package optimizer

import "fmt"

// debugDiff produces annotated output showing original vs optimized code.
// Lines that were removed are shown with "[removed]" annotation.
func debugDiff(original, optimized []asmLine) []asmLine {
	origCount := countCodeLines(original)
	optCount := countCodeLines(optimized)
	saved := origCount - optCount

	header := fmt.Sprintf("; --- peephole: %d asm lines → %d (%d saved) ---", origCount, optCount, saved)
	var result []asmLine
	result = append(result, asmLine{text: header, isComment: true})

	// Walk both arrays in sync. When optimized doesn't have a line
	// that original has, it was removed.
	oi := 0 // index into original (pre-stripped)
	opi := 0 // index into optimized

	for oi < len(original) {
		origLine := original[oi]

		if opi < len(optimized) && linesMatch(origLine, optimized[opi]) {
			result = append(result, optimized[opi])
			oi++
			opi++
		} else if !origLine.isCode {
			// Non-code line that doesn't match anything — pass through
			result = append(result, origLine)
			oi++
		} else {
			// Code line in original but not in optimized → removed
			result = append(result, asmLine{
				text:      fmt.Sprintf("; [removed] %s", origLine.text),
				isComment: true,
			})
			oi++
		}
	}

	// Append any remaining optimized lines (shouldn't happen in practice)
	for ; opi < len(optimized); opi++ {
		result = append(result, optimized[opi])
	}

	return result
}

// linesMatch returns true if two asmLines represent the same instruction.
func linesMatch(a, b asmLine) bool {
	return a.isCode == b.isCode && a.isLabel == b.isLabel && a.isComment == b.isComment && a.text == b.text
}

func countCodeLines(lines []asmLine) int {
	n := 0
	for _, l := range lines {
		if l.isCode {
			n++
		}
	}
	return n
}