package orbit

import (
	"bytes"
	"encoding/json"
	"io"
	"strconv"
	"unicode/utf8"

	"github.com/coder/websocket"
)

func parseWorkerFrame(kind websocket.MessageType, raw []byte) (workerFrame, error) {
	var f workerFrame
	if kind != websocket.MessageText || len(raw) > 512<<10 || validateWorkerJSON(raw) != nil {
		return f, ErrWorkerProtocol
	}
	// Envelope 字段严格区分大小写，防止 encoding/json 的大小写别名覆盖控制字段。
	var fields map[string]json.RawMessage
	if json.Unmarshal(raw, &fields) != nil || fields == nil {
		return f, ErrWorkerProtocol
	}
	for k := range fields {
		switch k {
		case "protocol_version", "type", "message_id", "reply_to", "session_id", "body", "error":
		default:
			return f, ErrWorkerProtocol
		}
	}
	if json.Unmarshal(raw, &f) != nil || f.Version != "1" || !validID(f.MessageID) || f.ReplyTo != "" && !validID(f.ReplyTo) || f.SessionID != "" && !validID(f.SessionID) {
		return f, ErrWorkerProtocol
	}
	if f.Type == "error" {
		if f.Error == nil || !workerName(f.Error.Code, 64) || len(f.Error.Message) > 1024 || len(f.Body) > 0 {
			return f, ErrWorkerProtocol
		}
	} else if f.Error != nil || len(f.Body) == 0 || bytes.Equal(f.Body, []byte("null")) {
		return f, ErrWorkerProtocol
	}
	return f, nil
}

// validateWorkerJSON 拒绝重复键、过深嵌套及非法 Unicode，保留数字原文。
// 数值的业务范围仍由服务端规范化器最终验证；SDK 不经由 float64 重编码。
func validateWorkerJSON(raw []byte) error {
	if len(raw) == 0 || !utf8.Valid(raw) || !json.Valid(raw) || !workerUnicode(raw) {
		return ErrWorkerProtocol
	}
	d := json.NewDecoder(bytes.NewReader(raw))
	d.UseNumber()
	var value func(int) error
	value = func(depth int) error {
		if depth > 32 {
			return ErrWorkerProtocol
		}
		t, err := d.Token()
		if err != nil {
			return err
		}
		switch t {
		case json.Delim('{'):
			keys := map[string]bool{}
			for d.More() {
				k, err := d.Token()
				if err != nil {
					return err
				}
				s, ok := k.(string)
				if !ok || keys[s] {
					return ErrWorkerProtocol
				}
				keys[s] = true
				if err := value(depth + 1); err != nil {
					return err
				}
			}
			_, err = d.Token()
			return err
		case json.Delim('['):
			for d.More() {
				if err := value(depth + 1); err != nil {
					return err
				}
			}
			_, err = d.Token()
			return err
		}
		return nil
	}
	if err := value(0); err != nil {
		return err
	}
	if _, err := d.Token(); err != io.EOF {
		return ErrWorkerProtocol
	}
	return nil
}

// JSON 的未配对 UTF-16 转义不能被静默替换为 U+FFFD。
func workerUnicode(raw []byte) bool {
	inside := false
	for i := 0; i < len(raw); i++ {
		if raw[i] == '"' {
			inside = !inside
			continue
		}
		if !inside || raw[i] != '\\' {
			continue
		}
		i++
		if i >= len(raw) {
			return false
		}
		if raw[i] != 'u' {
			continue
		}
		if i+4 >= len(raw) {
			return false
		}
		n, err := strconv.ParseUint(string(raw[i+1:i+5]), 16, 16)
		if err != nil {
			return false
		}
		i += 4
		if n < 0xd800 || n > 0xdfff {
			continue
		}
		if n > 0xdbff || i+6 >= len(raw) || raw[i+1] != '\\' || raw[i+2] != 'u' {
			return false
		}
		low, err := strconv.ParseUint(string(raw[i+3:i+7]), 16, 16)
		if err != nil || low < 0xdc00 || low > 0xdfff {
			return false
		}
		i += 6
	}
	return !inside
}