package web

import (
	"encoding/json"
	"io"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/scottyah/tracker/internal/store"
)

// gratitudeMax caps one gratitude line. It is a line, not an essay, and a cap
// keeps a stuck key from growing the data file without bound.
const gratitudeMax = 280

// ---------------------------------------------------------------- the day

func (s *Server) handleHome(w http.ResponseWriter, r *http.Request) {
	st := s.store.Settings()
	if !st.Configured() {
		s.render(w, http.StatusOK, "setup.html", pageData{
			Title:    "Set up the challenge",
			Settings: store.Defaults(),
		})
		return
	}
	s.showDay(w, r, s.landingDate(st))
}

// landingDate is the day the home page opens on: today while the challenge is
// running, and the nearest end of it otherwise, so the page always has
// something real to show.
func (s *Server) landingDate(st store.Settings) string {
	today := s.today()
	if st.DayNumber(today) > 0 {
		return today
	}
	if today < st.StartDate {
		return st.StartDate
	}
	return st.End().Format(store.DateLayout)
}

func (s *Server) handleDay(w http.ResponseWriter, r *http.Request) {
	st := s.store.Settings()
	if !st.Configured() {
		http.Redirect(w, r, "/", http.StatusSeeOther)
		return
	}

	date, ok := validDate(r.PathValue("date"))
	if !ok {
		s.fail(w, http.StatusNotFound, "That is not a date.")
		return
	}
	s.showDay(w, r, date)
}

func (s *Server) showDay(w http.ResponseWriter, r *http.Request, date string) {
	st := s.store.Settings()
	day := s.store.Day(date)
	card := s.card(st)

	data := pageData{
		Title:    "Day " + strconv.Itoa(st.DayNumber(date)),
		Settings: st,
		Day:      day,
		View:     s.view(st, day),
		Meters:   meters(st, day),
		Card:     card,
		Stats:    s.stats(st, card),
		PrevDate: s.step(st, date, -1),
		NextDate: s.step(st, date, +1),
		Status:   s.status(st),
	}
	if st.DayNumber(date) == 0 {
		data.Title = "Off the calendar"
	}
	if r.URL.Query().Get("saved") != "" {
		data.Flash = "Saved"
	}
	s.render(w, http.StatusOK, "day.html", data)
}

func (s *Server) handleSaveDay(w http.ResponseWriter, r *http.Request) {
	date, ok := validDate(r.PathValue("date"))
	if !ok {
		s.respondError(w, r, http.StatusNotFound, "That is not a date.")
		return
	}
	if err := r.ParseForm(); err != nil {
		s.respondError(w, r, http.StatusBadRequest, "That form did not arrive intact.")
		return
	}

	day := store.Day{Date: date, Workout: r.FormValue("workout") != ""}

	for _, field := range []struct {
		name  string
		label string
		into  **int
	}{
		{"protein", "Protein", &day.Protein},
		{"calories", "Calories", &day.Calories},
		{"water", "Water", &day.Water},
	} {
		value, ok := optionalInt(r.FormValue(field.name))
		if !ok {
			s.respondError(w, r, http.StatusBadRequest, field.label+" has to be a whole number.")
			return
		}
		*field.into = value
	}

	for i := range day.Gratitude {
		day.Gratitude[i] = truncate(strings.TrimSpace(r.FormValue("gratitude"+strconv.Itoa(i+1))), gratitudeMax)
	}

	if err := s.store.SaveDay(day); err != nil {
		s.respondError(w, r, http.StatusInternalServerError, "The day did not save: "+err.Error())
		return
	}

	st := s.store.Settings()
	marks := st.Marks(day)

	// The background save from the page wants the new score back to repaint
	// today's tile; a plain form post wants to land back on the day.
	if wantsJSON(r) {
		writeJSON(w, http.StatusOK, map[string]any{
			"score":    marks.Score(),
			"complete": marks.Complete(),
			"saved":    "Saved",
		})
		return
	}
	http.Redirect(w, r, "/d/"+date+"?saved=1", http.StatusSeeOther)
}

// ---------------------------------------------------------------- setup

func (s *Server) handleSetup(w http.ResponseWriter, r *http.Request) {
	if s.store.Settings().Configured() {
		http.Redirect(w, r, "/", http.StatusSeeOther)
		return
	}
	next, err := s.settingsFromForm(r, store.Defaults())
	if err != nil {
		s.render(w, http.StatusBadRequest, "setup.html", pageData{
			Title:    "Set up the challenge",
			Settings: next,
			Error:    err.Error(),
		})
		return
	}
	if err := s.store.SaveSettings(next); err != nil {
		s.fail(w, http.StatusInternalServerError, "The settings did not save: "+err.Error())
		return
	}
	http.Redirect(w, r, "/", http.StatusSeeOther)
}

func (s *Server) handleSettings(w http.ResponseWriter, r *http.Request) {
	st := s.store.Settings()
	if !st.Configured() {
		http.Redirect(w, r, "/", http.StatusSeeOther)
		return
	}
	data := pageData{Title: "Settings", Settings: st}
	if r.URL.Query().Get("saved") != "" {
		data.Flash = "Settings saved"
	}
	if r.URL.Query().Get("imported") != "" {
		data.Flash = "Log restored from the file"
	}
	s.render(w, http.StatusOK, "settings.html", data)
}

func (s *Server) handleSaveSettings(w http.ResponseWriter, r *http.Request) {
	current := s.store.Settings()
	next, err := s.settingsFromForm(r, current)
	if err != nil {
		s.render(w, http.StatusBadRequest, "settings.html", pageData{
			Title:    "Settings",
			Settings: next,
			Error:    err.Error(),
		})
		return
	}
	if err := s.store.SaveSettings(next); err != nil {
		s.fail(w, http.StatusInternalServerError, "The settings did not save: "+err.Error())
		return
	}
	http.Redirect(w, r, "/settings?saved=1", http.StatusSeeOther)
}

// settingsFromForm reads the setup and settings forms, which are the same
// fields. On error it returns what the user typed, so the form comes back
// filled in rather than reset.
func (s *Server) settingsFromForm(r *http.Request, current store.Settings) (store.Settings, error) {
	if err := r.ParseForm(); err != nil {
		return current, errText("That form did not arrive intact.")
	}
	next := current

	if raw := strings.TrimSpace(r.FormValue("start_date")); raw != "" {
		if _, err := time.Parse(store.DateLayout, raw); err != nil {
			return next, errText("The start date needs to look like 2026-08-01.")
		}
		next.StartDate = raw
	}
	if next.StartDate == "" {
		return next, errText("Pick the day you are counting from.")
	}

	for _, field := range []struct {
		name  string
		label string
		min   int
		max   int
		into  *int
	}{
		{"length", "The challenge", 1, 3650, &next.Length},
		{"protein_target", "The protein target", 1, 1000, &next.ProteinTarget},
		{"calorie_target", "The calorie target", 1, 20000, &next.CalorieTarget},
		{"water_target", "The water target", 1, 1000, &next.WaterTarget},
	} {
		n, err := strconv.Atoi(strings.TrimSpace(r.FormValue(field.name)))
		if err != nil || n < field.min || n > field.max {
			return next, errText(field.label + " needs a number between " +
				strconv.Itoa(field.min) + " and " + strconv.Itoa(field.max) + ".")
		}
		*field.into = n
	}

	next.CalorieMode = "under"
	if r.FormValue("calorie_mode") == "over" {
		next.CalorieMode = "over"
	}
	return next, nil
}

// ---------------------------------------------------------------- backup

func (s *Server) handleExport(w http.ResponseWriter, r *http.Request) {
	body, err := s.store.Export()
	if err != nil {
		s.fail(w, http.StatusInternalServerError, "The export did not build: "+err.Error())
		return
	}
	name := "tracker-" + s.today() + ".json"
	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Content-Disposition", `attachment; filename="`+name+`"`)
	w.Write(body)
}

func (s *Server) handleImport(w http.ResponseWriter, r *http.Request) {
	// A challenge this size is a few tens of kilobytes; the cap is only here
	// so a wrong file cannot be read into memory whole.
	r.Body = http.MaxBytesReader(w, r.Body, 4<<20)
	if err := r.ParseMultipartForm(4 << 20); err != nil {
		s.fail(w, http.StatusBadRequest, "That upload was too large or malformed.")
		return
	}
	file, _, err := r.FormFile("backup")
	if err != nil {
		s.fail(w, http.StatusBadRequest, "Choose an export file first.")
		return
	}
	defer file.Close()

	body, err := io.ReadAll(file)
	if err != nil {
		s.fail(w, http.StatusBadRequest, "That file could not be read.")
		return
	}
	if err := s.store.Import(body); err != nil {
		s.fail(w, http.StatusBadRequest, err.Error())
		return
	}
	http.Redirect(w, r, "/settings?imported=1", http.StatusSeeOther)
}

// handleManifest makes the page installable, so it opens from the home screen
// without Safari's chrome and keeps its own window.
func (s *Server) handleManifest(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/manifest+json")
	writeJSON(w, http.StatusOK, map[string]any{
		"name":             "75",
		"short_name":       "75",
		"start_url":        "/",
		"display":          "standalone",
		"background_color": "#E6EEEF",
		"theme_color":      "#0E3140",
		"icons": []map[string]any{{
			"src":   s.asset("/static/icon.svg"),
			"sizes": "any",
			"type":  "image/svg+xml",
		}},
	})
}

// ---------------------------------------------------------------- derived

func (s *Server) view(st store.Settings, day store.Day) dayView {
	t, _ := time.Parse(store.DateLayout, day.Date)
	marks := st.Marks(day)
	today := s.today()

	return dayView{
		Date:     day.Date,
		Time:     t,
		Number:   st.DayNumber(day.Date),
		Marks:    marks,
		Score:    marks.Score(),
		Logged:   day.Logged(),
		IsToday:  day.Date == today,
		IsFuture: day.Date > today,
	}
}

// card is every day of the challenge in order, blanks included.
func (s *Server) card(st store.Settings) []dayView {
	days := s.store.Days(st.Start(), st.Length)
	out := make([]dayView, 0, len(days))
	for _, d := range days {
		out = append(out, s.view(st, d))
	}
	return out
}

func (s *Server) stats(st store.Settings, card []dayView) stats {
	var out stats
	today := s.today()

	for _, v := range card {
		if v.Marks.Complete() {
			out.Complete++
		}
		if v.Logged {
			out.Logged++
		}
		if v.Date <= today {
			out.Elapsed++
		}
		for i, hit := range [5]bool{v.Marks.Workout, v.Marks.Protein, v.Marks.Calories, v.Marks.Water, v.Marks.Gratitude} {
			if hit {
				out.Marks[i]++
			}
		}
	}
	out.Remaining = st.Length - out.Elapsed

	// The streak runs back from the most recent day that could still count.
	// Today is skipped when it is not finished yet, so an unlogged morning
	// does not read as a broken streak.
	i := out.Elapsed - 1
	if i >= 0 && i < len(card) && !card[i].Marks.Complete() {
		i--
	}
	for ; i >= 0 && card[i].Marks.Complete(); i-- {
		out.Streak++
	}
	return out
}

// meters builds the three number bands. Protein and water fill towards a floor
// they should reach; calories fill towards a ceiling they should not cross,
// which is why the bar can overflow.
func meters(st store.Settings, day store.Day) []meter {
	calorieMode := "ceiling"
	calorieNote := "Stay under " + strconv.Itoa(st.CalorieTarget)
	if st.CalorieMode == "over" {
		calorieMode = "floor"
		calorieNote = "Eat at least " + strconv.Itoa(st.CalorieTarget)
	}

	out := []meter{
		{Key: "protein", Label: "Protein", Unit: "g", Value: day.Protein,
			Target: st.ProteinTarget, Mode: "floor",
			Note: "Hit " + strconv.Itoa(st.ProteinTarget) + " g"},
		{Key: "calories", Label: "Calories", Unit: "kcal", Value: day.Calories,
			Target: st.CalorieTarget, Mode: calorieMode, Note: calorieNote},
		{Key: "water", Label: "Water", Unit: "oz", Value: day.Water,
			Target: st.WaterTarget, Mode: "floor",
			Note: waterNote(st.WaterTarget)},
	}

	marks := st.Marks(day)
	met := [3]bool{marks.Protein, marks.Calories, marks.Water}
	for i := range out {
		out[i].Met = met[i]
		if out[i].Value == nil || out[i].Target <= 0 {
			continue
		}
		out[i].Pct = min(100, *out[i].Value*100/out[i].Target)
		out[i].Over = out[i].Mode == "ceiling" && *out[i].Value > out[i].Target
	}
	return out
}

func waterNote(target int) string {
	if target == 128 {
		return "A gallon"
	}
	return "Drink " + strconv.Itoa(target) + " oz"
}

// step returns the neighbouring date, held inside the challenge and never past
// today. It returns "" when there is nowhere to go, which hides the arrow.
func (s *Server) step(st store.Settings, date string, delta int) string {
	t, err := time.Parse(store.DateLayout, date)
	if err != nil {
		return ""
	}
	next := t.AddDate(0, 0, delta).Format(store.DateLayout)
	if next < st.StartDate || next > st.End().Format(store.DateLayout) {
		return ""
	}
	if next > s.today() {
		return ""
	}
	return next
}

func (s *Server) status(st store.Settings) string {
	today := s.today()
	switch {
	case today < st.StartDate:
		return "before"
	case today > st.End().Format(store.DateLayout):
		return "after"
	default:
		return "during"
	}
}

// ---------------------------------------------------------------- helpers

func (s *Server) fail(w http.ResponseWriter, status int, message string) {
	s.render(w, status, "error.html", pageData{Title: "Nothing here", Error: message})
}

// respondError answers in whichever form the request came in, so a background
// save reports the problem instead of failing silently.
func (s *Server) respondError(w http.ResponseWriter, r *http.Request, status int, message string) {
	if wantsJSON(r) {
		writeJSON(w, status, map[string]any{"error": message})
		return
	}
	s.fail(w, status, message)
}

func wantsJSON(r *http.Request) bool {
	return r.Header.Get("X-Sync") == "1"
}

func writeJSON(w http.ResponseWriter, status int, body any) {
	if w.Header().Get("Content-Type") == "" {
		w.Header().Set("Content-Type", "application/json")
	}
	w.WriteHeader(status)
	if err := json.NewEncoder(w).Encode(body); err != nil {
		return
	}
}

// validDate keeps anything but a real date out of the map keys and the URLs.
func validDate(raw string) (string, bool) {
	t, err := time.Parse(store.DateLayout, raw)
	if err != nil {
		return "", false
	}
	// Reject forms that parse but do not round-trip, so one day has one URL.
	if t.Format(store.DateLayout) != raw {
		return "", false
	}
	return raw, true
}

// optionalInt reads a number field that is allowed to be blank. Blank means
// not logged, which is deliberately different from zero.
func optionalInt(raw string) (*int, bool) {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return nil, true
	}
	n, err := strconv.Atoi(raw)
	if err != nil || n < 0 {
		return nil, false
	}
	if n > 100000 {
		n = 100000
	}
	return &n, true
}

func truncate(s string, max int) string {
	r := []rune(s)
	if len(r) <= max {
		return s
	}
	return strings.TrimSpace(string(r[:max]))
}

// errText is an error that is already phrased for the person reading it.
type errText string

func (e errText) Error() string { return string(e) }