package protocol

import (
	"errors"
	"fmt"
	"reflect"
	"strings"

	rpcv1 "code.icb4dc0.de/buildr/wasi-module-sdk-go/protocol/generated/rpc/v1"
)

var ErrUnmatchingType = errors.New("field type does not match wire value")

func Unmarshal(input *rpcv1.ModuleSpec, into any) error {
	cfg := unmarshalConfig{
		TagName: "hcl",
	}

	val := reflect.ValueOf(into)
	if val.Kind() != reflect.Ptr {
		return errors.New("into value must be a pointer")
	}
	return cfg.unmarshal(input.Values, val.Elem(), reflect.TypeOf(into).Elem())
}

type unmarshalConfig struct {
	TagName string
}

func (cfg unmarshalConfig) unmarshal(input map[string]*rpcv1.ModuleSpec_Value, into reflect.Value, intoType reflect.Type) error {
	for i := 0; i < intoType.NumField(); i++ {
		tf := intoType.Field(i)
		if !tf.IsExported() {
			continue
		}

		fieldName := cfg.fieldName(tf)

		val, ok := input[fieldName]
		if !ok {
			continue
		}

		if mapped, err := cfg.mapSpecValueTo(val, tf.Type); err != nil {
			return fmt.Errorf("failed to map value for field %s: %w", tf.Name, err)
		} else if into.Type().Kind() == reflect.Pointer {
			into.Elem().Field(i).Set(mapped)
		} else {
			into.Field(i).Set(mapped)
		}

		delete(input, fieldName)
	}

	if len(input) > 0 {
		keys := make([]string, 0, len(input))
		for k := range input {
			keys = append(keys, k)
		}
		return fmt.Errorf("unknown fields: %v", keys)
	}

	return nil
}

func (cfg unmarshalConfig) mapSpecValueTo(val *rpcv1.ModuleSpec_Value, targetType reflect.Type) (reflect.Value, error) {
	switch val.Type {
	case rpcv1.ModuleSpec_ValueTypeUnknown:
		return reflect.Value{}, ErrUnmatchingType
	case rpcv1.ModuleSpec_ValueTypeObject:
		if targetType.Kind() == reflect.Struct {
			structVal := reflect.New(targetType)
			if err := cfg.unmarshal(val.ComplexValue, structVal, targetType); err != nil {
				return reflect.Value{}, err
			} else {
				return structVal.Elem(), nil
			}
		} else if targetType.Kind() == reflect.Pointer && targetType.Elem().Kind() == reflect.Struct {
			structVal := reflect.New(targetType.Elem())
			if err := cfg.unmarshal(val.ComplexValue, structVal, targetType.Elem()); err != nil {
				return reflect.Value{}, err
			} else {
				return structVal, nil
			}
		} else if targetType.Kind() != reflect.Map {
			return reflect.Value{}, fmt.Errorf("%w: expected struct, got %s", ErrUnmatchingType, targetType.String())
		}
		fallthrough
	case rpcv1.ModuleSpec_ValueTypeMap:
		if targetType.Kind() != reflect.Map {
			return reflect.Value{}, fmt.Errorf("%w: expected map, got %v", ErrUnmatchingType, targetType)
		}

		mapVal := reflect.MakeMap(targetType)

		for k, v := range val.ComplexValue {
			if mappedVal, err := cfg.mapSpecValueTo(v, targetType.Elem()); err != nil {
				return reflect.Value{}, err
			} else {
				mapVal.SetMapIndex(reflect.ValueOf(k), mappedVal)
			}
		}

		return mapVal, nil

	case rpcv1.ModuleSpec_ValueTypeSingle:
		switch sv := val.SingleValue.(type) {
		case *rpcv1.ModuleSpec_Value_BoolValue:
			if targetType.Kind() != reflect.Bool {
				return reflect.Value{}, fmt.Errorf("%w: expected bool, got %v", ErrUnmatchingType, targetType)
			}
			return reflect.ValueOf(sv.BoolValue), nil
		case *rpcv1.ModuleSpec_Value_StringValue:
			if targetType.Kind() != reflect.String {
				return reflect.Value{}, fmt.Errorf("%w: expected string, got %v", ErrUnmatchingType, targetType)
			}
			return reflect.ValueOf(sv.StringValue), nil
		case *rpcv1.ModuleSpec_Value_IntValue:
			if targetType.Kind() != reflect.Int {
				return reflect.Value{}, fmt.Errorf("%w: expected int, got %v", ErrUnmatchingType, targetType)
			}
			return reflect.ValueOf(int(sv.IntValue)), nil
		case *rpcv1.ModuleSpec_Value_DoubleValue:
			if targetType.Kind() != reflect.Float64 {
				return reflect.Value{}, fmt.Errorf("%w: expected float64, got %v", ErrUnmatchingType, targetType)
			}
			return reflect.ValueOf(sv.DoubleValue), nil
		}
	case rpcv1.ModuleSpec_ValueTypeBoolSlice:
		if targetType.Kind() != reflect.Slice {
			return reflect.Value{}, fmt.Errorf("%w: expected slice, got %v", ErrUnmatchingType, targetType)
		} else if targetType.Elem().Kind() != reflect.Bool {
			return reflect.Value{}, fmt.Errorf("%w: expected bool, got %v", ErrUnmatchingType, targetType.Elem())
		}
		return reflect.ValueOf(val.BoolValues), nil
	case rpcv1.ModuleSpec_ValueTypeStringSlice:
		if targetType.Kind() != reflect.Slice {
			return reflect.Value{}, fmt.Errorf("%w: expected slice, got %v", ErrUnmatchingType, targetType)
		} else if targetType.Elem().Kind() != reflect.String {
			return reflect.Value{}, fmt.Errorf("%w: expected string, got %v", ErrUnmatchingType, targetType.Elem())
		}
		return reflect.ValueOf(val.StringValues), nil
	case rpcv1.ModuleSpec_ValueTypeIntSlice:
		if targetType.Kind() != reflect.Slice {
			return reflect.Value{}, fmt.Errorf("%w: expected slice, got %v", ErrUnmatchingType, targetType)
		}
		switch targetType.Elem().Kind() {
		case reflect.Int:
			return reflect.ValueOf(convertNumericSlice[int64, int](val.IntValues)), nil
		case reflect.Int8:
			return reflect.ValueOf(convertNumericSlice[int64, int8](val.IntValues)), nil
		case reflect.Int16:
			return reflect.ValueOf(convertNumericSlice[int64, int16](val.IntValues)), nil
		case reflect.Int32:
			return reflect.ValueOf(convertNumericSlice[int64, int32](val.IntValues)), nil
		case reflect.Int64:
			return reflect.ValueOf(val.IntValues), nil
		default:
			return reflect.Value{}, fmt.Errorf("%w: expected int, got %v", ErrUnmatchingType, targetType.Elem())
		}
	case rpcv1.ModuleSpec_ValueTypeDoubleSlice:
		if targetType.Kind() != reflect.Slice {
			return reflect.Value{}, fmt.Errorf("%w: expected slice, got %v", ErrUnmatchingType, targetType)
		}
		switch targetType.Elem().Kind() {
		case reflect.Float32:
			return reflect.ValueOf(convertNumericSlice[float64, float32](val.DoubleValues)), nil
		case reflect.Float64:
			return reflect.ValueOf(val.DoubleValues), nil
		default:
			return reflect.Value{}, fmt.Errorf("%w: expected int, got %v", ErrUnmatchingType, targetType.Elem())
		}
	}

	return reflect.Value{}, nil
}

func (cfg unmarshalConfig) fieldName(field reflect.StructField) string {
	tagVal, ok := field.Tag.Lookup(cfg.TagName)
	if !ok {
		return field.Name
	}

	split := strings.Split(tagVal, ",")

	switch {
	case len(split) == 0:
		fallthrough
	case split[0] == "":
		return strings.ToLower(field.Name)
	default:
		return strings.ToLower(split[0])
	}
}

type numeric interface {
	Integer | Float
}

func convertNumericSlice[TIn numeric, TOut numeric](input []TIn) []TOut {
	output := make([]TOut, len(input))
	for i, v := range input {
		output[i] = TOut(v)
	}
	return output
}