Implement HTML writer (#33)

Reviewed-on: #33
Co-authored-by: Natercio Moniz <[email protected]>

internal/writing/html/writer.go

@@ -0,0 +1,85 @@
+// Package html renders an internal.AggregatorWriter as a complete,
+// standalone HTML document: the report table fragment (built from the
+// shared table definition in internal/writing/internal/tabledef, so it can
+// never drift from the terminal layout) embedded in a Bootstrap-styled page
+// with a translated title and generation timestamp. The official Bootstrap
+// 5.3.3 stylesheet is inlined via go:embed, so the document renders fully
+// offline.
+package html
+
+import (
+	_ "embed"
+	"fmt"
+	"html/template"
+	"io"
+	"time"
+
+	"github.com/nmoniz/any2anexoj/internal"
+	"github.com/nmoniz/any2anexoj/internal/writing/internal/tabledef"
+)
+
+// bootstrapMinCSS is the official Bootstrap 5.3.3 minified CSS distribution
+// file, embedded so every rendered document renders fully offline. After any
+// version bump, re-verify provenance with:
+//
+//	openssl dgst -sha384 -binary bootstrap.min.css | base64
+//
+// It must print the official SRI hash published at
+// https://getbootstrap.com/docs/5.3/getting-started/download/
+// (sha384-QWTKZyjpPEjISv5WaRU9OFeRpok6YctnYmDr5pNlyT2bRjXh0JMhjY6hW+ALEwIH).
+//
+//go:embed bootstrap.min.css
+var bootstrapMinCSS string
+
+// Writer writes a complete HTML document for an AggregatorWriter.
+type Writer struct {
+	output     io.Writer
+	translator tabledef.Translator
+	lang       string
+}
+
+// NewWriter builds a Writer that writes a complete HTML document to w. The
+// report table is rendered from the shared table definition via tr, and the
+// document title is looked up from the "report_title" translation via tr,
+// so callers never pass a pre-baked title.
+func NewWriter(w io.Writer, tr tabledef.Translator, lang string) *Writer {
+	return &Writer{
+		output:     w,
+		translator: tr,
+		lang:       lang,
+	}
+}
+
+//go:embed document.tmpl
+var documentTemplateBody string
+
+// documentTemplate renders the full HTML page from document.tmpl. The table
+// fragment is typed as template.HTML so the template engine emits it
+// verbatim without escaping the angle brackets in the <table> markup.
+var documentTemplate = template.Must(template.New("html").Parse(documentTemplateBody))
+
+// Render writes a complete standalone HTML document for aw to the configured
+// output. The same Writer may be reused; each call rebuilds the table
+// fragment from aw so the rendered <tr> count reflects aw's current items and
+// no rows are duplicated across invocations.
+func (hw *Writer) Render(aw *internal.AggregatorWriter) error {
+	fragment := hw.renderTableFragment(aw)
+	title := hw.translator.Translate("report_title", 1, nil)
+	data := struct {
+		Lang          string
+		Title         string
+		CSS           template.CSS
+		TableFragment template.HTML
+		GeneratedAt   string
+	}{
+		Lang:          hw.lang,
+		Title:         title,
+		CSS:           template.CSS(bootstrapMinCSS),
+		TableFragment: template.HTML(fragment),
+		GeneratedAt:   time.Now().UTC().Format(time.RFC3339),
+	}
+	if err := documentTemplate.Execute(hw.output, data); err != nil {
+		return fmt.Errorf("render html document: %w", err)
+	}
+	return nil
+}