// Package adminui serves PawSQL's Barkstack UI plugin and small read-only status API.
package adminui

import (
	"embed"
	"encoding/json"
	"io/fs"
	"mime"
	"net/http"
	"path"
	"strings"
)

//go:embed dist
var embeddedUI embed.FS

const entryPath = "/barkstack/ui/assets/entry.js"

type manifest struct {
	APIVersion  string           `json:"apiVersion"`
	ID          string           `json:"id"`
	Name        string           `json:"name"`
	Description string           `json:"description"`
	Icon        string           `json:"icon"`
	Mount       string           `json:"mount"`
	Entry       string           `json:"entry"`
	Element     string           `json:"element"`
	Navigation  []navigationItem `json:"navigation"`
}

type navigationItem struct {
	Label string `json:"label"`
	Path  string `json:"path"`
	Icon  string `json:"icon"`
}

type RouteSummary struct {
	Name     string `json:"name"`
	Hostname string `json:"hostname,omitempty"`
	Managed  bool   `json:"managed"`
}

type statusResponse struct {
	Status   string         `json:"status"`
	Routes   []RouteSummary `json:"routes"`
	Endpoint string         `json:"endpoint"`
}

type handler struct {
	assets fs.FS
	routes []RouteSummary
}

func Handler(routes []RouteSummary) http.Handler {
	assets, err := fs.Sub(embeddedUI, "dist")
	if err != nil {
		panic(err)
	}
	copyRoutes := append([]RouteSummary(nil), routes...)
	return &handler{assets: assets, routes: copyRoutes}
}

func (h *handler) ServeHTTP(response http.ResponseWriter, request *http.Request) {
	if request.Method != http.MethodGet && request.Method != http.MethodHead {
		response.Header().Set("Allow", "GET, HEAD")
		http.Error(response, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	switch request.URL.Path {
	case "/barkstack/ui/manifest.json":
		h.serveJSON(response, request, manifest{
			APIVersion: "barkstack.dev/ui/v1", ID: "pawsql", Name: "PawSQL",
			Description: "PostgreSQL routing for Barkstack", Icon: "database", Mount: "/pawsql",
			Entry: entryPath, Element: "barkstack-pawsql",
			Navigation: []navigationItem{{Label: "PawSQL", Path: "/pawsql", Icon: "database"}},
		})
	case "/barkstack/ui/status.json":
		h.serveJSON(response, request, statusResponse{Status: "running", Routes: h.routes, Endpoint: "*.pawsql.barkstack.dev:5432"})
	default:
		h.serveAsset(response, request)
	}
}

func (h *handler) serveJSON(response http.ResponseWriter, request *http.Request, value any) {
	response.Header().Set("Content-Type", "application/json")
	response.Header().Set("Cache-Control", "no-store")
	if request.Method == http.MethodHead {
		return
	}
	_ = json.NewEncoder(response).Encode(value)
}

func (h *handler) serveAsset(response http.ResponseWriter, request *http.Request) {
	const prefix = "/barkstack/ui/assets/"
	if !strings.HasPrefix(request.URL.Path, prefix) {
		http.NotFound(response, request)
		return
	}
	assetName := strings.TrimPrefix(request.URL.Path, "/barkstack/ui/")
	if assetName == "" || !fs.ValidPath(assetName) || path.Clean(assetName) != assetName || strings.Contains(assetName, "\\") {
		http.NotFound(response, request)
		return
	}
	contents, err := fs.ReadFile(h.assets, assetName)
	if err != nil {
		http.NotFound(response, request)
		return
	}
	if contentType := mime.TypeByExtension(path.Ext(assetName)); contentType != "" {
		response.Header().Set("Content-Type", contentType)
	}
	response.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
	response.Header().Set("X-Content-Type-Options", "nosniff")
	if request.Method == http.MethodHead {
		return
	}
	_, _ = response.Write(contents)
}