// 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 Caller interface
type Caller interface {
	Call(vm *VM, arguments ...Value) []Value
}

// Callable value types
type CallableValue struct {
	Name string
}

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

func (val *CallableValue) Call(vm *VM, arguments ...Value) ListValue {
	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
}

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

// A script defined function
type DefinedValue struct {
	CallableValue
	Definition *Ast
}

func NewDefinedValue(name string, definition *Ast) DefinedValue {
	result := DefinedValue{}
	result.Name = name
	result.Definition = definition
	return result
}

func (defined *DefinedValue) Call(vm *VM, arguments ...Value) []Value {
	return vm.CallDefined(defined.Definition, arguments...)
}

/*
	Amount of types that will be considered inside a signature.
	Limited mosty to allow hashability.
*/
const TypesInSignature = 8

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

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

func (signature *Signature) IsMatch(arguments ...Value) bool {
	for i, kind := range signature.Types {
		if i > len(arguments) || arguments[i] == nil {
			return false
		}
		if kind != arguments[i].Type() && kind != AnyTypeValue {
			return false
		}
	}
	return true
}

/* An overload is an overloaded callable value that can be called. */
type Overload struct {
	CallableValue
}

/* 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 (cover *CoverValue) Call(vm *VM, arguments ...Value) ListValue {
	signature := CalculateSignature(arguments...)
	if overload, ok := cover.Overloads[signature]; ok {
		return overload.Call(vm, arguments...)
	} else {
		for signature, overload := range cover.Overloads {
			if signature.IsMatch(arguments...) {
				return overload.Call(vm, arguments...)
			}
		}
	}
	vm.Fail()
	return NewListValue(NewErrorValuef("Could not match cover %s with arguments.", cover.Name))
}

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

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

// 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) Parent(level int) *Scope {
	if level < 1 {
		return scope
	}
	parent := scope.parent
	for parent != nil && level > 1 {
		level--
		parent = parent.parent
	}
	return parent
}

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
}

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

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

// Virtual machine
type VM struct {
	TopScope *Scope // Top level scope
	TopFrame *Frame // Top level scope
	*Scope          // Current Scope
	*Frame          // Current frame
}

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

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

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

func (vm *VM) PopFrame() *Frame {
	if (vm.Frame != vm.TopFrame) && (vm.Frame.parent != nil) {
		frame := vm.Frame
		vm.Frame = frame.parent
		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 (vm *VM) CallDefined(ast *Ast, arguments ...Value) []Value {
	return ast.Run(vm, arguments)
}

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

func (vm *VM) CallNamed(name string, arguments ...Value) []Value {
	value := vm.Lookup(name)
	switch toCall := value.(type) {
	case BuiltinValue:
		return vm.CallBuiltin(toCall.Handler, arguments...)
	case DefinedValue:
		return vm.CallDefined(toCall.Definition, arguments...)
	default:
		return NewValueArray(NewErrorValuef("Cannot call %s: %v", name, value))
	}
}

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

}
*/

func (vm *VM) Register(name string, value Value) Value {
	return vm.Scope.Register(name, 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, ast *Ast) Value {
	value := NewDefinedValue(name, ast)
	return vm.Register(name, value)
}

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

func (vm *VM) RunChildren(ast Ast, args ...Value) []Value {
	result := NewValueArray()
	for _, child := range ast.Children() {
		val := child.Run(vm, args)
		result = append(result, val...)
	}
	return result
}

/*

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)}}
	}
}
*/