use std::fs::File;
use std::path::PathBuf;
use std::io::Read;
use std::time::{SystemTime, UNIX_EPOCH};
use time::{OffsetDateTime, format_description::well_known::Rfc2822};
use serde::{Serialize, Deserialize};
use serde_json;

#[derive(Serialize, Deserialize)]
pub struct Metadata {
    pub id: String,
    #[serde(alias = "createdOn")]
    pub created_on: u64
}

impl Metadata {
    pub fn read_or_create(file_path: &PathBuf) -> Metadata {
        match Metadata::read_metadata_file(file_path) {
            Some(metadata) => metadata,
            None => {
                let timestamp = SystemTime::now()
                    .duration_since(UNIX_EPOCH)
                    .map(|duration| duration.as_millis() as u64)
                    .unwrap_or_else(|_| 0);
                return Metadata {
                    id: timestamp.to_string(),
                    created_on: timestamp
                }
            }
        }
    }

    pub fn created_on_utc(&self) -> Option<String> {
        let date = OffsetDateTime::from_unix_timestamp_nanos(
            (self.created_on * 1_000_000).into()
        ).ok()?;
        return date.format(&Rfc2822).ok();
    }


    fn read_metadata_file(file_path: &PathBuf) -> Option<Metadata> {
        let mut file = File::open(file_path).ok()?;
        let mut contents = String::new();
        file.read_to_string(&mut contents).ok()?;
        serde_json::from_str(&contents).ok()
    }
}