// Package convert 三协议互转：OpenAI Chat / OpenAI Responses / Anthropic Messages。
// 网关以 OpenAI Chat 形状作为标准中间模型（PLANNING §5.1.1）。
// 请求与响应（非流式）走 JSON 转换；流式走逐行 SSE 转换（见 stream.go）。
package convert

import (
	"encoding/json"
	"fmt"
)

// 协议标识。
const (
	ProtoChat      = "chat"
	ProtoMessages  = "messages"
	ProtoResponses = "responses"
)

// ConvertRequest 转换请求体。from==to 时原样返回。
func ConvertRequest(body []byte, from, to string) ([]byte, error) {
	if from == to {
		return body, nil
	}
	switch {
	case from == ProtoMessages && to == ProtoChat:
		return messagesToChatReq(body)
	case from == ProtoChat && to == ProtoMessages:
		return chatToMessagesReq(body)
	case from == ProtoResponses && to == ProtoChat:
		return responsesToChatReq(body)
	case from == ProtoChat && to == ProtoResponses:
		return chatToResponsesReq(body)
	case from == ProtoResponses && to == ProtoMessages:
		mid, err := responsesToChatReq(body)
		if err != nil {
			return nil, err
		}
		return chatToMessagesReq(mid)
	case from == ProtoMessages && to == ProtoResponses:
		mid, err := messagesToChatReq(body)
		if err != nil {
			return nil, err
		}
		return chatToResponsesReq(mid)
	}
	return nil, fmt.Errorf("unsupported request conversion %s->%s", from, to)
}

// ConvertResponse 转换响应体（非流式）。from==to 时原样返回。
func ConvertResponse(body []byte, from, to string) ([]byte, error) {
	if from == to {
		return body, nil
	}
	switch {
	case from == ProtoMessages && to == ProtoChat:
		return messagesToChatResp(body)
	case from == ProtoChat && to == ProtoMessages:
		return chatToMessagesResp(body)
	case from == ProtoResponses && to == ProtoChat:
		return responsesToChatResp(body)
	case from == ProtoChat && to == ProtoResponses:
		return chatToResponsesResp(body)
	case from == ProtoResponses && to == ProtoMessages:
		mid, err := responsesToChatResp(body)
		if err != nil {
			return nil, err
		}
		return chatToMessagesResp(mid)
	case from == ProtoMessages && to == ProtoResponses:
		mid, err := messagesToChatResp(body)
		if err != nil {
			return nil, err
		}
		return chatToResponsesResp(mid)
	}
	return nil, fmt.Errorf("unsupported response conversion %s->%s", from, to)
}

// NewStreamTransformer 构造流式逐行转换器：输入上游 SSE 一行，返回客户端 SSE 行。
// 返回 nil 表示丢弃该行；(from==to 时无需转换)。
func NewStreamTransformer(from, to string) func([]byte) []byte {
	switch {
	case from == ProtoMessages && to == ProtoChat:
		return newMessagesToChat().line
	case from == ProtoChat && to == ProtoMessages:
		return newChatToMessages().line
	case from == ProtoResponses && to == ProtoChat:
		return newResponsesToChat().line
	case from == ProtoChat && to == ProtoResponses:
		return newChatToResponses().line
	case from == ProtoResponses && to == ProtoMessages:
		return newResponsesToMessages().line
	case from == ProtoMessages && to == ProtoResponses:
		return newMessagesToResponses().line
	}
	return nil
}

// ---------------------------------------------------------------------------
// 工具函数

// str 返回字符串字段；json.RawMessage 为字符串字面量时去引号。
func str(raw json.RawMessage) string {
	if len(raw) == 0 || string(raw) == "null" {
		return ""
	}
	var s string
	if json.Unmarshal(raw, &s) == nil {
		return s
	}
	// 数组/对象：尝试取 type=text 的 text
	var arr []map[string]any
	if json.Unmarshal(raw, &arr) == nil {
		var parts []string
		for _, b := range arr {
			if t, _ := b["type"].(string); t == "text" || t == "input_text" || t == "output_text" {
				if txt, _ := b["text"].(string); txt != "" {
					parts = append(parts, txt)
				}
			}
		}
		return joinNonEmpty(parts, "\n")
	}
	return ""
}

func joinNonEmpty(parts []string, sep string) string {
	out := ""
	for i, p := range parts {
		if p == "" {
			continue
		}
		if out != "" {
			out += sep
		}
		out += p
		_ = i
	}
	return out
}

// rawJSON 安全取字段；不存在或 null 返回 nil。
func rawJSON(m map[string]json.RawMessage, key string) json.RawMessage {
	raw, ok := m[key]
	if !ok || string(raw) == "null" {
		return nil
	}
	return raw
}

// decode 把 RawMessage 解到 map。
func decode(raw json.RawMessage) (map[string]any, error) {
	var m map[string]any
	if err := json.Unmarshal(raw, &m); err != nil {
		return nil, err
	}
	return m, nil
}