package cli

import (
	"context"
	"database/sql"
	"errors"
	"flag"
	"fmt"
	"log/slog"
	"math"
	"os"
	"sort"
	"text/tabwriter"
	"time"

	"github.com/martinlehoux/biking_home/config"
	"github.com/martinlehoux/biking_home/mountain_pass"
	"github.com/martinlehoux/biking_home/ride"
	"github.com/martinlehoux/biking_home/rides"
	"github.com/martinlehoux/biking_home/web"
	"github.com/martinlehoux/kagamigo/kcore"
)

var (
	fetchOSM   = flag.Bool("fetch-osm", false, "download the France OSM PBF (resumable) into france-latest.osm.pbf")
	extractOSM = flag.String("extract-osm", "", "extract mountain passes from an OSM PBF file into the database")
	backfill   = flag.Bool("backfill", false, "recompute all stored ride values")
	backtest   = flag.Bool("backtest", false, "run data benchmarks comparing computed values against stored reference values")
)

const (
	backtestMinimumDistanceM   = 10_000
	backtestMinimumMovingRatio = 0.8
)

func Run(db *sql.DB, configPath string, appConfig config.Config) {
	switch {
	case *fetchOSM:
		err := mountain_pass.FetchFrancePBF("france-latest.osm.pbf")
		kcore.Expect(err, "failed to download France OSM PBF")
	case *extractOSM != "":
		_, err := mountain_pass.ExtractMountainPasses(context.Background(), *extractOSM, db)
		kcore.Expect(err, "failed to extract mountain passes from OSM")
	case *backfill:
		count, err := rides.Backfill(db)
		kcore.Expect(err, "failed to backfill ride values")
		slog.Info("Backfilled ride values", "rides", count)
	case *backtest:
		kcore.Expect(runBacktest(db), "failed to run backtest")
	default:
		runServer(db, configPath, appConfig)
	}
}

func runServer(db *sql.DB, configPath string, appConfig config.Config) {
	server := web.NewServer(db, configPath)
	slog.Info("Starting web server", "address", appConfig.Server.PublicURL)
	kcore.Expect(server.ListenAndServe(appConfig.Server.Address), "web server stopped")
}

type backtestSample struct {
	externalID  string
	name        string
	computed    time.Duration
	reference   time.Duration
	relErrorPct float64
}

func runBacktest(db *sql.DB) error {
	items, err := rides.List(db)
	if err != nil {
		return err
	}
	var samples []backtestSample
	for i, item := range items {
		if i > 0 && i%50 == 0 {
			slog.Info("Backtest progress", "processed", i, "total", len(items))
		}
		if !isBacktestEligible(item) {
			continue
		}
		parsed, err := ride.ParseFile(ride.GPXRideParser{}, item.GPXPath)
		if err != nil {
			if errors.Is(err, ride.ErrNoTrackPoints) {
				continue
			}
			slog.Warn("Failed to parse ride GPX", "ride", item.ExternalID, "file", item.GPXPath, "error", err)
			continue
		}
		reference := time.Duration(item.ExternalMovingTimeS) * time.Second
		computed := ride.MovingTime(parsed)
		samples = append(samples, backtestSample{
			externalID:  item.ExternalID,
			name:        item.Name,
			computed:    computed,
			reference:   reference,
			relErrorPct: (float64(computed) - float64(reference)) / float64(reference) * 100,
		})
	}
	if len(samples) == 0 {
		slog.Info("No rides with GPX to backtest", "rides", len(items))
		return nil
	}
	sort.Slice(samples, func(i, j int) bool {
		return math.Abs(samples[i].relErrorPct) > math.Abs(samples[j].relErrorPct)
	})
	w := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
	fmt.Fprintln(w, "computed\treference\terr %\tride")
	limit := min(len(samples), 10)
	for _, s := range samples[:limit] {
		fmt.Fprintf(w, "%s\t%s\t%+.1f\t%s (%s)\n", s.computed.Round(time.Second), s.reference.Round(time.Second), s.relErrorPct, s.name, s.externalID)
	}
	w.Flush()

	absErrors := make([]float64, 0, len(samples))
	for _, s := range samples {
		absErrors = append(absErrors, math.Abs(s.relErrorPct))
	}
	percentiles := []float64{50, 75, 90, 95, 99}
	distribution := errorDistribution(absErrors, percentiles)
	table := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
	fmt.Fprintln(table, "percentile\tabs err %")
	for _, p := range percentiles {
		fmt.Fprintf(table, "p%g\t%.1f\n", p, distribution[p])
	}
	table.Flush()
	slog.Info("Moving time backtest", "rides", len(samples), "min_distance_m", backtestMinimumDistanceM, "min_moving_ratio", backtestMinimumMovingRatio, "mean_err_pct", math.Round(meanAbsErr(absErrors)*10)/10, "stderr_pct", math.Round(stdErrAbsErr(absErrors)*10)/10)
	return nil
}

func isBacktestEligible(item rides.Ride) bool {
	return item.GPXPath != "" &&
		item.DistanceM >= backtestMinimumDistanceM &&
		item.ExternalMovingTimeS > 0 &&
		item.ElapsedTimeS > 0 &&
		float64(item.ExternalMovingTimeS)/float64(item.ElapsedTimeS) >= backtestMinimumMovingRatio
}

func meanAbsErr(absErrors []float64) float64 {
	var sum float64
	for _, err := range absErrors {
		sum += err
	}
	return sum / float64(len(absErrors))
}

func stdErrAbsErr(absErrors []float64) float64 {
	mean := meanAbsErr(absErrors)
	var sumSquares float64
	for _, err := range absErrors {
		sumSquares += (err - mean) * (err - mean)
	}
	variance := sumSquares / float64(len(absErrors)-1)
	return math.Sqrt(variance / float64(len(absErrors)))
}

func errorDistribution(absErrors []float64, percentiles []float64) map[float64]float64 {
	sorted := append([]float64(nil), absErrors...)
	sort.Float64s(sorted)
	distribution := map[float64]float64{}
	for _, p := range percentiles {
		index := max(int(math.Ceil(p/100*float64(len(sorted)))-1), 0)
		if index >= len(sorted) {
			index = len(sorted) - 1
		}
		distribution[p] = sorted[index]
	}
	return distribution
}