package service

import (
	"errors"
	"sync"
	"testing"

	"github.com/stretchr/testify/require"
	"gorm.io/gorm"
	"wails-app/internal/dao"
	"wails-app/internal/global"
)

func TestPaymentRejectsNegativeAndInsufficientAmounts(t *testing.T) {
	svc := setupPaymentServiceTest(t)

	for _, amounts := range [][2]float64{{-1, 0}, {1, -1}, {-1, -1}} {
		_, _, err := svc.ValidatePayment(nil, PaymentCash, EntryCounter, amounts[0], amounts[1])
		require.Error(t, err)
	}

	_, _, err := svc.ValidatePayment(nil, PaymentCash, EntryCounter, 10, 0)
	require.Error(t, err)

	record := &dao.VehicleRecord{PaymentStatus: "unpaid"}
	require.NoError(t, global.GVA_DB.Create(record).Error)
	_, err = svc.ProcessPayment(record.ID, PaymentCash, -1, 0, 1)
	require.Error(t, err)

	var paymentCount int64
	require.NoError(t, global.GVA_DB.Model(&dao.PaymentRecord{}).Where("record_id = ?", record.ID).Count(&paymentCount).Error)
	require.Zero(t, paymentCount)
}

func TestZeroAmountPaymentIsAllowedForZeroFeeSettlement(t *testing.T) {
	svc := setupPaymentServiceTest(t)

	_, paidAmount, err := svc.ValidatePayment(nil, PaymentPOS, EntryCounter, 0, 999)
	require.NoError(t, err)
	require.Zero(t, paidAmount)

	record := &dao.VehicleRecord{PaymentStatus: "unpaid"}
	require.NoError(t, global.GVA_DB.Create(record).Error)
	payment, err := svc.ProcessPayment(record.ID, PaymentCash, 0, 0, 1)
	require.NoError(t, err)
	require.NotNil(t, payment)
	require.Zero(t, payment.Amount)
	require.Zero(t, payment.PaidAmount)
	require.Zero(t, payment.ChangeAmount)

	var persisted dao.VehicleRecord
	require.NoError(t, global.GVA_DB.First(&persisted, record.ID).Error)
	require.Equal(t, "paid", persisted.PaymentStatus)
}

func TestPaymentRejectsDuplicateSettlement(t *testing.T) {
	svc := setupPaymentServiceTest(t)
	record := &dao.VehicleRecord{PaymentStatus: "unpaid"}
	require.NoError(t, global.GVA_DB.Create(record).Error)

	_, err := svc.ProcessPayment(record.ID, PaymentCash, 10, 10, 1)
	require.NoError(t, err)
	_, err = svc.ProcessPayment(record.ID, PaymentCash, 10, 10, 1)
	require.ErrorIs(t, err, ErrPaymentAlreadyProcessed)

	var paymentCount int64
	require.NoError(t, global.GVA_DB.Model(&dao.PaymentRecord{}).Where("record_id = ?", record.ID).Count(&paymentCount).Error)
	require.EqualValues(t, 1, paymentCount)
}

func TestPaymentConcurrentSettlementHasSingleWinner(t *testing.T) {
	svc := setupPaymentServiceTest(t)
	record := &dao.VehicleRecord{PaymentStatus: "unpaid"}
	require.NoError(t, global.GVA_DB.Create(record).Error)

	const attempts = 8
	start := make(chan struct{})
	results := make(chan error, attempts)
	var wg sync.WaitGroup
	for i := 0; i < attempts; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			<-start
			_, err := svc.ProcessPayment(record.ID, PaymentCash, 0, 0, 1)
			results <- err
		}()
	}
	close(start)
	wg.Wait()
	close(results)

	successes := 0
	for err := range results {
		if err == nil {
			successes++
		}
	}
	require.Equal(t, 1, successes)

	var paymentCount int64
	require.NoError(t, global.GVA_DB.Model(&dao.PaymentRecord{}).Where("record_id = ?", record.ID).Count(&paymentCount).Error)
	require.EqualValues(t, 1, paymentCount)
}

func TestPaymentTransactionRollbackLeavesNoPartialState(t *testing.T) {
	svc := setupPaymentServiceTest(t)
	record := &dao.VehicleRecord{PaymentStatus: "unpaid"}
	require.NoError(t, global.GVA_DB.Create(record).Error)
	rollbackErr := errors.New("force rollback")

	err := global.GVA_DB.Transaction(func(tx *gorm.DB) error {
		if _, err := svc.ProcessPaymentTxAtEntry(tx, record.ID, EntryCounter, PaymentCash, 10, 10, 1); err != nil {
			return err
		}
		return rollbackErr
	})
	require.ErrorIs(t, err, rollbackErr)

	var persisted dao.VehicleRecord
	require.NoError(t, global.GVA_DB.First(&persisted, record.ID).Error)
	require.Equal(t, "unpaid", persisted.PaymentStatus)
	var paymentCount int64
	require.NoError(t, global.GVA_DB.Model(&dao.PaymentRecord{}).Where("record_id = ?", record.ID).Count(&paymentCount).Error)
	require.Zero(t, paymentCount)
}

func TestPaymentMissingVehicleRollsBackCreatedRecord(t *testing.T) {
	svc := setupPaymentServiceTest(t)

	_, err := svc.ProcessPayment(999999, PaymentCash, 0, 0, 1)
	require.ErrorIs(t, err, ErrVehicleRecordNotFound)

	var paymentCount int64
	require.NoError(t, global.GVA_DB.Model(&dao.PaymentRecord{}).Count(&paymentCount).Error)
	require.Zero(t, paymentCount)
}