probo/pkg/esign/certgen.go

// Copyright (c) 2026 Probo Inc <hello@probo.com>.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package esign

import (
	"bytes"
	"context"
	_ "embed"
	"fmt"
	"html/template"
	"io"
	"strings"
	"time"

	"github.com/digitorus/timestamp"
	"go.gearno.de/x/ref"
	"go.probo.inc/probo/pkg/coredata"
	"go.probo.inc/probo/pkg/html2pdf"
)

type (
	CertificateGenerator struct {
		HTML2PDFConverter *html2pdf.Converter
	}

	certificateData struct {
		SignatureID      string
		OrganizationID   string
		SignerFullName   string
		SignerEmail      string
		SignerIPAddress  string
		SignerUserAgent  string
		DocumentType     string
		DocumentTypeName string
		FileID           string
		FileHash         string
		Seal             string
		SealVersion      int
		ConsentText      string
		SignedAt         string
		TSAAuthority     string
		TSATime          string
		TSASerial        string
		Events           []certificateEvent
	}

	certificateEvent struct {
		EventType  string
		Source     string
		Actor      string
		IPAddress  string
		OccurredAt string
	}
)

var (
	//go:embed certificate.html.tmpl
	certificateTemplateHTML string

	certificateTemplate = template.Must(template.New("certificate").Parse(certificateTemplateHTML))
)

func (g *CertificateGenerator) Generate(
	ctx context.Context,
	signature *coredata.ElectronicSignature,
	events coredata.ElectronicSignatureEvents,
) (io.Reader, error) {
	data := certificateData{
		SignatureID:      signature.ID.String(),
		OrganizationID:   signature.OrganizationID.String(),
		SignerFullName:   ref.UnrefOrZero(signature.SignerFullName),
		SignerEmail:      signature.SignerEmail,
		SignerIPAddress:  ref.UnrefOrZero(signature.SignerIPAddress),
		SignerUserAgent:  ref.UnrefOrZero(signature.SignerUserAgent),
		DocumentType:     signature.DocumentType.String(),
		DocumentTypeName: signature.DocumentType.DisplayName(),
		FileID:           signature.FileID.String(),
		FileHash:         ref.UnrefOrZero(signature.FileHash),
		Seal:             ref.UnrefOrZero(signature.Seal),
		SealVersion:      signature.SealVersion,
		ConsentText:      signature.ConsentText,
	}

	if signature.SignedAt == nil {
		return nil, fmt.Errorf("cannot generate certificate: signature %s has no signed_at timestamp", signature.ID)
	}

	data.SignedAt = signature.SignedAt.UTC().Format(time.RFC3339)

	if len(signature.TSAToken) == 0 {
		return nil, fmt.Errorf("cannot generate certificate: signature %s has no TSA token", signature.ID)
	}

	tsResp, err := timestamp.ParseResponse(signature.TSAToken)
	if err != nil {
		return nil, fmt.Errorf("cannot parse TSA token for signature %s: %w", signature.ID, err)
	}

	data.TSATime = tsResp.Time.UTC().Format(time.RFC3339)
	data.TSASerial = tsResp.SerialNumber.String()
	data.TSAAuthority = tsaAuthorityName(tsResp)

	for _, evt := range events {
		data.Events = append(
			data.Events,
			certificateEvent{
				EventType:  evt.EventType.String(),
				Source:     evt.EventSource.String(),
				Actor:      evt.ActorEmail,
				IPAddress:  evt.ActorIPAddress,
				OccurredAt: evt.OccurredAt.UTC().Format(time.RFC3339),
			},
		)
	}

	var htmlBuf bytes.Buffer
	if err := certificateTemplate.Execute(&htmlBuf, data); err != nil {
		return nil, fmt.Errorf("cannot render certificate template: %w", err)
	}

	pdfReader, err := g.HTML2PDFConverter.GeneratePDF(
		ctx,
		htmlBuf.Bytes(),
		html2pdf.RenderConfig{
			PageFormat:      html2pdf.PageFormatA4,
			Orientation:     html2pdf.OrientationPortrait,
			MarginTop:       html2pdf.NewMarginMillimeters(20),
			MarginBottom:    html2pdf.NewMarginMillimeters(20),
			MarginLeft:      html2pdf.NewMarginMillimeters(20),
			MarginRight:     html2pdf.NewMarginMillimeters(20),
			PrintBackground: true,
		},
	)
	if err != nil {
		return nil, fmt.Errorf("cannot generate certificate PDF: %w", err)
	}

	return pdfReader, nil
}

func tsaAuthorityName(ts *timestamp.Timestamp) string {
	if len(ts.Certificates) == 0 {
		return ""
	}

	cert := ts.Certificates[0]

	if len(cert.Subject.Organization) > 0 {
		org := strings.Join(cert.Subject.Organization, ", ")
		if cert.Subject.CommonName != "" {
			return org + " (" + cert.Subject.CommonName + ")"
		}

		return org
	}

	return cert.Subject.CommonName
}