Implement preprocessing of post bodies for gemini

4 files changed, 155 insertions, 62 deletions

diff --git a/src/gmi/tpl.go b/src/gmi/tpl.go
index 7959b8e..7f41993 100644
--- a/src/gmi/tpl.go
+++ b/src/gmi/tpl.go
@@ -8,6 +8,7 @@ import (
 	"io"
 	"io/fs"
 	"net/url"
+	"path/filepath"
 	"strconv"
 	"strings"
 	"text/template"
@@ -83,6 +84,45 @@ func (r renderer) GetPostSeriesNextPrevious(p post.StoredPost) (rendererGetPostS
 	return res, nil
 }
 
+func (r renderer) PostBody(p post.StoredPost) (string, error) {
+
+	preprocessFuncs := post.PreprocessFunctions{
+		BlogURL: func(path string) string {
+			return filepath.Join("/", path)
+		},
+		AssetURL: func(id string) string {
+			return filepath.Join("/assets", id)
+		},
+		PostURL: func(id string) string {
+			return filepath.Join("/posts", id)
+		},
+		StaticURL: func(path string) string {
+			return filepath.Join("/static", path)
+		},
+		Image: func(args ...string) (string, error) {
+
+			var (
+				id    = args[0]
+				descr = "Image"
+			)
+
+			if len(args) > 1 {
+				descr = args[1]
+			}
+
+			return fmt.Sprintf("=> %s %s", filepath.Join("/assets", id), descr), nil
+		},
+	}
+
+	buf := new(bytes.Buffer)
+
+	if err := p.PreprocessBody(buf, preprocessFuncs); err != nil {
+		return "", fmt.Errorf("preprocessing post body: %w", err)
+	}
+
+	return buf.String(), nil
+}
+
 func (r renderer) GetQueryValue(key, def string) string {
 	v := r.url.Query().Get(key)
 	if v == "" {
diff --git a/src/gmi/tpl/posts/post.gmi b/src/gmi/tpl/posts/post.gmi
index 4f58c84..7d1719b 100644
--- a/src/gmi/tpl/posts/post.gmi
+++ b/src/gmi/tpl/posts/post.gmi
@@ -6,7 +6,7 @@
 > {{ $post.Description }}
 {{ end -}}
 
-{{ $post.Body }}
+{{ .PostBody $post }}
 
 --------------------------------------------------------------------------------
 
diff --git a/src/http/posts.go b/src/http/posts.go
index eff0eaa..cae8f43 100644
--- a/src/http/posts.go
+++ b/src/http/posts.go
@@ -21,68 +21,43 @@ import (
 	"github.com/mediocregopher/mediocre-go-lib/v2/mctx"
 )
 
-func (a *api) parsePostBody(p post.Post) (*txttpl.Template, error) {
-	tpl := txttpl.New("root")
-	tpl = tpl.Funcs(txttpl.FuncMap(a.tplFuncs()))
-
-	tpl = txttpl.Must(tpl.New("image.html").Parse(mustReadTplFile("image.html")))
-
-	if p.Format == post.FormatMarkdown {
-		tpl = tpl.Funcs(txttpl.FuncMap{
-			"Image": func(id string) (string, error) {
-
-				tplPayload := struct {
-					ID        string
-					Descr     string
-					Resizable bool
-				}{
-					ID: id,
-					// I could use variadic args to make this work, I think
-					Descr:     "TODO: proper alt text",
-					Resizable: isImgResizable(id),
-				}
-
-				buf := new(bytes.Buffer)
-				if err := tpl.ExecuteTemplate(buf, "image.html", tplPayload); err != nil {
-					return "", err
-				}
-
-				return buf.String(), nil
-			},
-		})
-	}
+func (a *api) postPreprocessFuncImage(args ...string) (string, error) {
+
+	var (
+		id    = args[0]
+		descr = "TODO"
+	)
 
-	if p.Format == post.FormatGemtext {
-		tpl = tpl.Funcs(txttpl.FuncMap{
-			"Image": func(id, descr string) (string, error) {
-
-				tplPayload := struct {
-					ID        string
-					Descr     string
-					Resizable bool
-				}{
-					ID:        id,
-					Descr:     descr,
-					Resizable: isImgResizable(id),
-				}
-
-				buf := new(bytes.Buffer)
-				if err := tpl.ExecuteTemplate(buf, "image.html", tplPayload); err != nil {
-					return "", err
-				}
-
-				return buf.String(), nil
-			},
-		})
+	if len(args) > 1 {
+		descr = args[1]
 	}
 
-	tpl, err := tpl.New(p.ID + "-body.html").Parse(p.Body)
+	tpl := txttpl.New("image.html")
 
-	if err != nil {
-		return nil, err
+	tpl.Funcs(txttpl.FuncMap{
+		"AssetURL": func(id string) string {
+			return a.assetURL(id, false)
+		},
+	})
+
+	tpl = txttpl.Must(tpl.Parse(mustReadTplFile("image.html")))
+
+	tplPayload := struct {
+		ID        string
+		Descr     string
+		Resizable bool
+	}{
+		ID:        id,
+		Descr:     descr,
+		Resizable: isImgResizable(id),
+	}
+
+	buf := new(bytes.Buffer)
+	if err := tpl.ExecuteTemplate(buf, "image.html", tplPayload); err != nil {
+		return "", err
 	}
 
-	return tpl, nil
+	return buf.String(), nil
 }
 
 type postTplPayload struct {
@@ -93,15 +68,27 @@ type postTplPayload struct {
 
 func (a *api) postToPostTplPayload(storedPost post.StoredPost) (postTplPayload, error) {
 
-	bodyTpl, err := a.parsePostBody(storedPost.Post)
-	if err != nil {
-		return postTplPayload{}, fmt.Errorf("parsing post body as template: %w", err)
+	preprocessFuncs := post.PreprocessFunctions{
+		BlogURL: func(path string) string {
+			return a.blogURL(path, false)
+		},
+		AssetURL: func(id string) string {
+			return a.assetURL(id, false)
+		},
+		PostURL: func(id string) string {
+			return a.postURL(id, false)
+		},
+		StaticURL: func(path string) string {
+			path = filepath.Join("static", path)
+			return a.blogURL(path, false)
+		},
+		Image: a.postPreprocessFuncImage,
 	}
 
 	bodyBuf := new(bytes.Buffer)
 
-	if err := bodyTpl.Execute(bodyBuf, nil); err != nil {
-		return postTplPayload{}, fmt.Errorf("executing post body as template: %w", err)
+	if err := storedPost.PreprocessBody(bodyBuf, preprocessFuncs); err != nil {
+		return postTplPayload{}, fmt.Errorf("preprocessing post body: %w", err)
 	}
 
 	if storedPost.Format == post.FormatGemtext {
diff --git a/src/post/preprocess.go b/src/post/preprocess.go
new file mode 100644
index 0000000..4d4be9d
--- /dev/null
+++ b/src/post/preprocess.go
@@ -0,0 +1,66 @@
+package post
+
+import (
+	"fmt"
+	"io"
+	"text/template"
+)
+
+// PreprocessFunctions are functions which can be used by posts themselves to
+// interleave dynamic content into their bodies. Usually this is used for
+// properly constructing URLs, but also for things like displaying images.
+type PreprocessFunctions struct {
+
+	// BlogURL returns the given string, rooted to the blog's base url (which
+	// may or may not include path components itself).
+	//
+	// The given path should not have a leading slash.
+	BlogURL func(path string) string
+
+	// AssetURL returns the URL of the asset with the given ID.
+	AssetURL func(id string) string
+
+	// PostURL returns the URL of the post with the given ID.
+	PostURL func(id string) string
+
+	// StaticURL returns the URL of a file being served from the static
+	// directory. The given path should _not_ include the prefixed 'static/'
+	// path element.
+	StaticURL func(path string) string
+
+	// Image returns a string which should be inlined into the post body in
+	// order to display an.
+	//
+	// The first argument to Image _must_ be the ID of an image asset. The
+	// second argument _may_ be a description of the image which will be used as
+	// alt text, or possibly displayed to the user with the image.
+	Image func(args ...string) (string, error)
+}
+
+// PreprocessBody interprets the Post's Body as a text template which may use
+// any of the functions found in PreprocessFunctions (all must be set). It
+// executes the template and writes the result to the given writer.
+func (p Post) PreprocessBody(into io.Writer, funcs PreprocessFunctions) error {
+
+	tpl := template.New("")
+
+	tpl.Funcs(template.FuncMap{
+		"BlogURL":   funcs.BlogURL,
+		"AssetURL":  funcs.AssetURL,
+		"PostURL":   funcs.PostURL,
+		"StaticURL": funcs.StaticURL,
+		"Image":     funcs.Image,
+	})
+
+	tpl, err := tpl.Parse(p.Body)
+
+	if err != nil {
+		return fmt.Errorf("parsing post body as template: %w", err)
+	}
+
+	if err := tpl.Execute(into, nil); err != nil {
+		return fmt.Errorf("executing post body as template: %w", err)
+	}
+
+	return nil
+}