package iostreams

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

	"github.com/briandowns/spinner"
	ghTerm "github.com/cli/go-gh/v2/pkg/term"
	"github.com/cli/safeexec"
	"github.com/google/shlex"
	"github.com/mattn/go-colorable"
	"github.com/mattn/go-isatty"
)

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 term interface {
	IsTerminalOutput() bool
	IsColorEnabled() bool
	Is256ColorSupported() bool
	IsTrueColorSupported() bool
	Theme() string
	Size() (int, int, error)
}

type IOStreams struct {
	term term

	In     fileReader
	Out    fileWriter
	ErrOut fileWriter

	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

	colorOverride           bool
	colorEnabled            bool
	colorLabels             bool
	accessibleColorsEnabled bool

	pagerCommand string
	pagerProcess *os.Process

	neverPrompt bool

	TempFileOverride *os.File
}

func (s *IOStreams) ColorEnabled() bool {
	if s.colorOverride {
		return s.colorEnabled
	}
	return s.term.IsColorEnabled()
}

func (s *IOStreams) ColorSupport256() bool {
	if s.colorOverride {
		return s.colorEnabled
	}
	return s.term.Is256ColorSupported()
}

func (s *IOStreams) HasTrueColor() bool {
	if s.colorOverride {
		return s.colorEnabled
	}
	return s.term.IsTrueColorSupported()
}

func (s *IOStreams) ColorLabels() bool {
	return s.colorLabels
}

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

	style := os.Getenv("GLAMOUR_STYLE")
	if style != "" && style != "auto" {
		// ensure GLAMOUR_STYLE takes precedence over "light" and "dark" themes
		s.terminalTheme = "none"
		return
	}

	s.terminalTheme = s.term.Theme()
}

// 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.colorOverride = true
	s.colorEnabled = colorEnabled
}

func (s *IOStreams) SetColorLabels(colorLabels bool) {
	s.colorLabels = colorLabels
}

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
	}
	// support GH_FORCE_TTY
	if s.term.IsTerminalOutput() {
		return true
	}
	stdout, ok := s.Out.(*os.File)
	return ok && isCygwinTerminal(stdout.Fd())
}

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) RunWithProgress(label string, run func() error) error {
	s.StartProgressIndicatorWithLabel(label)
	defer s.StopProgressIndicator()

	return run()
}

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.IsStdoutTTY() {
		// 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 controls the process
func (s *IOStreams) TerminalWidth() int {
	w, _, err := s.term.Size()
	if err == nil && w > 0 {
		return w
	}
	return DefaultWidth
}

func (s *IOStreams) ColorScheme() *ColorScheme {
	return &ColorScheme{
		Enabled:       s.ColorEnabled(),
		EightBitColor: s.ColorSupport256(),
		TrueColor:     s.HasTrueColor(),
		Accessible:    s.AccessibleColorsEnabled(),
		ColorLabels:   s.ColorLabels(),
		Theme:         s.TerminalTheme(),
	}
}

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 (s *IOStreams) SetAccessibleColorsEnabled(enabled bool) {
	s.accessibleColorsEnabled = enabled
}

func (s *IOStreams) AccessibleColorsEnabled() bool {
	return s.accessibleColorsEnabled
}

func System() *IOStreams {
	terminal := ghTerm.FromEnv()

	var stdout fileWriter = os.Stdout
	// On Windows with no virtual terminal processing support, translate ANSI escape
	// sequences to console syscalls.
	if colorableStdout := colorable.NewColorable(os.Stdout); colorableStdout != os.Stdout {
		// Ensure that the file descriptor of the original stdout is preserved.
		stdout = &fdWriter{
			fd:     os.Stdout.Fd(),
			Writer: colorableStdout,
		}
	}

	var stderr fileWriter = os.Stderr
	// On Windows with no virtual terminal processing support, translate ANSI escape
	// sequences to console syscalls.
	if colorableStderr := colorable.NewColorable(os.Stderr); colorableStderr != os.Stderr {
		// Ensure that the file descriptor of the original stderr is preserved.
		stderr = &fdWriter{
			fd:     os.Stderr.Fd(),
			Writer: colorableStderr,
		}
	}

	io := &IOStreams{
		In:           os.Stdin,
		Out:          stdout,
		ErrOut:       stderr,
		pagerCommand: os.Getenv("PAGER"),
		term:         &terminal,
	}

	stdoutIsTTY := io.IsStdoutTTY()
	stderrIsTTY := io.IsStderrTTY()

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

	if stdoutIsTTY && hasAlternateScreenBuffer(terminal.IsTrueColorSupported()) {
		io.alternateScreenBufferEnabled = true
	}

	return io
}

type fakeTerm struct{}

func (t fakeTerm) IsTerminalOutput() bool {
	return false
}

func (t fakeTerm) IsColorEnabled() bool {
	return false
}

func (t fakeTerm) Is256ColorSupported() bool {
	return false
}

func (t fakeTerm) IsTrueColorSupported() bool {
	return false
}

func (t fakeTerm) Theme() string {
	return ""
}

func (t fakeTerm) Size() (int, int, error) {
	return 80, -1, nil
}

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: &fdWriter{fd: 2, Writer: errOut},
		term:   &fakeTerm{},
	}
	io.SetStdinTTY(false)
	io.SetStdoutTTY(false)
	io.SetStderrTTY(false)
	return io, in, out, errOut
}

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

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

// fdReader 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
}