const NGX_VERSION = "0.2.0";

type ConfigNode = ConfigStatement | ConfigBlock | ConfigBreak | ConfigFile;

class ConfigBuildable {
  build(): string {
    throw new Error("build(..) not implemented!");
  }
}

class ConfigBlock extends ConfigBuildable {
  value: string;
  children: ConfigNode[];

  constructor(value: string, children: ConfigNode[]) {
    super();

    this.value = value;
    this.children = children;
  }

  override build(): string {
    let output = this.value;
    output += " {\n  ";
    output += this.children
      .map((child) => child.build().split("\n").join("\n  "))
      .join("\n  ");
    output += "\n}";
    return output;
  }
}

class ConfigStatement extends ConfigBuildable {
  value: string;
  constructor(value: string) {
    super();

    this.value = value;
  }

  override build(): string {
    return this.value + ";";
  }
}

class ConfigBreak extends ConfigBuildable {
  override build(): string {
    return "";
  }
}

class ConfigFile extends ConfigBuildable {
  nodes: ConfigNode[];
  constructor(nodes: ConfigNode[]) {
    super();

    this.nodes = nodes;
  }

  override build(): string {
    return this.nodes.map((n) => n.build()).join("\n");
  }
}

type LooseConfigNode = ConfigNode | string | LooseConfigNode[];

function conform(looseNode: LooseConfigNode): ConfigNode[] {
  if (typeof looseNode === "string") {
    return [new ConfigStatement(looseNode)];
  }
  if (typeof looseNode === "object" && looseNode instanceof Array) {
    if (looseNode.length === 0) {
      return [new ConfigBreak()];
    } else if (looseNode.length === 1) {
      return conform(looseNode[0]);
    } else {
      return looseNode
        .map((n) => conform(n))
        .reduceRight((b, a) =>
          a.length === 1 ? [...a, ...b] : [...a, new ConfigBreak(), ...b],
        );
    }
  }
  return [looseNode];
}

export function ngx(value?: string, children?: LooseConfigNode[]): ConfigNode {
  const hasValue = value !== undefined && value !== "";
  const hasChildren = children !== undefined;

  if (!hasValue && !hasChildren) {
    return new ConfigBreak();
  } else if (hasValue && !hasChildren) {
    return new ConfigStatement(value);
  } else if (hasValue && hasChildren) {
    return new ConfigBlock(value, conform(children));
  } else if (!hasValue && hasChildren) {
    return new ConfigFile(conform(children));
  }

  throw new Error("unreachable");
}

export const listen = (...extras: string[]) =>
  conform([
    `listen 443 ${["ssl", ...extras].join(" ")}`,
    `listen [::]:443 ${["ssl", ...extras].join(" ")}`,
    `http2 on`,
  ]);

export const serverName = (name: string) => conform([`server_name ${name}`]);

export const letsEncrypt = (
  domain: string,
  liveDir = "/etc/letsencrypt/live",
) =>
  conform([
    `ssl_certificate ${liveDir}/${domain}/fullchain.pem`,
    `ssl_certificate_key ${liveDir}/${domain}/privkey.pem`,
  ]);

// the default export is both the ngx function and a namespace:
export default Object.assign(
  (value?: string, children?: LooseConfigNode[]) => ngx(value, children),
  { NGX_VERSION, listen, letsEncrypt, serverName },
);