package health

import (
	"encoding/json"
	"net/http"
	"time"
)

// Response represents a health check response
type Response struct {
	Status    string    `json:"status"`
	Timestamp time.Time `json:"timestamp"`
	Version   string    `json:"version,omitempty"`
	Checks    []Check   `json:"checks,omitempty"`
}

// Check represents an individual health check
type Check struct {
	Name   string `json:"name"`
	Status string `json:"status"`
	Error  string `json:"error,omitempty"`
}

// Handler handles health check requests
type Handler struct {
	version string
	checks  []HealthChecker
}

// HealthChecker interface for health checks
type HealthChecker interface {
	Name() string
	Check() error
}

// NewHandler creates a new health check handler
func NewHandler(version string) *Handler {
	return &Handler{
		version: version,
		checks:  make([]HealthChecker, 0),
	}
}

// AddCheck adds a health checker
func (h *Handler) AddCheck(checker HealthChecker) {
	h.checks = append(h.checks, checker)
}

// ServeHTTP implements http.Handler
func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		w.WriteHeader(http.StatusMethodNotAllowed)
		return
	}

	response := Response{
		Status:    "ok",
		Timestamp: time.Now().UTC(),
		Version:   h.version,
		Checks:    make([]Check, 0, len(h.checks)),
	}

	allHealthy := true
	for _, checker := range h.checks {
		check := Check{
			Name:   checker.Name(),
			Status: "ok",
		}

		if err := checker.Check(); err != nil {
			check.Status = "error"
			check.Error = err.Error()
			allHealthy = false
		}

		response.Checks = append(response.Checks, check)
	}

	if !allHealthy {
		response.Status = "error"
		w.WriteHeader(http.StatusServiceUnavailable)
	} else {
		w.WriteHeader(http.StatusOK)
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(response)
}

// SimpleChecker is a basic health checker
type SimpleChecker struct {
	name string
	fn   func() error
}

// NewSimpleChecker creates a new simple health checker
func NewSimpleChecker(name string, fn func() error) *SimpleChecker {
	return &SimpleChecker{
		name: name,
		fn:   fn,
	}
}

// Name returns the checker name
func (c *SimpleChecker) Name() string {
	return c.name
}

// Check performs the health check
func (c *SimpleChecker) Check() error {
	return c.fn()
}