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package terminal

import (
	"errors"
	"io"
	"os"
	"path/filepath"
	"runtime"
	"strings"
	"testing"
	"time"
)

// skipWithoutPTY skips a test where a pseudo-terminal cannot be opened.
func skipWithoutPTY(t *testing.T) {
	t.Helper()

	// These tests speak to /bin/sh and stty; Windows has a pseudo-console
	// but neither of those, so they are Unix tests whatever the platform
	// supports.
	if runtime.GOOS != "linux" && runtime.GOOS != "darwin" {
		t.Skipf("these tests drive a Unix shell; not on %s", runtime.GOOS)
	}
	if _, err := os.Stat("/dev/ptmx"); err != nil {
		t.Skipf("no /dev/ptmx here: %v", err)
	}
}

// startSession opens a session running a bare shell, closed when the test ends.
func startSession(t *testing.T, options Options) *Session {
	t.Helper()
	skipWithoutPTY(t)

	if options.Shell == "" {
		options.Shell = "/bin/sh"
	}
	if options.Width == 0 {
		options.Width, options.Height = 80, 24
	}

	session, err := Start(options)
	if err != nil {
		t.Fatalf("Start() error = %v", err)
	}
	t.Cleanup(func() { session.Close() })
	return session
}

// readUntil reads from a session until the text appears or time runs out. It
// returns everything read, so a failure can show what did arrive.
func readUntil(t *testing.T, session *Session, want string) string {
	t.Helper()

	found := make(chan string, 1)
	go func() {
		var seen strings.Builder
		buffer := make([]byte, 4096)
		for {
			n, err := session.Read(buffer)
			if n > 0 {
				seen.Write(buffer[:n])
				if strings.Contains(seen.String(), want) {
					found <- seen.String()
					return
				}
			}
			if err != nil {
				found <- seen.String()
				return
			}
		}
	}()

	select {
	case seen := <-found:
		if !strings.Contains(seen, want) {
			t.Fatalf("the shell never wrote %q; it wrote %q", want, seen)
		}
		return seen
	case <-time.After(10 * time.Second):
		t.Fatalf("timed out waiting for %q", want)
		return ""
	}
}

func TestAShellRunsAndItsOutputComesBack(t *testing.T) {
	session := startSession(t, Options{})

	if _, err := session.Write([]byte("echo hello-from-the-pty\n")); err != nil {
		t.Fatalf("Write() error = %v", err)
	}

	readUntil(t, session, "hello-from-the-pty")
}

func TestTheShellStartsInTheDirectoryItWasGiven(t *testing.T) {
	directory := t.TempDir()
	// macOS reports /tmp through a symlink, so the name is what can be checked
	// rather than the whole path.
	marker := filepath.Base(directory)
	session := startSession(t, Options{Dir: directory})

	session.Write([]byte("pwd\n")) //nolint:errcheck

	readUntil(t, session, marker)
}

func TestTheShellIsToldWhichTerminalItHas(t *testing.T) {
	session := startSession(t, Options{})

	session.Write([]byte("echo \"[$TERM]\"\n")) //nolint:errcheck

	readUntil(t, session, "["+TermName+"]")
}

func TestTheShellIsToldItsSize(t *testing.T) {
	session := startSession(t, Options{Width: 100, Height: 40})

	// stty reads the size from the terminal itself, so this is the size the
	// kernel really recorded rather than the one we asked for.
	session.Write([]byte("stty size\n")) //nolint:errcheck

	readUntil(t, session, "40 100")
}

func TestResizeIsPassedOnToTheShell(t *testing.T) {
	session := startSession(t, Options{Width: 80, Height: 24})
	session.Write([]byte("echo ready\n")) //nolint:errcheck
	readUntil(t, session, "ready")

	if err := session.Resize(132, 50); err != nil {
		t.Fatalf("Resize() error = %v", err)
	}
	session.Write([]byte("stty size\n")) //nolint:errcheck

	readUntil(t, session, "50 132")
}

func TestResizeRefusesNothingSmallerThanOneCell(t *testing.T) {
	session := startSession(t, Options{})

	if err := session.Resize(0, -5); err != nil {
		t.Errorf("Resize() error = %v, want a size below one to be raised rather than refused", err)
	}
}

func TestTheShellSeesATerminalAndNotAPipe(t *testing.T) {
	// This is the whole point of a pseudo-terminal: a shell behind a pipe
	// turns off its prompt, its colours and its job control.
	session := startSession(t, Options{})

	session.Write([]byte("test -t 0 && echo is-a-terminal\n")) //nolint:errcheck

	readUntil(t, session, "is-a-terminal")
}

func TestCommandNamesTheShell(t *testing.T) {
	session := startSession(t, Options{Shell: "/bin/sh"})

	if got := session.Command(); got != "sh" {
		t.Errorf("Command() = %q, want %q", got, "sh")
	}
}

func TestClosingEndsTheShell(t *testing.T) {
	session := startSession(t, Options{})
	session.Write([]byte("echo started\n")) //nolint:errcheck
	readUntil(t, session, "started")

	if err := session.Close(); err != nil {
		t.Errorf("Close() error = %v", err)
	}

	// Reading a closed session must fail rather than block for ever.
	done := make(chan struct{})
	go func() {
		session.Read(make([]byte, 16)) //nolint:errcheck
		close(done)
	}()

	select {
	case <-done:
	case <-time.After(5 * time.Second):
		t.Error("reading a closed session did not return")
	}
}

func TestTheOutputOfARealShellDrivesTheEmulator(t *testing.T) {
	// The three pieces together: a shell writes escape sequences into a
	// pseudo-terminal, the parser reads them, and the screen shows the result.
	session := startSession(t, Options{Width: 40, Height: 10})
	screen := NewScreen(40, 10)
	parser := NewParser(screen)

	// clear puts the cursor home and erases; the text then lands on row 0
	// wherever the prompt had got to.
	session.Write([]byte("clear; printf 'plain \\033[1;31mred\\033[0m\\n'\n")) //nolint:errcheck
	readUntil(t, session, "red")

	// Everything the shell has written by now is replayed into the emulator.
	session.Write([]byte("exit\n")) //nolint:errcheck
	drain(t, session, parser)

	if !screenContains(screen, "plain red") {
		t.Errorf("the screen never showed the line; it shows:\n%s", screenText(screen))
	}
}

func TestStartRefusesAShellThatIsNotThere(t *testing.T) {
	skipWithoutPTY(t)

	_, err := Start(Options{Shell: "/nonexistent/shell", Width: 20, Height: 5})

	if err == nil {
		t.Fatal("Start() error = nil for a shell that does not exist")
	}
}

func TestUnsupportedPlatformsSaySo(t *testing.T) {
	if runtime.GOOS == "linux" || runtime.GOOS == "darwin" || runtime.GOOS == "windows" {
		t.Skip("this platform is supported")
	}

	_, err := Start(Options{Width: 20, Height: 5})

	if !errors.Is(err, ErrUnsupported) {
		t.Errorf("Start() error = %v, want ErrUnsupported", err)
	}
}

func TestTheEnvironmentAlwaysCarriesOurTerm(t *testing.T) {
	got := environment([]string{"PATH=/bin", "TERM=something-else", "HOME=/tmp"})

	var terms []string
	for _, entry := range got {
		if strings.HasPrefix(entry, "TERM=") {
			terms = append(terms, entry)
		}
	}

	if len(terms) != 1 || terms[0] != "TERM="+TermName {
		t.Errorf("the environment carries %v, want exactly TERM=%s", terms, TermName)
	}
	if !slicesContain(got, "PATH=/bin") || !slicesContain(got, "HOME=/tmp") {
		t.Errorf("the environment lost entries it should have kept: %v", got)
	}
}

// drain reads whatever is left of a session into a parser, until the shell has
// gone or time runs out.
func drain(t *testing.T, session *Session, parser *Parser) {
	t.Helper()

	done := make(chan struct{})
	go func() {
		io.Copy(parser, session) //nolint:errcheck
		close(done)
	}()

	select {
	case <-done:
	case <-time.After(10 * time.Second):
		t.Fatal("the shell did not finish")
	}
}

// screenContains reports whether any row of a screen holds the text.
func screenContains(s *Screen, text string) bool {
	_, height := s.Size()
	for row := range height {
		if strings.Contains(s.LineText(row), text) {
			return true
		}
	}
	return false
}

// screenText renders a whole screen, for a failure message.
func screenText(s *Screen) string {
	_, height := s.Size()
	rows := make([]string, height)
	for row := range height {
		rows[row] = s.LineText(row)
	}
	return strings.Join(rows, "\n")
}

// slicesContain reports whether a slice holds a value.
func slicesContain(list []string, want string) bool {
	for _, item := range list {
		if item == want {
			return true
		}
	}
	return false
}

func TestArgsRunOneCommandRatherThanAShell(t *testing.T) {
	// This is what lets a menu item run "go test ./..." in a window instead of
	// dropping the user into a shell and leaving them to type it.
	session := startSession(t, Options{
		Shell: "/bin/sh",
		Args:  []string{"-c", "echo one''-command-ran"},
	})

	if got := readUntil(t, session, "one-command-ran"); !strings.Contains(got, "one-command-ran") {
		t.Errorf("the command did not run; the session gave %q", got)
	}
}

func TestASessionWithNoArgsIsStillAnInteractiveShell(t *testing.T) {
	session := startSession(t, Options{Shell: "/bin/sh"})

	if _, err := session.Write([]byte("echo still''-interactive\r")); err != nil {
		t.Fatalf("writing to the shell: %v", err)
	}
	if got := readUntil(t, session, "still-interactive"); !strings.Contains(got, "still-interactive") {
		t.Errorf("the shell is not interactive; it gave %q", got)
	}
}