// Package originclient registers a running service with Origin
// (origin.warky.dev)'s public check-in endpoint and re-pings it on an
// interval, so Origin can track which instances of a service are alive,
// their version, and where they run. A check-in failure is logged and
// otherwise ignored: it must never affect the host application's own
// availability.
package originclient

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

const (
	// DefaultURL is Origin's public service-checkin endpoint.
	DefaultURL = "https://origin.warky.dev/api/public/service-checkin"
	// DefaultIntervalHours is how often Run repeats when Config.IntervalHours is unset.
	DefaultIntervalHours = 24

	requestTimeout = 10 * time.Second
)

// Config configures a Client. ServiceKey, Type, Version, and Name identify
// the caller to Origin and are required; everything else is optional
// metadata, or overrides for values Client would otherwise auto-detect.
type Config struct {
	// URL is the check-in endpoint. Defaults to DefaultURL.
	URL string
	// ServiceKey is sent as the X-Origin-Service-Key header. Required.
	ServiceKey string

	// Type is the Origin service type, which must already be registered in
	// Origin (e.g. "icy2"). Required.
	Type string
	// Version is the caller's own version string. Required.
	Version string
	// Name identifies this deployment/instance to Origin, e.g. "icy2-nova". Required.
	Name string

	Site         string
	Environment  string
	DatabaseType string
	DatabaseName string
	// AppType defaults to "go" when empty.
	AppType string
	// Hostname defaults to the OS hostname (see Hostname) when empty.
	Hostname    string
	Port        int
	BaseURL     string
	InternalURL string
	// ContainerID defaults to best-effort Docker/cgroup detection (see
	// ContainerID) when empty.
	ContainerID string
	// Orchestrator defaults to best-effort Kubernetes/Docker detection (see
	// Orchestrator) when empty.
	Orchestrator string
	Description  string

	// InstallID, if set, overrides machine-ID resolution entirely.
	InstallID string
	// InstallIDPath is where a generated fallback install ID is persisted
	// when no real OS machine ID is available. Defaults to the OS
	// user-config directory (see ResolveMachineID).
	InstallIDPath string

	// IntervalHours sets how often Run repeats. Defaults to DefaultIntervalHours.
	IntervalHours int

	// Logger receives non-fatal warnings. Defaults to discarding them.
	Logger Logger
}

// Client checks a service in with Origin.
type Client struct {
	cfg       Config
	http      *http.Client
	installID string
}

// New validates cfg, resolves the machine/install ID, and returns a ready
// Client. Resolution happens once, at construction, so every check-in made
// by this Client reports the same UniqueInstallID.
func New(cfg Config) (*Client, error) {
	if cfg.ServiceKey == "" || cfg.Type == "" || cfg.Version == "" || cfg.Name == "" {
		return nil, errors.New("originclient: ServiceKey, Type, Version, and Name are required")
	}
	if cfg.URL == "" {
		cfg.URL = DefaultURL
	}
	if cfg.AppType == "" {
		cfg.AppType = "go"
	}
	if cfg.IntervalHours <= 0 {
		cfg.IntervalHours = DefaultIntervalHours
	}
	if cfg.Logger == nil {
		cfg.Logger = noopLogger{}
	}

	return &Client{
		cfg:       cfg,
		http:      &http.Client{Timeout: requestTimeout},
		installID: ResolveMachineID(cfg.InstallID, cfg.InstallIDPath, cfg.Logger),
	}, nil
}

// Run performs an immediate check-in, then repeats every
// Config.IntervalHours until ctx is done. Run blocks the calling goroutine,
// so callers invoke it with `go client.Run(ctx)`. Check-in errors are
// logged via Config.Logger and otherwise ignored; call CheckinOnce directly
// if the caller needs to observe failures.
func (c *Client) Run(ctx context.Context) {
	_, _ = c.CheckinOnce(ctx)

	ticker := time.NewTicker(time.Duration(c.cfg.IntervalHours) * time.Hour)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			_, _ = c.CheckinOnce(ctx)
		}
	}
}

// CheckinOnce sends a single check-in request and returns Origin's
// response. Failures are logged via Config.Logger and also returned, so
// callers that only want the fire-and-forget behavior of Run can ignore
// the returned error.
func (c *Client) CheckinOnce(ctx context.Context) (*Response, error) {
	payload := c.buildPayload()

	body, err := json.Marshal(payload)
	if err != nil {
		c.cfg.Logger.Warn("origin checkin: encode payload failed", err)
		return nil, fmt.Errorf("originclient: encode payload: %w", err)
	}

	reqCtx, cancel := context.WithTimeout(ctx, requestTimeout)
	defer cancel()

	req, err := http.NewRequestWithContext(reqCtx, http.MethodPost, c.cfg.URL, bytes.NewReader(body))
	if err != nil {
		c.cfg.Logger.Warn("origin checkin: build request failed", err)
		return nil, fmt.Errorf("originclient: build request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("X-Origin-Service-Key", c.cfg.ServiceKey)

	resp, err := c.http.Do(req)
	if err != nil {
		c.cfg.Logger.Warn("origin checkin: request failed", err)
		return nil, fmt.Errorf("originclient: do request: %w", err)
	}
	defer func() {
		_ = resp.Body.Close()
	}()

	if resp.StatusCode >= 300 {
		err := fmt.Errorf("originclient: non-2xx response: %d", resp.StatusCode)
		c.cfg.Logger.Warn("origin checkin: non-2xx response", err)
		return nil, err
	}

	var result Response
	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
		c.cfg.Logger.Warn("origin checkin: decode response failed", err)
		return nil, fmt.Errorf("originclient: decode response: %w", err)
	}

	return &result, nil
}

func (c *Client) buildPayload() Payload {
	hostname := c.cfg.Hostname
	if hostname == "" {
		hostname = Hostname()
	}
	containerID := c.cfg.ContainerID
	if containerID == "" {
		containerID = ContainerID()
	}
	orchestrator := c.cfg.Orchestrator
	if orchestrator == "" {
		orchestrator = Orchestrator()
	}

	return Payload{
		Type:            c.cfg.Type,
		Version:         c.cfg.Version,
		Name:            c.cfg.Name,
		UniqueInstallID: c.installID,
		Site:            c.cfg.Site,
		Environment:     c.cfg.Environment,
		DatabaseType:    c.cfg.DatabaseType,
		DatabaseName:    c.cfg.DatabaseName,
		AppType:         c.cfg.AppType,
		Hostname:        hostname,
		Port:            c.cfg.Port,
		BaseURL:         c.cfg.BaseURL,
		InternalURL:     c.cfg.InternalURL,
		ContainerID:     containerID,
		Orchestrator:    orchestrator,
		Description:     c.cfg.Description,
	}
}