use clap::{Arg, ArgAction, ArgMatches, Command};
use mount::MntEntries;
use shitbox::Cmd;
use size_display::Size;
use std::{error::Error, fmt, io, path::PathBuf};

#[derive(Debug)]
pub struct Df;

impl Cmd for Df {
    fn cli(&self) -> Command {
        Command::new("df")
            .about("report free disk space")
            .author("Nathan Fisher")
            .version(env!("CARGO_PKG_VERSION"))
            .disable_help_flag(true)
            .args([
                Arg::new("kilobytes")
                    .help("Use 1024-byte units, instead of the default 512-byte units, when writing space figures.")
                    .short('k')
                    .long("kilobytes")
                    .action(ArgAction::SetTrue),
                Arg::new("human")
                    .help("print sizes in powers of 1024 (e.g., 1023M)")
                    .short('h')
                    .long("human-readable")
                    .conflicts_with("kilobytes")
                    .action(ArgAction::SetTrue),
                Arg::new("file")
                    .value_name("FILE")
                    .num_args(1..)
            ])
    }

    fn run(&self, matches: &ArgMatches) -> Result<(), Box<dyn Error>> {
        let units = if matches.get_flag("kilobytes") {
            Units::Kilo
        } else if matches.get_flag("human") {
            Units::Natural
        } else {
            Units::Posix
        };
        println!("Filesystem  {units}      Used     Avail Capacity  Mounted on");
        if let Some(files) = matches.get_many::<String>("file") {
            for f in files {
                let entry = MntEntries::new("/proc/mounts")?
                    .find(|e| e.dir.as_str() == f)
                    .ok_or(io::Error::new(io::ErrorKind::Other, "no such filesystem"))?;
                print_stats(&entry.fsname, &entry.dir, units)?;
            }
        } else {
            let entries = MntEntries::new("/proc/mounts")?.filter(|x| {
                x.fstype != "proc"
                    && x.fstype != "sysfs"
                    && x.fstype != "securityfs"
                    && x.fstype != "cgroup2"
                    && x.fstype != "pstore"
                    && x.fstype != "bpf"
                    && x.fstype != "autofs"
                    && x.fstype != "hugetlbfs"
                    && x.fstype != "tracefs"
                    && x.fstype != "debugfs"
                    && x.fstype != "configfs"
                    && x.fstype != "devpts"
                    && x.fstype != "efivarfs"
                    && x.fstype != "ramfs"
                    && x.fstype != "binfmt_misc"
                    && x.fstype != "fuse.gvfsd-fuse"
                    && x.fstype != "fuse.portal"
                    && x.fstype != "mqueue"
                    && x.fstype != "fusectl"
            });
            for e in entries {
                print_stats(&e.fsname, &e.dir, units)?;
            }
        }
        Ok(())
    }

    fn path(&self) -> Option<shitbox::Path> {
        Some(shitbox::Path::UsrBin)
    }
}

#[derive(Clone, Copy, PartialEq)]
enum Units {
    Posix,
    Kilo,
    Natural,
}

impl fmt::Display for Units {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Posix => write!(f, "512-blocks"),
            Self::Kilo => write!(f, " 1K-blocks"),
            Self::Natural => write!(f, "      Size"),
        }
    }
}

fn print_stats(fs: &str, mntpt: &str, units: Units) -> Result<(), Box<dyn Error>> {
    let p = PathBuf::from(mntpt);
    if p.exists() {
        let st = stat::statfs(mntpt)?;
        let bs = match units {
            Units::Posix => st.f_frsize / 512,
            Units::Kilo => st.f_frsize / 1024,
            Units::Natural => st.f_frsize,
        };
        let total = st.f_blocks * bs;
        let avail = st.f_bfree * bs;
        let used = total - avail;
        let mut capacity = if total > 0 { (used * 100) / total } else { 0 };
        if used * 100 != capacity * (used + avail) {
            capacity += 1;
        }
        if units == Units::Natural {
            print_human(fs, mntpt, total, avail, used, capacity);
            return Ok(());
        }
        println!("{fs:<12} {total:>9} {used:>9} {avail:>9} {capacity:>7}%  {mntpt}");
        Ok(())
    } else {
        Err(io::Error::new(io::ErrorKind::Other, "fs does not exist").into())
    }
}

fn print_human(fs: &str, mntpt: &str, total: u64, avail: u64, used: u64, capacity: u64) {
    // Unfortunately these strings must be printed separately due to the way the
    // library formats size display, as 0 will be a shorter string due to having
    // no suffix, throwing off column alignment
    print!("{fs:<12}");
    if total > 0 {
        print!("{:>9.1}", Size(total));
    } else {
        print!("{total:>10}");
    }
    if used > 0 {
        print!("{:>9.1}", Size(used));
    } else {
        print!("{used:>10}");
    }
    if avail > 0 {
        println!("{:9.1} {capacity:>7}%  {mntpt}", Size(avail));
    } else {
        println!("{avail:>10} {capacity:>7}%  {mntpt}");
    }
}