// Package healthcheck provides a service that reports
// application health, uptime, and version information.
package healthcheck

import (
	"context"
	"log/slog"
	"time"

	"sneak.berlin/go/netwatch/internal/config"
	"sneak.berlin/go/netwatch/internal/globals"
	"sneak.berlin/go/netwatch/internal/logger"

	"go.uber.org/fx"
)

// Params defines the dependencies for Healthcheck.
type Params struct {
	fx.In

	Config  *config.Config
	Globals *globals.Globals
	Logger  *logger.Logger
}

// Healthcheck tracks startup time and builds health responses.
type Healthcheck struct {
	StartupTime time.Time
	log         *slog.Logger
	params      *Params
}

// HealthcheckResponse is the JSON payload returned by the health
// check endpoint. Its name and its snake_case keys are the ones
// GO_HTTP_SERVER_CONVENTIONS.md gives.
//
//nolint:revive,tagliatelle // name and keys from the conventions
type HealthcheckResponse struct {
	Appname       string `json:"appname"`
	Now           string `json:"now"`
	Status        string `json:"status"`
	UptimeHuman   string `json:"uptime_human"`
	UptimeSeconds int64  `json:"uptime_seconds"`
	Version       string `json:"version"`
}

// New creates a Healthcheck, recording startup time via an
// fx lifecycle hook.
func New(
	lc fx.Lifecycle,
	params Params,
) (*Healthcheck, error) {
	s := new(Healthcheck)
	s.params = &params
	s.log = params.Logger.Get()

	lc.Append(fx.Hook{
		OnStart: func(_ context.Context) error {
			s.StartupTime = time.Now().UTC()

			return nil
		},
		OnStop: func(_ context.Context) error {
			return nil
		},
	})

	return s, nil
}

// Healthcheck returns the current health status of the application.
func (s *Healthcheck) Healthcheck() *HealthcheckResponse {
	return &HealthcheckResponse{
		Appname:       s.params.Globals.Appname,
		Now:           time.Now().UTC().Format(time.RFC3339Nano),
		Status:        "ok",
		UptimeHuman:   s.uptime().String(),
		UptimeSeconds: int64(s.uptime().Seconds()),
		Version:       s.params.Globals.Version,
	}
}

func (s *Healthcheck) uptime() time.Duration {
	return time.Since(s.StartupTime)
}