From 35fce3074a6041172e9369be03be567ee638accf Mon Sep 17 00:00:00 2001
From: MichaelHatherly <michaelhatherly@gmail.com>
Date: Tue, 19 Dec 2023 21:13:22 +0000
Subject: [PATCH] Markdown templates

---
 Project.toml                           |  4 ++
 docs/src/index.md                      | 38 +++++++++++++++++
 ext/HypertextTemplatesCommonMarkExt.jl | 37 ++++++++++++++++
 src/macro.jl                           | 59 +++++++++++++++++---------
 src/nodes/function.jl                  | 35 ++++++++-------
 test/Project.toml                      |  1 +
 test/runtests.jl                       | 11 +++++
 test/templates.jl                      |  8 ++++
 test/templates/markdown/markdown.1.txt |  3 ++
 test/templates/markdown/markdown.md    | 16 +++++++
 10 files changed, 178 insertions(+), 34 deletions(-)
 create mode 100644 ext/HypertextTemplatesCommonMarkExt.jl
 create mode 100644 test/templates/markdown/markdown.1.txt
 create mode 100644 test/templates/markdown/markdown.md

diff --git a/Project.toml b/Project.toml
index 8d2e3a7..a2a9f84 100644
--- a/Project.toml
+++ b/Project.toml
@@ -13,12 +13,15 @@ MacroTools = "1914dd2f-81c6-5fcd-8719-6d5c9610ff09"
 Match = "7eb4fadd-790c-5f42-8a69-bfa0b872bfbf"
 PackageExtensionCompat = "65ce6f38-6b18-4e1d-a461-8949797d7930"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
+TOML = "fa267f1f-6049-4f14-aa54-33bafae1ed76"
 
 [weakdeps]
+CommonMark = "a80b9123-70ca-4bc0-993e-6e3bcb318db6"
 HTTP = "cd3eb016-35fb-5094-929b-558a96fad6f3"
 Revise = "295af30f-e4ad-537b-8983-00126c2a3abe"
 
 [extensions]
+HypertextTemplatesCommonMarkExt = "CommonMark"
 HypertextTemplatesHTTPReviseExt = ["HTTP", "Revise"]
 HypertextTemplatesReviseExt = "Revise"
 
@@ -32,4 +35,5 @@ MacroTools = "0.5"
 Match = "2"
 PackageExtensionCompat = "1"
 Random = "1.6"
+TOML = "1"
 julia = "1.6"
diff --git a/docs/src/index.md b/docs/src/index.md
index 4861079..437c87b 100644
--- a/docs/src/index.md
+++ b/docs/src/index.md
@@ -313,6 +313,44 @@ julia> render(Templates.var"edit-contact-link"; id=123)
 "<a href=\"/contact/123/edit\">Edit</a>"
 ```
 
+## Markdown Template Files
+
+*Experimental Feature*
+
+You can also use Markdown files as templates. This requires the user to have
+imported the `CommonMark` package prior to using a markdown file in a template
+macro. Internally the markdown syntax is rendered to HTML using
+`CommonMark.jl`'s `html` function and then parsed into a template function using
+`HypertextTemplates.jl`.
+
+Extensions are enabled by default in the CommonMark parser, such as tables,
+admonitions, and footnotes. Since CommonMark supports embedding *some* basic
+HTML tags you can also use those in your markdown templates to call other HTML
+or markdown templates for composition. Don't expect complete HTML support to
+work though, and if you find yourself embedding large amounts of HTML in your
+markdown templates then you should probably just use HTML templates instead and
+then embed that custom template tag in your markdown template.
+
+TOML frontmatter syntax is used to allow the template name and props to be
+declared. When no `name` is provided the template name will be derived from the
+file name. When no `props` are provided the template will have no props.
+Frontmatter is optional and declared with `+++` fences at the top of the file.
+
+```markdown
++++
+name = "my-template"
+props = ["foo", "bar"]
++++
+
+<large-custom-template prop="foo" />
+
+# My Template
+
+This is a template that takes two props: `foo` and `bar`. Their values are
+<julia value="foo" /> and <julia value="bar" /> respectively.
+```
+
+
 ## Development vs. Production Usage
 
 `HypertextTemplates` supports integration with `Revise`-based development
diff --git a/ext/HypertextTemplatesCommonMarkExt.jl b/ext/HypertextTemplatesCommonMarkExt.jl
new file mode 100644
index 0000000..a9afc0f
--- /dev/null
+++ b/ext/HypertextTemplatesCommonMarkExt.jl
@@ -0,0 +1,37 @@
+module HypertextTemplatesCommonMarkExt
+
+import CommonMark
+import HypertextTemplates
+import TOML
+
+function HypertextTemplates._handle_commonmark_ext(
+    ::HypertextTemplates.CommonMarkExtensionType,
+    file,
+    mod,
+    suffix,
+)
+    if !isfile(file)
+        error("markdown template file does not exist: $file")
+    end
+
+    parser = CommonMark._init_parser(mod, suffix)
+    rule = CommonMark.FrontMatterRule(; toml = TOML.parse)
+    CommonMark.enable!(parser, rule)
+
+    ast = open(parser, file)
+
+    frontmatter = CommonMark.frontmatter(ast)
+    name = basename(file)
+    name, _ = splitext(name)
+    name = get(frontmatter, "name", name)
+
+    props = join(get(Vector{String}, frontmatter, "props"), " ")
+    props = isempty(props) ? props : " $props"
+
+    str = "<function $name$props>$(CommonMark.html(ast))</function>"
+    return HypertextTemplates._components_from_str(str, file, mod)
+end
+
+function format_prop(k) end
+
+end
diff --git a/src/macro.jl b/src/macro.jl
index 1afbb3d..6a1e2c6 100644
--- a/src/macro.jl
+++ b/src/macro.jl
@@ -3,8 +3,8 @@
 
 Define an HTML template. The string must be a path to a valid HTML file.
 """
-macro template_str(file::AbstractString)
-    return _template_str(file, __module__, __source__, create = false)
+macro template_str(file::AbstractString, suffix = "jmd")
+    return _template_str(file, __module__, __source__, suffix; create = false)
 end
 
 """
@@ -13,32 +13,53 @@ end
 A helper macro to create an empty template file. The string must be a path to a
 non-existant HTML file.
 """
-macro create_template_str(file::AbstractString)
-    return _template_str(file, __module__, __source__, create = true)
+macro create_template_str(file::AbstractString, suffix = "jmd")
+    return _template_str(file, __module__, __source__, suffix, create = true)
 end
 
-function _template_str(file::AbstractString, __module__, __source__; create::Bool)
+function _template_str(file::AbstractString, __module__, __source__, suffix; create::Bool)
     file = _template_file_path(file, __source__)
-    if endswith(file, ".html")
+    _, ext = splitext(file)
+    if ext in (".html", ".md")
         if create
-            if isfile(file)
-                @error "template file exists, replace `create_template` with the `template` string macro and implement the template function definition" file
-            else
-                mkpath(dirname(file))
-                touch(file)
-                @info "created empty template file" file
-                return nothing
-            end
-        else
-            defs = components(file, __module__)
-            exprs = expression.(defs)
-            return esc(Expr(:toplevel, :(include_dependency($file)), exprs...))
+            return _create_template(file)
+        end
+        if ext == ".html"
+            return _template_expr(file, components(file, __module__))
         end
+        if ext == ".md"
+            return _template_expr(file, _markdown_components(file, __module__, suffix))
+        end
+    end
+    error("template file must have an '.html' or '.md' extension: $file")
+end
+
+function _template_expr(file, defs)
+    exprs = expression.(defs)
+    return esc(Expr(:toplevel, :(include_dependency($file)), exprs...))
+end
+
+function _create_template(file::AbstractString)
+    if isfile(file)
+        @error "template file exists, replace `create_template` with the `template` string macro and implement the template function definition" file
     else
-        error("template file must have an '.html' extension: $file")
+        mkpath(dirname(file))
+        touch(file)
+        @info "created empty template file" file
+        return nothing
     end
 end
 
+function _markdown_components(file, mod, suffix)
+    return _handle_commonmark_ext(CommonMarkExtensionType(), file, mod, suffix)
+end
+
+struct CommonMarkExtensionType end
+
+function _handle_commonmark_ext(::Any, file, mod, suffix)
+    error("markdown template files require you to import the `CommonMark` package first.")
+end
+
 function _template_file_path(file, __source__)
     if isabspath(file) && isfile(file)
         return file
diff --git a/src/nodes/function.jl b/src/nodes/function.jl
index 329ddbd..d9be72f 100644
--- a/src/nodes/function.jl
+++ b/src/nodes/function.jl
@@ -312,26 +312,31 @@ AbstractTrees.children(c::TemplateFunction) = c.body
 
 function components(file::String, mod::Module)::Vector{TemplateFunction}
     if endswith(file, ".html")
-        content = _swap_special_symbols(read(file, String))
-        if isempty(content)
-            error("template file is empty: $file")
-        else
-            html = _with_filtered_logging() do
-                return EzXML.parsehtml(content)
-            end
-            roots = findall("//$TEMPLATE_FUNCTION_TAG", html)
-            roots = isempty(roots) ? findall("//html", html) : roots
-            if isempty(roots)
-                error("no '<function>' or '<html>' found in file: $file.")
-            else
-                return TemplateFunction.(roots, Ref(file), Ref(mod))
-            end
-        end
+        str = read(file, String)
+        return _components_from_str(str, file, mod)
     else
         error("template file must have an '.html' extension: $file")
     end
 end
 
+function _components_from_str(str::AbstractString, file::String, mod::Module)
+    content = _swap_special_symbols(str)
+    if isempty(content)
+        error("template file is empty: $file")
+    else
+        html = _with_filtered_logging() do
+            return EzXML.parsehtml(content)
+        end
+        roots = findall("//$TEMPLATE_FUNCTION_TAG", html)
+        roots = isempty(roots) ? findall("//html", html) : roots
+        if isempty(roots)
+            error("no '<function>' or '<html>' found in file: $file.")
+        else
+            return TemplateFunction.(roots, Ref(file), Ref(mod))
+        end
+    end
+end
+
 struct PropsAccessor{N<:NamedTuple}
     nt::N
 end
diff --git a/test/Project.toml b/test/Project.toml
index b4e6eb5..24eba67 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -1,4 +1,5 @@
 [deps]
+CommonMark = "a80b9123-70ca-4bc0-993e-6e3bcb318db6"
 HTTP = "cd3eb016-35fb-5094-929b-558a96fad6f3"
 ReferenceTests = "324d217c-45ce-50fc-942e-d289b448e8cf"
 Revise = "295af30f-e4ad-537b-8983-00126c2a3abe"
diff --git a/test/runtests.jl b/test/runtests.jl
index 06d70d2..60f571c 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,3 +1,4 @@
+using CommonMark
 using HypertextTemplates
 using Test
 using ReferenceTests
@@ -303,6 +304,16 @@ end
         @test_throws TypeError render(TK.var"typed-props"; props = "string")
     end
 
+    @testset "markdown" begin
+        markdown = joinpath(templates, "markdown")
+        TM = Templates.Markdown
+
+        @test_reference joinpath(markdown, "markdown.1.txt") render(
+            TM.var"custom-markdown-name";
+            prop = "prop-value",
+        )
+    end
+
     @testset "data-htloc" begin
         HypertextTemplates._DATA_FILENAME_ATTR[] = true
         html = render(Templates.Complex.app)
diff --git a/test/templates.jl b/test/templates.jl
index c9f0d29..471196b 100644
--- a/test/templates.jl
+++ b/test/templates.jl
@@ -45,3 +45,11 @@ using HypertextTemplates
 template"templates/keywords/keywords.html"
 
 end
+
+module Markdown
+
+using HypertextTemplates
+
+template"templates/markdown/markdown.md"
+
+end
diff --git a/test/templates/markdown/markdown.1.txt b/test/templates/markdown/markdown.1.txt
new file mode 100644
index 0000000..3f52f6f
--- /dev/null
+++ b/test/templates/markdown/markdown.1.txt
@@ -0,0 +1,3 @@
+<h1 id="markdown-template"><a href="#markdown-template" class="anchor"></a>Markdown Template</h1><p>prop-value<em>content</em><strong>here</strong>.</p><pre><code class="language-julia">function test()
+    return "test"
+end </code></pre>
\ No newline at end of file
diff --git a/test/templates/markdown/markdown.md b/test/templates/markdown/markdown.md
new file mode 100644
index 0000000..097f6c1
--- /dev/null
+++ b/test/templates/markdown/markdown.md
@@ -0,0 +1,16 @@
++++
+name = "custom-markdown-name"
+props = [
+    "prop"
+]
++++
+
+# Markdown Template
+
+<julia value=prop /> *content* **here**.
+
+```julia
+function test()
+    return "test"
+end
+```