package server

import (
	"errors"
	"fmt"
	"io"
	"mime"
	"mime/multipart"
	"net/http"
	"strings"
	"time"

	"uncensored-send/internal/auth"
	"uncensored-send/internal/config"
	"uncensored-send/internal/store"
)

const (
	// maxFieldBytes and maxFieldCount bound the non-file portion of a multipart
	// body. The file part needs no such bound: the store's own limit stops it
	// at exactly the caller's cap.
	maxFieldBytes = 4 << 10
	maxFieldCount = 16

	fileFieldName = "file"

	// stallTimeout is how long a single read from the body may take. It is
	// reset on every successful read, so a slow upload is fine and a stalled
	// one is not.
	stallTimeout = 2 * time.Minute
)

var errFieldTooLarge = errors.New("form field is too large")

// uploadRequest is the set of knobs a caller may turn, however they arrived.
type uploadRequest struct {
	token    string
	vanity   string
	expiry   string
	filename string
}

func (s *Server) handleUpload(w http.ResponseWriter, r *http.Request) {
	ip := clientIP(r, s.cfg)
	if !s.limiter.allow(ip, s.now()) {
		s.fail(w, r, http.StatusTooManyRequests, "Too many uploads; try again shortly.")
		return
	}

	// Bound concurrency so a handful of multi-gigabyte uploads cannot starve
	// the disk or the machine.
	select {
	case s.slots <- struct{}{}:
		defer func() { <-s.slots }()
	default:
		w.Header().Set("Retry-After", "30")
		s.fail(w, r, http.StatusServiceUnavailable, "Too many uploads in flight; try again shortly.")
		return
	}

	mediatype, params, err := mime.ParseMediaType(r.Header.Get("Content-Type"))
	if err == nil && mediatype == "multipart/form-data" {
		s.uploadMultipart(w, r, params["boundary"], ip)
		return
	}
	s.uploadRaw(w, r, ip)
}

// uploadRaw handles a body that is nothing but the file, as sent by curl.
// Options ride along in headers.
func (s *Server) uploadRaw(w http.ResponseWriter, r *http.Request, ip string) {
	req := uploadRequest{
		token:    bearer(r),
		vanity:   strings.TrimSpace(r.Header.Get("Vanity")),
		expiry:   strings.TrimSpace(r.Header.Get("Expiry")),
		filename: filenameFromDisposition(r.Header.Get("Content-Disposition")),
	}
	if req.token == "" {
		req.token = cookieCredential(r)
	}
	s.storeUpload(w, r, req, r.Body, ip)
}

// uploadMultipart streams a browser form post.
//
// The body is read with multipart.Reader rather than ParseMultipartForm: the
// latter spools the whole upload into its own temporary files with its own
// limits, which for a 2 GiB body is exactly what we are trying to avoid. The
// consequence is that fields must arrive before the file part, since the limits
// they select have to be known before the first byte of the file is accepted.
func (s *Server) uploadMultipart(w http.ResponseWriter, r *http.Request, boundary, ip string) {
	if boundary == "" {
		s.fail(w, r, http.StatusBadRequest, "Malformed multipart body: no boundary.")
		return
	}
	mr := multipart.NewReader(r.Body, boundary)

	// Headers seed the request even here, so that a caller mixing the two
	// shapes, curl -F with a Vanity header, say, is not silently given a
	// UUID instead of the name they asked for. A non-empty form field of the
	// same meaning overrides them.
	req := uploadRequest{
		token:  bearer(r),
		vanity: strings.TrimSpace(r.Header.Get("Vanity")),
		expiry: strings.TrimSpace(r.Header.Get("Expiry")),
	}

	for n := 0; ; n++ {
		if n > maxFieldCount {
			s.fail(w, r, http.StatusBadRequest, "Too many form fields.")
			return
		}
		part, err := mr.NextPart()
		if errors.Is(err, io.EOF) {
			s.fail(w, r, http.StatusBadRequest, "No file was included in the upload.")
			return
		}
		if err != nil {
			s.fail(w, r, http.StatusBadRequest, "Malformed multipart body.")
			return
		}

		if part.FormName() == fileFieldName {
			if req.filename == "" {
				req.filename = part.FileName()
			}
			// Nothing explicit was supplied, so fall back to what the browser
			// remembered. This happens after the fields precisely so a typed
			// token still wins.
			if req.token == "" {
				req.token = cookieCredential(r)
			}
			s.storeUpload(w, r, req, part, ip)
			return
		}

		value, err := readField(part)
		part.Close()
		if err != nil {
			s.fail(w, r, http.StatusBadRequest, "A form field was too large.")
			return
		}
		switch part.FormName() {
		case "token":
			if v := strings.TrimSpace(value); v != "" {
				req.token = v
			}
		case "vanity":
			if v := strings.TrimSpace(value); v != "" {
				req.vanity = v
			}
		case "expiry":
			if v := strings.TrimSpace(value); v != "" {
				req.expiry = v
			}
		case "filename":
			req.filename = value
		}
	}
}

func readField(p *multipart.Part) (string, error) {
	b, err := io.ReadAll(io.LimitReader(p, maxFieldBytes+1))
	if err != nil {
		return "", err
	}
	if len(b) > maxFieldBytes {
		return "", errFieldTooLarge
	}
	return string(b), nil
}

// filenameFromDisposition reads a filename from a request-side
// Content-Disposition header. There is no standard for using the header this
// way, but it is the established convention, and mime.ParseMediaType already
// understands both the plain and the RFC 5987 encoded forms.
func filenameFromDisposition(h string) string {
	if h == "" {
		return ""
	}
	_, params, err := mime.ParseMediaType(h)
	if err != nil {
		return ""
	}
	return params["filename"]
}

// storeUpload is the common tail of both upload shapes: resolve the caller's
// limits, claim a name, stream the bytes, then publish.
func (s *Server) storeUpload(w http.ResponseWriter, r *http.Request, req uploadRequest, body io.Reader, ip string) {
	now := s.now()

	lim, err := s.limitsFor(r, req.token)
	if err != nil {
		s.fail(w, r, http.StatusUnauthorized, "Unrecognised token.")
		return
	}
	if req.vanity != "" && !lim.AllowVanity {
		s.fail(w, r, http.StatusForbidden, "Custom names require a token.")
		return
	}
	expires, err := resolveExpiry(req.expiry, lim, now)
	if err != nil {
		s.fail(w, r, http.StatusBadRequest, err.Error())
		return
	}

	limit, err := s.capacity(lim.MaxSize)
	if err != nil {
		s.fail(w, r, http.StatusInsufficientStorage, err.Error())
		return
	}

	// Claim the name before reading a single byte, so a taken vanity name
	// fails instantly rather than after a multi-gigabyte transfer.
	up, err := s.reserve(req.vanity)
	switch {
	case errors.Is(err, store.ErrExists):
		s.fail(w, r, http.StatusConflict, "That name is already taken.")
		return
	case errors.Is(err, store.ErrBadID):
		s.fail(w, r, http.StatusBadRequest,
			"A custom name must be 2-64 characters of letters, digits, dot, dash or underscore.")
		return
	case err != nil:
		s.log.Error("reserving object", "err", err)
		s.fail(w, r, http.StatusInternalServerError, "Could not store the file.")
		return
	}
	committed := false
	defer func() {
		if !committed {
			up.Abort()
		}
	}()

	up.SetLimit(limit)
	if _, err := io.Copy(up, guardStalls(w, body)); err != nil {
		switch {
		case errors.Is(err, store.ErrTooLarge):
			s.fail(w, r, http.StatusRequestEntityTooLarge,
				fmt.Sprintf("That file is larger than the %s limit.", config.FormatSize(limit)))
		default:
			// A disconnect mid-upload lands here; there is rarely anyone left
			// to read the response.
			s.log.Info("upload aborted", "ip", ip, "id", up.ID(), "bytes", up.Size(), "err", err)
			s.fail(w, r, http.StatusBadRequest, "The upload did not complete.")
		}
		return
	}
	clearDeadline(w)

	secret, err := store.NewSecret()
	if err != nil {
		s.log.Error("generating delete token", "err", err)
		s.fail(w, r, http.StatusInternalServerError, "Could not store the file.")
		return
	}

	m := &store.Meta{
		Filename:   store.SanitizeFilename(req.filename),
		Created:    now,
		Expires:    expires,
		Owner:      lim.Name,
		Vanity:     req.vanity != "",
		DeleteHash: auth.HashSecret(secret),
	}
	if err := up.Commit(m); err != nil {
		s.log.Error("committing object", "id", up.ID(), "err", err)
		s.fail(w, r, http.StatusInternalServerError, "Could not store the file.")
		return
	}
	committed = true

	s.log.Info("stored", "id", m.ID, "bytes", m.Size, "owner", orAnonymous(lim.Name),
		"ip", ip, "expires", m.Expires)
	s.respondUploaded(w, r, m, secret)
}

func orAnonymous(name string) string {
	if name == "" {
		return "(anonymous)"
	}
	return name
}

// reserve claims either the requested vanity name or a fresh UUIDv4.
func (s *Server) reserve(vanity string) (*store.Upload, error) {
	if vanity == "" {
		return s.store.ReserveRandom()
	}
	id, err := store.CleanID(vanity)
	if err != nil {
		return nil, err
	}
	return s.store.Reserve(id)
}

// capacity narrows the caller's own limit to what the store can still hold.
func (s *Server) capacity(callerLimit int64) (int64, error) {
	full := errors.New("The service is out of space; try again later.")
	limit := callerLimit

	if s.cfg.MaxTotalBytes != config.Unlimited {
		remaining := s.cfg.MaxTotalBytes - s.store.Total()
		if remaining <= 0 {
			return 0, full
		}
		if limit == config.Unlimited || remaining < limit {
			limit = remaining
		}
	}
	if s.cfg.MinFreeBytes > 0 {
		if free, ok := freeBytes(s.store.DataDir()); ok {
			usable := free - s.cfg.MinFreeBytes
			if usable <= 0 {
				return 0, full
			}
			if limit == config.Unlimited || usable < limit {
				limit = usable
			}
		}
	}
	return limit, nil
}

// resolveExpiry turns a requested lifetime into a deadline, refusing anything
// longer than the caller is entitled to.
func resolveExpiry(requested string, lim auth.Limits, now time.Time) (*time.Time, error) {
	d := lim.DefaultExpiry
	if requested != "" {
		var err error
		if d, err = config.ParseDuration(requested); err != nil {
			return nil, fmt.Errorf("%s; try something like 3d, 12h or 90m", err)
		}
	}
	if d == config.Unlimited {
		if lim.MaxExpiry != config.Unlimited {
			return nil, fmt.Errorf("files here cannot be kept indefinitely; the longest lifetime available to you is %s",
				config.FormatDuration(lim.MaxExpiry))
		}
		return nil, nil
	}
	if lim.MaxExpiry != config.Unlimited && d > lim.MaxExpiry {
		return nil, fmt.Errorf("the longest lifetime available to you is %s",
			config.FormatDuration(lim.MaxExpiry))
	}
	if d < time.Minute {
		return nil, errors.New("the shortest lifetime is one minute")
	}
	t := now.Add(d)
	return &t, nil
}

// guardStalls resets the connection's read deadline before every read, so a
// legitimately slow transfer survives while a stalled one is dropped. The
// server's own ReadTimeout cannot do this job: it would have to be long enough
// for the largest permitted upload, which is no protection at all.
func guardStalls(w http.ResponseWriter, r io.Reader) io.Reader {
	rc := http.NewResponseController(w)
	if err := rc.SetReadDeadline(time.Now().Add(stallTimeout)); err != nil {
		return r // not a real connection (tests); nothing to guard
	}
	return &stallGuard{r: r, rc: rc}
}

type stallGuard struct {
	r  io.Reader
	rc *http.ResponseController
}

func (g *stallGuard) Read(p []byte) (int, error) {
	g.rc.SetReadDeadline(time.Now().Add(stallTimeout))
	return g.r.Read(p)
}

func clearDeadline(w http.ResponseWriter) {
	http.NewResponseController(w).SetReadDeadline(time.Time{})
}

type uploadResult struct {
	ID          string `json:"id"`
	Filename    string `json:"filename"`
	Size        int64  `json:"size"`
	SHA256      string `json:"sha256"`
	Expires     string `json:"expires"` // RFC 3339, or "" for never
	URL         string `json:"url"`
	InfoURL     string `json:"info_url"`
	DeleteToken string `json:"delete_token"`
	DeleteURL   string `json:"delete_url"`
}

// respondUploaded answers in whichever shape the caller asked for. The delete
// token appears exactly once, here, and is never recoverable afterwards.
func (s *Server) respondUploaded(w http.ResponseWriter, r *http.Request, m *store.Meta, secret string) {
	url := s.objectURL(r, m.ID)
	if wantsJSON(r) {
		expires := ""
		if m.Expires != nil {
			expires = m.Expires.UTC().Format(time.RFC3339)
		}
		writeJSON(w, http.StatusCreated, uploadResult{
			ID: m.ID, Filename: m.Filename, Size: m.Size, SHA256: m.SHA256,
			Expires:     expires,
			URL:         url,
			InfoURL:     s.absBase(r) + "i/" + m.ID,
			DeleteToken: secret,
			DeleteURL:   s.absBase(r) + "api/d/" + m.ID + "/delete",
		})
		return
	}
	// Rendered directly rather than redirected: a 303 would have to carry the
	// delete token in the URL, where it would end up in logs and history.
	s.render(w, http.StatusOK, "result.html", objectPage{
		// The script is loaded here only to enable the copy buttons, which stay
		// hidden without it rather than sitting there dead.
		page:        s.page(r, "Uploaded", true),
		Meta:        m,
		Size:        config.FormatSize(m.Size),
		Expires:     describeExpiry(m.Expires, s.now()),
		URL:         url,
		InfoURL:     s.absBase(r) + "i/" + m.ID,
		DeleteToken: secret,
	})
}