use rust_decimal::Decimal;
use serde::{Deserialize, Serialize};
use std::convert::AsRef;
use std::fs;
use std::hash::{Hash, Hasher};
use std::path::{Path, PathBuf};
use std::str::FromStr;
use structopt::StructOpt;
use twox_hash::XxHash64;

type Account = String;
type Category = String;

#[derive(Debug)]
#[derive(Hash)]
#[derive(Deserialize, Serialize)]
#[derive(StructOpt)]
pub enum TransactionKind {
    Expense,
    Income,
    //TODO Transfer,
}

impl FromStr for TransactionKind {
    type Err = String;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s {
            "expense" => Ok(TransactionKind::Expense),
            "income" => Ok(TransactionKind::Income),
            _ => Err(format!("Unknown transaction kind: {:?}", s)),
        }
    }
}

#[derive(Debug)]
#[derive(Hash)]
#[derive(Deserialize, Serialize)]
pub struct Transaction {
    pub description: String,
    pub category: Category,
    pub amount: Decimal,
    pub kind: TransactionKind,
    pub from: Account,
    pub to: Account,
}

#[derive(Debug)]
#[derive(Hash)]
#[derive(Deserialize, Serialize)]
pub struct Post {
    transaction: Transaction,
    removed: bool,
}

#[derive(Debug)]
pub struct Store {
    root: PathBuf,
    posts: Vec<Post>,
}

impl Store {
    //TODO Result
    pub fn open(root: PathBuf) -> Option<Self> {
        Some(Self {
            posts: Self::open_dir(&root)?,
            root,
        })
    }

    //TODO check if hash matches
    //TODO Result
    //TODO overkill? maybe we can use subfolders later on
    fn open_dir(dir: &Path) -> Option<Vec<Post>> {
        let mut res = Vec::new();
        for entry in std::fs::read_dir(dir).ok()? {
            let entry = entry.ok()?;
            if entry.file_type().ok()?.is_dir() {
                let mut posts = Self::open_dir(&entry.path())?;
                res.append(&mut posts);
            } else {
                res.push(Post::open(&entry.path())?);
            }
        }
        Some(res)
    }

    pub fn write(&self) -> std::io::Result<()> {
        for post in &self.posts {
            let mut path = self.root.clone();
            path.push(format!("{}", post.id()));
            post.write(&path)?;
        }
        Ok(())
    }
}

impl Post {
    pub fn new(transaction: Transaction) -> Self {
        Self {
            transaction,
            removed: false,
        }
    }

    fn write<P: AsRef<Path>>(&self, p: &P) -> std::io::Result<()> {
        fs::write(p, serde_json::to_string_pretty(self).unwrap()) //TODO control pretty or not
    }

    //TODO Result
    fn open<P: AsRef<Path>>(p: &P) -> Option<Self> {
        fs::read_to_string(p).ok().as_ref().and_then(|s| serde_json::from_str(s).ok())
    }

    fn id(&self) -> u64 {
        let mut h = XxHash64::default();
        self.hash(&mut h);
        h.finish()
    }
}