c65gm/internal/commands/case.go

package commands

import (
	"fmt"
	"strings"

	"c65gm/internal/compiler"
	"c65gm/internal/preproc"
	"c65gm/internal/utils"
)

// CaseCommand handles CASE statements within SWITCH
// Syntax: CASE <value>
type CaseCommand struct {
	caseValue *operandInfo
}

func (c *CaseCommand) WillHandle(line preproc.Line) bool {
	params, err := utils.ParseParams(line.Text)
	if err != nil || len(params) == 0 {
		return false
	}
	return strings.ToUpper(params[0]) == "CASE"
}

func (c *CaseCommand) Interpret(line preproc.Line, ctx *compiler.CompilerContext) error {
	params, err := utils.ParseParams(line.Text)
	if err != nil {
		return err
	}

	if len(params) != 2 {
		return fmt.Errorf("CASE: expected 2 parameters (CASE <value>), got %d", len(params))
	}

	// Check if we're inside a SWITCH
	if ctx.SwitchStack.IsEmpty() {
		return fmt.Errorf("CASE: not inside a SWITCH statement")
	}

	scope := ctx.CurrentScope()
	constLookup := func(name string) (int64, bool) {
		sym := ctx.SymbolTable.Lookup(name, scope)
		if sym != nil && sym.IsConst() {
			return int64(sym.Value), true
		}
		return 0, false
	}

	// Parse the case value
	varName, varKind, value, isVar, err := compiler.ParseOperandParam(
		params[1], ctx.SymbolTable, scope, constLookup)
	if err != nil {
		return fmt.Errorf("CASE: %w", err)
	}

	c.caseValue = &operandInfo{
		varName: varName,
		varKind: varKind,
		value:   value,
		isVar:   isVar,
	}

	// Get switch info to validate type compatibility
	switchInfo, err := ctx.SwitchStack.Peek()
	if err != nil {
		return fmt.Errorf("CASE: %w", err)
	}

	// Error if case value is out of range for switch variable type
	if !isVar && !switchInfo.SwitchOperand.IsVar {
		// Both are constants/literals
		if switchInfo.SwitchOperand.VarKind == compiler.KindByte && value > 255 {
			return fmt.Errorf("CASE: constant value %d exceeds BYTE range (0-255)", value)
		}
		if switchInfo.SwitchOperand.VarKind == compiler.KindByte && value < 0 {
			return fmt.Errorf("CASE: constant value %d below BYTE range (0-255)", value)
		}
	} else if !isVar {
		// Case is literal, switch is variable
		if switchInfo.SwitchOperand.VarKind == compiler.KindByte && value > 255 {
			return fmt.Errorf("CASE: literal value %d will never match BYTE variable '%s' (valid range: 0-255)",
				value, switchInfo.SwitchOperand.VarName)
		}
		if switchInfo.SwitchOperand.VarKind == compiler.KindByte && value < 0 {
			return fmt.Errorf("CASE: literal value %d will never match BYTE variable '%s' (valid range: 0-255)",
				value, switchInfo.SwitchOperand.VarName)
		}
	}

	return nil
}

func (c *CaseCommand) Generate(ctx *compiler.CompilerContext) ([]string, error) {
	switchInfo, err := ctx.SwitchStack.Peek()
	if err != nil {
		return nil, fmt.Errorf("CASE: %w", err)
	}

	// Check if DEFAULT has already been seen
	if switchInfo.HasDefault {
		return nil, fmt.Errorf("CASE: cannot have CASE after DEFAULT")
	}

	var asm []string

	// If there was a previous CASE, emit implicit break and skip label
	if switchInfo.NeedsPendingCode {
		// Implicit break: jump to end of switch
		asm = append(asm, fmt.Sprintf("\tjmp %s", switchInfo.EndLabel))

		// Emit the pending skip label
		asm = append(asm, switchInfo.PendingSkipLabel)
	}

	// Push a new skip label onto the CaseSkipStack (like IF does with ctx.IfStack)
	skipLabel := ctx.CaseSkipStack.Push()

	// Convert switch operand to operandInfo
	switchOp := &operandInfo{
		varName: switchInfo.SwitchOperand.VarName,
		varKind: switchInfo.SwitchOperand.VarKind,
		value:   switchInfo.SwitchOperand.Value,
		isVar:   switchInfo.SwitchOperand.IsVar,
	}

	// Generate comparison: if switch_var == case_value, execute case (don't jump)
	// Otherwise jump to skipLabel
	// comparisonGenerator jumps on FALSE, so we use opEqual:
	//   - When equal (TRUE): don't jump, execute case
	//   - When not equal (FALSE): jump to skip label
	gen, err := newComparisonGenerator(
		opEqual,
		switchOp,
		c.caseValue,
		switchInfo.UseLongJump,
		ctx.CaseSkipStack,
		ctx.GeneralStack,
	)
	if err != nil {
		return nil, fmt.Errorf("CASE: %w", err)
	}

	cmpAsm, err := gen.generate()
	if err != nil {
		return nil, fmt.Errorf("CASE: %w", err)
	}

	asm = append(asm, cmpAsm...)

	// Mark that we need to emit break + skip label next time
	switchInfo.NeedsPendingCode = true
	switchInfo.PendingSkipLabel = skipLabel

	return asm, nil
}