// SPDX-FileCopyrightText: 2025 Ruby Iris Juric <ruby@srxl.me>
//
// SPDX-License-Identifier: 0BSD

use std::{fs, process::Command};

use miette::{Context, IntoDiagnostic, Result, miette};

use crate::gleam_toml;

enum Target {
    Erlang,
    Javascript,
}

impl Target {
    fn filename(&self) -> String {
        match self {
            Target::Erlang => "gleam_entrypoint.erl".to_string(),
            Target::Javascript => "gleam_entrypoint.mjs".to_string(),
        }
    }
}

impl TryFrom<&str> for Target {
    type Error = miette::Report;

    fn try_from(target: &str) -> Result<Self, Self::Error> {
        match target {
            "erlang" => Ok(Self::Erlang),
            "javascript" => Ok(Self::Javascript),
            _ => Err(miette!("Unknown target {target}")),
        }
    }
}

fn generate_module_source(module_name: &str, target: &Target) -> String {
    match target {
        Target::Erlang => format!(
            r#"-module('gleam_entrypoint').
-export([run/0]).

run() ->
    {{ok, _}} = application:ensure_all_started('{module_name}'),
    {module_name}:main(),
    erlang:halt(0).
"#
        ),
        Target::Javascript => format!(
            r#"import {{ main }} from "./{module_name}/{module_name}.mjs";
main();
"#
        ),
    }
}

pub fn generate_module(target: &str) -> Result<()> {
    let target: Target = target.try_into()?;
    let gleam_toml = gleam_toml::parse("gleam.toml")?;
    let source = generate_module_source(&gleam_toml.name, &target);

    fs::write(target.filename(), source)
        .into_diagnostic()
        .wrap_err("While writing entrypoint module source:")?;

    match target {
        Target::Javascript => Ok(()),
        Target::Erlang => {
            let compile_result = Command::new("erlc")
                .arg(target.filename())
                .status()
                .into_diagnostic()
                .wrap_err("While running Erlang compiler:")?;

            if compile_result.success() {
                Ok(())
            } else {
                Err(miette!("Entrypoint compilation failed"))
            }
        }
    }
}