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

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

export const EnvVars: {[key: string]: EnvVar} = {
    "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;
    }
}