// Package shell is what the desktop app's webview loads: the web client,
// served through the same host package as warp-web, plus the few pages and
// endpoints only the desktop app has.
//
// Unlike warp-web, the desktop app isn't installed next to one homeserver,
// so nothing is proxied: the client calls the homeserver directly, as any
// Matrix client does (homeservers answer CORS for every origin). Which
// homeserver new sign-ins go to is asked on first run and kept in the
// settings file. A session already signed in keeps the base URL it signed
// in with, so changing the homeserver never sends one server's access
// token to another.
package shell

import (
	"context"
	"encoding/json"
	"errors"
	"html/template"
	"io/fs"
	"log/slog"
	"net/http"
	"net/url"
	"strings"
	"sync/atomic"
	"time"

	"github.com/dariuszjaniak/warp/apps/web/host"
)

const (
	// SetupPath is the first-run page, also where "Change homeserver…"
	// goes.
	SetupPath = "/_desktop/setup"
	// openPath takes a URL to open in the system browser: the page's links
	// to other sites go there instead of navigating the app's window.
	openPath = "/_desktop/open"
)

// Options configures the shell.
type Options struct {
	// Store keeps the chosen homeserver.
	Store *Store
	// Homeserver, when set, is used for this run instead of the saved
	// one, and isn't saved.
	Homeserver string
	// Client is the built web client; nil serves host's "not built" page.
	Client fs.FS
	// Version is reported in /config.json.
	Version string
	// Logger defaults to slog.Default().
	Logger *slog.Logger
	// OpenURL opens a URL in the system browser.
	OpenURL func(string) error
	// HTTPClient is used to find and check a homeserver on the setup
	// page. Defaults to a client with a 15 second timeout.
	HTTPClient *http.Client
	// Notify shows a system notification; nil drops them.
	Notify func(Notification) error
	// SetTitle gets the page's title whenever it changes.
	SetTitle func(string)
}

// Shell is the webview's http.Handler.
type Shell struct {
	opts Options
	app  atomic.Pointer[app]
}

// app is the web client configured for one homeserver.
type app struct {
	homeserver string
	handler    http.Handler
}

// New returns the shell, serving the client for the saved homeserver, or
// the setup page when there is none yet.
func New(opts Options) (*Shell, error) {
	if opts.Store == nil {
		return nil, errors.New("shell: Store is required")
	}
	if opts.Logger == nil {
		opts.Logger = slog.Default()
	}
	if opts.HTTPClient == nil {
		opts.HTTPClient = &http.Client{Timeout: 15 * time.Second}
	}
	if opts.Client != nil {
		client, ok, err := withDesktopScripts(opts.Client)
		if err != nil {
			return nil, err
		}
		if !ok {
			opts.Logger.Warn("the client's index.html has no <head>; links will open in the app's window, and there are no notifications")
		}
		opts.Client = client
	}
	s := &Shell{opts: opts}

	if opts.Homeserver != "" {
		if err := s.use(opts.Homeserver); err != nil {
			return nil, err
		}
		return s, nil
	}
	// A damaged settings file only costs the choice of server: the setup
	// page asks again and overwrites it.
	st, err := opts.Store.Load()
	if err != nil {
		opts.Logger.Warn("can't read the settings; asking for the homeserver again", "err", err)
	}
	if st.Homeserver != "" {
		if err := s.use(st.Homeserver); err != nil {
			opts.Logger.Warn("the saved homeserver isn't valid; asking again", "err", err)
		}
	}
	return s, nil
}

// Homeserver returns the base URL new sign-ins go to, or "" before setup.
func (s *Shell) Homeserver() string {
	if a := s.app.Load(); a != nil {
		return a.homeserver
	}
	return ""
}

func (s *Shell) use(homeserver string) error {
	u, err := parseBase(homeserver)
	if err != nil {
		return errors.New("shell: the homeserver must be an absolute http(s) URL, got " + homeserver)
	}
	h, err := host.New(host.Options{
		PublicHomeserver: u,
		Client:           s.opts.Client,
		Version:          s.opts.Version,
		Logger:           s.opts.Logger,
		AnyCallOrigin:    true,
	})
	if err != nil {
		return err
	}
	s.app.Store(&app{homeserver: u.String(), handler: h})
	return nil
}

func (s *Shell) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	switch r.URL.Path {
	case SetupPath:
		s.serveSetup(w, r)
		return
	case openPath:
		s.serveOpen(w, r)
		return
	case notifyPath:
		s.serveNotify(w, r)
		return
	case titlePath:
		s.serveTitle(w, r)
		return
	case linkScriptPath:
		writeScript(w, linkScript)
		return
	case bridgeScriptPath:
		writeScript(w, bridgeScript)
		return
	}

	a := s.app.Load()
	if a == nil {
		// Before setup every page is the setup page; there is no
		// homeserver to configure the client with yet.
		if r.Method == http.MethodGet || r.Method == http.MethodHead {
			s.renderSetup(w, setupPage{})
			return
		}
		http.Error(w, "the homeserver isn't set up yet", http.StatusServiceUnavailable)
		return
	}
	a.handler.ServeHTTP(w, r)
}

func writeScript(w http.ResponseWriter, script string) {
	h := w.Header()
	h.Set("Content-Type", "text/javascript; charset=utf-8")
	h.Set("Cache-Control", "no-cache")
	h.Set("X-Content-Type-Options", "nosniff")
	_, _ = w.Write([]byte(script))
}

func (s *Shell) serveOpen(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		w.Header().Set("Allow", "POST")
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	var body struct {
		URL string `json:"url"`
	}
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 16<<10)).Decode(&body); err != nil {
		http.Error(w, "bad request", http.StatusBadRequest)
		return
	}
	u, err := url.Parse(body.URL)
	if err != nil || !externalScheme(u) {
		http.Error(w, "only http, https and mailto links are opened", http.StatusBadRequest)
		return
	}
	if s.opts.OpenURL == nil {
		http.Error(w, "can't open links", http.StatusNotImplemented)
		return
	}
	if err := s.opts.OpenURL(u.String()); err != nil {
		s.opts.Logger.Warn("can't open a link in the browser", "err", err)
		http.Error(w, "can't open the link", http.StatusInternalServerError)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

func externalScheme(u *url.URL) bool {
	switch u.Scheme {
	case "http", "https":
		return u.Host != ""
	case "mailto":
		return u.Opaque != ""
	}
	return false
}

func (s *Shell) serveSetup(w http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case http.MethodGet, http.MethodHead:
		cur := s.Homeserver()
		s.renderSetup(w, setupPage{Server: cur, Current: cur})
	case http.MethodPost:
		r.Body = http.MaxBytesReader(w, r.Body, 8<<10)
		if err := r.ParseForm(); err != nil {
			http.Error(w, "bad request", http.StatusBadRequest)
			return
		}
		input := r.PostForm.Get("server")
		ctx, cancel := context.WithTimeout(r.Context(), 20*time.Second)
		defer cancel()
		base, err := Discover(ctx, s.opts.HTTPClient, input)
		if err == nil {
			err = s.use(base)
		}
		if err != nil {
			s.renderSetup(w, setupPage{Server: input, Current: s.Homeserver(), Error: err.Error()})
			return
		}
		// The rest of the settings stay; a damaged file is replaced.
		st, _ := s.opts.Store.Load()
		st.Homeserver = base
		if err := s.opts.Store.Save(st); err != nil {
			// The choice still holds for this run.
			s.opts.Logger.Warn("can't save the settings", "err", err)
		}
		s.opts.Logger.Info("homeserver set", "homeserver", base)
		// A meta refresh rather than a redirect: not every webview
		// follows a redirect from the app's own scheme handler.
		writePage(w, doneTemplate, nil)
	default:
		w.Header().Set("Allow", "GET, HEAD, POST")
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
	}
}

type setupPage struct {
	Server  string // the input's value
	Current string // the homeserver in use, if any
	Error   string
}

func (s *Shell) renderSetup(w http.ResponseWriter, p setupPage) {
	writePage(w, setupTemplate, p)
}

func writePage(w http.ResponseWriter, t *template.Template, data any) {
	h := w.Header()
	h.Set("Content-Type", "text/html; charset=utf-8")
	h.Set("Cache-Control", "no-store")
	h.Set("X-Content-Type-Options", "nosniff")
	h.Set("Content-Security-Policy",
		"default-src 'none'; style-src 'unsafe-inline'; img-src data:; form-action 'self'; base-uri 'none'; frame-ancestors 'none'")
	var b strings.Builder
	if err := t.Execute(&b, data); err != nil {
		http.Error(w, "template: "+err.Error(), http.StatusInternalServerError)
		return
	}
	_, _ = w.Write([]byte(b.String()))
}

// The pages use the design tokens from @warp/ui (apps/ui/src/styles/tokens.css).
const pageStyle = `
:root{--surface:#fff;--sunken:#f3f5f4;--line:#e1e6e4;--line-strong:#7b8682;--ink:#111114;--muted:#5b6461;
--teal:#00806a;--on-teal:#fff;--danger:#b42318;--danger-soft:#fde8e6;--ring:0 0 0 2px #fff,0 0 0 4px #00806a;color-scheme:light}
@media (prefers-color-scheme:dark){:root{--surface:#0f1213;--sunken:#161a1c;--line:#2a3134;--line-strong:#6e7976;
--ink:#eceeee;--muted:#9aa5a1;--teal:#22c3a6;--on-teal:#062a23;--danger:#f97066;--danger-soft:#3a1512;
--ring:0 0 0 2px #0f1213,0 0 0 4px #3ed6b8;color-scheme:dark}}
*{box-sizing:border-box}
body{margin:0;min-height:100vh;display:grid;place-items:center;background:var(--sunken);color:var(--ink);
font:14px/20px Figtree,system-ui,-apple-system,"Segoe UI",sans-serif;padding:16px}
main{width:100%;max-width:420px;background:var(--surface);border:1px solid var(--line);border-radius:18px;padding:32px}
h1{font:600 22px/28px Outfit,Figtree,system-ui,sans-serif;margin:0 0 8px}
p{margin:0 0 16px;color:var(--muted)}
label{display:block;font-weight:600;margin:0 0 6px}
input{width:100%;height:40px;padding:0 12px;border:1px solid var(--line-strong);border-radius:8px;
background:var(--surface);color:var(--ink);font:inherit}
input:focus{outline:none;box-shadow:var(--ring)}
.hint{font-size:13px;margin:6px 0 0}
.error{background:var(--danger-soft);color:var(--danger);border-radius:8px;padding:8px 12px;margin:0 0 16px}
.actions{display:flex;gap:8px;justify-content:flex-end;margin-top:24px}
button,a.button{height:40px;padding:0 16px;border-radius:9999px;border:1px solid transparent;font-family:inherit;font-size:14px;font-weight:600;line-height:38px;
cursor:pointer;text-decoration:none;display:inline-block}
button{background:var(--teal);color:var(--on-teal)}
a.button{color:var(--ink);border-color:var(--line)}
button:focus-visible,a.button:focus-visible{outline:none;box-shadow:var(--ring)}
code{font:13px/20px "JetBrains Mono",ui-monospace,monospace}
`

var setupTemplate = template.Must(template.New("setup").Parse(`<!doctype html>
<html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1">
<title>Choose a homeserver · Warp</title><style>` + pageStyle + `</style></head>
<body><main>
<h1>{{if .Current}}Change homeserver{{else}}Welcome to Warp{{end}}</h1>
<p>{{if .Current}}New sign-ins will go to this server. If you’re signed in, you stay signed in to <code>{{.Current}}</code> until you sign out.{{else}}Which Matrix homeserver is your account on?{{end}}</p>
{{if .Error}}<div class="error" role="alert">{{.Error}}</div>{{end}}
<form method="post" action="/_desktop/setup">
<label for="server">Homeserver</label>
<input id="server" name="server" value="{{.Server}}" placeholder="example.org" autocomplete="url" autocapitalize="off" spellcheck="false" required autofocus>
<p class="hint">A server name like <code>example.org</code>, or an address like <code>https://matrix.example.org</code>.</p>
<div class="actions">{{if .Current}}<a class="button" href="/">Cancel</a>{{end}}<button type="submit">Continue</button></div>
</form>
</main></body></html>
`))

var doneTemplate = template.Must(template.New("done").Parse(`<!doctype html>
<html lang="en"><head><meta charset="utf-8"><meta http-equiv="refresh" content="0; url=/">
<title>Warp</title><style>` + pageStyle + `</style></head><body></body></html>
`))