package api

import (
	"database/sql"
	"errors"
	"image"
	_ "image/gif"
	_ "image/jpeg"
	_ "image/png"
	"io"
	"log/slog"
	"mime"
	"net/http"
	"path/filepath"
	"strings"
	"time"
	"unicode"
	"unicode/utf8"

	"github.com/go-chi/chi/v5"
	"github.com/google/uuid"
	"github.com/owncord/server/auth"
	"github.com/owncord/server/db"
	"github.com/owncord/server/permissions"
	"github.com/owncord/server/service"
	"github.com/owncord/server/storage"
)

// uploadResponse is the JSON shape returned by POST /api/v1/uploads.
type uploadResponse struct {
	ID       string `json:"id"`
	Filename string `json:"filename"`
	Size     int64  `json:"size"`
	Mime     string `json:"mime"`
	URL      string `json:"url"`
	Width    *int   `json:"width,omitempty"`
	Height   *int   `json:"height,omitempty"`
}

// sanitizeUploadFilename cleans an upload filename: strips control and
// invisible formatting characters, removes path separators, and truncates to a
// safe length.
func sanitizeUploadFilename(name string) string {
	// Strip path components — use only the base name.
	name = filepath.Base(name)
	// filepath.Base only understands the *server* OS's separator, so a
	// backslash survives on a Linux server and is then a path separator on the
	// victim's Windows client, where the name is pre-filled into a save dialog.
	if i := strings.LastIndexByte(name, '\\'); i >= 0 {
		name = name[i+1:]
	}
	// Remove control characters, invisible formatting characters, and any
	// residual forward slash.
	var sb strings.Builder
	for _, r := range name {
		// unicode.Cf covers the bidi overrides (U+202A–U+202E, U+2066–U+2069):
		// invisible characters that reorder how the name renders, so an
		// attachment can display a harmless-looking extension to every other
		// member of the channel while really being an executable script — and
		// the same string is what the native save dialog pre-fills. This is the
		// rule auth.ValidateUsername already applies to usernames.
		//
		// A forward slash is dropped too: filepath.Base("/") returns "/" (root
		// is its own basename), so an upload literally named "/" would otherwise
		// slip through the reserved-name check below with a path separator
		// intact. Any residual '/' is unsafe as a basename, so strip it here.
		if unicode.IsControl(r) || unicode.In(r, unicode.Cf) || r == '/' {
			continue
		}
		sb.WriteRune(r)
	}
	name = strings.TrimSpace(sb.String())
	// Truncate to the filesystem limit. Slicing by byte offset can land in the
	// middle of a multibyte rune, so trim back to the last full rune to keep the
	// result valid UTF-8 (an invalid name misbehaves in JSON encoding, on disk,
	// and in the client's download-name handling).
	if len(name) > maxUploadFilenameLength {
		name = name[:maxUploadFilenameLength]
		for len(name) > 0 && !utf8.ValidString(name) {
			name = name[:len(name)-1]
		}
	}
	if name == "" || name == "." || name == ".." {
		name = "unnamed"
	}
	return name
}

// isUnsafeInlineMIME returns true for MIME types that could execute active
// content (scripts, markup) if served inline under the OwnCord origin.
func isUnsafeInlineMIME(mimeType string) bool {
	// Normalize: take the base type before any parameters (e.g. "text/html; charset=utf-8").
	base := strings.SplitN(mimeType, ";", 2)[0]
	base = strings.TrimSpace(strings.ToLower(base))
	switch base {
	case "text/html", "application/xhtml+xml",
		"image/svg+xml", "text/xml", "application/xml",
		"application/pdf",
		"text/xsl", "text/xslt":
		return true
	}
	return false
}

// safeStorageErrorMessage maps a storage.Save error to a client-safe
// "upload rejected" body. Full detail always goes to slog.Warn at the call
// site — this only decides what crosses the HTTP boundary. storage.Save's
// failure messages are built with fmt.Errorf("... %s", dst) / %w around
// path-bearing OS errors (creating the file, syncing it, or the destination
// resolving outside the storage dir), so echoing them verbatim hands any
// authenticated user the server's absolute storage layout the moment a save
// fails (disk full, permission change, read-only mount). The two validation
// failures below are the only ones that never embed a path, so they're the
// only ones whose detail is forwarded.
func safeStorageErrorMessage(err error) string {
	msg := err.Error()
	switch {
	case strings.HasPrefix(msg, "blocked file type:"),
		strings.HasPrefix(msg, "file exceeds maximum size"):
		return "upload rejected: " + msg
	default:
		return "upload rejected"
	}
}

// writeStorageSaveError maps a storage.Save failure onto the right HTTP
// class: server-side filesystem failures (storage.ErrIO — disk full,
// permissions, read-only mount) become 507 so they are distinguishable from
// bad uploads in any status dashboard; everything else stays the client's
// 400. Detail never crosses the HTTP boundary either way (path leakage —
// see safeStorageErrorMessage).
func writeStorageSaveError(w http.ResponseWriter, saveErr error, what string) {
	if errors.Is(saveErr, storage.ErrIO) {
		slog.Error(what+" failed: server storage error", "error", saveErr)
		writeJSON(w, http.StatusInsufficientStorage, errorResponse{
			Error:   "STORAGE_ERROR",
			Message: "upload failed: server storage error",
		})
		return
	}
	slog.Warn(what+" rejected", "error", saveErr)
	writeJSON(w, http.StatusBadRequest, errorResponse{
		Error:   "BAD_REQUEST",
		Message: safeStorageErrorMessage(saveErr),
	})
}

// MountUploadRoutes registers upload and file-serving endpoints.
// allowedOrigins controls the Access-Control-Allow-Origin header on served files.
//
// permSvc MUST be non-nil — handleServeFile dereferences it to enforce
// per-channel ACLs on every file download. A nil permSvc would panic for
// any authenticated file request, so we fail fast at mount time rather
// than let the first user hit a 500.
func MountUploadRoutes(r chi.Router, database *db.DB, store FileStore, limiter *auth.RateLimiter, allowedOrigins []string, permSvc *service.PermissionService) {
	if permSvc == nil {
		panic("api: MountUploadRoutes requires a non-nil PermissionService")
	}
	// Upload requires authentication and a higher body size limit (100 MB).
	r.With(
		AuthMiddleware(database),
		MaxBodySize(uploadMaxBodySize),
	).Post("/api/v1/uploads", handleUpload(database, store, limiter))
	// File serving requires authentication for channel-level access control.
	r.With(AuthMiddleware(database)).Get("/api/v1/files/{id}", handleServeFile(database, store, allowedOrigins, permSvc))
}

func handleUpload(database *db.DB, store FileStore, limiter *auth.RateLimiter) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		// BUG-131: Per-user upload rate limit to prevent disk exhaustion.
		user, ok := r.Context().Value(UserKey).(*db.User)
		if ok && user != nil {
			uploadKey := auth.Key("upload", user.ID)
			if !limiter.Allow(uploadKey, uploadRateLimitPerMinute, time.Minute) {
				writeJSON(w, http.StatusTooManyRequests, errorResponse{
					Error:   "RATE_LIMITED",
					Message: "upload rate limit exceeded, try again later",
				})
				return
			}
		}

		// Limit request body size to prevent abuse.
		r.Body = http.MaxBytesReader(w, r.Body, uploadMaxBodySize)

		// Parse multipart form — 10 MB in memory, rest on disk.
		if err := r.ParseMultipartForm(multipartMemoryLimit); err != nil {
			writeJSON(w, http.StatusBadRequest, errorResponse{
				Error:   "BAD_REQUEST",
				Message: "invalid multipart form",
			})
			return
		}

		file, header, err := r.FormFile("file")
		if err != nil {
			writeJSON(w, http.StatusBadRequest, errorResponse{
				Error:   "BAD_REQUEST",
				Message: "missing file field",
			})
			return
		}
		defer file.Close() //nolint:errcheck

		// Generate UUID for storage.
		fileID := uuid.New().String()

		// Detect MIME type from actual file bytes (never trust client header).
		var sniffBuf [512]byte
		n, readErr := file.Read(sniffBuf[:])
		if readErr != nil && !errors.Is(readErr, io.EOF) && !errors.Is(readErr, io.ErrUnexpectedEOF) {
			writeJSON(w, http.StatusBadRequest, errorResponse{
				Error:   "BAD_REQUEST",
				Message: "failed to read uploaded file",
			})
			return
		}
		detectedMime := http.DetectContentType(sniffBuf[:n])
		// Seek back so the full content is available for storage.
		if _, seekErr := file.Seek(0, 0); seekErr != nil {
			writeJSON(w, http.StatusInternalServerError, errorResponse{
				Error:   "INTERNAL_ERROR",
				Message: "failed to process uploaded file",
			})
			return
		}
		mime := detectedMime

		// Store file on disk (validates file type via magic bytes).
		writtenBytes, saveErr := store.Save(fileID, file)
		if saveErr != nil {
			writeStorageSaveError(w, saveErr, "file upload")
			return
		}

		// Extract image dimensions if the file is an image.
		var width, height *int
		if strings.HasPrefix(mime, "image/") {
			f, openErr := store.Open(fileID)
			if openErr == nil {
				cfg, _, decErr := image.DecodeConfig(f)
				f.Close() //nolint:errcheck
				if decErr == nil {
					w2, h2 := cfg.Width, cfg.Height
					width = &w2
					height = &h2
				} else {
					slog.Warn("failed to decode image dimensions", "id", fileID, "error", decErr)
				}
			}
		}

		// Insert attachment record in DB (unlinked — message_id is NULL).
		user, _ = r.Context().Value(UserKey).(*db.User)
		safeFilename := sanitizeUploadFilename(header.Filename)
		if err := database.CreateAttachment(r.Context(), fileID, user.ID, safeFilename, fileID, mime, writtenBytes, width, height); err != nil {
			// Clean up stored file on DB failure.
			_ = store.Delete(fileID)
			slog.Error("failed to create attachment record", "error", err)
			writeJSON(w, http.StatusInternalServerError, errorResponse{
				Error:   "INTERNAL_ERROR",
				Message: "failed to save attachment",
			})
			return
		}

		slog.Info("file uploaded", "id", fileID, "filename", safeFilename, "size", writtenBytes, "mime", mime)

		writeJSON(w, http.StatusCreated, uploadResponse{
			ID:       fileID,
			Filename: safeFilename,
			Size:     writtenBytes,
			Mime:     mime,
			URL:      "/api/v1/files/" + fileID,
			Width:    width,
			Height:   height,
		})
	}
}

func handleServeFile(database *db.DB, store FileStore, allowedOrigins []string, permSvc *service.PermissionService) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		fileID := chi.URLParam(r, "id")
		if fileID == "" {
			http.NotFound(w, r)
			return
		}

		user, _ := r.Context().Value(UserKey).(*db.User)
		role, _ := r.Context().Value(RoleKey).(*db.Role)

		// Look up attachment metadata with channel context.
		aa, err := database.GetAttachmentWithChannel(r.Context(), fileID)
		if err != nil {
			slog.Error("failed to look up attachment", "id", fileID, "error", err)
			writeJSON(w, http.StatusInternalServerError, errorResponse{
				Error:   "INTERNAL_ERROR",
				Message: "internal server error",
			})
			return
		}
		if aa == nil {
			http.NotFound(w, r)
			return
		}

		// A soft-deleted message's attachments must stop being servable the
		// moment the message is deleted — the client shows a tombstone, but
		// without this check the file stays reachable by URL forever (no
		// sweep can ever reclaim a linked row either, since the only reaper
		// requires message_id IS NULL). Checked before the ACL branch so it
		// also covers admins, matching the tombstone applying to everyone.
		//
		// Queried directly rather than through database.GetMessage: that
		// wrapper's SELECT list carries every message column, and the
		// `deleted` flag is the only one this check needs.
		if aa.MessageID != nil {
			var deleted bool
			deletedErr := database.QueryRowContext(r.Context(),
				`SELECT deleted FROM messages WHERE id = ?`, *aa.MessageID).Scan(&deleted)
			switch {
			case errors.Is(deletedErr, sql.ErrNoRows):
				// No message row — leave ACL to decide (unlinked-shaped by now).
			case deletedErr != nil:
				slog.Error("failed to look up message for attachment", "id", fileID, "error", deletedErr)
				writeJSON(w, http.StatusInternalServerError, errorResponse{
					Error:   "INTERNAL_ERROR",
					Message: "internal server error",
				})
				return
			case deleted:
				http.NotFound(w, r)
				return
			}
		}

		// ── Access control ──────────────────────────────────────────────
		isAdmin := role != nil && permissions.HasAdmin(role.Permissions)

		// DM participation is required of everyone, including admins — this
		// matches every other DM read gate in the codebase (requireChannelRead,
		// PermissionService.RequireChannelAccess, checkSendPermission), none of
		// which have an admin bypass. Checked ahead of the `!isAdmin` block so
		// the admin bypass below cannot skip it.
		if aa.ChannelID != nil && aa.ChannelType == "dm" {
			if user == nil {
				writeJSON(w, http.StatusForbidden, errorResponse{
					Error:   "FORBIDDEN",
					Message: "you do not have access to this file",
				})
				return
			}
			ok, dmErr := database.IsDMParticipant(r.Context(), user.ID, *aa.ChannelID)
			if dmErr != nil || !ok {
				writeJSON(w, http.StatusForbidden, errorResponse{
					Error:   "FORBIDDEN",
					Message: "you do not have access to this file",
				})
				return
			}
		}

		if !isAdmin {
			if aa.ChannelID == nil {
				// An unlinked attachment that some user's avatar points at is
				// readable by every authenticated user: an avatar has to be
				// visible to the people who see the messages it sits next to.
				// The check is by the exact URL the column stores, so the file
				// stops being public the instant the avatar is replaced.
				isAvatar, avatarErr := database.IsAvatarFileURL(r.Context(), service.AvatarFileURL(fileID))
				if avatarErr != nil {
					slog.Error("failed to check avatar file", "id", fileID, "error", avatarErr)
				}
				switch {
				case isAvatar:
					// Public while in use — fall through to serving.
				// Unlinked attachment — only the uploader may access.
				// M-2: Legacy rows (NULL uploader_id) are now denied rather than
				// served to any authenticated user.
				case aa.UploaderID == nil:
					slog.Warn("legacy attachment access denied (NULL uploader_id)", "id", fileID)
					writeJSON(w, http.StatusForbidden, errorResponse{
						Error:   "FORBIDDEN",
						Message: "you do not have access to this file",
					})
					return
				case user == nil || *aa.UploaderID != user.ID:
					writeJSON(w, http.StatusForbidden, errorResponse{
						Error:   "FORBIDDEN",
						Message: "you do not have access to this file",
					})
					return
				}
			} else if aa.ChannelType != "dm" {
				// Linked attachment in a guild channel — check channel
				// permissions. The DM case is handled unconditionally above.
				if user == nil || !permSvc.HasChannelPerm(r.Context(), user.ID, *aa.ChannelID, permissions.ReadMessages) {
					writeJSON(w, http.StatusForbidden, errorResponse{
						Error:   "FORBIDDEN",
						Message: "you do not have access to this file",
					})
					return
				}
			}
		}

		// Open file from storage.
		f, err := store.Open(aa.StoredAs)
		if err != nil {
			http.NotFound(w, r)
			return
		}
		defer f.Close() //nolint:errcheck

		// Set headers before ServeContent to ensure correct MIME type.
		w.Header().Set("Content-Type", aa.MimeType)
		// BUG-118: Force download for MIME types that could execute content
		// under the OwnCord origin (HTML, SVG, XML, PDF).
		disposition := "inline"
		if isUnsafeInlineMIME(aa.MimeType) {
			disposition = "attachment"
		}
		w.Header().Set("Content-Disposition", mime.FormatMediaType(disposition, map[string]string{"filename": aa.Filename}))
		// These downloads are access-controlled, so they must never be stored by
		// shared/proxy caches (info-leak). Mark private and force revalidation.
		// W3-4: no-cache forces revalidation on every use, so a max-age is dead
		// weight alongside it — private + no-cache expresses the intent exactly.
		w.Header().Set("Cache-Control", "private, no-cache")
		// The Access-Control-Allow-Origin header below reflects the request
		// Origin, so responses vary by Origin and must not be cross-served.
		w.Header().Set("Vary", "Origin")
		// CORS: allow webview to read the response body using configured origins.
		if origin := r.Header.Get("Origin"); origin != "" {
			for _, allowed := range allowedOrigins {
				if allowed == "*" || strings.EqualFold(allowed, origin) {
					w.Header().Set("Access-Control-Allow-Origin", origin)
					w.Header().Set("Access-Control-Expose-Headers", "Content-Type, Content-Length")
					break
				}
			}
		}

		w.Header().Set("X-Content-Type-Options", "nosniff")

		// Use the actual file modification time so If-Modified-Since works correctly.
		var modTime time.Time
		if info, statErr := f.Stat(); statErr == nil {
			modTime = info.ModTime()
		}
		http.ServeContent(w, r, aa.Filename, modTime, f)
	}
}