Adding diff and regctl cmds to compare manifests and blobs

Signed-off-by: Brandon Mitchell <git@bmitch.net>

internal/diff/diff.go

@@ -0,0 +1,112 @@
+// Package diff computes the efficient set of changes (insert/delete) between two arrays of strings
+package diff
+
+import "fmt"
+
+// opKind is used to denote the type of operation a line represents.
+type opKind int
+
+const (
+	// OpDelete is the operation kind for a line that is present in the input
+	// but not in the output.
+	OpDelete opKind = iota
+	// OpInsert is the operation kind for a line that is new in the output.
+	OpInsert
+)
+
+type operation struct {
+	Kind   opKind
+	X1, X2 int // indices of the line in a
+	Y1, Y2 int // indices of the line in b
+}
+
+type Opt func(*conf)
+
+type conf struct {
+	contextA    int
+	contextB    int
+	contextFull bool
+}
+
+func WithContext(a, b int) func(*conf) {
+	return func(c *conf) {
+		c.contextA = a
+		c.contextB = b
+	}
+}
+
+func WithFullContext() func(*conf) {
+	return func(c *conf) {
+		c.contextFull = true
+	}
+}
+
+// Diff returns the difference between two strings
+func Diff(a, b []string, opts ...Opt) []string {
+	c := conf{}
+	for _, fn := range opts {
+		fn(&c)
+	}
+
+	diffLines := []string{}
+	setLines := []string{}
+	ops := myersOperations(a, b)
+	sX1, sX2, sY1, sY2 := -1, -1, -1, -1
+	addSet := func() {
+		if len(setLines) == 0 {
+			return
+		}
+		// calculate how many lines of context to add
+		cA, cB := c.contextA, c.contextB
+		if sX1-cA < 0 || c.contextFull {
+			cA = sX1
+		}
+		if sX2+cB > len(a) || c.contextFull {
+			cB = len(a) - sX2
+		}
+		// add header
+		diffLines = append(diffLines, fmt.Sprintf("@@ -%d,%d +%d,%d @@", sX1-cA+1, sX2+cA+cB-sX1, sY1-cA+1, sY2+cA+cB-sY1))
+		// add context before, the change set, and context after
+		if cA > 0 {
+			for _, line := range a[sX1-cA : sX1] {
+				diffLines = append(diffLines, "  "+line)
+			}
+		}
+		diffLines = append(diffLines, setLines...)
+		setLines = []string{} // reset the setLines to a new array
+		if cB > 0 {
+			for _, line := range a[sX2 : sX2+cB] {
+				diffLines = append(diffLines, "  "+line)
+			}
+		}
+	}
+	for _, op := range ops {
+		// compare from last set
+		dX, dY := op.X1-sX2, op.Y1-sY2
+		if dX != dY || (dX > c.contextA && dX > c.contextB && !c.contextFull) {
+			// unexpected diff lines or gap exceeds context limits, create a new set
+			addSet()
+			sX1, sY1 = op.X1, op.Y1
+		} else if dX > 0 {
+			// add common lines between two diffs
+			for _, line := range a[sX2+1 : op.X1] {
+				setLines = append(setLines, "  "+line)
+			}
+		}
+		// add entries to this set, either delete or add
+		switch op.Kind {
+		case OpDelete:
+			for _, line := range a[op.X1:op.X2] {
+				setLines = append(setLines, "- "+line)
+			}
+		case OpInsert:
+			for _, line := range b[op.Y1:op.Y2] {
+				setLines = append(setLines, "+ "+line)
+			}
+		}
+		// update end of set
+		sX2, sY2 = op.X2, op.Y2
+	}
+	addSet()
+	return diffLines
+}