package generator

import (
	"fmt"
	"strings"

	"github.com/edmand46/arpack/parser"
)

func GenerateLuaSchema(schema parser.Schema, moduleName string) ([]byte, error) {
	if err := checkLuaUnsupportedTypes(schema); err != nil {
		return nil, err
	}

	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\n")

	b.WriteString("local M = {}\n\n")
	b.WriteString("-- Load BitOp library for bit operations (Defold/LuaJIT)\n")
	b.WriteString("local bit = require('bit')\n\n")

	writeLuaHelpers(&b)

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

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

	for _, msg := range messages {
		writeLuaConstructor(&b, msg, enumNames)
		b.WriteString("\n")
	}

	for _, msg := range messages {
		if err := writeLuaSerializer(&b, msg, enumNames); err != nil {
			return nil, fmt.Errorf("message %s: %w", msg.Name, err)
		}
		b.WriteString("\n")
	}

	for _, msg := range messages {
		if err := writeLuaDeserializer(&b, msg, enumNames); err != nil {
			return nil, fmt.Errorf("message %s: %w", msg.Name, err)
		}
		b.WriteString("\n")
	}

	b.WriteString("return M\n")

	return []byte(b.String()), nil
}

func writeLuaHelpers(b *strings.Builder) {
	b.WriteString("-- Inline helpers for little-endian byte operations\n\n")

	b.WriteString("-- Error handling for truncated data\n")
	b.WriteString("local function check_bounds(data, offset, needed, context)\n")
	b.WriteString("    local available = #data - offset + 1\n")
	b.WriteString("    if available < needed then\n")
	b.WriteString("        error(string.format(\"arpack: buffer too short for %s: need %d bytes, have %d\", context, needed, available))\n")
	b.WriteString("    end\n")
	b.WriteString("end\n\n")

	b.WriteString("local function read_u8(data, offset)\n")
	b.WriteString("    if offset > #data then error(\"arpack: buffer too short for u8\") end\n")
	b.WriteString("    return string.byte(data, offset), 1\n")
	b.WriteString("end\n\n")

	b.WriteString("local function write_u8(n)\n")
	b.WriteString("    return string.char(n)\n")
	b.WriteString("end\n\n")

	b.WriteString("local function read_u16_le(data, offset)\n")
	b.WriteString("    local b1, b2 = string.byte(data, offset, offset + 1)\n")
	b.WriteString("    if not b2 then error(\"arpack: buffer too short for u16\") end\n")
	b.WriteString("    return b1 + b2 * 256, 2\n")
	b.WriteString("end\n\n")

	b.WriteString("local function write_u16_le(n)\n")
	b.WriteString("    return string.char(n % 256, math.floor(n / 256))\n")
	b.WriteString("end\n\n")

	b.WriteString("local function read_u32_le(data, offset)\n")
	b.WriteString("    local b1, b2, b3, b4 = string.byte(data, offset, offset + 3)\n")
	b.WriteString("    if not b4 then error(\"arpack: buffer too short for u32\") end\n")
	b.WriteString("    return b1 + b2 * 256 + b3 * 65536 + b4 * 16777216, 4\n")
	b.WriteString("end\n\n")

	b.WriteString("local function write_u32_le(n)\n")
	b.WriteString("    return string.char(\n")
	b.WriteString("        n % 256,\n")
	b.WriteString("        math.floor(n / 256) % 256,\n")
	b.WriteString("        math.floor(n / 65536) % 256,\n")
	b.WriteString("        math.floor(n / 16777216) % 256\n")
	b.WriteString("    )\n")
	b.WriteString("end\n\n")

	b.WriteString("local function read_i8(data, offset)\n")
	b.WriteString("    if offset > #data then error(\"arpack: buffer too short for i8\") end\n")
	b.WriteString("    local v = string.byte(data, offset)\n")
	b.WriteString("    if v >= 128 then v = v - 256 end\n")
	b.WriteString("    return v, 1\n")
	b.WriteString("end\n\n")

	b.WriteString("local function write_i8(n)\n")
	b.WriteString("    if n < 0 then n = n + 256 end\n")
	b.WriteString("    return string.char(n)\n")
	b.WriteString("end\n\n")

	b.WriteString("local function read_i16_le(data, offset)\n")
	b.WriteString("    local v = read_u16_le(data, offset)\n")
	b.WriteString("    if v >= 32768 then v = v - 65536 end\n")
	b.WriteString("    return v, 2\n")
	b.WriteString("end\n\n")

	b.WriteString("local function write_i16_le(n)\n")
	b.WriteString("    if n < 0 then n = n + 65536 end\n")
	b.WriteString("    return write_u16_le(n)\n")
	b.WriteString("end\n\n")

	b.WriteString("local function read_i32_le(data, offset)\n")
	b.WriteString("    local v = read_u32_le(data, offset)\n")
	b.WriteString("    if v >= 2147483648 then v = v - 4294967296 end\n")
	b.WriteString("    return v, 4\n")
	b.WriteString("end\n\n")

	b.WriteString("local function write_i32_le(n)\n")
	b.WriteString("    if n < 0 then n = n + 4294967296 end\n")
	b.WriteString("    return write_u32_le(n)\n")
	b.WriteString("end\n\n")

	b.WriteString("local function read_f32_le(data, offset)\n")
	b.WriteString("    local u32 = read_u32_le(data, offset)\n")
	b.WriteString("    if u32 == 0 then return 0.0, 4 end\n")
	b.WriteString("    local sign = (u32 >= 2147483648) and -1 or 1\n")
	b.WriteString("    if sign < 0 then u32 = u32 - 2147483648 end\n")
	b.WriteString("    local exp = math.floor(u32 / 8388608) % 256\n")
	b.WriteString("    local mant = u32 % 8388608\n")
	b.WriteString("    if exp == 0 then\n")
	b.WriteString("        if mant == 0 then\n")
	b.WriteString("            return sign < 0 and (-1 / math.huge) or 0.0, 4\n")
	b.WriteString("        end\n")
	b.WriteString("        return sign * (mant / 8388608) * math.pow(2, -126), 4\n")
	b.WriteString("    elseif exp == 255 then\n")
	b.WriteString("        if mant == 0 then return sign * math.huge, 4\n")
	b.WriteString("        else return 0.0 / 0.0, 4 end\n")
	b.WriteString("    end\n")
	b.WriteString("    return sign * (1 + mant / 8388608) * math.pow(2, exp - 127), 4\n")
	b.WriteString("end\n\n")

	b.WriteString("local function write_f32_le(n)\n")
	b.WriteString("    if n ~= n then return write_u32_le(2143289344) end\n")
	b.WriteString("    if n == math.huge then return write_u32_le(2139095040) end\n")
	b.WriteString("    if n == -math.huge then return write_u32_le(4286578688) end\n")
	b.WriteString("    -- Check for negative zero: 1/-0.0 == -math.huge\n")
	b.WriteString("    if n == 0 then\n")
	b.WriteString("        if 1/n == -math.huge then return write_u32_le(2147483648) end\n")
	b.WriteString("        return write_u32_le(0)\n")
	b.WriteString("    end\n")
	b.WriteString("    local sign = 0\n")
	b.WriteString("    if n < 0 then sign = 2147483648; n = -n end\n")
	b.WriteString("    local exp\n")
	b.WriteString("    local mant\n")
	b.WriteString("    if n < math.pow(2, -126) then\n")
	b.WriteString("        mant = math.floor(n / math.pow(2, -149) + 0.5)\n")
	b.WriteString("        if mant <= 0 then return write_u32_le(sign) end\n")
	b.WriteString("        if mant >= 8388608 then\n")
	b.WriteString("            exp = 1\n")
	b.WriteString("            mant = 0\n")
	b.WriteString("        else\n")
	b.WriteString("            exp = 0\n")
	b.WriteString("        end\n")
	b.WriteString("    else\n")
	b.WriteString("        exp = math.floor(math.log(n, 2))\n")
	b.WriteString("        mant = math.floor((n / math.pow(2, exp) - 1) * 8388608 + 0.5)\n")
	b.WriteString("        if mant >= 8388608 then\n")
	b.WriteString("            exp = exp + 1\n")
	b.WriteString("            mant = 0\n")
	b.WriteString("        end\n")
	b.WriteString("        exp = exp + 127\n")
	b.WriteString("        if exp >= 255 then\n")
	b.WriteString("            return write_u32_le(sign + 2139095040)\n")
	b.WriteString("        end\n")
	b.WriteString("    end\n")
	b.WriteString("    return write_u32_le(sign + exp * 8388608 + mant)\n")
	b.WriteString("end\n\n")

	b.WriteString("local function read_f64_le(data, offset)\n")
	b.WriteString("    -- Read 8 bytes directly to avoid precision loss from 64-bit arithmetic\n")
	b.WriteString("    local b1, b2, b3, b4, b5, b6, b7, b8 = string.byte(data, offset, offset + 7)\n")
	b.WriteString("    if not b8 then error(\"arpack: buffer too short for f64\") end\n")
	b.WriteString("    local low = b1 + b2 * 256 + b3 * 65536 + b4 * 16777216\n")
	b.WriteString("    local high = b5 + b6 * 256 + b7 * 65536 + b8 * 16777216\n")
	b.WriteString("    -- Decode IEEE 754 double from low/high parts separately\n")
	b.WriteString("    if low == 0 and high == 0 then return 0.0, 8 end\n")
	b.WriteString("    local sign = (high >= 2147483648) and -1 or 1\n")
	b.WriteString("    if sign < 0 then high = high - 2147483648 end\n")
	b.WriteString("    local exp = math.floor(high / 1048576) % 2048\n")
	b.WriteString("    local high_mant = high % 1048576\n")
	b.WriteString("    if exp == 0 then\n")
	b.WriteString("        local mant = high_mant * 4294967296 + low\n")
	b.WriteString("        if mant == 0 then\n")
	b.WriteString("            return sign < 0 and (-1 / math.huge) or 0.0, 8\n")
	b.WriteString("        end\n")
	b.WriteString("        return sign * (mant / 4503599627370496) * math.pow(2, -1022), 8\n")
	b.WriteString("    elseif exp == 2047 then\n")
	b.WriteString("        if high_mant == 0 and low == 0 then return sign * math.huge, 8\n")
	b.WriteString("        else return 0.0 / 0.0, 8 end\n")
	b.WriteString("    end\n")
	b.WriteString("    local mant = high_mant * 4294967296 + low\n")
	b.WriteString("    return sign * (1 + mant / 4503599627370496) * math.pow(2, exp - 1023), 8\n")
	b.WriteString("end\n\n")

	b.WriteString("local function write_f64_le(n)\n")
	b.WriteString("    -- Handle special values\n")
	b.WriteString("    if n ~= n then -- NaN\n")
	b.WriteString("        return string.char(0, 0, 0, 0, 0, 0, 248, 127)\n")
	b.WriteString("    end\n")
	b.WriteString("    if n == math.huge then\n")
	b.WriteString("        return string.char(0, 0, 0, 0, 0, 0, 240, 127)\n")
	b.WriteString("    end\n")
	b.WriteString("    if n == -math.huge then\n")
	b.WriteString("        return string.char(0, 0, 0, 0, 0, 0, 240, 255)\n")
	b.WriteString("    end\n")
	b.WriteString("    -- Check for negative zero: 1/-0.0 == -math.huge\n")
	b.WriteString("    if n == 0 then\n")
	b.WriteString("        if 1/n == -math.huge then\n")
	b.WriteString("            return string.char(0, 0, 0, 0, 0, 0, 0, 128)\n")
	b.WriteString("        end\n")
	b.WriteString("        return string.char(0, 0, 0, 0, 0, 0, 0, 0)\n")
	b.WriteString("    end\n")
	b.WriteString("    local sign = 0\n")
	b.WriteString("    if n < 0 then sign = 2147483648; n = -n end\n")
	b.WriteString("    local exp\n")
	b.WriteString("    local mant\n")
	b.WriteString("    if n < math.pow(2, -1022) then\n")
	b.WriteString("        mant = math.floor(n / math.pow(2, -1074) + 0.5)\n")
	b.WriteString("        if mant <= 0 then\n")
	b.WriteString("            local high = sign\n")
	b.WriteString("            return string.char(0, 0, 0, 0, high % 256, math.floor(high / 256) % 256, math.floor(high / 65536) % 256, math.floor(high / 16777216) % 256)\n")
	b.WriteString("        end\n")
	b.WriteString("        if mant >= 4503599627370496 then\n")
	b.WriteString("            exp = 1\n")
	b.WriteString("            mant = 0\n")
	b.WriteString("        else\n")
	b.WriteString("            exp = 0\n")
	b.WriteString("        end\n")
	b.WriteString("    else\n")
	b.WriteString("        exp = math.floor(math.log(n, 2))\n")
	b.WriteString("        mant = (n / math.pow(2, exp) - 1) * 4503599627370496\n")
	b.WriteString("        mant = math.floor(mant + 0.5)\n")
	b.WriteString("        if mant >= 4503599627370496 then\n")
	b.WriteString("            exp = exp + 1\n")
	b.WriteString("            mant = 0\n")
	b.WriteString("        end\n")
	b.WriteString("        exp = exp + 1023\n")
	b.WriteString("        if exp >= 2047 then\n")
	b.WriteString("            exp = 2047\n")
	b.WriteString("            mant = 0\n")
	b.WriteString("        end\n")
	b.WriteString("    end\n")
	b.WriteString("    local high_mant = math.floor(mant / 4294967296)\n")
	b.WriteString("    local low = mant % 4294967296\n")
	b.WriteString("    local high = sign + exp * 1048576 + high_mant\n")
	b.WriteString("    return string.char(\n")
	b.WriteString("        low % 256,\n")
	b.WriteString("        math.floor(low / 256) % 256,\n")
	b.WriteString("        math.floor(low / 65536) % 256,\n")
	b.WriteString("        math.floor(low / 16777216) % 256,\n")
	b.WriteString("        high % 256,\n")
	b.WriteString("        math.floor(high / 256) % 256,\n")
	b.WriteString("        math.floor(high / 65536) % 256,\n")
	b.WriteString("        math.floor(high / 16777216) % 256\n")
	b.WriteString("    )\n")
	b.WriteString("end\n\n")

	b.WriteString("local function read_bool(data, offset)\n")
	b.WriteString("    if offset > #data then error(\"arpack: buffer too short for bool\") end\n")
	b.WriteString("    return string.byte(data, offset) ~= 0, 1\n")
	b.WriteString("end\n\n")

	b.WriteString("local function write_bool(v)\n")
	b.WriteString("    return string.char(v and 1 or 0)\n")
	b.WriteString("end\n\n")

	b.WriteString("local function read_string(data, offset)\n")
	b.WriteString("    local len, header_bytes = read_u16_le(data, offset)\n")
	b.WriteString("    if len == 0 then return '', header_bytes end\n")
	b.WriteString("    local available = #data - offset - header_bytes + 1\n")
	b.WriteString("    if available < len then\n")
	b.WriteString("        error(string.format(\"arpack: buffer too short for string: need %d bytes, have %d\", len, available))\n")
	b.WriteString("    end\n")
	b.WriteString("    -- string.sub is 1-based; data starts at offset + header_bytes\n")
	b.WriteString("    return string.sub(data, offset + header_bytes, offset + header_bytes + len - 1), header_bytes + len\n")
	b.WriteString("end\n\n")

	b.WriteString("local function write_string(s)\n")
	b.WriteString("    local len = #s\n")
	b.WriteString("    return write_u16_le(len) .. s\n")
	b.WriteString("end\n\n")
}

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

func writeLuaConstructor(b *strings.Builder, msg parser.Message, enumNames map[string]struct{}) {
	fmt.Fprintf(b, "function M.new_%s()\n", toSnakeCase(msg.Name))
	b.WriteString("    return {\n")
	for _, f := range msg.Fields {
		defaultValue := luaDefaultValue(f, enumNames)
		fmt.Fprintf(b, "        %s = %s,\n", luaFieldName(f.Name), defaultValue)
	}
	b.WriteString("    }\n")
	b.WriteString("end\n")
}

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

	fmt.Fprintf(b, "function M.serialize_%s(msg)\n", toSnakeCase(msg.Name))
	b.WriteString("    local parts = {}\n")
	b.WriteString("    local part_idx = 0\n")

	for i, seg := range segs {
		if seg.single != nil {
			if err := writeLuaSerializeField(b, "msg", *seg.single, "    ", enumNames); err != nil {
				return err
			}
		} else {
			writeLuaBoolGroupSerialize(b, "msg", seg.bools, i, "    ")
		}
	}

	b.WriteString("    return table.concat(parts)\n")
	b.WriteString("end\n")
	return nil
}

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

	fmt.Fprintf(b, "function M.deserialize_%s(data, offset)\n", toSnakeCase(msg.Name))
	b.WriteString("    offset = offset or 1\n")
	fmt.Fprintf(b, "    local msg = M.new_%s()\n", toSnakeCase(msg.Name))
	b.WriteString("    local start_offset = offset\n")
	b.WriteString("    local bytes_read = 0\n")
	fmt.Fprintf(b, "    if #data < offset + %d - 1 then\n", minSize)
	fmt.Fprintf(b, "        error(\"arpack: buffer too short for %s\")\n", msg.Name)
	b.WriteString("    end\n")

	for i, seg := range segs {
		if seg.single != nil {
			if err := writeLuaDeserializeField(b, "msg", *seg.single, "    ", enumNames); err != nil {
				return err
			}
		} else {
			writeLuaBoolGroupDeserialize(b, "msg", seg.bools, i, "    ")
		}
	}

	b.WriteString("    return msg, offset - start_offset\n")
	b.WriteString("end\n")
	return nil
}

func writeLuaBoolGroupSerialize(b *strings.Builder, recv string, bools []parser.Field, groupIdx int, indent string) {
	varName := fmt.Sprintf("_bool_byte_%d", groupIdx)
	fmt.Fprintf(b, "%slocal %s = 0\n", indent, varName)
	for bit, f := range bools {
		fmt.Fprintf(b, "%sif %s.%s then %s = bit.bor(%s, %d) end\n",
			indent, recv, luaFieldName(f.Name), varName, varName, 1<<bit)
	}
	fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_u8(%s)\n", indent, varName)
}

func writeLuaBoolGroupDeserialize(b *strings.Builder, recv string, bools []parser.Field, groupIdx int, indent string) {
	varName := fmt.Sprintf("_bool_byte_%d", groupIdx)
	fmt.Fprintf(b, "%sif #data < offset then error(\"arpack: buffer too short for bool group\") end\n", indent)
	fmt.Fprintf(b, "%slocal %s = string.byte(data, offset)\n", indent, varName)
	fmt.Fprintf(b, "%soffset = offset + 1\n", indent)
	for bit, f := range bools {
		fmt.Fprintf(b, "%s%s.%s = bit.band(%s, %d) ~= 0\n",
			indent, recv, luaFieldName(f.Name), varName, 1<<bit)
	}
}

func writeLuaSerializeField(b *strings.Builder, recv string, f parser.Field, indent string, enumNames map[string]struct{}) error {
	access := recv + "." + luaFieldName(f.Name)
	switch f.Kind {
	case parser.KindPrimitive:
		return writeLuaSerializePrimitive(b, access, f, indent, enumNames)
	case parser.KindNested:
		fmt.Fprintf(b, "%slocal _nested_%s = M.serialize_%s(%s)\n", indent, f.Name, toSnakeCase(f.TypeName), access)
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = _nested_%s\n", indent, f.Name)
	case parser.KindFixedArray:
		iVar := "_i_" + strings.ToLower(f.Name)
		fmt.Fprintf(b, "%sfor %s = 1, %d do\n", indent, iVar, f.FixedLen)
		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 := writeLuaSerializeField(b, recv, elemField, indent+"    ", enumNames); err != nil {
			return err
		}
		fmt.Fprintf(b, "%send\n", indent)
	case parser.KindSlice:
		lenVar := "_len_" + strings.ToLower(f.Name)
		fmt.Fprintf(b, "%slocal %s = #(%s or {})\n", indent, lenVar, access)
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_u16_le(%s)\n", indent, lenVar)
		iVar := "_i_" + strings.ToLower(f.Name)
		fmt.Fprintf(b, "%sfor %s = 1, %s do\n", indent, iVar, lenVar)

		if f.Elem.Kind == parser.KindNested {
			// For nested types in slices, serialize directly
			fmt.Fprintf(b, "%slocal _nested_%s = M.serialize_%s(%s[%s])\n",
				indent, f.Name, toSnakeCase(f.Elem.TypeName), access, iVar)
			fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = _nested_%s\n",
				indent, f.Name)
		} else {
			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 := writeLuaSerializeField(b, recv, elemField, indent+"    ", enumNames); err != nil {
				return err
			}
		}
		fmt.Fprintf(b, "%send\n", indent)
	}
	return nil
}

func writeLuaSerializePrimitive(b *strings.Builder, access string, f parser.Field, indent string, enumNames map[string]struct{}) error {
	if f.Quant != nil {
		return writeLuaSerializeQuant(b, access, f, indent)
	}

	valueExpr := luaSerializeValueExpr(access, f, enumNames)
	switch f.Primitive {
	case parser.KindFloat32:
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_f32_le(%s)\n", indent, valueExpr)
	case parser.KindFloat64:
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_f64_le(%s)\n", indent, valueExpr)
	case parser.KindInt8:
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_i8(%s)\n", indent, valueExpr)
	case parser.KindUint8:
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_u8(%s)\n", indent, valueExpr)
	case parser.KindBool:
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_bool(%s)\n", indent, valueExpr)
	case parser.KindInt16:
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_i16_le(%s)\n", indent, valueExpr)
	case parser.KindUint16:
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_u16_le(%s)\n", indent, valueExpr)
	case parser.KindInt32:
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_i32_le(%s)\n", indent, valueExpr)
	case parser.KindUint32:
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_u32_le(%s)\n", indent, valueExpr)
	case parser.KindInt64, parser.KindUint64:
		return fmt.Errorf("int64/uint64 serialization not supported in Lua")
	case parser.KindString:
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_string(%s or '')\n", indent, valueExpr)
	}
	return nil
}

func writeLuaSerializeQuant(b *strings.Builder, access string, f parser.Field, indent string) error {
	q := f.Quant
	maxUint := q.MaxUint()
	varName := "_q_" + sanitizeLuaVarName(access)
	fmt.Fprintf(b, "%slocal %s = math.floor(((%s - (%g)) / (%g - (%g))) * %g + 0.5)\n",
		indent, varName, access, q.Min, q.Max, q.Min, maxUint)
	if q.Bits == 8 {
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_u8(%s)\n", indent, varName)
	} else {
		fmt.Fprintf(b, "%spart_idx = part_idx + 1; parts[part_idx] = write_u16_le(%s)\n", indent, varName)
	}
	return nil
}

func writeLuaDeserializeField(b *strings.Builder, recv string, f parser.Field, indent string, enumNames map[string]struct{}) error {
	access := recv + "." + luaFieldName(f.Name)
	switch f.Kind {
	case parser.KindPrimitive:
		return writeLuaDeserializePrimitive(b, access, f, indent, enumNames)
	case parser.KindNested:
		fmt.Fprintf(b, "%slocal _nested_%s, _n_%s = M.deserialize_%s(data, offset)\n", indent, f.Name, f.Name, toSnakeCase(f.TypeName))
		fmt.Fprintf(b, "%s%s = _nested_%s\n", indent, access, f.Name)
		fmt.Fprintf(b, "%soffset = offset + _n_%s\n", indent, f.Name)
	case parser.KindFixedArray:
		iVar := "_i_" + strings.ToLower(f.Name)
		fmt.Fprintf(b, "%s%s = {}\n", indent, access)
		fmt.Fprintf(b, "%sfor %s = 1, %d do\n", indent, iVar, f.FixedLen)
		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 := writeLuaDeserializeField(b, recv, elemField, indent+"    ", enumNames); err != nil {
			return err
		}
		fmt.Fprintf(b, "%send\n", indent)
	case parser.KindSlice:
		lenVar := "_len_" + strings.ToLower(f.Name)
		fmt.Fprintf(b, "%slocal %s = read_u16_le(data, offset)\n", indent, lenVar)
		fmt.Fprintf(b, "%soffset = offset + 2\n", indent)
		fmt.Fprintf(b, "%s%s = {}\n", indent, access)
		iVar := "_i_" + strings.ToLower(f.Name)
		fmt.Fprintf(b, "%sfor %s = 1, %s do\n", indent, iVar, lenVar)

		if f.Elem.Kind == parser.KindNested {
			// For nested types in slices, deserialize directly
			fmt.Fprintf(b, "%slocal _nested_%s, _n_%s = M.deserialize_%s(data, offset)\n",
				indent, f.Name, f.Name, toSnakeCase(f.Elem.TypeName))
			fmt.Fprintf(b, "%s%s[%s] = _nested_%s\n",
				indent, access, iVar, f.Name)
			fmt.Fprintf(b, "%soffset = offset + _n_%s\n",
				indent, f.Name)
		} else {
			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 := writeLuaDeserializeField(b, recv, elemField, indent+"    ", enumNames); err != nil {
				return err
			}
		}
		fmt.Fprintf(b, "%send\n", indent)
	}
	return nil
}

func writeLuaDeserializePrimitive(b *strings.Builder, access string, f parser.Field, indent string, enumNames map[string]struct{}) error {
	if f.Quant != nil {
		return writeLuaDeserializeQuant(b, access, f, indent, enumNames)
	}

	varName := "_v_" + sanitizeLuaVarName(access)
	switch f.Primitive {
	case parser.KindFloat32:
		fmt.Fprintf(b, "%slocal %s, _n = read_f32_le(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(varName, f, enumNames))
		fmt.Fprintf(b, "%soffset = offset + _n\n", indent)
	case parser.KindFloat64:
		fmt.Fprintf(b, "%slocal %s, _n = read_f64_le(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(varName, f, enumNames))
		fmt.Fprintf(b, "%soffset = offset + _n\n", indent)
	case parser.KindInt8:
		fmt.Fprintf(b, "%slocal %s, _n = read_i8(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(varName, f, enumNames))
		fmt.Fprintf(b, "%soffset = offset + _n\n", indent)
	case parser.KindUint8:
		fmt.Fprintf(b, "%slocal %s, _n = read_u8(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(varName, f, enumNames))
		fmt.Fprintf(b, "%soffset = offset + _n\n", indent)
	case parser.KindBool:
		fmt.Fprintf(b, "%slocal %s, _n = read_bool(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(varName, f, enumNames))
		fmt.Fprintf(b, "%soffset = offset + _n\n", indent)
	case parser.KindInt16:
		fmt.Fprintf(b, "%slocal %s, _n = read_i16_le(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(varName, f, enumNames))
		fmt.Fprintf(b, "%soffset = offset + _n\n", indent)
	case parser.KindUint16:
		fmt.Fprintf(b, "%slocal %s, _n = read_u16_le(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(varName, f, enumNames))
		fmt.Fprintf(b, "%soffset = offset + _n\n", indent)
	case parser.KindInt32:
		fmt.Fprintf(b, "%slocal %s, _n = read_i32_le(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(varName, f, enumNames))
		fmt.Fprintf(b, "%soffset = offset + _n\n", indent)
	case parser.KindUint32:
		fmt.Fprintf(b, "%slocal %s, _n = read_u32_le(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(varName, f, enumNames))
		fmt.Fprintf(b, "%soffset = offset + _n\n", indent)
	case parser.KindInt64, parser.KindUint64:
		return fmt.Errorf("int64/uint64 deserialization not supported in Lua")
	case parser.KindString:
		fmt.Fprintf(b, "%slocal %s, _n = read_string(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(varName, f, enumNames))
		fmt.Fprintf(b, "%soffset = offset + _n\n", indent)
	}
	return nil
}

func writeLuaDeserializeQuant(b *strings.Builder, access string, f parser.Field, indent string, enumNames map[string]struct{}) error {
	q := f.Quant
	maxUint := q.MaxUint()
	varName := "_q_" + sanitizeLuaVarName(access)
	if q.Bits == 8 {
		fmt.Fprintf(b, "%slocal %s = read_u8(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%soffset = offset + 1\n", indent)
	} else {
		fmt.Fprintf(b, "%slocal %s = read_u16_le(data, offset)\n", indent, varName)
		fmt.Fprintf(b, "%soffset = offset + 2\n", indent)
	}
	expr := fmt.Sprintf("%s / %g * (%g - (%g)) + (%g)", varName, maxUint, q.Max, q.Min, q.Min)
	fmt.Fprintf(b, "%s%s = %s\n", indent, access, luaDeserializeValueExpr(expr, f, enumNames))
	return nil
}

func luaFieldName(name string) string {
	return toSnakeCase(name)
}

func toSnakeCase(s string) string {
	if s == "" {
		return ""
	}

	var b strings.Builder
	var prevUpper bool

	for i, c := range s {
		isUpper := c >= 'A' && c <= 'Z'

		// Add underscore before uppercase letter if:
		// - It's not the first character
		// - Previous character was lowercase, OR
		// - Previous character was uppercase AND next character (if exists) is lowercase
		//   (this handles cases like "PlayerID" -> "player_id", not "player_i_d")
		if i > 0 && isUpper {
			nextLower := false
			if i+1 < len(s) {
				nextChar := rune(s[i+1])
				nextLower = nextChar >= 'a' && nextChar <= 'z'
			}

			if !prevUpper || nextLower {
				b.WriteByte('_')
			}
		}

		b.WriteRune(c)
		prevUpper = isUpper
	}

	return strings.ToLower(b.String())
}

func luaDefaultValue(f parser.Field, enumNames map[string]struct{}) string {
	switch f.Kind {
	case parser.KindPrimitive:
		if luaIsEnumType(f, enumNames) {
			return "0"
		}
		switch f.Primitive {
		case parser.KindFloat32, parser.KindFloat64, parser.KindInt8, parser.KindInt16, parser.KindInt32,
			parser.KindUint8, parser.KindUint16, parser.KindUint32, parser.KindInt64, parser.KindUint64:
			return "0"
		case parser.KindBool:
			return "false"
		case parser.KindString:
			return "''"
		}
	case parser.KindNested:
		return fmt.Sprintf("M.new_%s()", toSnakeCase(f.TypeName))
	case parser.KindFixedArray, parser.KindSlice:
		return "{}"
	}
	return "nil"
}

func luaSerializeValueExpr(access string, f parser.Field, enumNames map[string]struct{}) string {
	if !luaIsEnumType(f, enumNames) {
		return access
	}
	return access
}

func luaDeserializeValueExpr(expr string, f parser.Field, enumNames map[string]struct{}) string {
	if !luaIsEnumType(f, enumNames) {
		return expr
	}
	return expr
}

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

func sanitizeLuaVarName(s string) string {
	var b strings.Builder
	for _, c := range s {
		if (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') {
			b.WriteRune(c)
		} else {
			b.WriteRune('_')
		}
	}
	return strings.ToLower(b.String())
}

func checkLuaUnsupportedTypes(schema parser.Schema) error {
	for _, msg := range schema.Messages {
		for _, f := range msg.Fields {
			if err := checkFieldLuaSupport(msg.Name, f); err != nil {
				return err
			}
		}
	}
	return nil
}

func checkFieldLuaSupport(msgName string, f parser.Field) error {
	switch f.Kind {
	case parser.KindPrimitive:
		if f.Primitive == parser.KindInt64 || f.Primitive == parser.KindUint64 {
			return fmt.Errorf("lua target does not support int64/uint64: field %s in message %s (LuaJIT/Defold uses double-precision floats which can only safely represent integers up to 2^53)", f.Name, msgName)
		}
	case parser.KindFixedArray, parser.KindSlice:
		if f.Elem != nil {
			return checkFieldLuaSupport(msgName, *f.Elem)
		}
	}
	return nil
}