package main

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

// Ran is what a command did: its output, its exit status, and why it never ran to an answer.
type Ran struct {
	Stdout string
	Stderr string
	Status int
	// Err is "ENOENT" when the program is not installed, or says it was ended for taking too long.
	Err string
}

// Runner runs one command with extra environment words, so every tool can be tested without ssh.
type Runner func(ctx context.Context, env []string, name string, args ...string) Ran

// CallTimeout bounds one command: below the runtime's thirty-second call limit.
const CallTimeout = 20 * time.Second

// ExecRunner runs a command on this machine, with no terminal and nothing on its stdin, bounded by
// CallTimeout.
func ExecRunner(ctx context.Context, env []string, name string, args ...string) Ran {
	ctx, cancel := context.WithTimeout(ctx, CallTimeout)
	defer cancel()
	cmd := exec.CommandContext(ctx, name, args...)
	cmd.Env = append(os.Environ(), env...)
	var out, errb bytes.Buffer
	cmd.Stdout, cmd.Stderr = &out, &errb
	err := cmd.Run()
	r := Ran{Stdout: out.String(), Stderr: errb.String()}
	var exitErr *exec.ExitError
	switch {
	case errors.Is(ctx.Err(), context.DeadlineExceeded):
		r.Status, r.Err = 124, fmt.Sprintf("no answer within %d s", int(CallTimeout/time.Second))
	case errors.Is(err, exec.ErrNotFound):
		r.Status, r.Err = 127, "ENOENT"
	case errors.As(err, &exitErr):
		r.Status = exitErr.ExitCode()
	case err != nil:
		r.Status, r.Err = 1, err.Error()
	}
	return r
}

func firstLine(s string) string {
	for _, l := range strings.Split(s, "\n") {
		if l = strings.TrimSpace(l); l != "" {
			return l
		}
	}
	return ""
}