package router

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

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

// SPADirEnv overrides where the built frontend lives. Without it the server
// looks for ./dist next to the working directory.
const SPADirEnv = "GOAUTO_WEB_DIST"

// InitSPARouter serves the built Vue app from the same origin as the API.
//
// Same-origin is what web/.env.production already assumes: VUE_APP_BASE_API is
// empty there, so the bundle issues relative requests. Serving dist from this
// binary makes that assumption true without a second web server and without
// CORS.
//
// `[必须]` Registering this is conditional on dist actually existing. In
// development the frontend runs under vite on its own port and there is no
// dist; a NoRoute handler installed anyway would turn every genuine 404 into
// an HTML page, which is far more confusing than a plain 404.
func InitSPARouter(engine *gin.Engine) {
	dist := strings.TrimSpace(os.Getenv(SPADirEnv))
	if dist == "" {
		dist = "dist"
	}
	index := filepath.Join(dist, "index.html")
	if _, err := os.Stat(index); err != nil {
		return
	}

	engine.Static("/assets", filepath.Join(dist, "assets"))
	for _, name := range []string{"favicon.ico", "logo.png"} {
		if path := filepath.Join(dist, name); fileExists(path) {
			engine.StaticFile("/"+name, path)
		}
	}

	// History-mode routing means any unmatched non-API GET is a client route
	// and must return index.html so the app can boot and route it itself.
	//
	// `[必须]` API paths are excluded. Answering a mistyped API call with 200
	// and an HTML body would surface in the client as a JSON parse error
	// instead of the 404 it actually is.
	engine.NoRoute(func(c *gin.Context) {
		if c.Request.Method != http.MethodGet || isAPIPath(c.Request.URL.Path) {
			c.Status(http.StatusNotFound)
			return
		}
		c.File(index)
	})
}

// isAPIPath reports whether a path belongs to the server rather than the SPA.
func isAPIPath(path string) bool {
	for _, prefix := range []string{"/api/", "/swagger/", "/static/", "/form-generator/", "/ws/", "/wslogout/", "/info"} {
		if strings.HasPrefix(path, prefix) {
			return true
		}
	}
	return false
}

func fileExists(path string) bool {
	info, err := os.Stat(path)
	return err == nil && !info.IsDir()
}