
): Promise<ReconciliationRunResult> {
  const { dateFrom, dateTo, dryRun = false } = options

  // Fetch unlinked GL lines via RPC
  const glLines = await fetchUnlinkedGLLines(supabase, userId, dateFrom, dateTo)

  // Fetch unmatched transactions
  let query = supabase
    .from('transactions')
    .select('*')
    .eq('user_id', userId)
    .is('journal_entry_id', null)
    .eq('currency', 'SEK')

  if (dateFrom) query = query.gte('date', dateFrom)
  if (dateTo) query = query.lte('date', dateTo)

  const { data: transactions } = await query

  if (!transactions || transactions.length === 0 || glLines.length === 0) {
    return { matches: [], applied: 0, errors: 0 }
  }

  // Run greedy matching, highest confidence first
  const matches = greedyMatch(transactions as Transaction[], glLines)

  if (dryRun) {
    return { matches, applied: 0, errors: 0 }
  }

  // Apply matches
  let applied = 0
  let errors = 0

  for (const match of matches) {
    try {
      const { error } = await supabase
        .from('transactions')
        .update({
          journal_entry_id: match.glLine.journal_entry_id,
          reconciliation_method: match.method,
          is_business: true,
        })
        .eq('id', match.transaction.id)
        .eq('user_id', userId)

      if (error) {
        errors++
      } else {
        applied++
        try {
          eventBus.emit({
            type: 'transaction.reconciled',
            payload: {
              transaction: match.transaction,
              journalEntryId: match.glLine.journal_entry_id,
              method: match.method,
              userId,
            },
          })
        } catch {
          // Event emission is non-critical
        }
      }
    } catch {
      errors++
    }
  }

  return { matches, applied, errors }
}

// ============================================================
// Reconciliation status
// ============================================================

/**
 * Compare bank transaction totals vs GL 1930 balance.
 */
export async function getReconciliationStatus(
  supabase: SupabaseClient,
  userId: string,
  dateFrom?: string,
  dateTo?: string
): Promise<ReconciliationStatus> {
  // Get all transactions in range
  let txQuery = supabase
    .from('transactions')
    .select('amount, journal_entry_id, reconciliation_method')
    .eq('user_id', userId)
    .eq('currency', 'SEK')

  if (dateFrom) txQuery = txQuery.gte('date', dateFrom)
  if (dateTo) txQuery = txQuery.lte('date', dateTo)

  const { data: transactions } = await txQuery

  // Get GL 1930 lines (all, not just unlinked)
  let glQuery = supabase
    .from('journal_entry_lines')
    .select('debit_amount, credit_amount, journal_entries!inner(user_id, entry_date, status)')
    .eq('account_number', '1930')
    .eq('journal_entries.user_id', userId)
    .eq('journal_entries.status', 'posted')

  if (dateFrom) glQuery = glQuery.gte('journal_entries.entry_date', dateFrom)
  if (dateTo) glQuery = glQuery.lte('journal_entries.entry_date', dateTo)

  const { data: glLines } = await glQuery

  // Calculate totals
  const bankTotal = (transactions || []).reduce(
    (sum, tx) => sum + (Number(tx.amount) || 0),
    0
  )

  const glBalance = (glLines || []).reduce(
    (sum, line) => sum + (Number(line.debit_amount) || 0) - (Number(line.credit_amount) || 0),
    0
  )

  const matchedCount = (transactions || []).filter(
    (tx) => tx.journal_entry_id !== null
  ).length

  const unmatchedTransactionCount = (transactions || []).filter(
    (tx) => tx.journal_entry_id === null
  ).length

  // Unlinked GL lines count
  const unlinkedLines = await fetchUnlinkedGLLines(supabase, userId, dateFrom, dateTo)

  const difference = Math.round((bankTotal - glBalance) * 100) / 100

  return {
    bank_transaction_total: Math.round(bankTotal * 100) / 100,
    gl_1930_balance: Math.round(glBalance * 100) / 100,
    difference,
    is_reconciled: Math.abs(difference) < 0.01,
    matched_count: matchedCount,
    unmatched_transaction_count: unmatchedTransactionCount,
    unmatched_gl_line_count: unlinkedLines.length,
  }
}

// ============================================================
// Manual link/unlink
// ============================================================

/**
 * Manually link a transaction to an existing journal entry.
 * Validates that the journal entry has a 1930 line and amounts are directionally compatible.
 */
export async function manualLink(
  supabase: SupabaseClient,
  userId: string,
  transactionId: string,
  journalEntryId: string
): Promise<{ success: boolean; error?: string }> {
  // Fetch transaction
  const { data: tx, error: txError } = await supabase
    .from('transactions')
    .select('*')
    .eq('id', transactionId)
    .eq('user_id', userId)
    .single()

  if (txError || !tx) {
    return { success: false, error: 'Transaction not found' }
  }

  if (tx.journal_entry_id) {
    return { success: false, error: 'Transaction is already linked to a journal entry' }
  }

  // Fetch journal entry + verify it has a 1930 line
  const { data: entry, error: entryError } = await supabase
    .from('journal_entries')
    .select('id, user_id, status')
    .eq('id', journalEntryId)
    .eq('user_id', userId)
    .single()

  if (entryError || !entry) {
    return { success: false, error: 'Journal entry not found' }
  }

  if (entry.status !== 'posted') {
    return { success: false, error: 'Journal entry is not posted' }
  }

  // Check for 1930 line
  const { data: lines } = await supabase
    .from('journal_entry_lines')
    .select('debit_amount, credit_amount')
    .eq('journal_entry_id', journalEntryId)
    .eq('account_number', '1930')

  if (!lines || lines.length === 0) {
    return { success: false, error: 'Journal entry has no line on account 1930' }
  }

  // Check that no other transaction is already linked to this entry
  const { data: existingLink } = await supabase
    .from('transactions')
    .select('id')
    .eq('journal_entry_id', journalEntryId)
    .eq('user_id', userId)
    .single()

  if (existingLink) {
    return { success: false, error: 'Another transaction is already linked to this journal entry' }
  }

  // Apply link
  const { error: updateError } = await supabase
    .from('transactions')
    .update({
      journal_entry_id: journalEntryId,
      reconciliation_method: 'manual' as ReconciliationMethod,
      is_business: true,
    })
    .eq('id', transactionId)
    .eq('user_id', userId)

  if (updateError) {
    return { success: false, error: 'Failed to link transaction' }
  }

  try {
    eventBus.emit({
      type: 'transaction.reconciled',
      payload: {
        transaction: tx as Transaction,
        journalEntryId,
        method: 'manual' as ReconciliationMethod,
        userId,
      },
    })
  } catch {
    // Non-critical
  }

  return { success: true }
}

/**
 * Remove a reconciliation link.
 * Only allowed when reconciliation_method IS NOT NULL (prevents unlinking categorization-created entries).
 */
export async function unlinkReconciliation(
  supabase: SupabaseClient,
  userId: string,
  transactionId: string
): Promise<{ success: boolean; error?: string }> {
  // Fetch transaction
  const { data: tx, error: txError } = await supabase
    .from('transactions')
    .select('id, journal_entry_id, reconciliation_method')
    .eq('id', transactionId)
    .eq('user_id', userId)
    .single()

  if (txError || !tx) {
    return { success: false, error: 'Transaction not found' }
  }

  if (!tx.journal_entry_id) {
    return { success: false, error: 'Transaction is not linked to any journal entry' }
  }

  if (!tx.reconciliation_method) {
    return { success: false, error: 'Cannot unlink a categorization-created entry. Use storno to reverse it instead.' }
  }

  const { error: updateError } = await supabase
    .from('transactions')
    .update({
      journal_entry_id: null,
      reconciliation_method: null,
      is_business: null,
    })
    .eq('id', transactionId)
    .eq('user_id', userId)

  if (updateError) {
    return { success: false, error: 'Failed to unlink transaction' }
  }

  return { success: true }
}

// ============================================================
// Helpers
// ============================================================

/** Fetch unlinked 1930 GL lines via the RPC function */
export async function fetchUnlinkedGLLines(
  supabase: SupabaseClient,
  userId: string,
  dateFrom?: string,
  dateTo?: string
): Promise<UnlinkedGLLine[]> {
  const { data, error } = await supabase.rpc('get_unlinked_1930_lines', {
    p_user_id: userId,
    p_date_from: dateFrom || null,
    p_date_to: dateTo || null,
  })

  if (error || !data) return []
  return data as UnlinkedGLLine[]
}

/** Get the net amount from a GL line (positive for debit, negative for credit) */
function getDirectionalAmount(line: UnlinkedGLLine): number {
  if (line.debit_amount > 0) return line.debit_amount
  if (line.credit_amount > 0) return -line.credit_amount
  return 0
}

/**
 * Check direction compatibility:
 * - Income (tx.amount > 0) matches debit on 1930 (money coming in to bank)
 * - Expense (tx.amount < 0) matches credit on 1930 (money going out of bank)
 */
function isDirectionCompatible(txAmount: number, line: UnlinkedGLLine): boolean {
  if (txAmount > 0 && line.debit_amount > 0) return true
  if (txAmount < 0 && line.credit_amount > 0) return true
  return false
}

/** Check if two dates are within ±dayRange of each other */
function isDateWithinRange(date1: string, date2: string, dayRange: number): boolean {
  const d1 = new Date(date1)
  const d2 = new Date(date2)
  const diffMs = Math.abs(d1.getTime() - d2.getTime())
  const diffDays = diffMs / (1000 * 60 * 60 * 24)
  return diffDays <= dayRange
}

/** Check if transaction description/reference matches the GL line description */
function hasReferenceMatch(
  txDescription: string,
  txReference: string,
  line: UnlinkedGLLine
): boolean {
  const lineDesc = (line.line_description || '').toLowerCase()
  const entryDesc = (line.entry_description || '').toLowerCase()

  if (!txReference && !txDescription) return false

  // Check OCR/reference number match
  if (txReference && txReference.length >= 4) {
    if (lineDesc.includes(txReference) || entryDesc.includes(txReference)) return true
  }

  // Check description overlap (at least 8 chars matching substring)
  if (txDescription && txDescription.length >= 8) {
    if (lineDesc.includes(txDescription) || entryDesc.includes(txDescription)) return true
    if (txDescription.includes(lineDesc) && lineDesc.length >= 8) return true
    if (txDescription.includes(entryDesc) && entryDesc.length >= 8) return true
  }

  return false
}

/**
 * Greedy matching: run 4-pass matching, each pass at a specific confidence level.
 * Track used GL lines and transactions to prevent double-matching.
 */
function greedyMatch(
  transactions: Transaction[],
  glLines: UnlinkedGLLine[]
): ReconciliationMatch[] {
  const usedTransactions = new Set<string>()
  const usedGLLines = new Set<string>()
  const allMatches: ReconciliationMatch[] = []

  // Collect all candidate matches with confidence
  const candidates: ReconciliationMatch[] = []

  for (const tx of transactions) {
    if (tx.currency !== 'SEK') continue

    for (const line of glLines) {
      const match = tryReconcileTransaction(tx, [line])
      if (match) {
        candidates.push(match)
      }
    }
  }

  // Sort by confidence descending, then by date proximity
  candidates.sort((a, b) => {
    if (b.confidence !== a.confidence) return b.confidence - a.confidence
    // Prefer closer dates
    const dateDistA = Math.abs(
      new Date(a.transaction.date).getTime() - new Date(a.glLine.entry_date).getTime()
    )
    const dateDistB = Math.abs(
      new Date(b.transaction.date).getTime() - new Date(b.glLine.entry_date).getTime()
    )
    return dateDistA - dateDistB
  })

  // Greedily assign matches
  for (const candidate of candidates) {
    const txId = candidate.transaction.id
    const lineId = candidate.glLine.line_id

    if (usedTransactions.has(txId) || usedGLLines.has(lineId)) continue

    usedTransactions.add(txId)
    usedGLLines.add(lineId)
    allMatches.push(candidate)
  }

  return allMatches
}