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path: root/gemini/gemtext/htmlconv/convert.go
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package htmlconv

import (
	"html/template"
	"io"

	"tildegit.org/tjp/gus/gemini/gemtext"
	"tildegit.org/tjp/gus/gemini/gemtext/internal"
)

// Convert writes markdown to a writer from the provided gemtext document.
//
// Templates can be provided to override the output for different line types.
// The templates supported are:
//   - "header" is called before any lines and is passed the full Document.
//   - "footer" is called after the lines and is passed the full Document.
//   - "textline" is called once per line of text and is passed a gemtext.TextLine.
//   - "linkline" is called once per link line and is passed an object which wraps
//     a gemtext.LinkLine but also supports a ValidatedURL() method returning a
//     string which html/template will always allow as href attributes.
//   - "preformattedtextlines" is called once for a block of preformatted text and is
//     passed a slice of gemtext.PreformattedTextLines.
//   - "heading1line" is called once per h1 line and is passed a gemtext.Heading1Line.
//   - "heading2line" is called once per h2 line and is passed a gemtext.Heading2Line.
//   - "heading3line" is called once per h3 line and is passed a gemtext.Heading3Line.
//   - "listitemlines" is called once for a block of contiguous list item lines and
//     is passed a slice of gemtext.ListItemLines.
//   - "quoteline" is passed once per blockquote line and is passed a gemtext.QuoteLine.
//
// There exist default implementations of each of these templates, so the "overrides"
// argument can be nil.
func Convert(wr io.Writer, doc gemtext.Document, overrides *template.Template) error {
	if err := internal.ValidateLinks(doc); err != nil {
		return err
	}

	tmpl, err := baseTmpl.Clone()
	if err != nil {
		return err
	}

	tmpl, err = internal.AddHTMLTemplates(tmpl, overrides)
	if err != nil {
		return err
	}

	for _, item := range internal.RenderItems(doc) {
		if err := tmpl.ExecuteTemplate(wr, item.Template, item.Object); err != nil {
			return err
		}
	}

	return nil
}

var baseTmpl = template.Must(template.New("htmlconv").Parse(`
{{ define "header" }}<html><body>{{ end }}
{{ define "textline" }}{{ if ne .String "\n" }}<p>{{ . }}</p>{{ end }}{{ end }}
{{ define "linkline" -}}
	<p>=> <a href="{{ .ValidatedURL }}">{{ if eq .Label "" -}}
		{{ .URL }}
	{{- else -}}
		{{ .Label }}
	{{- end -}}
	</a></p>
{{- end }}
{{ define "preformattedtextlines" -}}
	<pre>
	{{- range . -}}
		{{ . }}
	{{- end -}}
	</pre>
{{- end }}
{{ define "heading1line" }}<h1>{{ .Body }}</h1>{{ end }}
{{ define "heading2line" }}<h2>{{ .Body }}</h2>{{ end }}
{{ define "heading3line" }}<h3>{{ .Body }}</h3>{{ end }}
{{ define "listitemlines" -}}
	<ul>
	{{- range . -}}
		<li>{{ .Body }}</li>
	{{- end -}}
	</ul>
{{- end }}
{{ define "quoteline" }}<blockquote>{{ .Body }}</blockquote>{{ end }}
{{ define "footer" }}</body></html>{{ end }}
`))