add csv reading, routing

internal/csv.go

@@ -0,0 +1,72 @@
+package internal
+
+import (
+	"encoding/csv"
+	"errors"
+	"io"
+	"os"
+	"strconv"
+)
+
+type Headings []string
+
+func (h Headings) IndexOf(heading string) int {
+	for i, value := range h {
+		if value == heading {
+			return i
+		}
+	}
+
+	return -1
+}
+
+func ReadCsvRedirects(file string) (Redirects, error) {
+	reader, err := os.Open(file)
+	if err != nil {
+		return nil, err
+	}
+
+	csvReader := csv.NewReader(reader)
+
+	// Process headings
+	textHeadings, err := csvReader.Read()
+	if err != nil {
+		return nil, err
+	}
+	headings := Headings(textHeadings)
+	fromCol := headings.IndexOf("From")
+	toCol := headings.IndexOf("To")
+	statusCol := headings.IndexOf("Status Code")
+	if fromCol == -1 || toCol == -1 || statusCol == -1 {
+		return nil, errors.New("CSV must contain From, To, and Status Code headings")
+	}
+
+	redirects := Redirects{}
+	for {
+		row, err := csvReader.Read()
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			return nil, err
+		}
+		if row == nil {
+			break
+		}
+
+		statusCode, err := strconv.Atoi(row[statusCol])
+		if err != nil {
+			return nil, err
+		}
+
+		redirect := &Redirect{
+			From:       row[fromCol],
+			To:         row[toCol],
+			StatusCode: statusCode,
+		}
+
+		redirects = append(redirects, redirect)
+	}
+
+	return redirects, nil
+}