// Read-only question answering for the Hub (AGENTS.md §4 FR-12, §10 rule 9,
// §11 Phase 9).
//
// The answerer decides intent from the question text and answers from SQLite.
// It is not an LLM call: it is deterministic, answers in milliseconds, and
// never guesses. An unanswerable question returns answer=null plus a reason.
//
// Reader is the read-only data surface. *store.Store satisfies it. Keeping it
// an interface makes the read-only guarantee explicit: every method reads.
package hub

import (
	"context"
	"fmt"
	"strings"
	"time"

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

// Reader is the read-only data surface the answerer uses.
type Reader interface {
	ListDevices(ctx context.Context) ([]store.Device, error)
	EffectiveState(ctx context.Context, dev store.Device, now time.Time) (store.EffectiveState, error)
	UsageByDeviceForDay(ctx context.Context, day string) ([]store.DeviceDayUsage, error)
}

// Answerer answers one question at a time from a read-only Reader.
type Answerer struct {
	Reader Reader
	// Location is the schedule timezone, so "today" matches the day a device
	// stamped its telemetry in. Defaults to the process local zone.
	Location *time.Location
	// Now is injectable so the answer is deterministic in tests.
	Now func() time.Time
}

// NewAnswerer builds an Answerer over a read-only Reader.
func NewAnswerer(r Reader, loc *time.Location) *Answerer {
	if loc == nil {
		loc = time.Local
	}
	return &Answerer{Reader: r, Location: loc, Now: func() time.Time { return time.Now().In(loc) }}
}

func (a *Answerer) now() time.Time {
	if a.Now == nil {
		return time.Now().In(a.loc())
	}
	return a.Now()
}

func (a *Answerer) loc() *time.Location {
	if a.Location == nil {
		return time.Local
	}
	return a.Location
}

// Answer returns a short, speakable answer for one question. It never writes
// state.
func (a *Answerer) Answer(ctx context.Context, req AskRequest) AskResponse {
	now := a.now()

	asker := strings.ToLower(strings.TrimSpace(req.Asker))
	person := strings.ToLower(strings.TrimSpace(req.Person))
	switch {
	case asker == "":
		return cannotAnswer("no asker was given")
	case asker != "sam":
		return cannotAnswer("I only answer for Sam")
	}

	q := normalizeQuestion(req.Question)
	if q == "" {
		return cannotAnswer("no question was given")
	}

	// Resolve who the question is about. The person field wins when it names a
	// child; otherwise a child named in the question is used; otherwise every
	// device is included.
	child := ""
	switch person {
	case "", "sam", "kids", "children", "everyone", "both":
		// aggregate (or derive from the question below)
	case "harry", "finn":
		child = person
	default:
		return cannotAnswer("no data for that person")
	}
	if child == "" {
		switch {
		case strings.Contains(q, "harry"):
			child = "harry"
		case strings.Contains(q, "finn"):
			child = "finn"
		}
	}

	devs, err := a.Reader.ListDevices(ctx)
	if err != nil {
		return cannotAnswer("the device list could not be read")
	}
	if child != "" && !knownChild(devs, child) {
		return cannotAnswer("no data for that person")
	}

	switch {
	case containsAny(q, "screen time", "screentime", "screen-time",
		"on screens", "on screen", "screen", "how long", "spent", "usage", "used"):
		return a.answerScreenTime(ctx, now, child, q)
	case containsAny(q, "blocked", "block", "locked", "lock", "restricted", "restrict"):
		return a.answerBlocked(ctx, now, child, devs)
	case containsAny(q, "online", "offline", "connected", "reachable"):
		return a.answerPresence(ctx, now, child, devs)
	default:
		return cannotAnswer("I can answer questions about screen time, what is blocked, and whether a device is online")
	}
}

// answerScreenTime answers "how long have the kids been on screens today?" from
// the stored daily rollup. The day is "today" in the schedule timezone, or
// yesterday when the question says so.
func (a *Answerer) answerScreenTime(ctx context.Context, now time.Time, child, q string) AskResponse {
	day := now
	if containsAny(q, "yesterday", "last night") {
		day = now.AddDate(0, 0, -1)
	}
	dayStr := day.Format("2006-01-02")

	usage, err := a.Reader.UsageByDeviceForDay(ctx, dayStr)
	if err != nil {
		return cannotAnswer("usage could not be read")
	}

	total := 0
	byDevice := make([]map[string]any, 0, len(usage))
	for _, u := range usage {
		if child != "" && !strings.EqualFold(strings.TrimSpace(u.Child), child) {
			continue
		}
		seconds := ScreenSeconds(u.AppSeconds, u.DomainSeconds)
		total += seconds
		byDevice = append(byDevice, map[string]any{
			"device":         u.Name,
			"child":          u.Child,
			"seconds":        seconds,
			"app_seconds":    u.AppSeconds,
			"domain_seconds": u.DomainSeconds,
		})
	}

	when := "today"
	if strings.EqualFold(dayStr, now.AddDate(0, 0, -1).Format("2006-01-02")) {
		when = "yesterday"
	}
	subject := "The kids"
	verb := "have"
	if child != "" {
		subject = titleCase(child)
		verb = "has"
	}

	answer := fmt.Sprintf("%s %s had no recorded screen time %s.", subject, verb, when)
	if total > 0 {
		answer = fmt.Sprintf("%s %s had %s of screen time %s.", subject, verb, humanDuration(total), when)
	}
	return AskResponse{
		Answer:  answerText(answer),
		Data:    map[string]any{"day": dayStr, "total_seconds": total, "by_device": byDevice},
		Expires: expiresIn(now, 15*time.Minute),
	}
}

// answerBlocked reports whether anything is blocked right now, and until when.
func (a *Answerer) answerBlocked(ctx context.Context, now time.Time, child string, devs []store.Device) AskResponse {
	blocked := make([]map[string]any, 0, len(devs))
	for _, dev := range devs {
		if !matchesChild(dev, child) {
			continue
		}
		eff, err := a.Reader.EffectiveState(ctx, dev, now)
		if err != nil {
			return cannotAnswer("device state could not be read")
		}
		if !eff.Locked {
			continue
		}
		item := map[string]any{
			"device": dev.Name,
			"child":  dev.Child,
			"reason": eff.Reason,
		}
		if eff.Until != nil {
			item["until"] = eff.Until.UTC().Format(time.RFC3339)
			item["until_local"] = eff.Until.In(a.loc()).Format("15:04")
		}
		blocked = append(blocked, item)
	}

	resp := AskResponse{
		Data:    map[string]any{"blocked": blocked, "count": len(blocked)},
		Expires: expiresIn(now, 5*time.Minute),
	}
	switch len(blocked) {
	case 0:
		resp.Answer = answerText("Nothing is blocked right now.")
	case 1:
		name, _ := blocked[0]["device"].(string)
		reason, _ := blocked[0]["reason"].(string)
		if until, ok := blocked[0]["until_local"].(string); ok && until != "" {
			resp.Answer = answerText(fmt.Sprintf("%s is blocked until %s (%s).", name, until, reason))
		} else {
			resp.Answer = answerText(fmt.Sprintf("%s is blocked (%s).", name, reason))
		}
	default:
		resp.Answer = answerText(fmt.Sprintf("%d devices are blocked right now.", len(blocked)))
	}
	return resp
}

// answerPresence reports whether the devices are online. Presence comes from
// the broker's Last Will and Testament (FR-6).
func (a *Answerer) answerPresence(ctx context.Context, now time.Time, child string, devs []store.Device) AskResponse {
	selected := make([]store.Device, 0, len(devs))
	for _, dev := range devs {
		if matchesChild(dev, child) {
			selected = append(selected, dev)
		}
	}
	if len(selected) == 0 {
		return cannotAnswer("no devices are registered")
	}

	offline := make([]map[string]any, 0, len(selected))
	online := 0
	for _, dev := range selected {
		if dev.Online {
			online++
			continue
		}
		item := map[string]any{"device": dev.Name, "child": dev.Child}
		if dev.LastSeen != nil {
			item["last_seen"] = dev.LastSeen.UTC().Format(time.RFC3339)
			item["last_seen_local"] = dev.LastSeen.In(a.loc()).Format("15:04")
			item["offline_for"] = humanDuration(int(now.Sub(*dev.LastSeen).Seconds()))
		}
		offline = append(offline, item)
	}

	resp := AskResponse{
		Data:    map[string]any{"online": online, "offline": offline, "total": len(selected)},
		Expires: expiresIn(now, 5*time.Minute),
	}
	switch {
	case len(offline) == 0:
		if len(selected) == 1 {
			resp.Answer = answerText(fmt.Sprintf("%s is online.", selected[0].Name))
		} else {
			resp.Answer = answerText(fmt.Sprintf("All %d devices are online.", len(selected)))
		}
	case len(offline) == 1:
		name, _ := offline[0]["device"].(string)
		dur, _ := offline[0]["offline_for"].(string)
		resp.Answer = answerText(fmt.Sprintf("%s is offline (for %s).", name, dur))
	default:
		resp.Answer = answerText(fmt.Sprintf("%d devices are offline.", len(offline)))
	}
	return resp
}

// ScreenSeconds is the screen-time measure for one device-day. The
// foreground-app total is the measure; domain seconds are a browsing
// sub-measure and are only used when a device reported no app rows at all (the
// phone's VPN filter, for example). A report that carries both is not
// double-counted.
func ScreenSeconds(app, domain int) int {
	if app > 0 {
		return app
	}
	return domain
}

// knownChild reports whether any registered device belongs to child.
func knownChild(devs []store.Device, child string) bool {
	for _, dev := range devs {
		if strings.EqualFold(strings.TrimSpace(dev.Child), child) {
			return true
		}
	}
	return false
}

// matchesChild reports whether a device is in scope for a question. An empty
// child means every device.
func matchesChild(dev store.Device, child string) bool {
	return child == "" || strings.EqualFold(strings.TrimSpace(dev.Child), child)
}

// normalizeQuestion lowercases and collapses whitespace so intent matching is
// stable.
func normalizeQuestion(q string) string {
	return strings.Join(strings.Fields(strings.ToLower(q)), " ")
}

func containsAny(q string, subs ...string) bool {
	for _, s := range subs {
		if strings.Contains(q, s) {
			return true
		}
	}
	return false
}

// expiresIn formats an RFC3339 expiry used by data-bearing answers.
func expiresIn(now time.Time, d time.Duration) string {
	return now.UTC().Add(d).Format(time.RFC3339)
}

// titleCase upper-cases the first letter of a single-word name.
func titleCase(s string) string {
	s = strings.TrimSpace(s)
	if s == "" {
		return s
	}
	r := []rune(s)
	return strings.ToUpper(string(r[0])) + string(r[1:])
}

// humanDuration renders seconds compactly: "3h 20m", "45m", "under a minute".
func humanDuration(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)
}