//go:generate ../../../tools/readme_config_includer/generator
package exec

import (
	"bytes"
	_ "embed"
	"errors"
	"fmt"
	"io"
	"os"
	osExec "os/exec"
	"path/filepath"
	"runtime"
	"strings"
	"sync"
	"time"

	"github.com/kballard/go-shellquote"

	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/config"
	"github.com/influxdata/telegraf/internal"
	"github.com/influxdata/telegraf/models"
	"github.com/influxdata/telegraf/plugins/inputs"
	"github.com/influxdata/telegraf/plugins/parsers"
	"github.com/influxdata/telegraf/plugins/parsers/nagios"
)

//go:embed sample.conf
var sampleConfig string

const MaxStderrBytes int = 512

type exitcodeHandlerFunc func([]telegraf.Metric, error, []byte) []telegraf.Metric

type Exec struct {
	Commands    []string        `toml:"commands"`
	Command     string          `toml:"command"`
	Environment []string        `toml:"environment"`
	Timeout     config.Duration `toml:"timeout"`
	Log         telegraf.Logger `toml:"-"`

	parser parsers.Parser

	runner Runner

	// Allow post processing of command exit codes
	exitcodeHandler   exitcodeHandlerFunc
	parseDespiteError bool
}

func NewExec() *Exec {
	return &Exec{
		runner:  CommandRunner{},
		Timeout: config.Duration(time.Second * 5),
	}
}

type Runner interface {
	Run(string, []string, time.Duration) ([]byte, []byte, error)
}

type CommandRunner struct{}

func (c CommandRunner) Run(
	command string,
	environments []string,
	timeout time.Duration,
) ([]byte, []byte, error) {
	splitCmd, err := shellquote.Split(command)
	if err != nil || len(splitCmd) == 0 {
		return nil, nil, fmt.Errorf("exec: unable to parse command: %w", err)
	}

	cmd := osExec.Command(splitCmd[0], splitCmd[1:]...)

	if len(environments) > 0 {
		cmd.Env = append(os.Environ(), environments...)
	}

	var (
		out    bytes.Buffer
		stderr bytes.Buffer
	)
	cmd.Stdout = &out
	cmd.Stderr = &stderr

	runErr := internal.RunTimeout(cmd, timeout)

	out = removeWindowsCarriageReturns(out)
	if stderr.Len() > 0 && !telegraf.Debug {
		stderr = removeWindowsCarriageReturns(stderr)
		stderr = c.truncate(stderr)
	}

	return out.Bytes(), stderr.Bytes(), runErr
}

func (c CommandRunner) truncate(buf bytes.Buffer) bytes.Buffer {
	// Limit the number of bytes.
	didTruncate := false
	if buf.Len() > MaxStderrBytes {
		buf.Truncate(MaxStderrBytes)
		didTruncate = true
	}
	if i := bytes.IndexByte(buf.Bytes(), '\n'); i > 0 {
		// Only show truncation if the newline wasn't the last character.
		if i < buf.Len()-1 {
			didTruncate = true
		}
		buf.Truncate(i)
	}
	if didTruncate {
		buf.WriteString("...") //nolint:revive // will always return nil or panic
	}
	return buf
}

// removeWindowsCarriageReturns removes all carriage returns from the input if the
// OS is Windows. It does not return any errors.
func removeWindowsCarriageReturns(b bytes.Buffer) bytes.Buffer {
	if runtime.GOOS == "windows" {
		var buf bytes.Buffer
		for {
			byt, err := b.ReadBytes(0x0D)
			byt = bytes.TrimRight(byt, "\x0d")
			if len(byt) > 0 {
				_, _ = buf.Write(byt)
			}
			if errors.Is(err, io.EOF) {
				return buf
			}
		}
	}
	return b
}

func (*Exec) SampleConfig() string {
	return sampleConfig
}

func (e *Exec) ProcessCommand(command string, acc telegraf.Accumulator, wg *sync.WaitGroup) {
	defer wg.Done()

	out, errBuf, runErr := e.runner.Run(command, e.Environment, time.Duration(e.Timeout))
	if !e.parseDespiteError && runErr != nil {
		err := fmt.Errorf("exec: %w for command %q: %s", runErr, command, string(errBuf))
		acc.AddError(err)
		return
	}

	metrics, err := e.parser.Parse(out)
	if err != nil {
		acc.AddError(err)
		return
	}

	if e.exitcodeHandler != nil {
		metrics = e.exitcodeHandler(metrics, runErr, errBuf)
	}

	for _, m := range metrics {
		acc.AddMetric(m)
	}
}

func (e *Exec) SetParser(parser parsers.Parser) {
	e.parser = parser
	unwrapped, ok := parser.(*models.RunningParser)
	if ok {
		if _, ok := unwrapped.Parser.(*nagios.Parser); ok {
			e.exitcodeHandler = nagiosHandler
			e.parseDespiteError = true
		}
	}
}

func (e *Exec) Gather(acc telegraf.Accumulator) error {
	var wg sync.WaitGroup
	// Legacy single command support
	if e.Command != "" {
		e.Commands = append(e.Commands, e.Command)
		e.Command = ""
	}

	commands := make([]string, 0, len(e.Commands))
	for _, pattern := range e.Commands {
		cmdAndArgs := strings.SplitN(pattern, " ", 2)
		if len(cmdAndArgs) == 0 {
			continue
		}

		matches, err := filepath.Glob(cmdAndArgs[0])
		if err != nil {
			acc.AddError(err)
			continue
		}

		if len(matches) == 0 {
			// There were no matches with the glob pattern, so let's assume
			// that the command is in PATH and just run it as it is
			commands = append(commands, pattern)
		} else {
			// There were matches, so we'll append each match together with
			// the arguments to the commands slice
			for _, match := range matches {
				if len(cmdAndArgs) == 1 {
					commands = append(commands, match)
				} else {
					commands = append(commands,
						strings.Join([]string{match, cmdAndArgs[1]}, " "))
				}
			}
		}
	}

	wg.Add(len(commands))
	for _, command := range commands {
		go e.ProcessCommand(command, acc, &wg)
	}
	wg.Wait()
	return nil
}

func (e *Exec) Init() error {
	return nil
}

func nagiosHandler(metrics []telegraf.Metric, err error, msg []byte) []telegraf.Metric {
	return nagios.AddState(err, msg, metrics)
}

func init() {
	inputs.Add("exec", func() telegraf.Input {
		return NewExec()
	})
}
