summercms/modules/signpost/README.md

signpost

Menu item type registry that collects the typed menu item types plugins register at boot, layers their URL patterns with host overrides and resolves menu and sitemap items through the owning plugin.

import "git.golem15.com/golem15/summercms/modules/signpost"

Name: A beach signpost points the way to places; the registry tells menus and sitemaps where each item leads.

Overview

signpost is the typed successor of WinterCMS's pages.menuitem.listTypes, pages.menuitem.getTypeInfo and pages.menuitem.resolveItem events. A content plugin implements pact.HasMenuItemTypes and returns pact.MenuItemType values: each carries its key, label, default URL pattern, the records an item can point at (References) and a Resolve function. party calls signpost.Activate once at boot, after every Register and before the first Boot, and the registry is published on the application. Menu and sitemap plugins read it with app.Lookup[*signpost.Registry](), offer its types in their admin forms and resolve their items through it. No string event carries the list, the type info or the resolve call.

Role in the framework

A small registry between content plugins (which own records and their URLs) and consumer plugins (menus, sitemaps). It depends on backpack and pact only, so the framework never imports a plugin. Its one admin binding is signpost.ReferenceOptions, which a controller's pact.DependentOptionsProvider returns for a reference dropdown that depends on a type dropdown (see Forms).

Use cases:

• Let a blog plugin offer "post", "category" and "all posts" as menu item types without the menu plugin importing it.
• Build headless URLs from patterns such as /blog/:slug, and let the host application change them per type.
• Fill the reference dropdown of a menu entry or a sitemap row with the records of the chosen type.

Features

• Boot-time collection in plugin order, then declaration order. Every error is prefixed signpost: and fails the boot: an empty key, a key two plugins register (the message names the key and both plugin IDs), a nil Resolve, a DefaultPattern that is empty or does not start with /, a PatternFrom that names an unknown type, the type itself or a type that sets PatternFrom too, and a host override for an unknown type or one that does not start with /.
• URL patterns in layers (signpost.Registry.Pattern): the item's own override, else the host override of the type, else, for a list type that sets PatternFrom, the host override of the record type it lists, else the type's DefaultPattern. A host that changes the post URL once therefore also changes the children of every list of posts, unless the list type itself is overridden. An item override is taken only when it is a path (signpost.ValidItemPattern): it starts with a single / and has no surrounding whitespace or control characters. Any other override, such as a javascript: URL or a protocol-relative //host, is ignored and the next layer applies.
• signpost.Registry.Resolve hands the layered pattern to the type's Resolve in pact.MenuItemResolve.Pattern. The result, pact.ResolvedMenuItem, carries the title, URL, modification time, nested items, and the alternates per locale as an ordered []pact.MenuItemAlternate, never a map.
• Content descriptors: a record type that sets pact.MenuItemType.Content describes its records to consumers that work on every content type at once. signpost.Registry.ContentTypes lists those types, signpost.Registry.ContentTypeForModel maps the morph type a record event carries (pact.RecordSaved.Model) to its type, and signpost.Registry.Describe describes one record with the layered pattern. A descriptor without Model or Describe fails the boot.
• signpost.ReferenceOptions flattens a type's reference tree depth first into dropdown options with a Depth, and answers Applies false for a type that takes no reference or that no plugin registers.

Usage

A content plugin registers its types:

package blog

import (
	"context"
	"strings"

	"git.golem15.com/golem15/summercms/modules/pact"
)

var _ pact.HasMenuItemTypes = (*Plugin)(nil)

type Plugin struct{}

func (p *Plugin) MenuItemTypes() []pact.MenuItemType {
	return []pact.MenuItemType{{
		Key:            "acme-post",
		Label:          "acme.blog::lang.menuitem.post",
		DefaultPattern: "/blog/:slug",
		Placeholders:   []string{":slug"},
		References: func(ctx context.Context) ([]pact.MenuItemReference, error) {
			return []pact.MenuItemReference{{Value: "hello-world", Label: "Hello world"}}, nil
		},
		Resolve: func(ctx context.Context, in pact.MenuItemResolve) (*pact.ResolvedMenuItem, error) {
			url := strings.ReplaceAll(in.Pattern, ":slug", in.Reference)
			return &pact.ResolvedMenuItem{
				Title:      "Hello world",
				URL:        url,
				Alternates: []pact.MenuItemAlternate{{Locale: "en", URL: url, Title: "Hello world"}},
			}, nil
		},
	}, {
		Key:            "acme-all-posts",
		Label:          "acme.blog::lang.menuitem.all_posts",
		DefaultPattern: "/blog/:slug",
		PatternFrom:    "acme-post",
		Nesting:        true,
		Resolve:        resolveAllPosts,
	}}
}

A menu plugin resolves an entry and serves the reference dropdown of its form:

reg, _ := app.Lookup[*signpost.Registry]()
item, err := reg.Resolve(ctx, entry.Type, entry.Reference, entry.URLPattern, true, "")

func (c entriesController) DependentOptions(ctx context.Context, field string, values map[string]any) (pact.DependentOptionSet, error) {
	typ, _ := values["type"].(string)
	return signpost.ReferenceOptions(ctx, c.registry(), typ)
}

Content descriptors

A record type adds a pact.ContentDescriptor: the admin controller that edits the records, their morph type, and a Describe that answers each locale's URL (built from the pattern it receives, as Resolve builds alternates), title, description, image and word count:

{
	Key:            "acme-post",
	DefaultPattern: "/blog/:slug",
	Resolve:        resolvePost,
	Content: &pact.ContentDescriptor{
		Controller: "acme.blog.posts",
		Model:      "acme_blog_posts",
		Describe: func(ctx context.Context, in pact.ContentDescribe) (*pact.ContentRecord, error) {
			post, err := loadPost(ctx, in.ID)
			if err != nil || post == nil {
				return nil, err
			}
			return &pact.ContentRecord{
				ID:        in.ID,
				Published: post.Published,
				Locales: []pact.ContentLocale{{
					Locale: "en",
					URL:    strings.ReplaceAll(in.Pattern, ":slug", post.Slug),
					Title:  post.Title,
				}},
			}, nil
		},
	},
}

A consumer maps a record event to its type and reads the record's new URL:

app.Events.Listen("acme.audit", func(ctx context.Context, ev *pact.RecordSaved) error {
	reg, _ := app.Lookup[*signpost.Registry]()
	typ, ok := reg.ContentTypeForModel(ev.Model)
	if !ok {
		return nil
	}
	rec, err := reg.Describe(ctx, typ.Key, ev.ID, "")
	if err != nil || rec == nil {
		return err
	}
	log.Printf("%s now lives at %s", ev.ID, rec.Locales[0].URL)
	return nil
})

API reference

Identifier	Description
signpost.Activate	Collects the pact.HasMenuItemTypes types of the activated plugins, reads the host overrides and publishes one *signpost.Registry; party calls it after Register and before Boot.
signpost.Registry	The read-only registry of menu item types and host pattern overrides.
signpost.Registry.Types	Every registered type, in plugin order and then declaration order.
signpost.Registry.Type	The type registered under a key.
signpost.Registry.Pattern	The layered URL pattern of an item: item override, host override, the record type's host override for a list type, default.
signpost.ValidItemPattern	Whether a pattern may serve as an item override: a path starting with a single /, without surrounding whitespace or control characters. Plugins use it to refuse such a pattern on save.
signpost.Registry.Resolve	Resolves one item through its type with the layered pattern; an unknown type is an error.
signpost.Registry.ContentTypes	The types that carry a content descriptor, in registration order.
signpost.Registry.ContentTypeForModel	The content type whose descriptor declares a morph type, as record events carry it.
signpost.Registry.Describe	Describes one record of a content type through its descriptor with the layered pattern; an unknown type or one without a descriptor is an error, an unknown record answers nil.
signpost.ReferenceOptions	The dependent dropdown options of a type's references, flattened with their depth; Applies false for a type without references.
signpost.ConfigKey	menu_items.patterns, the host configuration key of the pattern overrides.

Configuration

The host application overrides a type's URL pattern in config/menu_items.yaml:

patterns:
    acme-post: /news/:slug
    acme-category: /:slug

menu_items.patterns is a map from type key to pattern, read once at boot. Type keys contain dashes, so the map can only be set in a YAML file: there is no SUMMER_ environment override for it. An override for a type no plugin registers, or one that does not start with /, fails the boot.

Dependencies

• SummerCMS modules: backpack, pact.
• Third-party: none.
• Standard library: context, fmt, strings.

Testing

go test ./modules/signpost/...

The tests use an in-memory configuration and need no external services.