package rrd

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"
)

type Manager struct {
	Tool     string
	Path     string
	GraphDir string
	mu       sync.Mutex
}

type Range struct{ Key, Start, Title string }

var Ranges = []Range{
	{"hour", "-12h", "Ostatnie 12 godzin"},
	{"day", "-24h", "Ostatnie 24 godziny"},
	{"72h", "-72h", "Ostatnie 72 godziny"},
	{"week", "-1w", "Ostatni tydzień"},
	{"month", "-1m", "Ostatni miesiąc"},
	{"year", "-1y", "Ostatni rok"},
}

func (m *Manager) Validate() error {
	if _, err := exec.LookPath(m.Tool); err != nil {
		return fmt.Errorf("rrdtool not found: %w", err)
	}
	if st, err := os.Stat(m.Path); err != nil || st.IsDir() {
		return fmt.Errorf("RRD file unavailable: %s", m.Path)
	}
	return os.MkdirAll(m.GraphDir, 0750)
}

func (m *Manager) Update(ctx context.Context, online int) error {
	if online < 0 {
		return errors.New("online count cannot be negative")
	}
	cmd := exec.CommandContext(ctx, m.Tool, "update", m.Path, "N:"+strconv.Itoa(online))
	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("rrd update: %w: %s", err, strings.TrimSpace(stderr.String()))
	}
	return nil
}

func (m *Manager) Last(ctx context.Context) (int, error) {
	cmd := exec.CommandContext(ctx, m.Tool, "lastupdate", m.Path)
	out, err := cmd.Output()
	if err != nil {
		return 0, err
	}
	lines := strings.Split(strings.TrimSpace(string(out)), "\n")
	if len(lines) < 2 {
		return 0, errors.New("unexpected rrd lastupdate output")
	}
	fields := strings.Fields(lines[len(lines)-1])
	if len(fields) < 2 {
		return 0, errors.New("unexpected rrd lastupdate data")
	}
	v := fields[len(fields)-1]
	if v == "U" {
		return 0, nil
	}
	f, err := strconv.ParseFloat(v, 64)
	return int(f + 0.5), err
}

func (m *Manager) Graph(ctx context.Context, key string) (string, error) {
	var rg *Range
	for i := range Ranges {
		if Ranges[i].Key == key {
			rg = &Ranges[i]
			break
		}
	}
	if rg == nil {
		return "", errors.New("unknown graph range")
	}
	if err := os.MkdirAll(m.GraphDir, 0750); err != nil {
		return "", err
	}
	out := filepath.Join(m.GraphDir, key+".png")

	m.mu.Lock()
	defer m.mu.Unlock()
	if st, err := os.Stat(out); err == nil && time.Since(st.ModTime()) < 55*time.Second {
		return out, nil
	}

	def := "DEF:online=" + m.Path + ":online:LAST"
	args := []string{"graph", out, "--imgformat", "PNG", "--start", rg.Start, "--end", "now", "--width", "1200", "--height", "320", "--lower-limit", "0", "--alt-autoscale-max", "--title", rg.Title, "--vertical-label", "użytkownicy", "--border", "0", def, "LINE2:online#2F6FED:Online", "GPRINT:online:LAST:Aktualnie\\: %4.0lf", "GPRINT:online:AVERAGE:Średnio\\: %4.0lf", "GPRINT:online:MAX:Maks.\\: %4.0lf\\n"}
	cmd := exec.CommandContext(ctx, m.Tool, args...)
	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	if err := cmd.Run(); err != nil {
		return "", fmt.Errorf("rrd graph: %w: %s", err, strings.TrimSpace(stderr.String()))
	}
	return out, nil
}