package main

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

// Root repeats an act with more rights than the account this runs as has (novox/hq ADR 0394 §2). It is an
// interface so a unit test uses a fake: no test runs sudo.
type Root interface {
	// Run runs one fixed binary with the arguments given, never through a shell, and answers what it wrote.
	Run(bin string, args ...string) ([]byte, error)
}

// rootBins are the only binaries that run as root. The argument list is the caller's, but each caller in this
// module builds it from fixed words and one path, and ends its options with `--`.
var rootBins = map[string]bool{
	"/usr/bin/cat": true, "/usr/bin/cp": true, "/usr/bin/mv": true, "/usr/bin/stat": true, "/usr/bin/chmod": true,
	"/usr/bin/chown": true, "/usr/bin/mkdir": true, "/usr/bin/rm": true, "/usr/bin/readlink": true, "/usr/bin/find": true,
}

func rootBinList() string {
	var l []string
	for b := range rootBins {
		l = append(l, b)
	}
	sort.Strings(l)
	return strings.Join(l, ", ")
}

// sudoRoot is the real runner: `sudo -n` (never a password prompt) with a binary from rootBins.
type sudoRoot struct{}

// capped keeps at most n bytes and drops the rest.
type capped struct {
	buf bytes.Buffer
	n   int
}

func (c *capped) Write(p []byte) (int, error) {
	if room := c.n - c.buf.Len(); room > 0 {
		if len(p) < room {
			room = len(p)
		}
		c.buf.Write(p[:room])
	}
	return len(p), nil
}

func (sudoRoot) Run(bin string, args ...string) ([]byte, error) {
	if !rootBins[bin] {
		return nil, fmt.Errorf("%s is not one of the binaries that run as root here (%s)", bin, rootBinList())
	}
	ctx, cancel := context.WithTimeout(context.Background(), SearchTime+10*time.Second)
	defer cancel()
	cmd := exec.CommandContext(ctx, "/usr/bin/sudo", append([]string{"-n", "--", bin}, args...)...)
	out, errs := &capped{n: MaxScan}, &capped{n: 4096}
	cmd.Stdout, cmd.Stderr = out, errs
	cmd.Stdin = io.LimitReader(strings.NewReader(""), 0)
	if err := cmd.Run(); err != nil {
		msg := strings.TrimSpace(errs.buf.String())
		if msg == "" {
			msg = err.Error()
		}
		return nil, fmt.Errorf("sudo -n %s: %s", bin, msg)
	}
	return out.buf.Bytes(), nil
}