package server

import (
	"encoding/json"
	"fmt"
	"net/http"
	"time"

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

func writeJSON(w http.ResponseWriter, status int, v any) {
	b, err := json.Marshal(v)
	if err != nil {
		http.Error(w, `{"error":"internal error"}`, http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	w.Write(append(b, '\n'))
}

// absBase is the absolute URL of this service, for links and examples.
//
// It prefers --public-url. Falling back to the request's Host is display-only:
// the header is caller-controlled, so it is never used for anything a third
// party would see.
func (s *Server) absBase(r *http.Request) string {
	if s.cfg.PublicURL != "" {
		return s.cfg.PublicURL + s.cfg.BasePath
	}
	scheme := "http"
	if r.TLS != nil || r.Header.Get("X-Forwarded-Proto") == "https" {
		scheme = "https"
	}
	return scheme + "://" + r.Host + s.cfg.BasePath
}

// objectURL builds the download link handed back to an uploader.
func (s *Server) objectURL(r *http.Request, id string) string {
	return s.absBase(r) + "d/" + id
}

type indexPage struct {
	page
	MaxSize       string
	MaxExpiry     string
	DefaultExpiry string
	AbsBase       string
	TokenName     string // the remembered token's name, if there is one
	AllowVanity   bool
	Stale         bool // a remembered token that no longer exists
}

func (s *Server) handleIndex(w http.ResponseWriter, r *http.Request) {
	// A remembered token is resolved server-side, so the page can show the real
	// limits without the cookie ever being readable by a script.
	remembered := cookieCredential(r)
	lim, err := s.limitsFor(remembered)
	stale := false
	if err != nil {
		// The token was revoked or the file was edited; drop the cookie rather
		// than leave the caller wondering why uploads fail.
		s.forget(w, r)
		lim, stale = auth.Anonymous(s.cfg), true
	}

	s.render(w, http.StatusOK, "index.html", indexPage{
		page:          s.page(r, "Upload", true),
		MaxSize:       config.FormatSize(lim.MaxSize),
		MaxExpiry:     config.FormatDuration(lim.MaxExpiry),
		DefaultExpiry: config.FormatDuration(lim.DefaultExpiry),
		AbsBase:       s.absBase(r),
		TokenName:     lim.Name,
		AllowVanity:   lim.AllowVanity,
		Stale:         stale,
	})
}

type limitsJSON struct {
	Name          string `json:"name"`
	Remembered    bool   `json:"remembered"`
	MaxSize       *int64 `json:"max_size"` // null means unlimited
	MaxExpiry     string `json:"max_expiry"`
	DefaultExpiry string `json:"default_expiry"`
	AllowVanity   bool   `json:"allow_vanity"`
}

// handleLimits reports the permissions belonging to the presented credential,
// so the page can show what the caller may actually do.
func (s *Server) handleLimits(w http.ResponseWriter, r *http.Request) {
	// Rate-limited like an upload: this is the one endpoint that reports
	// whether a token is valid, and it should not be a free oracle.
	if !s.limiter.allow(clientIP(r, s.cfg), s.now()) {
		s.fail(w, r, http.StatusTooManyRequests, "Too many requests; try again shortly.")
		return
	}
	lim, err := s.limitsFor(credential(r))
	if err != nil {
		s.fail(w, r, http.StatusUnauthorized, "Unrecognised token.")
		return
	}
	out := limitsJSON{
		Name:          lim.Name,
		Remembered:    lim.Name != "" && bearer(r) == "",
		MaxExpiry:     config.FormatDuration(lim.MaxExpiry),
		DefaultExpiry: config.FormatDuration(lim.DefaultExpiry),
		AllowVanity:   lim.AllowVanity,
	}
	if lim.MaxSize != config.Unlimited {
		n := lim.MaxSize
		out.MaxSize = &n
	}
	writeJSON(w, http.StatusOK, out)
}

type objectPage struct {
	page
	Meta        *store.Meta
	Size        string
	Expires     string
	URL         string
	InfoURL     string
	DeleteToken string
}

func (s *Server) handleInfo(w http.ResponseWriter, r *http.Request) {
	id, err := store.CleanID(r.PathValue("id"))
	if err != nil {
		s.fail(w, r, http.StatusNotFound, "No such file.")
		return
	}
	m, err := s.store.Get(id, s.now())
	if err != nil {
		s.fail(w, r, http.StatusNotFound, "No such file.")
		return
	}
	s.render(w, http.StatusOK, "info.html", objectPage{
		page:    s.page(r, m.Filename, false),
		Meta:    m,
		Size:    config.FormatSize(m.Size),
		Expires: describeExpiry(m.Expires, s.now()),
	})
}

// describeExpiry renders a deadline as an absolute time plus how far off it is.
func describeExpiry(t *time.Time, now time.Time) string {
	if t == nil {
		return "never"
	}
	d := t.Sub(now).Round(time.Minute)
	if d < 0 {
		return "expired"
	}
	return fmt.Sprintf("%s (in %s)", t.UTC().Format("2006-01-02 15:04 MST"),
		config.FormatDuration(d))
}