use std::fs::File;
use std::path::PathBuf;
use std::io::Read;
use std::time::{SystemTime, UNIX_EPOCH};

pub struct Metadata {
    pub id: String,
    pub created_on: u128
}

impl Metadata {
    pub fn serialize(&self) -> String {
        format!(r#"{{
  "id": "{}",
  "created_on": {}
}}"#, self.id, self.created_on)
    }

    pub fn deserialize(input: &str) -> Option<Metadata> {
        let clean_input = input
            .chars()
            .filter(|c| !c.is_whitespace())
            .collect::<String>();

        let id = Metadata::read_field(&clean_input, "id")?;
        let created_on = Metadata::read_field(&clean_input, "created_on")
            // createdOn kept for compatibility with blog < 7.0.0
            .or_else(|| Metadata::read_field(&clean_input, "createdOn"))?;

        Some(Metadata {
            id,
            created_on: created_on.parse().ok()?
        })
    }

    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 u128)
                    .unwrap_or_else(|_| 0);
                return Metadata {
                    id: timestamp.to_string(),
                    created_on: timestamp
                }
            }
        }
    }

    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()?;
        Metadata::deserialize(&contents)
    }


    fn read_field(input: &str, field_name: &str) -> Option<String> {
        let key_pattern = format!(r#""{}":"#, field_name);
        input.find(&key_pattern)
            .and_then(|start| {
                let value_start = start + key_pattern.len();
                let value_end = input[value_start..]
                    .find(|c: char| c == ',' || c == '}' || c == '\n')
                    .unwrap_or_else(|| input[value_start..].len()) + value_start;

                let raw_value = &input[value_start..value_end];
                let value = raw_value.trim_matches('"').to_string();
                Some(value)
            })
    }
}