package jsoniter

import (
	"fmt"
	"reflect"
	"strings"
	"unicode"
	"unsafe"
)

var typeDecoders = map[string]ValDecoder{}
var fieldDecoders = map[string]ValDecoder{}
var typeEncoders = map[string]ValEncoder{}
var fieldEncoders = map[string]ValEncoder{}
var extensions = []Extension{}

type StructDescriptor struct {
	Type   reflect.Type
	Fields []*Binding
}

func (structDescriptor *StructDescriptor) GetField(fieldName string) *Binding {
	for _, binding := range structDescriptor.Fields {
		if binding.Field.Name == fieldName {
			return binding
		}
	}
	return nil
}

type Binding struct {
	Field     *reflect.StructField
	FromNames []string
	ToNames   []string
	Encoder   ValEncoder
	Decoder   ValDecoder
}

type Extension interface {
	UpdateStructDescriptor(structDescriptor *StructDescriptor)
	CreateDecoder(typ reflect.Type) ValDecoder
	CreateEncoder(typ reflect.Type) ValEncoder
	DecorateDecoder(typ reflect.Type, decoder ValDecoder) ValDecoder
	DecorateEncoder(typ reflect.Type, encoder ValEncoder) ValEncoder
}

type DummyExtension struct {
}

func (extension *DummyExtension) UpdateStructDescriptor(structDescriptor *StructDescriptor) {
}

func (extension *DummyExtension) CreateDecoder(typ reflect.Type) ValDecoder {
	return nil
}

func (extension *DummyExtension) CreateEncoder(typ reflect.Type) ValEncoder {
	return nil
}

func (extension *DummyExtension) DecorateDecoder(typ reflect.Type, decoder ValDecoder) ValDecoder {
	return decoder
}

func (extension *DummyExtension) DecorateEncoder(typ reflect.Type, encoder ValEncoder) ValEncoder {
	return encoder
}

type funcDecoder struct {
	fun DecoderFunc
}

func (decoder *funcDecoder) Decode(ptr unsafe.Pointer, iter *Iterator) {
	decoder.fun(ptr, iter)
}

type funcEncoder struct {
	fun         EncoderFunc
	isEmptyFunc func(ptr unsafe.Pointer) bool
}

func (encoder *funcEncoder) Encode(ptr unsafe.Pointer, stream *Stream) {
	encoder.fun(ptr, stream)
}

func (encoder *funcEncoder) EncodeInterface(val interface{}, stream *Stream) {
	WriteToStream(val, stream, encoder)
}

func (encoder *funcEncoder) IsEmpty(ptr unsafe.Pointer) bool {
	if encoder.isEmptyFunc == nil {
		return false
	}
	return encoder.isEmptyFunc(ptr)
}

func RegisterTypeDecoderFunc(typ string, fun DecoderFunc) {
	typeDecoders[typ] = &funcDecoder{fun}
}

func RegisterTypeDecoder(typ string, decoder ValDecoder) {
	typeDecoders[typ] = decoder
}

func RegisterFieldDecoderFunc(typ string, field string, fun DecoderFunc) {
	RegisterFieldDecoder(typ, field, &funcDecoder{fun})
}

func RegisterFieldDecoder(typ string, field string, decoder ValDecoder) {
	fieldDecoders[fmt.Sprintf("%s/%s", typ, field)] = decoder
}

func RegisterTypeEncoderFunc(typ string, fun EncoderFunc, isEmptyFunc func(unsafe.Pointer) bool) {
	typeEncoders[typ] = &funcEncoder{fun, isEmptyFunc}
}

func RegisterTypeEncoder(typ string, encoder ValEncoder) {
	typeEncoders[typ] = encoder
}

func RegisterFieldEncoderFunc(typ string, field string, fun EncoderFunc, isEmptyFunc func(unsafe.Pointer) bool) {
	RegisterFieldEncoder(typ, field, &funcEncoder{fun, isEmptyFunc})
}

func RegisterFieldEncoder(typ string, field string, encoder ValEncoder) {
	fieldEncoders[fmt.Sprintf("%s/%s", typ, field)] = encoder
}

func RegisterExtension(extension Extension) {
	extensions = append(extensions, extension)
}

func getTypeDecoderFromExtension(typ reflect.Type) ValDecoder {
	decoder := _getTypeDecoderFromExtension(typ)
	if decoder != nil {
		for _, extension := range extensions {
			decoder = extension.DecorateDecoder(typ, decoder)
		}
	}
	return decoder
}
func _getTypeDecoderFromExtension(typ reflect.Type) ValDecoder {
	for _, extension := range extensions {
		decoder := extension.CreateDecoder(typ)
		if decoder != nil {
			return decoder
		}
	}
	typeName := typ.String()
	decoder := typeDecoders[typeName]
	if decoder != nil {
		return decoder
	}
	if typ.Kind() == reflect.Ptr {
		decoder := typeDecoders[typ.Elem().String()]
		if decoder != nil {
			return &optionalDecoder{typ.Elem(), decoder}
		}
	}
	return nil
}

func getTypeEncoderFromExtension(typ reflect.Type) ValEncoder {
	encoder := _getTypeEncoderFromExtension(typ)
	if encoder != nil {
		for _, extension := range extensions {
			encoder = extension.DecorateEncoder(typ, encoder)
		}
	}
	return encoder
}

func _getTypeEncoderFromExtension(typ reflect.Type) ValEncoder {
	for _, extension := range extensions {
		encoder := extension.CreateEncoder(typ)
		if encoder != nil {
			return encoder
		}
	}
	typeName := typ.String()
	encoder := typeEncoders[typeName]
	if encoder != nil {
		return encoder
	}
	if typ.Kind() == reflect.Ptr {
		encoder := typeEncoders[typ.Elem().String()]
		if encoder != nil {
			return &optionalEncoder{encoder}
		}
	}
	return nil
}

func describeStruct(cfg *frozenConfig, typ reflect.Type) (*StructDescriptor, error) {
	headAnonymousBindings := []*Binding{}
	tailAnonymousBindings := []*Binding{}
	bindings := []*Binding{}
	for i := 0; i < typ.NumField(); i++ {
		field := typ.Field(i)
		if field.Anonymous {
			if field.Type.Kind() == reflect.Struct {
				structDescriptor, err := describeStruct(cfg, field.Type)
				if err != nil {
					return nil, err
				}
				for _, binding := range structDescriptor.Fields {
					binding.Encoder = &structFieldEncoder{&field, binding.Encoder, false}
					binding.Decoder = &structFieldDecoder{&field, binding.Decoder}
					if field.Offset == 0 {
						headAnonymousBindings = append(headAnonymousBindings, binding)
					} else {
						tailAnonymousBindings = append(tailAnonymousBindings, binding)
					}
				}
				continue
			} else if field.Type.Kind() == reflect.Ptr && field.Type.Elem().Kind() == reflect.Struct {
				structDescriptor, err := describeStruct(cfg, field.Type.Elem())
				if err != nil {
					return nil, err
				}
				for _, binding := range structDescriptor.Fields {
					binding.Encoder = &optionalEncoder{binding.Encoder}
					binding.Encoder = &structFieldEncoder{&field, binding.Encoder, false}
					binding.Decoder = &optionalDecoder{field.Type, binding.Decoder}
					binding.Decoder = &structFieldDecoder{&field, binding.Decoder}
					if field.Offset == 0 {
						headAnonymousBindings = append(headAnonymousBindings, binding)
					} else {
						tailAnonymousBindings = append(tailAnonymousBindings, binding)
					}
				}
				continue
			}
		}
		tagParts := strings.Split(field.Tag.Get("json"), ",")
		fieldNames := calcFieldNames(field.Name, tagParts[0], string(field.Tag))
		fieldCacheKey := fmt.Sprintf("%s/%s", typ.String(), field.Name)
		decoder := fieldDecoders[fieldCacheKey]
		if decoder == nil {
			var err error
			decoder, err = decoderOfType(cfg, field.Type)
			if err != nil {
				return nil, err
			}
		}
		encoder := fieldEncoders[fieldCacheKey]
		if encoder == nil {
			var err error
			encoder, err = encoderOfType(cfg, field.Type)
			if err != nil {
				return nil, err
			}
			// map is stored as pointer in the struct
			if field.Type.Kind() == reflect.Map {
				encoder = &optionalEncoder{encoder}
			}
		}
		binding := &Binding{
			Field:     &field,
			FromNames: fieldNames,
			ToNames:   fieldNames,
			Decoder:   decoder,
			Encoder:   encoder,
		}
		bindings = append(bindings, binding)
	}
	return createStructDescriptor(cfg, typ, bindings, headAnonymousBindings, tailAnonymousBindings), nil
}
func createStructDescriptor(cfg *frozenConfig, typ reflect.Type, bindings []*Binding, headAnonymousBindings []*Binding, tailAnonymousBindings []*Binding) *StructDescriptor {
	structDescriptor := &StructDescriptor{
		Type:   typ,
		Fields: bindings,
	}
	for _, extension := range extensions {
		extension.UpdateStructDescriptor(structDescriptor)
	}
	processTags(structDescriptor, cfg)
	// insert anonymous bindings to the head
	structDescriptor.Fields = append(headAnonymousBindings, structDescriptor.Fields...)
	structDescriptor.Fields = append(structDescriptor.Fields, tailAnonymousBindings...)
	return structDescriptor
}

func processTags(structDescriptor *StructDescriptor, cfg *frozenConfig) {
	for _, binding := range structDescriptor.Fields {
		shouldOmitEmpty := false
		tagParts := strings.Split(binding.Field.Tag.Get("json"), ",")
		for _, tagPart := range tagParts[1:] {
			if tagPart == "omitempty" {
				shouldOmitEmpty = true
			} else if tagPart == "string" {
				if binding.Field.Type.Kind() == reflect.String {
					binding.Decoder = &stringModeStringDecoder{binding.Decoder, cfg}
					binding.Encoder = &stringModeStringEncoder{binding.Encoder, cfg}
				} else {
					binding.Decoder = &stringModeNumberDecoder{binding.Decoder}
					binding.Encoder = &stringModeNumberEncoder{binding.Encoder}
				}
			}
		}
		binding.Decoder = &structFieldDecoder{binding.Field, binding.Decoder}
		binding.Encoder = &structFieldEncoder{binding.Field, binding.Encoder, shouldOmitEmpty}
	}
}

func calcFieldNames(originalFieldName string, tagProvidedFieldName string, wholeTag string) []string {
	// ignore?
	if wholeTag == "-" {
		return []string{}
	}
	// rename?
	var fieldNames []string
	if tagProvidedFieldName == "" {
		fieldNames = []string{originalFieldName}
	} else {
		fieldNames = []string{tagProvidedFieldName}
	}
	// private?
	isNotExported := unicode.IsLower(rune(originalFieldName[0]))
	if isNotExported {
		fieldNames = []string{}
	}
	return fieldNames
}