toolkit/cmd/md-fmt/main.go

// md-fmt takes a csv or tsv input file and outputs a formatted markdown table
// with the data.
package main

import (
	"encoding/csv"
	"flag"
	"fmt"
	"log"
	"os"
	"strings"
)

var (
	sourcePath = flag.String("source", "", "path to the input file")
	separator  = flag.String("sep", ",", "separator character to use when reading the csv file")
	lazyQuotes = flag.Bool("lazy-quotes", false, "controls the lazy-quotes setting on the csv reader")
)

func main() {
	flag.Parse()

	fd, err := os.Open(*sourcePath)
	if err != nil {
		log.Fatalf("failed to open source file %s: %s\n", *sourcePath, err)
	}

	sep := []rune(*separator)[0]
	read := csv.NewReader(fd)
	read.Comma = sep
	read.TrimLeadingSpace = true
	read.LazyQuotes = *lazyQuotes

	records, err := read.ReadAll()
	if err != nil {
		log.Fatalf("failed to load records in memory: %s\n", err)
	}

	widths := make([]int, len(records[0]))
	for _, row := range records {
		for i, col := range row {
			widths[i] = max(widths[i], len(col))
		}
	}

	c := make([]string, len(records[0]))
	log.Println(records[0], len(c))
	for i := 0; i < len(c); i++ {
		c[i] = " %-*s "
	}
	pattern := fmt.Sprintf("|%s|\n", strings.Join(c, "|"))
	log.Println(pattern)

	sb := strings.Builder{}

	// Format header row
	curr := make([]any, 0, 2*len(widths))
	for i := range widths {
		curr = append(curr, widths[i], records[0][i])
	}
	sb.WriteString(fmt.Sprintf(pattern, curr...))

	// Format header separator row
	curr = curr[:0] // empty slice but preserve capacity
	for i := range widths {
		curr = append(curr, widths[i], strings.Repeat("-", widths[i]))
	}
	sb.WriteString(fmt.Sprintf(pattern, curr...))

	// Format rest of records
	for i := 1; i < len(records); i++ {
		curr = curr[:0]
		for j := range widths {
			curr = append(curr, widths[j], records[i][j])
		}
		sb.WriteString(fmt.Sprintf(pattern, curr...))
	}

	fmt.Print(sb.String())
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}