go-extractor/sites/kalshi/api.go

package kalshi

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"
)

const (
	defaultBaseURL = "https://api.elections.kalshi.com/trade-api/v2"
)

// apiMarket is the JSON shape returned by the Kalshi API for a market.
type apiMarket struct {
	Ticker        string `json:"ticker"`
	EventTicker   string `json:"event_ticker"`
	MarketType    string `json:"market_type"`
	Title         string `json:"title"`
	Subtitle      string `json:"subtitle"`
	Status        string `json:"status"`
	YesBid        int    `json:"yes_bid"`
	YesAsk        int    `json:"yes_ask"`
	NoBid         int    `json:"no_bid"`
	NoAsk         int    `json:"no_ask"`
	LastPrice     int    `json:"last_price"`
	Volume        int    `json:"volume"`
	Volume24h     int    `json:"volume_24h"`
	OpenInterest  int    `json:"open_interest"`
	Result        string `json:"result"`
	RulesPrimary  string `json:"rules_primary"`
	OpenTime      string `json:"open_time"`
	CloseTime     string `json:"close_time"`
	YesSubTitle   string `json:"yes_sub_title"`
	NoSubTitle    string `json:"no_sub_title"`
	CanCloseEarly bool   `json:"can_close_early"`
}

// apiEvent is the JSON shape returned by the Kalshi API for an event.
type apiEvent struct {
	EventTicker       string      `json:"event_ticker"`
	SeriesTicker      string      `json:"series_ticker"`
	Title             string      `json:"title"`
	Subtitle          string      `json:"sub_title"`
	Category          string      `json:"category"`
	MutuallyExclusive bool        `json:"mutually_exclusive"`
	Markets           []apiMarket `json:"markets"`
}

// apiEventsResponse wraps the events list endpoint response.
type apiEventsResponse struct {
	Events []apiEvent `json:"events"`
	Cursor string     `json:"cursor"`
}

// apiMarketResponse wraps the single market endpoint response.
type apiMarketResponse struct {
	Market apiMarket `json:"market"`
}

// apiEventResponse wraps the single event endpoint response.
type apiEventResponse struct {
	Event apiEvent `json:"event"`
}

func apiMarketToMarket(m apiMarket) Market {
	var closeTime time.Time
	if m.CloseTime != "" {
		closeTime, _ = time.Parse(time.RFC3339, m.CloseTime)
	}

	return Market{
		Ticker:       m.Ticker,
		EventTicker:  m.EventTicker,
		Title:        m.Title,
		Subtitle:     m.Subtitle,
		Status:       m.Status,
		YesBid:       float64(m.YesBid) / 100,
		YesAsk:       float64(m.YesAsk) / 100,
		NoBid:        float64(m.NoBid) / 100,
		NoAsk:        float64(m.NoAsk) / 100,
		LastPrice:    float64(m.LastPrice) / 100,
		Volume:       m.Volume,
		Volume24h:    m.Volume24h,
		OpenInterest: m.OpenInterest,
		Result:       m.Result,
		Rules:        m.RulesPrimary,
		CloseTime:    closeTime,
	}
}

func apiEventToEvent(e apiEvent) Event {
	markets := make([]Market, 0, len(e.Markets))
	for _, m := range e.Markets {
		markets = append(markets, apiMarketToMarket(m))
	}

	return Event{
		EventTicker:  e.EventTicker,
		SeriesTicker: e.SeriesTicker,
		Title:        e.Title,
		Subtitle:     e.Subtitle,
		Category:     e.Category,
		Markets:      markets,
	}
}

func (c Config) doGet(ctx context.Context, endpoint string) ([]byte, error) {
	base := c.BaseURL
	if base == "" {
		base = defaultBaseURL
	}

	reqURL := base + endpoint

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, reqURL, nil)
	if err != nil {
		return nil, fmt.Errorf("creating request: %w", err)
	}
	req.Header.Set("Accept", "application/json")

	client := c.HTTPClient
	if client == nil {
		client = http.DefaultClient
	}

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

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("reading response: %w", err)
	}

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("API returned status %d: %s", resp.StatusCode, string(body))
	}

	return body, nil
}

func (c Config) getMarketByTicker(ctx context.Context, ticker string) (*Market, error) {
	body, err := c.doGet(ctx, "/markets/"+url.PathEscape(ticker))
	if err != nil {
		return nil, fmt.Errorf("getting market: %w", err)
	}

	var resp apiMarketResponse
	if err := json.Unmarshal(body, &resp); err != nil {
		return nil, fmt.Errorf("parsing market: %w", err)
	}

	m := apiMarketToMarket(resp.Market)
	return &m, nil
}

func (c Config) getEventByTicker(ctx context.Context, ticker string) (*Event, error) {
	body, err := c.doGet(ctx, "/events/"+url.PathEscape(ticker)+"?with_nested_markets=true")
	if err != nil {
		return nil, fmt.Errorf("getting event: %w", err)
	}

	var resp apiEventResponse
	if err := json.Unmarshal(body, &resp); err != nil {
		return nil, fmt.Errorf("parsing event: %w", err)
	}

	ev := apiEventToEvent(resp.Event)
	return &ev, nil
}

// searchEvents fetches open events and filters by query substring match on title.
// Kalshi has no text search API, so we paginate through events client-side.
func (c Config) searchEvents(ctx context.Context, query string, maxResults int) ([]Event, error) {
	if maxResults <= 0 {
		maxResults = 20
	}

	queryLower := strings.ToLower(query)
	queryWords := strings.Fields(queryLower)
	var results []Event
	cursor := ""

	for {
		endpoint := "/events?status=open&limit=200&with_nested_markets=true"
		if cursor != "" {
			endpoint += "&cursor=" + url.QueryEscape(cursor)
		}

		body, err := c.doGet(ctx, endpoint)
		if err != nil {
			return results, fmt.Errorf("listing events: %w", err)
		}

		var resp apiEventsResponse
		if err := json.Unmarshal(body, &resp); err != nil {
			return results, fmt.Errorf("parsing events: %w", err)
		}

		for _, e := range resp.Events {
			if matchesQuery(e.Title, queryWords) {
				results = append(results, apiEventToEvent(e))
				if len(results) >= maxResults {
					return results, nil
				}
			}
		}

		if resp.Cursor == "" || len(resp.Events) == 0 {
			break
		}
		cursor = resp.Cursor
	}

	return results, nil
}

// matchesQuery checks if all query words appear in the text (case-insensitive).
func matchesQuery(text string, queryWords []string) bool {
	textLower := strings.ToLower(text)
	for _, word := range queryWords {
		if !strings.Contains(textLower, word) {
			return false
		}
	}
	return true
}

// parseKalshiURL extracts the market ticker from a Kalshi URL.
// Supported formats:
//   - https://kalshi.com/markets/<TICKER>
func parseKalshiURL(rawURL string) (ticker string, err error) {
	u, err := url.Parse(rawURL)
	if err != nil {
		return "", fmt.Errorf("parsing URL: %w", err)
	}

	host := strings.TrimPrefix(u.Host, "www.")
	if host != "kalshi.com" {
		return "", fmt.Errorf("not a Kalshi URL: %s", rawURL)
	}

	parts := strings.Split(strings.Trim(u.Path, "/"), "/")
	if len(parts) < 2 {
		return "", fmt.Errorf("invalid Kalshi URL path: %s", u.Path)
	}

	if parts[0] != "markets" {
		return "", fmt.Errorf("unsupported Kalshi URL type: %s", parts[0])
	}

	return parts[1], nil
}