// Copyright 2020 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Package utesting provides a standalone replacement for package testing.
//
// This package exists because package testing cannot easily be embedded into a
// standalone go program. It provides an API that mirrors the standard library
// testing API.
package utesting

import (
	"bytes"
	"fmt"
	"io"
	"regexp"
	"runtime"
	"sync"
	"time"
)

// Test represents a single test.
type Test struct {
	Name string
	Fn   func(*T)
	Slow bool
}

// Result is the result of a test execution.
type Result struct {
	Name     string
	Failed   bool
	Output   string
	Duration time.Duration
}

// MatchTests returns the tests whose name matches a regular expression.
func MatchTests(tests []Test, expr string) []Test {
	var results []Test
	re, err := regexp.Compile(expr)
	if err != nil {
		return nil
	}
	for _, test := range tests {
		if re.MatchString(test.Name) {
			results = append(results, test)
		}
	}
	return results
}

// RunTests executes all given tests in order and returns their results.
// If the report writer is non-nil, a test report is written to it in real time.
func RunTests(tests []Test, report io.Writer) []Result {
	if report == nil {
		report = io.Discard
	}
	results := run(tests, newConsoleOutput(report))
	fails := CountFailures(results)
	fmt.Fprintf(report, "%v/%v tests passed.\n", len(tests)-fails, len(tests))
	return results
}

// RunTAP runs the given tests and writes Test Anything Protocol output
// to the report writer.
func RunTAP(tests []Test, report io.Writer) []Result {
	return run(tests, newTAP(report, len(tests)))
}

func run(tests []Test, output testOutput) []Result {
	var results = make([]Result, len(tests))
	for i, test := range tests {
		buffer := new(bytes.Buffer)
		logOutput := io.MultiWriter(buffer, output)

		output.testStart(test.Name)
		start := time.Now()
		results[i].Name = test.Name
		results[i].Failed = runTest(test, logOutput)
		results[i].Duration = time.Since(start)
		results[i].Output = buffer.String()
		output.testResult(results[i])
	}
	return results
}

// testOutput is implemented by output formats.
type testOutput interface {
	testStart(name string)
	Write([]byte) (int, error)
	testResult(Result)
}

// consoleOutput prints test results similarly to go test.
type consoleOutput struct {
	out         io.Writer
	indented    *indentWriter
	curTest     string
	wroteHeader bool
}

func newConsoleOutput(w io.Writer) *consoleOutput {
	return &consoleOutput{
		out:      w,
		indented: newIndentWriter(" ", w),
	}
}

// testStart signals the start of a new test.
func (c *consoleOutput) testStart(name string) {
	c.curTest = name
	c.wroteHeader = false
}

// Write handles test log output.
func (c *consoleOutput) Write(b []byte) (int, error) {
	if !c.wroteHeader {
		// This is the first output line from the test. Print a "-- RUN" header.
		fmt.Fprintln(c.out, "-- RUN", c.curTest)
		c.wroteHeader = true
	}
	return c.indented.Write(b)
}

// testResult prints the final test result line.
func (c *consoleOutput) testResult(r Result) {
	c.indented.flush()
	pd := r.Duration.Truncate(100 * time.Microsecond)
	if r.Failed {
		fmt.Fprintf(c.out, "-- FAIL %s (%v)\n", r.Name, pd)
	} else {
		fmt.Fprintf(c.out, "-- OK %s (%v)\n", r.Name, pd)
	}
}

// tapOutput produces Test Anything Protocol v13 output.
type tapOutput struct {
	out      io.Writer
	indented *indentWriter
	counter  int
}

func newTAP(out io.Writer, numTests int) *tapOutput {
	fmt.Fprintf(out, "1..%d\n", numTests)
	return &tapOutput{
		out:      out,
		indented: newIndentWriter("# ", out),
	}
}

func (t *tapOutput) testStart(name string) {
	t.counter++
}

// Write does nothing for TAP because there is no real-time output of test logs.
func (t *tapOutput) Write(b []byte) (int, error) {
	return len(b), nil
}

func (t *tapOutput) testResult(r Result) {
	status := "ok"
	if r.Failed {
		status = "not ok"
	}
	fmt.Fprintln(t.out, status, t.counter, r.Name)
	t.indented.Write([]byte(r.Output))
	t.indented.flush()
}

// indentWriter indents all written text.
type indentWriter struct {
	out    io.Writer
	indent string
	inLine bool
}

func newIndentWriter(indent string, out io.Writer) *indentWriter {
	return &indentWriter{out: out, indent: indent}
}

func (w *indentWriter) Write(b []byte) (n int, err error) {
	for len(b) > 0 {
		if !w.inLine {
			if _, err = io.WriteString(w.out, w.indent); err != nil {
				return n, err
			}
			w.inLine = true
		}

		end := bytes.IndexByte(b, '\n')
		if end == -1 {
			nn, err := w.out.Write(b)
			n += nn
			return n, err
		}

		line := b[:end+1]
		nn, err := w.out.Write(line)
		n += nn
		if err != nil {
			return n, err
		}
		b = b[end+1:]
		w.inLine = false
	}
	return n, err
}

// flush ensures the current line is terminated.
func (w *indentWriter) flush() {
	if w.inLine {
		fmt.Println(w.out)
		w.inLine = false
	}
}

// CountFailures returns the number of failed tests in the result slice.
func CountFailures(rr []Result) int {
	count := 0
	for _, r := range rr {
		if r.Failed {
			count++
		}
	}
	return count
}

// Run executes a single test.
func Run(test Test) (bool, string) {
	output := new(bytes.Buffer)
	failed := runTest(test, output)
	return failed, output.String()
}

func runTest(test Test, output io.Writer) bool {
	t := &T{output: output}
	done := make(chan struct{})
	go func() {
		defer close(done)
		defer func() {
			if err := recover(); err != nil {
				buf := make([]byte, 4096)
				i := runtime.Stack(buf, false)
				t.Logf("panic: %v\n\n%s", err, buf[:i])
				t.Fail()
			}
		}()
		test.Fn(t)
	}()
	<-done
	return t.failed
}

// T is the value given to the test function. The test can signal failures
// and log output by calling methods on this object.
type T struct {
	mu     sync.Mutex
	failed bool
	output io.Writer
}

// Helper exists for compatibility with testing.T.
func (t *T) Helper() {}

// FailNow marks the test as having failed and stops its execution by calling
// runtime.Goexit (which then runs all deferred calls in the current goroutine).
func (t *T) FailNow() {
	t.Fail()
	runtime.Goexit()
}

// Fail marks the test as having failed but continues execution.
func (t *T) Fail() {
	t.mu.Lock()
	defer t.mu.Unlock()
	t.failed = true
}

// Failed reports whether the test has failed.
func (t *T) Failed() bool {
	t.mu.Lock()
	defer t.mu.Unlock()
	return t.failed
}

// Log formats its arguments using default formatting, analogous to Println, and records
// the text in the error log.
func (t *T) Log(vs ...interface{}) {
	t.mu.Lock()
	defer t.mu.Unlock()
	fmt.Fprintln(t.output, vs...)
}

// Logf formats its arguments according to the format, analogous to Printf, and records
// the text in the error log. A final newline is added if not provided.
func (t *T) Logf(format string, vs ...interface{}) {
	t.mu.Lock()
	defer t.mu.Unlock()
	if len(format) == 0 || format[len(format)-1] != '\n' {
		format += "\n"
	}
	fmt.Fprintf(t.output, format, vs...)
}

// Error is equivalent to Log followed by Fail.
func (t *T) Error(vs ...interface{}) {
	t.Log(vs...)
	t.Fail()
}

// Errorf is equivalent to Logf followed by Fail.
func (t *T) Errorf(format string, vs ...interface{}) {
	t.Logf(format, vs...)
	t.Fail()
}

// Fatal is equivalent to Log followed by FailNow.
func (t *T) Fatal(vs ...interface{}) {
	t.Log(vs...)
	t.FailNow()
}

// Fatalf is equivalent to Logf followed by FailNow.
func (t *T) Fatalf(format string, vs ...interface{}) {
	t.Logf(format, vs...)
	t.FailNow()
}