// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package scripttest adapts the script engine for use in tests.
package scripttest

import (
	"bufio"
	"cmd/go/internal/cfg"
	"cmd/go/internal/script"
	"errors"
	"io"
	"strings"
	"testing"
)

// DefaultCmds returns a set of broadly useful script commands.
//
// This set includes all of the commands in script.DefaultCmds,
// as well as a "skip" command that halts the script and causes the
// testing.TB passed to Run to be skipped.
func DefaultCmds() map[string]script.Cmd {
	cmds := script.DefaultCmds()
	cmds["skip"] = Skip()
	return cmds
}

// DefaultConds returns a set of broadly useful script conditions.
//
// This set includes all of the conditions in script.DefaultConds,
// as well as:
//
//   - Conditions of the form "exec:foo" are active when the executable "foo" is
//     found in the test process's PATH, and inactive when the executable is
//     not found.
//
//   - "short" is active when testing.Short() is true.
//
//   - "verbose" is active when testing.Verbose() is true.
func DefaultConds() map[string]script.Cond {
	conds := script.DefaultConds()
	conds["exec"] = CachedExec()
	conds["short"] = script.BoolCondition("testing.Short()", testing.Short())
	conds["verbose"] = script.BoolCondition("testing.Verbose()", testing.Verbose())
	return conds
}

// Run runs the script from the given filename starting at the given initial state.
// When the script completes, Run closes the state.
func Run(t testing.TB, e *script.Engine, s *script.State, filename string, testScript io.Reader) {
	t.Helper()
	err := func() (err error) {
		log := new(strings.Builder)
		log.WriteString("\n") // Start output on a new line for consistent indentation.

		// Defer writing to the test log in case the script engine panics during execution,
		// but write the log before we write the final "skip" or "FAIL" line.
		t.Helper()
		defer func() {
			t.Helper()

			if closeErr := s.CloseAndWait(log); err == nil {
				err = closeErr
			}

			if log.Len() > 0 {
				t.Log(strings.TrimSuffix(log.String(), "\n"))
			}
		}()

		if testing.Verbose() {
			// Add the environment to the start of the script log.
			wait, err := script.Env().Run(s)
			if err != nil {
				t.Fatal(err)
			}
			if wait != nil {
				stdout, stderr, err := wait(s)
				if err != nil {
					t.Fatalf("env: %v\n%s", err, stderr)
				}
				if len(stdout) > 0 {
					s.Logf("%s\n", stdout)
				}
			}
		}

		return e.Execute(s, filename, bufio.NewReader(testScript), log)
	}()

	if skip := (skipError{}); errors.As(err, &skip) {
		if skip.msg == "" {
			t.Skip("SKIP")
		} else {
			t.Skipf("SKIP: %v", skip.msg)
		}
	}
	if err != nil {
		t.Errorf("FAIL: %v", err)
	}
}

// Skip returns a sentinel error that causes Run to mark the test as skipped.
func Skip() script.Cmd {
	return script.Command(
		script.CmdUsage{
			Summary: "skip the current test",
			Args:    "[msg]",
		},
		func(_ *script.State, args ...string) (script.WaitFunc, error) {
			if len(args) > 1 {
				return nil, script.ErrUsage
			}
			if len(args) == 0 {
				return nil, skipError{""}
			}
			return nil, skipError{args[0]}
		})
}

type skipError struct {
	msg string
}

func (s skipError) Error() string {
	if s.msg == "" {
		return "skip"
	}
	return s.msg
}

// CachedExec returns a Condition that reports whether the PATH of the test
// binary itself (not the script's current environment) contains the named
// executable.
func CachedExec() script.Cond {
	return script.CachedCondition(
		"<suffix> names an executable in the test binary's PATH",
		func(name string) (bool, error) {
			_, err := cfg.LookPath(name)
			return err == nil, nil
		})
}