package iostreams

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"os/signal"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/briandowns/spinner"
	"github.com/cli/safeexec"
	"github.com/google/shlex"
	"github.com/mattn/go-colorable"
	"github.com/mattn/go-isatty"
	"github.com/muesli/termenv"
	"golang.org/x/term"
)

const DefaultWidth = 80

// ErrClosedPagerPipe is the error returned when writing to a pager that has been closed.
type ErrClosedPagerPipe struct {
	error
}

type fileWriter interface {
	io.Writer
	Fd() uintptr
}

type fileReader interface {
	io.ReadCloser
	Fd() uintptr
}

type IOStreams struct {
	In     fileReader
	Out    fileWriter
	ErrOut io.Writer

	colorEnabled  bool
	is256enabled  bool
	hasTrueColor  bool
	terminalTheme string

	progressIndicatorEnabled bool
	progressIndicator        *spinner.Spinner
	progressIndicatorMu      sync.Mutex

	alternateScreenBufferEnabled bool
	alternateScreenBufferActive  bool
	alternateScreenBufferMu      sync.Mutex

	stdinTTYOverride  bool
	stdinIsTTY        bool
	stdoutTTYOverride bool
	stdoutIsTTY       bool
	stderrTTYOverride bool
	stderrIsTTY       bool
	termWidthOverride int
	ttySize           func() (int, int, error)

	pagerCommand string
	pagerProcess *os.Process

	neverPrompt bool

	TempFileOverride *os.File
}

func (s *IOStreams) ColorEnabled() bool {
	return s.colorEnabled
}

func (s *IOStreams) ColorSupport256() bool {
	return s.is256enabled
}

func (s *IOStreams) HasTrueColor() bool {
	return s.hasTrueColor
}

// DetectTerminalTheme is a utility to call before starting the output pager so that the terminal background
// can be reliably detected.
func (s *IOStreams) DetectTerminalTheme() {
	if !s.ColorEnabled() {
		s.terminalTheme = "none"
		return
	}

	if s.pagerProcess != nil {
		s.terminalTheme = "none"
		return
	}

	style := os.Getenv("GLAMOUR_STYLE")
	if style != "" && style != "auto" {
		s.terminalTheme = "none"
		return
	}

	if termenv.HasDarkBackground() {
		s.terminalTheme = "dark"
		return
	}

	s.terminalTheme = "light"
}

// TerminalTheme returns "light", "dark", or "none" depending on the background color of the terminal.
func (s *IOStreams) TerminalTheme() string {
	if s.terminalTheme == "" {
		s.DetectTerminalTheme()
	}

	return s.terminalTheme
}

func (s *IOStreams) SetColorEnabled(colorEnabled bool) {
	s.colorEnabled = colorEnabled
}

func (s *IOStreams) SetStdinTTY(isTTY bool) {
	s.stdinTTYOverride = true
	s.stdinIsTTY = isTTY
}

func (s *IOStreams) IsStdinTTY() bool {
	if s.stdinTTYOverride {
		return s.stdinIsTTY
	}
	if stdin, ok := s.In.(*os.File); ok {
		return isTerminal(stdin)
	}
	return false
}

func (s *IOStreams) SetStdoutTTY(isTTY bool) {
	s.stdoutTTYOverride = true
	s.stdoutIsTTY = isTTY
}

func (s *IOStreams) IsStdoutTTY() bool {
	if s.stdoutTTYOverride {
		return s.stdoutIsTTY
	}
	if stdout, ok := s.Out.(*os.File); ok {
		return isTerminal(stdout)
	}
	return false
}

func (s *IOStreams) SetStderrTTY(isTTY bool) {
	s.stderrTTYOverride = true
	s.stderrIsTTY = isTTY
}

func (s *IOStreams) IsStderrTTY() bool {
	if s.stderrTTYOverride {
		return s.stderrIsTTY
	}
	if stderr, ok := s.ErrOut.(*os.File); ok {
		return isTerminal(stderr)
	}
	return false
}

func (s *IOStreams) SetPager(cmd string) {
	s.pagerCommand = cmd
}

func (s *IOStreams) GetPager() string {
	return s.pagerCommand
}

func (s *IOStreams) StartPager() error {
	if s.pagerCommand == "" || s.pagerCommand == "cat" || !s.IsStdoutTTY() {
		return nil
	}

	pagerArgs, err := shlex.Split(s.pagerCommand)
	if err != nil {
		return err
	}

	pagerEnv := os.Environ()
	for i := len(pagerEnv) - 1; i >= 0; i-- {
		if strings.HasPrefix(pagerEnv[i], "PAGER=") {
			pagerEnv = append(pagerEnv[0:i], pagerEnv[i+1:]...)
		}
	}
	if _, ok := os.LookupEnv("LESS"); !ok {
		pagerEnv = append(pagerEnv, "LESS=FRX")
	}
	if _, ok := os.LookupEnv("LV"); !ok {
		pagerEnv = append(pagerEnv, "LV=-c")
	}

	pagerExe, err := safeexec.LookPath(pagerArgs[0])
	if err != nil {
		return err
	}
	pagerCmd := exec.Command(pagerExe, pagerArgs[1:]...)
	pagerCmd.Env = pagerEnv
	pagerCmd.Stdout = s.Out
	pagerCmd.Stderr = s.ErrOut
	pagedOut, err := pagerCmd.StdinPipe()
	if err != nil {
		return err
	}
	s.Out = &fdWriteCloser{
		fd:          s.Out.Fd(),
		WriteCloser: &pagerWriter{pagedOut},
	}
	err = pagerCmd.Start()
	if err != nil {
		return err
	}
	s.pagerProcess = pagerCmd.Process
	return nil
}

func (s *IOStreams) StopPager() {
	if s.pagerProcess == nil {
		return
	}

	// if a pager was started, we're guaranteed to have a WriteCloser
	_ = s.Out.(io.WriteCloser).Close()
	_, _ = s.pagerProcess.Wait()
	s.pagerProcess = nil
}

func (s *IOStreams) CanPrompt() bool {
	if s.neverPrompt {
		return false
	}

	return s.IsStdinTTY() && s.IsStdoutTTY()
}

func (s *IOStreams) GetNeverPrompt() bool {
	return s.neverPrompt
}

func (s *IOStreams) SetNeverPrompt(v bool) {
	s.neverPrompt = v
}

func (s *IOStreams) StartProgressIndicator() {
	s.StartProgressIndicatorWithLabel("")
}

func (s *IOStreams) StartProgressIndicatorWithLabel(label string) {
	if !s.progressIndicatorEnabled {
		return
	}

	s.progressIndicatorMu.Lock()
	defer s.progressIndicatorMu.Unlock()

	if s.progressIndicator != nil {
		if label == "" {
			s.progressIndicator.Prefix = ""
		} else {
			s.progressIndicator.Prefix = label + " "
		}
		return
	}

	// https://github.com/briandowns/spinner#available-character-sets
	dotStyle := spinner.CharSets[11]
	sp := spinner.New(dotStyle, 120*time.Millisecond, spinner.WithWriter(s.ErrOut), spinner.WithColor("fgCyan"))
	if label != "" {
		sp.Prefix = label + " "
	}

	sp.Start()
	s.progressIndicator = sp
}

func (s *IOStreams) StopProgressIndicator() {
	s.progressIndicatorMu.Lock()
	defer s.progressIndicatorMu.Unlock()
	if s.progressIndicator == nil {
		return
	}
	s.progressIndicator.Stop()
	s.progressIndicator = nil
}

func (s *IOStreams) StartAlternateScreenBuffer() {
	if s.alternateScreenBufferEnabled {
		s.alternateScreenBufferMu.Lock()
		defer s.alternateScreenBufferMu.Unlock()

		if _, err := fmt.Fprint(s.Out, "\x1b[?1049h"); err == nil {
			s.alternateScreenBufferActive = true

			ch := make(chan os.Signal, 1)
			signal.Notify(ch, os.Interrupt)

			go func() {
				<-ch
				s.StopAlternateScreenBuffer()

				os.Exit(1)
			}()
		}
	}
}

func (s *IOStreams) StopAlternateScreenBuffer() {
	s.alternateScreenBufferMu.Lock()
	defer s.alternateScreenBufferMu.Unlock()

	if s.alternateScreenBufferActive {
		fmt.Fprint(s.Out, "\x1b[?1049l")
		s.alternateScreenBufferActive = false
	}
}

func (s *IOStreams) SetAlternateScreenBufferEnabled(enabled bool) {
	s.alternateScreenBufferEnabled = enabled
}

func (s *IOStreams) RefreshScreen() {
	if s.stdoutIsTTY {
		// Move cursor to 0,0
		fmt.Fprint(s.Out, "\x1b[0;0H")
		// Clear from cursor to bottom of screen
		fmt.Fprint(s.Out, "\x1b[J")
	}
}

// TerminalWidth returns the width of the terminal that stdout is attached to.
// TODO: investigate whether ProcessTerminalWidth could replace all this.
func (s *IOStreams) TerminalWidth() int {
	if s.termWidthOverride > 0 {
		return s.termWidthOverride
	}

	defaultWidth := DefaultWidth

	if w, _, err := terminalSize(s.Out.Fd()); err == nil {
		return w
	}

	if isCygwinTerminal(s.Out.Fd()) {
		tputExe, err := safeexec.LookPath("tput")
		if err != nil {
			return defaultWidth
		}
		tputCmd := exec.Command(tputExe, "cols")
		tputCmd.Stdin = os.Stdin
		if out, err := tputCmd.Output(); err == nil {
			if w, err := strconv.Atoi(strings.TrimSpace(string(out))); err == nil {
				return w
			}
		}
	}

	return defaultWidth
}

// ProcessTerminalWidth returns the width of the terminal that the process is attached to.
func (s *IOStreams) ProcessTerminalWidth() int {
	w, _, err := s.ttySize()
	if err != nil {
		return DefaultWidth
	}
	return w
}

func (s *IOStreams) ForceTerminal(spec string) {
	s.colorEnabled = !EnvColorDisabled()
	s.SetStdoutTTY(true)

	if w, err := strconv.Atoi(spec); err == nil {
		s.termWidthOverride = w
		return
	}

	ttyWidth, _, err := s.ttySize()
	if err != nil {
		return
	}
	s.termWidthOverride = ttyWidth

	if strings.HasSuffix(spec, "%") {
		if p, err := strconv.Atoi(spec[:len(spec)-1]); err == nil {
			s.termWidthOverride = int(float64(s.termWidthOverride) * (float64(p) / 100))
		}
	}
}

func (s *IOStreams) ColorScheme() *ColorScheme {
	return NewColorScheme(s.ColorEnabled(), s.ColorSupport256(), s.HasTrueColor())
}

func (s *IOStreams) ReadUserFile(fn string) ([]byte, error) {
	var r io.ReadCloser
	if fn == "-" {
		r = s.In
	} else {
		var err error
		r, err = os.Open(fn)
		if err != nil {
			return nil, err
		}
	}
	defer r.Close()
	return io.ReadAll(r)
}

func (s *IOStreams) TempFile(dir, pattern string) (*os.File, error) {
	if s.TempFileOverride != nil {
		return s.TempFileOverride, nil
	}
	return os.CreateTemp(dir, pattern)
}

func System() *IOStreams {
	stdoutIsTTY := isTerminal(os.Stdout)
	stderrIsTTY := isTerminal(os.Stderr)

	var stdout fileWriter = os.Stdout
	isVirtualTerminal := false
	if stdoutIsTTY {
		// enables ANSI escape sequences on modern Windows
		if err := enableVirtualTerminalProcessing(os.Stdout.Fd()); err == nil {
			isVirtualTerminal = true
		} else {
			// as a fallback, translate ANSI escape sequences to Windows console syscalls
			colorableStdout := colorable.NewColorable(os.Stdout)
			if colorableStdout != os.Stdout {
				// ensure that the file descriptor of the original stdout is preserved
				stdout = &fdWriter{
					fd:     os.Stdout.Fd(),
					Writer: colorableStdout,
				}
			}
		}
	}

	io := &IOStreams{
		In:           os.Stdin,
		Out:          stdout,
		ErrOut:       colorable.NewColorable(os.Stderr),
		colorEnabled: EnvColorForced() || (!EnvColorDisabled() && stdoutIsTTY),
		is256enabled: isVirtualTerminal || Is256ColorSupported(),
		hasTrueColor: isVirtualTerminal || IsTrueColorSupported(),
		pagerCommand: os.Getenv("PAGER"),
		ttySize:      ttySize,
	}

	if stdoutIsTTY && stderrIsTTY {
		io.progressIndicatorEnabled = true
	}

	if stdoutIsTTY && isVirtualTerminal {
		io.alternateScreenBufferEnabled = true
	}

	// prevent duplicate isTerminal queries now that we know the answer
	io.SetStdoutTTY(stdoutIsTTY)
	io.SetStderrTTY(stderrIsTTY)
	return io
}

func Test() (*IOStreams, *bytes.Buffer, *bytes.Buffer, *bytes.Buffer) {
	in := &bytes.Buffer{}
	out := &bytes.Buffer{}
	errOut := &bytes.Buffer{}
	io := &IOStreams{
		In: &fdReader{
			fd:         0,
			ReadCloser: io.NopCloser(in),
		},
		Out:    &fdWriter{fd: 1, Writer: out},
		ErrOut: errOut,
		ttySize: func() (int, int, error) {
			return -1, -1, errors.New("ttySize not implemented in tests")
		},
	}
	io.SetStdinTTY(false)
	io.SetStdoutTTY(false)
	io.SetStderrTTY(false)
	return io, in, out, errOut
}

func isTerminal(f *os.File) bool {
	return isatty.IsTerminal(f.Fd()) || isatty.IsCygwinTerminal(f.Fd())
}

func isCygwinTerminal(fd uintptr) bool {
	return isatty.IsCygwinTerminal(fd)
}

// terminalSize measures the viewport of the terminal that the output stream is connected to
func terminalSize(fd uintptr) (int, int, error) {
	return term.GetSize(int(fd))
}

// pagerWriter implements a WriteCloser that wraps all EPIPE errors in an ErrClosedPagerPipe type.
type pagerWriter struct {
	io.WriteCloser
}

func (w *pagerWriter) Write(d []byte) (int, error) {
	n, err := w.WriteCloser.Write(d)
	if err != nil && (errors.Is(err, io.ErrClosedPipe) || isEpipeError(err)) {
		return n, &ErrClosedPagerPipe{err}
	}
	return n, err
}

// fdWriter represents a wrapped stdout Writer that preserves the original file descriptor
type fdWriter struct {
	io.Writer
	fd uintptr
}

func (w *fdWriter) Fd() uintptr {
	return w.fd
}

// fdWriteCloser represents a wrapped stdout Writer that preserves the original file descriptor
type fdWriteCloser struct {
	io.WriteCloser
	fd uintptr
}

func (w *fdWriteCloser) Fd() uintptr {
	return w.fd
}

// fdWriter represents a wrapped stdin ReadCloser that preserves the original file descriptor
type fdReader struct {
	io.ReadCloser
	fd uintptr
}

func (r *fdReader) Fd() uintptr {
	return r.fd
}