package server

import (
	"html/template"
	"testing"
	"testing/fstest"
)

// TestComposeUITemplates covers the UIMount seam added for task 1.6
// (design.md Decision 8): an integration's Templates FS is parsed into the
// shared template set only when every "*.html" file it contributes carries
// the integration's slug prefix; a violation panics at startup rather than
// silently registering an unnamespaced template.
func TestComposeUITemplates(t *testing.T) {
	newBase := func() *template.Template {
		return template.Must(template.New("root").Parse(`{{define "root.html"}}root{{end}}`))
	}

	t.Run("no mounts is a no-op", func(t *testing.T) {
		base := newBase()
		got := composeUITemplates(base, nil)
		if got.Lookup("root.html") == nil {
			t.Fatalf("expected core template to survive an empty mount list")
		}
	})

	t.Run("mount with nil Templates is skipped", func(t *testing.T) {
		base := newBase()
		got := composeUITemplates(base, []UIMount{{Slug: "example", Templates: nil}})
		if got.Lookup("root.html") == nil {
			t.Fatalf("expected core template to survive a mount with nil Templates")
		}
	})

	t.Run("correctly slug-prefixed template is parsed in", func(t *testing.T) {
		base := newBase()
		mount := UIMount{
			Slug: "example",
			Templates: fstest.MapFS{
				"example_widget.html": &fstest.MapFile{Data: []byte("example widget")},
			},
		}
		got := composeUITemplates(base, []UIMount{mount})
		if got.Lookup("example_widget.html") == nil {
			t.Fatalf("expected example_widget.html to be registered")
		}
		if got.Lookup("root.html") == nil {
			t.Fatalf("expected core template to still be present after composing in a mount")
		}
	})

	t.Run("template name without slug prefix panics", func(t *testing.T) {
		base := newBase()
		mount := UIMount{
			Slug: "example",
			Templates: fstest.MapFS{
				"widget.html": &fstest.MapFile{Data: []byte("unnamespaced widget")},
			},
		}
		defer func() {
			if r := recover(); r == nil {
				t.Fatalf("expected composeUITemplates to panic on an unnamespaced template name")
			}
		}()
		composeUITemplates(base, []UIMount{mount})
	})
}