package service

import (
	"context"
	"sort"
	"testing"
	"time"

	"gorm.io/gorm"

	"github.com/kennethcheng/fuellog-api/internal/model"
)

// fakeVehicleRepo / fakeRefuelRepo 是用于单测的 in-memory 假实现,
// 不接 SQLite,直接塞到 service 的接口里。
type fakeVehicleRepo struct{ v *model.Vehicle }

func (f *fakeVehicleRepo) Create(context.Context, *model.Vehicle) error { return nil }
func (f *fakeVehicleRepo) Get(_ context.Context, id uint64) (*model.Vehicle, error) {
	if f.v != nil && f.v.ID == id {
		return f.v, nil
	}
	return nil, errNotFound
}
func (f *fakeVehicleRepo) List(context.Context) ([]model.Vehicle, error) { return nil, nil }
func (f *fakeVehicleRepo) Update(context.Context, *model.Vehicle) error   { return nil }
func (f *fakeVehicleRepo) Delete(context.Context, uint64) error          { return nil }
func (f *fakeVehicleRepo) ClearDefault(context.Context, *gorm.DB) error  { return nil }
func (f *fakeVehicleRepo) SetDefault(context.Context, *gorm.DB, uint64) error { return nil }

// fakeRefuelRepo:用切片装记录,支持 ListByVehicle(忽略时间窗,业务测试够用)。
type fakeRefuelRepo struct{ records []model.RefuelRecord }

func (f *fakeRefuelRepo) Create(context.Context, *model.RefuelRecord) error { return nil }
func (f *fakeRefuelRepo) Get(_ context.Context, id uint64) (*model.RefuelRecord, error) {
	for i := range f.records {
		if f.records[i].ID == id {
			return &f.records[i], nil
		}
	}
	return nil, errNotFound
}
func (f *fakeRefuelRepo) Update(context.Context, *model.RefuelRecord) error { return nil }
func (f *fakeRefuelRepo) Delete(context.Context, uint64) error             { return nil }
func (f *fakeRefuelRepo) ListByVehicle(_ context.Context, vehicleID uint64, _, _ *time.Time) ([]model.RefuelRecord, error) {
	out := make([]model.RefuelRecord, 0)
	for _, r := range f.records {
		if r.VehicleID == vehicleID {
			out = append(out, r)
		}
	}
	// 与真 repo 一致:按 refuel_time DESC,ID DESC
	sort.Slice(out, func(i, j int) bool {
		if out[i].RefuelTime.Equal(out[j].RefuelTime) {
			return out[i].ID > out[j].ID
		}
		return out[i].RefuelTime.After(out[j].RefuelTime)
	})
	return out, nil
}
func (f *fakeRefuelRepo) PrevFullRefuel(context.Context, uint64, time.Time) (*model.RefuelRecord, error) {
	return nil, errNotFound
}

var errNotFound = sentinel("NOT_FOUND")

type sentinel string

func (s sentinel) Error() string { return string(s) }

func newRefuelSvc(records []model.RefuelRecord) *refuelService {
	v := &model.Vehicle{ID: 1, Name: "test", FuelType: "gasoline"}
	return &refuelService{
		recRepo:     &fakeRefuelRepo{records: records},
		vehicleRepo: &fakeVehicleRepo{v: v},
	}
}

func TestStatistics_TwoConsecutiveFull(t *testing.T) {
	t1 := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
	t2 := time.Date(2025, 1, 10, 0, 0, 0, 0, time.UTC)
	recs := []model.RefuelRecord{
		{ID: 1, VehicleID: 1, RefuelTime: t1, Odometer: 10000, Liters: 40, PricePerLiter: 8.0, TotalAmount: 320, IsFull: true},
		{ID: 2, VehicleID: 1, RefuelTime: t2, Odometer: 10500, Liters: 40, PricePerLiter: 8.0, TotalAmount: 320, IsFull: true},
	}
	svc := newRefuelSvc(recs)
	stats, err := svc.Statistics(context.Background(), 1)
	if err != nil {
		t.Fatal(err)
	}
	if stats.TotalRecords != 2 {
		t.Errorf("TotalRecords = %d, want 2", stats.TotalRecords)
	}
	if !floatNear(stats.TotalLiters, 80) {
		t.Errorf("TotalLiters = %v, want 80", stats.TotalLiters)
	}
	if !floatNear(stats.TotalAmount, 640) {
		t.Errorf("TotalAmount = %v, want 640", stats.TotalAmount)
	}
	if !floatNear(stats.AvgPrice, 8.0) {
		t.Errorf("AvgPrice = %v, want 8.0", stats.AvgPrice)
	}
	// mileage = 500km, liters = 40, 40/500*100 = 8.0 L/100km
	if !floatNear(stats.AvgConsumption, 8.0) {
		t.Errorf("AvgConsumption = %v, want 8.0 (plan example)", stats.AvgConsumption)
	}
	// cost = 320/500 = 0.64
	if !floatNear(stats.CostPerKm, 0.64) {
		t.Errorf("CostPerKm = %v, want 0.64", stats.CostPerKm)
	}
}

func TestStatistics_HalfTankDoesNotPollute(t *testing.T) {
	t1 := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
	t2 := time.Date(2025, 1, 10, 0, 0, 0, 0, time.UTC)
	t3 := time.Date(2025, 1, 15, 0, 0, 0, 0, time.UTC)
	recs := []model.RefuelRecord{
		{ID: 1, VehicleID: 1, RefuelTime: t1, Odometer: 10000, Liters: 40, TotalAmount: 320, PricePerLiter: 8.0, IsFull: true},
		{ID: 2, VehicleID: 1, RefuelTime: t2, Odometer: 10500, Liters: 40, TotalAmount: 320, PricePerLiter: 8.0, IsFull: true},
		{ID: 3, VehicleID: 1, RefuelTime: t3, Odometer: 10600, Liters: 10, TotalAmount: 80, PricePerLiter: 8.0, IsFull: false}, // 半箱油
	}
	svc := newRefuelSvc(recs)
	stats, err := svc.Statistics(context.Background(), 1)
	if err != nil {
		t.Fatal(err)
	}
	if stats.TotalRecords != 3 {
		t.Errorf("TotalRecords = %d, want 3", stats.TotalRecords)
	}
	if !floatNear(stats.TotalLiters, 90) {
		t.Errorf("TotalLiters = %v, want 90 (40+40+10)", stats.TotalLiters)
	}
	// 关键断言:半箱油不污染油耗采样,仍应是 8.0(只对 #1 → #2 计算)
	if !floatNear(stats.AvgConsumption, 8.0) {
		t.Errorf("AvgConsumption = %v, want 8.0 (half-tank must be excluded)", stats.AvgConsumption)
	}
	// avg price 全部三条:8.0, 8.0, 8.0 -> 8.0
	if !floatNear(stats.AvgPrice, 8.0) {
		t.Errorf("AvgPrice = %v, want 8.0", stats.AvgPrice)
	}
}

func TestStatistics_OnlyHalfTanks(t *testing.T) {
	// 全是半箱油,标准油耗应为 0(没有 is_full 序列)
	t1 := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
	t2 := time.Date(2025, 1, 5, 0, 0, 0, 0, time.UTC)
	recs := []model.RefuelRecord{
		{ID: 1, VehicleID: 1, RefuelTime: t1, Odometer: 10000, Liters: 20, TotalAmount: 160, PricePerLiter: 8.0, IsFull: false},
		{ID: 2, VehicleID: 1, RefuelTime: t2, Odometer: 10500, Liters: 20, TotalAmount: 160, PricePerLiter: 8.0, IsFull: false},
	}
	svc := newRefuelSvc(recs)
	stats, err := svc.Statistics(context.Background(), 1)
	if err != nil {
		t.Fatal(err)
	}
	if !floatNear(stats.AvgConsumption, 0) {
		t.Errorf("AvgConsumption = %v, want 0 (no is_full sequence)", stats.AvgConsumption)
	}
	if !floatNear(stats.CostPerKm, 0) {
		t.Errorf("CostPerKm = %v, want 0 (no is_full sequence)", stats.CostPerKm)
	}
}

func TestStatistics_MultipleFullSamples(t *testing.T) {
	// 三次加满,应有两个油耗样本
	t1 := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
	t2 := time.Date(2025, 1, 10, 0, 0, 0, 0, time.UTC)
	t3 := time.Date(2025, 1, 20, 0, 0, 0, 0, time.UTC)
	recs := []model.RefuelRecord{
		{ID: 1, VehicleID: 1, RefuelTime: t1, Odometer: 10000, Liters: 40, TotalAmount: 320, PricePerLiter: 8.0, IsFull: true},
		{ID: 2, VehicleID: 1, RefuelTime: t2, Odometer: 10500, Liters: 40, TotalAmount: 320, PricePerLiter: 8.0, IsFull: true},
		{ID: 3, VehicleID: 1, RefuelTime: t3, Odometer: 11000, Liters: 40, TotalAmount: 320, PricePerLiter: 8.0, IsFull: true},
	}
	svc := newRefuelSvc(recs)
	stats, err := svc.Statistics(context.Background(), 1)
	if err != nil {
		t.Fatal(err)
	}
	if !floatNear(stats.AvgConsumption, 8.0) {
		t.Errorf("AvgConsumption = %v, want 8.0 (3 full samples avg)", stats.AvgConsumption)
	}
	if !floatNear(stats.CostPerKm, 0.64) {
		t.Errorf("CostPerKm = %v, want 0.64", stats.CostPerKm)
	}
}

func TestStatistics_EmptyVehicle(t *testing.T) {
	svc := newRefuelSvc(nil)
	stats, err := svc.Statistics(context.Background(), 1)
	if err != nil {
		t.Fatal(err)
	}
	if stats.TotalRecords != 0 {
		t.Errorf("TotalRecords = %d, want 0", stats.TotalRecords)
	}
	if stats.LastRefuel != nil {
		t.Errorf("LastRefuel should be nil, got %+v", stats.LastRefuel)
	}
}

func floatNear(a, b float64) bool {
	const eps = 0.05
	if a == b {
		return true
	}
	diff := a - b
	if diff < 0 {
		diff = -diff
	}
	return diff < eps
}