package commands

import (
	"fmt"
	"strings"

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

// SubtractCommand handles SUBTRACT operations
// Syntax:
//
//	SUBTRACT <param2> FROM <param1> GIVING <dest>   # old syntax: param1 - param2
//	SUBT <param1> - <param2> -> <dest>              # old syntax: param1 - param2
//	<dest> = <param1> - <param2>                    # new syntax: param1 - param2
//
// Note: FROM syntax swaps parameter order (SUBTRACT a FROM b means b-a)
type SubtractCommand struct {
	param1VarName string
	param1VarKind compiler.VarKind
	param1Value   uint16
	param1IsVar   bool

	param2VarName string
	param2VarKind compiler.VarKind
	param2Value   uint16
	param2IsVar   bool

	destVarName string
	destVarKind compiler.VarKind
}

func (c *SubtractCommand) WillHandle(line preproc.Line) bool {
	params, err := utils.ParseParams(line.Text)
	if err != nil || len(params) == 0 {
		return false
	}

	// Old syntax: SUBTRACT/SUBT ... (must have exactly 6 params)
	kw := strings.ToUpper(params[0])
	if (kw == "SUBTRACT" || kw == "SUBT") && len(params) == 6 {
		return true
	}

	// New syntax: <dest> = <param1> - <param2>
	if len(params) == 5 && params[1] == "=" && params[3] == "-" {
		return true
	}

	return false
}

func (c *SubtractCommand) Interpret(line preproc.Line, ctx *compiler.CompilerContext) error {
	// Clear state
	c.param1VarName = ""
	c.param1IsVar = false
	c.param1Value = 0
	c.param2VarName = ""
	c.param2IsVar = false
	c.param2Value = 0
	c.destVarName = ""

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

	paramCount := len(params)
	scope := ctx.CurrentScope()

	// Create constant lookup function
	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
	}

	// Determine syntax and parse accordingly
	kw := strings.ToUpper(params[0])
	if kw == "SUBTRACT" || kw == "SUBT" {
		// Old syntax: SUBTRACT/SUBT <p1> FROM/- <p2> GIVING/-> <dest>
		if paramCount != 6 {
			return fmt.Errorf("SUBTRACT: wrong number of parameters (%d), expected 6", paramCount)
		}

		separator1 := strings.ToUpper(params[2])
		if separator1 != "FROM" && separator1 != "-" {
			return fmt.Errorf("SUBTRACT: parameter #3 must be 'FROM' or '-', got %q", params[2])
		}

		separator2 := strings.ToUpper(params[4])
		if separator2 != "GIVING" && separator2 != "->" {
			return fmt.Errorf("SUBTRACT: parameter #5 must be 'GIVING' or '->', got %q", params[4])
		}

		// Parse destination
		destName := params[5]
		destSym := ctx.SymbolTable.Lookup(destName, scope)
		if destSym == nil {
			return fmt.Errorf("SUBTRACT: unknown variable %q", destName)
		}
		if destSym.IsConst() {
			return fmt.Errorf("SUBTRACT: cannot assign to constant %q", destName)
		}
		c.destVarName = destSym.FullName()
		c.destVarKind = destSym.GetVarKind()

		// Parse parameters based on separator
		// FROM syntax: SUBTRACT a FROM b means b - a (swap needed)
		// Minus syntax: SUBT a - b means a - b (no swap)
		var minuendParam, subtrahendParam string
		if separator1 == "FROM" {
			// Swap: position 4 becomes minuend, position 2 becomes subtrahend
			minuendParam = params[3]
			subtrahendParam = params[1]
		} else {
			// No swap: position 2 is minuend, position 4 is subtrahend
			minuendParam = params[1]
			subtrahendParam = params[3]
		}

		// Parse minuend (param1)
		var err error
		c.param1VarName, c.param1VarKind, c.param1Value, c.param1IsVar, err = compiler.ParseOperandParam(
			minuendParam, ctx.SymbolTable, scope, constLookup)
		if err != nil {
			return fmt.Errorf("SUBTRACT: minuend: %w", err)
		}

		// Parse subtrahend (param2)
		c.param2VarName, c.param2VarKind, c.param2Value, c.param2IsVar, err = compiler.ParseOperandParam(
			subtrahendParam, ctx.SymbolTable, scope, constLookup)
		if err != nil {
			return fmt.Errorf("SUBTRACT: subtrahend: %w", err)
		}

	} else {
		// New syntax: <dest> = <param1> - <param2>
		if paramCount != 5 {
			return fmt.Errorf("SUBTRACT: wrong number of parameters (%d), expected 5", paramCount)
		}

		if params[1] != "=" {
			return fmt.Errorf("SUBTRACT: expected '=' at position 2, got %q", params[1])
		}

		if params[3] != "-" {
			return fmt.Errorf("SUBTRACT: expected '-' at position 4, got %q", params[3])
		}

		// Parse destination
		destName := params[0]
		destSym := ctx.SymbolTable.Lookup(destName, scope)
		if destSym == nil {
			return fmt.Errorf("SUBTRACT: unknown variable %q", destName)
		}
		if destSym.IsConst() {
			return fmt.Errorf("SUBTRACT: cannot assign to constant %q", destName)
		}
		c.destVarName = destSym.FullName()
		c.destVarKind = destSym.GetVarKind()

		// Parse param1 (minuend)
		var err error
		c.param1VarName, c.param1VarKind, c.param1Value, c.param1IsVar, err = compiler.ParseOperandParam(
			params[2], ctx.SymbolTable, scope, constLookup)
		if err != nil {
			return fmt.Errorf("SUBTRACT: param1: %w", err)
		}

		// Parse param2 (subtrahend)
		c.param2VarName, c.param2VarKind, c.param2Value, c.param2IsVar, err = compiler.ParseOperandParam(
			params[4], ctx.SymbolTable, scope, constLookup)
		if err != nil {
			return fmt.Errorf("SUBTRACT: param2: %w", err)
		}
	}

	return nil
}

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

	// If both params are literals, fold at compile time
	if !c.param1IsVar && !c.param2IsVar {
		// param1 - param2 (minuend - subtrahend)
		result := uint16(int32(c.param1Value) - int32(c.param2Value))
		lo := uint8(result & 0xFF)
		hi := uint8((result >> 8) & 0xFF)

		asm = append(asm, fmt.Sprintf("\tlda #$%02x", lo))
		asm = append(asm, fmt.Sprintf("\tsta %s", c.destVarName))

		if c.destVarKind == compiler.KindWord {
			asm = append(asm, fmt.Sprintf("\tlda #$%02x", hi))
			asm = append(asm, fmt.Sprintf("\tsta %s+1", c.destVarName))
		}

		return asm, nil
	}

	// At least one param is a variable - generate subtract code
	// SEC sets carry for borrow
	asm = append(asm, "\tsec")

	// Load minuend (param1)
	if c.param1IsVar {
		asm = append(asm, fmt.Sprintf("\tlda %s", c.param1VarName))
	} else {
		asm = append(asm, fmt.Sprintf("\tlda #$%02x", uint8(c.param1Value&0xFF)))
	}

	// Subtract subtrahend (param2)
	if c.param2IsVar {
		asm = append(asm, fmt.Sprintf("\tsbc %s", c.param2VarName))
	} else {
		asm = append(asm, fmt.Sprintf("\tsbc #$%02x", uint8(c.param2Value&0xFF)))
	}

	// Store low byte
	asm = append(asm, fmt.Sprintf("\tsta %s", c.destVarName))

	// If destination is word, handle high byte
	if c.destVarKind == compiler.KindWord {
		// Load high byte of minuend (param1)
		if c.param1IsVar {
			if c.param1VarKind == compiler.KindWord {
				asm = append(asm, fmt.Sprintf("\tlda %s+1", c.param1VarName))
			} else {
				asm = append(asm, "\tlda #0")
			}
		} else {
			hi := uint8((c.param1Value >> 8) & 0xFF)
			asm = append(asm, fmt.Sprintf("\tlda #$%02x", hi))
		}

		// Subtract high byte of subtrahend (param2)
		if c.param2IsVar {
			if c.param2VarKind == compiler.KindWord {
				asm = append(asm, fmt.Sprintf("\tsbc %s+1", c.param2VarName))
			} else {
				asm = append(asm, "\tsbc #0")
			}
		} else {
			hi := uint8((c.param2Value >> 8) & 0xFF)
			asm = append(asm, fmt.Sprintf("\tsbc #$%02x", hi))
		}

		// Store high byte
		asm = append(asm, fmt.Sprintf("\tsta %s+1", c.destVarName))
	}

	return asm, nil
}