feat(p/uassert, p/diff): Support Diff in p/uassert Package

examples/gno.land/p/demo/diff/diff.gno

@@ -0,0 +1,217 @@
+// The diff package implements the Myers diff algorithm to compute the edit distance
+// and generate a minimal edit script between two strings.
+//
+// Edit distance, also known as Levenshtein distance, is a measure of the similarity
+// between two strings. It is defined as the minimum number of single-character edits (insertions,
+// deletions, or substitutions) required to change one string into the other.
+package diff
+
+import (
+	"strings"
+)
+
+// EditType represents the type of edit operation in a diff.
+type EditType uint8
+
+const (
+	// EditKeep indicates that a character is unchanged in both strings.
+	EditKeep EditType = iota
+
+	// EditInsert indicates that a character was inserted in the new string.
+	EditInsert
+
+	// EditDelete indicates that a character was deleted from the old string.
+	EditDelete
+)
+
+// Edit represent a single edit operation in a diff.
+type Edit struct {
+	// Type is the kind of edit operation.
+	Type EditType
+
+	// Char is the character involved in the edit operation.
+	Char rune
+}
+
+// MyersDiff computes the difference between two strings using Myers' diff algorithm.
+// It returns a slice of Edit operations that transform the old string into the new string.
+// This implementation finds the shortest edit script (SES) that represents the minimal
+// set of operations to transform one string into the other.
+//
+// The function handles both ASCII and non-ASCII characters correctly.
+//
+// Time complexity: O((N+M)D), where N and M are the lengths of the input strings,
+// and D is the size of the minimum edit script.
+//
+// Space complexity: O((N+M)D)
+//
+// In the worst case, where the strings are completely different, D can be as large as N+M,
+// leading to a time and space complexity of O((N+M)^2). However, for strings with many
+// common substrings, the performance is much better, often closer to O(N+M).
+//
+// Parameters:
+//   - old: the original string.
+//   - new: the modified string.
+//
+// Returns:
+//   - A slice of Edit operations representing the minimum difference between the two strings.
+func MyersDiff(old, new string) []Edit {
+	oldRunes, newRunes := []rune(old), []rune(new)
+	n, m := len(oldRunes), len(newRunes)
+
+	if n == 0 && m == 0 {
+		return []Edit{}
+	}
+
+	// old is empty
+	if n == 0 {
+		edits := make([]Edit, m)
+		for i, r := range newRunes {
+			edits[i] = Edit{Type: EditInsert, Char: r}
+		}
+		return edits
+	}
+
+	if m == 0 {
+		edits := make([]Edit, n)
+		for i, r := range oldRunes {
+			edits[i] = Edit{Type: EditDelete, Char: r}
+		}
+		return edits
+	}
+
+	max := n + m
+	v := make([]int, 2*max+1)
+	var trace [][]int
+search:
+	for d := 0; d <= max; d++ {
+		// iterate through diagonals
+		for k := -d; k <= d; k += 2 {
+			var x int
+			if k == -d || (k != d && v[max+k-1] < v[max+k+1]) {
+				x = v[max+k+1] // move down
+			} else {
+				x = v[max+k-1] + 1 // move right
+			}
+			y := x - k
+
+			// extend the path as far as possible with matching characters
+			for x < n && y < m && oldRunes[x] == newRunes[y] {
+				x++
+				y++
+			}
+
+			v[max+k] = x
+
+			// check if we've reached the end of both strings
+			if x == n && y == m {
+				trace = append(trace, append([]int(nil), v...))
+				break search
+			}
+		}
+		trace = append(trace, append([]int(nil), v...))
+	}
+
+	// backtrack to construct the edit script
+	edits := make([]Edit, 0, n+m)
+	x, y := n, m
+	for d := len(trace) - 1; d >= 0; d-- {
+		vPrev := trace[d]
+		k := x - y
+		var prevK int
+		if k == -d || (k != d && vPrev[max+k-1] < vPrev[max+k+1]) {
+			prevK = k + 1
+		} else {
+			prevK = k - 1
+		}
+		prevX := vPrev[max+prevK]
+		prevY := prevX - prevK
+
+		// add keep edits for matching characters
+		for x > prevX && y > prevY {
+			if x > 0 && y > 0 {
+				edits = append([]Edit{{Type: EditKeep, Char: oldRunes[x-1]}}, edits...)
+			}
+			x--
+			y--
+		}
+		if y > prevY {
+			if y > 0 {
+				edits = append([]Edit{{Type: EditInsert, Char: newRunes[y-1]}}, edits...)
+			}
+			y--
+		} else if x > prevX {
+			if x > 0 {
+				edits = append([]Edit{{Type: EditDelete, Char: oldRunes[x-1]}}, edits...)
+			}
+			x--
+		}
+	}
+
+	return edits
+}
+
+// Format converts a slice of Edit operations into a human-readable string representation.
+// It groups consecutive edits of the same type and formats them as follows:
+//   - Unchanged characters are left as-is
+//   - Inserted characters are wrapped in [+...]
+//   - Deleted characters are wrapped in [-...]
+//
+// This function is useful for visualizing the differences between two strings
+// in a compact and intuitive format.
+//
+// Parameters:
+//   - edits: A slice of Edit operations, typically produced by MyersDiff
+//
+// Returns:
+//   - A formatted string representing the diff
+//
+// Example output:
+//
+//	For the diff between "abcd" and "acbd", the output might be:
+//	"a[-b]c[+b]d"
+//
+// Note:
+//
+//	The function assumes that the input slice of edits is in the correct order.
+//	An empty input slice will result in an empty string.
+func Format(edits []Edit) string {
+	if len(edits) == 0 {
+		return ""
+	}
+
+	var (
+		result       strings.Builder
+		currentType  EditType
+		currentChars strings.Builder
+	)
+
+	flushCurrent := func() {
+		if currentChars.Len() > 0 {
+			switch currentType {
+			case EditKeep:
+				result.WriteString(currentChars.String())
+			case EditInsert:
+				result.WriteString("[+")
+				result.WriteString(currentChars.String())
+				result.WriteByte(']')
+			case EditDelete:
+				result.WriteString("[-")
+				result.WriteString(currentChars.String())
+				result.WriteByte(']')
+			}
+			currentChars.Reset()
+		}
+	}
+
+	for _, edit := range edits {
+		if edit.Type != currentType {
+			flushCurrent()
+			currentType = edit.Type
+		}
+		currentChars.WriteRune(edit.Char)
+	}
+	flushCurrent()
+
+	return result.String()
+}