package api

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"slices"
	"strconv"
	"strings"
	"time"
	"unicode"

	usermodels "git.golem15.com/golem15/sm-user-plugin/models"
	"git.golem15.com/golem15/summercms/modules/bouncer"
	"git.golem15.com/golem15/summercms/modules/lagoon"
	"git.golem15.com/golem15/summercms/modules/lagoon/attach"
	"git.golem15.com/golem15/summercms/modules/surf"
	"git.golem15.com/golem15/summercms/modules/wire"
	"git.golem15.com/jakub/sm-bm-plugin/classes"
	"git.golem15.com/jakub/sm-bm-plugin/models"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

// The management API (/api/v1/bm) is what the console commands do, over
// HTTP: it runs behind golem15.user's shared API-token, scope, and permission
// middleware, not the students' jwt.auth.

// flag reads a boolean query parameter: 1 and true are on.
func flag(r *http.Request, name string) bool {
	v := r.URL.Query().Get(name)
	return v == "1" || v == "true"
}

func writeInvalid(w http.ResponseWriter, message string) {
	wire.WriteJSON(w, http.StatusUnprocessableEntity, map[string]any{"message": message})
}

// body reads the request body and answers 413 or 400 itself when it cannot.
func body(w http.ResponseWriter, r *http.Request) ([]byte, bool) {
	raw, err := io.ReadAll(r.Body)
	var tooLarge *http.MaxBytesError
	switch {
	case errors.As(err, &tooLarge):
		wire.WriteJSON(w, http.StatusRequestEntityTooLarge, map[string]any{"error": true, "message": "Request body too large."})
		return nil, false
	case err != nil:
		wire.WriteJSON(w, http.StatusBadRequest, map[string]any{"error": true, "message": "Unreadable request body."})
		return nil, false
	}
	return raw, true
}

type tokenJSON struct {
	ID        uint     `json:"id"`
	Name      string   `json:"name"`
	Scopes    []string `json:"scopes"`
	ExpiresAt *string  `json:"expires_at"`
}

// TokenInfo answers GET /me: the user and the token of the request, to
// check a token without changing anything.
func (h *Handlers) TokenInfo(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	out := map[string]any{"user_id": userID}
	cred, _ := bouncer.Credential(r.Context())
	if t, ok := cred.(*usermodels.APIToken); ok {
		name := ""
		if t.Name != nil {
			name = *t.Name
		}
		tj := tokenJSON{ID: t.ID, Name: name, Scopes: wire.Slice(t.Scopes.Get())}
		if t.ExpiresAt != nil {
			s := models.FormatDateTime(*t.ExpiresAt)
			tj.ExpiresAt = &s
		}
		out["token"] = tj
	}
	writeData(w, out)
}

type seedCountsJSON struct {
	Created   int `json:"created"`
	Updated   int `json:"updated"`
	Unchanged int `json:"unchanged"`
	Deleted   int `json:"deleted"`
}

func newSeedCountsJSON(c classes.SeedCounts) seedCountsJSON {
	return seedCountsJSON{Created: c.Created, Updated: c.Updated, Unchanged: c.Unchanged, Deleted: c.Deleted}
}

// ApplySeed answers POST /seed?dry_run=&prune=: bm:seed over HTTP. The body
// is the seed document; the answer is the summary the command prints. A
// document that does not parse or validate is a 422 and writes nothing.
func (h *Handlers) ApplySeed(w http.ResponseWriter, r *http.Request) {
	raw, ok := body(w, r)
	if !ok {
		return
	}
	file, err := classes.ParseSeed(bytes.NewReader(raw))
	if err == nil {
		err = file.Validate()
	}
	if err != nil {
		writeInvalid(w, err.Error())
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	opts := classes.SeedOptions{DryRun: flag(r, "dry_run"), Prune: flag(r, "prune")}
	sum, err := classes.SeedWith(r.Context(), db, file, opts)
	if err != nil {
		writeOpaque500(w)
		return
	}
	writeData(w, map[string]any{
		"dry_run": opts.DryRun,
		"prune":   opts.Prune,
		"summary": map[string]seedCountsJSON{
			"meetings":       newSeedCountsJSON(sum.Meetings),
			"courses":        newSeedCountsJSON(sum.Courses),
			"class_sessions": newSeedCountsJSON(sum.ClassSessions),
			"deadlines":      newSeedCountsJSON(sum.Deadlines),
			"readings":       newSeedCountsJSON(sum.Readings),
		},
		"removed": wire.Slice(sum.Removed),
	})
}

// managedMaterialJSON is a material as the management API shows it: drafts
// too, so published_at may be null, and private ones with their author and
// the users they are shared with.
type managedMaterialJSON struct {
	ID          uint       `json:"id"`
	CourseID    *uint      `json:"course_id"`
	Course      *courseRef `json:"course"`
	MeetingID   *uint      `json:"meeting_id"`
	Title       string     `json:"title"`
	Type        string     `json:"type"`
	Body        *string    `json:"body"`
	Source      *string    `json:"source"`
	URL         *string    `json:"url"`
	PublishedAt *string    `json:"published_at"`
	Tags        []tagJSON  `json:"tags"`

	IsPrivate    bool          `json:"is_private"`
	AuthorUserID *uint         `json:"author_user_id"`
	Author       *userRefJSON  `json:"author"`
	Shares       []userRefJSON `json:"shares"`
	// Revision is the material's content revision, which a write may send
	// back to be refused when the material changed since; UpdatedAt is
	// when the row was last written.
	Revision  uint   `json:"revision"`
	UpdatedAt string `json:"updated_at"`
	// Snippet is the matched passage of a search result, as on the
	// student list; nil, and the key absent, without q.
	Snippet any `json:"snippet,omitempty"`
}

// materialPeople are the authors and shares of a batch of materials, as
// loadMaterialPeople reads them.
type materialPeople struct {
	authors map[uint]userRefJSON
	shares  map[uint][]userRefJSON
}

// loadMaterialPeople reads the authors and the shares of rows in two
// queries plus one for the shared users.
func loadMaterialPeople(db *gorm.DB, rows ...models.Material) (materialPeople, error) {
	var authorIDs, materialIDs []uint
	for _, m := range rows {
		materialIDs = append(materialIDs, m.ID)
		if m.AuthorUserID != nil {
			authorIDs = append(authorIDs, *m.AuthorUserID)
		}
	}
	authors, err := userRefsByID(db, authorIDs)
	if err != nil {
		return materialPeople{}, err
	}
	shares, err := materialShareRefs(db, materialIDs)
	if err != nil {
		return materialPeople{}, err
	}
	return materialPeople{authors: authors, shares: shares}, nil
}

func newManagedMaterialJSON(m models.Material, people materialPeople) managedMaterialJSON {
	out := managedMaterialJSON{
		ID: m.ID, CourseID: m.CourseID, Course: newCourseRef(m.Course), MeetingID: m.MeetingID, Title: m.Title, Type: m.Type,
		Body: m.Body, Source: m.Source, URL: m.URL, Tags: newTagsJSON(m.Tags),
		IsPrivate: m.IsPrivate, AuthorUserID: m.AuthorUserID, Shares: people.shares[m.ID],
		Revision: m.Revision, UpdatedAt: models.FormatDateTime(m.UpdatedAt),
	}
	if m.AuthorUserID != nil {
		if a, ok := people.authors[*m.AuthorUserID]; ok {
			out.Author = &a
		}
	}
	if out.Shares == nil {
		out.Shares = []userRefJSON{}
	}
	if m.PublishedAt != nil {
		s := models.FormatDateTime(*m.PublishedAt)
		out.PublishedAt = &s
	}
	return out
}

// ManagedMaterials answers GET /materials?q=&include_body=: every material,
// drafts and private ones included, newest first. With q (2 to 100
// characters) the engine answers candidates, which are loaded in rank order
// with at most one snippet each; when the engine cannot answer the request
// is a 503. An MCP call gets the bodies only with include_body (see
// managedMaterialView) and the snippets as plain text.
func (h *Handlers) ManagedMaterials(w http.ResponseWriter, r *http.Request) {
	in := query(r, "q", "include_body")
	if !h.validate(w, r, in, manageMaterialsRules) {
		return
	}
	var cands *classes.MaterialCandidates
	if q := searchQuery(in); q != "" {
		c, err := h.MaterialIndex.Search(r.Context(), classes.MaterialSearch{Q: q})
		if err != nil {
			writeSearchUnavailable(w)
			return
		}
		cands = &c
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	var rows []models.Material
	if cands == nil || len(cands.IDs) > 0 {
		q := preloadMaterial(db)
		if cands != nil {
			q = q.Where("jz_bm_materials.id IN ?", cands.IDs).Order(rankOrder(cands.IDs))
		} else {
			q = q.Order("jz_bm_materials.id DESC")
		}
		if err := q.Find(&rows).Error; err != nil {
			writeOpaque500(w)
			return
		}
	}
	people, err := loadMaterialPeople(db, rows...)
	if err != nil {
		writeOpaque500(w)
		return
	}
	var files map[uint][]models.IndexedFile
	if cands != nil {
		files, err = snippetFiles(db, materialIDs(rows), cands.Hits)
		if err != nil {
			writeOpaque500(w)
			return
		}
	}
	mcp := viaMCP(r)
	out := make([]any, 0, len(rows))
	for _, m := range rows {
		row := newManagedMaterialJSON(m, people)
		if cands != nil {
			if hit, ok := cands.Hits[m.ID]; ok {
				row.Snippet = snippetValue(pickSnippet(hit, m, files[m.ID]), mcp)
			}
		}
		out = append(out, managedMaterialView(row, mcp, includeBody(r)))
	}
	writeData(w, out)
}

// materialInput is the body of POST /materials and PUT /materials/{id}.
// Revision is the revision the writer last read: when sent and not the
// stored one the write is a 409 and nothing is written; absent means
// unchecked, so the write overwrites as callers that never send it expect
// (D-04).
type materialInput struct {
	CourseID    *uint     `json:"course_id"`
	MeetingID   *uint     `json:"meeting_id"`
	Title       string    `json:"title"`
	Type        string    `json:"type"`
	Body        *string   `json:"body"`
	Source      *string   `json:"source"`
	URL         *string   `json:"url"`
	PublishedAt *string   `json:"published_at"`
	Tags        *[]string `json:"tags"`

	IsPrivate    *bool   `json:"is_private"`
	AuthorUserID *uint   `json:"author_user_id"`
	ShareUserIDs *[]uint `json:"share_user_ids"`

	Revision *uint `json:"revision"`
}

// materialDraft is a decoded and validated material body, ready to apply.
type materialDraft struct {
	in materialInput
	// hasPublishedAt tells a sent published_at (null included) from an
	// absent one.
	hasPublishedAt bool
	// hasMeetingID tells a sent meeting_id (null included) from an absent
	// one: absent keeps the stored meeting, so scripts that never send it
	// keep working.
	hasMeetingID bool
	// hasAuthor tells a sent author_user_id (null included) from an absent
	// one.
	hasAuthor   bool
	publishedAt *time.Time
	tags        []models.Tag
	// shares is the checked share_user_ids, when sent.
	shares []uint
}

// readMaterial decodes and validates the body of POST /materials and
// PUT /materials/{id}. It answers 400, 413, 422 or 500 itself and returns
// false then.
func (h *Handlers) readMaterial(w http.ResponseWriter, r *http.Request, db *gorm.DB) (materialDraft, bool) {
	raw, ok := body(w, r)
	if !ok {
		return materialDraft{}, false
	}
	d, err := decodeMaterial(raw)
	if err != nil {
		writeInvalid(w, "invalid JSON: "+err.Error())
		return d, false
	}
	if !h.checkMaterial(w, db, &d, nil) {
		return d, false
	}
	return d, true
}

// decodeMaterial decodes a material body, refusing unknown keys, and notes
// which of published_at, meeting_id and author_user_id were sent. It does
// not validate the values; checkMaterial does.
func decodeMaterial(raw []byte) (materialDraft, error) {
	var d materialDraft
	dec := json.NewDecoder(bytes.NewReader(raw))
	dec.DisallowUnknownFields()
	if err := dec.Decode(&d.in); err != nil {
		return d, err
	}
	var keys map[string]json.RawMessage
	_ = json.Unmarshal(raw, &keys)
	_, d.hasPublishedAt = keys["published_at"]
	_, d.hasMeetingID = keys["meeting_id"]
	_, d.hasAuthor = keys["author_user_id"]
	return d, nil
}

// checkMaterial validates a decoded material body against db and fills in
// its published_at, tags and shares. Its messages join errs, which a caller
// may pre-fill with its own rules (nil means none); when there are any it
// answers one 422 with all of them, and on a database error a 500, and
// returns false then.
func (h *Handlers) checkMaterial(w http.ResponseWriter, db *gorm.DB, d *materialDraft, errs map[string][]string) bool {
	if errs == nil {
		errs = map[string][]string{}
	}
	in := &d.in
	in.Title = strings.TrimSpace(in.Title)
	if in.Title == "" || len(in.Title) > 255 {
		errs["title"] = []string{"The title is required and may not be longer than 255 characters."}
	}
	if !slices.Contains(models.MaterialTypes, in.Type) {
		errs["type"] = []string{"The type must be one of: " + strings.Join(models.MaterialTypes, ", ") + "."}
	}
	if in.Source != nil && len(*in.Source) > 500 {
		errs["source"] = []string{"The source may not be longer than 500 characters."}
	}
	if in.URL != nil && len(*in.URL) > 2048 {
		errs["url"] = []string{"The url may not be longer than 2048 characters."}
	}
	if in.PublishedAt != nil {
		t, err := models.ParseDateTime(*in.PublishedAt)
		if err != nil {
			errs["published_at"] = []string{"The published_at is not a valid date and time."}
		}
		d.publishedAt = &t
	}
	if in.Tags != nil {
		for _, name := range *in.Tags {
			name = strings.TrimSpace(name)
			slug := slugify(name)
			if slug == "" || len(name) > 100 || len(slug) > 100 {
				errs["tags"] = []string{"Each tag must be a name of 1 to 100 characters."}
				break
			}
			if !slices.ContainsFunc(d.tags, func(t models.Tag) bool { return t.Slug == slug }) {
				d.tags = append(d.tags, models.Tag{Name: name, Slug: slug})
			}
		}
	}
	if in.CourseID != nil {
		var n int64
		if err := db.Model(&models.Course{}).Where("id = ?", *in.CourseID).Count(&n).Error; err != nil {
			writeOpaque500(w)
			return false
		}
		if n == 0 {
			errs["course_id"] = []string{"The selected course_id is invalid."}
		}
	}
	if in.MeetingID != nil {
		var n int64
		if err := db.Model(&models.Meeting{}).Where("id = ?", *in.MeetingID).Count(&n).Error; err != nil {
			writeOpaque500(w)
			return false
		}
		if n == 0 {
			errs["meeting_id"] = []string{"The selected meeting_id is invalid."}
		}
	}
	if in.AuthorUserID != nil {
		found, err := userRefsByID(db, []uint{*in.AuthorUserID})
		if err != nil {
			writeOpaque500(w)
			return false
		}
		if _, ok := found[*in.AuthorUserID]; !ok {
			errs["author_user_id"] = []string{"The selected author_user_id is invalid."}
		}
	}
	if in.ShareUserIDs != nil {
		clean, msg, err := cleanUserIDs(db, *in.ShareUserIDs)
		if err != nil {
			writeOpaque500(w)
			return false
		}
		if msg != "" {
			errs["share_user_ids"] = []string{msg}
		}
		d.shares = clean
	}
	if len(errs) > 0 {
		writeValidation(w, errs)
		return false
	}
	return true
}

// identity scopes a query to the materials with the draft's title and
// course: the identity POST /materials upserts on.
func (d materialDraft) identity(q *gorm.DB) *gorm.DB {
	q = q.Where("title = ?", d.in.Title)
	if d.in.CourseID != nil {
		return q.Where("course_id = ?", *d.in.CourseID)
	}
	return q.Where("course_id IS NULL")
}

// apply writes the draft onto m inside tx. published_at: absent publishes
// a new material now and keeps an existing one as it is; null makes a
// draft; otherwise the sent time. meeting_id: absent keeps it; null clears
// it. tags: absent keeps them; otherwise the list replaces them, and unknown
// tags are created. is_private: absent keeps it (a new material is public).
// author_user_id: absent keeps it (a new material gets callerID); null
// clears it. share_user_ids: absent keeps the shares; otherwise the list
// replaces them.
func (d materialDraft) apply(tx *gorm.DB, m *models.Material, created bool, now time.Time, callerID uint) error {
	in := d.in
	m.CourseID, m.Title, m.Type = in.CourseID, in.Title, in.Type
	m.Body, m.Source, m.URL = in.Body, in.Source, in.URL
	if d.hasMeetingID {
		m.MeetingID = in.MeetingID
	}
	if in.IsPrivate != nil {
		m.IsPrivate = *in.IsPrivate
	}
	switch {
	case d.hasAuthor:
		m.AuthorUserID = in.AuthorUserID
	case created && callerID != 0:
		id := callerID
		m.AuthorUserID = &id
	}
	switch {
	case d.hasPublishedAt:
		m.PublishedAt = d.publishedAt
	case created:
		m.PublishedAt = &now
	}
	if err := tx.Omit("Course", "Meeting", "Tags").Save(m).Error; err != nil {
		return err
	}
	if in.ShareUserIDs != nil {
		if err := replaceMaterialShares(tx, m.ID, d.shares); err != nil {
			return err
		}
	}
	if in.Tags == nil {
		return nil
	}
	if err := tx.Where("material_id = ?", m.ID).Delete(&models.MaterialTag{}).Error; err != nil {
		return err
	}
	for _, t := range d.tags {
		var tag models.Tag
		res := tx.Where("slug = ?", t.Slug).Limit(1).Find(&tag)
		if res.Error != nil {
			return res.Error
		}
		if res.RowsAffected == 0 {
			tag = t
			if err := tx.Create(&tag).Error; err != nil {
				return err
			}
		}
		if err := tx.Create(&models.MaterialTag{MaterialID: m.ID, TagID: tag.ID}).Error; err != nil {
			return err
		}
	}
	return nil
}

// writeManaged answers a write of r with the material id, reloaded with its
// course and tags, plus any extra top-level keys. Under MCP the answer never
// echoes the body.
func writeManaged(w http.ResponseWriter, r *http.Request, db *gorm.DB, id uint, status int, extra map[string]any) {
	var out models.Material
	if err := preloadMaterial(db).First(&out, id).Error; err != nil {
		writeOpaque500(w)
		return
	}
	people, err := loadMaterialPeople(db, out)
	if err != nil {
		writeOpaque500(w)
		return
	}
	payload := map[string]any{"data": managedMaterialView(newManagedMaterialJSON(out, people), viaMCP(r), false)}
	for k, v := range extra {
		payload[k] = v
	}
	wire.WriteJSON(w, status, payload)
}

// UpsertMaterial answers POST /materials: it creates the material, or
// updates the one with the same title and course, so sending a document
// twice changes nothing. body, source and url are replaced as sent; see
// materialDraft.apply for published_at and tags. A renamed material is a
// new one here: PUT /materials/{id} renames.
func (h *Handlers) UpsertMaterial(w http.ResponseWriter, r *http.Request) {
	callerID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	d, ok := h.readMaterial(w, r, db)
	if !ok {
		return
	}
	var m models.Material
	created := false
	err := lagoon.Transaction(r.Context(), db, func(_ context.Context, tx *gorm.DB) error {
		res := d.identity(tx).Order("id").Limit(1).Find(&m)
		if res.Error != nil {
			return res.Error
		}
		created = res.RowsAffected == 0
		return d.apply(tx, &m, created, h.now(), callerID)
	})
	if err != nil {
		writeOpaque500(w)
		return
	}
	h.MaterialIndex.Sync(r.Context(), db, m.ID)
	status := http.StatusOK
	if created {
		status = http.StatusCreated
	}
	writeManaged(w, r, db, m.ID, status, map[string]any{"created": created})
}

// UpdateMaterial answers PUT /materials/{id}: the same body as POST, applied
// to that material, so a title or course can change. A title and course
// another material already has is a 422, because POST would then be
// ambiguous. An unknown id is a 404. The row is locked for the write: a sent
// revision that is not the stored one is a 409 with the current version
// (writeConflict) and nothing is written; without revision the write
// overwrites. The revision goes up only when the content changed
// (models.ReviseMaterial).
func (h *Handlers) UpdateMaterial(w http.ResponseWriter, r *http.Request) {
	callerID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return
	}
	d, ok := h.readMaterial(w, r, db)
	if !ok {
		return
	}
	var m models.Material
	found, taken, conflict := false, false, false
	err := lagoon.Transaction(r.Context(), db, func(ctx context.Context, tx *gorm.DB) error {
		res := tx.Clauses(clause.Locking{Strength: "UPDATE"}).Where("id = ?", id).Limit(1).Find(&m)
		if res.Error != nil {
			return res.Error
		}
		if res.RowsAffected == 0 {
			return nil
		}
		found = true
		if staleRevision(d.in.Revision, m.Revision) {
			conflict = true
			return nil
		}
		before, err := models.MaterialContent(tx, m.ID)
		if err != nil {
			return err
		}
		var n int64
		if err := d.identity(tx.Model(&models.Material{})).Where("id <> ?", m.ID).Count(&n).Error; err != nil {
			return err
		}
		if n > 0 {
			taken = true
			return nil
		}
		if err := d.apply(tx, &m, false, h.now(), callerID); err != nil {
			return err
		}
		return h.revise(ctx, tx, m.ID, before)
	})
	switch {
	case err != nil:
		writeOpaque500(w)
	case !found:
		writeNotFound(w)
	case conflict:
		writeConflict(w, r, db, m.ID)
	case taken:
		writeValidation(w, map[string][]string{"title": {"Another material already has this title and course."}})
	default:
		h.MaterialIndex.Sync(r.Context(), db, m.ID)
		writeManaged(w, r, db, m.ID, http.StatusOK, nil)
	}
}

// managedMaterialDetailJSON is GET /materials/{id}: the material with its
// public files.
type managedMaterialDetailJSON struct {
	managedMaterialJSON
	Files []fileJSON `json:"files"`
}

// ManagedMaterial answers GET /materials/{id}: one material, draft or not,
// with its public files.
func (h *Handlers) ManagedMaterial(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return
	}
	h.writeMaterialDetail(w, r, db, uint(id), http.StatusOK)
}

// writeMaterialDetail answers r with the material id as GET /materials/{id}
// shows it, or 404 when there is none. Under MCP a GET carries the body only
// with include_body, and any other method's answer never does.
func (h *Handlers) writeMaterialDetail(w http.ResponseWriter, r *http.Request, db *gorm.DB, id uint, status int) {
	h.writeMaterialDetailWith(w, r, db, id, status, nil)
}

// writeMaterialDetailWith is writeMaterialDetail with extra top-level keys
// beside data (the file warning of the inline upload).
func (h *Handlers) writeMaterialDetailWith(w http.ResponseWriter, r *http.Request, db *gorm.DB, id uint, status int, extra map[string]any) {
	var m models.Material
	res := preloadMaterial(db).Where("jz_bm_materials.id = ?", id).Limit(1).Find(&m)
	if res.Error != nil {
		writeOpaque500(w)
		return
	}
	if res.RowsAffected == 0 {
		writeNotFound(w)
		return
	}
	var files []attach.File
	if err := materialFiles(db, m).Order("sort_order, id").Find(&files).Error; err != nil {
		writeOpaque500(w)
		return
	}
	people, err := loadMaterialPeople(db, m)
	if err != nil {
		writeOpaque500(w)
		return
	}
	out := managedMaterialDetailJSON{managedMaterialJSON: newManagedMaterialJSON(m, people), Files: make([]fileJSON, 0, len(files))}
	for i := range files {
		f := &files[i]
		if !f.Public() {
			continue
		}
		out.Files = append(out.Files, fileJSON{ID: f.ID, URL: f.URL(), Name: f.FileName, Size: f.FileSize, Mime: f.ContentType})
	}
	answer := map[string]any{"data": managedMaterialDetailView(out, viaMCP(r), r.Method == http.MethodGet && includeBody(r))}
	for k, v := range extra {
		answer[k] = v
	}
	wire.WriteJSON(w, status, answer)
}

// DeleteMaterial answers DELETE /materials/{id}.
func (h *Handlers) DeleteMaterial(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return
	}
	var keys []string
	found := false
	err := lagoon.Transaction(r.Context(), db, func(_ context.Context, tx *gorm.DB) error {
		res := tx.Where("id = ?", id).Delete(&models.Material{})
		if res.Error != nil || res.RowsAffected == 0 {
			return res.Error
		}
		found = true
		return attach.DeleteForOwner(tx, models.Material{}, strconv.FormatInt(id, 10), func(k []string) error {
			keys = k
			return nil
		})
	})
	switch {
	case err != nil:
		writeOpaque500(w)
		return
	case !found:
		writeNotFound(w)
		return
	}
	// The delete statement has no primary key on its model, so no callback
	// removes the document: remove it now that the transaction committed.
	h.MaterialIndex.Remove(r.Context(), db, uint(id))
	// The files go with the material: rows in the transaction, blobs after it.
	if b := h.Bucket; b != nil && len(keys) > 0 {
		if bucket := b(); bucket != nil {
			_ = attach.DeleteKeys(r.Context(), bucket, keys)
		}
	}
	w.WriteHeader(http.StatusNoContent)
}

// polish maps the Polish letters slugify cannot fold by case alone.
var polish = strings.NewReplacer("ą", "a", "ć", "c", "ę", "e", "ł", "l", "ń", "n", "ó", "o", "ś", "s", "ź", "z", "ż", "z")

// slugify turns a tag name into its slug: lower-case ASCII letters and
// digits, with a hyphen for every run of anything else.
func slugify(name string) string {
	var b strings.Builder
	hyphen := false
	for _, r := range polish.Replace(strings.ToLower(name)) {
		if r < unicode.MaxASCII && (unicode.IsLetter(r) || unicode.IsDigit(r)) {
			if hyphen && b.Len() > 0 {
				b.WriteByte('-')
			}
			hyphen = false
			b.WriteRune(r)
			continue
		}
		hyphen = true
	}
	return b.String()
}

// managedAccessChange loads the material of r by id and, unless decode
// refuses the body, applies the access change it returns inside a
// transaction with the claim rule (a material with no author gets the
// caller). It answers 404, 422 or 500 itself, and on success the material as
// writeManaged shows it, so under MCP the body is never echoed.
func (h *Handlers) managedAccessChange(w http.ResponseWriter, r *http.Request, decode func(db *gorm.DB, raw []byte) (isPrivate *bool, setShares bool, shares []uint, ok bool)) {
	callerID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return
	}
	var m models.Material
	res := db.Where("id = ?", id).Limit(1).Find(&m)
	if res.Error != nil {
		writeOpaque500(w)
		return
	}
	if res.RowsAffected == 0 {
		writeNotFound(w)
		return
	}
	raw, ok := body(w, r)
	if !ok {
		return
	}
	isPrivate, setShares, shares, ok := decode(db, raw)
	if !ok {
		return
	}
	err := lagoon.Transaction(r.Context(), db, func(_ context.Context, tx *gorm.DB) error {
		return applyMaterialAccess(tx, &m, callerID, isPrivate, setShares, shares)
	})
	if err != nil {
		writeOpaque500(w)
		return
	}
	// An access change touches only visibility (and the author), which the
	// search index does not hold, so it does not sync.
	writeManaged(w, r, db, m.ID, http.StatusOK, nil)
}

// SetMaterialVisibility answers PATCH /materials/{id}/visibility, body
// {"is_private": bool}: private means only the author and the users it is
// shared with see the material. A material with no author gets the caller
// as author. An unknown id is a 404.
func (h *Handlers) SetMaterialVisibility(w http.ResponseWriter, r *http.Request) {
	h.managedAccessChange(w, r, func(_ *gorm.DB, raw []byte) (*bool, bool, []uint, bool) {
		var in struct {
			IsPrivate *bool `json:"is_private"`
		}
		dec := json.NewDecoder(bytes.NewReader(raw))
		dec.DisallowUnknownFields()
		if err := dec.Decode(&in); err != nil {
			writeInvalid(w, "invalid JSON: "+err.Error())
			return nil, false, nil, false
		}
		if in.IsPrivate == nil {
			writeValidation(w, map[string][]string{"is_private": {"The is_private field is required and must be true or false."}})
			return nil, false, nil, false
		}
		return in.IsPrivate, false, nil, true
	})
}

// SetMaterialShares answers PUT /materials/{id}/shares, body
// {"user_ids": [id]}: the list (null meaning none) replaces the users the
// material is shared with. The claim rule is as for SetMaterialVisibility.
func (h *Handlers) SetMaterialShares(w http.ResponseWriter, r *http.Request) {
	h.managedAccessChange(w, r, func(db *gorm.DB, raw []byte) (*bool, bool, []uint, bool) {
		var in struct {
			UserIDs []uint `json:"user_ids"`
		}
		dec := json.NewDecoder(bytes.NewReader(raw))
		dec.DisallowUnknownFields()
		if err := dec.Decode(&in); err != nil {
			writeInvalid(w, "invalid JSON: "+err.Error())
			return nil, false, nil, false
		}
		var keys map[string]json.RawMessage
		_ = json.Unmarshal(raw, &keys)
		if _, ok := keys["user_ids"]; !ok {
			writeValidation(w, map[string][]string{"user_ids": {"The user_ids field is required: a list of user ids, empty for none."}})
			return nil, false, nil, false
		}
		clean, msg, err := cleanUserIDs(db, in.UserIDs)
		if err != nil {
			writeOpaque500(w)
			return nil, false, nil, false
		}
		if msg != "" {
			writeValidation(w, map[string][]string{"user_ids": {msg}})
			return nil, false, nil, false
		}
		return nil, true, clean, true
	})
}

// ManagedUsers answers GET /users: the id, display name and email of every
// user, to pick a material's author or shares.
func (h *Handlers) ManagedUsers(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	users, err := listUserRefs(db, 0)
	if err != nil {
		writeOpaque500(w)
		return
	}
	writeData(w, users)
}