//! Abstractions over different storage backends.
//!
//! The main trait to use here is [`Storage`], which provides the necessary interface to store
//! tiles. Usually you want to have a `dyn Storage`, and then instantiate it with a concrete
//! implementation (either [`Folder`] or [`Sqlite`]), depending on the command line flags or
//! similar.
use color_eyre::{
    eyre::{bail, WrapErr},
    Result,
};
use rusqlite::{params, Connection};
use std::{
    fs,
    io::ErrorKind,
    path::{Path, PathBuf},
};

/// The trait that provides the interface for storing tiles.
pub trait Storage {
    /// Prepare the storage.
    ///
    /// This can be used to e.g. ensure the directory exists, or to create the database.
    fn prepare(&mut self) -> Result<()>;
    /// Prepare for a given zoom level.
    ///
    /// This function is called once per zoom, and can be used e.g. to set up the inner folder for
    /// the level. This can avoid unnecesary syscalls if this setup would be done in
    /// [`Storage::store`] instead.
    fn prepare_zoom(&mut self, zoom: u32) -> Result<()>;
    /// Store the given data for the tile.
    fn store(&mut self, zoom: u32, x: u64, y: u64, data: &[u8]) -> Result<()>;
    /// Finish the storing operation.
    ///
    /// This can flush any buffers, commit database changes, and so on.
    fn finish(&mut self) -> Result<()>;
}

/// Folder-based storage.
///
/// This stores the tiles according to the [slippy map
/// tilenames](https://wiki.openstreetmap.org/wiki/Slippy_map_tilenames).
#[derive(Debug)]
pub struct Folder {
    base_dir: PathBuf,
}

impl Folder {
    /// Create a new folder based storage.
    ///
    /// The given directory is the "root" directory, so a tile would be saved as
    /// `base_dir/{zoom}/{x}/{y}.png`.
    pub fn new(base_dir: PathBuf) -> Self {
        Folder { base_dir }
    }
}

impl Storage for Folder {
    fn prepare(&mut self) -> Result<()> {
        let path = &self.base_dir;
        let metadata = fs::metadata(path);
        match metadata {
            Err(e) if e.kind() == ErrorKind::NotFound => {
                let parent = path.parent().unwrap_or_else(|| Path::new("/"));
                fs::create_dir(path)
                    .context(format!("Could not create output directory at {parent:?}"))?
            }
            Err(e) => Err(e).context("Error while checking output directory")?,
            Ok(m) if m.is_dir() => (),
            Ok(_) => bail!("Output directory is not a directory"),
        }
        Ok(())
    }

    fn prepare_zoom(&mut self, zoom: u32) -> Result<()> {
        let target = [&self.base_dir, &zoom.to_string().into()]
            .iter()
            .collect::<PathBuf>();
        fs::create_dir(target)?;
        Ok(())
    }

    fn store(&mut self, zoom: u32, x: u64, y: u64, data: &[u8]) -> Result<()> {
        let folder = self.base_dir.join(zoom.to_string()).join(x.to_string());
        let metadata = folder.metadata();
        match metadata {
            Err(_) => fs::create_dir(&folder)?,
            Ok(m) if !m.is_dir() => bail!("Output path is not a directory"),
            _ => {}
        }
        let file = folder.join(format!("{y}.png"));
        fs::write(file, data)?;
        Ok(())
    }

    fn finish(&mut self) -> Result<()> {
        Ok(())
    }
}

/// SQLite based storage.
///
/// This stores tiles in a SQLite database. The database will have a single table:
///
/// ```sql
/// CREATE TABLE tiles (
///     zoom INTEGER,
///     x INTEGER,
///     y INTEGER,
///     data BLOB,
///     PRIMARY KEY (zoom, x, y)
/// );
/// ```
#[derive(Debug)]
pub struct Sqlite {
    connection: Connection,
}

impl Sqlite {
    /// Create a new SQLite backed tile store.
    ///
    /// The database will be saved at the given location. Note that the database must not yet
    /// exist.
    pub fn connect<P: AsRef<Path>>(file: P) -> Result<Self> {
        let path = file.as_ref();
        if fs::metadata(path).is_ok() {
            bail!("Path {path:?} already exists, refusing to open")
        }
        let connection = Connection::open(path)?;
        Ok(Sqlite { connection })
    }
}

impl Storage for Sqlite {
    fn prepare(&mut self) -> Result<()> {
        self.connection.execute(
            "CREATE TABLE tiles (
            zoom INTEGER,
            x INTEGER,
            y INTEGER,
            data BLOB,
            PRIMARY KEY (zoom, x, y)
        );",
            (),
        )?;
        self.connection.execute("BEGIN;", ())?;
        Ok(())
    }

    fn prepare_zoom(&mut self, _zoom: u32) -> Result<()> {
        Ok(())
    }

    fn store(&mut self, zoom: u32, x: u64, y: u64, data: &[u8]) -> Result<()> {
        self.connection.execute(
            "INSERT INTO tiles (zoom, x, y, data) VALUES (?, ?, ?, ?)",
            params![zoom, x, y, data],
        )?;
        Ok(())
    }

    fn finish(&mut self) -> Result<()> {
        self.connection.execute("COMMIT;", ())?;
        Ok(())
    }
}