// vm, the virtual low level machine that runs MUESLI.
package muesli

import "fmt"

// Handler function
type Handler func(vm *VM, arguments ...Value) []Value

func (handler *Handler) Call(vm *VM, arguments ...Value) []Value {
	return (*handler)(vm, arguments...)
}

// A callable Value must implement the Callable interface
type Callable interface {
	// Callable can be called
	Call(vm *VM, arguments ...Value) []Value
	// Callable has a position here it was defined. Needed for tracebacks.
	Position() *Position
}

// A helper Value has a help text available.
// This help text can be set as well.
type Helper interface {
	HelperName() string
	Help() string
	SetHelp(string) string
}


// Callable value types
type CallableValue struct {
	// Name of the callable
	Name string
	// Help string for the callable.
	HelpText string
}

// Implement Helper interface
func (val CallableValue) Help() string {
	return val.HelpText
}

// Implement Helper interface
func (val * CallableValue) SetHelp(help string) string {
	val.HelpText = help
	return val.HelpText
}

// Implement Helper interface
func (val CallableValue) HelperName() string {
	return val.Name
}

// AppendHelp appends help to an existing helper. 
func AppendHelp(helper Helper, extra string) string {
	return helper.SetHelp( helper.Help() + extra)
}

// ClearHelp rresets the help text to an empty string.
func ClearHelp(helper Helper, extra string) string {
	return helper.SetHelp("")
}


func (val CallableValue) String() string {
	return val.Name
}

func (val CallableValue) Type() TypeValue {
	return TypeValue("Callable")
}

func (from CallableValue) Convert(to interface{}) error {
	return NewErrorValuef("Cannot convert the callable value %v to %v", from, to)
}

func (val *CallableValue) Call(vm *VM, arguments ...Value) []Value {
	panic("Not implemented")
}

// A struct to store a built in function
type BuiltinValue struct {
	CallableValue
	Handler
}

func NewCallableValue(name string) CallableValue {
	return CallableValue{name, ""}
}

func NewBuiltinValue(name string, handler Handler) *BuiltinValue {
	result := &BuiltinValue{}
	result.Name = name
	result.Handler = handler
	return result
}

// A block in a script.
type BlockValue struct {
	CallableValue
	Ast *Ast
}

func NewBlockValue(definition *Ast) *BlockValue {
	result := &BlockValue{}
	result.Name = fmt.Sprintf("<block:%s>", definition.String())
	result.Ast = definition
	return result
}

func (block * BlockValue) Position() *Position {
	if block == nil {
		return nil
	}

	if block.Ast == nil {
		return nil
	}	
	pos := block.Ast.Token().Position
	return &pos
}

func (defined * DefinedValue) Position() *Position {
	if defined == nil {
		return nil
	}

	if defined.Body == nil {
		return nil
	}	
	return defined.Body.Position()
}

func (cv CallableValue) Position() *Position {
	pos := Position{cv.Name, 1, 1}
	return &pos
}


/* Parameters for a defined value */
type Parameter struct {
	Name WordValue
	Type TypeValue
}


// A script defined function
type DefinedValue struct {	
	CallableValue
	Body *BlockValue
	Parameters []*Parameter
}

func NewDefinedValue(name string, params []*Parameter, body *BlockValue) *DefinedValue {
	result := &DefinedValue{}
	result.Name = name
	result.Body = body
	result.Parameters = params
	return result
}

func (defined *DefinedValue) Call(vm *VM, arguments ...Value) []Value {
	for i , arg := range arguments {
		if i >= len(defined.Parameters) {
			break
		}
		param := defined.Parameters[i]
		expectedType := param.Type
		if !expectedType.IsMatch(arg.Type()) {
			return Fail(NewErrorValuef("Argument %d type mismatch: %s<->%s", i, expectedType, arg.Type()))
		}
		vm.Register(param.Name.String(), arg)
	}
	
	res := defined.Body.Call(vm, arguments...)
	return res

}

func (defined *DefinedValue) Help() string {
	help := defined.CallableValue.Help()
	extra := "["
	for _, parameter := range defined.Parameters {
		extra = fmt.Sprintf("%s %s %s", extra, parameter.Name, parameter.Type)
	}
	extra = extra + "]:"
	return extra + help
}


/*
	Amount of types that will be considered inside a signature.
	Limited mosty to allow hashability, that is, Signature is a map key.
*/
const TypesInSignature = 32

/* A signature describes the desired types of an overloaded function call. */
type Signature struct {
	Types [TypesInSignature]TypeValue
}

func (s Signature) String() string {
	res := "["
	sep := ""
	for _, typ := range s.Types {
		if typ != ZeroTypeValue { 
			res = res + sep + typ.String()
			sep = " "
		}
	}
	res = res + "]"
	return res
}

func CalculateSignature(arguments ...Value) Signature {
	signature := Signature{}
	for i := 0; i < len(signature.Types); i++ {
		if i < len(arguments) {
			signature.Types[i] = arguments[i].Type()
		} else {			
			signature.Types[i] = AnyTypeValue
		}
	}
	return signature
}

func (tv TypeValue) IsMatch(other TypeValue) bool {
	if tv == AnyTypeValue || other == AnyTypeValue {
		return true
	}
	if tv == ZeroTypeValue || other == ZeroTypeValue {
		return true
	}
	return tv == other
}

func (signature Signature) IsMatch(other Signature) bool {
	for i, kind := range signature.Types {
		t1 := kind
		t2 := other.Types[i]
		if !t1.IsMatch(t2) {
			return false
		}
	}
	return true
}

/* An overload is an overloaded value that can be called. */
type Overload struct {
	Name string
	Callable
}

/* A cover is a callable that dispatches to other callables depending on
the types of the arguments, in particular the first one. The individual
callable functions are the overloads
*/
type CoverValue struct {
	CallableValue
	Overloads map[Signature]Overload
}

func (cv CoverValue) String() string {
	res := fmt.Sprintf("cover %s [ ", cv.Name)
	for k, v := range cv.Overloads {
		res = fmt.Sprintf("%s [%v] %s", res, k, v.Name)
	}
	res = fmt.Sprintf("%s].", res)
	return res;
}

func NewCoverValue(name string) *CoverValue {
	result := &CoverValue{}
	result.Name = name
	result.Overloads = make(map[Signature]Overload)
	return result
}


func (cover *CoverValue) Help() string {
	help := cover.CallableValue.Help()
	extra := "\n"
	for signature, overload := range cover.Overloads {
		// fmt.Printf("overload: %v", signature)
		extra = extra + fmt.Sprintf("* %v -> %s\n", signature.String(), overload.Name)
	}
	return help + extra
}



func (cover *CoverValue) Call(vm *VM, arguments ...Value) []Value {
	signature := CalculateSignature(arguments...)
	if overload, ok := cover.Overloads[signature]; ok {
		return overload.Call(vm, arguments...)
	} else {
		for overloadSignature, overload := range cover.Overloads {
			if signature.IsMatch(overloadSignature) {
				return overload.Call(vm, arguments...)
			}
		}
	}
	vm.Fail()
	return Fail(NewErrorValuef("Could not match cover %s with arguments: %s<->%v", cover.String(), signature, arguments))
}

const (
	CoverTypeValue   = TypeValue("Cover")
	BuiltinTypeValue = TypeValue("Builtin")
	DefinedTypeValue = TypeValue("Defined")
	BlockTypeValue = TypeValue("Block")
)

func (v CoverValue) Type() TypeValue   { return CoverTypeValue }
func (v BuiltinValue) Type() TypeValue { return BuiltinTypeValue }
func (v DefinedValue) Type() TypeValue { return DefinedTypeValue }
func (v BlockValue) Type() TypeValue { return BlockTypeValue }

func (from CoverValue) Convert(to interface{}) error {
	return NewErrorValuef("Cannot convert the cover value %v to %v", from, to)
}

func (from BuiltinValue) Convert(to interface{}) error {
	return NewErrorValuef("Cannot convert the builtin value %v to %v", from, to)
}

func (from DefinedValue) Convert(to interface{}) error {
	return NewErrorValuef("Cannot convert the defined value %v to %v", from, to)
}

func (from BlockValue) Convert(to interface{}) error {
	if toValue, isOk := to.(*BlockValue) ; isOk {
		(*toValue) = from
		return nil
	} 
	return NewErrorValuef("Cannot convert the block value %v to %v", from, to)
}


func (cv * CoverValue) AddOverload(name string, callable Callable, tv ... TypeValue) error {
	// fmt.Printf("AddOverload: %v\n", tv)
	
	signature := Signature{}
	length := len(tv)
	if length > len(signature.Types) {
		length = len(signature.Types)
	}
	
	for i := 0; i < length; i++ {
		signature.Types[i] = tv[i]
	}
		
	cv.Overloads[signature] = Overload { Name: name, Callable: callable } 
	
	// fmt.Printf("Overloads: %v\n", cv.Overloads)
	
	return nil
}

func (vm * VM) AddOverload(from, target string, level int, tv... TypeValue) error {
	var cover *CoverValue
	var callable Callable
	var ok bool	
	lookup := vm.Lookup(from)
	if lookup == nil { 
		cover = vm.RegisterCover(from, level)
	} else if cover, ok = lookup.(*CoverValue) ; !ok {
		return fmt.Errorf("%s exists and is not a cover value", from)
	}
	
	// fmt.Printf("AddOverload: %v %v\n", lookup, cover)
	
	lookup = vm.Lookup(target)
	if lookup == nil { 
		return fmt.Errorf("target %s is not defined", target)
	}
	// fmt.Printf("AddOverload lookup: %v\n", lookup)
	
	if callable, ok = lookup.(Callable) ; !ok {
		return fmt.Errorf("%s is not a callable value", target)
	}
	res := cover.AddOverload(target, callable, tv...)
	
	// fmt.Printf("AddOverload: %v %v\n", lookup, cover)
	
	return res
}

type OverloadDescription struct {
	Target string
	Types []TypeValue
	Level int
}

func (vm * VM) AddOverloads(from string, descriptions ... OverloadDescription) error {
	for _, od := range descriptions {
		err := vm.AddOverload(from, od.Target, od.Level, od.Types...)
		if err != nil {
			panic(fmt.Errorf("internal error: could not register overloads: %s", err))
		}
	}
	return nil
}

func Over(target string, level int, types ... TypeValue) OverloadDescription {
	return OverloadDescription { Target: target, Level: level, Types: types}
}

func (vm * VM) SetHelp(target, help string) error {
	var helper Helper
	var ok bool	
	lookup := vm.Lookup(target)
	if lookup == nil {
		return fmt.Errorf("%s not found", target) 
	} else if helper, ok = lookup.(Helper) ; !ok {
		return fmt.Errorf("%s exists but cannot set help text.", target)
	}
	helper.SetHelp(help)	
	return nil
} 


// Scope of symbols defined in the VM, hierarchical
type Scope struct {
	parent   *Scope
	children []*Scope
	symbols  map[string]Value
}

func NewScope(parent *Scope) *Scope {
	return &Scope{parent, make([]*Scope, 0), make(map[string]Value)}
}


func (scope *Scope) Lookup(name string) Value {
	value, ok := scope.symbols[name]
	if ok {
		return value
	}
	if scope.parent != nil {
		return scope.parent.Lookup(name)
	}
	return NilValue
}

func (scope *Scope) Register(name string, value Value) Value {
	scope.symbols[name] = value
	return value
}

func (scope * Scope) Known(filter func(string, Value) bool) map[string]Value {
	res := make(map[string]Value)
	if scope.parent != nil {
		res = scope.parent.Known(filter)
	}
	for k, v := range scope.symbols {
		if (filter == nil) || filter(k, v) {
			res[k] = v
		}
	}
	return res
}

func (scope * Scope) ForEachDefined(do func(string, Value) (bool, error)) (bool, error)  {
	var res bool = true
	var err error
	
	if (do == nil) {
		return false, fmt.Errorf("do may not be nil")
	}
			
	if scope.parent != nil {
		res, err = scope.parent.ForEachDefined(do)
	}
	if res == false || err != nil {
		return res, err
	}
	for k, v := range scope.symbols {
		res, err = do(k, v)
		if res == false || err != nil {
			return res, err
		}		
	}
	return res, err
}


func (scope* Scope) DefinedHelpers() []Helper {
	res := []Helper{}
	scope.ForEachDefined(func (k string, v Value) (bool, error) {
		helper, hok := v.(Helper)
		if hok {
			res = append(res, helper)
		}
		return true, nil
	})
	return res
}


// Frame of execution of a function
type Frame struct {	
	parent    *Frame
	arguments []Value
	results   []Value
	failed    bool
	returned  bool
	position  *Position
}

func NewFrame(parent *Frame, position *Position) *Frame {
	return &Frame{parent, EmptyValueArray(), EmptyValueArray(), false, false, position}
}

type Tracer interface {
	Trace(vm VM, ast Ast, values ...Value) bool
}

// Virtual machine
type VM struct {
	TopScope *Scope // Top level scope
	TopFrame *Frame // Top level scope
	*Scope          // Current Scope
	*Frame          // Current frame
	Tracer			// Tracer to emit tracing info to, could be used for logging or debugging
	ExitStatus int
}

func NewVM() *VM {
	vm := &VM{NewScope(nil), NewFrame(nil, nil), nil, nil, nil, 0}
	vm.Scope = vm.TopScope
	vm.Frame = vm.TopFrame
	return vm
}

func (vm *VM) PushNewFrame(position *Position) *Frame {
	frame := NewFrame(vm.Frame, position)
	vm.Frame = frame
	return frame
}

func (vm *VM) PushNewScope() *Scope {
	scope := NewScope(vm.Scope)
	vm.Scope = scope
	return scope
}

func (vm *VM) Return(results ...Value) []Value {
	return results
}


func (vm *VM) PopFrame() *Frame {
	if (vm.Frame != vm.TopFrame) && (vm.Frame.parent != nil) {
		frame := vm.Frame
		if frame.returned || frame.failed {
			
		}
		
		
		vm.Frame = frame.parent
		vm.Frame.returned = frame.returned
		vm.Frame.failed = frame.failed
		vm.Frame.results = frame.results
		return frame
	}
	return nil
}

func (vm *VM) PopScope() *Scope {
	if (vm.Scope != vm.TopScope) && (vm.Scope.parent != nil) {
		scope := vm.Scope
		vm.Scope = scope.parent
		return scope
	}
	return nil
}

func (block * BlockValue) Call(vm *VM, arguments ...Value) []Value {
	ast := block.Ast
	arr := vm.RunChildren(*ast, arguments...)
	return arr
}

func (builtin * BuiltinValue) Call(vm *VM, arguments ...Value) []Value {
	handler := builtin.Handler
	return handler.Call(vm, arguments...)
}

/*
func (vm *VM) CallDefined(ast *Ast, arguments ...Value) []Value {	
	arr := vm.RunChildren(*ast, arguments...)
	return arr
}

func (vm *VM) CallBlock(ast *Ast, arguments ...Value) []Value {
	arr := vm.RunChildren(*ast, arguments...)
	return arr
}

func (vm *VM) CallBuiltin(handler Handler, arguments ...Value) []Value {
	return handler.Call(vm, arguments...)
}

func (vm *VM) CallCover(cover * CoverValue, arguments ...Value) []Value {
	return cover.Call(vm, arguments...)
}
*/


func (vm *VM) AddTrace(err error) error {
	res := ""
	for frame := vm.Frame; frame != nil; frame = frame.parent {
		if frame.position == nil {
			res = fmt.Sprintf("%s\nIn frame %v", res, frame)
		} else {
			res = fmt.Sprintf("%s\nIn %s", res, frame.position.String())
		}
	}
	return fmt.Errorf("%s: %s", res, err)
}

func (vm *VM) CallCallable(callable Callable, arguments ...Value) []Value {
	defer vm.PopFrame()
	defer vm.PopScope()
	vm.PushNewFrame(callable.Position())
	vm.PushNewScope()
	return callable.Call(vm, arguments...)
}

func (vm *VM) CallNamed(name string, arguments ...Value) []Value {
	value := vm.Lookup(name)
	if value == nil {
		return ReturnError(vm.AddTrace(NewErrorValuef("Cannot call %s: not found.", name)))
	}
	
	if callable, ok := value.(Callable) ; ok {
		return vm.CallCallable(callable, arguments...)
	} else {
		return ReturnError(vm.AddTrace(NewErrorValuef("Cannot call %s: %v. Not callable", name, value)))
	}
	
	/*
	value := vm.Lookup(name)
	switch toCall := value.(type) {
	case *BuiltinValue:
		return vm.CallBuiltin(toCall.Handler, arguments...)
	case *DefinedValue:
		return vm.CallDefined(toCall.Body.Ast, arguments...)
	case *CoverValue:
		return vm.CallCover(toCall, arguments...)
	case *BlockValue:
		return vm.CallBlock(toCall.Ast, arguments...)	
	default:
		return ReturnError(vm.AddTrace(NewErrorValuef("Cannot call %s: %v. Not callable", name, value)))
	}
	*/
}

/*
func (vm * VM) CallNamedFramed(name string, arguments ...) []Value {
	frame := vm.PushNewFrame()

}
*/

// ScopeUp Returns the levelth scope up from the current one where 0 is the 
// current scope. Returns the toplevel scope if l is greather than the current 
// scope stack depth.
func (vm * VM) ScopeUp(level int) *Scope {
	scope := vm.Scope
	for now := 0; now < level; now++ {
		if scope.parent == nil {
			return scope
		}
		scope = scope.parent
	}
	return scope
}

// RegisterUp registers in klevel scopes up from the current scope, 
// or at toplevel if the level is greater than the total depth
func (vm *VM) RegisterUp(name string, value Value, level int) Value {
	scope := vm.ScopeUp(level)	
	return scope.Register(name, value)
}

func (vm *VM) Register(name string, value Value) Value {
	return vm.Scope.Register(name, value)
}

func (vm *VM) RegisterCover(name string, level int) *CoverValue {
	value := NewCoverValue(name)
	vm.RegisterUp(name, value, level)
	return value
}

func (vm *VM) RegisterBuiltin(name string, handler Handler) Value {
	value := NewBuiltinValue(name, handler)
	return vm.Register(name, value)
}

func (vm *VM) RegisterDefined(name string, params []*Parameter, block *BlockValue, level int) Value {
	value := NewDefinedValue(name, params, block)
	return vm.RegisterUp(name, value, level)
}

// RegisterBuiltinWithHelp
func (vm *VM) RegisterBuiltinWithHelp(name string, handler Handler, help string) Value {
	res := vm.RegisterBuiltin(name, handler)
	vm.SetHelp(name, help)
	return res
}

func (vm *VM) Fail() {
	vm.Frame.failed = true
}

func (vm *VM) RunChildren(ast Ast, args ...Value) []Value {	
	if ast.CountChildren() < 1 {
		return ReturnEmpty()
	}
	/* if ast.CountChildren() == 1 {
		return ast.Child(0).Run(vm, args)
	}
	*/	
	result := []Value{}
	for _, child := range ast.Children() {
		val := child.Run(vm, args...)
		
		if vm.Frame.returned || vm.Frame.failed {
			fmt.Printf("Returned.\n")
			return vm.Frame.results
		}
		
		// skip empty results
		if len(val) < 1  {
			continue
		}
		
		first := val[0]
		if _, isEmpty := first.(EmptyValue); isEmpty  {
			continue
		}
		
		last := val[len(val) -1]
		// errors in the results at the last position take precendence and are propagated upwards.
		if _, isErr := last.(ErrorValue); isErr  {
			return val
		}
			
		result = append(result, val...)
	}
	return result
}

func (vm *VM) RunChildrenLastResult(ast Ast, args ...Value) Value {
	var result Value = EmptyValue{}
	for _, child := range ast.Children() {
		val := child.Run(vm, args...)
		
		if vm.Frame.returned || vm.Frame.failed {
			fmt.Printf("Returned.\n")
			res := vm.Frame.results
			return res[len(res)-1]
		}
				
		// skip empty results
		if len(val) < 1  {
			continue
		}
		
		first := val[0]
		if _, isEmpty := first.(EmptyValue); isEmpty  {
			continue
		}
		
		last := val[len(val) -1]
		// errors in the results at the last position take precendence and are propagated upwards.
		if _, isErr := last.(ErrorValue); isErr  {
			return last
		}

		result = last
	}
	// The last non empty result is the result of this function.
	return result
}

func (vm *VM) RunChildrenFirstResult(ast Ast, args ...Value) Value {
	var result Value = EmptyValue{}
	for _, child := range ast.Children() {
		val := child.Run(vm, args...)
		
		if vm.Frame.returned || vm.Frame.failed {
			fmt.Printf("Returned.\n")
			res := vm.Frame.results
			return res[0]
		}
						
		// skip empty results
		if len(val) < 1  {
			continue
		}
		
		first := val[0]
		if _, isEmpty := first.(EmptyValue); isEmpty  {
			continue
		}
		// otherwise if non empty return the result. 
		return first
	}
	return result
}




func (vm *VM) RunAst(ast Ast, args ...Value) []Value {
	return ast.Run(vm, args...)
}


func (vm *VM) DefinedHelpers() []Helper {
	return vm.Scope.DefinedHelpers()
}



/*

func (vm *VM) RunProgram(ast *BasicAst) ListValue {
	return vm.RunChildren(ast, (*VM).RunStatements)
}

func (vm *VM) RunStatements(ast *BasicAst) ListValue {
	return vm.RunChildren(ast, (*VM).RunStatement)
}

func (vm *VM) RunStatement(ast *BasicAst) ListValue {
	return NewListValue()
}

func (vm *VM) RunSet(ast *BasicAst) ListValue         { return NewListValue() }
func (vm *VM) RunGet(ast *BasicAst) ListValue         { return NewListValue() }
func (vm *VM) RunTarget(ast *BasicAst) ListValue      { return NewListValue() }
func (vm *VM) RunCommand(ast *BasicAst) ListValue     { return NewListValue() }
func (vm *VM) RunArguments(ast *BasicAst) ListValue   { return NewListValue() }
func (vm *VM) RunArgument(ast *BasicAst) ListValue    { return NewListValue() }
func (vm *VM) RunExpression(ast *BasicAst) ListValue  { return NewListValue() }
func (vm *VM) RunBlock(ast *BasicAst) ListValue       { return NewListValue() }
func (vm *VM) RunParenthesis(ast *BasicAst) ListValue { return NewListValue() }
func (vm *VM) RunList(ast *BasicAst) ListValue        { return NewListValue() }
func (vm *VM) RunCapture(ast *BasicAst) ListValue     { return NewListValue() }
func (vm *VM) RunWordValue(ast *BasicAst) ListValue   { return NewListValue() }
func (vm *VM) RunWord(ast *BasicAst) ListValue        { return NewListValue() }
func (vm *VM) RunType(ast *BasicAst) ListValue        { return NewListValue() }
func (vm *VM) RunValue(ast *BasicAst) ListValue       { return NewListValue() }
func (vm *VM) RunEnd(ast *BasicAst) ListValue         { return NewListValue() }
func (vm *VM) RunError(ast *BasicAst) ListValue       { return NewListValue() }

func (vm *VM) Run(ast *BasicAst) ListValue {
	switch ast.AstKind {
	case AstKindProgram:
		return vm.RunProgram(ast)
	case AstKindStatements:
		return vm.RunStatements(ast)
	case AstKindStatement:
		return vm.RunStatement(ast)
	case AstKindSet:
		return vm.RunSet(ast)
	case AstKindGet:
		return vm.RunGet(ast)
	case AstKindTarget:
		return vm.RunTarget(ast)
	case AstKindCommand:
		return vm.RunCommand(ast)
	case AstKindArguments:
		return vm.RunArguments(ast)
	case AstKindArgument:
		return vm.RunArgument(ast)
	case AstKindExpression:
		return vm.RunExpression(ast)
	case AstKindBlock:
		return vm.RunBlock(ast)
	case AstKindParenthesis:
		return vm.RunParenthesis(ast)
	case AstKindList:
		return vm.RunList(ast)
	case AstKindCapture:
		return vm.RunCapture(ast)
	case AstKindWordValue:
		return vm.RunWordValue(ast)
	case AstKindWord:
		return vm.RunWord(ast)
	case AstKindType:
		return vm.RunType(ast)
	case AstKindValue:
		return vm.RunValue(ast)
	case AstKindEnd:
		return vm.RunEnd(ast)
	case AstKindError:
		return vm.RunError(ast)
	default:
		return ListValue{[]Value{NewErrorValuef("Unknown ast node type: %d", ast.AstKind)}}
	}
}
*/