c65gm/internal/commands/peek.go

package commands

import (
	"fmt"
	"strings"

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

// PeekCommand handles PEEK statements
// Syntax: PEEK <address>[offset] GIVING|-> <dest>
// Where address is:
//   - Byte variable (self-modifying code)
//   - Word variable (self-modifying code or ZP pointer with offset)
//   - Expression (direct addressing)
type PeekCommand struct {
	addrVarName string
	addrVarKind compiler.VarKind
	addrValue   uint16
	isAddrVar   bool
	isZPPointer bool

	offsetVarName string
	offsetValue   uint8
	hasOffset     bool
	isOffsetVar   bool

	destVarName string
	destVarKind compiler.VarKind

	pragmaSet preproc.PragmaSet
}

func (c *PeekCommand) WillHandle(line preproc.Line) bool {
	params, err := utils.ParseParams(line.Text)
	if err != nil || len(params) != 4 {
		return false
	}
	return strings.ToUpper(params[0]) == "PEEK"
}

func (c *PeekCommand) Interpret(line preproc.Line, ctx *compiler.CompilerContext) error {
	// Clear state
	c.addrVarName = ""
	c.addrValue = 0
	c.isAddrVar = false
	c.isZPPointer = false
	c.offsetVarName = ""
	c.offsetValue = 0
	c.hasOffset = false
	c.isOffsetVar = false
	c.destVarName = ""

	// Store pragma set for Generate phase
	c.pragmaSet = ctx.Pragma.GetPragmaSetByIndex(line.PragmaSetIndex)

	params, err := utils.ParseParams(line.Text)
	if err != nil {
		return err
	}

	if len(params) != 4 {
		return fmt.Errorf("PEEK: expected 4 parameters, got %d", len(params))
	}

	scope := ctx.CurrentScope()

	// Validate separator (param 3)
	sep := strings.ToUpper(params[2])
	if sep != "GIVING" && sep != "->" {
		return fmt.Errorf("PEEK: parameter #3 must be 'GIVING' or '->', got %q", params[2])
	}

	// Parse address (param 2) - may have [offset]
	addrParam := params[1]
	baseAddr, offsetParam := parseOffset(addrParam)

	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
	}

	// Try to parse base address
	varName, varKind, value, isVar, err := compiler.ParseOperandParam(
		baseAddr, ctx.SymbolTable, scope, constLookup)

	if err != nil {
		return fmt.Errorf("PEEK: invalid address: %w", err)
	}

	if isVar {
		// It's a variable
		c.addrVarName = varName
		c.addrVarKind = varKind
		c.isAddrVar = true

		// Check if it's a ZP pointer
		addrSym := ctx.SymbolTable.Lookup(baseAddr, scope)
		if addrSym != nil {
			c.isZPPointer = addrSym.IsZeroPagePointer()
		}
	} else {
		// It's an expression/constant
		c.addrValue = value
		c.isAddrVar = false
	}

	// Parse offset if present
	if offsetParam != "" {
		// Offset only allowed with ZP pointers
		if !c.isZPPointer {
			return fmt.Errorf("PEEK: offset [%s] only allowed with zero-page word pointer", offsetParam)
		}

		c.hasOffset = true

		// Try to parse offset as variable or expression
		offsetVarName, _, offsetValue, isOffsetVar, err := compiler.ParseOperandParam(
			offsetParam, ctx.SymbolTable, scope, constLookup)

		if err != nil {
			return fmt.Errorf("PEEK: invalid offset: %w", err)
		}

		if isOffsetVar {
			// Check it's a byte variable
			offsetSym := ctx.SymbolTable.Lookup(offsetParam, scope)
			if offsetSym != nil && !offsetSym.IsByte() {
				return fmt.Errorf("PEEK: offset variable %q must be byte type", offsetParam)
			}
			c.offsetVarName = offsetVarName
			c.isOffsetVar = true
		} else {
			// Numeric offset - must fit in byte
			if offsetValue > 255 {
				return fmt.Errorf("PEEK: offset value %d out of byte range", offsetValue)
			}
			c.offsetValue = uint8(offsetValue)
			c.isOffsetVar = false
		}
	}

	// Parse destination variable (param 4)
	destParam := params[3]
	destSym := ctx.SymbolTable.Lookup(destParam, scope)
	if destSym == nil {
		return fmt.Errorf("PEEK: unknown destination variable %q", destParam)
	}
	if destSym.IsConst() {
		return fmt.Errorf("PEEK: cannot PEEK into constant %q", destParam)
	}
	c.destVarName = destSym.FullName()
	c.destVarKind = destSym.GetVarKind()

	return nil
}

func (c *PeekCommand) Generate(ctx *compiler.CompilerContext) ([]string, error) {
	var asm []string

	// Check for immutable code pragma when using self-modifying code
	if c.isAddrVar && !c.isZPPointer {
		if c.pragmaSet.GetPragma("_P_USE_IMMUTABLE_CODE") != "" {
			return nil, fmt.Errorf("PEEK: USE_IMMUTABLE_CODE pragma set but construct requires self-modifying code (consider using zero page word for address)")
		}
	}

	// Case 1: ZP pointer with offset
	if c.isZPPointer {
		// Load offset into Y
		if c.hasOffset {
			if c.isOffsetVar {
				asm = append(asm, fmt.Sprintf("\tldy %s", c.offsetVarName))
			} else {
				asm = append(asm, fmt.Sprintf("\tldy #%d", c.offsetValue))
			}
		} else {
			asm = append(asm, "\tldy #0")
		}

		// Clear high byte for word destination
		if c.destVarKind == compiler.KindWord {
			// Optimization: if offset is 0 and not a variable, use Y register (which is 0)
			if !c.hasOffset || (!c.isOffsetVar && c.offsetValue == 0) {
				asm = append(asm, fmt.Sprintf("\tsty %s+1", c.destVarName))
			} else {
				asm = append(asm, "\tldx #0")
				asm = append(asm, fmt.Sprintf("\tstx %s+1", c.destVarName))
			}
		}

		// Indexed indirect load
		asm = append(asm, fmt.Sprintf("\tlda (%s),y", c.addrVarName))
		asm = append(asm, fmt.Sprintf("\tsta %s", c.destVarName))
		return asm, nil
	}

	// Case 2: Byte variable (self-modifying code)
	if c.isAddrVar && c.addrVarKind == compiler.KindByte {
		label := ctx.GeneralStack.Push()
		asm = append(asm, fmt.Sprintf("\tlda %s", c.addrVarName))
		asm = append(asm, fmt.Sprintf("\tsta %s+1", label))
		asm = append(asm, label)
		asm = append(asm, "\tlda $ff")
		asm = append(asm, fmt.Sprintf("\tsta %s", c.destVarName))

		// Clear high byte for word destination
		if c.destVarKind == compiler.KindWord {
			asm = append(asm, "\tlda #0")
			asm = append(asm, fmt.Sprintf("\tsta %s+1", c.destVarName))
		}
		return asm, nil
	}

	// Case 3: Word variable (self-modifying code)
	if c.isAddrVar && c.addrVarKind == compiler.KindWord {
		label := ctx.GeneralStack.Push()
		asm = append(asm, fmt.Sprintf("\tlda %s", c.addrVarName))
		asm = append(asm, fmt.Sprintf("\tsta %s+1", label))
		asm = append(asm, fmt.Sprintf("\tlda %s+1", c.addrVarName))
		asm = append(asm, fmt.Sprintf("\tsta %s+2", label))
		asm = append(asm, label)
		asm = append(asm, "\tlda $ffff")
		asm = append(asm, fmt.Sprintf("\tsta %s", c.destVarName))

		// Clear high byte for word destination
		if c.destVarKind == compiler.KindWord {
			asm = append(asm, "\tlda #0")
			asm = append(asm, fmt.Sprintf("\tsta %s+1", c.destVarName))
		}
		return asm, nil
	}

	// Case 4: Expression/constant address (direct addressing)
	asm = append(asm, fmt.Sprintf("\tlda %d", c.addrValue))
	asm = append(asm, fmt.Sprintf("\tsta %s", c.destVarName))

	// Clear high byte for word destination
	if c.destVarKind == compiler.KindWord {
		asm = append(asm, "\tlda #0")
		asm = append(asm, fmt.Sprintf("\tsta %s+1", c.destVarName))
	}

	return asm, nil
}

// parseOffset extracts offset from syntax like "var[offset]"
// Returns (base, offset) where offset is empty if no brackets found
func parseOffset(param string) (base string, offset string) {
	openBracket := strings.IndexByte(param, '[')
	closeBracket := strings.IndexByte(param, ']')

	if openBracket == -1 || closeBracket == -1 {
		return param, ""
	}

	if closeBracket <= openBracket || closeBracket != len(param)-1 {
		return param, ""
	}

	base = param[:openBracket]
	offset = param[openBracket+1 : closeBracket]
	return base, offset
}