package main

import (
	"database/sql"
	"errors"
	"fmt"
	"html/template"
	"log"
	"net/http"
	"os"
	"sort"
	"strconv"
	"strings"
	"time"

	_ "github.com/go-sql-driver/mysql"
)

var monthNames = []string{
	"Januar", "Februar", "Maerz", "April", "Mai", "Juni",
	"Juli", "August", "September", "Oktober", "November", "Dezember",
}

type App struct {
	db   *sql.DB
	tmpl *template.Template
}

type Field struct {
	ID     int64
	Number int
	Name   string
}

type Crop struct {
	ID            int64
	Name          string
	SowStartMonth int
	SowEndMonth   int
	GrowMonths    int
}

type Plan struct {
	ID           int64
	FieldID      int64
	FieldNumber  int
	FieldName    string
	CropID       int64
	CropName     string
	StartMonth   int
	StartDay     int
	HarvestMonth int
	HarvestDay   int
	Notes        string
}

type Task struct {
	Type      string
	Field     string
	Message   string
	SortOrder int
}

type MonthOption struct {
	Value int
	Label string
}

type PageData struct {
	NowMonth     int
	NowDay       int
	DaysPerMonth int
	Months       []MonthOption
	Fields       []Field
	Crops        []Crop
	Plans        []Plan
	Tasks        []Task
	Error        string
	Info         string
}

func main() {
	addr := readEnv("APP_ADDR", ":8080")
	dsn := readEnv("DB_DSN", "farmcal:farmcal@tcp(127.0.0.1:3306)/farmcal?parseTime=true")

	db, err := sql.Open("mysql", dsn)
	if err != nil {
		log.Fatalf("db open failed: %v", err)
	}
	defer db.Close()

	if err := db.Ping(); err != nil {
		log.Fatalf("db ping failed: %v", err)
	}
	if err := ensureSchema(db); err != nil {
		log.Fatalf("schema setup failed: %v", err)
	}

	tmpl, err := template.ParseFiles("templates/index.html")
	if err != nil {
		log.Fatalf("template parse failed: %v", err)
	}

	app := &App{db: db, tmpl: tmpl}
	mux := http.NewServeMux()
	mux.HandleFunc("/", app.handleIndex)
	mux.HandleFunc("/fields", app.handleCreateField)
	mux.HandleFunc("/plans", app.handleCreatePlan)
	mux.HandleFunc("/settings", app.handleSettings)
	mux.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.Dir("static"))))

	srv := &http.Server{
		Addr:              addr,
		Handler:           withLogging(mux),
		ReadHeaderTimeout: 5 * time.Second,
	}
	log.Printf("FarmCal listening on %s", addr)
	if err := srv.ListenAndServe(); !errors.Is(err, http.ErrServerClosed) {
		log.Fatalf("server stopped: %v", err)
	}
}

func (a *App) handleIndex(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	daysPerMonth, err := a.getDaysPerMonth()
	if err != nil {
		http.Error(w, "settings read failed", http.StatusInternalServerError)
		return
	}

	nowMonth := mustInt(r.URL.Query().Get("month"), 1)
	nowDay := mustInt(r.URL.Query().Get("day"), 1)
	if nowMonth < 1 || nowMonth > 12 {
		nowMonth = 1
	}
	if nowDay < 1 || nowDay > daysPerMonth {
		nowDay = 1
	}

	fields, err := a.listFields()
	if err != nil {
		http.Error(w, "fields read failed", http.StatusInternalServerError)
		return
	}
	crops, err := a.listCrops()
	if err != nil {
		http.Error(w, "crops read failed", http.StatusInternalServerError)
		return
	}
	plans, err := a.listPlans()
	if err != nil {
		http.Error(w, "plans read failed", http.StatusInternalServerError)
		return
	}

	data := PageData{
		NowMonth:     nowMonth,
		NowDay:       nowDay,
		DaysPerMonth: daysPerMonth,
		Months:       monthOptions(),
		Fields:       fields,
		Crops:        crops,
		Plans:        plans,
		Tasks:        buildTasksForDay(plans, nowMonth, nowDay),
		Error:        r.URL.Query().Get("error"),
		Info:         r.URL.Query().Get("info"),
	}

	if err := a.tmpl.Execute(w, data); err != nil {
		http.Error(w, "template render failed", http.StatusInternalServerError)
	}
}

func (a *App) handleCreateField(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	if err := r.ParseForm(); err != nil {
		http.Redirect(w, r, "/?error=form+ungueltig", http.StatusSeeOther)
		return
	}
	number := mustInt(r.FormValue("number"), 0)
	name := strings.TrimSpace(r.FormValue("name"))
	if number <= 0 {
		http.Redirect(w, r, "/?error=Feldnummer+ungueltig", http.StatusSeeOther)
		return
	}
	if _, err := a.db.Exec(`INSERT INTO fields(number,name) VALUES (?,?)`, number, name); err != nil {
		http.Redirect(w, r, "/?error=Feld+nicht+angelegt", http.StatusSeeOther)
		return
	}
	http.Redirect(w, r, "/?info=Feld+angelegt", http.StatusSeeOther)
}

func (a *App) handleCreatePlan(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	if err := r.ParseForm(); err != nil {
		http.Redirect(w, r, "/?error=form+ungueltig", http.StatusSeeOther)
		return
	}

	fieldID := mustInt64(r.FormValue("field_id"), 0)
	cropID := mustInt64(r.FormValue("crop_id"), 0)
	startMonth := mustInt(r.FormValue("start_month"), 1)
	startDay := mustInt(r.FormValue("start_day"), 1)
	notes := strings.TrimSpace(r.FormValue("notes"))

	if fieldID <= 0 || cropID <= 0 {
		http.Redirect(w, r, "/?error=Feld+oder+Frucht+ungueltig", http.StatusSeeOther)
		return
	}

	daysPerMonth, err := a.getDaysPerMonth()
	if err != nil {
		http.Redirect(w, r, "/?error=Einstellungen+nicht+lesbar", http.StatusSeeOther)
		return
	}
	if startMonth < 1 || startMonth > 12 || startDay < 1 || startDay > daysPerMonth {
		http.Redirect(w, r, "/?error=Startdatum+ungueltig", http.StatusSeeOther)
		return
	}

	var c Crop
	err = a.db.QueryRow(`SELECT id,name,sow_start_month,sow_end_month,grow_months FROM crops WHERE id=?`, cropID).
		Scan(&c.ID, &c.Name, &c.SowStartMonth, &c.SowEndMonth, &c.GrowMonths)
	if err != nil {
		http.Redirect(w, r, "/?error=Feldfrucht+nicht+gefunden", http.StatusSeeOther)
		return
	}

	if !monthInWindow(startMonth, c.SowStartMonth, c.SowEndMonth) {
		http.Redirect(w, r, "/?error=Aussaat+ausserhalb+des+Zeitfensters", http.StatusSeeOther)
		return
	}

	harvestMonth := wrapMonth(startMonth + c.GrowMonths)
	harvestDay := startDay
	_, err = a.db.Exec(
		`INSERT INTO plans(field_id,crop_id,start_month,start_day,harvest_month,harvest_day,notes) VALUES (?,?,?,?,?,?,?)`,
		fieldID, cropID, startMonth, startDay, harvestMonth, harvestDay, notes,
	)
	if err != nil {
		http.Redirect(w, r, "/?error=Plan+nicht+gespeichert", http.StatusSeeOther)
		return
	}
	http.Redirect(w, r, "/?info=Plan+gespeichert", http.StatusSeeOther)
}

func (a *App) handleSettings(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	if err := r.ParseForm(); err != nil {
		http.Redirect(w, r, "/?error=form+ungueltig", http.StatusSeeOther)
		return
	}
	daysPerMonth := mustInt(r.FormValue("days_per_month"), 2)
	if daysPerMonth < 1 || daysPerMonth > 31 {
		http.Redirect(w, r, "/?error=Tage+pro+Monat+1-31", http.StatusSeeOther)
		return
	}
	if _, err := a.db.Exec(`UPDATE settings SET days_per_month=? WHERE id=1`, daysPerMonth); err != nil {
		http.Redirect(w, r, "/?error=Einstellungen+nicht+gespeichert", http.StatusSeeOther)
		return
	}
	http.Redirect(w, r, "/?info=Einstellungen+gespeichert", http.StatusSeeOther)
}

func (a *App) getDaysPerMonth() (int, error) {
	var v int
	err := a.db.QueryRow(`SELECT days_per_month FROM settings WHERE id=1`).Scan(&v)
	return v, err
}

func (a *App) listFields() ([]Field, error) {
	rows, err := a.db.Query(`SELECT id,number,name FROM fields ORDER BY number`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []Field
	for rows.Next() {
		var x Field
		if err := rows.Scan(&x.ID, &x.Number, &x.Name); err != nil {
			return nil, err
		}
		out = append(out, x)
	}
	return out, rows.Err()
}

func (a *App) listCrops() ([]Crop, error) {
	rows, err := a.db.Query(`SELECT id,name,sow_start_month,sow_end_month,grow_months FROM crops ORDER BY name`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []Crop
	for rows.Next() {
		var x Crop
		if err := rows.Scan(&x.ID, &x.Name, &x.SowStartMonth, &x.SowEndMonth, &x.GrowMonths); err != nil {
			return nil, err
		}
		out = append(out, x)
	}
	return out, rows.Err()
}

func (a *App) listPlans() ([]Plan, error) {
	rows, err := a.db.Query(`
		SELECT p.id,p.field_id,f.number,COALESCE(f.name,''),p.crop_id,c.name,p.start_month,p.start_day,p.harvest_month,p.harvest_day,COALESCE(p.notes,'')
		FROM plans p
		JOIN fields f ON f.id=p.field_id
		JOIN crops c ON c.id=p.crop_id
		ORDER BY p.start_month,p.start_day,f.number`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []Plan
	for rows.Next() {
		var x Plan
		if err := rows.Scan(&x.ID, &x.FieldID, &x.FieldNumber, &x.FieldName, &x.CropID, &x.CropName, &x.StartMonth, &x.StartDay, &x.HarvestMonth, &x.HarvestDay, &x.Notes); err != nil {
			return nil, err
		}
		out = append(out, x)
	}
	return out, rows.Err()
}

func ensureSchema(db *sql.DB) error {
	stmts := []string{
		`CREATE TABLE IF NOT EXISTS settings(id TINYINT PRIMARY KEY,days_per_month INT NOT NULL DEFAULT 2)`,
		`INSERT INTO settings(id,days_per_month) VALUES (1,2) ON DUPLICATE KEY UPDATE id=id`,
		`CREATE TABLE IF NOT EXISTS fields(id BIGINT AUTO_INCREMENT PRIMARY KEY,number INT NOT NULL UNIQUE,name VARCHAR(120) NOT NULL DEFAULT '',created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP)`,
		`CREATE TABLE IF NOT EXISTS crops(id BIGINT AUTO_INCREMENT PRIMARY KEY,name VARCHAR(80) NOT NULL UNIQUE,sow_start_month TINYINT NOT NULL,sow_end_month TINYINT NOT NULL,grow_months TINYINT NOT NULL)`,
		`CREATE TABLE IF NOT EXISTS plans(id BIGINT AUTO_INCREMENT PRIMARY KEY,field_id BIGINT NOT NULL,crop_id BIGINT NOT NULL,start_month TINYINT NOT NULL,start_day TINYINT NOT NULL,harvest_month TINYINT NOT NULL,harvest_day TINYINT NOT NULL,notes VARCHAR(255) NOT NULL DEFAULT '',created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,CONSTRAINT fk_plans_fields FOREIGN KEY(field_id) REFERENCES fields(id) ON DELETE CASCADE,CONSTRAINT fk_plans_crops FOREIGN KEY(crop_id) REFERENCES crops(id) ON DELETE RESTRICT)`,
	}
	for _, stmt := range stmts {
		if _, err := db.Exec(stmt); err != nil {
			return err
		}
	}
	return seedCrops(db)
}

func seedCrops(db *sql.DB) error {
	items := []Crop{
		{Name: "Weizen", SowStartMonth: 9, SowEndMonth: 11, GrowMonths: 10},
		{Name: "Gerste", SowStartMonth: 9, SowEndMonth: 10, GrowMonths: 9},
		{Name: "Hafer", SowStartMonth: 3, SowEndMonth: 4, GrowMonths: 4},
		{Name: "Raps", SowStartMonth: 8, SowEndMonth: 9, GrowMonths: 11},
		{Name: "Mais", SowStartMonth: 4, SowEndMonth: 5, GrowMonths: 6},
		{Name: "Sorghum", SowStartMonth: 4, SowEndMonth: 5, GrowMonths: 5},
		{Name: "Sojabohnen", SowStartMonth: 4, SowEndMonth: 5, GrowMonths: 5},
		{Name: "Sonnenblumen", SowStartMonth: 4, SowEndMonth: 5, GrowMonths: 5},
		{Name: "Kartoffeln", SowStartMonth: 3, SowEndMonth: 4, GrowMonths: 7},
		{Name: "Zuckerrueben", SowStartMonth: 3, SowEndMonth: 4, GrowMonths: 8},
		{Name: "Baumwolle", SowStartMonth: 2, SowEndMonth: 3, GrowMonths: 8},
	}
	for _, c := range items {
		if _, err := db.Exec(`INSERT INTO crops(name,sow_start_month,sow_end_month,grow_months) VALUES (?,?,?,?) ON DUPLICATE KEY UPDATE sow_start_month=VALUES(sow_start_month),sow_end_month=VALUES(sow_end_month),grow_months=VALUES(grow_months)`, c.Name, c.SowStartMonth, c.SowEndMonth, c.GrowMonths); err != nil {
			return err
		}
	}
	return nil
}

func buildTasksForDay(plans []Plan, month, day int) []Task {
	var tasks []Task
	for _, p := range plans {
		field := fmt.Sprintf("Feld %d", p.FieldNumber)
		if p.FieldName != "" {
			field = fmt.Sprintf("Feld %d (%s)", p.FieldNumber, p.FieldName)
		}
		if p.StartMonth == month && p.StartDay == day {
			tasks = append(tasks, Task{Type: "Aussaat", Field: field, Message: fmt.Sprintf("%s auf %s aussaeen", p.CropName, field), SortOrder: 1})
		}
		if p.HarvestMonth == month && p.HarvestDay == day {
			tasks = append(tasks, Task{Type: "Ernte", Field: field, Message: fmt.Sprintf("%s auf %s ernten", p.CropName, field), SortOrder: 2})
		}
	}
	sort.Slice(tasks, func(i, j int) bool {
		if tasks[i].SortOrder == tasks[j].SortOrder {
			return tasks[i].Field < tasks[j].Field
		}
		return tasks[i].SortOrder < tasks[j].SortOrder
	})
	return tasks
}

func monthOptions() []MonthOption {
	out := make([]MonthOption, 0, 12)
	for i, m := range monthNames {
		out = append(out, MonthOption{Value: i + 1, Label: m})
	}
	return out
}

func monthInWindow(month, start, end int) bool {
	if start <= end {
		return month >= start && month <= end
	}
	return month >= start || month <= end
}

func wrapMonth(v int) int {
	m := v % 12
	if m == 0 {
		return 12
	}
	return m
}

func mustInt(v string, fallback int) int {
	n, err := strconv.Atoi(strings.TrimSpace(v))
	if err != nil {
		return fallback
	}
	return n
}

func mustInt64(v string, fallback int64) int64 {
	n, err := strconv.ParseInt(strings.TrimSpace(v), 10, 64)
	if err != nil {
		return fallback
	}
	return n
}

func readEnv(key, fallback string) string {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return fallback
	}
	return v
}

func withLogging(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		next.ServeHTTP(w, r)
		log.Printf("%s %s %s", r.Method, r.URL.Path, time.Since(start).Round(time.Millisecond))
	})
}