// Package compose executes Docker Compose through a fixed executable and argument arrays.
package compose

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
)

// Result is the captured output and process exit code for one Docker invocation.
type Result struct {
	Stdout   string
	Stderr   string
	ExitCode int
}

// Runner executes the Docker CLI. It never invokes a shell.
type Runner struct {
	binary string
}

// NewRunner returns a runner for binary. An empty binary selects docker from PATH.
func NewRunner(binary string) Runner {
	if binary == "" {
		binary = "docker"
	}
	return Runner{binary: binary}
}

// Run invokes Docker with the supplied argument array and optional standard input.
func (r Runner) Run(ctx context.Context, args []string, stdin io.Reader) (Result, error) {
	command := exec.CommandContext(ctx, r.binary, args...)
	command.Stdin = stdin
	var stdout, stderr bytes.Buffer
	command.Stdout = &stdout
	command.Stderr = &stderr
	err := command.Run()
	result := Result{Stdout: stdout.String(), Stderr: stderr.String()}
	if err == nil {
		return result, nil
	}
	var exitError *exec.ExitError
	if errors.As(err, &exitError) {
		result.ExitCode = exitError.ExitCode()
		return result, err
	}
	if errors.Is(err, exec.ErrNotFound) || errors.Is(err, os.ErrNotExist) {
		result.ExitCode = 127
		return result, fmt.Errorf("%w: %w", exec.ErrNotFound, err)
	}
	return result, err
}