// Package hub implements the project side of the frozen Hub contract
// (central_ai_llm_master/docs/ask-contract.md) for the Compass / NHS service:
//
//	GET  /capabilities  -> the topics this project can answer (Hub routing)
//	POST /ask           -> a short, read-only answer about school work
//	POST /notify        -> accept the contract's notification shape
//
// The Hub is the expert on routing and reply shape. It must never learn this
// project's data model, so /ask answers in one short sentence and never exposes
// a token, a path or a database id. /ask and /capabilities are read-only: they
// call only store read methods, so "read only" is a testable property
// (TestAskReadsOnly), not a comment (AGENTS.md §10 rule 5, FR-11).
//
// The answers are deterministic. No model is in the path: the Hub already caps
// the call at 3 seconds, and a school question must answer on the first try.
package hub

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

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

// ProjectName is the value the Hub matches in routing.md. The Hub's topic map
// (and central_ai_llm_master/routing.md) already names this project
// `compass_nhs`, and the contract requires /capabilities to report the same
// name, so this is the Hub-facing name. The repository, module and service keep
// the fuller "Compass / NHS" name.
const ProjectName = "compass_nhs"

// DefaultStaleAfter is how old the last successful scan may be before /ask says
// so. The 6:00am schedule scans daily, so a day and a half means the schedule
// did not run (AGENTS.md §13 decision 7).
const DefaultStaleAfter = 36 * time.Hour

// Capabilities is the GET /capabilities reply. The Hub reads it to route a
// question to this project. Keep the topic list short and plain; it holds no
// private data.
type Capabilities struct {
	Project string   `json:"project"`
	Topics  []string `json:"topics"`
	People  []string `json:"people"`
}

// DefaultCapabilities returns the topics this project answers. They match the
// school domain in AGENTS.md §1 and §4 and the Hub's routing.md row.
func DefaultCapabilities() Capabilities {
	return Capabilities{
		Project: ProjectName,
		Topics:  []string{"school", "compass", "homework", "timetable", "class", "overdue", "school notices"},
		People:  []string{"harry", "finn"},
	}
}

// AskRequest is the POST /ask body (ask-contract.md).
type AskRequest struct {
	Question string `json:"question"`
	Asker    string `json:"asker"`
	Person   string `json:"person,omitempty"`
	Source   string `json:"source,omitempty"`
}

// AskResponse is the POST /ask reply. A nil Answer means the project cannot
// answer and Reason explains why. The shape is frozen by the contract.
type AskResponse struct {
	Answer  *string        `json:"answer"`
	Data    map[string]any `json:"data,omitempty"`
	Expires string         `json:"expires,omitempty"`
	Reason  string         `json:"reason,omitempty"`
}

// NotifyRequest is the POST /notify body (ask-contract.md, "Notify"). The
// contract defines it as project-to-Hub; this service accepts the same shape so
// the Hub (or a future caller) can have a person notified without inventing a
// second shape. Delivery is the only write on this surface.
type NotifyRequest struct {
	From    string `json:"from"`
	Level   string `json:"level"`
	Message string `json:"message"`
	Person  string `json:"person,omitempty"`
}

// Reader is the read-only slice of the store that /ask and /capabilities use.
// It is an interface so the answer logic is testable without a database, and so
// the "read only" promise is enforced by the type: there is no write method to
// call.
type Reader interface {
	ListChildren(ctx context.Context) ([]store.Child, error)
	ItemsForChild(ctx context.Context, childID int64) ([]store.Item, error)
	ScanSummaryForChild(ctx context.Context, childID int64) (store.ScanStatus, error)
}

// Answerer answers /ask from stored school items. It holds no state of its own
// beyond the clock, so the same instance serves every request.
type Answerer struct {
	reader Reader
	loc    *time.Location
	// Now is the clock. It is a field so tests are deterministic.
	Now func() time.Time
	// StaleAfter is how old the last scan may be before the answer says so.
	// Zero means DefaultStaleAfter.
	StaleAfter time.Duration
	// Parents are the askers who may see any child. Every other asker may see
	// only themselves (ask-contract.md, "Rules for the project" rule 2).
	Parents []string
}

// NewAnswerer builds an answerer for the given reader and family timezone.
func NewAnswerer(reader Reader, loc *time.Location) *Answerer {
	if loc == nil {
		loc = time.UTC
	}
	return &Answerer{
		reader:     reader,
		loc:        loc,
		Now:        time.Now,
		StaleAfter: DefaultStaleAfter,
		Parents:    []string{"sam", "jo"},
	}
}

// SetParents replaces the askers who may see any child.
func (a *Answerer) SetParents(names ...string) {
	clean := make([]string, 0, len(names))
	for _, n := range names {
		if n = normalize(n); n != "" {
			clean = append(clean, n)
		}
	}
	if len(clean) > 0 {
		a.Parents = clean
	}
}

// Answer answers one question about this project's own data. It always returns
// a value: either an answer or a reason. It never guesses and never returns an
// answer for a question it cannot place.
func (a *Answerer) Answer(ctx context.Context, req AskRequest) AskResponse {
	if strings.TrimSpace(req.Question) == "" {
		return cannotAnswer("the question is required")
	}
	asker := normalize(req.Asker)
	if asker == "" {
		return cannotAnswer("the asker is required")
	}
	person := normalize(req.Person)
	if person == "" {
		person = asker
	}

	children, err := a.reader.ListChildren(ctx)
	if err != nil {
		return cannotAnswer("the school data could not be read")
	}
	child := findChild(children, person)
	if child == nil {
		return cannotAnswer("no data for that person")
	}
	if !a.maySee(asker, child.Name) {
		return cannotAnswer("that person is not allowed to ask about " + child.Name)
	}

	items, err := a.reader.ItemsForChild(ctx, child.ID)
	if err != nil {
		return cannotAnswer("the school data could not be read")
	}
	scan, err := a.reader.ScanSummaryForChild(ctx, child.ID)
	if err != nil {
		return cannotAnswer("the scan state could not be read")
	}

	now := a.Now().In(a.loc)
	buckets := dashboard.Classify(items, now, a.loc)
	state := scanHealthOf(scan, now, a.staleAfter())

	resp := a.compose(child, buckets, state, req.Question, now)
	return resp
}

// scanHealth is the fail-loudly view of the scan for one child (FR-12). It never
// lets a failed or missing scan read as "nothing due".
type scanHealth struct {
	OK      bool
	EverRun bool
	Stale   bool
	Age     time.Duration
	At      *time.Time
	Error   string
}

func scanHealthOf(st store.ScanStatus, now time.Time, staleAfter time.Duration) scanHealth {
	s := scanHealth{EverRun: st.EverRun}
	if st.Last == nil {
		return s
	}
	at := st.Last.StartedAt.In(now.Location())
	s.At = &at
	s.Age = now.Sub(at)
	if !st.Last.OK {
		s.Error = strings.TrimSpace(st.Last.Error)
		return s
	}
	s.OK = true
	s.Stale = staleAfter > 0 && s.Age > staleAfter
	return s
}

// compose turns one child's buckets into the contract's reply. The answer is
// one short sentence (with a second sentence only when the data is stale), and
// the structured detail lives in `data` for the Hub to ignore or use.
func (a *Answerer) compose(child *store.Child, b dashboard.Buckets, scan scanHealth, question string, now time.Time) AskResponse {
	data := map[string]any{
		"child":      child.Name,
		"scan_ok":    scan.OK,
		"scan_stale": scan.Stale,
	}
	if scan.At != nil {
		data["scan_at"] = scan.At.UTC().Format(time.RFC3339)
	}
	if scan.Age > 0 {
		data["scan_age_hours"] = int(scan.Age.Hours())
	}
	if scan.Error != "" {
		data["scan_error"] = scan.Error
	}

	// Fail loudly: a missing or failed scan is reported as its own answer, never
	// as an empty day (FR-12, AGENTS.md §10 rule 2).
	if !scan.OK {
		return AskResponse{
			Answer: answerText(unavailableAnswer(child.Name, scan)),
			Data:   data,
		}
	}

	data["overdue"] = itemList(b.Overdue, a.loc)
	data["due_today"] = itemList(b.DueToday, a.loc)
	data["due_week"] = itemList(b.DueWeek, a.loc)
	data["messages"] = itemList(b.Messages, a.loc)

	text := a.sentence(child.Name, b, focusFor(question), a.loc)
	if scan.Stale {
		text += " " + staleNote(child.Name, scan.Age)
	}
	return AskResponse{
		Answer:  answerText(text),
		Data:    data,
		Expires: endOfDay(now).UTC().Format(time.RFC3339),
	}
}

// focus is the part of the data the question asks about.
type focus int

const (
	focusAll focus = iota
	focusToday
	focusWeek
	focusOverdue
	focusMessages
)

// focusFor reads the question. It is deliberately simple: the Hub routes the
// question, so this project only has to place the few school shapes. An unknown
// question still answers with the whole picture rather than guessing a bucket.
func focusFor(question string) focus {
	q := strings.ToLower(question)
	switch {
	case contains(q, "overdue", "not done", "outstanding", "late work", "behind"):
		return focusOverdue
	case contains(q, "this week", "next week", "week"):
		return focusWeek
	case contains(q, "message", "notice", "news", "email", "announcement"):
		return focusMessages
	case contains(q, "today", "timetable", "schedule", "class", "period", "lesson", "at school", "on at school"):
		return focusToday
	case contains(q, "due", "homework", "assignment", "assessment", "task", "sac", "exam"):
		return focusAll
	default:
		return focusAll
	}
}

// sentence builds the one-sentence answer for a focus. Every part is a phrase
// ("8 classes today from 8:55am", "2 overdue tasks"), so the joined sentence
// stays grammatical.
func (a *Answerer) sentence(name string, b dashboard.Buckets, f focus, loc *time.Location) string {
	events := onlyType(b.DueToday, "event")
	today := onlyType(b.DueToday, "task")

	var parts []string
	add := func(s string) {
		if s != "" {
			parts = append(parts, s)
		}
	}
	overdue := countPhrase(len(b.Overdue), "overdue task")
	week := countPhrase(len(b.DueWeek), "task due this week")

	switch f {
	case focusOverdue:
		add(overdue)
		if len(parts) == 0 {
			add(countPhrase(len(today), "task due today"))
		}
	case focusWeek:
		add(overdue)
		add(week)
	case focusMessages:
		add(countPhrase(len(b.Messages), "school notice"))
	case focusToday:
		add(eventsPhrase(events, loc))
		add(countPhrase(len(today), "task due today"))
		add(overdue)
	default: // focusAll
		add(eventsPhrase(events, loc))
		add(countPhrase(len(today), "task due today"))
		add(overdue)
		add(week)
	}

	if len(parts) == 0 {
		return name + " has nothing due today."
	}
	return name + " has " + joinParts(parts) + "."
}

// eventsPhrase is the today's-schedule part: "8 classes today from 8:55am".
func eventsPhrase(events []store.Item, loc *time.Location) string {
	if len(events) == 0 {
		return ""
	}
	first, last := time.Time{}, time.Time{}
	for _, it := range events {
		if it.DueAt == nil {
			continue
		}
		t := it.DueAt.In(loc)
		if first.IsZero() || t.Before(first) {
			first = t
		}
		if last.IsZero() || t.After(last) {
			last = t
		}
	}
	word := "events"
	if len(events) == 1 {
		word = "event"
	}
	if first.IsZero() {
		return fmt.Sprintf("%d school %s today", len(events), word)
	}
	if first.Format("15:04") == last.Format("15:04") {
		return fmt.Sprintf("%d school %s today from %s", len(events), word, clock(first))
	}
	return fmt.Sprintf("%d school %s today from %s to %s", len(events), word, clock(first), clock(last))
}

// unavailableAnswer is the fail-loudly sentence for a missing or failed scan.
func unavailableAnswer(name string, scan scanHealth) string {
	if !scan.EverRun {
		return fmt.Sprintf("I have no school data for %s yet: the Compass scan has not run, so due work is unknown.", name)
	}
	if scan.At != nil {
		return fmt.Sprintf("I cannot say what %s has due: the last Compass scan on %s failed, so due work is unknown.",
			name, scan.At.In(time.UTC).Format("Mon 02 Jan 15:04 MST"))
	}
	return fmt.Sprintf("I cannot say what %s has due: the last Compass scan failed, so due work is unknown.", name)
}

// staleNote qualifies an answer built on old data, so an out-of-date list is
// never read as today's work.
func staleNote(name string, age time.Duration) string {
	days := int(age.Hours() / 24)
	if days >= 2 {
		return fmt.Sprintf("The last Compass scan for %s was %d days ago, so this may be out of date.", name, days)
	}
	return fmt.Sprintf("The last Compass scan for %s was %d hours ago, so this may be out of date.", name, int(age.Hours()))
}

// maySee checks the contract's permission rule: a parent may see any child, and
// anyone else may see only themselves.
func (a *Answerer) maySee(asker, child string) bool {
	a2, c := normalize(asker), normalize(child)
	if a2 == c {
		return true
	}
	for _, p := range a.Parents {
		if normalize(p) == a2 {
			return true
		}
	}
	return false
}

func (a *Answerer) staleAfter() time.Duration {
	if a.StaleAfter > 0 {
		return a.StaleAfter
	}
	return DefaultStaleAfter
}

// findChild matches a name case-insensitively: the Hub lower-cases names, while
// the database stores "Harry".
func findChild(children []store.Child, name string) *store.Child {
	for i := range children {
		if normalize(children[i].Name) == name {
			return &children[i]
		}
	}
	return nil
}

func onlyType(items []store.Item, typ string) []store.Item {
	out := make([]store.Item, 0, len(items))
	for _, it := range items {
		if it.Type == typ {
			out = append(out, it)
		}
	}
	return out
}

// itemList is the structured detail for `data`. It holds no secret and no path.
func itemList(items []store.Item, loc *time.Location) []map[string]any {
	out := make([]map[string]any, 0, len(items))
	for _, it := range items {
		m := map[string]any{
			"type":  it.Type,
			"title": strings.TrimSpace(it.Title),
		}
		if s := strings.TrimSpace(it.Subject); s != "" {
			m["subject"] = s
		}
		if t := strings.TrimSpace(it.Teacher); t != "" {
			m["teacher"] = t
		}
		if it.DueAt != nil {
			m["due_at"] = it.DueAt.In(loc).Format(time.RFC3339)
		}
		out = append(out, m)
	}
	return out
}

func countPhrase(n int, noun string) string {
	switch {
	case n == 0:
		return ""
	case n == 1:
		return "1 " + noun
	default:
		return fmt.Sprintf("%d %ss", n, noun)
	}
}

// joinParts renders "a", "a and b" or "a, b and c".
func joinParts(parts []string) string {
	switch len(parts) {
	case 0:
		return ""
	case 1:
		return parts[0]
	case 2:
		return parts[0] + " and " + parts[1]
	default:
		return strings.Join(parts[:len(parts)-1], ", ") + " and " + parts[len(parts)-1]
	}
}

func contains(haystack string, needles ...string) bool {
	for _, n := range needles {
		if strings.Contains(haystack, n) {
			return true
		}
	}
	return false
}

func clock(t time.Time) string { return t.Format("3:04pm") }

func endOfDay(t time.Time) time.Time {
	return time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, t.Location()).AddDate(0, 0, 1)
}

func normalize(s string) string { return strings.ToLower(strings.TrimSpace(s)) }

// answerText is a small helper so pointer handling stays in one place.
func answerText(s string) *string { return &s }

// cannotAnswer builds the contract's "cannot answer" reply.
func cannotAnswer(reason string) AskResponse {
	return AskResponse{Answer: nil, Reason: reason}
}