package store

import (
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"time"
)

// ---------------------------------------------------------------------------
// Gerenciador de arquivos: árvore de pastas + arquivos com associação opcional
// a uma nota. Persistência: folders.json, files.json e blobs em files/<id>.<ext>.
// ---------------------------------------------------------------------------

// MaxFileBytes limita o tamanho de cada anexo (64 MiB).
const MaxFileBytes = 64 << 20

// Folder é um nó da árvore de pastas (parent "" = raiz).
type Folder struct {
	ID        string    `json:"id"`
	Name      string    `json:"name"`
	Parent    string    `json:"parent"`
	CreatedAt time.Time `json:"created_at"`
}

// FileMeta descreve um arquivo anexado ou avulso.
type FileMeta struct {
	ID        string    `json:"id"`
	Name      string    `json:"name"`
	Folder    string    `json:"folder"` // "" = raiz da árvore de arquivos
	Note      string    `json:"note"`   // "" = avulso (sem nota)
	Size      int64     `json:"size"`
	MIME      string    `json:"mime"`
	SHA256    string    `json:"sha256"`
	CreatedAt time.Time `json:"created_at"`
}

// FileNode é a visão de API (meta + URL para <img>/<video>/<a>).
type FileNode struct {
	FileMeta
	URL string `json:"url"`
}

// TreeNode é a hierarquia completa (pastas aninhadas + arquivos).
type TreeNode struct {
	Folder
	Children []*TreeNode `json:"children"`
	Files    []*FileNode `json:"files"`
}

var fileNameRe = regexp.MustCompile(`^[\p{L}\p{N} .,_\-()#]+$`)

func nodeFromFile(m FileMeta) *FileNode {
	return &FileNode{FileMeta: m, URL: "/api/files/static/" + m.ID}
}

func (s *Store) foldersPath() string   { return filepath.Join(s.dir, "folders.json") }
func (s *Store) filesJSONPath() string { return filepath.Join(s.dir, "files.json") }
func (s *Store) filesRoot() string     { return filepath.Join(s.dir, "files") }

// loadFiles carrega os índices de pastas/arquivos (chamado por New).
func (s *Store) loadFiles() error {
	s.folders = nil
	s.fileMetas = nil
	var f []Folder
	if err := readJSON(s.foldersPath(), &f); err == nil {
		s.folders = f
	} else if !errors.Is(err, ErrNotFound) {
		return err
	}
	var m []FileMeta
	if err := readJSON(s.filesJSONPath(), &m); err == nil {
		s.fileMetas = m
	} else if !errors.Is(err, ErrNotFound) {
		return err
	}
	return os.MkdirAll(s.filesRoot(), 0o750)
}

func (s *Store) saveFolders() error   { return writeJSONAtomic(s.foldersPath(), s.folders) }
func (s *Store) saveFileMetas() error { return writeJSONAtomic(s.filesJSONPath(), s.fileMetas) }

func (s *Store) folderByID(id string) *Folder {
	for i := range s.folders {
		if s.folders[i].ID == id {
			return &s.folders[i]
		}
	}
	return nil
}

func (s *Store) fileByID(id string) *FileMeta {
	for i := range s.fileMetas {
		if s.fileMetas[i].ID == id {
			return &s.fileMetas[i]
		}
	}
	return nil
}

func (s *Store) folderSubtree(id string) []string {
	out := []string{id}
	for i := 0; i < len(out); i++ {
		for _, f := range s.folders {
			if f.Parent == out[i] {
				out = append(out, f.ID)
			}
		}
	}
	return out
}

func cleanFileName(name string) (string, error) {
	name = strings.TrimSpace(name)
	name = filepath.Base(name) // nunca aceita path (anti-traversal no nome)
	if name == "" || name == "." || name == ".." || len(name) > 200 || !fileNameRe.MatchString(name) {
		return "", fmt.Errorf("%w: nome de arquivo inválido", ErrInvalid)
	}
	return name, nil
}

// extByMime normaliza o MIME detectado quando o sniffing é genérico.
func extByMime(name, sniffed string) string {
	switch strings.ToLower(filepath.Ext(name)) {
	case ".md", ".markdown":
		if strings.HasPrefix(sniffed, "text/plain") {
			return "text/markdown; charset=utf-8"
		}
	case ".html", ".htm":
		if strings.HasPrefix(sniffed, "text/plain") {
			return "text/html; charset=utf-8"
		}
	case ".css":
		if strings.HasPrefix(sniffed, "text/plain") {
			return "text/css; charset=utf-8"
		}
	case ".js", ".mjs":
		if strings.HasPrefix(sniffed, "text/plain") {
			return "text/javascript; charset=utf-8"
		}
	case ".json":
		if strings.HasPrefix(sniffed, "text/plain") {
			return "application/json"
		}
	case ".svg":
		if strings.Contains(sniffed, "xml") || strings.HasPrefix(sniffed, "text/plain") {
			return "image/svg+xml"
		}
	case ".webp":
		if sniffed == "application/octet-stream" {
			return "image/webp"
		}
	case ".mp3":
		if sniffed == "application/octet-stream" {
			return "audio/mpeg"
		}
	case ".mp4", ".m4v":
		if sniffed == "application/octet-stream" {
			return "video/mp4"
		}
	case ".flac":
		if sniffed == "application/octet-stream" {
			return "audio/flac"
		}
	case ".ogg":
		if strings.HasPrefix(sniffed, "application/ogg") {
			return "audio/ogg"
		}
	case ".txt", ".log":
		if strings.HasPrefix(sniffed, "text/plain") {
			return "text/plain; charset=utf-8"
		}
	}
	return sniffed
}

// safeExt decide a extensão física do blob. Extensões perigosas (html/svg/…)
// viram sufixo neutro: o MIME real só vive no metadado e é aplicado no serve.
func safeExt(name, mime string) string {
	ext := strings.ToLower(filepath.Ext(name))
	if len(ext) > 8 || !regexp.MustCompile(`^\.[a-z0-9]+$`).MatchString(ext) ||
		ext == ".html" || ext == ".htm" || ext == ".xhtml" || ext == ".svg" || ext == ".js" || ext == ".mjs" {
		switch {
		case strings.HasPrefix(mime, "image/"):
			return ".img"
		case strings.HasPrefix(mime, "video/"):
			return ".vid"
		case strings.HasPrefix(mime, "audio/"):
			return ".aud"
		default:
			return ".bin"
		}
	}
	return ext
}

func (s *Store) fileBlobPath(id, ext string) string {
	return filepath.Join(s.filesRoot(), id+ext)
}

// ---------------------------------------------------------------------------
// Pastas
// ---------------------------------------------------------------------------

// CreateFolder cria uma pasta na árvore de arquivos.
func (s *Store) CreateFolder(name, parent string) (*Folder, error) {
	name = strings.TrimSpace(name)
	if name == "" || len([]rune(name)) > 100 || !fileNameRe.MatchString(name) {
		return nil, fmt.Errorf("%w: nome de pasta inválido", ErrInvalid)
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if parent != "" && s.folderByID(parent) == nil {
		return nil, fmt.Errorf("%w: pasta pai inexistente", ErrInvalid)
	}
	lower := strings.ToLower(name)
	for _, f := range s.folders {
		if f.Parent == parent && strings.ToLower(f.Name) == lower {
			return nil, fmt.Errorf("%w: já existe pasta %q nesse nível", ErrInvalid, name)
		}
	}
	f := Folder{ID: newID(), Name: name, Parent: parent, CreatedAt: time.Now().UTC()}
	s.folders = append(s.folders, f)
	if err := s.saveFolders(); err != nil {
		return nil, err
	}
	return &f, nil
}

// UpdateFolder renomeia/move pasta com checagem de ciclo.
func (s *Store) UpdateFolder(id, name string, parent *string) (*Folder, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	f := s.folderByID(id)
	if f == nil {
		return nil, ErrNotFound
	}
	if parent != nil && *parent != f.Parent {
		if *parent != "" && s.folderByID(*parent) == nil {
			return nil, fmt.Errorf("%w: pasta pai inexistente", ErrInvalid)
		}
		for _, d := range s.folderSubtree(id) {
			if d == *parent {
				return nil, fmt.Errorf("%w: não é possível mover uma pasta para dentro dela mesma", ErrInvalid)
			}
		}
		f.Parent = *parent
	}
	if n := strings.TrimSpace(name); n != "" && n != f.Name {
		if len([]rune(n)) > 100 || !fileNameRe.MatchString(n) {
			return nil, fmt.Errorf("%w: nome de pasta inválido", ErrInvalid)
		}
		lower := strings.ToLower(n)
		for _, other := range s.folders {
			if other.ID != id && other.Parent == f.Parent && strings.ToLower(other.Name) == lower {
				return nil, fmt.Errorf("%w: já existe pasta %q nesse nível", ErrInvalid, n)
			}
		}
		f.Name = n
	}
	if err := s.saveFolders(); err != nil {
		return nil, err
	}
	cp := *f
	return &cp, nil
}

// DeleteFolder remove a pasta e todo o subtree (incluindo arquivos).
func (s *Store) DeleteFolder(id string) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.folderByID(id) == nil {
		return ErrNotFound
	}
	sub := map[string]bool{}
	for _, d := range s.folderSubtree(id) {
		sub[d] = true
	}
	keptFolders := s.folders[:0]
	for _, f := range s.folders {
		if !sub[f.ID] {
			keptFolders = append(keptFolders, f)
		}
	}
	s.folders = keptFolders

	keptFiles := s.fileMetas[:0]
	for _, m := range s.fileMetas {
		if sub[m.Folder] {
			_ = os.Remove(s.fileBlobPath(m.ID, safeExt(m.Name, m.MIME)))
			continue
		}
		keptFiles = append(keptFiles, m)
	}
	s.fileMetas = keptFiles
	if err := s.saveFolders(); err != nil {
		return err
	}
	return s.saveFileMetas()
}

// ---------------------------------------------------------------------------
// Arquivos
// ---------------------------------------------------------------------------

// AddFile persiste um upload: valida nome/pasta/nota, calcula SHA-256 e MIME
// reais (content sniffing) e grava o blob atomicamente. Limite: MaxFileBytes.
func (s *Store) AddFile(name, folder, note string, r io.Reader) (*FileMeta, error) {
	clean, err := cleanFileName(name)
	if err != nil {
		return nil, err
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if folder != "" && s.folderByID(folder) == nil {
		return nil, fmt.Errorf("%w: pasta inexistente", ErrInvalid)
	}
	if note != "" {
		if _, err := s.get(note); err != nil {
			return nil, fmt.Errorf("%w: nota inexistente", ErrInvalid)
		}
	}

	id := newID()
	tmp := s.fileBlobPath(id, ".tmp")
	f, err := os.OpenFile(tmp, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o640)
	if err != nil {
		return nil, err
	}
	fail := func(err error) (*FileMeta, error) {
		f.Close()
		os.Remove(tmp)
		return nil, err
	}

	h := sha256.New()
	head := make([]byte, 512)
	n, err := io.ReadFull(r, head)
	if err != nil && !errors.Is(err, io.EOF) && !errors.Is(err, io.ErrUnexpectedEOF) {
		return fail(err)
	}
	head = head[:n]
	if _, err := f.Write(head); err != nil {
		return fail(err)
	}
	if _, err := h.Write(head); err != nil {
		return fail(err)
	}
	rest, err := io.Copy(io.MultiWriter(f, h), r)
	if err != nil {
		return fail(err)
	}
	size := int64(n) + rest
	if size > MaxFileBytes {
		return fail(fmt.Errorf("%w: arquivo excede %d MiB", ErrTooLarge, MaxFileBytes>>20))
	}
	if err := f.Close(); err != nil {
		os.Remove(tmp)
		return nil, err
	}

	mime := extByMime(clean, http.DetectContentType(head))
	ext := safeExt(clean, mime)
	if err := os.Rename(tmp, s.fileBlobPath(id, ext)); err != nil {
		os.Remove(tmp)
		return nil, err
	}

	meta := FileMeta{
		ID: id, Name: clean, Folder: folder, Note: note, Size: size,
		MIME: mime, SHA256: hex.EncodeToString(h.Sum(nil)), CreatedAt: time.Now().UTC(),
	}
	s.fileMetas = append(s.fileMetas, meta)
	if err := s.saveFileMetas(); err != nil {
		return nil, err
	}
	return &meta, nil
}

// Files devolve todos os metadados (ordenados por data desc).
func (s *Store) Files() []FileMeta {
	s.mu.RLock()
	defer s.mu.RUnlock()
	out := make([]FileMeta, len(s.fileMetas))
	copy(out, s.fileMetas)
	sort.Slice(out, func(i, j int) bool { return out[i].CreatedAt.After(out[j].CreatedAt) })
	return out
}

// GetFile devolve o metadado.
func (s *Store) GetFile(id string) (*FileMeta, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	m := s.fileByID(id)
	if m == nil {
		return nil, ErrNotFound
	}
	cp := *m
	return &cp, nil
}

// MoveFile altera pasta/nome/associação de nota (nil = manter).
func (s *Store) MoveFile(id, name string, folder, note *string) (*FileMeta, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	m := s.fileByID(id)
	if m == nil {
		return nil, ErrNotFound
	}
	if folder != nil {
		if *folder != "" && s.folderByID(*folder) == nil {
			return nil, fmt.Errorf("%w: pasta inexistente", ErrInvalid)
		}
		m.Folder = *folder
	}
	if note != nil {
		if *note != "" {
			if _, err := s.get(*note); err != nil {
				return nil, fmt.Errorf("%w: nota inexistente", ErrInvalid)
			}
		}
		m.Note = *note
	}
	if n := strings.TrimSpace(name); n != "" && n != m.Name {
		clean, err := cleanFileName(n)
		if err != nil {
			return nil, err
		}
		m.Name = clean
	}
	if err := s.saveFileMetas(); err != nil {
		return nil, err
	}
	cp := *m
	return &cp, nil
}

// DeleteFile remove metadado + blob.
func (s *Store) DeleteFile(id string) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	idx := -1
	for i := range s.fileMetas {
		if s.fileMetas[i].ID == id {
			idx = i
			break
		}
	}
	if idx < 0 {
		return ErrNotFound
	}
	m := s.fileMetas[idx]
	_ = os.Remove(s.fileBlobPath(m.ID, safeExt(m.Name, m.MIME)))
	s.fileMetas = append(s.fileMetas[:idx], s.fileMetas[idx+1:]...)
	return s.saveFileMetas()
}

// FileTree monta a hierarquia de pastas com arquivos.
func (s *Store) FileTree() []*TreeNode {
	s.mu.RLock()
	defer s.mu.RUnlock()
	nodes := map[string]*TreeNode{}
	for _, f := range s.folders {
		nodes[f.ID] = &TreeNode{Folder: f, Children: []*TreeNode{}, Files: []*FileNode{}}
	}
	var roots []*TreeNode
	for _, f := range s.folders {
		n := nodes[f.ID]
		if p, ok := nodes[f.Parent]; ok && f.Parent != "" {
			p.Children = append(p.Children, n)
		} else {
			roots = append(roots, n)
		}
	}
	if roots == nil {
		roots = []*TreeNode{}
	}
	rootFiles := []*FileNode{}
	for _, m := range s.fileMetas {
		n := nodeFromFile(m)
		if t, ok := nodes[m.Folder]; ok && m.Folder != "" {
			t.Files = append(t.Files, n)
		} else {
			rootFiles = append(rootFiles, n)
		}
	}
	sort.Slice(roots, func(i, j int) bool { return roots[i].Name < roots[j].Name })
	return roots
}

// RootFiles devolve os arquivos da raiz (folder "").
func (s *Store) RootFiles() []*FileNode {
	s.mu.RLock()
	defer s.mu.RUnlock()
	out := []*FileNode{}
	for _, m := range s.fileMetas {
		if m.Folder == "" {
			out = append(out, nodeFromFile(m))
		}
	}
	return out
}

// inlineSafe diz se o tipo pode ser exibido inline com segurança. html/js/svg
// e afins viram download (attachment) — previne stored-XSS same-origin.
func inlineSafe(mime string) bool {
	base := strings.ToLower(strings.TrimSpace(strings.Split(mime, ";")[0]))
	switch {
	case strings.HasPrefix(base, "image/"):
		return base != "image/svg+xml"
	case strings.HasPrefix(base, "video/"), strings.HasPrefix(base, "audio/"):
		return true
	case base == "text/plain", base == "text/markdown", base == "text/css",
		base == "application/json", base == "application/pdf",
		base == "text/csv":
		return true
	default:
		return false
	}
}

// ServeFile entrega o blob com headers endurecidos (MIME real, ETag, Range via
// ServeContent, CSP sandbox e attachment para tipos não-inline-seguros).
// A URL aceita apenas o id gerado — nada de path do disco.
func (s *Store) ServeFile(w http.ResponseWriter, r *http.Request, id string) error {
	s.mu.RLock()
	m := s.fileByID(id)
	var p string
	if m != nil {
		p = s.fileBlobPath(m.ID, safeExt(m.Name, m.MIME))
	}
	cp := m
	s.mu.RUnlock()
	if cp == nil {
		return ErrNotFound
	}
	f, err := os.Open(p)
	if err != nil {
		return ErrNotFound
	}
	defer f.Close()
	w.Header().Set("Content-Security-Policy", "sandbox")
	w.Header().Set("X-Content-Type-Options", "nosniff")
	if !inlineSafe(cp.MIME) {
		w.Header().Set("Content-Disposition", `attachment; filename="`+sanitizeHeaderName(cp.Name)+`"`)
	}
	w.Header().Set("ETag", `"`+cp.SHA256+`"`)
	http.ServeContent(w, r, cp.Name, cp.CreatedAt, f)
	return nil
}

func sanitizeHeaderName(name string) string {
	return strings.Map(func(r rune) rune {
		switch r {
		case '"', '\\', '\n', '\r', '/':
			return '_'
		}
		return r
	}, name)
}

// Folders devolve todas as pastas (lista plana; a UI monta a árvore).
func (s *Store) Folders() []Folder {
	s.mu.RLock()
	defer s.mu.RUnlock()
	out := make([]Folder, len(s.folders))
	copy(out, s.folders)
	return out
}