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use std::fmt;
use std::fs::OpenOptions;
use std::io::prelude::*;
use str_util::empty_string;

/// All possible tags which are applied to log entries.
const TAGS: [&str; 4] = ["[info]", "[debug]", "[warning]", "[error]"];
const CLEAR_THRESHOLD: usize = 8192;

/// A complete log entry.
#[derive(Debug, Clone)]
struct Entry {
    level: usize,
    message: String,
}

impl Entry {
    /// Create a new Entry structure.
    #[inline]
    fn new(level: usize, message: String) -> Entry {
        Entry {
            level: level,
            message: message,
        }
    }

    /// Render the Entry to a String for display.
    #[inline]
    fn render(&self) -> String {
        format!("{} {}", TAGS[self.level], self.message)
    }
}

/// A basic log structure containing a vector of entries.
#[derive(Debug)]
pub struct Log {
    log: Vec<Entry>,
    write_status: u32,
    log_file: String,
}

impl Log {
    /// Create a new Log structure.
    #[inline]
    pub fn new() -> Log {
        Log {
            log: Vec::new(),
            write_status: 0,
            log_file: empty_string(),
        }
    }

    /// Add an entry to the log.
    #[inline]
    fn add_entry(&mut self, level: usize, message: String) {
        if self.log.len() > CLEAR_THRESHOLD {
            self.clear();
        }

        let entry = Entry::new(level, message);
        let log_len: usize = self.log.len();
        self.log.push(entry.clone());

        match self.write_status {
            1 => {
                println!("{}", entry.render());
            }
            2 => {
                self.save_entry(log_len);
            }
            3 => {
                println!("{}", entry.render());
                self.save_entry(log_len);
            }
            _ => {}
        }
    }

    fn save_entry(&self, index: usize) {
        let entry: String = self.log[index].render();

        let mut handle = OpenOptions::new()
            .write(true)
            .append(true)
            .create(true)
            .open(&self.log_file)
            .unwrap();

        let _ = writeln!(&mut handle, "{}", entry);
    }

    /// Set the file which log entries will be written to.
    #[inline]
    pub fn set_log_file(&mut self, log_path: String) {
        self.log_file = log_path;
    }

    #[inline]
    pub fn info(&mut self, message: String) {
        self.add_entry(0, message);
    }

    #[inline]
    pub fn debug(&mut self, message: String) {
        self.add_entry(1, message);
    }

    #[inline]
    pub fn warning(&mut self, message: String) {
        self.add_entry(2, message);
    }

    #[inline]
    pub fn error(&mut self, message: String) {
        self.add_entry(3, message);
    }

    /** Set the write status of the log. This dictates what and how stuff is logged. Must be a value between 0-3. Below
    is a list of what the values mean. Note that all modes write the log to memory.

    0 # Log entries are written to memory but nothing else.

    1 # Log entries are automatically printed as they are created.

    2 # Log entries are written to a set file as they are created.

    3 # Mode 3 is a combination of mode 1 and 2. */
    #[inline]
    pub fn set_write(&mut self, mode: u32) {
        self.write_status = mode;
    }

    /// Clear all entries in the log.
    #[inline]
    pub fn clear(&mut self) {
        self.log.clear();
    }

    /// Render the log to a vector of strings.
    pub fn render(&self) -> Vec<String> {
        let mut textlog: Vec<String> = Vec::new();

        for entry in &self.log {
            textlog.push(format!("{} {}", TAGS[entry.level], entry.message));
        }

        textlog
    }
}

impl fmt::Display for Entry {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        writeln!(f, "{}", &self.render())?;
        Ok(())
    }
}

impl fmt::Display for Log {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        for line in &self.render() {
            writeln!(f, "{}", line)?;
        }
        Ok(())
    }
}