//! Miscellaneous utilities.

use std::{
    fs,
    io,
    path::{Path, PathBuf},
    time::{self, Duration, SystemTime, UNIX_EPOCH},
};

use anyhow::Result;
use chrono::NaiveDateTime;

use sequoia_openpgp as openpgp;
use openpgp::{
    Cert,
    policy::Policy,
};

use crate::{
    argparse::utils::{
        sink_from_fd,
        source_from_fd,
        special_filename_fd,
    },
};
use crate::common;

/// Opens a (special) file.
pub fn open(control: &dyn common::Common, name: &str)
            -> Result<Box<dyn io::Read + Send + Sync>>
{
    if name == "-" {
        Ok(Box::new(io::stdin()))
    } else if control.special_filenames()
        && special_filename_fd(name).is_some()
    {
        let fd = special_filename_fd(name).expect("checked above");
        Ok(Box::new(source_from_fd(fd)?))
    } else {
        Ok(Box::new(fs::File::open(name)?))
    }
}

/// Opens multiple (special) files, joining them into one stream.
pub fn open_multiple(control: &dyn common::Common, names: &[String])
                     -> Result<Box<dyn io::Read + Send + Sync>>
{
    let mut streams: Vec<Box<dyn io::Read + Send + Sync>> = Vec::new();
    for name in names.iter().rev() {
        streams.push(if name == "-" {
            Box::new(io::stdin())
        } else if control.special_filenames()
            && special_filename_fd(&name).is_some()
        {
            let fd = special_filename_fd(&name).expect("checked above");
            source_from_fd(fd)
                .map(|f| Box::new(f))
                .map_err(|e| io::Error::new(io::ErrorKind::Other, e))?
        } else {
            Box::new(fs::File::open(name)
                     .map_err(|e| {
                         control.error(format_args!(
                             "can't open signed data '{}'", name));
                         control.error(format_args!(
                             "can't hash datafile: {}", e));
                         e
                     })?)
        });
    }

    Ok(Box::new(MultiReader {
        streams,
        current: None,
    }))
}

struct MultiReader {
    streams: Vec<Box<dyn io::Read + Send + Sync>>,
    current: Option<Box<dyn io::Read + Send + Sync>>,
}

impl io::Read for MultiReader {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        // First, try the currently opened file.
        if let Some(mut current) = self.current.take() {
            let bytes_read = current.read(buf)?;
            if bytes_read > 0 {
                self.current = Some(current);
                return Ok(bytes_read);
            } else {
                // Try the next file.
                return self.read(buf);
            }
        }

        // Second, try to open the next file.
        if let Some(stream) = self.streams.pop() { // streams are reversed.
            self.current = Some(stream);
            self.read(buf)
        } else {
            // Final EOF.
            Ok(0)
        }
    }
}

/// Opens a (special) file for writing.
pub fn create(control: &dyn common::Common, name: &str)
              -> Result<Box<dyn io::Write + Send + Sync>>
{
    create_intern(control, name, None)
}

/// Opens a (special) file for writing, adding an extension to `name`
/// unless `name` refers to a file descriptor.
pub fn create_with_extension(control: &dyn common::Common, name: &str,
                             add_extension: &str)
                             -> Result<Box<dyn io::Write + Send + Sync>>
{
    create_intern(control, name, Some(add_extension))
}

/// Opens a (special) file for writing, optionally adding an extension
/// to `name` unless `name` refers to a file descriptor.
fn create_intern(control: &dyn common::Common,
                 name: &str,
                 add_extension: Option<&str>)
                 -> Result<Box<dyn io::Write + Send + Sync>>
{
    if name == "-" {
        Ok(Box::new(crate::io::stdout()))
    } else if control.special_filenames()
        && special_filename_fd(name).is_some()
    {
        let fd = special_filename_fd(name).expect("checked above");
        sink_from_fd(fd)
    } else {
        let name_;
        let mut name = name;

        if let Some(e) = add_extension {
            name_ = format!("{}.{}", name, e);
            name = &name_;
        }

        Ok(Box::new(fs::File::create(name)?))
    }
}

/// Best-effort heuristic to compute the primary User ID of a given cert.
pub fn best_effort_primary_uid(policy: &dyn Policy, cert: &Cert) -> String {
    // Try to be more helpful by including a User ID in the
    // listing.  We'd like it to be the primary one.  Use
    // decreasingly strict policies.
    let mut primary_uid = None;

    // First, apply our policy.
    if let Ok(vcert) = cert.with_policy(policy, None) {
        if let Ok(primary) = vcert.primary_userid() {
            primary_uid = Some(primary.value().to_vec());
        }
    }

    // Second, apply the null policy.
    if primary_uid.is_none() {
        let null = openpgp::policy::NullPolicy::new();
        if let Ok(vcert) = cert.with_policy(&null, None) {
            if let Ok(primary) = vcert.primary_userid() {
                primary_uid = Some(primary.value().to_vec());
            }
        }
    }

    // As a last resort, pick the first user id.
    if primary_uid.is_none() {
        if let Some(primary) = cert.userids().next() {
            primary_uid = Some(primary.value().to_vec());
        } else {
            // Special case, there is no user id.
            primary_uid = Some(b"(NO USER ID)"[..].into());
        }
    }

    String::from_utf8_lossy(&primary_uid.expect("set at this point")).into()
}

/// Returns a line with the same length of `t` (up to 80 characters).
pub fn undeline_for(t: &str) -> &[u8] {
    const U: [u8; 80] = ['-' as u8; 80];
    let l = U.len().min(t.len());
    &U[..l]
}

/// Robustly canonicalizes the given path.
///
/// This function works even in cases where std::fs::canonicalize does
/// not, notably when a component doesn't yet exist.
pub fn robustly_canonicalize<P: AsRef<Path>>(path: P) -> PathBuf {
    if let Ok(p) = path.as_ref().canonicalize() {
        return p;
    }

    let mut p = path.as_ref().to_path_buf();
    let mut tail = if let Some(t) = p.file_name() {
        PathBuf::from(t)
    } else {
        return p; // Somewhat odd corner case.
    };

    // Walk up, trying to canonicalize the parents.
    while p.pop() {
        if let Ok(p) = p.canonicalize() {
            return p.join(tail);
        }
        tail = p.file_name().map(PathBuf::from)
            .or_else(|| std::env::current_dir().ok())
            .unwrap_or_else(|| PathBuf::from(".")) // Technically a failure.
            .join(tail);
    }

    p.join(tail)
}

/// Strips known extensions from filename.
///
/// Returns an error if we didn't recognize the file extension.
pub fn make_outfile_name<S: AsRef<str>>(name: S) -> Result<String> {
    let s = name.as_ref();
    if s.ends_with(".gpg") {
        Ok(s[..s.len() - 4].into())
    } else if s.ends_with(".gpg") {
        Ok(s[..s.len() - 4].into())
    } else if s.ends_with(".pgp") {
        Ok(s[..s.len() - 4].into())
    } else if s.ends_with(".sig") {
        Ok(s[..s.len() - 4].into())
    } else if s.ends_with(".asc") {
        Ok(s[..s.len() - 4].into())
    } else if s.ends_with(".sign") {
        Ok(s[..s.len() - 5].into())
    } else {
        Err(anyhow::anyhow!("{}: unknown suffix", s))
    }
}

/// Converts S2K::Iterated's `hash_bytes` into coded count
/// representation.
///
/// # Errors
///
/// Fails with `Error::InvalidArgument` if `hash_bytes` cannot be
/// encoded. See also `S2K::nearest_hash_count()`.
///
// Notes: Copied from S2K::encode_count.
pub fn s2k_encode_iteration_count(hash_bytes: u32) -> Result<u8> {
    use openpgp::Error;
    // eeee.mmmm -> (16 + mmmm) * 2^(6 + e)

    let msb = 32 - hash_bytes.leading_zeros();
    let (mantissa_mask, tail_mask) = match msb {
        0..=10 => {
            return Err(Error::InvalidArgument(
                format!("S2K: cannot encode iteration count of {}",
                        hash_bytes)).into());
        }
        11..=32 => {
            let m = 0b11_1100_0000 << (msb - 11);
            let t = 1 << (msb - 11);

            (m, t - 1)
        }
        _ => unreachable!()
    };
    let exp = if msb < 11 { 0 } else { msb - 11 };
    let mantissa = (hash_bytes & mantissa_mask) >> (msb - 5);

    if tail_mask & hash_bytes != 0 {
        return Err(Error::InvalidArgument(
            format!("S2K: cannot encode iteration count of {}",
                    hash_bytes)).into());
    }

    Ok(mantissa as u8 | (exp as u8) << 4)
}

/// Sanitizes an ASCII string for display purposes.
pub fn sanitize_ascii_str(s: &[u8], escape: &[u8]) -> String {
    let mut o = String::with_capacity(s.len());

    for c in s.iter().cloned() {
        if c < 0x20 || c == 0x7f || escape.contains(&c) || c == b'\\' {
            o.push('\\');
            match c {
                b'\n' => o.push('n'),
                b'\r' => o.push('r'),
                0x0c => o.push('f'),
                0x0b => o.push('v'),
                0x08 => o.push('b'),
                b'\x00' => o.push('0'),
                _ => o.push_str(&format!("x{:02x}", c)),
            }
        } else {
            o.push(c as char);
        }
    }

    o
}

/// Parses an "iso-date".
///
/// XXX: Documentation is not clear on timezone and format.
pub fn parse_iso_date(s: &str) -> Result<SystemTime> {
    for fmt in [
        "%Y%m%dT%H%M%S",
        "%Y-%m-%d",
    ] {
        if let Ok(naive) = NaiveDateTime::parse_from_str(s, fmt) {
            return Ok(UNIX_EPOCH.checked_add(Duration::new(
                naive.timestamp().try_into()?, 0))
                      .ok_or(anyhow::anyhow!("Duration overflows time type"))?);
        }
    }

    Err(anyhow::anyhow!("malformed ISO date"))
}

pub fn parse_expiration(now: time::SystemTime, s: &str)
                        -> Result<Option<time::Duration>>
{
    let now: chrono::DateTime<chrono::Utc> = now.into();

    match s {
        "" | "none" | "never" | "-" | "0" => Ok(None),
        s if s.starts_with("seconds=") => {
            match s[8..].parse::<u64>() {
                Ok(v) => Ok(Some(time::Duration::new(v, 0))),
                Err(e) => Err(anyhow::Error::from(e)
                              .context("Invalid number of seconds")),
            }
        },
        _ => {
            // ISO date.  Curiously, GnuPG uses mktime(3) to convert
            // the ISO date to a timestamp, and mktime(3) is
            // timezone-aware.  Therefore, in contrast to parsing the
            // ISO time below, we use the local timezone.
            if let Ok(d) = chrono::NaiveDate::parse_from_str(s, "%Y-%m-%d")
            {
                // At noon, or, as GnuPG would say, 86400/2.
                let dt = d.and_hms_opt(12, 0, 0).unwrap()
                    .and_local_timezone(chrono::offset::Local).unwrap();
                let dtu = chrono::DateTime::<chrono::Utc>::from(dt);
                if dtu > now {
                    let duration = dtu - now;
                    return Ok(Some(duration.to_std().expect("non-negative")));
                }
            }

            // ISO time.  The only supported format is
            // "yyyymmddThhmmss[Z]" delimited by white space, nul, a
            // colon or a comma.
            if let Ok(dt) = chrono::NaiveDateTime::parse_from_str(
                &s[..15.min(s.len())], "%Y%m%dT%H%M%S")
            {
                let dtu = chrono::DateTime::from_utc(dt, chrono::Utc);
                if dtu > now {
                    let duration = dtu - now;
                    return Ok(Some(duration.to_std().expect("non-negative")));
                }
            }

            // Days, in the format [0-9]+[dDwWmMyY]?.
            if s.chars().rev().skip(1).all(|c| c.is_ascii_digit())
                && s.chars().last().map(|c| c.is_ascii_digit()
                                        || c == 'd' || c == 'D'
                                        || c == 'w' || c == 'W'
                                        || c == 'm' || c == 'M'
                                        || c == 'y' || c == 'Y')
                .unwrap_or(false)
            {
                let last_is_digit =
                    s.chars().last().map(|c| c.is_ascii_digit())
                    .unwrap_or(false);
                if last_is_digit {
                    return Ok(Some(time::Duration::new(s.parse()?, 0)));
                } else {
                    let days = match s.chars().last().unwrap()
                        .to_ascii_lowercase()
                    {
                        'd' => 1,
                        'w' => 7,
                        'm' => 30,
                        'y' => 365,
                        _ => unreachable!("checked above"),
                    };
                    return Ok(Some(time::Duration::new(
                        s[..s.len()-1].parse::<u64>()? * days * 24 * 60 * 60, 0)));
                }
            }

            Err(anyhow::anyhow!("Invalid expiration date: {:?}", s))
        }
    }
}

pub fn mailbox_from_userid(s: &str) -> Result<Option<String>> {
    openpgp::packet::UserID::from(s).email2()
        .map(|o| o.map(ToString::to_string))
}

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

    #[test]
    fn robustly_canonicalize() {
        use super::robustly_canonicalize as rc;
        let current_dir = std::env::current_dir().unwrap();

        assert_eq!(rc(""), Path::new(""));
        assert_eq!(rc("/"), Path::new("/"));
        assert_eq!(rc("."), current_dir);
        assert_eq!(rc("./"), current_dir);
        assert_eq!(rc("/dev"), Path::new("/dev"));
        assert_eq!(rc("/dev/null"), Path::new("/dev/null"));
        assert_eq!(rc("/dev/i/dont/exist"), Path::new("/dev/i/dont/exist"));
        assert_eq!(rc("/i/dont/exist"), Path::new("/i/dont/exist"));
        assert_eq!(rc("i/dont/exist"), current_dir.join("i/dont/exist"));
    }

    #[test]
    fn parse_expiration() {
        use std::time::Duration;
        use super::parse_expiration as pe;
        let c = UNIX_EPOCH + Duration::new(1671553073, 0);
        assert_eq!(pe(c, "").unwrap(), None);
        assert_eq!(pe(c, "0").unwrap(), None);
        assert_eq!(pe(c, "none").unwrap(), None);
        assert_eq!(pe(c, "never").unwrap(), None);
        assert_eq!(pe(c, "-").unwrap(), None);
        assert_eq!(pe(c, "1").unwrap().unwrap(),
                   Duration::new(1, 0));
        assert_eq!(pe(c, "1d").unwrap().unwrap(),
                   Duration::new(1 * 24 * 60 * 60 , 0));
        assert_eq!(pe(c, "1D").unwrap().unwrap(),
                   Duration::new(1 * 24 * 60 * 60, 0));
        assert_eq!(pe(c, "1w").unwrap().unwrap(),
                   Duration::new(7 * 24 * 60 * 60 , 0));
        assert_eq!(pe(c, "1W").unwrap().unwrap(),
                   Duration::new(7 * 24 * 60 * 60, 0));
        assert_eq!(pe(c, "1m").unwrap().unwrap(),
                   Duration::new(30 * 24 * 60 * 60 , 0));
        assert_eq!(pe(c, "1M").unwrap().unwrap(),
                   Duration::new(30 * 24 * 60 * 60, 0));
        assert_eq!(pe(c, "1y").unwrap().unwrap(),
                   Duration::new(365 * 24 * 60 * 60 , 0));
        assert_eq!(pe(c, "1Y").unwrap().unwrap(),
                   Duration::new(365 * 24 * 60 * 60, 0));
        // Note: Exact value depends on the local timezone.
        assert!(pe(c, "2023-01-01").is_ok());
        assert_eq!(pe(c, "20230101T123456").unwrap().unwrap(),
                   Duration::new(1021327 + 34 * 60 + 56, 0));
    }
}
