use crate::errors::{HgError, HgResultExt, IoErrorContext, IoResultExt};

use crate::vfs::Vfs;

use std::io::Write;

/// An utility to append to a log file with the given name, and optionally

/// rotate it after it reaches a certain maximum size.

///

/// Rotation works by renaming "example.log" to "example.log.1", after renaming

/// "example.log.1" to "example.log.2" etc up to the given maximum number of

/// files.

pub struct LogFile<'a> {

    vfs: Vfs<'a>,

    name: &'a str,

    max_size: Option<u64>,

    max_files: u32,

}

impl<'a> LogFile<'a> {

    pub fn new(vfs: Vfs<'a>, name: &'a str) -> Self {

        Self {

            vfs,

            name,

            max_size: None,

            max_files: 0,

        }

    }

    /// Rotate before writing to a log file that was already larger than the

    /// given size, in bytes. `None` disables rotation.

    pub fn max_size(mut self, value: Option<u64>) -> Self {

        self.max_size = value;

        self

    }

    /// Keep this many rotated files `{name}.1` up to `{name}.{max}`, in

    /// addition to the original `{name}` file.

    pub fn max_files(mut self, value: u32) -> Self {

        self.max_files = value;

        self

    }

    /// Append the given `bytes` as-is to the log file, after rotating if

    /// needed.

    ///

    /// No trailing newline is added. Make sure to include one in `bytes` if

    /// desired.

    pub fn write(&self, bytes: &[u8]) -> Result<(), HgError> {

        let path = self.vfs.join(self.name);

        let context = || IoErrorContext::WritingFile(path.clone());

        let open = || {

            std::fs::OpenOptions::new()

                .create(true)

                .append(true)

                .open(&path)

                .with_context(context)

        };

        let mut file = open()?;

        if let Some(max_size) = self.max_size {

            if file.metadata().with_context(context)?.len() >= max_size {

                // For example with `max_files == 5`, the first iteration of

                // this loop has `i == 4` and renames `{name}.4` to `{name}.5`.

                // The last iteration renames `{name}.1` to

                // `{name}.2`

                for i in (1..self.max_files).rev() {

                    self.vfs

                        .rename(

                            format!("{}.{}", self.name, i),

                            format!("{}.{}", self.name, i + 1),

                        )

                        .io_not_found_as_none()?;

                }

                // Then rename `{name}` to `{name}.1`. This is the

                // previously-opened `file`.

                self.vfs

                    .rename(self.name, format!("{}.1", self.name))

                    .io_not_found_as_none()?;

                // Finally, create a new `{name}` file and replace our `file`

                // handle.

                file = open()?;

            }

        }

        file.write_all(bytes).with_context(context)?;

        file.sync_all().with_context(context)

    }

}

#[test]

fn test_rotation() {

    let temp = tempfile::tempdir().unwrap();

    let vfs = Vfs { base: temp.path() };

    let logger = LogFile::new(vfs, "log").max_size(Some(3)).max_files(2);

    logger.write(b"one\n").unwrap();

    logger.write(b"two\n").unwrap();

    logger.write(b"3\n").unwrap();

    logger.write(b"four\n").unwrap();

    logger.write(b"five\n").unwrap();

    assert_eq!(vfs.read("log").unwrap(), b"five\n");

    assert_eq!(vfs.read("log.1").unwrap(), b"3\nfour\n");

    assert_eq!(vfs.read("log.2").unwrap(), b"two\n");

    assert!(vfs.read("log.3").io_not_found_as_none().unwrap().is_none());

}