package cabana

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"math"
	"net/http"
	"regexp"
	"slices"
	"strconv"
	"strings"
	"time"

	"git.golem15.com/golem15/summercms/modules/backpack"
	"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/pact"
	"git.golem15.com/golem15/summercms/modules/phrasebook"
	"github.com/goccy/go-yaml/ast"
	"gocloud.dev/blob"
	"gocloud.dev/gcerrors"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

// fileuploadKeys are valid only on `type: fileupload` (D-08). mode is shared
// with other types and gated by value in compileFileuploadKeys.
var fileuploadKeys = []string{
	"fileTypes", "mimeTypes", "maxFilesize", "maxFiles", "imageWidth",
	"imageHeight", "thumbOptions", "useCaption", "prompt",
}

// fileuploadRefusedKeys are generic field keys that have no meaning on a
// fileupload field.
var fileuploadRefusedKeys = []string{"options", "emptyOption", "nameFrom"}

var (
	fileTypePattern = regexp.MustCompile(`^[a-z0-9]{1,10}$`)
	mimeTypePattern = regexp.MustCompile(`^[a-z0-9*][a-z0-9.+*-]*(/[a-z0-9*][a-z0-9.+*-]*)?$`)
	thumbModes      = map[string]struct{}{"auto": {}, "exact": {}, "crop": {}, "fit": {}}
)

const (
	// defaultThumbEdge is the preview thumbnail edge when imageWidth and
	// imageHeight are not set (A11).
	defaultThumbEdge = 240
	// maxImageEdge bounds imageWidth and imageHeight, the thumbnailer's limit.
	maxImageEdge = 4096
	// multipartOverhead is the room the upload body cap leaves above
	// maxFilesize for the multipart framing.
	multipartOverhead = 64 << 10
	// defaultUploadCap is the upload body cap when neither
	// http.body_limits.upload_bytes nor maxFilesize is set.
	defaultUploadCap = 128 << 20
	// megabyte is the unit of maxFilesize.
	megabyte = 1 << 20
)

// compileFileuploadKeys decodes the D-08 keys of a `type: fileupload` field.
// They are refused on every other type.
func compileFileuploadKeys(typ string, values map[string]ast.Node, field *FormField) error {
	if typ != "fileupload" {
		for _, key := range fileuploadKeys {
			if _, ok := values[key]; ok {
				return fmt.Errorf("%s is only valid on type: fileupload", key)
			}
		}
		if _, ok := values["mode"]; ok && typ != "datepicker" {
			return fmt.Errorf("mode is only valid on type: fileupload or datepicker")
		}
		return nil
	}
	for _, key := range fileuploadRefusedKeys {
		if _, ok := values[key]; ok {
			return fmt.Errorf("%s is not valid on type: fileupload", key)
		}
	}
	field.Mode = "file"
	if node, ok := values["mode"]; ok {
		mode, err := nodeString(node)
		if err != nil || (mode != "image" && mode != "file") {
			return fmt.Errorf("mode %q must be image or file on type: fileupload", nodeText(node))
		}
		field.Mode = mode
	}
	if node, ok := values["fileTypes"]; ok {
		types, err := tokenList(node)
		if err != nil {
			return fmt.Errorf("fileTypes: %w", err)
		}
		for i, t := range types {
			t = strings.ToLower(strings.TrimPrefix(t, "."))
			if !fileTypePattern.MatchString(t) {
				return fmt.Errorf("fileTypes: %q is not a file extension", types[i])
			}
			if field.Mode == "image" && !slices.Contains(attach.DefaultImageExtensions, t) {
				return fmt.Errorf("fileTypes: %s is not an image type (mode: image allows %s)", t, strings.Join(attach.DefaultImageExtensions, ", "))
			}
			types[i] = t
		}
		field.FileTypes = types
	}
	if node, ok := values["mimeTypes"]; ok {
		types, err := tokenList(node)
		if err != nil {
			return fmt.Errorf("mimeTypes: %w", err)
		}
		for i, t := range types {
			t = strings.ToLower(t)
			if !mimeTypePattern.MatchString(t) {
				return fmt.Errorf("mimeTypes: %q is not a MIME type or extension", types[i])
			}
			types[i] = t
		}
		field.MimeTypes = types
	}
	if node, ok := values["maxFilesize"]; ok {
		mb, err := nodeNumber(node)
		if err != nil || mb <= 0 || math.IsInf(mb, 0) || math.IsNaN(mb) {
			return fmt.Errorf("maxFilesize %q must be a positive number of megabytes", nodeText(node))
		}
		field.MaxFilesize = &mb
	}
	if node, ok := values["maxFiles"]; ok {
		n, err := nodeInt(node)
		if err != nil || n < 1 {
			return fmt.Errorf("maxFiles %q must be a positive integer", nodeText(node))
		}
		v := int(n)
		field.MaxFiles = &v
	}
	for _, key := range []string{"imageWidth", "imageHeight"} {
		node, ok := values[key]
		if !ok {
			continue
		}
		n, err := nodeInt(node)
		if err != nil || n < 1 || n > maxImageEdge {
			return fmt.Errorf("%s %q must be an integer from 1 to %d", key, nodeText(node), maxImageEdge)
		}
		v := int(n)
		if key == "imageWidth" {
			field.ImageWidth = &v
		} else {
			field.ImageHeight = &v
		}
	}
	if node, ok := values["thumbOptions"]; ok {
		opts, err := compileThumbOptions(node)
		if err != nil {
			return fmt.Errorf("thumbOptions: %w", err)
		}
		field.ThumbOptions = opts
	}
	if node, ok := values["useCaption"]; ok {
		v, err := nodeBool(node)
		if err != nil {
			return fmt.Errorf("useCaption: %w", err)
		}
		field.UseCaption = v
	}
	if node, ok := values["prompt"]; ok {
		prompt, err := nodeString(node)
		if err != nil {
			return fmt.Errorf("prompt: %w", err)
		}
		field.Prompt = prompt
	}
	return nil
}

func compileThumbOptions(node ast.Node) (*ThumbOptions, error) {
	mapping, ok := node.(*ast.MappingNode)
	if !ok {
		return nil, fmt.Errorf("must be a mapping")
	}
	opts := &ThumbOptions{}
	for _, entry := range mapping.Values {
		key, err := nodeString(unwrapNode(entry.Key))
		if err != nil {
			return nil, err
		}
		if key != "mode" {
			return nil, fmt.Errorf("unknown field %s (only mode is supported)", key)
		}
		mode, err := nodeString(unwrapNode(entry.Value))
		if _, known := thumbModes[mode]; err != nil || !known {
			return nil, fmt.Errorf("mode %q must be auto, exact, crop or fit", nodeText(entry.Value))
		}
		opts.Mode = mode
	}
	if opts.Mode == "" {
		return nil, fmt.Errorf("mode is required")
	}
	return opts, nil
}

// tokenList reads a comma- or pipe-separated string or a YAML list of strings.
func tokenList(node ast.Node) ([]string, error) {
	var raw []string
	switch n := unwrapNode(node).(type) {
	case *ast.StringNode:
		raw = strings.FieldsFunc(n.Value, func(r rune) bool { return r == ',' || r == '|' })
	case *ast.SequenceNode:
		for _, item := range sequenceValues(n) {
			text, err := nodeString(unwrapNode(item))
			if err != nil {
				return nil, fmt.Errorf("want a list of strings")
			}
			raw = append(raw, text)
		}
	default:
		return nil, fmt.Errorf("want a string or a list")
	}
	out := make([]string, 0, len(raw))
	for _, item := range raw {
		if item = strings.TrimSpace(item); item != "" {
			out = append(out, item)
		}
	}
	if len(out) == 0 {
		return nil, fmt.Errorf("list is empty")
	}
	return out, nil
}

func nodeInt(node ast.Node) (int64, error) {
	n, ok := unwrapNode(node).(*ast.IntegerNode)
	if !ok {
		return 0, fmt.Errorf("want an integer")
	}
	switch v := n.Value.(type) {
	case int64:
		return v, nil
	case uint64:
		if v > math.MaxInt32 {
			return 0, fmt.Errorf("integer out of range")
		}
		return int64(v), nil
	case int:
		return int64(v), nil
	default:
		return 0, fmt.Errorf("want an integer")
	}
}

func nodeNumber(node ast.Node) (float64, error) {
	switch n := unwrapNode(node).(type) {
	case *ast.IntegerNode:
		i, err := nodeInt(n)
		return float64(i), err
	case *ast.FloatNode:
		return n.Value, nil
	default:
		return 0, fmt.Errorf("want a number")
	}
}

// compiledFile is one fileupload field bound to its model's attach.Relation
// at boot (D-06).
type compiledFile struct {
	name      string
	field     *FormField
	relation  attach.Relation
	limits    attach.Limits
	maxFiles  int
	required  bool
	thumbW    int
	thumbH    int
	thumbMode string
	// maxBytes is maxFilesize in bytes, 0 when not set.
	maxBytes int64
}

// compileFileFields binds every fileupload field of the controller's form to
// an attach.Relation the record model declares. The model must implement
// attach.Owner and attach.HasRelations.
func compileFileFields(pluginID string, cc *CompiledController) error {
	if cc == nil || cc.Form == nil {
		return nil
	}
	ctlID := controllerID(cc)
	var record any
	for i := range cc.Form.Fields {
		field := &cc.Form.Fields[i]
		if field.Type != "fileupload" {
			continue
		}
		fail := func(format string, args ...any) error {
			return bootErr(pluginID, ctlID, cc.Form.fieldsPath, fmt.Errorf("field %s: "+format, append([]any{field.Name}, args...)...))
		}
		if record == nil {
			src, ok := cc.Controller.(pact.AdminRecordSource)
			if !ok || src == nil || src.NewRecord() == nil {
				return fail("type fileupload needs a controller with NewRecord")
			}
			record = src.NewRecord()
		}
		if _, ok := record.(attach.Owner); !ok {
			return fail("type fileupload needs a model implementing attach.Owner (MorphName)")
		}
		declared, ok := record.(attach.HasRelations)
		if !ok {
			return fail("type fileupload needs a model implementing attach.HasRelations (AttachRelations)")
		}
		var rel *attach.Relation
		for _, candidate := range declared.AttachRelations() {
			if candidate.Name == field.Name {
				c := candidate
				rel = &c
				break
			}
		}
		if rel == nil {
			return fail("is not an attachment relation the model declares in AttachRelations")
		}
		if field.MaxFiles != nil && !rel.Many {
			return fail("maxFiles is only valid on an attachMany relation")
		}
		field.Multiple = rel.Many
		field.Protected = !rel.Public
		cf := &compiledFile{
			name:      field.Name,
			field:     field,
			relation:  *rel,
			required:  field.Required,
			thumbW:    defaultThumbEdge,
			thumbH:    defaultThumbEdge,
			thumbMode: "crop",
			limits: attach.Limits{
				Extensions: append([]string(nil), field.FileTypes...),
				MIMETypes:  append([]string(nil), field.MimeTypes...),
				Image:      field.Mode == "image",
			},
		}
		if field.MaxFiles != nil {
			cf.maxFiles = *field.MaxFiles
		}
		if field.MaxFilesize != nil {
			cf.maxBytes = int64(math.Ceil(*field.MaxFilesize * megabyte))
			cf.limits.MaxBytes = cf.maxBytes
		}
		switch {
		case field.ImageWidth != nil && field.ImageHeight != nil:
			cf.thumbW, cf.thumbH = *field.ImageWidth, *field.ImageHeight
		case field.ImageWidth != nil:
			cf.thumbW, cf.thumbH = *field.ImageWidth, *field.ImageWidth
		case field.ImageHeight != nil:
			cf.thumbW, cf.thumbH = *field.ImageHeight, *field.ImageHeight
		}
		if field.ThumbOptions != nil && field.ThumbOptions.Mode != "" {
			cf.thumbMode = field.ThumbOptions.Mode
		}
		if cc.files == nil {
			cc.files = map[string]*compiledFile{}
		}
		cc.files[field.Name] = cf
	}
	return nil
}

// checkFileLimits refuses a maxFilesize above http.body_limits.upload_bytes,
// as WinterCMS refuses one above upload_max_filesize.
func checkFileLimits(reg *Registry, uploadBytes int64) error {
	if reg == nil || uploadBytes <= 0 {
		return nil
	}
	for _, cc := range reg.byID {
		for _, cf := range cc.files {
			if cf.maxBytes > uploadBytes {
				path := ""
				if cc.Form != nil {
					path = cc.Form.fieldsPath
				}
				return bootErr(cc.PluginID, controllerID(cc), path, fmt.Errorf("field %s: maxFilesize exceeds http.body_limits.upload_bytes", cf.name))
			}
		}
	}
	return nil
}

// configBytes reads a whole positive byte count with surf's
// http.body_limits rules. An absent key (or no config) is 0.
func configBytes(app *backpack.App, key string) (int64, error) {
	if app == nil || app.Config == nil {
		return 0, nil
	}
	raw, ok := app.Config.Lookup(key)
	if !ok || raw == nil {
		return 0, nil
	}
	var n int64
	switch v := raw.(type) {
	case int:
		n = int64(v)
	case int64:
		n = v
	case uint64:
		if v > math.MaxInt64 {
			return 0, fmt.Errorf("cabana: config %s out of range", key)
		}
		n = int64(v)
	case float64:
		if v != math.Trunc(v) || v > 9007199254740992 {
			return 0, fmt.Errorf("cabana: config %s must be a whole number", key)
		}
		n = int64(v)
	default:
		return 0, fmt.Errorf("cabana: config %s must be numeric, got %T", key, raw)
	}
	if n < 1 {
		return 0, fmt.Errorf("cabana: config %s must be >= 1", key)
	}
	return n, nil
}

// FileItem is one file of a fileupload field as the admin API lists it.
// Pending is true for an upload bound to the request's session key that the
// record's next save attaches. URL and ThumbURL are set only for a public
// relation; a protected file is read through the admin download and thumb
// routes.
type FileItem struct {
	ID          uint      `json:"id"`
	FileName    string    `json:"file_name"`
	FileSize    int64     `json:"file_size"`
	ContentType string    `json:"content_type"`
	Title       string    `json:"title"`
	Description string    `json:"description"`
	SortOrder   int       `json:"sort_order"`
	Pending     bool      `json:"pending"`
	URL         string    `json:"url,omitempty"`
	ThumbURL    string    `json:"thumb_url,omitempty"`
	CreatedAt   time.Time `json:"created_at"`
}

// fileScope is a resolved file route: one fileupload field of one owner
// record (ownerID 0 is the record being created in this session) and, when
// the request carries a session key, the admin's deferred-binding key.
type fileScope struct {
	cc      *CompiledController
	file    *compiledFile
	ownerID uint
	owner   any
	morph   string
	key     lagoon.DeferredKey
	hasKey  bool
}

func (sc *fileScope) ownerText() string { return uitoa(sc.ownerID) }

// parentFileScope resolves the field, the operation context and the owner of
// a file route inside tx. An unknown field, a field its context hides, an
// unsaved owner (id 0) without a session key and an owner outside
// FormExtendQuery are all recordNotFound.
func parentFileScope(ctx context.Context, tx *gorm.DB, r *http.Request, cc *CompiledController) (*fileScope, error) {
	cf := cc.files[r.PathValue("field")]
	if cf == nil {
		return nil, recordNotFound{}
	}
	id, err := pathID(r)
	if err != nil {
		return nil, err
	}
	key, hasKey, err := sessionKeyFrom(r)
	if err != nil {
		return nil, err
	}
	op := "update"
	if id == 0 {
		op = "create"
		if !hasKey || !cc.operationDeclared("create") {
			return nil, recordNotFound{}
		}
	}
	if !contextAllows(cc, cf.name, op) {
		return nil, recordNotFound{}
	}
	sc := &fileScope{cc: cc, file: cf, ownerID: id}
	proto, err := newWritableModel(cc)
	if err != nil {
		return nil, err
	}
	sc.morph, err = lagoon.MorphType(tx, proto)
	if err != nil {
		return nil, lifecycleFailure(cc, err)
	}
	if hasKey {
		principal, _ := bouncer.User(ctx)
		if principal == nil || principal.ID == 0 {
			return nil, recordNotFound{}
		}
		sc.key = lagoon.DeferredKey{SessionKey: key, AdminID: principal.ID, MasterType: sc.morph}
		sc.hasKey = true
	}
	if id > 0 {
		if err := loadRecord(ctx, tx, cc, proto, castPK(proto, id)); err != nil {
			return nil, err
		}
		sc.owner = proto
	}
	return sc, nil
}

// visibleFiles is WinterCMS's withDeferred for one file field: the files
// attached to the owner minus the session's pending removals, plus the
// session's pending uploads, in sort_order then id order.
func (sc *fileScope) visibleFiles(tx *gorm.DB) ([]attach.File, map[uint]bool, error) {
	q := tx.Session(&gorm.Session{NewDB: true}).Model(&attach.File{})
	var attached *gorm.DB
	if sc.ownerID > 0 {
		attached = tx.Session(&gorm.Session{NewDB: true}).
			Where("attachment_type = ? AND attachment_id = ? AND field = ?", sc.morph, sc.ownerText(), sc.file.name)
		if sc.hasKey {
			attached = attached.Where("CAST(id AS TEXT) NOT IN (?)", lagoon.DeferredSlaves(tx, sc.key, sc.file.name, lagoon.DeferredFileType, false))
		}
	}
	var pending *gorm.DB
	if sc.hasKey {
		pending = tx.Session(&gorm.Session{NewDB: true}).
			Where("(attachment_id IS NULL OR attachment_id = '') AND CAST(id AS TEXT) IN (?)", lagoon.DeferredSlaves(tx, sc.key, sc.file.name, lagoon.DeferredFileType, true))
	}
	switch {
	case attached != nil && pending != nil:
		q = q.Where(attached).Or(pending)
	case attached != nil:
		q = q.Where(attached)
	case pending != nil:
		q = q.Where(pending)
	default:
		return nil, nil, nil
	}
	var files []attach.File
	if err := q.Order("sort_order").Order("id").Find(&files).Error; err != nil {
		return nil, nil, err
	}
	isPending := map[uint]bool{}
	for _, f := range files {
		if f.AttachmentID == "" {
			isPending[f.ID] = true
		}
	}
	return files, isPending, nil
}

// fileItem projects a stored file. Public URLs are emitted only for a
// public relation (never for a protected file, D-10).
func fileItem(ctx context.Context, bucket *blob.Bucket, cf *compiledFile, f *attach.File, pending bool) FileItem {
	item := FileItem{
		ID:          f.ID,
		FileName:    f.FileName,
		FileSize:    f.FileSize,
		ContentType: f.ContentType,
		SortOrder:   f.SortOrder,
		Pending:     pending,
		CreatedAt:   f.CreatedAt,
	}
	if f.Title != nil {
		item.Title = *f.Title
	}
	if f.Description != nil {
		item.Description = *f.Description
	}
	if !cf.relation.Public || !f.Public() {
		return item
	}
	item.URL = f.URL()
	if bucket != nil && slices.Contains(attach.AllowedImageMIMEs, f.ContentType) {
		thumb, err := f.Thumb(ctx, bucket, cf.thumbW, cf.thumbH, cf.thumbMode)
		if err != nil {
			slog.Default().WarnContext(ctx, "cabana: file thumbnail failed", "file_id", f.ID, "error", err)
		} else {
			item.ThumbURL = thumb
		}
	}
	return item
}

// fileList serves GET .../{id}/files/{field} (dispatched by nestedGet).
func (s *service) fileList(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) { s.fileListOn(w, r, cc, parentFiles(cc)) })
}

func (s *service) fileListOn(w http.ResponseWriter, r *http.Request, cc *CompiledController, fr fileRoute) {
	db, err := s.db()
	if err != nil {
		WriteError(w, http.StatusInternalServerError, "error", msgServerError)
		return
	}
	bucket := s.bucket()
	var items []FileItem
	err = lagoon.Transaction(r.Context(), db, func(ctx context.Context, tx *gorm.DB) error {
		ctx = withTx(ctx, tx)
		sc, err := fr.scope(ctx, tx, r)
		if err != nil {
			return err
		}
		files, pending, err := sc.visibleFiles(tx)
		if err != nil {
			return lifecycleFailure(cc, err)
		}
		items = make([]FileItem, 0, len(files))
		for i := range files {
			items = append(items, fileItem(ctx, bucket, sc.file, &files[i], pending[files[i].ID]))
		}
		return nil
	})
	if err != nil {
		writeCRUDError(w, err)
		return
	}
	WriteData(w, http.StatusOK, items, nil)
}

// fileUpload serves POST .../{id}/files/{field}: it stores one multipart
// file_data part with attach.Store and binds it to the session key (D-03).
// The record's next save attaches it.
func (s *service) fileUpload(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) { s.fileUploadOn(w, r, cc, parentFiles(cc)) })
}

func (s *service) fileUploadOn(w http.ResponseWriter, r *http.Request, cc *CompiledController, fr fileRoute) {
	cf := fr.field(r)
	if cf == nil {
		writeNotFound(w, r)
		return
	}
	if !requireKey(w, r, fr) {
		return
	}
	db, err := s.db()
	if err != nil {
		WriteError(w, http.StatusInternalServerError, "error", msgServerError)
		return
	}
	bucket := s.bucket()
	if bucket == nil {
		slog.Default().ErrorContext(r.Context(), "cabana: file upload without a storage bucket", "controller", controllerID(cc))
		WriteError(w, http.StatusInternalServerError, "error", msgServerError)
		return
	}
	body := &bodyReader{r: http.MaxBytesReader(w, r.Body, s.uploadCap(cf))}
	r.Body = io.NopCloser(body)
	mr, err := r.MultipartReader()
	if err != nil {
		writeCRUDError(w, invalidBody())
		return
	}
	part, err := mr.NextPart()
	if err != nil {
		s.writeFileError(w, r, cf, body, err)
		return
	}
	if part.FormName() != "file_data" || strings.TrimSpace(part.FileName()) == "" {
		writeCRUDError(w, invalidBody())
		return
	}
	var stored *attach.File
	var item FileItem
	err = lagoon.Transaction(r.Context(), db, func(ctx context.Context, tx *gorm.DB) error {
		ctx = withTx(ctx, tx)
		sc, err := fr.scope(ctx, tx, r)
		if err != nil {
			return err
		}
		if cf.relation.Many && cf.maxFiles > 0 {
			files, _, err := sc.visibleFiles(tx)
			if err != nil {
				return lifecycleFailure(cc, err)
			}
			if len(files) >= cf.maxFiles {
				return &ValidationError{Details: fieldDetail(cf.name, fieldMessage(ctx, s.translator(), "max.array", cf.name, map[string]string{"max": strconv.Itoa(cf.maxFiles)}))}
			}
		}
		f, err := attach.Store(ctx, tx, bucket, attach.Upload{FileName: part.FileName(), Body: part, Public: cf.relation.Public}, cf.limits)
		if err != nil {
			return err
		}
		stored = f
		// Exactly one part: anything after file_data is refused.
		if _, err := mr.NextPart(); !errors.Is(err, io.EOF) {
			if err == nil {
				return invalidBody()
			}
			return err
		}
		if err := lagoon.DeferredBind(ctx, tx, sc.key, cf.name, lagoon.DeferredFileType, uitoa(f.ID), nil); err != nil {
			return lifecycleFailure(cc, err)
		}
		item = fileItem(ctx, bucket, cf, f, true)
		return nil
	})
	if err != nil {
		// attach.Store wrote the blob before the row; a rolled-back
		// transaction leaves it to this caller (12.2-01).
		if stored != nil {
			_ = attach.DeleteKeys(context.WithoutCancel(r.Context()), bucket, attach.BlobKeys(*stored))
		}
		s.writeFileError(w, r, cf, body, err)
		return
	}
	WriteData(w, http.StatusCreated, item, nil)
}

// uploadCap is the request body cap of an upload: the smaller of
// http.body_limits.upload_bytes and maxFilesize plus the multipart framing.
func (s *service) uploadCap(cf *compiledFile) int64 {
	limit := int64(0)
	if s != nil && s.uploadBytes > 0 {
		limit = s.uploadBytes
	}
	if cf != nil && cf.maxBytes > 0 {
		if field := cf.maxBytes + multipartOverhead; limit == 0 || field < limit {
			limit = field
		}
	}
	if limit == 0 {
		limit = defaultUploadCap
	}
	return limit
}

// writeFileError maps file route failures: a body past the cap is 413
// payload_too_large, an attach.Store refusal is a 422 on the field, and a
// malformed multipart body is a 422 on body.
func (s *service) writeFileError(w http.ResponseWriter, r *http.Request, cf *compiledFile, body *bodyReader, err error) {
	var tooBig *http.MaxBytesError
	if errors.As(err, &tooBig) || (body != nil && errors.As(body.err, &tooBig)) {
		WriteError(w, http.StatusRequestEntityTooLarge, "payload_too_large", msgPayloadTooLarge)
		return
	}
	ctx, tr := r.Context(), s.translator()
	var detail string
	switch {
	case cf == nil:
	case errors.Is(err, attach.ErrTooLarge):
		kb := strconv.FormatInt(cf.maxBytes/1024, 10)
		detail = fieldMessage(ctx, tr, "max.file", cf.name, map[string]string{"max": kb})
	case errors.Is(err, attach.ErrFileType):
		types := cf.limits.Extensions
		if len(types) == 0 {
			types = attach.DefaultFileExtensions
			if cf.limits.Image {
				types = attach.DefaultImageExtensions
			}
		}
		detail = fieldMessage(ctx, tr, "mimes", cf.name, map[string]string{"values": strings.Join(types, ", ")})
	case errors.Is(err, attach.ErrMIMEType):
		detail = fieldMessage(ctx, tr, "mimetypes", cf.name, map[string]string{"values": strings.Join(cf.limits.MIMETypes, ", ")})
	case errors.Is(err, attach.ErrNotImage):
		detail = fieldMessage(ctx, tr, "image", cf.name, nil)
	}
	if detail != "" {
		writeCRUDError(w, &ValidationError{Details: fieldDetail(cf.name, detail)})
		return
	}
	if body != nil && body.err != nil {
		writeCRUDError(w, invalidBody())
		return
	}
	logFileFailure(r, err)
	writeCRUDError(w, err)
}

// logFileFailure logs an unexpected file route error (a storage or
// database failure) before it becomes the generic 500 body.
func logFileFailure(r *http.Request, err error) {
	var ve *ValidationError
	var missing recordNotFound
	if errors.As(err, &ve) || errors.As(err, &missing) {
		return
	}
	controller := r.PathValue("vendor") + "." + r.PathValue("plugin") + "." + r.PathValue("controller")
	slog.Default().ErrorContext(r.Context(), "cabana: file route failed", "controller", controller, "field", r.PathValue("field"), "error", err)
}

// bodyReader remembers the first read error of the request body other than
// EOF, so a failed upload tells a malformed body from a storage failure.
type bodyReader struct {
	r   io.Reader
	err error
}

func (b *bodyReader) Read(p []byte) (int, error) {
	n, err := b.r.Read(p)
	if err != nil && !errors.Is(err, io.EOF) && b.err == nil {
		b.err = err
	}
	return n, err
}

func invalidBody() error {
	return &ValidationError{Details: map[string]any{"body": []string{"The request body is invalid."}}}
}

func fieldDetail(field, message string) map[string]any {
	return map[string]any{field: []string{message}}
}

// fieldMessage is a lagoon::validation line for a file or date field, with
// Laravel's English text when no translator has the key.
func fieldMessage(ctx context.Context, tr *phrasebook.Translator, rule, field string, params map[string]string) string {
	if params == nil {
		params = map[string]string{}
	}
	attr := strings.ReplaceAll(field, "_", " ")
	params["attribute"] = attr
	key := "lagoon::validation." + rule
	if tr != nil && tr.Has(key) {
		if s := tr.Get(ctx, key, params); s != "" && s != key {
			return s
		}
	}
	switch rule {
	case "max.file":
		return "The " + attr + " may not be greater than " + params["max"] + " kilobytes."
	case "max.array":
		return "The " + attr + " may not have more than " + params["max"] + " items."
	case "mimes", "mimetypes":
		return "The " + attr + " must be a file of type: " + params["values"] + "."
	case "image":
		return "The " + attr + " must be an image."
	case "required":
		return "The " + attr + " field is required."
	case "after_or_equal":
		return "The " + attr + " must be a date after or equal to " + params["date"] + "."
	case "before_or_equal":
		return "The " + attr + " must be a date before or equal to " + params["date"] + "."
	}
	return "The " + attr + " is invalid."
}

// bucket is the application's attachment bucket (attach.Publish), or nil.
func (s *service) bucket() *blob.Bucket {
	if s == nil || s.app == nil {
		return nil
	}
	b, ok := s.app.Lookup[*blob.Bucket]()
	if !ok {
		return nil
	}
	return b
}

// lockFile loads one system_files row FOR UPDATE, or nil when it is gone.
func lockFile(ctx context.Context, tx *gorm.DB, id uint) (*attach.File, error) {
	var f attach.File
	err := tx.Session(&gorm.Session{NewDB: true, Context: ctx}).
		Clauses(clause.Locking{Strength: "UPDATE"}).
		Where("id = ?", id).Take(&f).Error
	if errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	return &f, nil
}

// AdminFileCaptionRequest is the body of the file caption route. A nil
// field is left unchanged; unknown keys are refused.
type AdminFileCaptionRequest struct {
	Title       *string `json:"title,omitempty"`
	Description *string `json:"description,omitempty"`
}

// pathFileID parses {file}; anything but a positive integer is not found.
func pathFileID(r *http.Request) (uint, error) {
	n, err := strconv.ParseUint(strings.TrimSpace(r.PathValue("file")), 10, 64)
	if err != nil || n == 0 {
		return 0, recordNotFound{}
	}
	return uint(n), nil
}

// findFile loads one file of the scope with a single parent-scoped query:
// it must be attached to the scope's owner and field, or be a pending upload
// bound to the scope's session key. Anything else, a file of another record
// included, is recordNotFound (never 403).
func (sc *fileScope) findFile(ctx context.Context, tx *gorm.DB, id uint, lock bool) (*attach.File, error) {
	fresh := func() *gorm.DB { return tx.Session(&gorm.Session{NewDB: true, Context: ctx}) }
	var group *gorm.DB
	if sc.ownerID > 0 {
		group = fresh().Where("attachment_type = ? AND attachment_id = ? AND field = ?", sc.morph, sc.ownerText(), sc.file.name)
	}
	if sc.hasKey {
		pending := "(attachment_id IS NULL OR attachment_id = '') AND CAST(id AS TEXT) IN (?)"
		slaves := lagoon.DeferredSlaves(tx, sc.key, sc.file.name, lagoon.DeferredFileType, true)
		if group == nil {
			group = fresh().Where(pending, slaves)
		} else {
			group = group.Or(pending, slaves)
		}
	}
	if group == nil {
		return nil, recordNotFound{}
	}
	q := fresh().Where("id = ?", id).Where(group)
	if lock {
		q = q.Clauses(clause.Locking{Strength: "UPDATE"})
	}
	var f attach.File
	err := q.Take(&f).Error
	if errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, recordNotFound{}
	}
	if err != nil {
		return nil, err
	}
	return &f, nil
}

// withFileScope runs fn on the resolved scope of a file route inside one
// transaction and writes the error envelope on failure.
func (s *service) withFileScope(w http.ResponseWriter, r *http.Request, cc *CompiledController, fr fileRoute, fn func(ctx context.Context, tx *gorm.DB, sc *fileScope) error) bool {
	db, err := s.db()
	if err != nil {
		WriteError(w, http.StatusInternalServerError, "error", msgServerError)
		return false
	}
	err = lagoon.Transaction(r.Context(), db, func(ctx context.Context, tx *gorm.DB) error {
		ctx = withTx(ctx, tx)
		sc, err := fr.scope(ctx, tx, r)
		if err != nil {
			return err
		}
		return fn(ctx, tx, sc)
	})
	if err != nil {
		s.writeFileError(w, r, fr.field(r), nil, err)
		return false
	}
	return true
}

// requireKey answers 422 when the request has no valid file session key:
// X-Session-Key on a record's file routes, X-Child-Session-Key on a
// relation child's.
func requireKey(w http.ResponseWriter, r *http.Request, fr fileRoute) bool {
	_, ok, err := fr.keyFrom(r)
	if err == nil && !ok {
		err = &ValidationError{Details: map[string]any{fr.keyName: []string{"The " + strings.ReplaceAll(fr.keyName, "_", " ") + " field is required."}}}
	}
	if err != nil {
		writeCRUDError(w, err)
		return false
	}
	return true
}

// fileRoute is the target of a file route: a record's own fileupload fields
// (the record file routes) or the manage form fields of a relation child
// (the child file routes, D-17). The handlers are shared; the route decides
// which fields exist, which header carries the file session key and how the
// owner is scoped.
type fileRoute struct {
	files   map[string]*compiledFile
	keyFrom func(*http.Request) (string, bool, error)
	keyName string
	scope   func(ctx context.Context, tx *gorm.DB, r *http.Request) (*fileScope, error)
}

// field is the route's fileupload field, or nil.
func (fr fileRoute) field(r *http.Request) *compiledFile { return fr.files[r.PathValue("field")] }

// parentFiles is the file route of the record's own fileupload fields.
func parentFiles(cc *CompiledController) fileRoute {
	return fileRoute{
		files:   cc.files,
		keyFrom: sessionKeyFrom,
		keyName: "session_key",
		scope: func(ctx context.Context, tx *gorm.DB, r *http.Request) (*fileScope, error) {
			return parentFileScope(ctx, tx, r, cc)
		},
	}
}

// childFiles is the file route of a relation child form's fileupload
// fields (D-17), after the capability check: child 0 (a child not created
// yet) needs the create button, else 404 as for a record's id 0; a saved
// child needs the update button to write and update or a view form to
// read, else 403. An unknown relation or child form is 404.
func (s *service) childFiles(w http.ResponseWriter, r *http.Request, cc *CompiledController, write bool) (fileRoute, bool) {
	cr, err := relationOf(cc, r.PathValue("name"))
	if err == nil && cr.child == nil {
		err = recordNotFound{}
	}
	if err != nil {
		writeCRUDError(w, err)
		return fileRoute{}, false
	}
	n, err := strconv.ParseUint(strings.TrimSpace(r.PathValue("child")), 10, 64)
	if err != nil {
		writeNotFound(w, r)
		return fileRoute{}, false
	}
	childID := uint(n)
	switch {
	case childID == 0 && !cr.allows("create"):
		writeNotFound(w, r)
		return fileRoute{}, false
	case childID > 0 && (write && !cr.allows("update") || !write && cr.childForm() == nil):
		if principal, _ := bouncer.User(r.Context()); principal != nil {
			s.logAuth(r, "denied", principal.ID)
		}
		WriteError(w, http.StatusForbidden, "forbidden", msgForbidden)
		return fileRoute{}, false
	}
	return fileRoute{
		files:   cr.child.files,
		keyFrom: childSessionKeyFrom,
		keyName: "child_session_key",
		scope: func(ctx context.Context, tx *gorm.DB, r *http.Request) (*fileScope, error) {
			return childFileScope(ctx, tx, r, cc, cr, childID)
		},
	}, true
}

// relationChildFileList and the six handlers below serve the file routes
// of a relation child form under .../relations/{name}/records/{child}.
func (s *service) relationChildFileList(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) {
		if fr, ok := s.childFiles(w, r, cc, false); ok {
			s.fileListOn(w, r, cc, fr)
		}
	})
}

func (s *service) relationChildFileUpload(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) {
		if fr, ok := s.childFiles(w, r, cc, true); ok {
			s.fileUploadOn(w, r, cc, fr)
		}
	})
}

func (s *service) relationChildFileUpdate(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) {
		if fr, ok := s.childFiles(w, r, cc, true); ok {
			s.fileUpdateOn(w, r, cc, fr)
		}
	})
}

func (s *service) relationChildFileRemove(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) {
		if fr, ok := s.childFiles(w, r, cc, true); ok {
			s.fileRemoveOn(w, r, cc, fr)
		}
	})
}

func (s *service) relationChildFileReorder(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) {
		if fr, ok := s.childFiles(w, r, cc, true); ok {
			s.fileReorderOn(w, r, cc, fr)
		}
	})
}

func (s *service) relationChildFileDownload(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) {
		if fr, ok := s.childFiles(w, r, cc, false); ok {
			s.serveProtectedFileOn(w, r, cc, fr, false)
		}
	})
}

func (s *service) relationChildFileThumb(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) {
		if fr, ok := s.childFiles(w, r, cc, false); ok {
			s.serveProtectedFileOn(w, r, cc, fr, true)
		}
	})
}

// deleteBlobsAfterCommit removes a deleted file's blob and thumbnails once
// the surrounding transaction has committed.
func deleteBlobsAfterCommit(ctx context.Context, tx *gorm.DB, bucket *blob.Bucket, f attach.File) {
	keys := attach.BlobKeys(f)
	lagoon.AfterCommit(ctx, tx, func(ctx context.Context, _ *gorm.DB) {
		if bucket == nil {
			slog.Default().WarnContext(ctx, "cabana: no storage bucket; blobs of a deleted file were kept", "file_id", f.ID)
			return
		}
		if err := attach.DeleteKeys(ctx, bucket, keys); err != nil {
			slog.Default().WarnContext(ctx, "cabana: deleting a file's blobs failed", "file_id", f.ID, "error", err)
		}
	})
}

// fileRemove serves DELETE .../{id}/files/{field}/{file}: it defers the
// removal of an attached file to the next save, or cancels a pending upload
// at once (its row now, its blob after commit).
func (s *service) fileRemove(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) { s.fileRemoveOn(w, r, cc, parentFiles(cc)) })
}

func (s *service) fileRemoveOn(w http.ResponseWriter, r *http.Request, cc *CompiledController, fr fileRoute) {
	if fr.field(r) == nil {
		writeNotFound(w, r)
		return
	}
	if !requireKey(w, r, fr) {
		return
	}
	fileID, err := pathFileID(r)
	if err != nil {
		writeCRUDError(w, err)
		return
	}
	bucket := s.bucket()
	ok := s.withFileScope(w, r, cc, fr, func(ctx context.Context, tx *gorm.DB, sc *fileScope) error {
		f, err := sc.findFile(ctx, tx, fileID, true)
		if err != nil {
			return err
		}
		cancelled, err := lagoon.DeferredUnbind(ctx, tx, sc.key, sc.file.name, lagoon.DeferredFileType, uitoa(f.ID))
		if err != nil {
			return err
		}
		if cancelled != nil && f.AttachmentID == "" {
			if err := tx.Session(&gorm.Session{NewDB: true, Context: ctx}).Where("id = ?", f.ID).Delete(&attach.File{}).Error; err != nil {
				return err
			}
			deleteBlobsAfterCommit(ctx, tx, bucket, *f)
		}
		return nil
	})
	if ok {
		WriteData(w, http.StatusOK, FileMutationResult{Removed: 1}, nil)
	}
}

// jsonCap is the body cap of the JSON file routes: http.body_limits.
// default_bytes, or 1 MiB when it is not configured.
func (s *service) jsonCap() int64 {
	if s != nil && s.defaultBytes > 0 {
		return s.defaultBytes
	}
	return 1 << 20
}

// decodeStrictBody decodes a capped JSON body into dest with unknown keys
// and trailing data refused.
func (s *service) decodeStrictBody(w http.ResponseWriter, r *http.Request, dest any) error {
	dec := json.NewDecoder(http.MaxBytesReader(w, r.Body, s.jsonCap()))
	dec.DisallowUnknownFields()
	if err := dec.Decode(dest); err != nil {
		var tooBig *http.MaxBytesError
		if errors.As(err, &tooBig) {
			return err
		}
		return invalidBody()
	}
	var trailing any
	if err := dec.Decode(&trailing); err != io.EOF {
		return invalidBody()
	}
	return nil
}

// fileUpdate serves PUT .../{id}/files/{field}/{file}: it saves a file's
// title and description at once (WinterCMS's onSaveAttachmentConfig). The
// field must declare useCaption.
func (s *service) fileUpdate(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) { s.fileUpdateOn(w, r, cc, parentFiles(cc)) })
}

func (s *service) fileUpdateOn(w http.ResponseWriter, r *http.Request, cc *CompiledController, fr fileRoute) {
	cf := fr.field(r)
	if cf == nil {
		writeNotFound(w, r)
		return
	}
	if !cf.field.UseCaption {
		WriteError(w, http.StatusForbidden, "forbidden", msgForbidden)
		return
	}
	fileID, err := pathFileID(r)
	if err != nil {
		writeCRUDError(w, err)
		return
	}
	var in AdminFileCaptionRequest
	if err := s.decodeStrictBody(w, r, &in); err != nil {
		s.writeFileError(w, r, cf, nil, err)
		return
	}
	bucket := s.bucket()
	var item FileItem
	ok := s.withFileScope(w, r, cc, fr, func(ctx context.Context, tx *gorm.DB, sc *fileScope) error {
		f, err := sc.findFile(ctx, tx, fileID, true)
		if err != nil {
			return err
		}
		updates := map[string]any{}
		if in.Title != nil {
			updates["title"] = *in.Title
			f.Title = in.Title
		}
		if in.Description != nil {
			updates["description"] = *in.Description
			f.Description = in.Description
		}
		if len(updates) > 0 {
			if err := tx.Session(&gorm.Session{NewDB: true, Context: ctx}).Model(&attach.File{}).Where("id = ?", f.ID).Updates(updates).Error; err != nil {
				return err
			}
		}
		item = fileItem(ctx, bucket, cf, f, f.AttachmentID == "")
		return nil
	})
	if ok {
		WriteData(w, http.StatusOK, item, nil)
	}
}

// fileReorder serves POST .../{id}/files/{field}/reorder: the submitted ids
// must be exactly the field's visible files, and they receive the visible
// files' existing sort_order values, ascending, in the submitted order.
func (s *service) fileReorder(w http.ResponseWriter, r *http.Request) {
	s.protect(w, r, func(cc *CompiledController) { s.fileReorderOn(w, r, cc, parentFiles(cc)) })
}

func (s *service) fileReorderOn(w http.ResponseWriter, r *http.Request, cc *CompiledController, fr fileRoute) {
	cf := fr.field(r)
	if cf == nil {
		writeNotFound(w, r)
		return
	}
	if !cf.relation.Many {
		WriteError(w, http.StatusForbidden, "forbidden", msgForbidden)
		return
	}
	var in AdminIDsRequest
	if err := s.decodeStrictBody(w, r, &in); err != nil {
		s.writeFileError(w, r, cf, nil, err)
		return
	}
	bucket := s.bucket()
	var items []FileItem
	ok := s.withFileScope(w, r, cc, fr, func(ctx context.Context, tx *gorm.DB, sc *fileScope) error {
		files, _, err := sc.visibleFiles(tx)
		if err != nil {
			return err
		}
		byID := make(map[uint]int, len(files))
		orders := make([]int, len(files))
		for i, f := range files {
			byID[f.ID] = i
			orders[i] = f.SortOrder
		}
		seen := map[uint]bool{}
		valid := len(in.IDs) == len(files)
		for _, raw := range in.IDs {
			id := uint(raw)
			if _, known := byID[id]; !known || seen[id] || uint64(id) != raw {
				valid = false
				break
			}
			seen[id] = true
		}
		if !valid {
			return &ValidationError{Details: map[string]any{"ids": []string{"The ids field must list every file of the field exactly once."}}}
		}
		slices.Sort(orders)
		q := tx.Session(&gorm.Session{NewDB: true, Context: ctx})
		for i, raw := range in.IDs {
			if err := q.Model(&attach.File{}).Where("id = ?", uint(raw)).Update("sort_order", orders[i]).Error; err != nil {
				return err
			}
		}
		files, pending, err := sc.visibleFiles(tx)
		if err != nil {
			return err
		}
		items = make([]FileItem, 0, len(files))
		for i := range files {
			items = append(items, fileItem(ctx, bucket, cf, &files[i], pending[files[i].ID]))
		}
		return nil
	})
	if ok {
		WriteData(w, http.StatusOK, items, nil)
	}
}

// fileDownload serves GET .../{id}/files/{field}/{file}/download.
func (s *service) fileDownload(w http.ResponseWriter, r *http.Request) {
	s.serveProtectedFile(w, r, false)
}

// fileThumb serves GET .../{id}/files/{field}/{file}/thumb.
func (s *service) fileThumb(w http.ResponseWriter, r *http.Request) {
	s.serveProtectedFile(w, r, true)
}

// serveProtectedFile streams a protected (is_public false) file or its
// thumbnail (D-10). The file must belong to a record the admin may load
// through FormExtendQuery, or be pending in the admin's own session; a
// public file, a file of another record and a thumbnail of a non-image are
// 404. Only JPEG, PNG, GIF and WebP are served inline; everything else is an
// application/octet-stream attachment. Every response is nosniff, private
// and no-store, under a sandboxing CSP.
func (s *service) serveProtectedFile(w http.ResponseWriter, r *http.Request, thumb bool) {
	s.protect(w, r, func(cc *CompiledController) { s.serveProtectedFileOn(w, r, cc, parentFiles(cc), thumb) })
}

func (s *service) serveProtectedFileOn(w http.ResponseWriter, r *http.Request, cc *CompiledController, fr fileRoute, thumb bool) {
	cf := fr.field(r)
	if cf == nil {
		writeNotFound(w, r)
		return
	}
	fileID, err := pathFileID(r)
	if err != nil {
		writeCRUDError(w, err)
		return
	}
	bucket := s.bucket()
	if bucket == nil {
		slog.Default().ErrorContext(r.Context(), "cabana: protected file route without a storage bucket", "controller", controllerID(cc))
		WriteError(w, http.StatusInternalServerError, "error", msgServerError)
		return
	}
	var f *attach.File
	ok := s.withFileScope(w, r, cc, fr, func(ctx context.Context, tx *gorm.DB, sc *fileScope) error {
		found, err := sc.findFile(ctx, tx, fileID, false)
		if err != nil {
			return err
		}
		if found.Public() {
			return recordNotFound{}
		}
		f = found
		return nil
	})
	if !ok {
		return
	}
	ctx := r.Context()
	key := attach.BlobKey(f.DiskName)
	contentType := f.ContentType
	if thumb {
		if !slices.Contains(attach.AllowedImageMIMEs, f.ContentType) {
			writeNotFound(w, r)
			return
		}
		key, err = f.ThumbKey(ctx, bucket, cf.thumbW, cf.thumbH, cf.thumbMode)
		if err != nil {
			slog.Default().ErrorContext(ctx, "cabana: protected thumbnail failed", "file_id", f.ID, "error", err)
			WriteError(w, http.StatusInternalServerError, "error", msgServerError)
			return
		}
		contentType = ""
	}
	reader, err := bucket.NewReader(ctx, key, nil)
	if err != nil {
		if gcerrors.Code(err) == gcerrors.NotFound {
			writeNotFound(w, r)
			return
		}
		slog.Default().ErrorContext(ctx, "cabana: protected file read failed", "file_id", f.ID, "error", err)
		WriteError(w, http.StatusInternalServerError, "error", msgServerError)
		return
	}
	defer reader.Close()
	if contentType == "" {
		contentType = reader.ContentType()
	}
	contentType = strings.ToLower(strings.TrimSpace(strings.SplitN(contentType, ";", 2)[0]))
	h := w.Header()
	h.Set("X-Content-Type-Options", "nosniff")
	h.Set("Cache-Control", "private, no-store")
	h.Set("Content-Security-Policy", "default-src 'none'; sandbox")
	if slices.Contains(attach.AllowedImageMIMEs, contentType) {
		h.Set("Content-Type", contentType)
	} else {
		h.Set("Content-Type", "application/octet-stream")
		h.Set("Content-Disposition", "attachment; filename*=UTF-8''"+rfc5987(f.FileName))
	}
	h.Set("Content-Length", strconv.FormatInt(reader.Size(), 10))
	w.WriteHeader(http.StatusOK)
	_, _ = io.Copy(w, reader)
}

// rfc5987 percent-encodes a file name for a filename* parameter: only
// RFC 5987 attr-char bytes stay literal.
func rfc5987(name string) string {
	const hex = "0123456789ABCDEF"
	var b strings.Builder
	for i := 0; i < len(name); i++ {
		c := name[i]
		switch {
		case c >= 'a' && c <= 'z', c >= 'A' && c <= 'Z', c >= '0' && c <= '9',
			strings.IndexByte("!#$&+-.^_`|~", c) >= 0:
			b.WriteByte(c)
		default:
			b.WriteByte('%')
			b.WriteByte(hex[c>>4])
			b.WriteByte(hex[c&15])
		}
	}
	if b.Len() == 0 {
		return "file"
	}
	return b.String()
}