use anyhow::{anyhow, bail, Error, Result};
use std::{
    fs::{create_dir_all, remove_file, rename, File},
    path::{PathBuf, MAIN_SEPARATOR},
    str::FromStr,
    thread,
    time::{Duration, SystemTime, UNIX_EPOCH},
};

const TMP_SUFFIX: &str = ".tmp";

pub struct Item {
    pub file: File,
    pub path: PathBuf,
    // pub id: u64,
}

impl Item {
    // Constructors

    /// Build new `Self` from URL (request)
    /// * e.g. 123 -> /directory/1/2/3
    pub fn from_url(url: &str, directory: &str) -> Result<Self> {
        let s = match url.rfind('/') {
            Some(pos) => match url.get(pos + 1..) {
                Some(u) => u.parse::<u64>()?,
                None => bail!("Invalid request"),
            },
            None => bail!("ID not found"),
        }
        .to_string();
        let mut p = String::with_capacity(s.len());
        for (i, d) in s.chars().enumerate() {
            if i > 0 {
                p.push(MAIN_SEPARATOR)
            }
            p.push(d)
        }
        let path = PathBuf::from_str(&format!(
            "{}{MAIN_SEPARATOR}{p}",
            directory.trim_end_matches(MAIN_SEPARATOR),
        ))?;
        Ok(Self {
            file: File::open(&path)?,
            path,
        })
    }

    /// Create new `Self` with unique pathname in the root `directory`
    pub fn create(directory: &str) -> Result<Self> {
        loop {
            // generate file id from current unix time
            let id = SystemTime::now().duration_since(UNIX_EPOCH)?.as_secs();

            // build optimized fs path:
            // add directory separator after every digit to keep up to 10 files per directory
            let path = PathBuf::from(format!(
                "{}{MAIN_SEPARATOR}{}{TMP_SUFFIX}",
                directory.trim_end_matches(MAIN_SEPARATOR),
                id.to_string().chars().fold(String::new(), |mut acc, c| {
                    if !acc.is_empty() {
                        acc.push(MAIN_SEPARATOR);
                    }
                    acc.push(c);
                    acc
                })
            ));

            // recursively create directories
            // * parent directory is expected
            create_dir_all(path.parent().unwrap())?;

            // build `Self`
            match File::create_new(&path) {
                // make sure slot is not taken (by another thread)
                Ok(file) => {
                    return Ok(Self {
                        file,
                        path,
                        // id
                    });
                }
                Err(_) => {
                    println!("[warning] Could not init location: {:?}", path.to_str());
                    // find free slot after some delay..
                    thread::sleep(Duration::from_secs(1));
                    continue;
                }
            }
        }
    }

    // Actions

    /// Commit changes, return permanent Self
    pub fn commit(mut self) -> Result<Self, (Self, Error)> {
        match self.path.to_str() {
            Some(old) => match old.strip_suffix(TMP_SUFFIX) {
                Some(new) => match rename(old, new) {
                    Ok(()) => {
                        self.path = match PathBuf::from_str(new) {
                            Ok(path) => path,
                            Err(e) => return Err((self, anyhow!(e))),
                        };
                        Ok(self)
                    }
                    Err(e) => Err((self, anyhow!(e))),
                },
                None => Err((self, anyhow!("Unexpected suffix"))),
            },
            None => Err((self, anyhow!("Unexpected file path"))),
        }
    }

    /// Delete `Self`, cleanup FS
    pub fn delete(self) -> Result<()> {
        Ok(remove_file(self.path)?)
    }

    // Getters

    /// Shared helper to build public URI
    pub fn to_uri(&self, directory: &str) -> String {
        self.path
            .to_str()
            .unwrap()
            .replace(directory, "")
            .replace("/", "")
    }
}