package generator

import (
	"edmand46/arpack/parser"
	"fmt"
	"strings"
)

// GenerateCSharp генерирует C# unsafe код для списка сообщений.
// namespace — пространство имён (например, "Ragono.Messages").
func GenerateCSharp(messages []parser.Message, namespace string) ([]byte, error) {
	return GenerateCSharpSchema(parser.Schema{Messages: messages}, namespace)
}

// GenerateCSharpSchema генерирует C# код для полной схемы, включая enum-ы.
func GenerateCSharpSchema(schema parser.Schema, namespace string) ([]byte, error) {
	messages := schema.Messages
	var b strings.Builder

	b.WriteString("// <auto-generated> arpack </auto-generated>\n")
	b.WriteString("// Code generated by arpack. DO NOT EDIT.\n")
	b.WriteString("#pragma warning disable CS8500\n\n")

	b.WriteString("using System;\n")
	if needsTextEncoding(messages) {
		b.WriteString("using System.Text;\n")
	}
	b.WriteString("\n")

	fmt.Fprintf(&b, "namespace %s\n{\n", namespace)

	enumNames := make(map[string]struct{}, len(schema.Enums))
	for _, enum := range schema.Enums {
		enumNames[enum.Name] = struct{}{}
	}

	wroteSection := false
	for _, enum := range schema.Enums {
		writeCSharpEnum(&b, enum)
		b.WriteString("\n")
		wroteSection = true
	}

	for i, msg := range messages {
		if err := writeCSharpMessage(&b, msg, enumNames); err != nil {
			return nil, fmt.Errorf("message %s: %w", msg.Name, err)
		}
		if i < len(messages)-1 {
			b.WriteString("\n")
		} else if wroteSection {
			// leave a single blank line between the last enum and the first struct only
		}
	}

	b.WriteString("}\n")
	return []byte(b.String()), nil
}

func writeCSharpEnum(b *strings.Builder, enum parser.Enum) {
	fmt.Fprintf(b, "    public enum %s : %s\n    {\n", enum.Name, csharpEnumBaseType(enum))
	for i, value := range enum.Values {
		fmt.Fprintf(b, "        %s = %s", csharpEnumValueName(enum.Name, value.Name), value.Value)
		if i < len(enum.Values)-1 {
			b.WriteString(",")
		}
		b.WriteString("\n")
	}
	b.WriteString("    }\n")
}

func writeCSharpMessage(b *strings.Builder, msg parser.Message, enumNames map[string]struct{}) error {
	segs := segmentFields(msg.Fields)

	b.WriteString("    public unsafe struct ")
	b.WriteString(msg.Name)
	b.WriteString("\n    {\n")

	// Поля
	for _, f := range msg.Fields {
		fmt.Fprintf(b, "        public %s %s;\n", csharpTypeName(f, enumNames), f.Name)
	}
	b.WriteString("\n")

	// Serialize
	b.WriteString("        public int Serialize(byte* buffer)\n")
	b.WriteString("        {\n")
	b.WriteString("            byte* ptr = buffer;\n")
	for i, seg := range segs {
		if seg.single != nil {
			if err := writeCSharpSerializeField(b, *seg.single, "            ", enumNames); err != nil {
				return err
			}
		} else {
			writeCSharpBoolGroupSerialize(b, seg.bools, i, "            ")
		}
	}
	b.WriteString("            return (int)(ptr - buffer);\n")
	b.WriteString("        }\n\n")

	// Deserialize
	fmt.Fprintf(b, "        public static int Deserialize(byte* buffer, out %s msg)\n", msg.Name)
	b.WriteString("        {\n")
	b.WriteString("            byte* ptr = buffer;\n")
	b.WriteString("            msg = default;\n")
	for i, seg := range segs {
		if seg.single != nil {
			if err := writeCSharpDeserializeField(b, "msg", *seg.single, "            ", enumNames); err != nil {
				return err
			}
		} else {
			writeCSharpBoolGroupDeserialize(b, "msg", seg.bools, i, "            ")
		}
	}
	b.WriteString("            return (int)(ptr - buffer);\n")
	b.WriteString("        }\n")

	b.WriteString("    }\n")
	return nil
}

func writeCSharpBoolGroupSerialize(b *strings.Builder, bools []parser.Field, groupIdx int, indent string) {
	varName := fmt.Sprintf("_boolByte%d", groupIdx)
	fmt.Fprintf(b, "%sbyte %s = 0;\n", indent, varName)
	for bit, f := range bools {
		fmt.Fprintf(b, "%sif (%s) %s |= (byte)(1 << %d);\n", indent, f.Name, varName, bit)
	}
	fmt.Fprintf(b, "%s*ptr = %s; ptr++;\n", indent, varName)
}

func writeCSharpBoolGroupDeserialize(b *strings.Builder, recv string, bools []parser.Field, groupIdx int, indent string) {
	varName := fmt.Sprintf("_boolByte%d", groupIdx)
	fmt.Fprintf(b, "%sbyte %s = *ptr; ptr++;\n", indent, varName)
	for bit, f := range bools {
		fmt.Fprintf(b, "%s%s.%s = (%s & (1 << %d)) != 0;\n", indent, recv, f.Name, varName, bit)
	}
}

// --- Serialize ---

func writeCSharpSerializeField(b *strings.Builder, f parser.Field, indent string, enumNames map[string]struct{}) error {
	switch f.Kind {
	case parser.KindPrimitive:
		return writeCSharpSerializePrimitive(b, f.Name, f, indent, enumNames)
	case parser.KindNested:
		fmt.Fprintf(b, "%sptr += %s.Serialize(ptr);\n", indent, f.Name)
	case parser.KindFixedArray:
		iVar := "_i" + f.Name
		fmt.Fprintf(b, "%sfor (int %s = 0; %s < %d; %s++)\n%s{\n",
			indent, iVar, iVar, f.FixedLen, iVar, indent)
		elemField := parser.Field{
			Name:      f.Name + "[" + iVar + "]",
			Kind:      f.Elem.Kind,
			Primitive: f.Elem.Primitive,
			NamedType: f.Elem.NamedType,
			Quant:     f.Elem.Quant,
			TypeName:  f.Elem.TypeName,
			Elem:      f.Elem.Elem,
			FixedLen:  f.Elem.FixedLen,
		}
		if err := writeCSharpSerializeField(b, elemField, indent+"    ", enumNames); err != nil {
			return err
		}
		fmt.Fprintf(b, "%s}\n", indent)
	case parser.KindSlice:
		fmt.Fprintf(b, "%s*(ushort*)ptr = (ushort)(%s?.Length ?? 0); ptr += 2;\n", indent, f.Name)
		fmt.Fprintf(b, "%sif (%s != null)\n%s{\n", indent, f.Name, indent)
		iVar := "_i" + f.Name
		fmt.Fprintf(b, "%s    for (int %s = 0; %s < %s.Length; %s++)\n%s    {\n",
			indent, iVar, iVar, f.Name, iVar, indent)
		elemField := parser.Field{
			Name:      f.Name + "[" + iVar + "]",
			Kind:      f.Elem.Kind,
			Primitive: f.Elem.Primitive,
			NamedType: f.Elem.NamedType,
			Quant:     f.Elem.Quant,
			TypeName:  f.Elem.TypeName,
			Elem:      f.Elem.Elem,
			FixedLen:  f.Elem.FixedLen,
		}
		if err := writeCSharpSerializeField(b, elemField, indent+"        ", enumNames); err != nil {
			return err
		}
		fmt.Fprintf(b, "%s    }\n%s}\n", indent, indent)
	}
	return nil
}

func writeCSharpSerializePrimitive(
	b *strings.Builder,
	access string,
	f parser.Field,
	indent string,
	enumNames map[string]struct{},
) error {
	if f.Quant != nil {
		return writeCSharpSerializeQuant(b, access, f, indent)
	}
	valueExpr := csharpSerializeValueExpr(access, f, enumNames)
	switch f.Primitive {
	case parser.KindFloat32:
		fmt.Fprintf(b, "%s*(float*)ptr = %s; ptr += 4;\n", indent, valueExpr)
	case parser.KindFloat64:
		fmt.Fprintf(b, "%s*(double*)ptr = %s; ptr += 8;\n", indent, valueExpr)
	case parser.KindInt8:
		fmt.Fprintf(b, "%s*(sbyte*)ptr = %s; ptr += 1;\n", indent, valueExpr)
	case parser.KindUint8:
		fmt.Fprintf(b, "%s*ptr = %s; ptr += 1;\n", indent, valueExpr)
	case parser.KindBool:
		fmt.Fprintf(b, "%s*ptr = (byte)(%s ? 1 : 0); ptr += 1;\n", indent, valueExpr)
	case parser.KindInt16:
		fmt.Fprintf(b, "%s*(short*)ptr = %s; ptr += 2;\n", indent, valueExpr)
	case parser.KindUint16:
		fmt.Fprintf(b, "%s*(ushort*)ptr = %s; ptr += 2;\n", indent, valueExpr)
	case parser.KindInt32:
		fmt.Fprintf(b, "%s*(int*)ptr = %s; ptr += 4;\n", indent, valueExpr)
	case parser.KindUint32:
		fmt.Fprintf(b, "%s*(uint*)ptr = %s; ptr += 4;\n", indent, valueExpr)
	case parser.KindInt64:
		fmt.Fprintf(b, "%s*(long*)ptr = %s; ptr += 8;\n", indent, valueExpr)
	case parser.KindUint64:
		fmt.Fprintf(b, "%s*(ulong*)ptr = %s; ptr += 8;\n", indent, valueExpr)
	case parser.KindString:
		// UTF-8: uint16 byteCount + bytes
		lenVar := "_slen" + sanitizeVarName(access)
		fmt.Fprintf(b, "%sint %s = %s != null ? Encoding.UTF8.GetByteCount(%s) : 0;\n",
			indent, lenVar, valueExpr, valueExpr)
		fmt.Fprintf(b, "%s*(ushort*)ptr = (ushort)%s; ptr += 2;\n", indent, lenVar)
		fmt.Fprintf(b, "%sif (%s != null && %s > 0)\n%s{\n", indent, valueExpr, lenVar, indent)
		fmt.Fprintf(b, "%s    fixed (char* _chars%s = %s)\n%s    {\n",
			indent, sanitizeVarName(access), valueExpr, indent)
		fmt.Fprintf(b, "%s        Encoding.UTF8.GetBytes(_chars%s, %s.Length, ptr, %s);\n",
			indent, sanitizeVarName(access), valueExpr, lenVar)
		fmt.Fprintf(b, "%s    }\n", indent)
		fmt.Fprintf(b, "%s}\n", indent)
		fmt.Fprintf(b, "%sptr += %s;\n", indent, lenVar)
	}
	return nil
}

func writeCSharpSerializeQuant(b *strings.Builder, access string, f parser.Field, indent string) error {
	q := f.Quant
	maxUint := q.MaxUint()
	if q.Bits == 8 {
		fmt.Fprintf(b, "%s*ptr = (byte)((%s - (%gf)) / (%gf - (%gf)) * %gf); ptr += 1;\n",
			indent, access, q.Min, q.Max, q.Min, maxUint)
	} else {
		fmt.Fprintf(b, "%s*(ushort*)ptr = (ushort)((%s - (%gf)) / (%gf - (%gf)) * %gf); ptr += 2;\n",
			indent, access, q.Min, q.Max, q.Min, maxUint)
	}
	return nil
}

// --- Deserialize ---

func writeCSharpDeserializeField(
	b *strings.Builder,
	recv string,
	f parser.Field,
	indent string,
	enumNames map[string]struct{},
) error {
	access := recv + "." + f.Name
	switch f.Kind {
	case parser.KindPrimitive:
		return writeCSharpDeserializePrimitive(b, access, f, indent, enumNames)
	case parser.KindNested:
		fmt.Fprintf(b, "%sptr += %s.Deserialize(ptr, out %s);\n", indent, f.TypeName, access)
	case parser.KindFixedArray:
		iVar := "_i" + f.Name
		fmt.Fprintf(b, "%s%s = new %s[%d];\n", indent, access, csharpTypeName(*f.Elem, enumNames), f.FixedLen)
		fmt.Fprintf(b, "%sfor (int %s = 0; %s < %d; %s++)\n%s{\n",
			indent, iVar, iVar, f.FixedLen, iVar, indent)
		elemField := parser.Field{
			Name:      f.Name + "[" + iVar + "]",
			Kind:      f.Elem.Kind,
			Primitive: f.Elem.Primitive,
			NamedType: f.Elem.NamedType,
			Quant:     f.Elem.Quant,
			TypeName:  f.Elem.TypeName,
			Elem:      f.Elem.Elem,
			FixedLen:  f.Elem.FixedLen,
		}
		if err := writeCSharpDeserializeField(b, recv, elemField, indent+"    ", enumNames); err != nil {
			return err
		}
		fmt.Fprintf(b, "%s}\n", indent)
	case parser.KindSlice:
		lenVar := "_len" + sanitizeVarName(f.Name)
		fmt.Fprintf(b, "%sint %s = *(ushort*)ptr; ptr += 2;\n", indent, lenVar)
		fmt.Fprintf(b, "%s%s = new %s[%s];\n", indent, access, csharpTypeName(*f.Elem, enumNames), lenVar)
		iVar := "_i" + sanitizeVarName(f.Name)
		fmt.Fprintf(b, "%sfor (int %s = 0; %s < %s; %s++)\n%s{\n",
			indent, iVar, iVar, lenVar, iVar, indent)
		elemField := parser.Field{
			Name:      f.Name + "[" + iVar + "]",
			Kind:      f.Elem.Kind,
			Primitive: f.Elem.Primitive,
			NamedType: f.Elem.NamedType,
			Quant:     f.Elem.Quant,
			TypeName:  f.Elem.TypeName,
			Elem:      f.Elem.Elem,
			FixedLen:  f.Elem.FixedLen,
		}
		if err := writeCSharpDeserializeField(b, recv, elemField, indent+"    ", enumNames); err != nil {
			return err
		}
		fmt.Fprintf(b, "%s}\n", indent)
	}
	return nil
}

func writeCSharpDeserializePrimitive(
	b *strings.Builder,
	access string,
	f parser.Field,
	indent string,
	enumNames map[string]struct{},
) error {
	if f.Quant != nil {
		return writeCSharpDeserializeQuant(b, access, f, indent)
	}
	switch f.Primitive {
	case parser.KindFloat32:
		fmt.Fprintf(b, "%s%s = %s; ptr += 4;\n", indent, access,
			csharpDeserializeValueExpr("*(float*)ptr", f, enumNames))
	case parser.KindFloat64:
		fmt.Fprintf(b, "%s%s = %s; ptr += 8;\n", indent, access,
			csharpDeserializeValueExpr("*(double*)ptr", f, enumNames))
	case parser.KindInt8:
		fmt.Fprintf(b, "%s%s = %s; ptr += 1;\n", indent, access,
			csharpDeserializeValueExpr("*(sbyte*)ptr", f, enumNames))
	case parser.KindUint8:
		fmt.Fprintf(b, "%s%s = %s; ptr += 1;\n", indent, access,
			csharpDeserializeValueExpr("*ptr", f, enumNames))
	case parser.KindBool:
		fmt.Fprintf(b, "%s%s = %s; ptr += 1;\n", indent, access,
			csharpDeserializeValueExpr("*ptr != 0", f, enumNames))
	case parser.KindInt16:
		fmt.Fprintf(b, "%s%s = %s; ptr += 2;\n", indent, access,
			csharpDeserializeValueExpr("*(short*)ptr", f, enumNames))
	case parser.KindUint16:
		fmt.Fprintf(b, "%s%s = %s; ptr += 2;\n", indent, access,
			csharpDeserializeValueExpr("*(ushort*)ptr", f, enumNames))
	case parser.KindInt32:
		fmt.Fprintf(b, "%s%s = %s; ptr += 4;\n", indent, access,
			csharpDeserializeValueExpr("*(int*)ptr", f, enumNames))
	case parser.KindUint32:
		fmt.Fprintf(b, "%s%s = %s; ptr += 4;\n", indent, access,
			csharpDeserializeValueExpr("*(uint*)ptr", f, enumNames))
	case parser.KindInt64:
		fmt.Fprintf(b, "%s%s = %s; ptr += 8;\n", indent, access,
			csharpDeserializeValueExpr("*(long*)ptr", f, enumNames))
	case parser.KindUint64:
		fmt.Fprintf(b, "%s%s = %s; ptr += 8;\n", indent, access,
			csharpDeserializeValueExpr("*(ulong*)ptr", f, enumNames))
	case parser.KindString:
		lenVar := "_slen" + sanitizeVarName(access)
		fmt.Fprintf(b, "%sint %s = *(ushort*)ptr; ptr += 2;\n", indent, lenVar)
		expr := fmt.Sprintf("%s > 0 ? Encoding.UTF8.GetString(ptr, %s) : string.Empty", lenVar, lenVar)
		fmt.Fprintf(b, "%s%s = %s;\n", indent, access, csharpDeserializeValueExpr(expr, f, enumNames))
		fmt.Fprintf(b, "%sptr += %s;\n", indent, lenVar)
	}
	return nil
}

func writeCSharpDeserializeQuant(b *strings.Builder, access string, f parser.Field, indent string) error {
	q := f.Quant
	maxUint := q.MaxUint()
	if q.Bits == 8 {
		if f.Primitive == parser.KindFloat32 {
			fmt.Fprintf(b, "%s%s = (float)(*ptr) / %gf * (%gf - (%gf)) + (%gf); ptr += 1;\n",
				indent, access, maxUint, q.Max, q.Min, q.Min)
		} else {
			fmt.Fprintf(b, "%s%s = (double)(*ptr) / %g * (%g - (%g)) + (%g); ptr += 1;\n",
				indent, access, maxUint, q.Max, q.Min, q.Min)
		}
	} else {
		if f.Primitive == parser.KindFloat32 {
			fmt.Fprintf(b, "%s%s = (float)(*(ushort*)ptr) / %gf * (%gf - (%gf)) + (%gf); ptr += 2;\n",
				indent, access, maxUint, q.Max, q.Min, q.Min)
		} else {
			fmt.Fprintf(b, "%s%s = (double)(*(ushort*)ptr) / %g * (%g - (%g)) + (%g); ptr += 2;\n",
				indent, access, maxUint, q.Max, q.Min, q.Min)
		}
	}
	return nil
}

func needsTextEncoding(messages []parser.Message) bool {
	for _, msg := range messages {
		for _, f := range msg.Fields {
			if fieldNeedsEncoding(f) {
				return true
			}
		}
	}
	return false
}

func fieldNeedsEncoding(f parser.Field) bool {
	switch f.Kind {
	case parser.KindPrimitive:
		return f.Primitive == parser.KindString
	case parser.KindFixedArray, parser.KindSlice:
		if f.Elem != nil {
			return fieldNeedsEncoding(*f.Elem)
		}
	}
	return false
}

func csharpTypeName(f parser.Field, enumNames map[string]struct{}) string {
	switch f.Kind {
	case parser.KindPrimitive:
		if csharpIsEnumType(f, enumNames) {
			return f.NamedType
		}
		return f.CSharpPrimitiveTypeName()
	case parser.KindNested:
		return f.TypeName
	case parser.KindFixedArray:
		return csharpTypeName(*f.Elem, enumNames) + "[]"
	case parser.KindSlice:
		return csharpTypeName(*f.Elem, enumNames) + "[]"
	}
	return "unknown"
}

func csharpSerializeValueExpr(access string, f parser.Field, enumNames map[string]struct{}) string {
	if !csharpIsEnumType(f, enumNames) {
		return access
	}
	return "(" + f.CSharpPrimitiveTypeName() + ")" + access
}

func csharpDeserializeValueExpr(expr string, f parser.Field, enumNames map[string]struct{}) string {
	if !csharpIsEnumType(f, enumNames) {
		return expr
	}
	return "(" + f.NamedType + ")(" + expr + ")"
}

func csharpIsEnumType(f parser.Field, enumNames map[string]struct{}) bool {
	if f.NamedType == "" {
		return false
	}
	_, ok := enumNames[f.NamedType]
	return ok
}

func csharpEnumBaseType(enum parser.Enum) string {
	field := parser.Field{Primitive: enum.Primitive}
	return field.CSharpPrimitiveTypeName()
}

func csharpEnumValueName(enumName, valueName string) string {
	if !strings.HasPrefix(valueName, enumName) || len(valueName) == len(enumName) {
		return valueName
	}

	suffix := valueName[len(enumName):]
	if suffix == "" {
		return valueName
	}
	if suffix[0] == '_' {
		suffix = suffix[1:]
	}
	if suffix == "" {
		return valueName
	}

	first := suffix[0]
	if !((first >= 'A' && first <= 'Z') || (first >= '0' && first <= '9') || first == '_') {
		return valueName
	}

	return suffix
}