remove adapters, create wrappers

package diff now has a simple, single-call API.
for more control, people can use the subpackages.

Part of #18.

Author: josharian

adapter.go

@@ -3,24 +3,16 @@
 package main
 
 import (
-	"bufio"
-	"context"
 	"flag"
 	"fmt"
 	"log"
 	"os"
 
 	"github.com/pkg/diff"
-	"github.com/pkg/diff/ctxt"
-	"github.com/pkg/diff/myers"
 	"github.com/pkg/diff/write"
 )
 
-var (
-	color   = flag.Bool("color", false, "colorize the output")
-	timeout = flag.Duration("timeout", 0, "timeout")
-	unified = flag.Int("unified", 3, "lines of unified context")
-)
+var color = flag.Bool("color", false, "colorize the output")
 
 // check logs a fatal error and exits if err is not nil.
 func check(err error) {
@@ -29,22 +21,6 @@ func check(err error) {
 	}
 }
 
-// fileLines returns the lines of the file called name.
-func fileLines(name string) ([]string, error) {
-	f, err := os.Open(name)
-	if err != nil {
-		return nil, err
-	}
-	defer f.Close()
-
-	var lines []string
-	s := bufio.NewScanner(f)
-	for s.Scan() {
-		lines = append(lines, s.Text())
-	}
-	return lines, s.Err()
-}
-
 func usage() {
 	fmt.Fprintf(os.Stderr, "pkg-diff-example [flags] file1 file2\n")
 	flag.PrintDefaults()
@@ -62,28 +38,13 @@ func main() {
 	}
 
 	aName := flag.Arg(0)
-	aLines, err := fileLines(aName)
-	check(err)
-
 	bName := flag.Arg(1)
-	bLines, err := fileLines(bName)
-	check(err)
 
-	ab := diff.Strings(aLines, bLines)
-	ctx := context.Background()
-	if *timeout != 0 {
-		var cancel context.CancelFunc
-		ctx, cancel = context.WithTimeout(ctx, *timeout)
-		defer cancel()
-	}
-	e := myers.Diff(ctx, ab)
-	e = ctxt.Size(e, *unified) // limit amount of output context
-	opts := []write.Option{
-		write.Names(aName, bName),
-	}
+	var opts []write.Option
 	if *color {
 		opts = append(opts, write.TerminalColor())
 	}
-	_, err = write.Unified(e, os.Stdout, ab, opts...)
+
+	err := diff.Text(aName, bName, nil, nil, os.Stdout, opts...)
 	check(err)
 }

cmd/pkg-diff-example/main.go

@@ -1 +1,136 @@
+// Package diff and its subpackages create, modify, and print diffs.
+//
+// Package diff contains high level routines that generate a textual diff.
+// It is implemented in terms of the diff/* subpackages.
+// If you want fine-grained control,
+// want to inspect an diff programmatically,
+// want to provide a context for cancellation,
+// need to diff gigantic files that don't fit in memory,
+// or want to diff unusual things,
+// use the subpackages.
 package diff
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"strings"
+
+	"github.com/pkg/diff/ctxt"
+	"github.com/pkg/diff/myers"
+	"github.com/pkg/diff/write"
+)
+
+// lines returns the lines contained in text/filename.
+// text and filename are interpreted as described in the docs for Text.
+func lines(filename string, text interface{}) ([]string, error) {
+	var r io.Reader
+	switch text := text.(type) {
+	case nil:
+		f, err := os.Open(filename)
+		if err != nil {
+			return nil, err
+		}
+		defer f.Close()
+		r = f
+	case string:
+		r = strings.NewReader(text)
+	case []byte:
+		r = bytes.NewReader(text)
+	case io.Reader:
+		r = text
+	default:
+		return nil, fmt.Errorf("unexpected type %T, want string, []byte, io.Reader, or nil", text)
+	}
+	var x []string
+	scan := bufio.NewScanner(r)
+	for scan.Scan() {
+		// TODO: intern? See intern comment in todo.go.
+		x = append(x, scan.Text())
+	}
+	return x, scan.Err()
+}
+
+// addNames adds a Names write.Option using aName and bName,
+// taking care to put it at the end,
+// so as not to overwrite any competing option.
+func addNames(aName, bName string, options []write.Option) []write.Option {
+	opts := make([]write.Option, len(options)+1)
+	opts[0] = write.Names(aName, bName)
+	copy(opts[1:], options)
+	return opts
+}
+
+// Text diffs a and b and writes the result to w.
+// It treats a and b as text, and splits them into lines using bufio.ScanLines.
+// aFile and bFile are filenames to use in the output.
+// a and b each may be nil or may have type string, []byte, or io.Reader.
+// If nil, the text is read from the filename.
+func Text(aFile, bFile string, a, b interface{}, w io.Writer, options ...write.Option) error {
+	aLines, err := lines(aFile, a)
+	if err != nil {
+		return err
+	}
+	bLines, err := lines(bFile, b)
+	if err != nil {
+		return err
+	}
+	ab := &diffStrings{a: aLines, b: bLines}
+	s := myers.Diff(context.Background(), ab)
+	s = ctxt.Size(s, 3)
+	opts := addNames(aFile, bFile, options)
+	_, err = write.Unified(s, w, ab, opts...)
+	return err
+}
+
+type diffStrings struct {
+	a, b []string
+}
+
+func (ab *diffStrings) LenA() int                                { return len(ab.a) }
+func (ab *diffStrings) LenB() int                                { return len(ab.b) }
+func (ab *diffStrings) Equal(ai, bi int) bool                    { return ab.a[ai] == ab.b[bi] }
+func (ab *diffStrings) WriteATo(w io.Writer, i int) (int, error) { return io.WriteString(w, ab.a[i]) }
+func (ab *diffStrings) WriteBTo(w io.Writer, i int) (int, error) { return io.WriteString(w, ab.b[i]) }
+
+// Slices diffs slices a and b and writes the result to w.
+// It uses fmt.Print to print the elements of a and b.
+// It uses reflect.DeepEqual to compare elements of a and b.
+// It uses aName and bName as the names of a and b in the output.
+func Slices(aName, bName string, a, b interface{}, w io.Writer, options ...write.Option) error {
+	ab := &diffSlices{a: reflect.ValueOf(a), b: reflect.ValueOf(b)}
+	if err := ab.validateTypes(); err != nil {
+		return err
+	}
+	s := myers.Diff(context.Background(), ab)
+	s = ctxt.Size(s, 3)
+	opts := addNames(aName, bName, options)
+	_, err := write.Unified(s, w, ab, opts...)
+	return err
+}
+
+type diffSlices struct {
+	a, b reflect.Value
+}
+
+func (ab *diffSlices) LenA() int                                { return ab.a.Len() }
+func (ab *diffSlices) LenB() int                                { return ab.b.Len() }
+func (ab *diffSlices) atA(i int) interface{}                    { return ab.a.Index(i).Interface() }
+func (ab *diffSlices) atB(i int) interface{}                    { return ab.b.Index(i).Interface() }
+func (ab *diffSlices) Equal(ai, bi int) bool                    { return reflect.DeepEqual(ab.atA(ai), ab.atB(bi)) }
+func (ab *diffSlices) WriteATo(w io.Writer, i int) (int, error) { return fmt.Fprint(w, ab.atA(i)) }
+func (ab *diffSlices) WriteBTo(w io.Writer, i int) (int, error) { return fmt.Fprint(w, ab.atB(i)) }
+
+func (ab *diffSlices) validateTypes() error {
+	if t := ab.a.Type(); t.Kind() != reflect.Slice {
+		return fmt.Errorf("a has type %v, must be a slice", t)
+	}
+	if t := ab.b.Type(); t.Kind() != reflect.Slice {
+		return fmt.Errorf("b has type %v, must be a slice", t)
+	}
+	return nil
+}