// Package barcode wraps the system zbarimg binary (Debian package
// zbar-tools) as a best-effort barcode decoding sidecar, consistent with
// archivdms's general philosophy of shelling out to small CLI tools via
// os/exec instead of adding CGO/native Go dependencies (see
// internal/ocr/ocr.go package comment for the same rationale applied to
// tesseract/poppler-utils).
//
// Barcode decoding failures (binary missing, non-zero exit because no
// barcode was found, timeout) are never fatal to an upload: DecodeBarcodes
// returns an empty slice and a nil error in the "nothing found / binary
// missing" cases, matching how OCR failures are tolerated by callers.
package barcode

import (
	"bytes"
	"context"
	"fmt"
	"os/exec"
	"strings"
	"time"
)

const defaultTimeout = 20 * time.Second

// DecodeBarcodes runs `zbarimg --raw -q <imagePath>` and returns the
// decoded raw values, one per line of output. If zbarimg is not installed,
// this returns an empty slice and a nil error (tolerant, no hard-fail) —
// callers that want to warn about a missing binary should check
// exec.LookPath("zbarimg") themselves if they need to distinguish
// "not installed" from "installed, nothing found".
func DecodeBarcodes(ctx context.Context, imagePath string) ([]string, error) {
	if _, err := exec.LookPath("zbarimg"); err != nil {
		// Binary not present: tolerated, same as a missing tesseract binary.
		return nil, nil
	}

	cctx, cancel := context.WithTimeout(ctx, defaultTimeout)
	defer cancel()

	cmd := exec.CommandContext(cctx, "zbarimg", "--raw", "-q", imagePath)
	var out, stderr bytes.Buffer
	cmd.Stdout = &out
	cmd.Stderr = &stderr
	err := cmd.Run()
	if err != nil {
		// zbarimg exits non-zero (typically exit code 4) when no barcode is
		// found in the image at all — that is a normal, expected outcome for
		// the vast majority of scanned documents, not an error condition.
		if exitErr, ok := err.(*exec.ExitError); ok {
			_ = exitErr
			return nil, nil
		}
		return nil, fmt.Errorf("barcode: zbarimg failed: %w (%s)", err, strings.TrimSpace(stderr.String()))
	}

	var values []string
	for _, line := range strings.Split(out.String(), "\n") {
		line = strings.TrimSpace(line)
		if line != "" {
			values = append(values, line)
		}
	}
	return values, nil
}