//! `config migrate` subcommand

mod v20240701;

use crate::config::{Revision, CLIENT_CONFIG_PATH, OLD_CONFIG_PATH, SERVER_CONFIG_PATH};
use serde::Deserialize;
use std::{fs, io::Read, path::Path};

#[derive(thiserror::Error, Debug)]
pub(crate) enum MigrationError {
    #[error("failed to determine the current config revision ({0})")]
    UnknownRevision(&'static str),
    #[error(transparent)]
    ReadFile(#[from] std::io::Error),
    #[error(transparent)]
    InvalidConfig(#[from] toml::de::Error),
    #[error(transparent)]
    V20240701(#[from] v20240701::Error),
}

fn next_revision() -> Result<Option<Revision>, MigrationError> {
    let old_config_exists = Path::new(OLD_CONFIG_PATH).is_file();
    let server_config_exists = Path::new(SERVER_CONFIG_PATH).is_file();
    let client_config_exists = Path::new(CLIENT_CONFIG_PATH).is_file();

    if server_config_exists && !client_config_exists {
        return Err(MigrationError::UnknownRevision(
            "client config file does not exist",
        ));
    }
    if !server_config_exists && client_config_exists {
        return Err(MigrationError::UnknownRevision(
            "server config file does not exist",
        ));
    }
    if !old_config_exists && !server_config_exists && !client_config_exists {
        return Err(MigrationError::UnknownRevision(
            "config file does not exist",
        ));
    }

    if old_config_exists && !server_config_exists && !client_config_exists {
        return Ok(Some(Revision::V20240701));
    }

    #[derive(Deserialize)]
    struct Config {
        config_revision: Revision,
    }

    let mut buffer = String::new();

    let mut server_toml = fs::File::open(SERVER_CONFIG_PATH)?;
    server_toml.read_to_string(&mut buffer)?;

    let server_config_revision = toml::from_str::<Config>(&buffer)?.config_revision;

    let mut client_toml = fs::File::open(CLIENT_CONFIG_PATH)?;
    client_toml.read_to_string(&mut buffer)?;

    let client_config_revision = toml::from_str::<Config>(&buffer)?.config_revision;

    if server_config_revision != client_config_revision {
        return Err(MigrationError::UnknownRevision(
            "server config revision and client config revision are different",
        ));
    }

    let next_revision = match server_config_revision {
        Revision::V20240701 => None,
    };

    Ok(next_revision)
}

async fn update_to_latest() -> Result<(), MigrationError> {
    if next_revision()?.is_none() {
        println!("Your config files are already up-to-date! (as of this fishctl release)");
        return Ok(());
    }

    while let Some(next_revision) = next_revision()? {
        run_impl(next_revision).await?;
    }
    Ok(())
}

async fn run_impl(revision: Revision) -> Result<(), MigrationError> {
    match revision {
        Revision::V20240701 => v20240701::run().await?,
    }
    Ok(())
}

pub(super) async fn run(revision: Option<Revision>) -> Result<(), MigrationError> {
    match revision {
        Some(revision) => run_impl(revision).await,
        None => update_to_latest().await,
    }
}