rewrite

internal/codec/detect.go

@@ -0,0 +1,72 @@
+package codec
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"path/filepath"
+	"strings"
+)
+
+func Sniff(reader io.Reader) (Codec, io.Reader, error) {
+	buf, err := io.ReadAll(reader)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	ra := bytes.NewReader(buf)
+
+	var (
+		guess Codec
+		best  int
+	)
+
+	for _, codec := range codecs {
+		confidence, err := codec.Sniff(ra)
+		if err != nil {
+			return nil, nil, err
+		}
+
+		if confidence > best {
+			best = confidence
+			guess = codec
+		}
+	}
+
+	if guess == nil {
+		return nil, nil, errors.New("unknown format")
+	}
+
+	return guess, bytes.NewReader(buf), nil
+}
+
+func Detect(output, override string) (Codec, error) {
+	if override != "" {
+		codec, ok := codecs[override]
+		if !ok {
+			return nil, fmt.Errorf("unsupported output codec: %q", override)
+		}
+
+		return codec, nil
+	}
+
+	if output == "-" {
+		return nil, errors.New("missing codec for output")
+	}
+
+	ext := strings.ToLower(strings.TrimPrefix(filepath.Ext(output), "."))
+	if ext == "" {
+		return nil, fmt.Errorf("output filename %q has no extension", output)
+	}
+
+	for _, codec := range codecs {
+		for _, alias := range codec.Extensions() {
+			if ext == strings.ToLower(alias) {
+				return codec, nil
+			}
+		}
+	}
+
+	return nil, fmt.Errorf("unsupported or unknown file extension: %q", ext)
+}