lottie: add convert function

Signed-off-by: Sumner Evans <[email protected]>

ffmpeg/convert.go

@@ -68,7 +68,7 @@ func ConvertPath(ctx context.Context, inputFile string, outputExtension string,
 	cmd.Stderr = logWriter
 	err := cmd.Run()
 	if err != nil {
-		return "", fmt.Errorf("ffmpeg error: %+v", err)
+		return "", fmt.Errorf("ffmpeg error: %w", err)
 	}
 
 	if removeInput {

lottie/convert.go

@@ -0,0 +1,90 @@
+// Copyright (c) 2024 Sumner Evans
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package lottie
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os/exec"
+
+	"github.com/rs/zerolog"
+	"go.mau.fi/util/exzerolog"
+)
+
+var lottieconverterPath string
+
+func init() {
+	lottieconverterPath, _ = exec.LookPath("lottieconverter")
+}
+
+// Supported returns whether lottieconverter is available on the system.
+//
+// lottieconverter is considered to be available if a binary called
+// lottieconverter is found in $PATH, or if [SetPath] has been called
+// explicitly with a non-empty path.
+func Supported() bool {
+	return lottieconverterPath != ""
+}
+
+// SetPath overrides the path to the lottieconverter binary.
+func SetPath(path string) {
+	lottieconverterPath = path
+}
+
+// Convert converts lottie data an image or image(s) using lottieconverter.
+//
+// Args:
+//   - inputFilename: the filename the lottie file to convert.
+//   - inputReader: an io.Reader containing the lottie data to convert.
+//   - outputFilename: the filename to write the output to.
+//   - outputWriter: an io.Writer to write the output to.
+//   - format: the output format. Can be one of: png, gif, or pngs.
+//   - width: the width of the output image(s).
+//   - height: the height of the output image(s).
+//   - extraArgs: additional arguments to pass to lottieconverter.
+//
+// The inputFilename and inputReader parameters are mutually exclusive.
+// The outputFilename and outputWriter parameters are mutually exclusive.
+func Convert(ctx context.Context, inputFilename string, inputReader io.Reader, outputFilename string, outputWriter io.Writer, format string, width, height int, extraArgs ...string) error {
+	// Verify the input parameters and calculate the actual filenames that will
+	// be used when shelling out to lottieconverter.
+	//
+	// We are panicking here because it's a programming error to call this
+	// function with invalid parameters.
+	in := inputFilename
+	out := outputFilename
+	if inputFilename == "" && inputReader == nil {
+		panic("lottie.Convert: either inputFile or inputReader must be provided")
+	} else if outputFilename == "" && outputWriter == nil {
+		panic("lottie.Convert: either outputFile or outputWriter must be provided")
+	} else if inputReader != nil {
+		if inputFilename != "" {
+			panic("lottie.Convert: only one of inputFile or inputReader can be provided")
+		}
+		in = "-"
+	} else if outputWriter != nil {
+		if outputFilename != "" {
+			panic("lottie.Convert: only one of outputFile or outputWriter can be provided")
+		}
+		out = "-"
+	}
+
+	args := []string{in, out, format, fmt.Sprintf("%dx%d", width, height)}
+	args = append(args, extraArgs...)
+
+	cmd := exec.CommandContext(ctx, lottieconverterPath, args...)
+	cmd.Stdin = inputReader
+	cmd.Stdout = outputWriter
+	log := zerolog.Ctx(ctx).With().Str("command", "lottieconverter").Logger()
+	cmd.Stderr = exzerolog.NewLogWriter(log).WithLevel(zerolog.WarnLevel)
+
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("lottieconverter error: %w", err)
+	}
+	return nil
+}