extern crate proc_macro;

use proc_macro::{Span, TokenStream};
use std::{
    collections::{hash_map::Entry, HashMap},
    env,
    fs::{read_dir, read_to_string},
    str::FromStr,
};
use syn::Error;

/// Recursively build engine system
#[proc_macro]
pub fn addfn(_: TokenStream) -> TokenStream {
    let dir = match env::var_os("CARGO_MANIFEST_DIR") {
        Some(d) => match d.to_str() {
            Some(s) => s.to_owned(),
            None => return error("CARGO_MANIFEST_DIR contains non-printable characters"),
        },
        None => return error("Can't fetch the environment variable CARGO_MANIFEST_DIR"),
    };
    let list = match load_files(&dir) {
        Ok(l) => l,
        Err(_) => HashMap::new(),
    };
    let mut vec = Vec::new();
    vec.push(format!("// Add funtions from {}", dir));
    vec.push(
        "let mut app: BTreeMap<i64, BTreeMap<i64, BTreeMap<i64, Act>>> = BTreeMap::new();"
            .to_string(),
    );
    for (key, v) in list {
        vec.push(format!(
            "let mut {}: BTreeMap<i64, BTreeMap<i64, Act>> = BTreeMap::new();",
            key
        ));
        for file in v {
            let func = get_func(&dir, &key, &file);
            vec.push(format!(
                "let mut {}_{}: BTreeMap<i64, Act> = BTreeMap::new();",
                key, file
            ));
            for f in func {
                vec.push(format!(
                    "{0}_{1}.insert({2}_i64, |action| Box::pin(crate::app::{0}::{1}::{3}(action)));",
                    key,
                    file,
                    fnv1a_64(&f),
                    f
                ));
            }
            vec.push(format!(
                "{0}.insert({1}_i64, {0}_{2});",
                key,
                fnv1a_64(&file),
                file
            ));
        }
        vec.push(format!("app.insert({}_i64, {});", fnv1a_64(&key), key));
    }
    vec.push("return app;".to_owned());

    TokenStream::from_str(&vec.join("\n")).unwrap()
}

/// Gets functions list from directory
///
/// Each function have to start `pub async fn ` and finish `( this : &mut Action ) -> Answer {`.
fn get_func(dir: &str, key: &str, file: &str) -> Vec<String> {
    let mut vec = Vec::new();
    let file = format!("{}/src/app/{}/{}.rs", dir, key, file);
    if let Ok(str) = read_to_string(file) {
        let mut str = str
            .replace('(', " ( ")
            .replace(')', " ) ")
            .replace(':', " : ")
            .replace("->", " -> ")
            .replace('{', " { ");
        loop {
            if str.contains("  ") {
                str = str.replace("  ", " ");
                continue;
            }
            break;
        }
        let mut ind = 0;
        while let Some(i) = &str[ind..].find("pub async fn ") {
            match &str[ind + i + 13..].find(" ( this : &mut Action ) -> Answer {") {
                Some(j) => {
                    vec.push(str[ind + i + 13..ind + i + 13 + j].to_owned());
                    ind += i + j + 13;
                }
                None => break,
            }
        }
    }
    vec.shrink_to_fit();
    vec
}

/// Recursively links all files with `.rs` extension from `./src/app/*` directory.
#[proc_macro]
pub fn addmod(_: TokenStream) -> TokenStream {
    // Get project dir
    let dir = match env::var_os("CARGO_MANIFEST_DIR") {
        Some(d) => match d.to_str() {
            Some(s) => s.to_owned(),
            None => return error("CARGO_MANIFEST_DIR contains non-printable characters"),
        },
        None => return error("Can't fetch the environment variable CARGO_MANIFEST_DIR"),
    };
    // load all files
    let list = match load_files(&dir) {
        Ok(l) => l,
        Err(e) => return error(&e),
    };
    // Forms an answer
    let mut vec = Vec::new();
    vec.push(format!("// Add mods from {}", dir));
    for (key, v) in list {
        vec.push(format!("pub mod {} {{", check_name(key)));
        for f in v {
            vec.push(format!("    pub mod {};", check_name(f)));
        }
        vec.push("}".to_owned());
    }
    TokenStream::from_str(&vec.join("\n")).unwrap()
}

/// If the name contains the symbol "-", it replaces it with "_"
fn check_name(text: String) -> String {
    if text.contains('-') {
        return text.replace('-', "_");
    }
    text
}

/// Load all file names with `.rs` extension from `./src/app/*` directory
fn load_files(dir: &str) -> Result<HashMap<String, Vec<String>>, String> {
    let src = format!("{}/src/app", dir);
    let mut list: HashMap<String, Vec<String>> = HashMap::new();
    // Reads dir from first level
    match read_dir(&src) {
        Ok(dir) => {
            for entry in dir.flatten() {
                let path = entry.path();
                if !path.is_dir() {
                    continue;
                }
                if let Some(name) = path.file_name() {
                    let dir_name = match name.to_str() {
                        Some(n) => n,
                        None => continue,
                    };
                    // Reads dir from second level
                    let dir = match read_dir(format!("{}/{}", &src, dir_name)) {
                        Ok(d) => d,
                        Err(_) => continue,
                    };
                    for entry in dir.flatten() {
                        let path = entry.path();
                        if !path.is_file() {
                            continue;
                        }
                        let file_name = match path.file_name() {
                            Some(name) => match name.to_str() {
                                Some(file_name) => file_name,
                                None => continue,
                            },
                            None => continue,
                        };
                        // Checks extension
                        if file_name.len() > 3 && file_name.ends_with(".rs") {
                            let file_name = file_name[..file_name.len() - 3].to_owned();
                            match list.entry(dir_name.to_owned()) {
                                Entry::Occupied(mut o) => {
                                    let vec = o.get_mut();
                                    vec.push(file_name);
                                    vec.shrink_to_fit();
                                }
                                Entry::Vacant(v) => {
                                    let vec = vec![file_name];
                                    v.insert(vec);
                                }
                            }
                        }
                    }
                }
            }
        }
        Err(e) => return Err(format!("{}. File name: {}", e, src)),
    };
    list.shrink_to_fit();
    Ok(list)
}

/// Returns error text
fn error(text: &str) -> TokenStream {
    TokenStream::from(Error::new(Span::call_site().into(), text).to_compile_error())
}

/// fnv1a_64 hash function
///
/// # Parameters
///
/// * `text: &str` - Origin string.
///
/// # Return
///
/// i64 hash
#[inline]
fn fnv1a_64(text: &str) -> i64 {
    let mut hash: u64 = 0xcbf29ce484222325;
    let prime: u64 = 0x100000001b3;

    for c in text.bytes() {
        hash ^= u64::from(c);
        hash = hash.wrapping_mul(prime);
    }
    unsafe { *(&hash as *const u64 as *const i64) }
}