reader.go

package main

import (
	"bytes"
	"encoding/csv"
	"fmt"
	"io"
)

type (
	// Reader reads from a CSV data and mask it.
	Reader struct {
		r        *csv.Reader
		template Template
		lineNum  int

		// If SkipHeader is true, the first line is skipped masking as header.
		SkipHeader bool
	}
)

// NewReader returns a new reader that reads from r while masking data according to the rule.
func NewReader(r io.Reader, template Template) *Reader {
	return &Reader{
		r:        csv.NewReader(r),
		template: template,
	}
}

// Read reads one record from r.r while masking and return it as a CSV string.
// If there is no data left to be read, Read returns "", io.EOF.
func (r *Reader) Read() (string, error) {
	record, err := r.r.Read()
	if err != nil {
		return "", err
	}
	r.lineNum++

	var tmpl Template
	if r.lineNum == 1 && r.SkipHeader {
		tmpl, err = r.template.CloneWithEcho()
		if err != nil {
			return "", fmt.Errorf("failed clone with echo: %v", err)
		}
	} else {
		tmpl = r.template
	}

	buf := bytes.Buffer{}
	err = tmpl.Execute(&buf, toFieldsMap(record))
	if err != nil {
		return "", fmt.Errorf("failed to execute template: %v", err)
	}

	return buf.String(), nil
}

func toFieldsMap(record []string) map[string]string {
	out := make(map[string]string)
	for i, field := range record {
		key := fmt.Sprintf("Field%d", i+1)
		out[key] = field
	}
	return out
}