// Copyright 2018 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 modfile

import (
	"bytes"
	"fmt"
	"io/ioutil"
	"os"
	"os/exec"
	"path/filepath"
	"reflect"
	"strings"
	"testing"
)

// exists reports whether the named file exists.
func exists(name string) bool {
	_, err := os.Stat(name)
	return err == nil
}

// Test that reading and then writing the golden files
// does not change their output.
func TestPrintGolden(t *testing.T) {
	outs, err := filepath.Glob("testdata/*.golden")
	if err != nil {
		t.Fatal(err)
	}
	for _, out := range outs {
		testPrint(t, out, out)
	}
}

// testPrint is a helper for testing the printer.
// It reads the file named in, reformats it, and compares
// the result to the file named out.
func testPrint(t *testing.T, in, out string) {
	data, err := ioutil.ReadFile(in)
	if err != nil {
		t.Error(err)
		return
	}

	golden, err := ioutil.ReadFile(out)
	if err != nil {
		t.Error(err)
		return
	}

	base := "testdata/" + filepath.Base(in)
	f, err := parse(in, data)
	if err != nil {
		t.Error(err)
		return
	}

	ndata := Format(f)

	if !bytes.Equal(ndata, golden) {
		t.Errorf("formatted %s incorrectly: diff shows -golden, +ours", base)
		tdiff(t, string(golden), string(ndata))
		return
	}
}

// Test that when files in the testdata directory are parsed
// and printed and parsed again, we get the same parse tree
// both times.
func TestPrintParse(t *testing.T) {
	outs, err := filepath.Glob("testdata/*")
	if err != nil {
		t.Fatal(err)
	}
	for _, out := range outs {
		data, err := ioutil.ReadFile(out)
		if err != nil {
			t.Error(err)
			continue
		}

		base := "testdata/" + filepath.Base(out)
		f, err := parse(base, data)
		if err != nil {
			t.Errorf("parsing original: %v", err)
			continue
		}

		ndata := Format(f)
		f2, err := parse(base, ndata)
		if err != nil {
			t.Errorf("parsing reformatted: %v", err)
			continue
		}

		eq := eqchecker{file: base}
		if err := eq.check(f, f2); err != nil {
			t.Errorf("not equal: %v", err)
		}

		pf1, err := Parse(base, data)
		if err == nil {
			pf2, err := Parse(base, ndata)
			if err != nil {
				t.Errorf("Parsing reformatted: %v", err)
				continue
			}
			eq := eqchecker{file: base}
			if err := eq.check(pf1, pf2); err != nil {
				t.Errorf("not equal: %v", err)
			}
		}

		if strings.HasSuffix(out, ".in") {
			golden, err := ioutil.ReadFile(strings.TrimSuffix(out, ".in") + ".golden")
			if err != nil {
				t.Error(err)
				continue
			}
			if !bytes.Equal(ndata, golden) {
				t.Errorf("formatted %s incorrectly: diff shows -golden, +ours", base)
				tdiff(t, string(golden), string(ndata))
				return
			}
		}
	}
}

// An eqchecker holds state for checking the equality of two parse trees.
type eqchecker struct {
	file string
	pos  Position
}

// errorf returns an error described by the printf-style format and arguments,
// inserting the current file position before the error text.
func (eq *eqchecker) errorf(format string, args ...interface{}) error {
	return fmt.Errorf("%s:%d: %s", eq.file, eq.pos.Line,
		fmt.Sprintf(format, args...))
}

// check checks that v and w represent the same parse tree.
// If not, it returns an error describing the first difference.
func (eq *eqchecker) check(v, w interface{}) error {
	return eq.checkValue(reflect.ValueOf(v), reflect.ValueOf(w))
}

var (
	posType      = reflect.TypeOf(Position{})
	commentsType = reflect.TypeOf(Comments{})
)

// checkValue checks that v and w represent the same parse tree.
// If not, it returns an error describing the first difference.
func (eq *eqchecker) checkValue(v, w reflect.Value) error {
	// inner returns the innermost expression for v.
	// if v is a non-nil interface value, it returns the concrete
	// value in the interface.
	inner := func(v reflect.Value) reflect.Value {
		for {
			if v.Kind() == reflect.Interface && !v.IsNil() {
				v = v.Elem()
				continue
			}
			break
		}
		return v
	}

	v = inner(v)
	w = inner(w)
	if v.Kind() == reflect.Invalid && w.Kind() == reflect.Invalid {
		return nil
	}
	if v.Kind() == reflect.Invalid {
		return eq.errorf("nil interface became %s", w.Type())
	}
	if w.Kind() == reflect.Invalid {
		return eq.errorf("%s became nil interface", v.Type())
	}

	if v.Type() != w.Type() {
		return eq.errorf("%s became %s", v.Type(), w.Type())
	}

	if p, ok := v.Interface().(Expr); ok {
		eq.pos, _ = p.Span()
	}

	switch v.Kind() {
	default:
		return eq.errorf("unexpected type %s", v.Type())

	case reflect.Bool, reflect.Int, reflect.String:
		vi := v.Interface()
		wi := w.Interface()
		if vi != wi {
			return eq.errorf("%v became %v", vi, wi)
		}

	case reflect.Slice:
		vl := v.Len()
		wl := w.Len()
		for i := 0; i < vl || i < wl; i++ {
			if i >= vl {
				return eq.errorf("unexpected %s", w.Index(i).Type())
			}
			if i >= wl {
				return eq.errorf("missing %s", v.Index(i).Type())
			}
			if err := eq.checkValue(v.Index(i), w.Index(i)); err != nil {
				return err
			}
		}

	case reflect.Struct:
		// Fields in struct must match.
		t := v.Type()
		n := t.NumField()
		for i := 0; i < n; i++ {
			tf := t.Field(i)
			switch {
			default:
				if err := eq.checkValue(v.Field(i), w.Field(i)); err != nil {
					return err
				}

			case tf.Type == posType: // ignore positions
			case tf.Type == commentsType: // ignore comment assignment
			}
		}

	case reflect.Ptr, reflect.Interface:
		if v.IsNil() != w.IsNil() {
			if v.IsNil() {
				return eq.errorf("unexpected %s", w.Elem().Type())
			}
			return eq.errorf("missing %s", v.Elem().Type())
		}
		if err := eq.checkValue(v.Elem(), w.Elem()); err != nil {
			return err
		}
	}
	return nil
}

// diff returns the output of running diff on b1 and b2.
func diff(b1, b2 []byte) (data []byte, err error) {
	f1, err := ioutil.TempFile("", "testdiff")
	if err != nil {
		return nil, err
	}
	defer os.Remove(f1.Name())
	defer f1.Close()

	f2, err := ioutil.TempFile("", "testdiff")
	if err != nil {
		return nil, err
	}
	defer os.Remove(f2.Name())
	defer f2.Close()

	f1.Write(b1)
	f2.Write(b2)

	data, err = exec.Command("diff", "-u", f1.Name(), f2.Name()).CombinedOutput()
	if len(data) > 0 {
		// diff exits with a non-zero status when the files don't match.
		// Ignore that failure as long as we get output.
		err = nil
	}
	return
}

// tdiff logs the diff output to t.Error.
func tdiff(t *testing.T, a, b string) {
	data, err := diff([]byte(a), []byte(b))
	if err != nil {
		t.Error(err)
		return
	}
	t.Error(string(data))
}