khosra/internal/ext/shortcodes/shortcodes.go

package shortcodes

import (
	"bytes"
	"fmt"
	"io/fs"
	"log/slog"
	"path"
	"slices"
	"sort"
	"strings"

	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/ast"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/renderer"
	"github.com/yuin/goldmark/text"
	"github.com/yuin/goldmark/util"

	"khosra/internal/render"
)

// open and close delimit a call. Chosen to be something no Markdown construct claims and no author types
// by accident; the syntax is a disk contract, so it does not change (ADR-0036).
const (
	opener = "{{<"
	closer = ">}}"
)

// New returns the Markdown extension, rendering each call through partial.
//
// The feature never writes markup: it hands the call's name and arguments to a theme template of the same
// name and writes whatever comes back (ADR-0036).
func New(partial render.Partial) goldmark.Extender {
	return extension{partial: partial}
}

type extension struct {
	partial render.Partial
}

// Extend registers the block parser, the include expander, and the node renderer. Priorities sit above
// goldmark's paragraph parser so a line that is only a call never becomes a paragraph.
//
// The expander is handed md itself, because an included file is converted by the same configuration as the
// page including it — not by a second pipeline that could drift from this one (ADR-0038).
func (e extension) Extend(md goldmark.Markdown) {
	md.Parser().AddOptions(
		parser.WithBlockParsers(util.Prioritized(blocks{}, 100)),
		parser.WithASTTransformers(util.Prioritized(includes{md: md}, 100)),
	)
	md.Renderer().AddOptions(renderer.WithNodeRenderers(
		util.Prioritized(fragments{partial: e.partial}, 100)))
}

// nested marks a parse that is already inside an included file, so one level is all there is (ADR-0038).
var nested = parser.NewContextKey()

// includes fills in each include call with the converted content of the file it names.
//
// A transformer, running after the parse, rather than a node renderer: converting needs the parse context to
// know which bundle this is, and a node renderer never receives one. The included file is converted on its
// own bytes and its output stored on the node — never by splicing its nodes into this tree, which cannot
// work, since a goldmark node holds offsets into the source it came from (ADR-0038).
type includes struct {
	md goldmark.Markdown
}

func (in includes) Transform(doc *ast.Document, reader text.Reader, pc parser.Context) {
	insideInclude := pc.Get(nested) != nil
	for _, call := range pending(doc) {
		if insideInclude {
			slog.Error("ignoring an include inside an included file", "file", call.args["file"])
			continue
		}
		content, err := in.convert(call.args["file"], pc)
		if err != nil {
			slog.Error("skipping include", "file", call.args["file"], "err", err)
			continue
		}
		call.content = content
	}
}

// convert reads one included file and renders it, relative to the bundle being rendered.
//
// The nested parse carries the same Origin, so a gallery inside an included file still resolves against the
// bundle, and it is marked nested, so an include there renders nothing.
func (in includes) convert(name string, pc parser.Context) ([]byte, error) {
	if name == "" {
		return nil, fmt.Errorf("include needs a file argument")
	}
	// A name is relative to the bundle and stays inside it. os.Root already refuses a path leaving the site
	// root, but path.Join collapses ".." long before it gets there, so without this an include could read
	// anything else in the site root — a template, a stray dotfile — and publish it. Sharing one fragment
	// between bundles is a fair wish and not this: it needs somewhere to put shared parts, chosen on purpose.
	if strings.Contains(name, "..") {
		return nil, fmt.Errorf("include stays inside its bundle: %s", name)
	}
	origin, ok := render.OriginFrom(pc)
	if !ok || origin.Files == nil {
		return nil, fmt.Errorf("no site root to include from")
	}
	data, err := fs.ReadFile(origin.Files, path.Join(origin.Dir, name))
	if err != nil {
		return nil, err
	}
	inner := parser.NewContext()
	render.WithOrigin(inner, origin)
	inner.Set(nested, true)
	var out bytes.Buffer
	if err := in.md.Convert(data, &out, parser.WithContext(inner)); err != nil {
		return nil, err
	}
	return out.Bytes(), nil
}

// pending lists the include calls in a tree.
func pending(doc *ast.Document) []*node {
	var found []*node
	err := ast.Walk(doc, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
		if !entering {
			return ast.WalkContinue, nil
		}
		if call, is := n.(*node); is && call.name == "include" {
			found = append(found, call)
		}
		return ast.WalkContinue, nil
	})
	if err != nil {
		slog.Error("walking for includes", "err", err)
	}
	return found
}

// kind identifies a parsed call in the tree.
var kind = ast.NewNodeKind("Shortcode")

// node is one call: everything the renderer needs, and nothing from the source bytes.
type node struct {
	ast.BaseBlock
	name string
	args map[string]string
	// items are what the feature gathered at parse time, when it still knew which bundle this is.
	items []string
	// content is output the feature produced itself, written instead of a theme fragment. An included file
	// is content, not decoration, so it has no template (ADR-0038).
	content []byte
	// isContent marks a call whose output is content, so a failure renders nothing rather than falling
	// through to a fragment lookup and reporting a missing template that was never expected to exist.
	isContent bool
}

func (n *node) Kind() ast.NodeKind { return kind }

func (n *node) Dump(source []byte, level int) { ast.DumpHelper(n, source, level, nil, nil) }

// blocks parses a line that is nothing but a call.
type blocks struct{}

func (blocks) Trigger() []byte { return []byte{'{'} }

func (blocks) Open(parent ast.Node, reader text.Reader, pc parser.Context) (ast.Node, parser.State) {
	line, seg := reader.PeekLine()
	name, args, ok := parse(string(line))
	if !ok {
		return nil, parser.NoChildren
	}
	reader.Advance(seg.Len() - 1)
	n := &node{name: name, args: args}
	switch name {
	case "gallery":
		// Reading the filesystem happens here, where the parse context says which bundle this is; the
		// renderer never gets one, so anything gathered has to be gathered now.
		n.items = images(pc)
	case "include":
		// Filled in by the transformer, which runs once this parse is complete.
		n.isContent = true
	}
	return n, parser.NoChildren
}

// pictures are the extensions a gallery treats as an image. A file the browser cannot show is not a
// gallery entry, and guessing by content would mean reading every file in the directory.
var pictures = []string{".avif", ".gif", ".jpeg", ".jpg", ".png", ".svg", ".webp"}

// images lists the pictures sitting beside the bundle being rendered, sorted by filename.
//
// Sorted because the sparse numeric-prefix convention orders entries without putting numbers in URLs
// (ADR-0016), and because a directory read has no order worth relying on. A renderer without a site root
// gathers nothing rather than guessing.
func images(pc parser.Context) []string {
	origin, ok := render.OriginFrom(pc)
	if !ok || origin.Files == nil {
		return nil
	}
	entries, err := fs.ReadDir(origin.Files, origin.Dir)
	if err != nil {
		slog.Error("gallery cannot read its bundle directory", "dir", origin.Dir, "err", err)
		return nil
	}
	var found []string
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		if slices.Contains(pictures, strings.ToLower(path.Ext(e.Name()))) {
			found = append(found, e.Name())
		}
	}
	sort.Strings(found)
	return found
}

// Continue never runs: a call is one line, closed as soon as it opens.
func (blocks) Continue(n ast.Node, reader text.Reader, pc parser.Context) parser.State {
	return parser.Close
}

func (blocks) Close(n ast.Node, reader text.Reader, pc parser.Context) {}

func (blocks) CanInterruptParagraph() bool { return true }

func (blocks) CanAcceptIndentedLine() bool { return false }

// fragments renders a parsed call through the theme.
type fragments struct {
	partial render.Partial
}

func (f fragments) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
	reg.Register(kind, f.render)
}

// render writes the theme's fragment for this call.
//
// A missing or broken template logs and renders nothing: a shortcode is content decoration, and one typo
// in a bundle must not take a page down (extensions.md rule 5, ADR-0029).
func (f fragments) render(w util.BufWriter, source []byte, n ast.Node, entering bool) (ast.WalkStatus, error) {
	if !entering {
		return ast.WalkContinue, nil
	}
	call := n.(*node)
	if call.isContent {
		if _, err := w.Write(call.content); err != nil {
			return ast.WalkStop, err
		}
		return ast.WalkContinue, nil
	}
	out, err := f.partial(call.name, render.Fragment{Args: call.args, Items: call.items})
	if err != nil {
		slog.Error("skipping shortcode", "name", call.name, "err", err)
		return ast.WalkContinue, nil
	}
	if _, err := w.Write(out); err != nil {
		return ast.WalkStop, err
	}
	return ast.WalkContinue, nil
}

// parse reads one line as a call, reporting false for anything else.
//
// The whole line must be the call, and every argument is key="value" — one spelling, so there is nothing
// to guess and no half-parsed state. Values are returned raw; escaping is the template's job, which is
// what keeps an author's text out of the markup (ADR-0036).
func parse(line string) (name string, args map[string]string, ok bool) {
	body, found := strings.CutPrefix(strings.TrimSpace(line), opener)
	if !found {
		return "", nil, false
	}
	body, found = strings.CutSuffix(strings.TrimSpace(body), closer)
	if !found {
		return "", nil, false
	}
	body = strings.TrimSpace(body)
	name, rest, _ := strings.Cut(body, " ")
	if name == "" || strings.ContainsAny(name, `="`) {
		return "", nil, false
	}
	args = map[string]string{}
	for rest = strings.TrimSpace(rest); rest != ""; {
		key, value, remainder, valid := argument(rest)
		if !valid {
			return "", nil, false
		}
		args[key] = value
		rest = remainder
	}
	return name, args, true
}

// argument reads one key="value" pair and returns what follows it.
func argument(s string) (key, value, rest string, ok bool) {
	key, after, found := strings.Cut(s, "=")
	key = strings.TrimSpace(key)
	if !found || key == "" || strings.ContainsAny(key, `" `) {
		return "", "", "", false
	}
	quoted, found := strings.CutPrefix(after, `"`)
	if !found {
		return "", "", "", false
	}
	value, rest, found = strings.Cut(quoted, `"`)
	if !found {
		return "", "", "", false
	}
	return key, value, strings.TrimSpace(rest), true
}