package pay

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
)

const domesticRefundPath = "/v3/refund/domestic/refunds"

func (c *Client) Refund(ctx context.Context, req *RefundRequest) (*RefundResponse, error) {
	if req == nil {
		return nil, fmt.Errorf("request is required")
	}
	if req.OutTradeNo == "" && req.TransactionID == "" {
		return nil, fmt.Errorf("out_trade_no or transaction_id is required")
	}
	if req.OutRefundNo == "" {
		return nil, fmt.Errorf("out_refund_no is required")
	}
	if req.Amount.Refund <= 0 {
		return nil, fmt.Errorf("amount.refund must be greater than 0")
	}
	if req.Amount.Total <= 0 {
		return nil, fmt.Errorf("amount.total must be greater than 0")
	}
	if req.Amount.Refund > req.Amount.Total {
		return nil, fmt.Errorf("amount.refund cannot be greater than amount.total")
	}

	currency := req.Amount.Currency
	if currency == "" {
		currency = "CNY"
	}

	body := RefundRequest{
		OutTradeNo:    req.OutTradeNo,
		TransactionID: req.TransactionID,
		OutRefundNo:   req.OutRefundNo,
		Reason:        req.Reason,
		NotifyURL:     req.NotifyURL,
		Amount: RefundAmount{
			Refund:   req.Amount.Refund,
			Total:    req.Amount.Total,
			Currency: currency,
		},
	}

	reqBody, err := json.Marshal(body)
	if err != nil {
		return nil, err
	}

	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, c.Host+domesticRefundPath, bytes.NewReader(reqBody))
	if err != nil {
		return nil, err
	}

	httpReq.Header.Set("Accept", "application/json")
	httpReq.Header.Set("Content-Type", "application/json")
	if c.platformSerial != "" {
		httpReq.Header.Set("Wechatpay-Serial", c.platformSerial)
	}

	authorization, err := c.buildAuthorization(http.MethodPost, domesticRefundPath, reqBody)
	if err != nil {
		return nil, err
	}
	httpReq.Header.Set("Authorization", authorization)

	resp, err := c.httpClient.Do(httpReq)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	respBody, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, err
	}

	if !isSuccessStatus(resp.StatusCode) {
		return nil, newAPIError(resp.StatusCode, respBody)
	}

	if err := c.validateResponse(resp.Header, respBody); err != nil {
		return nil, err
	}

	var result RefundResponse
	if err := json.Unmarshal(respBody, &result); err != nil {
		return nil, err
	}
	if result.RefundID == "" {
		return nil, fmt.Errorf("empty refund_id in response")
	}

	return &result, nil
}