package main

import (
	"context"
	"encoding/csv"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"os"
	"path"
	"regexp"
	"strconv"
	"time"

	"gopkg.in/yaml.v3"
)

type Show struct {
	Name  string     `json:"name"`
	Start time.Time  `json:"start"`
	End   *time.Time `json:"end,omitempty"`
}

type TimeTable struct {
	Title     string `json:"title"`
	Location  string `json:"location"`
	Shows     []Show `json:"shows"`
}

func (tt TimeTable) findShowAt(when time.Time) (int) {
	for i, s := range(tt.Shows) {
		if when.After(s.Start) && (s.End == nil || when.Before(*s.End)) {
			return i
		}
	}
	return -1
}

func (tt TimeTable) ShowAt(when time.Time) (Show, bool) {
	if idx := tt.findShowAt(when); idx >= 0 {
		return tt.Shows[idx], true
	} else {
		return Show{}, false
	}
}

func (tt TimeTable) CurrentShow() (Show, bool) {
	return tt.ShowAt(time.Now())
}

func (tt TimeTable) NextShowAt(when time.Time) (Show, bool) {
	if idx := tt.findShowAt(when); idx >= 0 && (idx+1) < len(tt.Shows) {
		return tt.Shows[idx], true
	} else {
		return Show{}, false
	}
}

func (tt TimeTable) NextShow() (Show, bool) {
	return tt.NextShowAt(time.Now())
}

type TimeTableSource struct {
	ID            string `yaml:"id"`
	URL           string `yaml:"url"`
	Title         string `yaml:"title,omitempty"`
	Location      string `yaml:"location,omitempty"`
	StartDate     string `yaml:"startDate,omitempty"`
	TimeColumn    int    `yaml:"timeColumn"`
	NameColumn    int    `yaml:"nameColumn"`
	CountdownPath string `yaml:"countDownPath"`
}

type Config struct {
	Listen    string            `yaml:"listen"`
	StaticDir string            `yaml:"staticdir"`
	Sources   []TimeTableSource `yaml:"sources,omitempty"`
}

func getCSV(src string, ctx context.Context) ([][]string, error) {
	req, err := http.NewRequestWithContext(ctx, "GET", src, nil)
	if err != nil {
		return nil, err
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return nil, err
	}

	if resp.StatusCode > 299 {
		return nil, fmt.Errorf("HTTP error %d: %s", resp.StatusCode, resp.Status)
	}

	ct := resp.Header.Get("Content-Type")
	if ct != "text/csv" && ct != "" {
		return nil, fmt.Errorf("Content is not CSV: %s", ct)
	}

	return csv.NewReader(resp.Body).ReadAll()
}

func timeAtHour(t time.Time, h int) time.Time {
	return time.Date(t.Year(), t.Month(), t.Day(), h, 0, 0, 0, t.Location())
}

func (src *TimeTableSource) GetTimetable(ctx context.Context) (TimeTable, error) {
	records, err := getCSV(src.URL, ctx)
	if err != nil {
		return TimeTable{}, err
	}

	start, err := time.ParseInLocation(time.DateOnly, src.StartDate, time.Local)
	if err != nil {
		return TimeTable{}, err
	}

	tt := TimeTable{
		Title: src.Title,
		Location: src.Location,
	}

	numColumns := src.TimeColumn + 1
	if src.NameColumn > src.TimeColumn {
		numColumns = src.NameColumn + 1
	}

	timeSlotRe := regexp.MustCompile(`([0-9]+)-([0-9]+)?`)
	for _, row := range(records) {
		// Check that we have enought columns
		if (len(row) < numColumns) {
			continue
		}

		// Parse the time slot, skip if invalid
		timeSlot := timeSlotRe.FindStringSubmatch(row[src.TimeColumn])
		if len(timeSlot) < 2 {
			continue
		}

		startHour, err := strconv.Atoi(timeSlot[1])
		if err != nil {
			continue
		}

		start = timeAtHour(start, startHour)
		end  := start

		if len(timeSlot) > 2 {
			endHour, err := strconv.Atoi(timeSlot[2])
			if err != nil {
				continue
			}
			if endHour < startHour {
				end = end.Add(time.Hour * 24)
			}
			end = timeAtHour(end, endHour)
		}

		show := Show{
			Name:  row[src.NameColumn],
			Start: start,
		}

		if end != start {
			show.End = &end
		}

		if show.Name != "" {
			tt.Shows = append(tt.Shows, show)
		}

		start = end
	}

	return tt, nil
}

func (src TimeTableSource) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	// Early validity check
	switch when := r.PathValue("when"); when {
	case "":
	case "now":
	case "next":
	case "first":
	default:
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
	}

	ctx, cancel := context.WithTimeout(r.Context(), time.Second*10)
	defer cancel()

	tt, err := src.GetTimetable(ctx)
	if err != nil {
		log.Printf("Failed to get timetable: %s", err)
		http.Error(w, http.StatusText(http.StatusBadGateway), http.StatusBadGateway)
		return
	}

	var data any
	found := true
	switch when := r.PathValue("when"); when {
	case "":
		data = tt
	case "now":
		data, found  = tt.CurrentShow()
	case "next":
		data, found = tt.NextShow()
	case "first":
		if len(tt.Shows) > 0 {
			data = tt.Shows[0]
		} else {
			found = false
		}
	default:
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}

	w.Header().Set("Content-Type", "application/json")

	// Send an empty object if nothing was found
	if !found {
		data = make(map[string]string)
	}
	json.NewEncoder(w).Encode(data)
}

func LoadConfig(path string) (Config, error) {
	rd, err := os.Open(path)
	if err != nil {
		return Config{}, fmt.Errorf("Failed to open config: %w", err)
	}
	defer rd.Close()

	var cfg Config
	err = yaml.NewDecoder(rd).Decode(&cfg)
	if err != nil {
		return Config{}, fmt.Errorf("Failed to parse config: %w", err)
	}

	return cfg, nil
}

func main() {
	cfgFile := "timetables.yaml"

	cfg, err := LoadConfig(cfgFile)
	if err != nil {
		log.Fatal(err)
	}

	staticDir := cfg.StaticDir
	if staticDir == "" {
		staticDir = "static"
	}

	http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.Dir(staticDir))))

	for _, src := range(cfg.Sources) {
		if src.ID == "" || src.URL == "" {
			log.Printf("Skipping invalid source: %s\n", src)
			continue
		}
		log.Printf("Registering timetable %s\n", src.ID)

		if src.CountdownPath == "" {
			src.CountdownPath = "countdown.html"
		}

		http.Handle(fmt.Sprintf("/timetable/%s", src.ID), src)
		http.Handle(fmt.Sprintf("/timetable/%s/{when}", src.ID), src)
		http.HandleFunc(fmt.Sprintf("/countdown/%s", src.ID),
			func (w http.ResponseWriter, req *http.Request) {
				http.ServeFile(w, req, path.Join(staticDir, src.CountdownPath))
			})
	}

	listen := cfg.Listen
	if listen == "" {
		listen = ":8080"
	}

	log.Fatal(http.ListenAndServe(listen, nil))
}