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
}

// Graph colors mirror the dashboard's theme tokens (internal/web/assets/app.css)
// so rendered PNGs sit visually in place inside the panel cards. Each range
// is rendered twice (dark + light) so the client can pick the variant that
// matches the active site theme without round-tripping through rrdtool.
const (
	graphColorPanel      = "#181c19" // --panel (dark)
	graphColorField      = "#121713" // --field (dark plot canvas)
	graphColorLine       = "#313832" // --line (dark minor grid)
	graphColorLine2      = "#485149" // --line2 (dark axis / major grid)
	graphColorText       = "#edf0ecCC"
	graphColorAccent     = "#8fb9a4" // --accent (dark)
	graphColorAccentFill = "#8fb9a43d"

	graphLightColorPanel      = "#ffffff" // --panel (light)
	graphLightColorField      = "#f7f8f6" // --panel2 (light plot canvas)
	graphLightColorLine       = "#cbd2cb" // --line (light minor grid)
	graphLightColorLine2      = "#aeb8af" // --line2 (light axis / major grid)
	graphLightColorText       = "#202622CC"
	graphLightColorAccent     = "#507b67" // --accent (light)
	graphLightColorAccentFill = "#507b673d"
)

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, theme 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
	}

	panel, field, line, line2, text, accent, accentFill := graphColorPanel, graphColorField, graphColorLine, graphColorLine2, graphColorText, graphColorAccent, graphColorAccentFill
	suffix := ""
	if theme == "light" {
		panel, field, line, line2, text, accent, accentFill = graphLightColorPanel, graphLightColorField, graphLightColorLine, graphLightColorLine2, graphLightColorText, graphLightColorAccent, graphLightColorAccentFill
		suffix = "-light"
	}
	out := filepath.Join(m.GraphDir, key+suffix+".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"
	watermark := "linuxiarz.pl  ·  " + time.Now().Format("2006-01-02 15:04")
	args := []string{
		"graph", out,
		"--imgformat", "PNG",
		"--start", rg.Start, "--end", "now",
		// By default rrdtool's --width/--height size only the plot canvas;
		// the title, legend rows and axis-label margins then pad the final
		// PNG to something larger and variable (depends on title/legend
		// text length). --full-size-mode makes --width/--height the exact
		// *total* image size instead, so the PNG is always precisely
		// 1200x320 -- matching the CSS aspect-ratio on the <img> exactly,
		// with no letterboxing from a size mismatch.
		"--full-size-mode",
		"--width", "1200", "--height", "320",
		"--lower-limit", "0", "--alt-autoscale-max", "--rigid",
		"--slope-mode",
		"--title", rg.Title,
		"--vertical-label", "użytkownicy",
		"--border", "0",
		"--color", "BACK" + panel,
		"--color", "CANVAS" + field,
		"--color", "FONT" + text,
		"--color", "AXIS" + line2,
		"--color", "ARROW" + line2,
		"--color", "GRID" + line,
		"--color", "MGRID" + line2,
		"--color", "FRAME" + panel,
		"--font", "DEFAULT:0:",
		"--font", "TITLE:13:",
		"--font", "AXIS:9:",
		"--font", "LEGEND:10:",
		"--font", "UNIT:9:",
		"--watermark", watermark,
		def,
		"AREA:online" + accentFill,
		"LINE2:online" + accent + ":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
}