// Usage screen (AGENTS.md §5 screen 5, §11 Phase 7). It reads the daily rollup
// and the per-app/domain detail. Read-only: telemetry only ever arrives from a
// device, and the Control Service only stores and displays it.
package web

import (
	"context"
	"fmt"
	"net/http"
	"time"

	"gitea.lab.audasmedia.com.au/sam/internet_use_control/internal/store"
)

// usageDayView is one row of the week grid.
type usageDayView struct {
	Day           string // YYYY-MM-DD
	Weekday       string // Mon
	Date          string // 13 Oct
	IsToday       bool
	AppSeconds    int
	DomainSeconds int
	AppLabel      string
	DomainLabel   string
	// Progress is a percentage of the busiest day in the week.
	AppPercent    int
	DomainPercent int
}

// usageTotalView is one row of the top apps or top domains list.
type usageTotalView struct {
	Name    string
	Seconds int
	Label   string
	Percent int
}

type usageData struct {
	editorCommon
	WeekLabel   string
	PrevWeek    string
	NextWeek    string
	IsThisWeek  bool
	Days        []usageDayView
	WeekApps    int
	WeekDomains int
	WeekAppsTxt string
	WeekSiteTxt string
	MaxApp      int
	MaxDomain   int
	TopApps     []usageTotalView
	TopDomains  []usageTotalView
	HasUsage    bool
	Retention   string
}

// formatSeconds renders a duration compactly: "9h 05m", "42m", "under a minute".
func formatSeconds(seconds int) string {
	if seconds <= 0 {
		return "0m"
	}
	if seconds < 60 {
		return "under a minute"
	}
	m := seconds / 60
	h := m / 60
	m %= 60
	if h == 0 {
		return fmt.Sprintf("%dm", m)
	}
	return fmt.Sprintf("%dh %02dm", h, m)
}

// weekStart returns the Monday 00:00 of the week that contains t, in t's
// location. The family's week is Monday to Sunday.
func weekStart(t time.Time) time.Time {
	offset := (int(t.Weekday()) + 6) % 7 // Monday = 0
	d := t.AddDate(0, 0, -offset)
	return time.Date(d.Year(), d.Month(), d.Day(), 0, 0, 0, 0, d.Location())
}

// parseWeekAnchor reads the ?week=YYYY-MM-DD query, falling back to now. An
// unparseable value is ignored, never an error: the screen must always render.
func parseWeekAnchor(raw string, now time.Time) time.Time {
	if raw != "" {
		if t, err := time.ParseInLocation("2006-01-02", raw, now.Location()); err == nil {
			return t
		}
	}
	return now
}

func (s *Server) handleDeviceUsage(w http.ResponseWriter, r *http.Request) {
	id, ok := s.deviceID(w, r)
	if !ok {
		return
	}
	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
	defer cancel()

	dev, err := s.store.GetDevice(ctx, id)
	if err != nil {
		s.deviceLookupError(w, r, err)
		return
	}

	now := s.now()
	anchor := parseWeekAnchor(r.URL.Query().Get("week"), now)
	start := weekStart(anchor)
	end := start.AddDate(0, 0, 6)
	from, to := start.Format("2006-01-02"), end.Format("2006-01-02")

	rangeRows, err := s.store.UsageRange(ctx, id, from, to)
	if err != nil {
		s.log.Error("usage range", "device", dev.Name, "err", err)
		http.Error(w, "internal server error", http.StatusInternalServerError)
		return
	}
	byDay := make(map[string]store.DayUsage, len(rangeRows))
	for _, d := range rangeRows {
		byDay[d.Day] = d
	}

	topApps, err := s.store.TopUsage(ctx, id, from, to, "app", 10)
	if err != nil {
		s.log.Error("top apps", "device", dev.Name, "err", err)
		http.Error(w, "internal server error", http.StatusInternalServerError)
		return
	}
	topDomains, err := s.store.TopUsage(ctx, id, from, to, "domain", 10)
	if err != nil {
		s.log.Error("top domains", "device", dev.Name, "err", err)
		http.Error(w, "internal server error", http.StatusInternalServerError)
		return
	}

	data := usageData{
		editorCommon: editorCommon{
			Title:         "Usage — " + dev.Name,
			Heading:       "Usage",
			Sub:           fmt.Sprintf("%s · %s", dev.Name, platformLabel(dev.Platform)),
			Username:      s.cfg.AdminUsername,
			CSRF:          s.auth.EnsureCSRF(w, r),
			Version:       s.cfg.Version,
			AppEnv:        s.cfg.AppEnv,
			DeviceID:      dev.ID,
			DeviceName:    dev.Name,
			PlatformLabel: platformLabel(dev.Platform),
		},
		WeekLabel:  fmt.Sprintf("%s – %s", start.Format("Mon 2 Jan"), end.Format("Mon 2 Jan 2006")),
		PrevWeek:   start.AddDate(0, 0, -7).Format("2006-01-02"),
		NextWeek:   start.AddDate(0, 0, 7).Format("2006-01-02"),
		IsThisWeek: start.Equal(weekStart(now)),
		Retention:  "Daily rollups are kept long; the raw detail is what the dashboard sums for the top lists.",
	}

	for i := 0; i < 7; i++ {
		day := start.AddDate(0, 0, i)
		key := day.Format("2006-01-02")
		row := byDay[key]
		v := usageDayView{
			Day:           key,
			Weekday:       day.Format("Mon"),
			Date:          day.Format("2 Jan"),
			IsToday:       key == now.Format("2006-01-02"),
			AppSeconds:    row.AppSeconds,
			DomainSeconds: row.DomainSeconds,
			AppLabel:      formatSeconds(row.AppSeconds),
			DomainLabel:   formatSeconds(row.DomainSeconds),
		}
		data.Days = append(data.Days, v)
		data.WeekApps += row.AppSeconds
		data.WeekDomains += row.DomainSeconds
		if row.AppSeconds > data.MaxApp {
			data.MaxApp = row.AppSeconds
		}
		if row.DomainSeconds > data.MaxDomain {
			data.MaxDomain = row.DomainSeconds
		}
	}
	data.HasUsage = data.WeekApps > 0 || data.WeekDomains > 0
	data.WeekAppsTxt = formatSeconds(data.WeekApps)
	data.WeekSiteTxt = formatSeconds(data.WeekDomains)

	// Percentages for the day bars, relative to the busiest day of the week.
	for i := range data.Days {
		data.Days[i].AppPercent = percent(data.Days[i].AppSeconds, data.MaxApp)
		data.Days[i].DomainPercent = percent(data.Days[i].DomainSeconds, data.MaxDomain)
	}
	data.TopApps = totalViews(topApps)
	data.TopDomains = totalViews(topDomains)

	s.render(w, r, "usage.html", data)
}

// percent returns value as a 0–100 integer of max. A non-positive max yields 0,
// so an empty week renders empty bars rather than a division by zero.
func percent(value, max int) int {
	if max <= 0 || value <= 0 {
		return 0
	}
	p := value * 100 / max
	if p > 100 {
		p = 100
	}
	return p
}

// totalViews turns store totals into view rows, with each bar relative to the
// biggest entry.
func totalViews(totals []store.UsageTotal) []usageTotalView {
	max := 0
	for _, t := range totals {
		if t.Seconds > max {
			max = t.Seconds
		}
	}
	out := make([]usageTotalView, 0, len(totals))
	for _, t := range totals {
		out = append(out, usageTotalView{
			Name:    t.Name,
			Seconds: t.Seconds,
			Label:   formatSeconds(t.Seconds),
			Percent: percent(t.Seconds, max),
		})
	}
	return out
}