package optimizer

// passImmElimination removes redundant immediate loads.
// Pattern: lda #N; ... (no A modification) ...; lda #N → remove second
// Applies to A, X, Y.
func passImmElimination(lines []asmLine) []asmLine {
	rs := newRegState()
	var result []asmLine

	for _, line := range lines {
		if !line.isCode {
			if line.optMarker {
				continue
			}
			if line.isLabel {
				rs.reset()
			}
			result = append(result, line)
			continue
		}

		if isChainBreaker(line.opcode) {
			rs.reset()
			result = append(result, line)
			continue
		}

		if isRedundantImm(line, rs) {
			continue // remove line
		}

		updateRegState(line, rs)
		result = append(result, line)
	}

	return result
}

func isRedundantImm(line asmLine, rs *regState) bool {
	switch line.opcode {
	case "lda":
		if isImmediate(line.operand) {
			val := parseHexOrDec(line.operand[1:])
			if rs.a.val == val {
				return true
			}
			rs.loadImm("a", val)
		}
	case "ldx":
		if isImmediate(line.operand) {
			val := parseHexOrDec(line.operand[1:])
			if rs.x.val == val {
				return true
			}
			rs.loadImm("x", val)
		}
	case "ldy":
		if isImmediate(line.operand) {
			val := parseHexOrDec(line.operand[1:])
			if rs.y.val == val {
				return true
			}
			rs.loadImm("y", val)
		}
	}
	return false
}