use std::{
    env::{self, current_dir},
    fs,
    path::{self, PathBuf},
};

use dunce::canonicalize;
use mlua::prelude::*;

use crate::lua::table::TableBuilder;

const REQUIRE_IMPL_LUA: &str = r#"
local source = info(1, "s")
if source == '[string "require"]' then
    source = info(2, "s")
end
local absolute, relative = paths(source, ...)
if loaded[absolute] ~= true then
    local first, second = load(absolute, relative)
    if first == nil or second ~= nil then
        error("Module did not return exactly one value")
    end
    loaded[absolute] = true
    cache[absolute] = first
    return first
else
    return cache[absolute]
end
"#;

pub fn create(lua: &'static Lua) -> LuaResult<LuaTable> {
    // Preserve original require behavior if we have a special env var set,
    // returning an empty table since there are no globals to overwrite
    if env::var_os("LUAU_PWD_REQUIRE").is_some() {
        return TableBuilder::new(lua)?.build_readonly();
    }
    // Store the current pwd, and make the functions for path conversions & loading a file
    let mut require_pwd = current_dir()?.to_string_lossy().to_string();
    if !require_pwd.ends_with(path::MAIN_SEPARATOR) {
        require_pwd = format!("{require_pwd}{}", path::MAIN_SEPARATOR)
    }
    let require_info: LuaFunction = lua.named_registry_value("dbg.info")?;
    let require_error: LuaFunction = lua.named_registry_value("error")?;
    let require_get_abs_rel_paths = lua
        .create_function(
            |_, (require_pwd, require_source, require_path): (String, String, String)| {
                let path_relative_to_pwd = PathBuf::from(
                    &require_source
                        .trim_start_matches("[string \"")
                        .trim_end_matches("\"]"),
                )
                .parent()
                .unwrap()
                .join(&require_path);
                // Try to normalize and resolve relative path segments such as './' and '../'
                let file_path = match (
                    canonicalize(path_relative_to_pwd.with_extension("luau")),
                    canonicalize(path_relative_to_pwd.with_extension("lua")),
                ) {
                    (Ok(luau), _) => luau,
                    (_, Ok(lua)) => lua,
                    _ => {
                        return Err(LuaError::RuntimeError(format!(
                            "File does not exist at path '{require_path}'"
                        )))
                    }
                };
                let absolute = file_path.to_string_lossy().to_string();
                let relative = absolute.trim_start_matches(&require_pwd).to_string();
                Ok((absolute, relative))
            },
        )?
        .bind(require_pwd)?;
    // Note that file loading must be blocking to guarantee the require cache works, if it
    // were async then one lua script may require a module during the file reading process
    let require_get_loaded_file = lua.create_function(
        |lua: &Lua, (path_absolute, path_relative): (String, String)| {
            // Use a name without extensions for loading the chunk, the
            // above code assumes the require path is without extensions
            let path_relative_no_extension = path_relative
                .trim_end_matches(".lua")
                .trim_end_matches(".luau");
            // Try to read the wanted file, note that we use bytes instead of reading
            // to a string since lua scripts are not necessarily valid utf-8 strings
            match fs::read(path_absolute) {
                Ok(contents) => lua
                    .load(&contents)
                    .set_name(path_relative_no_extension)?
                    .eval::<LuaValue>(),
                Err(e) => Err(LuaError::external(e)),
            }
        },
    )?;
    /*
        We need to get the source file where require was
        called to be able to do path-relative requires,
        so we make a small wrapper to do that here, this
        will then call our actual async require function

        This must be done in lua because due to how our
        scheduler works mlua can not preserve debug info
    */
    let require_env = TableBuilder::new(lua)?
        .with_value("loaded", lua.create_table()?)?
        .with_value("cache", lua.create_table()?)?
        .with_value("info", require_info)?
        .with_value("error", require_error)?
        .with_value("paths", require_get_abs_rel_paths)?
        .with_value("load", require_get_loaded_file)?
        .build_readonly()?;
    let require_fn_lua = lua
        .load(REQUIRE_IMPL_LUA)
        .set_name("require")?
        .set_environment(require_env)?
        .into_function()?;
    TableBuilder::new(lua)?
        .with_value("require", require_fn_lua)?
        .build_readonly()
}