package interpreter

import (
	"fmt"
	"strings"

	"usebox.net/lang/ast"
	"usebox.net/lang/errors"
	"usebox.net/lang/tokens"
)

type Var struct {
	Value any
	Loc   tokens.Location
}

type Env struct {
	env    map[string]Var
	parent *Env
}

func NewEnv(parent *Env) *Env {
	return &Env{make(map[string]Var), parent}
}

func (e *Env) Get(key string, local bool) (Var, bool) {
	p := e
	for {
		if v, ok := p.env[key]; ok {
			return v, true
		}

		if !local && p.parent != nil {
			p = p.parent
			continue
		}

		return Var{}, false
	}
}

func (e *Env) GetArray(key string, local bool) ([]any, bool) {
	v, ok := e.Get(key, local)
	if !ok {
		return nil, false
	}
	arr, ok := v.Value.([]any)
	return arr, ok
}

// Set will create a new enviroment if this new value shadows an existing one.
func (e *Env) Set(key string, value Var) *Env {
	p := e
	if _, ok := e.Get(key, false); ok {
		p = NewEnv(e)
	}
	p.env[key] = value
	return p
}

func (e *Env) Update(key string, value any) error {
	p := e
	for {
		if v, ok := p.env[key]; ok {
			v.Value = value
			p.env[key] = v
			return nil
		}

		if p.parent != nil {
			p = p.parent
			continue
		}

		// should not happen
		return fmt.Errorf("variable not found '%s'", key)
	}
}

func (e *Env) string(pad string) string {
	b := strings.Builder{}

	b.WriteString(fmt.Sprintf("%senv {\n", pad))
	for k, v := range e.env {
		b.WriteString(fmt.Sprintf("%s%s = %v\n", pad+"  ", k, v))
	}
	if e.parent != nil {
		b.WriteString(e.parent.string(pad + "  "))
	}
	b.WriteString(fmt.Sprintf("%s}", pad))

	if pad != "" {
		b.WriteRune('\n')
	}

	return b.String()
}

func (e Env) String() string {
	return e.string("")
}

func (e *Env) Copy() *Env {
	ne := NewEnv(e.parent)
	for k, v := range e.env {
		val := Var{Value: v.Value, Loc: v.Loc}
		// FIXME: structs
		switch v := val.Value.(type) {
		// update the closures to the new environment
		case Function:
			v.closure = ne
			val.Value = v
		// copy the array
		case []any:
			arr := make([]any, len(v))
			copy(arr, v)
			val.Value = arr
		}
		ne.env[k] = val
	}

	return ne
}

type Struct struct {
	name string
	env  *Env
	inst bool
}

func (s Struct) String() string {
	if s.inst {
		return fmt.Sprintf("<struct %s>", s.name)
	} else {
		return fmt.Sprintf("struct %s", s.name)
	}
}

func (s Struct) Instance() Struct {
	return Struct{name: s.name, env: s.env.Copy(), inst: true}
}

type PanicJumpType int

const (
	PanicJumpReturn PanicJumpType = iota
	PanicJumpTailCall
	PanicJumpContinue
	PanicJumpBreak
)

type PanicJump struct {
	typ   PanicJumpType
	value any
	loc   tokens.Location
}

type Interpreter struct {
	env *Env
	// location of the last node evaluated
	last   tokens.Location
	fError bool
}

func NewInterpreter() Interpreter {
	global := NewEnv(nil)
	for k, v := range builtInFuncs {
		// not shadowing any value
		global.Set(k, Var{Value: v})
	}
	return Interpreter{env: global}
}

func (i *Interpreter) Interp(expr any) (val any, err error) {
	val, err = i.evaluate(expr)
	if err != nil {
		return nil, err
	}
	return val, nil
}

func (i *Interpreter) isTrue(expr any) bool {
	switch v := expr.(type) {
	case ast.Number:
		return v != 0
	case string:
		return v != ""
	case bool:
		return v
	case Function, Callable:
		return true
	default:
		return false
	}
}

func (i *Interpreter) unaryNumeric(op tokens.Token, right any) (ast.Number, error) {
	if vr, ok := right.(ast.Number); ok {
		return vr, nil
	}

	// shouldn't happen
	return 0, errors.NewError(errors.Unexpected, op.Loc, "invalid operand")
}

func (i *Interpreter) binaryNumeric(left any, op tokens.Token, right any) (ast.Number, ast.Number, error) {
	vl, okl := left.(ast.Number)
	vr, okr := right.(ast.Number)
	if okl && okr {
		return vl, vr, nil
	}

	// shouldn't happen
	return 0, 0, errors.NewError(errors.Unexpected, op.Loc, "invalid operands")
}

func (i *Interpreter) evaluate(expr any) (any, error) {
	switch v := expr.(type) {
	case ast.Var:
		i.last = v.Name.Loc
		return i.declare(v)
	case ast.Variable:
		i.last = v.Name.Loc
		return i.variable(v)
	case ast.Assign:
		return i.assignment(v)
	case ast.Binary:
		i.last = v.Op.Loc
		return i.binaryExpr(v)
	case ast.Unary:
		i.last = v.Op.Loc
		return i.unaryExpr(v)
	case ast.Literal:
		i.last = v.Value.Loc
		return i.literalExpr(v)
	case ast.Group:
		return i.groupExpr(v)
	case ast.Block:
		return i.block(v)
	case ast.IfElse:
		return i.ifElse(v)
	case ast.For:
		return i.forStmt(v)
	case ast.ForIn:
		return i.forInStmt(v)
	case ast.Call:
		i.last = v.Loc
		return i.call(v)
	case ast.Func:
		i.last = v.Name.Loc
		return i.fun(v)
	case ast.Return:
		return i.returnStmt(v)
	case ast.Continue:
		return i.continueStmt(v)
	case ast.Break:
		return i.breakStmt(v)
	case ast.ExprList:
		return i.exprList(v)
	case ast.Struct:
		return i.strct(v)
	case ast.GetExpr:
		return i.getExpr(v)
	default:
		// XXX
		return nil, errors.Error{
			Code:    errors.Unimplemented,
			Message: fmt.Sprintf("evaluation unimplemented: %s", v),
		}
	}
}

func (i *Interpreter) defVal(typ ast.Type) any {
	switch typ.Value.Id {
	case tokens.TNumber:
		return ast.Number(0)
	case tokens.TBool:
		return false
	case tokens.TString:
		return ""
	case tokens.TArray:
		arr := make([]any, *typ.Len)
		for n := range arr {
			arr[n] = i.defVal(*typ.Ret)
		}
		return arr
	case tokens.TStruct:
		val, _ := i.env.Get(typ.Value.Value, false)
		strct := val.Value.(Struct)
		return strct.Instance()
	default:
		return nil
	}
}

func (i *Interpreter) declare(v ast.Var) (any, error) {
	var initv any
	var err error

	if v.Type.Value.Id == tokens.TArray && *v.Type.Len <= 0 {
		return nil, errors.NewError(errors.InvalidLength, v.Name.Loc, "invalid array length")
	}

	if v.Initv != nil {
		initv, err = i.evaluate(v.Initv)
		if err != nil {
			return 0, err
		}

		i.env = i.env.Set(v.Name.Value, Var{initv, v.Name.Loc})
		return initv, nil
	} else {
		// defaults
		initv = i.defVal(v.Type)
		value := Var{initv, v.Name.Loc}
		i.env = i.env.Set(v.Name.Value, value)
		return initv, nil
	}
}

func (i *Interpreter) variable(v ast.Variable) (any, error) {
	if val, ok := i.env.Get(v.Name.Value, false); ok {
		value := val.Value
		if v.Index != nil {
			index, err := i.evaluate(v.Index)
			if err != nil {
				return nil, err
			}
			idx, ok := index.(ast.Number)
			if !ok || idx < 0 || int(idx) >= *v.Type.Len {
				return nil, errors.NewError(errors.InvalidIndex, v.Name.Loc, "invalid index for", v.Type.String())
			}
			arr, ok := i.env.GetArray(v.Name.Value, false)
			if !ok {
				return nil, errors.NewError(errors.Unexpected, v.Name.Loc, "expected array")
			}
			value = arr[idx]
		}
		return value, nil
	}
	// shouldn't happen
	return nil, errors.NewError(errors.Unexpected, v.Name.Loc, "undefined variable", v.String())
}

func (i *Interpreter) assignment(v ast.Assign) (any, error) {
	env := i.env
	vLeft := v.Left

	if getExpr, ok := v.Left.(ast.GetExpr); ok {
		obj, err := i.evaluate(getExpr.Object)
		if err != nil {
			return nil, err
		}
		strct := obj.(Struct)
		env = strct.env
		vLeft = getExpr.Expr
	}

	left, ok := vLeft.(ast.Variable)
	if !ok {
		return nil, errors.NewError(errors.Unexpected, v.Loc, "expected variable in assignation")
	}
	right, err := i.evaluate(v.Right)
	if err != nil {
		return nil, err
	}

	if left.Type.Value.Id == tokens.TArray && v.Right.Resolve().Value.Id != tokens.TArray {
		if left.Index == nil {
			return nil, errors.NewError(errors.Unexpected, v.Loc, "expected index in assignation")
		}
		index, err := i.evaluate(left.Index)
		if err != nil {
			return nil, err
		}
		idx, ok := index.(ast.Number)
		if !ok || idx < 0 || int(idx) >= *left.Type.Len {
			return nil, errors.NewError(errors.InvalidIndex, v.Loc, "invalid index for", left.Type.String())
		}
		arr, ok := i.env.GetArray(left.Name.Value, false)
		if !ok {
			return nil, errors.NewError(errors.Unexpected, v.Loc, "expected array")
		}
		arr[idx] = right
		right = arr
	}

	err = env.Update(left.Name.Value, right)
	if err != nil {
		return nil, errors.NewError(errors.InvalidValue, left.Name.Loc, err.Error())
	}
	return right, nil
}

func (i *Interpreter) binaryExpr(expr ast.Binary) (any, error) {
	// first lazy operators
	if expr.Op.Id == tokens.And || expr.Op.Id == tokens.Or {
		left, err := i.evaluate(expr.Left)
		if err != nil {
			return nil, err
		}
		if expr.Op.Id == tokens.And {
			if !i.isTrue(left) {
				return false, nil
			}
		} else {
			if i.isTrue(left) {
				return true, nil
			}
		}
		right, err := i.evaluate(expr.Right)
		if err != nil {
			return nil, err
		}
		return i.isTrue(right), nil
	}

	left, err := i.evaluate(expr.Left)
	if err != nil {
		return nil, err
	}
	right, err := i.evaluate(expr.Right)
	if err != nil {
		return nil, err
	}

	// equality compares two values as long as they are the same type
	switch expr.Op.Id {
	case tokens.Ne:
		return right != left, nil
	case tokens.Eq:
		return right == left, nil
	}

	vl, vr, err := i.binaryNumeric(left, expr.Op, right)
	if err != nil {
		return 0, err
	}

	switch expr.Op.Id {
	case tokens.Sub:
		return vl - vr, nil
	case tokens.Add:
		return vl + vr, nil
	case tokens.Mul:
		return vl * vr, nil
	case tokens.Div:
		if vr == 0 {
			return nil, errors.NewError(errors.InvalidOperation, expr.Op.Loc, "invalid operation: division by zero")
		}
		return vl / vr, nil
	case tokens.Mod:
		if vr == 0 {
			return nil, errors.NewError(errors.InvalidOperation, expr.Op.Loc, "invalid operation: division by zero")
		}
		return vl % vr, nil
	case tokens.BitAnd:
		return vl & vr, nil
	case tokens.BitShl:
		return vl << vr, nil
	case tokens.BitShr:
		return vl >> vr, nil
	case tokens.BitOr:
		return vl | vr, nil
	case tokens.BitXor:
		return vl ^ vr, nil
	case tokens.Lt:
		return vl < vr, nil
	case tokens.Le:
		return vl <= vr, nil
	case tokens.Gt:
		return vl > vr, nil
	case tokens.Ge:
		return vl >= vr, nil
	default:
		return nil, errors.NewError(errors.Unimplemented, expr.Op.Loc, "unimplemented operator", expr.Op.Value)
	}

}

func (i *Interpreter) unaryExpr(expr ast.Unary) (any, error) {
	if expr.Op.Id == tokens.TestE {
		i.fError = false
	}

	right, err := i.evaluate(expr.Right)
	if err != nil {
		return nil, err
	}

	switch expr.Op.Id {
	case tokens.TestE:
		return i.fError, nil
	case tokens.Sub:
		vr, err := i.unaryNumeric(expr.Op, right)
		if err != nil {
			return nil, err
		}
		return -vr, nil
	case tokens.Neg:
		vr, err := i.unaryNumeric(expr.Op, right)
		if err != nil {
			return nil, err
		}
		return ^vr, nil
	case tokens.Not:
		vr := i.isTrue(right)
		return !vr, nil
	default:
		return nil, errors.NewError(errors.Unimplemented, expr.Op.Loc, "unimplemented operator", expr.Op.Value)
	}
}

func (i *Interpreter) literalExpr(expr ast.Literal) (any, error) {
	switch expr.Value.Id {
	case tokens.Number:
		return expr.Numval, nil
	case tokens.String:
		return expr.Value.Value, nil
	case tokens.True:
		return true, nil
	case tokens.False:
		return false, nil
	case tokens.None:
		return nil, nil
	default:
		return nil, errors.NewError(errors.Unimplemented, expr.Value.Loc, "unimplemented type", expr.Value.String())
	}
}

func (i *Interpreter) groupExpr(expr ast.Group) (any, error) {
	return i.evaluate(expr.Expr)
}

func (i *Interpreter) blockNoEnv(block ast.Block) (any, error) {
	var v any
	var err error
	for _, expr := range block.Stmts {
		v, err = i.evaluate(expr)
		if err != nil {
			return nil, err
		}
	}
	return v, nil
}

func (i *Interpreter) block(block ast.Block) (any, error) {
	pEnv := i.env
	i.env = NewEnv(pEnv)
	defer func() {
		i.env = pEnv
	}()

	return i.blockNoEnv(block)
}

func (i *Interpreter) ifElse(ifElse ast.IfElse) (any, error) {
	cond, err := i.evaluate(ifElse.Cond)
	if err != nil {
		return nil, err
	}
	if i.isTrue(cond) {
		return i.evaluate(ifElse.True)
	} else {
		return i.evaluate(ifElse.False)
	}
}

func (i *Interpreter) forEval(fcond func() (bool, error), stmts ast.Expr) (any, error) {
	var last any

	for {
		end, result, err := func() (end bool, result any, err error) {
			// handle "interruptions"
			defer func() {
				if r := recover(); r != nil {
					if val, ok := r.(*PanicJump); ok {
						if val.typ == PanicJumpContinue {
							end = false
							return
						}
						if val.typ == PanicJumpBreak {
							end = true
							result = last
							err = nil
							return
						}
					}
					panic(r)
				}
			}()
			for {
				if fcond != nil {
					cond, err := fcond()
					if err != nil {
						return true, nil, err
					}
					if !cond {
						return true, last, nil
					}
				}

				last, err = i.evaluate(stmts)
				if err != nil {
					return true, nil, err
				}
			}
		}()
		if end {
			return result, err
		}
	}
}

func (i *Interpreter) forStmt(forStmt ast.For) (any, error) {
	if forStmt.Cond == nil {
		return i.forEval(nil, forStmt.Stmts)
	} else {
		return i.forEval(func() (bool, error) {
			cond, err := i.evaluate(forStmt.Cond)
			if err != nil {
				return false, err
			}
			return i.isTrue(cond), nil
		}, forStmt.Stmts)
	}
}

func (i *Interpreter) forInStmt(forInStmt ast.ForIn) (any, error) {
	expr, err := i.evaluate(forInStmt.Expr)
	if err != nil {
		return nil, err
	}

	index := 0
	arr := expr.([]any)

	pEnv := i.env
	i.env = NewEnv(pEnv)
	defer func() {
		i.env = pEnv
	}()
	i.env = i.env.Set(forInStmt.Name.Value, Var{Loc: forInStmt.Name.Loc})

	return i.forEval(func() (bool, error) {
		if index == len(arr) {
			return false, nil
		}
		i.env.Update(forInStmt.Name.Value, arr[index])
		index++
		return true, nil
	}, forInStmt.Stmts)
}

func (i *Interpreter) evalArgs(name string, loc tokens.Location, params []ast.Type, args []ast.Expr) ([]any, error) {
	vals := make([]any, 0, 16)
	for _, a := range args {
		arg, err := i.evaluate(a)
		if err != nil {
			return nil, err
		}
		vals = append(vals, arg)
	}

	return vals, nil
}

func (i *Interpreter) call(call ast.Call) (result any, err error) {
	callee, err := i.evaluate(call.Callee)
	if err != nil {
		return nil, err
	}

	fun, ok := callee.(Callable)
	if !ok {
		return nil, errors.NewError(errors.NotCallable, call.Loc, "value is not callable")
	}

	args, err := i.evalArgs(fun.Name(), call.Loc, fun.Params(), call.Args)
	if err != nil {
		return nil, err
	}

	// handle return via panic call
	defer func() {
		if r := recover(); r != nil {
			if val, ok := r.(*PanicJump); ok && val.typ == PanicJumpReturn {
				result = val.value
				err = nil
			} else {
				// won't be handled here
				panic(r)
			}
		}
	}()

	_, err = fun.Call(i, args, call.Loc)
	if err != nil {
		e := errors.NewError(errors.CallError, call.Loc, "error calling", fun.Name()).(errors.Error)
		e.Err = err
		return nil, e
	}

	// clear return if there's no return value
	if fun.Ret() == nil {
		return nil, nil
	}

	return nil, errors.NewError(errors.NoReturn, i.last, "no return value in", fun.Name(), "expected", fun.Ret().String())
}

func (i *Interpreter) fun(v ast.Func) (any, error) {
	callable := Function{fun: v, closure: i.env}
	i.env = i.env.Set(v.Name.Value, Var{callable, v.Name.Loc})
	return nil, nil
}

func (i *Interpreter) strct(v ast.Struct) (any, error) {
	pEnv := i.env
	sEnv := NewEnv(pEnv)
	i.env = sEnv
	defer func() {
		i.env = pEnv
		strct := Struct{name: v.Name.Value, env: sEnv}
		i.env = i.env.Set(v.Name.Value, Var{Value: strct, Loc: v.Name.Loc})
	}()

	_, err := i.blockNoEnv(v.Body)
	if err != nil {
		return nil, err
	}

	return nil, nil
}

func (i *Interpreter) getExpr(v ast.GetExpr) (any, error) {
	obj, err := i.evaluate(v.Object)
	if err != nil {
		return nil, err
	}

	if val, ok := obj.(Struct); ok {
		name := v.Expr.(ast.Variable)
		if name.Index == nil {
			expr, _ := val.env.Get(name.Name.Value, true)
			return expr.Value, nil
		}

		arr, _ := val.env.GetArray(name.Name.Value, true)
		index, err := i.evaluate(name.Index)
		if err != nil {
			return nil, err
		}
		return arr[index.(ast.Number)], nil
	}

	// shouldn't happen
	return nil, errors.NewError(errors.Unimplemented, v.Resolve().Value.Loc, "unimplemented get-expr")
}

func (i *Interpreter) returnStmt(v ast.Return) (any, error) {
	var val any

	if v.Value != nil {
		// could be a tail call we could optimize
		if call, ok := v.Value.(ast.Call); ok {
			i.fError = v.Error
			panic(&PanicJump{typ: PanicJumpTailCall, value: call, loc: v.Loc})
		}

		var err error
		val, err = i.evaluate(v.Value)
		if err != nil {
			return nil, err
		}
	}

	i.fError = v.Error
	panic(&PanicJump{typ: PanicJumpReturn, value: val, loc: v.Loc})
}

func (i *Interpreter) continueStmt(v ast.Continue) (any, error) {
	panic(&PanicJump{typ: PanicJumpContinue, loc: v.Loc})
}

func (i *Interpreter) breakStmt(v ast.Break) (any, error) {
	panic(&PanicJump{typ: PanicJumpBreak, loc: v.Loc})
}

func (i *Interpreter) exprList(v ast.ExprList) (any, error) {
	// XXX: should we set last?
	vals := make([]any, len(v.Exprs))
	for n, expr := range v.Exprs {
		val, err := i.evaluate(expr)
		if err != nil {
			return nil, err
		}
		vals[n] = val
	}
	return vals, nil
}