package main

import (
	"database/sql"
	"fmt"
	"strings"

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

const sqliteSchema = `
CREATE TABLE IF NOT EXISTS lists (
	id TEXT PRIMARY KEY,
	created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);
CREATE TABLE IF NOT EXISTS sublists (
	id INTEGER PRIMARY KEY AUTOINCREMENT,
	list_id TEXT NOT NULL REFERENCES lists(id),
	name TEXT NOT NULL,
	color TEXT NOT NULL,
	created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);
CREATE TABLE IF NOT EXISTS items (
	id INTEGER PRIMARY KEY AUTOINCREMENT,
	list_id TEXT NOT NULL REFERENCES lists(id),
	name TEXT NOT NULL,
	quantity INTEGER NOT NULL DEFAULT 1,
	done INTEGER NOT NULL DEFAULT 0,
	position REAL NOT NULL DEFAULT 0,
	sublist_id INTEGER REFERENCES sublists(id),
	created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);`

const mysqlSchema = `
CREATE TABLE IF NOT EXISTS lists (
	id VARCHAR(64) PRIMARY KEY,
	created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);
CREATE TABLE IF NOT EXISTS sublists (
	id INTEGER PRIMARY KEY AUTO_INCREMENT,
	list_id VARCHAR(64) NOT NULL,
	name VARCHAR(255) NOT NULL,
	color VARCHAR(32) NOT NULL,
	created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
	FOREIGN KEY (list_id) REFERENCES lists(id)
);
CREATE TABLE IF NOT EXISTS items (
	id INTEGER PRIMARY KEY AUTO_INCREMENT,
	list_id VARCHAR(64) NOT NULL,
	name VARCHAR(255) NOT NULL,
	quantity INTEGER NOT NULL DEFAULT 1,
	done BOOLEAN NOT NULL DEFAULT FALSE,
	position DOUBLE NOT NULL DEFAULT 0,
	sublist_id INTEGER,
	created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
	FOREIGN KEY (list_id) REFERENCES lists(id),
	FOREIGN KEY (sublist_id) REFERENCES sublists(id)
);`

func openDB(databaseURL string) (*sql.DB, error) {
	driver, dsn, found := strings.Cut(databaseURL, "://")
	if !found {
		return nil, fmt.Errorf("DATABASE_URL must be in the form driver://dsn, got %q", databaseURL)
	}

	var schema string
	switch driver {
	case "sqlite":
		schema = sqliteSchema
	case "mysql":
		driver = "mysql"
		schema = mysqlSchema
	default:
		return nil, fmt.Errorf("unsupported database driver %q, expected sqlite or mysql", driver)
	}

	db, err := sql.Open(driver, dsn)
	if err != nil {
		return nil, fmt.Errorf("opening database: %w", err)
	}

	if err := db.Ping(); err != nil {
		return nil, fmt.Errorf("connecting to database: %w", err)
	}

	if _, err := db.Exec(schema); err != nil {
		return nil, fmt.Errorf("running migration: %w", err)
	}

	// Best-effort: adds columns for databases created before they existed.
	// Fails harmlessly if a column is already there.
	db.Exec("ALTER TABLE items ADD COLUMN position REAL NOT NULL DEFAULT 0")
	db.Exec("ALTER TABLE items ADD COLUMN sublist_id INTEGER")

	return db, nil
}