use std::path::Path;

use anyhow::{Context, Result, bail};
use russh_sftp::client::SftpSession;
use tokio::io::AsyncWriteExt;
use walkdir::WalkDir;

use crate::ssh::{Session, runtime};

pub struct Stats {
    pub files: u64,
    pub bytes: u64,
}

impl std::fmt::Display for Stats {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{} file(s), {}", self.files, human_size(self.bytes))
    }
}

fn human_size(bytes: u64) -> String {
    const KIB: f64 = 1024.0;
    const MIB: f64 = 1024.0 * 1024.0;
    let b = bytes as f64;
    if b >= MIB {
        format!("{:.1} MiB", b / MIB)
    } else if b >= KIB {
        format!("{:.1} KiB", b / KIB)
    } else {
        format!("{bytes} B")
    }
}

pub fn upload(session: &mut Session, source: &Path, target: &str) -> Result<Stats> {
    runtime().block_on(async {
        if source.is_dir() {
            upload_dir(session, source, target).await
        } else if source.is_file() {
            upload_file(session, source, target).await
        } else {
            bail!(
                "sync source '{}' does not exist (relative paths are resolved against project workdir)",
                source.display()
            );
        }
    })
}

async fn open_sftp(session: &mut Session) -> Result<SftpSession> {
    let channel = session
        .handle()
        .channel_open_session()
        .await
        .context("failed to open SFTP channel")?;
    channel
        .request_subsystem(true, "sftp")
        .await
        .context("remote host has no SFTP subsystem")?;
    let sftp = SftpSession::new(channel.into_stream())
        .await
        .context("SFTP session init failed")?;
    Ok(sftp)
}

async fn mkdir_if_missing(sftp: &SftpSession, path: &str) -> Result<()> {
    match sftp.metadata(path).await {
        Ok(meta) if meta.is_dir() => return Ok(()),
        Ok(_) => bail!("remote path exists but is not a directory: {path}"),
        Err(_) => {}
    }
    sftp.create_dir(path)
        .await
        .with_context(|| format!("cannot create remote directory {path}"))
}

fn join_remote(base: &str, rel: &str) -> String {
    let rel = rel.replace('\\', "/");
    if rel.is_empty() {
        base.trim_end_matches('/').to_string()
    } else {
        format!("{}/{}", base.trim_end_matches('/'), rel)
    }
}

async fn upload_dir(session: &mut Session, source: &Path, target: &str) -> Result<Stats> {
    let sftp = open_sftp(session).await?;
    mkdir_if_missing(&sftp, target).await?;

    let mut stats = Stats { files: 0, bytes: 0 };
    for entry in WalkDir::new(source) {
        let entry = entry.with_context(|| format!("cannot read local dir {}", source.display()))?;
        let rel = entry
            .path()
            .strip_prefix(source)
            .expect("walkdir entry is inside source");
        let remote_path = join_remote(target, &rel.to_string_lossy());

        if entry.file_type().is_dir() {
            if !rel.as_os_str().is_empty() {
                mkdir_if_missing(&sftp, &remote_path).await?;
            }
        } else if entry.file_type().is_file() {
            write_remote_file(&sftp, entry.path(), &remote_path).await?;
            stats.files += 1;
            stats.bytes += std::fs::metadata(entry.path())
                .map(|m| m.len())
                .unwrap_or(0);
        }
    }
    Ok(stats)
}

async fn upload_file(session: &mut Session, source: &Path, target: &str) -> Result<Stats> {
    let sftp = open_sftp(session).await?;
    let dest_is_dir = sftp
        .metadata(target)
        .await
        .map(|meta| meta.is_dir())
        .unwrap_or(false);
    let dest = if dest_is_dir {
        let name = source
            .file_name()
            .with_context(|| format!("cannot determine file name of {}", source.display()))?;
        join_remote(target, &name.to_string_lossy())
    } else {
        target.to_string()
    };
    write_remote_file(&sftp, source, &dest).await?;
    let size = std::fs::metadata(source).map(|m| m.len()).unwrap_or(0);
    Ok(Stats {
        files: 1,
        bytes: size,
    })
}

async fn write_remote_file(sftp: &SftpSession, local: &Path, remote_path: &str) -> Result<()> {
    let data = std::fs::read(local).with_context(|| format!("cannot read {}", local.display()))?;
    let mut remote_file = sftp
        .create(remote_path)
        .await
        .with_context(|| format!("cannot create remote file {remote_path}"))?;
    remote_file
        .write_all(&data)
        .await
        .with_context(|| format!("upload interrupted: {remote_path}"))?;
    remote_file
        .shutdown()
        .await
        .with_context(|| format!("cannot finish writing {remote_path}"))?;
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn join_remote_handles_slashes_and_edges() {
        assert_eq!(join_remote("/var/www/pages", "dist"), "/var/www/pages/dist");
        assert_eq!(
            join_remote("/var/www/pages/", "a/b.js"),
            "/var/www/pages/a/b.js"
        );
        assert_eq!(join_remote("/var/www/pages", ""), "/var/www/pages");
        assert_eq!(
            join_remote("/var/www/pages", "sub\\file.css"),
            "/var/www/pages/sub/file.css"
        );
    }

    #[test]
    fn human_size_formats() {
        assert_eq!(human_size(0), "0 B");
        assert_eq!(human_size(512), "512 B");
        assert_eq!(human_size(2048), "2.0 KiB");
        assert_eq!(human_size(3 * 1024 * 1024), "3.0 MiB");
    }
}