// Package server is the catalog's HTTP API (t5de-hub's docs/products.md, "Catalog API").
package server

import (
	"encoding/json"
	"errors"
	"log"
	"net/http"
	"strconv"
	"strings"
	"time"

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

// Config is what the server needs.
type Config struct {
	Store     *store.Store
	Verifier  *token.Verifier
	Hub       *hub.Client
	CatalogID string
	WebOrigin string // the hub website's origin, allowed to upload from browsers (CORS); empty for none
	Logger    *log.Logger
	// MaxUploads is how many uploads are checked at once (each can hold up to 256 MiB of files in memory);
	// default 2.
	MaxUploads int
}

// Server serves the catalog's API.
type Server struct {
	cfg     Config
	uploads chan struct{}
	mux     *http.ServeMux
}

// New returns the catalog's API.
func New(cfg Config) *Server {
	if cfg.MaxUploads < 1 {
		cfg.MaxUploads = 2
	}
	if cfg.Logger == nil {
		cfg.Logger = log.Default()
	}
	cfg.WebOrigin = strings.TrimRight(cfg.WebOrigin, "/")
	s := &Server{cfg: cfg, uploads: make(chan struct{}, cfg.MaxUploads), mux: http.NewServeMux()}
	s.mux.HandleFunc("GET /health", s.health)
	s.mux.HandleFunc("OPTIONS /api/v1/uploads", s.preflight)
	s.mux.HandleFunc("POST /api/v1/uploads", s.upload)
	s.mux.HandleFunc("GET /api/v1/files/{sha256}", s.file)
	s.mux.HandleFunc("GET /api/v1/revisions/{product}/{revision}", s.revision)
	return s
}

// ServeHTTP serves a request and logs it.
func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	start := time.Now()
	rec := &recorder{ResponseWriter: w, status: http.StatusOK}
	s.mux.ServeHTTP(rec, r)
	s.cfg.Logger.Printf("%s %s %d %dB %s", r.Method, r.URL.Path, rec.status, rec.bytes, time.Since(start).Round(time.Millisecond))
}

type recorder struct {
	http.ResponseWriter
	status int
	bytes  int64
	wrote  bool
}

func (r *recorder) WriteHeader(status int) {
	if !r.wrote {
		r.status, r.wrote = status, true
	}
	r.ResponseWriter.WriteHeader(status)
}

func (r *recorder) Write(b []byte) (int, error) {
	r.wrote = true
	n, err := r.ResponseWriter.Write(b)
	r.bytes += int64(n)
	return n, err
}

func (r *recorder) Unwrap() http.ResponseWriter { return r.ResponseWriter }

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(v)
}

func writeError(w http.ResponseWriter, status int, code, message string) {
	if w.Header().Get("Cache-Control") == "" {
		w.Header().Set("Cache-Control", "no-store")
	}
	writeJSON(w, status, map[string]string{"error": code, "message": message})
}

func (s *Server) health(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Cache-Control", "no-store")
	writeJSON(w, http.StatusOK, map[string]bool{"ok": true})
}

// bearer returns the request's bearer token, if any.
func bearer(r *http.Request) string {
	scheme, tok, ok := strings.Cut(r.Header.Get("Authorization"), " ")
	if !ok || !strings.EqualFold(scheme, "Bearer") {
		return ""
	}
	return strings.TrimSpace(tok)
}

func (s *Server) file(w http.ResponseWriter, r *http.Request) {
	hash := r.PathValue("sha256")
	if !store.ValidHash(hash) {
		writeError(w, http.StatusNotFound, "not_found", "No such file.")
		return
	}
	hosted, adultOnly, err := s.cfg.Store.FileAccess(hash)
	if err != nil {
		s.cfg.Logger.Printf("files: %s: %v", hash, err)
		writeError(w, http.StatusInternalServerError, "internal", "Something went wrong.")
		return
	}
	if !hosted {
		writeError(w, http.StatusNotFound, "not_found", "No such file.")
		return
	}
	h := w.Header()
	if adultOnly {
		h.Set("Cache-Control", "private, no-store")
		h.Set("Vary", "Authorization")
		tok := bearer(r)
		if tok == "" {
			h.Set("WWW-Authenticate", `Bearer realm="t5de-catalog"`)
			writeError(w, http.StatusUnauthorized, "token_required", "This file needs an access token.")
			return
		}
		c, err := s.cfg.Verifier.Verify(r.Context(), tok, token.Access)
		if err != nil {
			h.Set("WWW-Authenticate", `Bearer realm="t5de-catalog", error="invalid_token"`)
			writeError(w, http.StatusUnauthorized, "bad_token", "The access token isn't valid.")
			return
		}
		if !c.Adult {
			writeError(w, http.StatusForbidden, "adult_only", "This file is for adults only.")
			return
		}
	}
	f, err := s.cfg.Store.Open(hash)
	if errors.Is(err, store.ErrNotFound) {
		s.cfg.Logger.Printf("files: %s is in a hosted revision but missing on disk", hash)
		writeError(w, http.StatusNotFound, "not_found", "No such file.")
		return
	}
	if err != nil {
		s.cfg.Logger.Printf("files: %s: %v", hash, err)
		writeError(w, http.StatusInternalServerError, "internal", "Something went wrong.")
		return
	}
	defer f.Close()
	if adultOnly {
		h.Set("Cache-Control", "private, max-age=31536000, immutable")
	} else {
		h.Set("Cache-Control", "public, max-age=31536000, immutable")
	}
	h.Set("ETag", `"`+hash+`"`)
	h.Set("Content-Type", "application/octet-stream")
	h.Set("X-Content-Type-Options", "nosniff")
	http.ServeContent(w, r, "", time.Time{}, f)
}

func (s *Server) revision(w http.ResponseWriter, r *http.Request) {
	product := r.PathValue("product")
	n, err := strconv.Atoi(r.PathValue("revision"))
	if !hub.ValidProduct(product) || err != nil || n < 1 {
		writeError(w, http.StatusNotFound, "not_found", "No such revision.")
		return
	}
	rev, err := s.cfg.Store.Revision(product, n)
	if errors.Is(err, store.ErrNotFound) {
		writeError(w, http.StatusNotFound, "not_found", "No such revision.")
		return
	}
	if err != nil {
		s.cfg.Logger.Printf("revisions: %s/%d: %v", product, n, err)
		writeError(w, http.StatusInternalServerError, "internal", "Something went wrong.")
		return
	}
	// Revisions never change, but moderation can remove one.
	w.Header().Set("Cache-Control", "public, max-age=3600")
	writeJSON(w, http.StatusOK, rev)
}