package stats

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strconv"
	"strings"
	"time"
)

type Queryer interface {
	QueryContext(context.Context, string, ...any) (*sql.Rows, error)
}

type MetricQuery struct {
	VIN          string
	Protocol     string
	IncludeTotal bool
	DateFrom     string
	DateTo       string
	Limit        int
	Offset       int
}

type MetricRow struct {
	VIN                  string   `json:"vin"`
	StatDate             string   `json:"stat_date"`
	Protocol             string   `json:"protocol"`
	DailyMileageKM       float64  `json:"daily_mileage_km"`
	FirstTotalMileageKM  *float64 `json:"first_total_mileage_km,omitempty"`
	LatestTotalMileageKM *float64 `json:"latest_total_mileage_km,omitempty"`
	SampleCount          int64    `json:"sample_count"`
	UpdatedAt            string   `json:"updated_at"`
}

type MetricRepository struct {
	db Queryer
}

func NewMetricRepository(db Queryer) *MetricRepository {
	if db == nil {
		panic("metric query db must not be nil")
	}
	return &MetricRepository{db: db}
}

func (r *MetricRepository) Query(ctx context.Context, query MetricQuery) ([]MetricRow, error) {
	query = normalizeMetricQuery(query)
	sqlText, args := buildMetricSQL(query)
	rows, err := r.db.QueryContext(ctx, sqlText, args...)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	out := make([]MetricRow, 0)
	for rows.Next() {
		var row MetricRow
		var statDate scanDate
		var updatedAt scanDateTime
		var first sql.NullFloat64
		var latest sql.NullFloat64
		if err := rows.Scan(
			&row.VIN,
			&statDate,
			&row.Protocol,
			&row.DailyMileageKM,
			&first,
			&latest,
			&row.SampleCount,
			&updatedAt,
		); err != nil {
			return nil, err
		}
		row.StatDate = statDate.String
		row.UpdatedAt = updatedAt.String
		if first.Valid {
			row.FirstTotalMileageKM = &first.Float64
		}
		if latest.Valid {
			row.LatestTotalMileageKM = &latest.Float64
		}
		out = append(out, row)
	}
	return out, rows.Err()
}

func (r *MetricRepository) Count(ctx context.Context, query MetricQuery) (int64, error) {
	query = normalizeMetricQuery(query)
	sqlText, args := buildMetricCountSQL(query)
	rows, err := r.db.QueryContext(ctx, sqlText, args...)
	if err != nil {
		return 0, err
	}
	defer rows.Close()

	var total int64
	if rows.Next() {
		if err := rows.Scan(&total); err != nil {
			return 0, err
		}
	}
	return total, rows.Err()
}

func normalizeMetricQuery(query MetricQuery) MetricQuery {
	query.VIN = strings.TrimSpace(query.VIN)
	query.Protocol = strings.ToUpper(strings.TrimSpace(query.Protocol))
	query.DateFrom = strings.TrimSpace(query.DateFrom)
	query.DateTo = strings.TrimSpace(query.DateTo)
	if query.Limit <= 0 {
		query.Limit = 50
	}
	return query
}

func buildMetricSQL(query MetricQuery) (string, []any) {
	where, args := buildMetricWhere(query)
	sqlText := `SELECT vin, stat_date, protocol, daily_mileage_km, first_total_mileage_km, latest_total_mileage_km, sample_count, updated_at FROM vehicle_daily_mileage`
	if len(where) > 0 {
		sqlText += " WHERE " + strings.Join(where, " AND ")
	}
	sqlText += " ORDER BY stat_date DESC, vin ASC, protocol ASC LIMIT ? OFFSET ?"
	args = append(args, query.Limit, query.Offset)
	return sqlText, args
}

func buildMetricCountSQL(query MetricQuery) (string, []any) {
	where, args := buildMetricWhere(query)
	sqlText := `SELECT COUNT(*) FROM vehicle_daily_mileage`
	if len(where) > 0 {
		sqlText += " WHERE " + strings.Join(where, " AND ")
	}
	return sqlText, args
}

func buildMetricWhere(query MetricQuery) ([]string, []any) {
	var where []string
	var args []any
	add := func(clause string, value any) {
		where = append(where, clause)
		args = append(args, value)
	}
	if query.VIN != "" {
		add("vin = ?", query.VIN)
	}
	if query.Protocol != "" {
		add("protocol = ?", query.Protocol)
	}
	if query.DateFrom != "" {
		add("stat_date >= ?", query.DateFrom)
	}
	if query.DateTo != "" {
		add("stat_date <= ?", query.DateTo)
	}
	return where, args
}

type MetricHandler struct {
	repository *MetricRepository
}

func NewMetricHandler(repository *MetricRepository) *MetricHandler {
	if repository == nil {
		panic("metric repository must not be nil")
	}
	return &MetricHandler{repository: repository}
}

func (h *MetricHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		writeMetricError(w, http.StatusMethodNotAllowed, "method not allowed")
		return
	}
	if strings.Trim(r.URL.Path, "/") != "api/stats/daily-metrics" {
		writeMetricError(w, http.StatusNotFound, "route not found")
		return
	}
	query, err := parseMetricQuery(r)
	if err != nil {
		writeMetricError(w, http.StatusBadRequest, err.Error())
		return
	}
	var total int64
	if query.IncludeTotal {
		total, err = h.repository.Count(r.Context(), query)
		if err != nil {
			writeMetricError(w, http.StatusInternalServerError, err.Error())
			return
		}
	}
	rows, err := h.repository.Query(r.Context(), query)
	if err != nil {
		writeMetricError(w, http.StatusInternalServerError, err.Error())
		return
	}
	if !query.IncludeTotal {
		total = int64(len(rows))
	}
	w.Header().Set("Content-Type", "application/json")
	_ = json.NewEncoder(w).Encode(map[string]any{
		"items":  rows,
		"total":  total,
		"limit":  query.Limit,
		"offset": query.Offset,
	})
}

func parseMetricQuery(r *http.Request) (MetricQuery, error) {
	values := r.URL.Query()
	limit, err := parseBoundedInt(values.Get("limit"), 50, 1, 1000, "limit")
	if err != nil {
		return MetricQuery{}, err
	}
	offset, err := parseBoundedInt(values.Get("offset"), 0, 0, 1_000_000, "offset")
	if err != nil {
		return MetricQuery{}, err
	}
	query := MetricQuery{
		VIN:          values.Get("vin"),
		Protocol:     values.Get("protocol"),
		IncludeTotal: strings.EqualFold(strings.TrimSpace(values.Get("includeTotal")), "true"),
		DateFrom:     values.Get("dateFrom"),
		DateTo:       values.Get("dateTo"),
		Limit:        limit,
		Offset:       offset,
	}
	if !validDate(query.DateFrom) || !validDate(query.DateTo) {
		return MetricQuery{}, errors.New("dateFrom/dateTo must use YYYY-MM-DD")
	}
	return normalizeMetricQuery(query), nil
}

func parseBoundedInt(raw string, fallback int, min int, max int, name string) (int, error) {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return fallback, nil
	}
	value, err := strconv.Atoi(raw)
	if err != nil || value < min || value > max {
		return 0, fmt.Errorf("%s must be between %d and %d", name, min, max)
	}
	return value, nil
}

func validDate(value string) bool {
	value = strings.TrimSpace(value)
	if value == "" {
		return true
	}
	if len(value) != len("2006-01-02") {
		return false
	}
	for i, r := range value {
		switch i {
		case 4, 7:
			if r != '-' {
				return false
			}
		default:
			if r < '0' || r > '9' {
				return false
			}
		}
	}
	return true
}

func writeMetricError(w http.ResponseWriter, status int, message string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(map[string]any{"error": message})
}

type scanDate struct {
	String string
}

func (s *scanDate) Scan(value any) error {
	s.String = formatSQLTime(value, "2006-01-02")
	return nil
}

type scanDateTime struct {
	String string
}

func (s *scanDateTime) Scan(value any) error {
	s.String = formatSQLTime(value, "2006-01-02 15:04:05")
	return nil
}

func formatSQLTime(value any, layout string) string {
	switch typed := value.(type) {
	case nil:
		return ""
	case time.Time:
		return typed.Format(layout)
	case []byte:
		return strings.TrimSpace(string(typed))
	case string:
		return strings.TrimSpace(typed)
	default:
		return strings.TrimSpace(fmt.Sprint(typed))
	}
}