// dbasik provides a service with which to convert spreadsheets containing
// data to JSON for further processing.

// Copyright (C) 2024 M R Lemon

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

// Package main is the entry point for dbasik.
// It provides the main functionality for the dbasik application.
package main

import (
	"context"
	"database/sql"
	"flag"
	"fmt"
	"log"
	"log/slog"
	"net/http"
	"os"
	"time"

	"github.com/joho/godotenv"
	_ "github.com/lib/pq"
)

const version = "0.0.1"

// holds the config for our application
// We will read this from the command line flags when we run the application
type config struct {
	port int
	env  string
	db   struct {
		dsn          string
		maxOpenConns int
		maxIdleConns int
		maxIdleTime  string
	}
}

// This application struct holds the dependencies for our HTTP handlers, helpers and
// middleware.
type application struct {
	config config
	logger *slog.Logger
	models Models
}

func main() {
	// Instance of config
	var cfg config

	err := godotenv.Load()
	if err != nil {
		log.Fatal("Cannot load .env file - is it present?")
	}

	// Read the flags into the config struct. Defaults are provided if none given.
	flag.IntVar(&cfg.port, "port", 5000, "API server port")
	flag.StringVar(&cfg.env, "env", "development", "Environment (development|staging|production)")
	flag.StringVar(&cfg.db.dsn, "db-dsn", os.Getenv("DBASIK_DB_DSN"), "PostgreSQL DSN")

	//Read connection pool settings (explained in Configuring the pool in the book)
	flag.IntVar(&cfg.db.maxOpenConns, "db-max-open-conns", 25, "PostgreSQL max open connections")
	flag.IntVar(&cfg.db.maxIdleConns, "db-max-idle-conns", 25, "PostgreSQL max idle connections")
	flag.StringVar(&cfg.db.maxIdleTime, "db-max-idle-time", "15m", "PostgreSQL max connection idle time")

	flag.Parse()

	// Initialize a new structured logger which writes to stdout
	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))

	// set up the database pool
	db, err := openDB(cfg)
	if err != nil {
		logger.Error(err.Error())
		os.Exit(1)
	}
	defer db.Close()
	logger.Info("database connection pool established")

	// An instance of application struct, containing the config struct and the logger
	app := &application{
		config: cfg,
		logger: logger,
		models: NewModels(db),
	}

	// Declare an http server which listens provided in the config struct and has
	// sensible timeout settings and writes log messages to the structured logger at
	// Error level.
	srv := &http.Server{
		Addr:         fmt.Sprintf(":%d", cfg.port),
		Handler:      app.routes(),
		IdleTimeout:  time.Minute,
		ReadTimeout:  5 * time.Second,
		WriteTimeout: 10 * time.Second,
		ErrorLog:     slog.NewLogLogger(logger.Handler(), slog.LevelError),
	}

	logger.Info("starting server", "addr", srv.Addr, "env", cfg.env)

	err = srv.ListenAndServe()
	logger.Error(err.Error())
	os.Exit(1)
}

func openDB(cfg config) (*sql.DB, error) {
	db, err := sql.Open("postgres", cfg.db.dsn)
	if err != nil {
		return nil, err
	}

	// set up pool config
	db.SetMaxOpenConns(cfg.db.maxOpenConns)
	db.SetMaxIdleConns(cfg.db.maxIdleConns)
	duration, err := time.ParseDuration(cfg.db.maxIdleTime)
	if err != nil {
		return nil, err
	}
	db.SetConnMaxIdleTime(duration)

	// create a context with a 5 second timeout
	// if the database hasn't connected within this time, there is a problem
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	err = db.PingContext(ctx)
	if err != nil {
		return nil, err
	}

	return db, nil
}