package vm

import (
	"fmt"
	"log"
	"monkey/internal/builtins"
	"monkey/internal/code"
	"monkey/internal/compiler"
	"monkey/internal/lexer"
	"monkey/internal/object"
	"monkey/internal/parser"
	"monkey/internal/utils"
	"os"
	"path/filepath"
	"strings"
	"time"
	"unicode"
)

const StackSize = 2048
const GlobalsSize = 65536
const MaxFrames = 1024

var Null = &object.Null{}
var True = &object.Boolean{Value: true}
var False = &object.Boolean{Value: false}

func isTruthy(obj object.Object) bool {
	switch obj := obj.(type) {

	case *object.Boolean:
		return obj.Value

	case *object.Null:
		return false

	default:
		return true
	}
}

func nativeBoolToBooleanObject(input bool) *object.Boolean {
	if input {
		return True
	}
	return False
}

// executeModule compiles the named module and returns a *object.Module object
func executeModule(name string, state *VMState) (object.Object, error) {
	filename := utils.FindModule(name)
	if filename == "" {
		return nil, fmt.Errorf("ImportError: no module named '%s'", name)
	}

	b, err := os.ReadFile(filename)
	if err != nil {
		return nil, fmt.Errorf("IOError: error reading module '%s': %s", name, err)
	}

	l := lexer.New(string(b))
	p := parser.New(fmt.Sprintf("<module %s>", name), l)

	module := p.ParseProgram()
	if len(p.Errors()) != 0 {
		return nil, fmt.Errorf("ParseError: %s", p.Errors())
	}

	c := compiler.NewWithState(state.Symbols, &state.Constants)
	err = c.Compile(module)
	if err != nil {
		return nil, fmt.Errorf("CompileError: %s", err)
	}

	code := c.Bytecode()
	state.Constants = code.Constants

	machine := NewWithState(fmt.Sprintf("<module %s>", name), code, state)
	err = machine.Run()
	if err != nil {
		return nil, fmt.Errorf("RuntimeError: error loading module '%s'", err)
	}

	return state.ExportedHash(), nil
}

type VMState struct {
	Constants []object.Object
	Globals   []object.Object
	Symbols   *compiler.SymbolTable
}

func NewVMState() *VMState {
	symbolTable := compiler.NewSymbolTable()
	for i, builtin := range builtins.BuiltinsIndex {
		symbolTable.DefineBuiltin(i, builtin.Name)
	}

	return &VMState{
		Constants: []object.Object{},
		Globals:   make([]object.Object, GlobalsSize),
		Symbols:   symbolTable,
	}
}

// exported binding in the vm state. That is every binding that starts with a
// capital letter. This is used by the module import system to wrap up the
// compiled and evaulated module into an object.
func (s *VMState) ExportedHash() *object.Hash {
	pairs := make(map[object.HashKey]object.HashPair)
	for name, symbol := range s.Symbols.Store {
		if unicode.IsUpper(rune(name[0])) {
			if symbol.Scope == compiler.GlobalScope {
				obj := s.Globals[symbol.Index]
				s := &object.String{Value: name}
				pairs[s.HashKey()] = object.HashPair{Key: s, Value: obj}
			}
		}
	}
	return &object.Hash{Pairs: pairs}
}

type VM struct {
	Debug bool

	state *VMState

	dir  string
	file string

	stack []object.Object
	sp    int // Always points to the next value. Top of stack is stack[sp-1]

	frames []*Frame
	frame  *Frame // Current frame or nil
	fp     int    // Always points to the current frame. Current frame is frames[fp-1]
}

func (vm *VM) pushFrame(f *Frame) {
	vm.frame = f
	vm.frames[vm.fp] = f
	vm.fp++
}

func (vm *VM) popFrame() *Frame {
	vm.fp--
	vm.frame = vm.frames[vm.fp-1]
	return vm.frames[vm.fp]
}

// New constructs a new monkey-lang bytecode virtual machine
func New(fn string, bytecode *compiler.Bytecode) *VM {
	mainFn := &object.CompiledFunction{Instructions: bytecode.Instructions}
	mainClosure := &object.Closure{Fn: mainFn}
	mainFrame := NewFrame(mainClosure, 0)

	frames := make([]*Frame, MaxFrames)
	frames[0] = mainFrame

	state := NewVMState()
	state.Constants = bytecode.Constants

	vm := &VM{
		state: state,

		stack: make([]object.Object, StackSize),
		sp:    0,

		frames: frames,
		frame:  mainFrame,
		fp:     1,
	}

	vm.dir, vm.file = filepath.Split(fn)

	return vm
}

func NewWithState(fn string, bytecode *compiler.Bytecode, state *VMState) *VM {
	mainFn := &object.CompiledFunction{Instructions: bytecode.Instructions}
	mainClosure := &object.Closure{Fn: mainFn}
	mainFrame := NewFrame(mainClosure, 0)

	frames := make([]*Frame, MaxFrames)
	frames[0] = mainFrame

	vm := &VM{
		state: state,

		frames: frames,
		frame:  mainFrame,
		fp:     1,

		stack: make([]object.Object, StackSize),
		sp:    0,
	}

	vm.dir, vm.file = filepath.Split(fn)

	return vm
}

func (vm *VM) push(o object.Object) error {
	if vm.sp >= StackSize {
		return fmt.Errorf("stack overflow")
	}

	vm.stack[vm.sp] = o
	vm.sp++

	return nil
}

func (vm *VM) pop() object.Object {
	o := vm.stack[vm.sp-1]
	vm.sp--
	return o
}

func (vm *VM) executeLoadModule() error {
	name := vm.pop()
	return vm.loadModule(name)
}

func (vm *VM) buildHash(startIndex, endIndex int) (object.Object, error) {
	hashedPairs := make(map[object.HashKey]object.HashPair)

	for i := startIndex; i < endIndex; i += 2 {
		key := vm.stack[i]
		value := vm.stack[i+1]

		pair := object.HashPair{Key: key, Value: value}

		hashKey, ok := key.(object.Hashable)
		if !ok {
			return nil, fmt.Errorf("unusable as hash key: %s", key.Type())
		}

		hashedPairs[hashKey.HashKey()] = pair
	}

	return &object.Hash{Pairs: hashedPairs}, nil
}

func (vm *VM) executeMakeHash(startIndex, endIndex int) error {
	hash, err := vm.buildHash(startIndex, endIndex)
	if err != nil {
		return err
	}
	vm.sp = startIndex
	return vm.push(hash)
}

func (vm *VM) buildArray(startIndex, endIndex int) (object.Object, error) {
	elements := make([]object.Object, endIndex-startIndex)

	for i := startIndex; i < endIndex; i++ {
		elements[i-startIndex] = vm.stack[i]
	}

	return &object.Array{Elements: elements}, nil
}

func (vm *VM) executeMakeArray(startIndex, endIndex int) error {
	hash, err := vm.buildArray(startIndex, endIndex)
	if err != nil {
		return err
	}
	vm.sp = startIndex
	return vm.push(hash)
}

func (vm *VM) executeAdd() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Add); ok {
		val, err := obj.Add(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "+")
}

func (vm *VM) executeSub() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Sub); ok {
		val, err := obj.Sub(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "+")
}

func (vm *VM) executeMul() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Mul); ok {
		val, err := obj.Mul(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "*")
}

func (vm *VM) executeDiv() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Div); ok {
		val, err := obj.Div(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "+")
}

func (vm *VM) executeMod() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Mod); ok {
		val, err := obj.Mod(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "%")
}

func (vm *VM) executeOr() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.LogicalOr); ok {
		val, err := obj.LogicalOr(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "||")
}

func (vm *VM) executeAnd() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.LogicalAnd); ok {
		val, err := obj.LogicalAnd(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "&&")
}

func (vm *VM) executeBitwiseOr() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.BitwiseOr); ok {
		val, err := obj.BitwiseOr(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "|")
}

func (vm *VM) executeBitwiseXor() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.BitwiseXor); ok {
		val, err := obj.BitwiseXor(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "^")
}

func (vm *VM) executeBitwiseAnd() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.BitwiseAnd); ok {
		val, err := obj.BitwiseAnd(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "&")
}

func (vm *VM) executeBitwiseNot() error {
	left := vm.pop()

	if obj, ok := left.(object.BitwiseNot); ok {
		return vm.push(obj.BitwiseNot())
	}

	return fmt.Errorf("unsupported types for unary operation: ~%s", left.Type())
}

func (vm *VM) executeLeftShift() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.LeftShift); ok {
		val, err := obj.LeftShift(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, "<<")
}

func (vm *VM) executeRightShift() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.RightShift); ok {
		val, err := obj.RightShift(right)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return object.NewBinaryOpError(left, right, ">>")
}

func (vm *VM) executeEqual() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Comparable); ok {
		val := obj.Compare(right)
		if val == 0 {
			return vm.push(True)
		}
		return vm.push(False)
	}

	return object.NewBinaryOpError(left, right, "==")
}

func (vm *VM) executeNotEqual() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Comparable); ok {
		val := obj.Compare(right)
		if val != 0 {
			return vm.push(True)
		}
		return vm.push(False)
	}

	return object.NewBinaryOpError(left, right, "!=")
}

func (vm *VM) executeGreaterThan() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Comparable); ok {
		val := obj.Compare(right)
		if val == 1 {
			return vm.push(True)
		}
		return vm.push(False)
	}

	return object.NewBinaryOpError(left, right, ">")
}

func (vm *VM) executeGreaterThanOrEqual() error {
	right := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Comparable); ok {
		val := obj.Compare(right)
		if val >= 0 {
			return vm.push(True)
		}
		return vm.push(False)
	}

	return object.NewBinaryOpError(left, right, ">")
}

func (vm *VM) executeNot() error {
	left := vm.pop()

	if obj, ok := left.(object.LogicalNot); ok {
		return vm.push(obj.LogicalNot())
	}

	return fmt.Errorf("unsupported types for unary operation: !%s", left.Type())
}

func (vm *VM) executeMinus() error {
	left := vm.pop()

	if obj, ok := left.(object.Negate); ok {
		return vm.push(obj.Negate())
	}

	return fmt.Errorf("unsupported types for unary operation: -%s", left.Type())
}

func (vm *VM) executeSetItem() error {
	right := vm.pop()
	index := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Setter); ok {
		err := obj.Set(index, right)
		if err != nil {
			return err
		}
		return vm.push(Null)
	}

	return fmt.Errorf(
		"set item operation not supported: left=%s index=%s",
		left.Type(), index.Type(),
	)
}

func (vm *VM) executeGetItem() error {
	index := vm.pop()
	left := vm.pop()

	if obj, ok := left.(object.Getter); ok {
		val, err := obj.Get(index)
		if err != nil {
			return err
		}
		return vm.push(val)
	}

	return fmt.Errorf(
		"index operator not supported: left=%s index=%s",
		left.Type(), index.Type(),
	)
}

func (vm *VM) executeCall(args int) error {
	callee := vm.stack[vm.sp-1-args]
	switch callee := callee.(type) {
	case *object.Closure:
		return vm.callClosure(callee, args)
	case *object.Builtin:
		return vm.callBuiltin(callee, args)
	default:
		return fmt.Errorf(
			"calling non-closure and non-builtin: %T %v",
			callee, callee,
		)
	}
}

func (vm *VM) executeReturn() error {
	returnValue := vm.pop()

	frame := vm.popFrame()
	vm.sp = frame.basePointer - 1

	return vm.push(returnValue)
}

func (vm *VM) callClosure(cl *object.Closure, numArgs int) error {
	if numArgs != cl.Fn.NumParameters {
		return fmt.Errorf("wrong number of arguments: want=%d, got=%d", cl.Fn.NumParameters, numArgs)
	}

	// Optimize tail calls and avoid a new frame
	if cl.Fn == vm.frame.cl.Fn {
		nextOP := vm.frame.NextOp()
		if nextOP == code.OpReturn {
			for p := 0; p < numArgs; p++ {
				vm.stack[vm.frame.basePointer+p] = vm.stack[vm.sp-numArgs+p]
			}
			vm.sp -= numArgs + 1
			vm.frame.ip = -1 // reset IP to the beginning of the frame
			return nil
		}
	}

	frame := NewFrame(cl, vm.sp-numArgs)
	vm.pushFrame(frame)
	vm.sp = frame.basePointer + cl.Fn.NumLocals

	return nil
}

func (vm *VM) callBuiltin(builtin *object.Builtin, numArgs int) error {
	args := vm.stack[vm.sp-numArgs : vm.sp]

	result := builtin.Fn(args...)
	vm.sp = vm.sp - numArgs - 1

	if result != nil {
		err := vm.push(result)
		if err != nil {
			return err
		}
	} else {
		err := vm.push(Null)
		if err != nil {
			return err
		}
	}

	return nil
}

func (vm *VM) pushClosure(constIndex, numFree int) error {
	constant := vm.state.Constants[constIndex]
	function, ok := constant.(*object.CompiledFunction)
	if !ok {
		return fmt.Errorf("not a function %+v", constant)
	}

	free := make([]object.Object, numFree)
	for i := 0; i < numFree; i++ {
		free[i] = vm.stack[vm.sp-numFree+i]
	}
	vm.sp = vm.sp - numFree

	closure := &object.Closure{Fn: function, Free: free}
	return vm.push(closure)
}

func (vm *VM) loadModule(name object.Object) error {
	s, ok := name.(*object.String)
	if !ok {
		return fmt.Errorf(
			"TypeError: import() expected argument #1 to be `str` got `%s`",
			name.Type(),
		)
	}

	attrs, err := executeModule(s.Value, vm.state)
	if err != nil {
		return err
	}

	module := &object.Module{Name: s.Value, Attrs: attrs}
	return vm.push(module)
}

func (vm *VM) LastPoppedStackElem() object.Object {
	return vm.stack[vm.sp]
}

func (vm *VM) Run() error {
	var n int
	var ip int
	var ins code.Instructions
	var op code.Opcode

	if vm.Debug {
		start := time.Now()
		defer func() {
			log.Printf("%d instructions executeuted in %s", n, time.Now().Sub(start))
		}()
	}

	var err error

	for vm.frame.ip < len(vm.frame.Instructions())-1 && err == nil {
		vm.frame.ip++

		ip = vm.frame.ip
		ins = vm.frame.Instructions()
		op = code.Opcode(ins[ip])

		if vm.Debug {
			n++
			log.Printf(
				"%-25s %-20s\n",
				fmt.Sprintf(
					"%04d %s", ip,
					strings.Split(ins[ip:].String(), "\n")[0][4:],
				),
				fmt.Sprintf(
					"[ip=%02d fp=%02d, sp=%02d]",
					ip, vm.fp-1, vm.sp,
				),
			)
		}

		switch op {
		case code.OpConstant:
			constIndex := code.ReadUint16(ins[ip+1:])
			vm.frame.ip += 2
			err = vm.push(vm.state.Constants[constIndex])

		case code.OpPop:
			vm.pop()

		case code.OpTrue:
			err = vm.push(True)

		case code.OpFalse:
			err = vm.push(False)

		case code.OpJump:
			pos := int(code.ReadUint16(ins[ip+1:]))
			vm.frame.ip = pos - 1

		case code.OpJumpNotTruthy:
			pos := int(code.ReadUint16(ins[ip+1:]))
			vm.frame.ip += 2
			if !isTruthy(vm.pop()) {
				vm.frame.ip = pos - 1
			}

		case code.OpNull:
			err = vm.push(Null)

		case code.OpSetGlobal:
			globalIndex := code.ReadUint16(ins[ip+1:])
			vm.frame.ip += 2

			ref := vm.pop()
			if immutable, ok := ref.(object.Immutable); ok {
				vm.state.Globals[globalIndex] = immutable.Clone()
			} else {
				vm.state.Globals[globalIndex] = ref
			}

			err = vm.push(Null)

		case code.OpAssignGlobal:
			globalIndex := code.ReadUint16(ins[ip+1:])
			vm.frame.ip += 2
			vm.state.Globals[globalIndex] = vm.pop()

			err = vm.push(Null)

		case code.OpAssignLocal:
			localIndex := code.ReadUint8(ins[ip+1:])
			vm.frame.ip += 1

			vm.stack[vm.frame.basePointer+int(localIndex)] = vm.pop()

			err = vm.push(Null)

		case code.OpGetGlobal:
			globalIndex := code.ReadUint16(ins[ip+1:])
			vm.frame.ip += 2
			err = vm.push(vm.state.Globals[globalIndex])

		case code.OpArray:
			numElements := int(code.ReadUint16(ins[ip+1:]))
			vm.frame.ip += 2
			err = vm.executeMakeArray(vm.sp-numElements, vm.sp)

		case code.OpHash:
			numElements := int(code.ReadUint16(ins[ip+1:]))
			vm.frame.ip += 2
			err = vm.executeMakeHash(vm.sp-numElements, vm.sp)

		case code.OpSetItem:
			err = vm.executeSetItem()

		case code.OpGetItem:
			err = vm.executeGetItem()

		case code.OpCall:
			args := int(code.ReadUint8(ins[ip+1:]))
			vm.frame.ip++
			err = vm.executeCall(args)

		case code.OpReturn:
			err = vm.executeReturn()

		case code.OpSetLocal:
			localIndex := code.ReadUint8(ins[ip+1:])
			vm.frame.ip += 1

			ref := vm.pop()
			if immutable, ok := ref.(object.Immutable); ok {
				vm.stack[vm.frame.basePointer+int(localIndex)] = immutable.Clone()
			} else {
				vm.stack[vm.frame.basePointer+int(localIndex)] = ref
			}

			err = vm.push(Null)

		case code.OpGetLocal:
			localIndex := code.ReadUint8(ins[ip+1:])
			vm.frame.ip += 1
			err = vm.push(vm.stack[vm.frame.basePointer+int(localIndex)])

		case code.OpGetBuiltin:
			builtinIndex := code.ReadUint8(ins[ip+1:])
			vm.frame.ip++
			builtin := builtins.BuiltinsIndex[builtinIndex]
			err = vm.push(builtin)

		case code.OpClosure:
			constIndex := code.ReadUint16(ins[ip+1:])
			numFree := code.ReadUint8(ins[ip+3:])
			vm.frame.ip += 3
			err = vm.pushClosure(int(constIndex), int(numFree))

		case code.OpGetFree:
			freeIndex := code.ReadUint8(ins[ip+1:])
			vm.frame.ip += 1
			err = vm.push(vm.frame.cl.Free[freeIndex])

		case code.OpCurrentClosure:
			currentClosure := vm.frame.cl
			err = vm.push(currentClosure)

		case code.OpLoadModule:
			err = vm.executeLoadModule()

		case code.OpAdd:
			err = vm.executeAdd()
		case code.OpSub:
			err = vm.executeSub()
		case code.OpMul:
			err = vm.executeMul()
		case code.OpDiv:
			err = vm.executeDiv()
		case code.OpMod:
			err = vm.executeMod()
		case code.OpOr:
			err = vm.executeOr()
		case code.OpAnd:
			err = vm.executeAnd()
		case code.OpBitwiseOR:
			err = vm.executeBitwiseOr()
		case code.OpBitwiseXOR:
			err = vm.executeBitwiseXor()
		case code.OpBitwiseAND:
			err = vm.executeBitwiseAnd()
		case code.OpLeftShift:
			err = vm.executeLeftShift()
		case code.OpRightShift:
			err = vm.executeRightShift()

		case code.OpEqual:
			err = vm.executeEqual()
		case code.OpNotEqual:
			err = vm.executeNotEqual()
		case code.OpGreaterThan:
			err = vm.executeGreaterThan()
		case code.OpGreaterThanEqual:
			err = vm.executeGreaterThanOrEqual()

		case code.OpNot:
			err = vm.executeNot()

		case code.OpBitwiseNOT:
			err = vm.executeBitwiseNot()

		case code.OpMinus:
			err = vm.executeMinus()

		default:
			err = fmt.Errorf("unhandled opcode: %s", op)
		}

		if vm.Debug {
			log.Printf(
				"%-25s [ip=%02d fp=%02d, sp=%02d]",
				"", ip, vm.fp-1, vm.sp,
			)
		}
	}

	return err
}