package api

import (
	"io/fs"
	"net/http"
	"path"
	"strings"

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

// RegisterSPA serves the embedded single-page app for every route gin didn't
// otherwise match. A request whose path maps to a real file (e.g. a hashed asset
// bundle) is served directly; any other non-API path falls back to index.html so
// client-side deep links like /gardens/42 load the app. Unmatched /api paths
// return a JSON 404 rather than HTML.
func RegisterSPA(r *gin.Engine, dist fs.FS) {
	fileServer := http.FileServer(http.FS(dist))

	r.NoRoute(func(c *gin.Context) {
		reqPath := c.Request.URL.Path

		if strings.HasPrefix(reqPath, "/api/") {
			c.JSON(http.StatusNotFound, gin.H{"error": gin.H{
				"code": "NOT_FOUND", "message": "no such endpoint",
			}})
			return
		}

		if c.Request.Method != http.MethodGet && c.Request.Method != http.MethodHead {
			c.JSON(http.StatusMethodNotAllowed, gin.H{"error": gin.H{
				"code": "METHOD_NOT_ALLOWED", "message": "method not allowed",
			}})
			return
		}

		name := strings.TrimPrefix(path.Clean(reqPath), "/")
		if name == "" {
			name = "index.html"
		}

		if f, err := dist.Open(name); err == nil {
			f.Close()
			// Vite emits content-hashed filenames under assets/, so those are safe
			// to cache forever; index.html must always revalidate to pick up new builds.
			if strings.HasPrefix(name, "assets/") {
				c.Header("Cache-Control", "public, max-age=31536000, immutable")
			} else {
				c.Header("Cache-Control", "no-cache")
			}
			fileServer.ServeHTTP(c.Writer, c.Request)
			return
		}

		// A missing file under assets/ is a genuine 404, not a client route:
		// falling back to index.html would return HTML with a 200 for a .js/.css
		// request, which the browser rejects with a confusing MIME-type error.
		if strings.HasPrefix(name, "assets/") {
			c.JSON(http.StatusNotFound, gin.H{"error": gin.H{
				"code": "NOT_FOUND", "message": "asset not found",
			}})
			return
		}

		serveIndex(c, dist)
	})
}

// serveIndex writes index.html as the SPA fallback for an unmatched client route.
func serveIndex(c *gin.Context, dist fs.FS) {
	data, err := fs.ReadFile(dist, "index.html")
	if err != nil {
		c.String(http.StatusInternalServerError, "index.html missing from build")
		return
	}
	c.Header("Cache-Control", "no-cache")
	c.Data(http.StatusOK, "text/html; charset=utf-8", data)
}