package httpclient

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

type GraphQLRequest struct {
	Query     string `json:"query"`
	Variables any    `json:"variables,omitempty"`
}

type graphQLResponse[T any] struct {
	Data   T `json:"data"`
	Errors []struct {
		Message string `json:"message"`
	} `json:"errors"`
}

// Post sends a GraphQL request and unmarshals the `data` field into T.
func Post[T any](ctx context.Context, client *http.Client, url string, req GraphQLRequest, headers map[string]string) (T, error) {
	var zero T
	body, err := json.Marshal(req)
	if err != nil {
		return zero, err
	}

	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))
	if err != nil {
		return zero, err
	}
	httpReq.Header.Set("Content-Type", "application/json")
	httpReq.Header.Set("Accept", "application/json")
	for k, v := range headers {
		httpReq.Header.Set(k, v)
	}

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

	var gqlResp graphQLResponse[T]
	if err := json.NewDecoder(resp.Body).Decode(&gqlResp); err != nil {
		return zero, err
	}
	if len(gqlResp.Errors) > 0 {
		return zero, fmt.Errorf("graphql: %s", gqlResp.Errors[0].Message)
	}
	return gqlResp.Data, nil
}