package api

import (
	"net/http"
	"os"
	"path/filepath"
	"strings"

	"github.com/gin-gonic/gin"
)

// configureWebUI adds an optional SPA fallback to the existing GoAdmin Gin
// engine. API and framework routes keep their normal handlers; the fallback is
// enabled only for Windows delivery packages that set SENSE_WEB_ROOT.
func configureWebUI(r *gin.Engine) {
	root := strings.TrimSpace(os.Getenv("SENSE_WEB_ROOT"))
	if root == "" {
		return
	}
	absRoot, err := filepath.Abs(root)
	if err != nil {
		return
	}
	index := filepath.Join(absRoot, "index.html")
	if info, statErr := os.Stat(index); statErr != nil || info.IsDir() {
		return
	}

	r.NoRoute(func(c *gin.Context) {
		if c.Request.Method != http.MethodGet && c.Request.Method != http.MethodHead {
			c.Status(http.StatusNotFound)
			return
		}
		if isBackendPath(c.Request.URL.Path) {
			c.Status(http.StatusNotFound)
			return
		}

		requested := filepath.Clean(filepath.FromSlash(strings.TrimPrefix(c.Request.URL.Path, "/")))
		if requested == "." {
			requested = ""
		}
		candidate := filepath.Join(absRoot, requested)
		if withinRoot(absRoot, candidate) {
			if info, statErr := os.Stat(candidate); statErr == nil && !info.IsDir() {
				c.File(candidate)
				return
			}
		}
		if filepath.Ext(requested) != "" {
			c.Status(http.StatusNotFound)
			return
		}
		c.File(index)
	})
}

func withinRoot(root, candidate string) bool {
	rel, err := filepath.Rel(root, candidate)
	return err == nil && rel != ".." && !strings.HasPrefix(rel, ".."+string(filepath.Separator))
}

func isBackendPath(path string) bool {
	for _, prefix := range []string{"/api/", "/swagger/", "/static/", "/form-generator/"} {
		if strings.HasPrefix(path, prefix) {
			return true
		}
	}
	return false
}