feat(myers-diff): init commit

Signed-off-by: Swarit Pandey <[email protected]>

Author: swarit-pandey

go.mod

@@ -0,0 +1,7 @@
+module github.com/swarit-pandey/diff
+
+go 1.21.4
+
+require github.com/olekukonko/tablewriter v0.0.5
+
+require github.com/mattn/go-runewidth v0.0.9 // indirect

go.sum

@@ -0,0 +1,4 @@
+github.com/mattn/go-runewidth v0.0.9 h1:Lm995f3rfxdpd6TSmuVCHVb/QhupuXlYr8sCI/QdE+0=
+github.com/mattn/go-runewidth v0.0.9/go.mod h1:H031xJmbD/WCDINGzjvQ9THkh0rPKHF+m2gUSrubnMI=
+github.com/olekukonko/tablewriter v0.0.5 h1:P2Ga83D34wi1o9J6Wh1mRuqd4mF/x/lgBS7N7AbDhec=
+github.com/olekukonko/tablewriter v0.0.5/go.mod h1:hPp6KlRPjbx+hW8ykQs1w3UBbZlj6HuIJcUGPhkA7kY=

main.go

@@ -0,0 +1,189 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/olekukonko/tablewriter"
+)
+
+type EditAction interface{}
+
+type Keep struct {
+	line string
+}
+
+type Insert struct {
+	line string
+}
+
+type Remove struct {
+	line string
+}
+
+type Frontier struct {
+	x       int
+	history []EditAction
+}
+
+// Myers diff algorithm
+// Amazing read: blog.jcoglan.com/2017/02/12/the-myers-diff-algorithm-part-1/ and other parts
+// Few more reads: [https://www.nathaniel.ai/myers-diff/] [https://epxx.co/artigos/diff_en.html]
+// Complexity: O((N+M)D) where N and M are the lengths of the sequences and D is the number of edits
+// Space: O(N+M)
+// Reference implementation in Python: https://gist.github.com/adamnew123456/37923cf53f51d6b9af32a539cdfa7cc4
+func myersDiff(aLines, bLines []string) []EditAction {
+	frontier := make(map[int]Frontier)
+	frontier[1] = Frontier{0, []EditAction{}}
+
+	aMax := len(aLines)
+	bMax := len(bLines)
+	for d := 0; d <= aMax+bMax; d++ {
+		for k := -d; k <= d; k += 2 {
+			goDown := k == -d || (k != d && frontier[k-1].x < frontier[k+1].x)
+
+			var oldX int
+			var history []EditAction
+
+			if goDown {
+				oldX = frontier[k+1].x
+				history = append([]EditAction{}, frontier[k+1].history...)
+			} else {
+				oldX = frontier[k-1].x + 1
+				history = append([]EditAction{}, frontier[k-1].history...)
+			}
+
+			y := oldX - k
+
+			if 1 <= y && y <= bMax && goDown {
+				history = append(history, Insert{bLines[y-1]})
+			} else if 1 <= oldX && oldX <= aMax {
+				history = append(history, Remove{aLines[oldX-1]})
+			}
+
+			for oldX < aMax && y < bMax && aLines[oldX] == bLines[y] {
+				history = append(history, Keep{aLines[oldX]})
+				oldX++
+				y++
+			}
+
+			if oldX >= aMax && y >= bMax {
+				return history
+			} else {
+				frontier[k] = Frontier{oldX, history}
+			}
+		}
+	}
+
+	panic("No file found")
+}
+
+func printHorizontal(aLines, bLines []string, diff []EditAction) {
+	table := tablewriter.NewWriter(os.Stdout)
+	table.SetHeader([]string{"Original", "Change", "Updated"})
+
+	aIndex, bIndex := 0, 0
+	for _, action := range diff {
+		var row []string
+		switch e := action.(type) {
+		case Keep:
+			row = []string{aLines[aIndex], " ", bLines[bIndex]}
+			aIndex++
+			bIndex++
+		case Insert:
+			row = []string{" ", "\033[32m+\033[0m", e.line}
+			bIndex++
+		case Remove:
+			row = []string{e.line, "\033[31m-\033[0m", " "}
+			aIndex++
+		}
+
+		table.Append(row)
+	}
+
+	table.Render()
+}
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Println("Usage:", os.Args[0], "getdiff <string1> <string2> or <file1>.txt <file2>.txt")
+		os.Exit(1)
+	}
+
+	mode := os.Args[1]
+
+	switch mode {
+	case "getdiff": // CL args
+		if len(os.Args) != 4 {
+			fmt.Println("Usage: getdiff <string1> <string2>")
+			os.Exit(1)
+		}
+		aLines := strings.Split(os.Args[2], "")
+		bLines := strings.Split(os.Args[3], "")
+		diff := myersDiff(aLines, bLines)
+		// printDiff(aLines, bLines, diff)
+		printHorizontal(aLines, bLines, diff)
+	default: // File args
+		if len(os.Args) != 3 {
+			fmt.Println("Usage:", os.Args[0], "<file1> <file2>")
+			os.Exit(1)
+		}
+		aLines := readLines(os.Args[1])
+		bLines := readLines(os.Args[2])
+		diff := myersDiff(aLines, bLines)
+		// printDiff(aLines, bLines, diff)
+		printHorizontal(aLines, bLines, diff)
+	}
+}
+
+func readLines(filePath string) []string {
+	file, err := os.Open(filePath)
+	if err != nil {
+		panic(err)
+	}
+	defer file.Close()
+
+	var lines []string
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		lines = append(lines, strings.TrimSpace(scanner.Text()))
+	}
+
+	if err := scanner.Err(); err != nil {
+		panic(err)
+	}
+
+	return lines
+}
+
+// No table print (a bit confusing)
+/* func printDiff(aLines, bLines []string, diff []EditAction) {
+	aIndex, bIndex := 0, 0
+
+	for _, action := range diff {
+		var original, updated, change string
+
+		switch e := action.(type) {
+		case Keep:
+			original = aLines[aIndex]
+			updated = bLines[bIndex]
+			change = " "
+			aIndex++
+			bIndex++
+		case Insert:
+			original = ""
+			updated = e.line
+			change = "\033[32m+\033[0m" // Green plus
+			bIndex++
+		case Remove:
+			original = e.line
+			updated = ""
+			change = "\033[31m-\033[0m" // Red minus
+			aIndex++
+		}
+
+		fmt.Printf("%-15s %-15s %-3s\n", original, updated, change)
+	}
+} */

main_test.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestMyersDiff(t *testing.T) {
+	tests := []struct {
+		name     string
+		aLines   []string
+		bLines   []string
+		expected []EditAction
+	}{
+		{
+			name:     "No changes",
+			aLines:   []string{"line1", "line2", "line3"},
+			bLines:   []string{"line1", "line2", "line3"},
+			expected: []EditAction{Keep{"line1"}, Keep{"line2"}, Keep{"line3"}},
+		},
+		{
+			name:     "Insertion",
+			aLines:   []string{"line1", "line2"},
+			bLines:   []string{"line1", "line2", "line3"},
+			expected: []EditAction{Keep{"line1"}, Keep{"line2"}, Insert{"line3"}},
+		},
+		{
+			name:     "Removal",
+			aLines:   []string{"line1", "line2", "line3"},
+			bLines:   []string{"line1", "line2"},
+			expected: []EditAction{Keep{"line1"}, Keep{"line2"}, Remove{"line3"}},
+		},
+		{
+			name:     "Replacement",
+			aLines:   []string{"line1", "line2", "line3"},
+			bLines:   []string{"line1", "newLine2", "line3"},
+			expected: []EditAction{Keep{"line1"}, Remove{"line2"}, Insert{"newLine2"}, Keep{"line3"}},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := myersDiff(tt.aLines, tt.bLines)
+			if !reflect.DeepEqual(result, tt.expected) {
+				t.Errorf("myersDiff() = %v, want %v", result, tt.expected)
+			}
+		})
+	}
+}