use crate::nixbase32;
use data_encoding::{DecodeError, BASE64};
use serde::{Deserialize, Serialize};
use std::{
    fmt::{self, Display},
    ops::Deref,
    path::Path,
    str::{self, FromStr},
};
use thiserror;

mod utils;

pub use utils::*;

pub const DIGEST_SIZE: usize = 20;
pub const ENCODED_DIGEST_SIZE: usize = nixbase32::encode_len(DIGEST_SIZE);

// The store dir prefix, without trailing slash.
// That's usually where the Nix store is mounted at.
pub const STORE_DIR: &str = "/nix/store";
pub const STORE_DIR_WITH_SLASH: &str = "/nix/store/";

/// Errors that can occur when parsing a literal store path
#[derive(Debug, PartialEq, Eq, thiserror::Error)]
pub enum Error {
    #[error("Dash is missing between hash and name")]
    MissingDash,
    #[error("Hash encoding is invalid: {0}")]
    InvalidHashEncoding(#[from] DecodeError),
    #[error("Invalid length")]
    InvalidLength,
    #[error(
        "Invalid name: \"{}\", character at position {} is invalid",
        std::str::from_utf8(.0).unwrap_or(&BASE64.encode(.0)),
        .1,
    )]
    InvalidName(Vec<u8>, u8),
    #[error("Tried to parse an absolute path which was missing the store dir prefix.")]
    MissingStoreDir,
}

/// Represents a path in the Nix store (a direct child of [STORE_DIR]).
///
/// It consists of a digest (20 bytes), and a name, which is a string.
/// The name may only contain ASCII alphanumeric, or one of the following
/// characters: `-`, `_`, `.`, `+`, `?`, `=`.
/// The name is usually used to describe the pname and version of a package.
/// Derivation paths can also be represented as store paths, their names just
/// end with the `.drv` prefix.
///
/// A [StorePath] does not encode any additional subpath "inside" the store
/// path.
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct StorePath<S>
where
    S: std::cmp::Eq + std::cmp::PartialEq,
{
    digest: [u8; DIGEST_SIZE],
    name: S,
}
/// Like [StorePath], but without a heap allocation for the name.
/// Used by [StorePath] for parsing.
pub type StorePathRef<'a> = StorePath<&'a str>;

impl<S> StorePath<S>
where
    S: std::cmp::Eq + Deref<Target = str>,
{
    pub fn digest(&self) -> &[u8; DIGEST_SIZE] {
        &self.digest
    }

    pub fn name(&self) -> &S {
        &self.name
    }

    pub fn as_ref(&self) -> StorePathRef<'_> {
        StorePathRef {
            digest: self.digest,
            name: &self.name,
        }
    }

    pub fn to_owned(&self) -> StorePath<String> {
        StorePath {
            digest: self.digest,
            name: self.name.to_string(),
        }
    }

    /// Construct a [StorePath] by passing the `$digest-$name` string
    /// that comes after [STORE_DIR_WITH_SLASH].
    pub fn from_bytes<'a>(s: &'a [u8]) -> Result<Self, Error>
    where
        S: From<&'a str>,
    {
        // the whole string needs to be at least:
        //
        // - 32 characters (encoded hash)
        // - 1 dash
        // - 1 character for the name
        if s.len() < ENCODED_DIGEST_SIZE + 2 {
            Err(Error::InvalidLength)?
        }

        let digest = nixbase32::decode_fixed(&s[..ENCODED_DIGEST_SIZE])?;

        if s[ENCODED_DIGEST_SIZE] != b'-' {
            return Err(Error::MissingDash);
        }

        Ok(StorePath {
            digest,
            name: validate_name(&s[ENCODED_DIGEST_SIZE + 1..])?.into(),
        })
    }

    /// Construct a [StorePathRef] from a name and digest.
    /// The name is validated, and the digest checked for size.
    pub fn from_name_and_digest<'a>(name: &'a str, digest: &[u8]) -> Result<Self, Error>
    where
        S: From<&'a str>,
    {
        let digest_fixed = digest.try_into().map_err(|_| Error::InvalidLength)?;
        Self::from_name_and_digest_fixed(name, digest_fixed)
    }

    /// Construct a [StorePathRef] from a name and digest of correct length.
    /// The name is validated.
    pub fn from_name_and_digest_fixed<'a>(
        name: &'a str,
        digest: [u8; DIGEST_SIZE],
    ) -> Result<Self, Error>
    where
        S: From<&'a str>,
    {
        Ok(Self {
            name: validate_name(name)?.into(),
            digest,
        })
    }

    /// Construct a [StorePathRef] from an absolute store path string.
    /// This is equivalent to calling [StorePathRef::from_bytes], but stripping
    /// the [STORE_DIR_WITH_SLASH] prefix before.
    pub fn from_absolute_path<'a>(s: &'a [u8]) -> Result<Self, Error>
    where
        S: From<&'a str>,
    {
        match s.strip_prefix(STORE_DIR_WITH_SLASH.as_bytes()) {
            Some(s_stripped) => Self::from_bytes(s_stripped),
            None => Err(Error::MissingStoreDir),
        }
    }

    /// Decompose a string into a [StorePath] and a [PathBuf] containing the
    /// rest of the path, or an error.
    #[cfg(target_family = "unix")]
    pub fn from_absolute_path_full<'a, P>(path: &'a P) -> Result<(Self, &'a Path), Error>
    where
        S: From<&'a str>,
        P: AsRef<std::path::Path> + ?Sized,
    {
        // strip [STORE_DIR_WITH_SLASH] from s
        let p = path
            .as_ref()
            .strip_prefix(STORE_DIR_WITH_SLASH)
            .map_err(|_e| Error::MissingStoreDir)?;

        let mut it = Path::new(p).components();

        // The first component of the rest must be parse-able as a [StorePath]
        let first_component = it.next().ok_or(Error::InvalidLength)?;
        let store_path = StorePath::from_bytes(first_component.as_os_str().as_encoded_bytes())?;

        // collect rest
        let rest_buf = it.as_path();

        Ok((store_path, rest_buf))
    }

    /// Returns an absolute store path string.
    /// That is just the string representation, prefixed with the store prefix
    /// ([STORE_DIR_WITH_SLASH]),
    pub fn to_absolute_path(&self) -> String
    where
        S: Display,
    {
        format!("{}{}", STORE_DIR_WITH_SLASH, self)
    }
}

impl<S> PartialOrd for StorePath<S>
where
    S: std::cmp::PartialEq + std::cmp::Eq,
{
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        Some(self.cmp(other))
    }
}

/// `StorePath`s are sorted by their reverse digest to match the sorting order
/// of the nixbase32-encoded string.
impl<S> Ord for StorePath<S>
where
    S: std::cmp::PartialEq + std::cmp::Eq,
{
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.digest.iter().rev().cmp(other.digest.iter().rev())
    }
}

impl<'a, 'b: 'a> FromStr for StorePath<String> {
    type Err = Error;

    /// Construct a [StorePath] by passing the `$digest-$name` string
    /// that comes after [STORE_DIR_WITH_SLASH].
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        StorePath::<String>::from_bytes(s.as_bytes())
    }
}

impl<'a, 'de: 'a, S> Deserialize<'de> for StorePath<S>
where
    S: std::cmp::Eq + Deref<Target = str> + From<&'a str>,
{
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        let string: &'de str = Deserialize::deserialize(deserializer)?;
        let stripped: Option<&str> = string.strip_prefix(STORE_DIR_WITH_SLASH);
        let stripped: &str = stripped.ok_or_else(|| {
            serde::de::Error::invalid_value(
                serde::de::Unexpected::Str(string),
                &"store path prefix",
            )
        })?;
        StorePath::from_bytes(stripped.as_bytes()).map_err(|_| {
            serde::de::Error::invalid_value(serde::de::Unexpected::Str(string), &"StorePath")
        })
    }
}

impl<S> Serialize for StorePath<S>
where
    S: std::cmp::Eq + Deref<Target = str> + Display,
{
    fn serialize<SR>(&self, serializer: SR) -> Result<SR::Ok, SR::Error>
    where
        SR: serde::Serializer,
    {
        let string: String = self.to_absolute_path();
        string.serialize(serializer)
    }
}

/// NAME_CHARS contains `true` for bytes that are valid in store path names.
static NAME_CHARS: [bool; 256] = {
    let mut tbl = [false; 256];
    let mut c = 0;

    loop {
        tbl[c as usize] = matches!(c, b'a'..=b'z' | b'A'..=b'Z' | b'0'..=b'9' | b'+' | b'-' | b'_' | b'?' | b'=' | b'.');

        if c == u8::MAX {
            break;
        }

        c += 1;
    }

    tbl
};

/// Checks a given &[u8] to match the restrictions for [StorePath::name], and
/// returns the name as string if successful.
pub(crate) fn validate_name(s: &(impl AsRef<[u8]> + ?Sized)) -> Result<&str, Error> {
    let s = s.as_ref();

    // Empty or excessively long names are not allowed.
    if s.is_empty() || s.len() > 211 {
        return Err(Error::InvalidLength);
    }

    let mut valid = true;
    for &c in s {
        valid = valid && NAME_CHARS[c as usize];
    }

    if !valid {
        for (i, &c) in s.iter().enumerate() {
            if !NAME_CHARS[c as usize] {
                return Err(Error::InvalidName(s.to_vec(), i as u8));
            }
        }

        unreachable!();
    }

    // SAFETY: We permit a subset of ASCII, which guarantees valid UTF-8.
    Ok(unsafe { str::from_utf8_unchecked(s) })
}

impl<S> fmt::Display for StorePath<S>
where
    S: fmt::Display + std::cmp::Eq,
{
    /// The string representation of a store path starts with a digest (20
    /// bytes), [crate::nixbase32]-encoded, followed by a `-`,
    /// and ends with the name.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}-{}", nixbase32::encode(&self.digest), self.name)
    }
}

#[cfg(test)]
mod tests {
    use super::Error;
    use std::cmp::Ordering;
    use std::path::PathBuf;

    use crate::store_path::{StorePath, StorePathRef, DIGEST_SIZE};
    use hex_literal::hex;
    use pretty_assertions::assert_eq;
    use rstest::rstest;
    use serde::Deserialize;

    #[derive(Deserialize)]
    /// An example struct, holding a StorePathRef.
    /// Used to test deserializing StorePathRef.
    struct Container<'a> {
        #[serde(borrow)]
        store_path: StorePathRef<'a>,
    }

    #[test]
    fn happy_path() {
        let example_nix_path_str =
            "00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432";
        let nixpath = StorePathRef::from_bytes(example_nix_path_str.as_bytes())
            .expect("Error parsing example string");

        let expected_digest: [u8; DIGEST_SIZE] = hex!("8a12321522fd91efbd60ebb2481af88580f61600");

        assert_eq!("net-tools-1.60_p20170221182432", *nixpath.name());
        assert_eq!(nixpath.digest, expected_digest);

        assert_eq!(example_nix_path_str, nixpath.to_string())
    }

    #[test]
    fn store_path_ordering() {
        let store_paths = [
            "/nix/store/0lk5dgi01r933abzfj9c9wlndg82yd3g-psutil-5.9.6.tar.gz.drv",
            "/nix/store/1xj43bva89f9qmwm37zl7r3d7m67i9ck-shorttoc-1.3-tex.drv",
            "/nix/store/2gb633czchi20jq1kqv70rx2yvvgins8-lifted-base-0.2.3.12.tar.gz.drv",
            "/nix/store/2vksym3r3zqhp15q3fpvw2mnvffv11b9-docbook-xml-4.5.zip.drv",
            "/nix/store/5q918awszjcz5720xvpc2czbg1sdqsf0-rust_renaming-0.1.0-lib",
            "/nix/store/7jw30i342sr2p1fmz5xcfnch65h4zbd9-dbus-1.14.10.tar.xz.drv",
            "/nix/store/96yqwqhnp3qya4rf4n0rcl0lwvrylp6k-eap8021x-222.40.1.tar.gz.drv",
            "/nix/store/9gjqg36a1v0axyprbya1hkaylmnffixg-virtualenv-20.24.5.tar.gz.drv",
            "/nix/store/a4i5mci2g9ada6ff7ks38g11dg6iqyb8-perl-5.32.1.drv",
            "/nix/store/a5g76ljava4h5pxlggz3aqdhs3a4fk6p-ToolchainInfo.plist.drv",
            "/nix/store/db46l7d6nswgz4ffp1mmd56vjf9g51v6-version.plist.drv",
            "/nix/store/g6f7w20sd7vwy0rc1r4bfsw4ciclrm4q-crates-io-num_cpus-1.12.0.drv",
            "/nix/store/iw82n1wwssb8g6772yddn8c3vafgv9np-bootstrap-stage1-sysctl-stdenv-darwin.drv",
            "/nix/store/lp78d1y5wxpcn32d5c4r7xgbjwiw0cgf-logo.svg.drv",
            "/nix/store/mf00ank13scv1f9l1zypqdpaawjhfr3s-python3.11-psutil-5.9.6.drv",
            "/nix/store/mpfml61ra7pz90124jx9r3av0kvkz2w1-perl5.36.0-Encode-Locale-1.05",
            "/nix/store/qhsvwx4h87skk7c4mx0xljgiy3z93i23-source.drv",
            "/nix/store/riv7d73adim8hq7i04pr8kd0jnj93nav-fdk-aac-2.0.2.tar.gz.drv",
            "/nix/store/s64b9031wga7vmpvgk16xwxjr0z9ln65-human-signals-5.0.0.tgz-extracted",
            "/nix/store/w6svg3m2xdh6dhx0gl1nwa48g57d3hxh-thiserror-1.0.49",
        ];

        for w in store_paths.windows(2) {
            if w.len() < 2 {
                continue;
            }
            let (pa, _) = StorePathRef::from_absolute_path_full(w[0]).expect("parseable");
            let (pb, _) = StorePathRef::from_absolute_path_full(w[1]).expect("parseable");
            assert_eq!(
                Ordering::Less,
                pa.cmp(&pb),
                "{:?} not less than {:?}",
                w[0],
                w[1]
            );
        }
    }

    /// This is the store path *accepted* when `nix-store --add`'ing an
    /// empty `.gitignore` file.
    ///
    /// Nix 2.4 accidentally permitted this behaviour, but the revert came
    /// too late to beat Hyrum's law. It is now considered permissible.
    ///
    /// https://github.com/NixOS/nix/pull/9095 (revert)
    /// https://github.com/NixOS/nix/pull/9867 (revert-of-revert)
    #[test]
    fn starts_with_dot() {
        StorePathRef::from_bytes(b"fli4bwscgna7lpm7v5xgnjxrxh0yc7ra-.gitignore")
            .expect("must succeed");
    }

    #[test]
    fn empty_name() {
        StorePathRef::from_bytes(b"00bgd045z0d4icpbc2yy-").expect_err("must fail");
    }

    #[test]
    fn excessive_length() {
        StorePathRef::from_bytes(b"00bgd045z0d4icpbc2yy-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
            .expect_err("must fail");
    }

    #[test]
    fn invalid_hash_length() {
        StorePathRef::from_bytes(b"00bgd045z0d4icpbc2yy-net-tools-1.60_p20170221182432")
            .expect_err("must fail");
    }

    #[test]
    fn invalid_encoding_hash() {
        StorePathRef::from_bytes(
            b"00bgd045z0d4icpbc2yyz4gx48aku4la-net-tools-1.60_p20170221182432",
        )
        .expect_err("must fail");
    }

    #[test]
    fn more_than_just_the_bare_nix_store_path() {
        StorePathRef::from_bytes(
            b"00bgd045z0d4icpbc2yyz4gx48aku4la-net-tools-1.60_p20170221182432/bin/arp",
        )
        .expect_err("must fail");
    }

    #[test]
    fn no_dash_between_hash_and_name() {
        StorePathRef::from_bytes(b"00bgd045z0d4icpbc2yyz4gx48ak44lanet-tools-1.60_p20170221182432")
            .expect_err("must fail");
    }

    #[test]
    fn absolute_path() {
        let example_nix_path_str =
            "00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432";
        let nixpath_expected =
            StorePathRef::from_bytes(example_nix_path_str.as_bytes()).expect("must parse");

        let nixpath_actual = StorePathRef::from_absolute_path(
            "/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432".as_bytes(),
        )
        .expect("must parse");

        assert_eq!(nixpath_expected, nixpath_actual);

        assert_eq!(
            "/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432",
            nixpath_actual.to_absolute_path(),
        );
    }

    #[test]
    fn absolute_path_missing_prefix() {
        assert_eq!(
            Error::MissingStoreDir,
            StorePathRef::from_absolute_path(b"foobar-123").expect_err("must fail")
        );
    }

    #[test]
    fn serialize_ref() {
        let nixpath_actual = StorePathRef::from_bytes(
            b"00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432",
        )
        .expect("can parse");

        let serialized = serde_json::to_string(&nixpath_actual).expect("can serialize");

        assert_eq!(
            "\"/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432\"",
            &serialized
        );
    }

    #[test]
    fn serialize_owned() {
        let nixpath_actual = StorePathRef::from_bytes(
            b"00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432",
        )
        .expect("can parse");

        let serialized = serde_json::to_string(&nixpath_actual).expect("can serialize");

        assert_eq!(
            "\"/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432\"",
            &serialized
        );
    }

    #[test]
    fn deserialize_ref() {
        let store_path_str_json =
            "\"/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432\"";

        let store_path: StorePathRef<'_> =
            serde_json::from_str(store_path_str_json).expect("valid json");

        assert_eq!(
            "/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432",
            store_path.to_absolute_path()
        );
    }

    #[test]
    fn deserialize_ref_container() {
        let str_json = "{\"store_path\":\"/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432\"}";

        let container: Container<'_> = serde_json::from_str(str_json).expect("must deserialize");

        assert_eq!(
            "/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432",
            container.store_path.to_absolute_path()
        );
    }

    #[test]
    fn deserialize_owned() {
        let store_path_str_json =
            "\"/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432\"";

        let store_path: StorePath<String> =
            serde_json::from_str(store_path_str_json).expect("valid json");

        assert_eq!(
            "/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432",
            store_path.to_absolute_path()
        );
    }

    #[rstest]
    #[case::without_prefix(
        "/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432",
        StorePath::from_bytes(b"00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432").unwrap(), PathBuf::new())]
    #[case::without_prefix_but_trailing_slash(
        "/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432/",
        StorePath::from_bytes(b"00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432").unwrap(), PathBuf::new())]
    #[case::with_prefix(
        "/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432/bin/arp",
        StorePath::from_bytes(b"00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432").unwrap(), PathBuf::from("bin/arp"))]
    #[case::with_prefix_and_trailing_slash(
        "/nix/store/00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432/bin/arp/",
        StorePath::from_bytes(b"00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432").unwrap(), PathBuf::from("bin/arp/"))]
    fn from_absolute_path_full(
        #[case] s: &str,
        #[case] exp_store_path: StorePath<&str>,
        #[case] exp_path: PathBuf,
    ) {
        let (actual_store_path, actual_path) =
            StorePath::from_absolute_path_full(s).expect("must succeed");

        assert_eq!(exp_store_path, actual_store_path);
        assert_eq!(exp_path, actual_path);
    }

    #[test]
    fn from_absolute_path_errors() {
        assert_eq!(
            Error::InvalidLength,
            StorePathRef::from_absolute_path_full("/nix/store/").expect_err("must fail")
        );
        assert_eq!(
            Error::InvalidLength,
            StorePathRef::from_absolute_path_full("/nix/store/foo").expect_err("must fail")
        );
        assert_eq!(
            Error::MissingStoreDir,
            StorePathRef::from_absolute_path_full(
                "00bgd045z0d4icpbc2yyz4gx48ak44la-net-tools-1.60_p20170221182432"
            )
            .expect_err("must fail")
        );
    }
}