// Package adminui serves TreatVault's write-only Barkstack plugin and API.
package adminui

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

	barkfile "cloud.campbellwireless.net/git/barkstack/barkfile-parser/v2"
	"cloud.campbellwireless.net/git/barkstack/treatvault/internal/manager"
	"cloud.campbellwireless.net/git/barkstack/treatvault/internal/vault"
)

//go:embed dist
var embeddedUI embed.FS

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

type SecretManager interface {
	Status() manager.Status
	Set(context.Context, string, []byte) error
	Delete(context.Context, string) error
}

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 handler struct {
	assets  fs.FS
	manager SecretManager
}

func Handler(secretManager SecretManager) http.Handler {
	assets, err := fs.Sub(embeddedUI, "dist")
	if err != nil {
		panic(err)
	}
	return &handler{assets: assets, manager: secretManager}
}

func (h *handler) ServeHTTP(response http.ResponseWriter, request *http.Request) {
	switch {
	case request.URL.Path == "/barkstack/ui/manifest.json":
		h.serveManifest(response, request)
	case request.URL.Path == "/barkstack/api/secrets":
		h.serveSecretList(response, request)
	case strings.HasPrefix(request.URL.Path, "/barkstack/api/secrets/"):
		h.serveSecret(response, request)
	case request.URL.Path == "/healthz":
		h.serveHealth(response, request)
	default:
		h.serveAsset(response, request)
	}
}

func (h *handler) serveManifest(response http.ResponseWriter, request *http.Request) {
	if !allow(response, request, http.MethodGet, http.MethodHead) {
		return
	}
	h.serveJSON(response, request, http.StatusOK, manifest{
		APIVersion: "barkstack.dev/ui/v1", ID: "treatvault", Name: "TreatVault",
		Description: "Encrypted secret management for Barkstack", Icon: "key", Mount: "/treatvault",
		Entry: entryPath, Element: "barkstack-treatvault",
		Navigation: []navigationItem{{Label: "TreatVault", Path: "/treatvault", Icon: "key"}},
	})
}

func (h *handler) serveSecretList(response http.ResponseWriter, request *http.Request) {
	if !allow(response, request, http.MethodGet, http.MethodHead) {
		return
	}
	h.serveJSON(response, request, http.StatusOK, h.manager.Status())
}

func (h *handler) serveSecret(response http.ResponseWriter, request *http.Request) {
	name := strings.TrimPrefix(request.URL.Path, "/barkstack/api/secrets/")
	if !barkfile.ValidSecretReference(name) || strings.Contains(name, "/") {
		h.serveError(response, http.StatusBadRequest, "invalid secret name")
		return
	}
	switch request.Method {
	case http.MethodPut:
		var body struct {
			Value string `json:"value"`
		}
		decoder := json.NewDecoder(io.LimitReader(request.Body, 512*1024+1))
		decoder.DisallowUnknownFields()
		if err := decoder.Decode(&body); err != nil {
			h.serveError(response, http.StatusBadRequest, "invalid JSON request")
			return
		}
		if body.Value == "" {
			h.serveError(response, http.StatusBadRequest, "secret value must not be empty")
			return
		}
		if err := h.manager.Set(request.Context(), name, []byte(body.Value)); err != nil {
			h.serveError(response, http.StatusBadGateway, err.Error())
			return
		}
		response.WriteHeader(http.StatusNoContent)
	case http.MethodDelete:
		if err := h.manager.Delete(request.Context(), name); err != nil {
			switch {
			case errors.Is(err, vault.ErrSecretNotFound):
				h.serveError(response, http.StatusNotFound, "secret not found")
			case manager.IsSecretInUse(err):
				h.serveError(response, http.StatusConflict, "secret is still referenced by a managed service")
			default:
				h.serveError(response, http.StatusBadGateway, err.Error())
			}
			return
		}
		response.WriteHeader(http.StatusNoContent)
	default:
		response.Header().Set("Allow", "PUT, DELETE")
		h.serveError(response, http.StatusMethodNotAllowed, "method not allowed")
	}
}

func (h *handler) serveHealth(response http.ResponseWriter, request *http.Request) {
	if !allow(response, request, http.MethodGet, http.MethodHead) {
		return
	}
	status := h.manager.Status()
	code := http.StatusOK
	if status.State != "ready" {
		code = http.StatusServiceUnavailable
	}
	h.serveJSON(response, request, code, map[string]string{"status": status.State})
}

func (h *handler) serveAsset(response http.ResponseWriter, request *http.Request) {
	if !allow(response, request, http.MethodGet, http.MethodHead) {
		return
	}
	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 {
		_, _ = response.Write(contents)
	}
}

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

func (h *handler) serveError(response http.ResponseWriter, code int, message string) {
	response.Header().Set("Content-Type", "application/json")
	response.Header().Set("Cache-Control", "no-store")
	response.WriteHeader(code)
	_ = json.NewEncoder(response).Encode(map[string]string{"error": message})
}

func allow(response http.ResponseWriter, request *http.Request, methods ...string) bool {
	for _, method := range methods {
		if request.Method == method {
			return true
		}
	}
	response.Header().Set("Allow", strings.Join(methods, ", "))
	http.Error(response, "method not allowed", http.StatusMethodNotAllowed)
	return false
}