use std::{path::PathBuf, process::ExitCode};

use anyhow::{Context, Result};
use directories::UserDirs;
use rustyline::{error::ReadlineError, DefaultEditor};

use lune::Lune;

const MESSAGE_WELCOME: &str = concat!("Lune v", env!("CARGO_PKG_VERSION"));
const MESSAGE_INTERRUPT: &str = "Interrupt: ^C again to exit";

enum PromptState {
    Regular,
    Continuation,
}

pub async fn show_interface() -> Result<ExitCode> {
    println!("{MESSAGE_WELCOME}");

    let history_file_path: &PathBuf = &UserDirs::new()
        .context("Failed to find user home directory")?
        .home_dir()
        .join(".lune_history");
    if !history_file_path.exists() {
        tokio::fs::write(history_file_path, &[]).await?;
    }

    let mut repl = DefaultEditor::new()?;
    repl.load_history(history_file_path)?;

    let mut interrupt_counter = 0;
    let mut prompt_state = PromptState::Regular;
    let mut source_code = String::new();

    let mut lune_instance = Lune::new();

    loop {
        let prompt = match prompt_state {
            PromptState::Regular => "> ",
            PromptState::Continuation => ">> ",
        };

        match repl.readline(prompt) {
            Ok(code) => {
                interrupt_counter = 0;

                // TODO: Should we add history entries for each separate line?
                // Or should we add and save history only when we have complete
                // lua input that may or may not be multiple lines long?
                repl.add_history_entry(&code)?;
                repl.save_history(history_file_path)?;

                match prompt_state {
                    PromptState::Regular => source_code = code,
                    PromptState::Continuation => source_code.push_str(&code),
                }
            }

            Err(ReadlineError::Eof) => break,
            Err(ReadlineError::Interrupted) => {
                interrupt_counter += 1;

                // NOTE: We actually want the user to do ^C twice to exit,
                // and if we get an interrupt we should continue to the next
                // readline loop iteration so we don't run input code twice
                if interrupt_counter == 1 {
                    println!("{MESSAGE_INTERRUPT}");
                    continue;
                }

                break;
            }

            Err(err) => {
                eprintln!("REPL ERROR: {err}");
                return Ok(ExitCode::FAILURE);
            }
        };

        // TODO: Preserve context here somehow?
        let eval_result = lune_instance.run("REPL", &source_code).await;

        match eval_result {
            Ok(_) => prompt_state = PromptState::Regular,

            Err(err) => {
                if err.is_incomplete_input() {
                    prompt_state = PromptState::Continuation;
                    source_code.push('\n');
                } else {
                    eprintln!("{err}");
                }
            }
        };
    }

    repl.save_history(history_file_path)?;

    Ok(ExitCode::SUCCESS)
}