labmcp/internal/monitoring/prometheus.go

package monitoring

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

// PrometheusClient is an HTTP client for the Prometheus API.
type PrometheusClient struct {
	baseURL    string
	httpClient *http.Client
}

// NewPrometheusClient creates a new Prometheus API client.
func NewPrometheusClient(baseURL string) *PrometheusClient {
	return &PrometheusClient{
		baseURL: strings.TrimRight(baseURL, "/"),
		httpClient: &http.Client{
			Timeout: 30 * time.Second,
		},
	}
}

// Query executes an instant PromQL query. If ts is zero, the current time is used.
func (c *PrometheusClient) Query(ctx context.Context, promql string, ts time.Time) (*PromQueryData, error) {
	params := url.Values{}
	params.Set("query", promql)
	if !ts.IsZero() {
		params.Set("time", fmt.Sprintf("%d", ts.Unix()))
	}

	body, err := c.get(ctx, "/api/v1/query", params)
	if err != nil {
		return nil, fmt.Errorf("query failed: %w", err)
	}

	var data PromQueryData
	if err := json.Unmarshal(body, &data); err != nil {
		return nil, fmt.Errorf("failed to parse query data: %w", err)
	}
	return &data, nil
}

// LabelValues returns all values for a given label name.
func (c *PrometheusClient) LabelValues(ctx context.Context, label string) ([]string, error) {
	path := fmt.Sprintf("/api/v1/label/%s/values", url.PathEscape(label))
	body, err := c.get(ctx, path, nil)
	if err != nil {
		return nil, fmt.Errorf("label values failed: %w", err)
	}

	var values []string
	if err := json.Unmarshal(body, &values); err != nil {
		return nil, fmt.Errorf("failed to parse label values: %w", err)
	}
	return values, nil
}

// Metadata returns metadata for metrics. If metric is empty, returns metadata for all metrics.
func (c *PrometheusClient) Metadata(ctx context.Context, metric string) (map[string][]PromMetadata, error) {
	params := url.Values{}
	if metric != "" {
		params.Set("metric", metric)
	}

	body, err := c.get(ctx, "/api/v1/metadata", params)
	if err != nil {
		return nil, fmt.Errorf("metadata failed: %w", err)
	}

	var metadata map[string][]PromMetadata
	if err := json.Unmarshal(body, &metadata); err != nil {
		return nil, fmt.Errorf("failed to parse metadata: %w", err)
	}
	return metadata, nil
}

// Targets returns the current scrape targets.
func (c *PrometheusClient) Targets(ctx context.Context) (*PromTargetsData, error) {
	body, err := c.get(ctx, "/api/v1/targets", nil)
	if err != nil {
		return nil, fmt.Errorf("targets failed: %w", err)
	}

	var data PromTargetsData
	if err := json.Unmarshal(body, &data); err != nil {
		return nil, fmt.Errorf("failed to parse targets data: %w", err)
	}
	return &data, nil
}

// get performs a GET request and returns the "data" field from the Prometheus response envelope.
func (c *PrometheusClient) get(ctx context.Context, path string, params url.Values) (json.RawMessage, error) {
	u := c.baseURL + path
	if len(params) > 0 {
		u += "?" + params.Encode()
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to create request: %w", err)
	}

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("request failed: %w", err)
	}
	defer resp.Body.Close() //nolint:errcheck // cleanup on exit

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

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

	var promResp PromResponse
	if err := json.Unmarshal(body, &promResp); err != nil {
		return nil, fmt.Errorf("failed to parse response: %w", err)
	}

	if promResp.Status != "success" {
		return nil, fmt.Errorf("prometheus error (%s): %s", promResp.ErrorType, promResp.Error)
	}

	return promResp.Data, nil
}