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 IOStreams struct {
	In     io.ReadCloser
	Out    io.Writer
	ErrOut io.Writer

	// the original (non-colorable) output stream
	originalOut   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 = &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
	}

	_ = 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
	out := s.Out
	if s.originalOut != nil {
		out = s.originalOut
	}

	if w, _, err := terminalSize(out); err == nil {
		return w
	}

	if isCygwinTerminal(out) {
		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)

	isVirtualTerminal := false
	if stdoutIsTTY {
		if err := enableVirtualTerminalProcessing(os.Stdout); err == nil {
			isVirtualTerminal = true
		}
	}

	io := &IOStreams{
		In:           os.Stdin,
		originalOut:  os.Stdout,
		Out:          colorable.NewColorable(os.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{}
	return &IOStreams{
		In:     io.NopCloser(in),
		Out:    out,
		ErrOut: errOut,
		ttySize: func() (int, int, error) {
			return -1, -1, errors.New("ttySize not implemented in tests")
		},
	}, in, out, errOut
}

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

func isCygwinTerminal(w io.Writer) bool {
	if f, isFile := w.(*os.File); isFile {
		return isatty.IsCygwinTerminal(f.Fd())
	}
	return false
}

// terminalSize measures the viewport of the terminal that the output stream is connected to
func terminalSize(w io.Writer) (int, int, error) {
	if f, isFile := w.(*os.File); isFile {
		return term.GetSize(int(f.Fd()))
	}
	return 0, 0, fmt.Errorf("%v is not a file", w)
}

// 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
}