package compiler

// Opcode represents a single bytecode instruction
type Opcode uint8

const (
	// Stack Operations
	OpLoadConst   Opcode = iota // Load constant onto stack [idx]
	OpLoadLocal                 // Load local variable [slot]
	OpStoreLocal                // Store top of stack to local [slot]
	OpLoadGlobal                // Load global variable [idx]
	OpStoreGlobal               // Store top of stack to global [idx]
	OpPop                       // Pop top value from stack
	OpDup                       // Duplicate top value on stack

	// Specialized Local Operations (no operands needed)
	OpLoadLocal0  // Load local slot 0
	OpLoadLocal1  // Load local slot 1
	OpLoadLocal2  // Load local slot 2
	OpStoreLocal0 // Store to local slot 0
	OpStoreLocal1 // Store to local slot 1
	OpStoreLocal2 // Store to local slot 2

	// Specialized Constants (no operands needed)
	OpLoadTrue  // Load true constant
	OpLoadFalse // Load false constant
	OpLoadNil   // Load nil constant
	OpLoadZero  // Load number 0
	OpLoadOne   // Load number 1

	// Arithmetic Operations
	OpAdd // a + b
	OpSub // a - b
	OpMul // a * b
	OpDiv // a / b
	OpNeg // -a
	OpMod // a % b

	// Specialized Arithmetic
	OpAddConst // local + constant [constIdx]
	OpSubConst // local - constant [constIdx]
	OpInc      // increment local [slot]
	OpDec      // decrement local [slot]

	// Comparison Operations
	OpEq  // a == b
	OpNeq // a != b
	OpLt  // a < b
	OpLte // a <= b
	OpGt  // a > b
	OpGte // a >= b

	// Logical Operations
	OpNot // not a
	OpAnd // a and b
	OpOr  // a or b

	// Control Flow
	OpJump        // Unconditional jump [offset]
	OpJumpIfTrue  // Jump if top of stack is true [offset]
	OpJumpIfFalse // Jump if top of stack is false [offset]
	OpCall        // Call function [argCount]
	OpReturn      // Return from function
	OpReturnNil   // Return nil from function

	// Specialized Control Flow
	OpTestAndJump // Test local and jump [slot, offset]
	OpLoopBack    // Optimized loop back jump [offset]

	// Table Operations
	OpNewTable    // Create new empty table
	OpGetIndex    // table[key] -> value
	OpSetIndex    // table[key] = value
	OpGetField    // table.field -> value [fieldIdx]
	OpSetField    // table.field = value [fieldIdx]
	OpTableInsert // Insert value into table at next index

	// Specialized Table Operations
	OpGetLocalField // local.field -> value [slot, fieldIdx]
	OpSetLocalField // local.field = value [slot, fieldIdx]
	OpGetConstField // table.constField -> value [fieldName]

	// Struct Operations
	OpNewStruct   // Create new struct instance [structId]
	OpGetProperty // struct.field -> value [fieldIdx]
	OpSetProperty // struct.field = value [fieldIdx]
	OpCallMethod  // Call method on struct [methodIdx, argCount]

	// Function Operations
	OpClosure      // Create closure from function [funcIdx, upvalueCount]
	OpGetUpvalue   // Get upvalue [idx]
	OpSetUpvalue   // Set upvalue [idx]
	OpCloseUpvalue // Close upvalue (move to heap)

	// Specialized Function Operations
	OpCallLocal0 // Call function in local slot 0 [argCount]
	OpCallLocal1 // Call function in local slot 1 [argCount]

	// Array Operations
	OpNewArray    // Create new array with size [size]
	OpArrayAppend // Append value to array
	OpArrayGet    // Optimized array[index] access
	OpArraySet    // Optimized array[index] = value
	OpArrayLen    // Get array length

	// Type Operations
	OpGetType // Get type of value on stack
	OpCast    // Cast value to type [typeId]
	OpIsType  // Check if value is type [typeId]

	// Type Checks (faster than generic OpGetType)
	OpIsNumber // Check if top of stack is number
	OpIsString // Check if top of stack is string
	OpIsTable  // Check if top of stack is table
	OpIsBool   // Check if top of stack is bool
	OpIsNil    // Check if top of stack is nil

	// I/O Operations
	OpEcho // Echo value to output
	OpExit // Exit with code

	// Special Operations
	OpNoop     // No operation
	OpBreak    // Break from loop
	OpContinue // Continue loop iteration

	// Debug Operations
	OpDebugPrint // Debug print stack top
	OpDebugStack // Debug print entire stack
)

// Instruction represents a single bytecode instruction with operands
type Instruction struct {
	Op       Opcode
	Operands []uint16 // Variable length operands
}

// Chunk represents a compiled chunk of bytecode
type Chunk struct {
	Code      []uint8    // Raw bytecode stream
	Constants []Value    // Constant pool
	Lines     []int      // Line numbers for debugging
	Functions []Function // Function definitions
	Structs   []Struct   // Struct definitions
}

// Value represents a runtime value in the VM
type Value struct {
	Type ValueType
	Data any // Actual value data
}

// ValueType represents the type of a runtime value
type ValueType uint8

const (
	ValueNil ValueType = iota
	ValueBool
	ValueNumber
	ValueString
	ValueTable
	ValueFunction
	ValueStruct
	ValueArray
	ValueUpvalue
)

// Function represents a compiled function
type Function struct {
	Name       string  // Function name (empty for anonymous)
	Arity      int     // Number of parameters
	Variadic   bool    // Whether function accepts variable args
	LocalCount int     // Number of local variable slots
	UpvalCount int     // Number of upvalues
	Chunk      Chunk   // Function bytecode
	Defaults   []Value // Default parameter values
}

// Struct represents a compiled struct definition
type Struct struct {
	Name    string            // Struct name
	Fields  []StructField     // Field definitions
	Methods map[string]uint16 // Method name -> function index
	ID      uint16            // Unique struct identifier
}

// StructField represents a field in a struct
type StructField struct {
	Name   string    // Field name
	Type   ValueType // Field type
	Offset uint16    // Offset in struct layout
}

// Table represents a key-value table/map
type Table struct {
	Array map[int]Value    // Array part (integer keys)
	Hash  map[string]Value // Hash part (string keys)
	Meta  *Table           // Metatable for operations
}

// Array represents a dynamic array
type Array struct {
	Elements []Value // Array elements
	Count    int     // Current element count
	Capacity int     // Current capacity
}

// StructInstance represents an instance of a struct
type StructInstance struct {
	StructID uint16           // Reference to struct definition
	Fields   map[string]Value // Field values
}

// Upvalue represents a captured variable
type Upvalue struct {
	Location *Value // Pointer to actual value location
	Closed   Value  // Closed-over value (when moved to heap)
	IsClosed bool   // Whether upvalue has been closed
}

// Instruction encoding helpers

// EncodeInstruction encodes an instruction into bytecode
func EncodeInstruction(op Opcode, operands ...uint16) []uint8 {
	bytes := []uint8{uint8(op)}
	for _, operand := range operands {
		bytes = append(bytes, uint8(operand&0xFF), uint8(operand>>8))
	}
	return bytes
}

// DecodeInstruction decodes bytecode into instruction
func DecodeInstruction(code []uint8, offset int) (Opcode, []uint16, int) {
	if offset >= len(code) {
		return OpNoop, nil, offset
	}

	op := Opcode(code[offset])
	operands := []uint16{}
	nextOffset := offset + 1

	// Decode operands based on instruction type
	operandCount := GetOperandCount(op)
	for range operandCount {
		if nextOffset+1 >= len(code) {
			break
		}
		operand := uint16(code[nextOffset]) | (uint16(code[nextOffset+1]) << 8)
		operands = append(operands, operand)
		nextOffset += 2
	}

	return op, operands, nextOffset
}

// GetOperandCount returns the number of operands for an instruction
func GetOperandCount(op Opcode) int {
	switch op {
	// No operand instructions
	case OpPop, OpDup, OpAdd, OpSub, OpMul, OpDiv, OpNeg, OpMod,
		OpEq, OpNeq, OpLt, OpLte, OpGt, OpGte, OpNot, OpAnd, OpOr,
		OpReturn, OpReturnNil, OpNewTable, OpGetIndex, OpSetIndex,
		OpTableInsert, OpArrayAppend, OpArrayGet, OpArraySet, OpArrayLen,
		OpGetType, OpIsNumber, OpIsString, OpIsTable, OpIsBool, OpIsNil,
		OpEcho, OpExit, OpNoop, OpBreak, OpContinue, OpDebugPrint, OpDebugStack,
		OpLoadLocal0, OpLoadLocal1, OpLoadLocal2, OpStoreLocal0, OpStoreLocal1, OpStoreLocal2,
		OpLoadTrue, OpLoadFalse, OpLoadNil, OpLoadZero, OpLoadOne:
		return 0

	// Single operand instructions
	case OpLoadConst, OpLoadLocal, OpStoreLocal, OpLoadGlobal, OpStoreGlobal,
		OpJump, OpJumpIfTrue, OpJumpIfFalse, OpCall, OpGetField, OpSetField,
		OpNewStruct, OpGetProperty, OpSetProperty, OpNewArray, OpCast, OpIsType,
		OpAddConst, OpSubConst, OpInc, OpDec, OpGetConstField, OpCallLocal0, OpCallLocal1:
		return 1

	// Two operand instructions
	case OpCallMethod, OpClosure, OpTestAndJump, OpGetLocalField, OpSetLocalField:
		return 2

	default:
		return 0
	}
}

// Instruction size calculation
func InstructionSize(op Opcode) int {
	return 1 + (GetOperandCount(op) * 2) // 1 byte opcode + 2 bytes per operand
}

// Check if instruction is a specialized version of another
func IsSpecializedInstruction(op Opcode) bool {
	switch op {
	case OpLoadLocal0, OpLoadLocal1, OpLoadLocal2,
		OpStoreLocal0, OpStoreLocal1, OpStoreLocal2,
		OpLoadTrue, OpLoadFalse, OpLoadNil, OpLoadZero, OpLoadOne,
		OpAddConst, OpSubConst, OpInc, OpDec,
		OpGetLocalField, OpSetLocalField, OpGetConstField,
		OpCallLocal0, OpCallLocal1, OpTestAndJump, OpLoopBack:
		return true
	default:
		return false
	}
}

var opcodeNames = map[Opcode]string{
	OpLoadConst:     "OP_LOAD_CONST",
	OpLoadLocal:     "OP_LOAD_LOCAL",
	OpStoreLocal:    "OP_STORE_LOCAL",
	OpLoadLocal0:    "OP_LOAD_LOCAL_0",
	OpLoadLocal1:    "OP_LOAD_LOCAL_1",
	OpLoadLocal2:    "OP_LOAD_LOCAL_2",
	OpStoreLocal0:   "OP_STORE_LOCAL_0",
	OpStoreLocal1:   "OP_STORE_LOCAL_1",
	OpStoreLocal2:   "OP_STORE_LOCAL_2",
	OpLoadTrue:      "OP_LOAD_TRUE",
	OpLoadFalse:     "OP_LOAD_FALSE",
	OpLoadNil:       "OP_LOAD_NIL",
	OpLoadZero:      "OP_LOAD_ZERO",
	OpLoadOne:       "OP_LOAD_ONE",
	OpAdd:           "OP_ADD",
	OpSub:           "OP_SUB",
	OpMul:           "OP_MUL",
	OpDiv:           "OP_DIV",
	OpAddConst:      "OP_ADD_CONST",
	OpSubConst:      "OP_SUB_CONST",
	OpInc:           "OP_INC",
	OpDec:           "OP_DEC",
	OpJump:          "OP_JUMP",
	OpJumpIfTrue:    "OP_JUMP_TRUE",
	OpJumpIfFalse:   "OP_JUMP_FALSE",
	OpTestAndJump:   "OP_TEST_AND_JUMP",
	OpLoopBack:      "OP_LOOP_BACK",
	OpReturn:        "OP_RETURN",
	OpGetLocalField: "OP_GET_LOCAL_FIELD",
	OpSetLocalField: "OP_SET_LOCAL_FIELD",
	OpCallLocal0:    "OP_CALL_LOCAL_0",
	OpCallLocal1:    "OP_CALL_LOCAL_1",
	OpEcho:          "OP_ECHO",
}