package jsonrpc2

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

type httpClient struct {
	c   *http.Client
	url string
}

// NewHTTPClient returns a Client which will use HTTP POST requests against the
// given URL as a transport for JSONRPC2 method calls.
func NewHTTPClient(url string) Client {
	return &httpClient{
		c: &http.Client{
			Transport: http.DefaultTransport.(*http.Transport).Clone(),
		},
		url: url,
	}
}

func (c *httpClient) Call(
	ctx context.Context, rcv any, method string, params any,
) error {
	var (
		body = new(bytes.Buffer)
		enc  = json.NewEncoder(body)
	)

	id, err := encodeRequest(enc, method, params)
	if err != nil {
		return fmt.Errorf("encoding request: %w", err)
	}

	req, err := http.NewRequestWithContext(ctx, "POST", c.url, body)
	if err != nil {
		return fmt.Errorf("constructing POST request to %q: %w", c.url, err)
	}

	res, err := c.c.Do(req)
	if err != nil {
		return fmt.Errorf("performing request: %w", err)
	}
	defer res.Body.Close()

	dec := json.NewDecoder(res.Body)

	resID, err := decodeResponse(dec, rcv)
	if err != nil {
		return fmt.Errorf("decoding response: %w", err)
	} else if resID != id {
		return fmt.Errorf(
			"expected response with ID %q, got %q", id, resID,
		)
	}

	return nil
}