package vm

import (
	"errors"
	"fmt"
	"math"
	"os"
	"reflect"
	"strconv"
	"strings"

	"github.com/mattn/kinako/ast"
)

var (
	NilValue   = reflect.ValueOf((*interface{})(nil))
	NilType    = reflect.TypeOf((*interface{})(nil))
	TrueValue  = reflect.ValueOf(true)
	FalseValue = reflect.ValueOf(false)
)

// Error provides a convenient interface for handling runtime error.
// It can be Error interface with type cast which can call Pos().
type Error struct {
	Message string
}

var (
	BreakError     = errors.New("Unexpected break statement")
	ContinueError  = errors.New("Unexpected continue statement")
	ReturnError    = errors.New("Unexpected return statement")
	InterruptError = errors.New("Execution interrupted")
)

// Error returns the error message.
func (e *Error) Error() string {
	return e.Message
}

// Func is function interface to reflect functions internaly.
type Func func(args ...reflect.Value) (reflect.Value, error)

// Run executes statements in the specified environment.
func Run(stmts []ast.Stmt, env *Env) (reflect.Value, error) {
	rv := NilValue
	var err error
	for _, stmt := range stmts {
		rv, err = RunSingleStmt(stmt, env)
		if err != nil {
			return rv, err
		}
	}
	return rv, nil
}

// Interrupts the execution of any running statements in the specified environment.
//
// Note that the execution is not instantly aborted: after a call to Interrupt,
// the current running statement will finish, but the next statement will not run,
// and instead will return a NilValue and an InterruptError.
func Interrupt(env *Env) {
	env.Lock()
	*(env.interrupt) = true
	env.Unlock()
}

// RunSingleStmt executes one statement in the specified environment.
func RunSingleStmt(stmt ast.Stmt, env *Env) (reflect.Value, error) {
	env.Lock()
	if *(env.interrupt) {
		*(env.interrupt) = false
		env.Unlock()

		return NilValue, InterruptError
	}
	env.Unlock()

	switch stmt := stmt.(type) {
	case *ast.ExprStmt:
		rv, err := invokeExpr(stmt.Expr, env)
		if err != nil {
			return rv, err
		}
		return rv, nil
	case *ast.LetStmt:
		rv := NilValue
		var err error
		rv, err = invokeExpr(stmt.Rhs, env)
		if err != nil {
			return rv, err
		}
		_, err = invokeLetExpr(stmt.Lhs, rv, env)
		if err != nil {
			return rv, err
		}
		return rv, nil
	default:
		return NilValue, errors.New("unknown statement")
	}
}

// toString converts all reflect.Value-s into string.
func toString(v reflect.Value) string {
	if v.Kind() == reflect.Interface {
		v = v.Elem()
	}
	if v.Kind() == reflect.String {
		return v.String()
	}
	if !v.IsValid() {
		return "nil"
	}
	return fmt.Sprint(v.Interface())
}

// toBool converts all reflect.Value-s into bool.
func toBool(v reflect.Value) bool {
	if v.Kind() == reflect.Interface {
		v = v.Elem()
	}

	switch v.Kind() {
	case reflect.Float32, reflect.Float64:
		return v.Float() != 0.0
	case reflect.Int, reflect.Int32, reflect.Int64:
		return v.Int() != 0
	case reflect.Bool:
		return v.Bool()
	case reflect.String:
		if v.String() == "true" {
			return true
		}
		if toInt64(v) != 0 {
			return true
		}
	}
	return false
}

// toFloat64 converts all reflect.Value-s into float64.
func toFloat64(v reflect.Value) float64 {
	if v.Kind() == reflect.Interface {
		v = v.Elem()
	}
	switch v.Kind() {
	case reflect.Float32, reflect.Float64:
		return v.Float()
	case reflect.Int, reflect.Int32, reflect.Int64:
		return float64(v.Int())
	}
	return 0.0
}

func isNil(v reflect.Value) bool {
	if !v.IsValid() || v.Kind().String() == "unsafe.Pointer" {
		return true
	}
	if (v.Kind() == reflect.Interface || v.Kind() == reflect.Ptr) && v.IsNil() {
		return true
	}
	return false
}

func isNum(v reflect.Value) bool {
	switch v.Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr, reflect.Float32, reflect.Float64:
		return true
	}
	return false
}

// equal returns true when lhsV and rhsV is same value.
func equal(lhsV, rhsV reflect.Value) bool {
	lhsIsNil, rhsIsNil := isNil(lhsV), isNil(rhsV)
	if lhsIsNil && rhsIsNil {
		return true
	}
	if (!lhsIsNil && rhsIsNil) || (lhsIsNil && !rhsIsNil) {
		return false
	}
	if lhsV.Kind() == reflect.Interface || lhsV.Kind() == reflect.Ptr {
		lhsV = lhsV.Elem()
	}
	if rhsV.Kind() == reflect.Interface || rhsV.Kind() == reflect.Ptr {
		rhsV = rhsV.Elem()
	}
	if !lhsV.IsValid() || !rhsV.IsValid() {
		return true
	}
	if isNum(lhsV) && isNum(rhsV) {
		if rhsV.Type().ConvertibleTo(lhsV.Type()) {
			rhsV = rhsV.Convert(lhsV.Type())
		}
	}
	if lhsV.CanInterface() && rhsV.CanInterface() {
		return reflect.DeepEqual(lhsV.Interface(), rhsV.Interface())
	}
	return reflect.DeepEqual(lhsV, rhsV)
}

// toInt64 converts all reflect.Value-s into int64.
func toInt64(v reflect.Value) int64 {
	if v.Kind() == reflect.Interface {
		v = v.Elem()
	}
	switch v.Kind() {
	case reflect.Float32, reflect.Float64:
		return int64(v.Float())
	case reflect.Int, reflect.Int32, reflect.Int64:
		return v.Int()
	case reflect.String:
		s := v.String()
		var i int64
		var err error
		if strings.HasPrefix(s, "0x") {
			i, err = strconv.ParseInt(s, 16, 64)
		} else {
			i, err = strconv.ParseInt(s, 10, 64)
		}
		if err == nil {
			return int64(i)
		}
	}
	return 0
}

func invokeLetExpr(expr ast.Expr, rv reflect.Value, env *Env) (reflect.Value, error) {
	switch lhs := expr.(type) {
	case *ast.IdentExpr:
		if env.Set(lhs.Lit, rv) != nil {
			if strings.Contains(lhs.Lit, ".") {
				return NilValue, fmt.Errorf("Undefined symbol '%s'", lhs.Lit)
			}
			env.Define(lhs.Lit, rv)
		}
		return rv, nil
	}
	return NilValue, errors.New("Invalid operation")
}

// invokeExpr evaluates one expression.
func invokeExpr(expr ast.Expr, env *Env) (reflect.Value, error) {
	switch e := expr.(type) {
	case *ast.NumberExpr:
		if strings.Contains(e.Lit, ".") || strings.Contains(e.Lit, "e") {
			v, err := strconv.ParseFloat(e.Lit, 64)
			if err != nil {
				return NilValue, err
			}
			return reflect.ValueOf(float64(v)), nil
		}
		var i int64
		var err error
		if strings.HasPrefix(e.Lit, "0x") {
			i, err = strconv.ParseInt(e.Lit[2:], 16, 64)
		} else {
			i, err = strconv.ParseInt(e.Lit, 10, 64)
		}
		if err != nil {
			return NilValue, err
		}
		return reflect.ValueOf(i), nil
	case *ast.IdentExpr:
		return env.Get(e.Lit)
	case *ast.StringExpr:
		return reflect.ValueOf(e.Lit), nil
	case *ast.UnaryExpr:
		v, err := invokeExpr(e.Expr, env)
		if err != nil {
			return v, err
		}
		switch e.Operator {
		case "-":
			if v.Kind() == reflect.Float64 {
				return reflect.ValueOf(-v.Float()), nil
			}
			return reflect.ValueOf(-v.Int()), nil
		case "^":
			return reflect.ValueOf(^toInt64(v)), nil
		case "!":
			return reflect.ValueOf(!toBool(v)), nil
		default:
			return NilValue, errors.New("Unknown operator ''")
		}
	case *ast.ParenExpr:
		v, err := invokeExpr(e.SubExpr, env)
		if err != nil {
			return v, err
		}
		return v, nil
	case *ast.BinOpExpr:
		lhsV := NilValue
		rhsV := NilValue
		var err error

		lhsV, err = invokeExpr(e.Lhs, env)
		if err != nil {
			return lhsV, err
		}
		if lhsV.Kind() == reflect.Interface {
			lhsV = lhsV.Elem()
		}
		if e.Rhs != nil {
			rhsV, err = invokeExpr(e.Rhs, env)
			if err != nil {
				return rhsV, err
			}
			if rhsV.Kind() == reflect.Interface {
				rhsV = rhsV.Elem()
			}
		}
		switch e.Operator {
		case "+":
			if lhsV.Kind() == reflect.String || rhsV.Kind() == reflect.String {
				return reflect.ValueOf(toString(lhsV) + toString(rhsV)), nil
			}
			if (lhsV.Kind() == reflect.Array || lhsV.Kind() == reflect.Slice) && (rhsV.Kind() != reflect.Array && rhsV.Kind() != reflect.Slice) {
				return reflect.Append(lhsV, rhsV), nil
			}
			if (lhsV.Kind() == reflect.Array || lhsV.Kind() == reflect.Slice) && (rhsV.Kind() == reflect.Array || rhsV.Kind() == reflect.Slice) {
				return reflect.AppendSlice(lhsV, rhsV), nil
			}
			if lhsV.Kind() == reflect.Float64 || rhsV.Kind() == reflect.Float64 {
				return reflect.ValueOf(toFloat64(lhsV) + toFloat64(rhsV)), nil
			}
			return reflect.ValueOf(toInt64(lhsV) + toInt64(rhsV)), nil
		case "-":
			if lhsV.Kind() == reflect.Float64 || rhsV.Kind() == reflect.Float64 {
				return reflect.ValueOf(toFloat64(lhsV) - toFloat64(rhsV)), nil
			}
			return reflect.ValueOf(toInt64(lhsV) - toInt64(rhsV)), nil
		case "*":
			if lhsV.Kind() == reflect.String && (rhsV.Kind() == reflect.Int || rhsV.Kind() == reflect.Int32 || rhsV.Kind() == reflect.Int64) {
				return reflect.ValueOf(strings.Repeat(toString(lhsV), int(toInt64(rhsV)))), nil
			}
			if lhsV.Kind() == reflect.Float64 || rhsV.Kind() == reflect.Float64 {
				return reflect.ValueOf(toFloat64(lhsV) * toFloat64(rhsV)), nil
			}
			return reflect.ValueOf(toInt64(lhsV) * toInt64(rhsV)), nil
		case "/":
			return reflect.ValueOf(toFloat64(lhsV) / toFloat64(rhsV)), nil
		case "%":
			return reflect.ValueOf(toInt64(lhsV) % toInt64(rhsV)), nil
		case "==":
			return reflect.ValueOf(equal(lhsV, rhsV)), nil
		case "!=":
			return reflect.ValueOf(equal(lhsV, rhsV) == false), nil
		case ">":
			return reflect.ValueOf(toFloat64(lhsV) > toFloat64(rhsV)), nil
		case ">=":
			return reflect.ValueOf(toFloat64(lhsV) >= toFloat64(rhsV)), nil
		case "<":
			return reflect.ValueOf(toFloat64(lhsV) < toFloat64(rhsV)), nil
		case "<=":
			return reflect.ValueOf(toFloat64(lhsV) <= toFloat64(rhsV)), nil
		case "|":
			return reflect.ValueOf(toInt64(lhsV) | toInt64(rhsV)), nil
		case "||":
			if toBool(lhsV) {
				return lhsV, nil
			}
			return rhsV, nil
		case "&":
			return reflect.ValueOf(toInt64(lhsV) & toInt64(rhsV)), nil
		case "&&":
			if toBool(lhsV) {
				return rhsV, nil
			}
			return lhsV, nil
		case "**":
			if lhsV.Kind() == reflect.Float64 {
				return reflect.ValueOf(math.Pow(toFloat64(lhsV), toFloat64(rhsV))), nil
			}
			return reflect.ValueOf(int64(math.Pow(toFloat64(lhsV), toFloat64(rhsV)))), nil
		case ">>":
			return reflect.ValueOf(toInt64(lhsV) >> uint64(toInt64(rhsV))), nil
		case "<<":
			return reflect.ValueOf(toInt64(lhsV) << uint64(toInt64(rhsV))), nil
		default:
			return NilValue, errors.New("Unknown operator")
		}
	case *ast.CallExpr:
		f, err := env.Get(e.Name)
		if err != nil {
			return f, err
		}

		args := []reflect.Value{}
		for i, expr := range e.SubExprs {
			arg, err := invokeExpr(expr, env)
			if err != nil {
				return arg, err
			}

			if i < f.Type().NumIn() {
				if !f.Type().IsVariadic() {
					it := f.Type().In(i)
					if arg.Kind().String() == "unsafe.Pointer" {
						arg = reflect.New(it).Elem()
					}
					if arg.Kind() != it.Kind() && arg.IsValid() && arg.Type().ConvertibleTo(it) {
						arg = arg.Convert(it)
					} else if arg.Kind() == reflect.Func {
						if _, isFunc := arg.Interface().(Func); isFunc {
							rfunc := arg
							arg = reflect.MakeFunc(it, func(args []reflect.Value) []reflect.Value {
								for i := range args {
									args[i] = reflect.ValueOf(args[i])
								}
								return rfunc.Call(args)[:it.NumOut()]
							})
						}
					} else if !arg.IsValid() {
						arg = reflect.Zero(it)
					}
				}
			}
			if !arg.IsValid() {
				arg = NilValue
			}

			args = append(args, arg)
		}
		ret := NilValue
		fnc := func() {
			defer func() {
				if os.Getenv("KINAKO_DEBUG") == "" {
					if ex := recover(); ex != nil {
						if e, ok := ex.(error); ok {
							err = e
						} else {
							err = errors.New(fmt.Sprint(ex))
						}
					}
				}
			}()
			if f.Kind() == reflect.Interface {
				f = f.Elem()
			}
			rets := f.Call(args)
			if f.Type().NumOut() == 1 {
				ret = rets[0]
			} else {
				var result []interface{}
				for _, r := range rets {
					result = append(result, r.Interface())
				}
				ret = reflect.ValueOf(result)
			}
		}
		fnc()
		if err != nil {
			return ret, err
		}
		return ret, nil
	case *ast.TernaryOpExpr:
		rv, err := invokeExpr(e.Expr, env)
		if err != nil {
			return rv, err
		}
		if toBool(rv) {
			lhsV, err := invokeExpr(e.Lhs, env)
			if err != nil {
				return lhsV, err
			}
			return lhsV, nil
		}
		rhsV, err := invokeExpr(e.Rhs, env)
		if err != nil {
			return rhsV, err
		}
		return rhsV, nil
	default:
		return NilValue, errors.New("Unknown expression")
	}
}