import { createClient } from '@/lib/supabase/server'
import { NextResponse } from 'next/server'
import { eventBus } from '@/lib/events'
import { ensureInitialized } from '@/lib/init'
import { buildMappingResultFromCategory } from '@/lib/bookkeeping/category-mapping'
import { getTemplateById, buildMappingResultFromTemplate, validateTemplateForEntity } from '@/lib/bookkeeping/booking-templates'
import { createTransactionJournalEntry } from '@/lib/bookkeeping/transaction-entries'
import { saveUserMappingRule } from '@/lib/bookkeeping/mapping-engine'
import { validateBody } from '@/lib/api/validate'
import { CategorizeTransactionSchema } from '@/lib/api/schemas'
import type { Transaction, TransactionCategory, EntityType } from '@/types'

ensureInitialized()

/**
 * Ensure a fiscal period exists for the given date, create one if needed
 */
async function ensureFiscalPeriod(
  supabase: Awaited<ReturnType<typeof createClient>>,
  userId: string,
  date: string,
  fiscalYearStartMonth: number = 1
): Promise<boolean> {
  // Check if a fiscal period already covers this date
  const { data: existing } = await supabase
    .from('fiscal_periods')
    .select('id')
    .eq('user_id', userId)
    .lte('period_start', date)
    .gte('period_end', date)
    .eq('is_closed', false)
    .limit(1)

  if (existing && existing.length > 0) {
    return true
  }

  // Compute fiscal year period based on start month
  const txDate = new Date(date)
  const txMonth = txDate.getMonth() + 1
  const txYear = txDate.getFullYear()

  let periodStartYear: number
  if (fiscalYearStartMonth === 1) {
    periodStartYear = txYear
  } else if (txMonth >= fiscalYearStartMonth) {
    periodStartYear = txYear
  } else {
    periodStartYear = txYear - 1
  }

  const startMonth = String(fiscalYearStartMonth).padStart(2, '0')
  const periodStart = `${periodStartYear}-${startMonth}-01`

  // Period ends the day before the next fiscal year starts
  const endYear = fiscalYearStartMonth === 1 ? periodStartYear : periodStartYear + 1
  const endMonth = fiscalYearStartMonth === 1 ? 12 : fiscalYearStartMonth - 1
  const lastDay = new Date(endYear, endMonth, 0).getDate()
  const periodEnd = `${endYear}-${String(endMonth).padStart(2, '0')}-${String(lastDay).padStart(2, '0')}`

  const periodName = fiscalYearStartMonth === 1
    ? `Räkenskapsår ${periodStartYear}`
    : `Räkenskapsår ${periodStartYear}/${endYear}`

  const { error } = await supabase
    .from('fiscal_periods')
    .upsert({
      user_id: userId,
      name: periodName,
      period_start: periodStart,
      period_end: periodEnd,
    }, {
      onConflict: 'user_id,period_start,period_end',
    })

  if (error) {
    console.error('Failed to create fiscal period:', error)
    return false
  }

  return true
}

export async function POST(
  request: Request,
  { params }: { params: Promise<{ id: string }> }
) {
  const supabase = await createClient()
  const { id } = await params

  const { data: { user } } = await supabase.auth.getUser()

  if (!user) {
    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
  }

  // Parse and validate request body
  const validation = await validateBody(request, CategorizeTransactionSchema)
  if (!validation.success) return validation.response
  const body = validation.data
  const { is_business, category } = body

  // Fetch the transaction (validates ownership)
  const { data: transaction, error: fetchError } = await supabase
    .from('transactions')
    .select('*')
    .eq('id', id)
    .eq('user_id', user.id)
    .single()

  if (fetchError || !transaction) {
    return NextResponse.json({ error: 'Transaction not found' }, { status: 404 })
  }

  // If already has a journal entry, just update category and is_business (skip journal entry creation)
  if (transaction.journal_entry_id) {
    const finalCat: TransactionCategory = is_business
      ? (category || 'uncategorized')
      : 'private'

    const { error: updateErr } = await supabase
      .from('transactions')
      .update({
        is_business,
        category: finalCat,
      })
      .eq('id', id)

    if (updateErr) {
      return NextResponse.json(
        { error: 'Failed to update transaction' },
        { status: 500 }
      )
    }

    return NextResponse.json({
      success: true,
      journal_entry_created: false,
      journal_entry_id: transaction.journal_entry_id,
      journal_entry_error: null,
      category: finalCat,
      already_had_journal_entry: true,
    })
  }

  // Fetch company settings to get entity type and fiscal year start
  const { data: settings } = await supabase
    .from('company_settings')
    .select('entity_type, fiscal_year_start_month')
    .eq('user_id', user.id)
    .single()

  const entityType: EntityType = (settings?.entity_type as EntityType) || 'enskild_firma'
  const fiscalYearStartMonth: number = settings?.fiscal_year_start_month ?? 1

  // Determine the category to use
  let finalCategory: TransactionCategory
  if (body.template_id) {
    const template = getTemplateById(body.template_id)
    if (template) {
      // Hard entity guard — reject templates that don't match the user's entity type
      const entityValidation = validateTemplateForEntity(template, entityType)
      if (!entityValidation.valid) {
        return NextResponse.json({ error: entityValidation.error }, { status: 400 })
      }

      finalCategory = is_business ? template.fallback_category : 'private'
      console.log(`[categorize] tx=${id} using template="${body.template_id}" (${template.name_sv}) → category=${finalCategory}, debit=${template.debit_account}, credit=${template.credit_account}, vat=${template.vat_treatment}`)
    } else {
      return NextResponse.json({ error: 'Invalid template_id' }, { status: 400 })
    }
  } else {
    finalCategory = is_business ? (category || 'uncategorized') : 'private'
    console.log(`[categorize] tx=${id} using category="${finalCategory}" vat=${body.vat_treatment || 'default'} account_override=${body.account_override || 'none'}`)
  }

  if (body.inbox_item_id) {
    console.log(`[categorize] tx=${id} will confirm inbox item=${body.inbox_item_id} and link document`)
  }

  // Build mapping result from template or category
  let mappingResult
  if (body.template_id) {
    const template = getTemplateById(body.template_id)!
    mappingResult = buildMappingResultFromTemplate(
      template,
      transaction as Transaction,
      entityType
    )
  } else {
    mappingResult = buildMappingResultFromCategory(
      finalCategory,
      transaction as Transaction,
      is_business,
      entityType,
      body.vat_treatment
    )
  }

  console.log(`[categorize] tx=${id} mapping result:`, {
    debit: mappingResult.debit_account,
    credit: mappingResult.credit_account,
    vatLines: mappingResult.vat_lines.map((v) => `${v.account_number} debit=${v.debit_amount} credit=${v.credit_amount}`),
  })

  // Apply account override if provided (only for business transactions)
  if (is_business && body.account_override) {
    // Validate the account exists in the user's chart of accounts
    const { data: accountExists } = await supabase
      .from('chart_of_accounts')
      .select('account_number, account_class')
      .eq('user_id', user.id)
      .eq('account_number', body.account_override)
      .single()

    if (!accountExists) {
      return NextResponse.json(
        { error: 'Invalid account number' },
        { status: 400 }
      )
    }

    // Apply override: expenses override debit account, income overrides credit account
    if (transaction.amount < 0) {
      mappingResult.debit_account = body.account_override
    } else {
      mappingResult.credit_account = body.account_override
    }

    // If override account is a liability/equity account (class 2), clear VAT lines
    if (accountExists.account_class === 2) {
      mappingResult.vat_lines = []
    }
  }

  // Validate that both accounts are present before proceeding
  if (!mappingResult.debit_account || !mappingResult.credit_account) {
    return NextResponse.json(
      { error: 'Invalid account mapping: debit and credit accounts are required' },
      { status: 400 }
    )
  }

  // Ensure fiscal period exists for the transaction date
  await ensureFiscalPeriod(supabase, user.id, transaction.date, fiscalYearStartMonth)

  // Try to create journal entry
  let journalEntryCreated = false
  let journalEntryId: string | null = null
  let journalEntryError: string | null = null

  try {
    const journalEntry = await createTransactionJournalEntry(
      supabase,
      user.id,
      transaction as Transaction,
      mappingResult
    )

    if (journalEntry) {
      journalEntryCreated = true
      journalEntryId = journalEntry.id
    }
  } catch (err) {
    console.error('Failed to create journal entry:', err)
    journalEntryError = err instanceof Error ? err.message : 'Unknown error'
    // Continue - we still want to save the categorization
  }

  // Save mapping rule for future auto-categorization (only for business expenses with merchant)
  if (is_business && transaction.merchant_name) {
    try {
      await saveUserMappingRule(
        supabase,
        user.id,
        transaction.merchant_name,
        mappingResult.debit_account,
        mappingResult.credit_account,
        !is_business,
        body.user_description,
        body.template_id
      )
    } catch (err) {
      console.error('Failed to save mapping rule:', err)
      // Non-critical, continue
    }
  }

  // Link receipt document to journal entry if both exist
  if (journalEntryId && transaction.receipt_id) {
    try {
      const { data: receipt } = await supabase
        .from('receipts')
        .select('document_id')
        .eq('id', transaction.receipt_id)
        .single()

      if (receipt?.document_id) {
        await supabase
          .from('document_attachments')
          .update({ journal_entry_id: journalEntryId })
          .eq('id', receipt.document_id)
          .eq('user_id', user.id)
      }
    } catch (linkErr) {
      console.error('[categorize] Failed to link receipt document:', linkErr)
    }
  }

  // Confirm matched inbox item and link its document to the journal entry
  if (body.inbox_item_id) {
    try {
      await supabase
        .from('invoice_inbox_items')
        .update({ status: 'confirmed' })
        .eq('id', body.inbox_item_id)
        .eq('user_id', user.id)

      // Link inbox item's document to the journal entry
      if (journalEntryId) {
        const { data: inboxItem } = await supabase
          .from('invoice_inbox_items')
          .select('document_id')
          .eq('id', body.inbox_item_id)
          .single()

        if (inboxItem?.document_id) {
          await supabase
            .from('document_attachments')
            .update({ journal_entry_id: journalEntryId })
            .eq('id', inboxItem.document_id)
            .eq('user_id', user.id)
        }
      }
    } catch (inboxErr) {
      console.error('[categorize] Failed to update inbox item:', inboxErr)
    }
  }

  // Update the transaction
  const { error: updateError } = await supabase
    .from('transactions')
    .update({
      is_business,
      category: finalCategory,
      journal_entry_id: journalEntryId,
    })
    .eq('id', id)

  if (updateError) {
    console.error('Failed to update transaction:', updateError)
    return NextResponse.json(
      { error: 'Failed to update transaction' },
      { status: 500 }
    )
  }

  await eventBus.emit({
    type: 'transaction.categorized',
    payload: {
      transaction: transaction as Transaction,
      account: mappingResult.debit_account,
      taxCode: mappingResult.vat_lines[0]?.account_number || '',
      userId: user.id,
    },
  })

  return NextResponse.json({
    success: true,
    journal_entry_created: journalEntryCreated,
    journal_entry_id: journalEntryId,
    journal_entry_error: journalEntryError,
    category: finalCategory,
  })
}