const PREFIX = 'DWENGO_';
const DB_PREFIX = PREFIX + 'DB_';

type EnvVar = { key: string; required?: boolean; defaultValue?: any };

export const EnvVars: { [key: string]: EnvVar } = {
    Port: { key: PREFIX + 'PORT', defaultValue: 3000 },
    DbHost: { key: DB_PREFIX + 'HOST', required: true },
    DbPort: { key: DB_PREFIX + 'PORT', defaultValue: 5432 },
    DbName: { key: DB_PREFIX + 'NAME', defaultValue: 'dwengo' },
    DbUsername: { key: DB_PREFIX + 'USERNAME', required: true },
    DbPassword: { key: DB_PREFIX + 'PASSWORD', required: true },
    DbUpdate: { key: DB_PREFIX + 'UPDATE', defaultValue: false },
} as const;

/**
 * Returns the value of the given environment variable if it is set.
 * Otherwise,
 * - throw an error if the environment variable was required,
 * - return the default value if there is one and it was not required,
 * - return an empty string if the environment variable is not required and there is also no default.
 * @param envVar The properties of the environment variable (from the EnvVar object).
 */
export function getEnvVar(envVar: EnvVar): string {
    const value: string | undefined = process.env[envVar.key];
    if (value) {
        return value;
    } else if (envVar.required) {
        throw new Error(`Missing environment variable: ${envVar.key}`);
    } else {
        return envVar.defaultValue || '';
    }
}

export function getNumericEnvVar(envVar: EnvVar): number {
    const valueString = getEnvVar(envVar);
    const value = parseInt(valueString);
    if (isNaN(value)) {
        throw new Error(
            `Invalid value for environment variable ${envVar.key}: ${valueString}. Expected a number.`
        );
    } else {
        return value;
    }
}