use std::collections::hash_map::HashMap;
use std::fs::File;
use std::io::Read;
use std::fmt::{Display, Formatter, Error};

#[derive(Clone)]
pub enum ConfigValue {
    Str(String),
    UInt(usize)
}

impl Display for ConfigValue {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
        match self {
            ConfigValue::Str(s) => write!(f, "{}", s),
            ConfigValue::UInt(u) => write!(f, "{}", u)
        }
    }
}

struct ConfigItem {
    default_value: ConfigValue,
    parse_func: Box<dyn Fn(String) -> Option<ConfigValue>>,
}

pub struct Config {
    v: HashMap<String, ConfigValue>,
}

fn stripped_str(s: String) -> Option<ConfigValue> {
    Some(ConfigValue::Str(String::from(s.trim())))
}

fn parse_usize(s: String) -> Option<ConfigValue> {
    if let Ok(r) = usize::from_str_radix(&s, 10) {
        Some(ConfigValue::UInt(r))
    } else { None }
}

pub fn split_at_first<'a, 'b>(s: &'a str, sp: &'b str) -> (&'a str, &'a str) {
    if let Some(p) = s.find(sp) {
        (&s[.. p], &s[p + sp.len()..])
    } else { (s, "") }
}

impl Config {
    fn items() -> HashMap<&'static str, ConfigItem> {
        HashMap::from([
            ("SERVED_DATA_ROOT", ConfigItem{default_value: ConfigValue::Str(String::from("")), parse_func: Box::new(stripped_str)}),
            ("POSTS_PER_PAGE", ConfigItem{default_value: ConfigValue::UInt(20), parse_func: Box::new(parse_usize)}),
            ("DISPLAY_TIMEZONE", ConfigItem{default_value: ConfigValue::Str(String::from("UTC")), parse_func: Box::new(stripped_str)}),
            ("VERSION_STRING", ConfigItem{default_value: ConfigValue::Str(String::from("1.0")), parse_func: Box::new(stripped_str)}),
        ])
    }
    pub fn parse_config(filename: &str) -> Config {
        let mut v = HashMap::from_iter(
            Config::items().iter()
            .map(|(k, v)| {(String::from(*k), v.default_value.clone())})
        );
        let mut f = File::open(filename).unwrap();
        let mut s = String::new();
        if let Ok(_) = f.read_to_string(&mut s) {
            for l in s.split("\n") {
                let (sname, svalue) = split_at_first(l, "=");
                if let Some(ConfigItem{default_value: _, parse_func}) = Config::items().get(sname) {
                    if let Some(value) = parse_func(String::from(svalue)) {
                        v.insert(String::from(sname), value);
                    }
                }
            }
        }
        Config { v }
    }
    pub fn get(&self, key: &str) -> ConfigValue {
        self.v.get(&String::from(key)).unwrap().clone()
    }
    pub fn get_str(&self, key: &str) -> String {
        if let ConfigValue::Str(s) = self.get(key) {
            s
        } else { String::from("") }
    }
}