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"
	"io"
	"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

	rec, err := read.Read()
	if err != nil {
		log.Fatalf("error reading from csv file: %s", err)
	}

	widths := make([]int, len(rec))
	for i, col := range rec {
		widths[i] = max(widths[i], len(col))
	}
	for {
		rec, err := read.Read()
		if err == io.EOF {
			break
		}
		if err != nil {
			log.Fatalf("error reading from csv file: %s", err)
		}

		for i, col := range rec {
			widths[i] = max(widths[i], len(col))
		}
	}

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

	// Reset file descriptor cursor and take new CSV reader from it
	fd.Seek(0, 0)
	read = csv.NewReader(fd)
	read.Comma = sep
	read.TrimLeadingSpace = true
	read.LazyQuotes = *lazyQuotes

	// Format header row
	rec, err = read.Read()
	if err != nil {
		log.Fatalf("failed to read next csv record: %s", err)
	}

	curr := make([]any, 0, 2*len(widths))
	for i := range widths {
		curr = append(curr, widths[i], rec[i])
	}
	fmt.Printf(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]))
	}
	fmt.Printf(pattern, curr...)

	for {
		rec, err := read.Read()
		if err == io.EOF {
			break
		}
		if err != nil {
			log.Fatalf("error reading from csv file: %s", err)
		}

		curr = curr[:0]
		for i := range widths {
			curr = append(curr, widths[i], rec[i])
		}
		fmt.Printf(pattern, curr...)
	}
}

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