package server

import (
	"archive/zip"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"mime"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"unicode/utf8"

	"git.t5de.dev/t5de/t5de-api/pack"

	"git.t5de.dev/t5de/t5de-catalog/internal/hub"
	"git.t5de.dev/t5de/t5de-catalog/internal/store"
	"git.t5de.dev/t5de/t5de-catalog/internal/token"
)

// MaxBody caps an upload request: the zip (whose files may hold pack.MaxTotalSize uncompressed) and the notes.
const MaxBody = 300 << 20

// MaxNotes caps the revision notes.
const MaxNotes = 64 << 10

// corsHeaders adds CORS headers for the hub website's origin.
func (s *Server) corsHeaders(w http.ResponseWriter, r *http.Request) bool {
	h := w.Header()
	h.Add("Vary", "Origin")
	origin := r.Header.Get("Origin")
	if origin == "" || s.cfg.WebOrigin == "" || origin != s.cfg.WebOrigin {
		return false
	}
	h.Set("Access-Control-Allow-Origin", origin)
	return true
}

func (s *Server) preflight(w http.ResponseWriter, r *http.Request) {
	if s.corsHeaders(w, r) {
		h := w.Header()
		h.Add("Vary", "Access-Control-Request-Method")
		h.Add("Vary", "Access-Control-Request-Headers")
		h.Set("Access-Control-Allow-Methods", "POST")
		h.Set("Access-Control-Allow-Headers", "Authorization, Content-Type")
		h.Set("Access-Control-Max-Age", "600")
	}
	w.WriteHeader(http.StatusNoContent)
}

// upload takes a product (docs/products.md, POST /api/v1/uploads): checks the token and the files, stores the
// files, registers the revision with the hub, and records it as hosted once the hub has accepted it.
func (s *Server) upload(w http.ResponseWriter, r *http.Request) {
	s.corsHeaders(w, r)
	tok := bearer(r)
	if tok == "" {
		writeError(w, http.StatusUnauthorized, "bad_token", "An upload token is needed.")
		return
	}
	claims, err := s.cfg.Verifier.Verify(r.Context(), tok, token.Upload)
	if err != nil {
		s.cfg.Logger.Printf("uploads: %v", err)
		writeError(w, http.StatusUnauthorized, "bad_token", "The upload token isn't valid. Start the upload again.")
		return
	}
	if claims.Catalog != s.cfg.CatalogID {
		writeError(w, http.StatusUnauthorized, "bad_token", "The upload token is for another catalog.")
		return
	}
	if claims.Product != "" && !hub.ValidProduct(claims.Product) {
		writeError(w, http.StatusUnauthorized, "bad_token", "The upload token names no valid product.")
		return
	}

	select {
	case s.uploads <- struct{}{}:
		defer func() { <-s.uploads }()
	case <-r.Context().Done():
		return
	}

	tmp, err := os.MkdirTemp(s.cfg.Store.TempDir(), "upload-*")
	if err != nil {
		s.cfg.Logger.Printf("uploads: %v", err)
		writeError(w, http.StatusInternalServerError, "internal", "Something went wrong.")
		return
	}
	defer os.RemoveAll(tmp)

	r.Body = http.MaxBytesReader(w, r.Body, MaxBody)
	notes, status, code, msg := readForm(r, filepath.Join(tmp, pack.ChknName))
	if status != 0 {
		if status == http.StatusInternalServerError {
			s.cfg.Logger.Printf("uploads: %s", msg)
			msg = "Something went wrong."
		}
		writeError(w, status, code, msg)
		return
	}
	if claims.Product != "" && notes == "" {
		writeError(w, http.StatusBadRequest, "notes_required", "Say what changed in this revision.")
		return
	}

	p, rating, err := checkProduct(tmp)
	if err != nil {
		writeError(w, http.StatusBadRequest, "bad_files", "These product files can't be used: "+err.Error())
		return
	}

	files := make([]store.File, len(p.Files))
	for i, f := range p.Files {
		hash, err := s.cfg.Store.PutFile(f.Data)
		if err != nil {
			s.cfg.Logger.Printf("uploads: storing %q: %v", f.Name, err)
			writeError(w, http.StatusInternalServerError, "internal", "Something went wrong.")
			return
		}
		files[i] = store.File{Name: f.Name, SHA256: hash, Size: int64(len(f.Data))}
	}
	index := p.Index
	p = nil // the files' data can go before the hub answers

	reg, err := s.cfg.Hub.RegisterRevision(r.Context(), hub.NewRevision{
		UploadToken: tok, Files: files, Rating: rating, Parent: index.Parent, Name: strings.TrimSpace(index.Name), Notes: notes,
	})
	if err != nil {
		var refused *hub.Error
		if errors.As(err, &refused) {
			s.cfg.Logger.Printf("uploads: %v", err)
			code, msg := refused.Code, refused.Message
			if code == "" {
				code = "hub_refused"
			}
			if msg == "" {
				msg = fmt.Sprintf("T5DE's hub refused the upload (%d).", refused.Status)
			}
			writeError(w, http.StatusBadGateway, code, msg)
			return
		}
		s.cfg.Logger.Printf("uploads: registering with the hub: %v", err)
		writeError(w, http.StatusBadGateway, "hub_unavailable", "T5DE's hub couldn't be reached. Try again later.")
		return
	}
	if claims.Product != "" && reg.Product != claims.Product {
		s.cfg.Logger.Printf("uploads: the hub registered product %s, but the token was for %s", reg.Product, claims.Product)
		writeError(w, http.StatusBadGateway, "hub_failed", "T5DE's hub answered for another product.")
		return
	}
	if err := s.cfg.Store.AddRevision(store.Revision{Product: reg.Product, Revision: reg.Revision, Rating: rating, Files: files}); err != nil {
		s.cfg.Logger.Printf("uploads: recording %s/%d: %v", reg.Product, reg.Revision, err)
		writeError(w, http.StatusInternalServerError, "internal", "Something went wrong.")
		return
	}
	s.cfg.Logger.Printf("uploads: %s/%d (%s, %d files) from %s", reg.Product, reg.Revision, rating, len(files), claims.Subject)
	writeJSON(w, http.StatusCreated, reg)
}

// readForm reads the upload's multipart form: the zip (part "file") into chkn, and the notes (part "notes").
// Other parts are skipped. A non-zero status is an error to answer.
func readForm(r *http.Request, chkn string) (notes string, status int, code, msg string) {
	mt, _, err := mime.ParseMediaType(r.Header.Get("Content-Type"))
	if err != nil || mt != "multipart/form-data" {
		return "", http.StatusBadRequest, "bad_request", "Send the product as multipart/form-data."
	}
	mr, err := r.MultipartReader()
	if err != nil {
		return "", http.StatusBadRequest, "bad_request", "Send the product as multipart/form-data."
	}
	tooLarge := func(err error) bool {
		var mbe *http.MaxBytesError
		return errors.As(err, &mbe)
	}
	haveFile, haveNotes := false, false
	for {
		part, err := mr.NextPart()
		if err == io.EOF {
			break
		}
		if err != nil {
			if tooLarge(err) {
				return "", http.StatusRequestEntityTooLarge, "too_large", fmt.Sprintf("Uploads can be at most %d MiB.", MaxBody>>20)
			}
			return "", http.StatusBadRequest, "bad_request", "The upload is cut short or malformed."
		}
		switch part.FormName() {
		case "file":
			if haveFile {
				return "", http.StatusBadRequest, "bad_request", "Send one file."
			}
			haveFile = true
			f, err := os.Create(chkn)
			if err != nil {
				return "", http.StatusInternalServerError, "internal", err.Error()
			}
			_, err = io.Copy(f, part)
			if cerr := f.Close(); err == nil && cerr != nil {
				return "", http.StatusInternalServerError, "internal", cerr.Error()
			}
			if err != nil {
				if tooLarge(err) {
					return "", http.StatusRequestEntityTooLarge, "too_large", fmt.Sprintf("Uploads can be at most %d MiB.", MaxBody>>20)
				}
				return "", http.StatusBadRequest, "bad_request", "The upload is cut short or malformed."
			}
		case "notes":
			if haveNotes {
				return "", http.StatusBadRequest, "bad_request", "Send the notes once."
			}
			haveNotes = true
			data, err := io.ReadAll(io.LimitReader(part, MaxNotes+1))
			if err != nil {
				if tooLarge(err) {
					return "", http.StatusRequestEntityTooLarge, "too_large", fmt.Sprintf("Uploads can be at most %d MiB.", MaxBody>>20)
				}
				return "", http.StatusBadRequest, "bad_request", "The upload is cut short or malformed."
			}
			if len(data) > MaxNotes {
				return "", http.StatusBadRequest, "bad_request", fmt.Sprintf("The notes can be at most %d KiB.", MaxNotes>>10)
			}
			if !utf8.Valid(data) {
				return "", http.StatusBadRequest, "bad_request", "The notes aren't valid UTF-8."
			}
			notes = strings.TrimSpace(string(data))
		default:
			if _, err := io.Copy(io.Discard, part); err != nil {
				if tooLarge(err) {
					return "", http.StatusRequestEntityTooLarge, "too_large", fmt.Sprintf("Uploads can be at most %d MiB.", MaxBody>>20)
				}
				return "", http.StatusBadRequest, "bad_request", "The upload is cut short or malformed."
			}
		}
		part.Close()
	}
	if !haveFile {
		return "", http.StatusBadRequest, "bad_request", "No file: send the product's .chkn as \"file\"."
	}
	return notes, 0, "", ""
}

// ratings maps index.xml's ProductRating to the hub's ratings.
var ratings = map[string]string{"GA": store.General, "AP": store.Adult}

// checkProduct checks the zip dir/product.chkn by the pack rules (t5de-api's pack package): it reads the rating
// from its index.xml, writes a manifest with that rating beside it, and loads dir as a pack. It returns the pack
// and its rating.
func checkProduct(dir string) (*pack.Pack, string, error) {
	index, err := readIndex(filepath.Join(dir, pack.ChknName))
	if err != nil {
		return nil, "", err
	}
	rating := ratings[index.Rating]
	manifest, err := json.Marshal(pack.Manifest{Format: pack.Format, ID: "upload", Revision: 1, Name: "upload", Rating: rating})
	if err != nil {
		return nil, "", err
	}
	if err := os.WriteFile(filepath.Join(dir, pack.ManifestName), manifest, 0o644); err != nil {
		return nil, "", err
	}
	p, err := pack.Load(dir)
	if err != nil {
		return nil, "", err
	}
	return p, rating, nil
}

// readIndex reads index.xml from the zip at path, its size counted while reading.
func readIndex(path string) (*pack.Index, error) {
	z, err := zip.OpenReader(path)
	if err != nil {
		return nil, errors.New("not a zip file")
	}
	defer z.Close()
	for _, f := range z.File {
		if f.Name != pack.IndexName {
			continue
		}
		rc, err := f.Open()
		if err != nil {
			return nil, fmt.Errorf("%s: %v", pack.IndexName, err)
		}
		data, err := io.ReadAll(io.LimitReader(rc, pack.MaxFileSize+1))
		rc.Close()
		if err != nil {
			return nil, fmt.Errorf("%s: %v", pack.IndexName, err)
		}
		if len(data) > pack.MaxFileSize {
			return nil, fmt.Errorf("%s: over %d MiB", pack.IndexName, pack.MaxFileSize>>20)
		}
		index, err := pack.ParseIndex(data)
		if err != nil {
			return nil, fmt.Errorf("%s: %v", pack.IndexName, err)
		}
		return index, nil
	}
	return nil, fmt.Errorf("no %s at the top of the zip", pack.IndexName)
}