//! OAuth2-specific

use std::{
    collections::{btree_set, BTreeSet},
    convert::TryFrom,
    fmt, iter,
    iter::FromIterator,
    str::FromStr,
};

use aliri::jwt;
use aliri_braid::braid;
use aliri_clock::UnixTime;
use serde::{Deserialize, Serialize};
use thiserror::Error;

/// An invalid scope token
#[derive(Debug, Error)]
pub enum InvalidScopeToken {
    /// The scope token was the empty string
    #[error("scope token cannot be empty")]
    EmptyString,
    /// The scope token contained an invalid byte
    #[error("invalid scope token byte at position {position}: 0x{value:02x}")]
    InvalidByte {
        /// The index in the scope token where the invalid byte was found
        position: usize,
        /// The invalid byte value
        value: u8,
    },
}
aliri_braid::from_infallible!(InvalidScopeToken);

/// An OAuth2 (or OIDC) scope token as defined in [RFC 6749, Section 3.3][RFC6749 3.3]
///
/// A scope token must be composed of printable ASCII characters excluding
/// ` ` (space), `"` (double quote), and `\` (backslash).
///
///   [RFC6749 3.3]: (https://datatracker.ietf.org/doc/html/rfc6749#section-3.3)
#[braid(
    serde,
    validator,
    ref_doc = "A borrowed reference to an OAuth2 (or OIDC) [`ScopeToken`]"
)]
#[must_use]
pub struct ScopeToken(compact_str::CompactString);

impl aliri_braid::Validator for ScopeToken {
    type Error = InvalidScopeToken;

    /// Validates that the scope token is valid
    ///
    /// A valid scope token is non-empty and composed of printable
    /// ASCII characters except ` `, `"`, and `\`.
    fn validate(s: &str) -> Result<(), Self::Error> {
        Self::const_validate(s)
    }
}

impl ScopeToken {
    /// Construct a new `ScopeToken` from a string
    ///
    /// # Errors
    ///
    /// This function will return an error if the provided string is not a valid scope token.
    #[inline]
    pub fn from_string(value: String) -> Result<Self, InvalidScopeToken> {
        Self::try_from(value)
    }

    /// Construct a new `ScopeToken` from a string slice at compile time
    ///
    /// # Panics
    ///
    /// If the provided scope token is not valid or is longer than 24 bytes, this function will
    /// panic or fail at compile time.
    #[inline]
    #[track_caller]
    pub const fn new_const(value: &str) -> Self {
        if let Err(err) = Self::const_validate(value) {
            match err {
                InvalidScopeToken::EmptyString => panic!("scope token cannot be empty"),
                InvalidScopeToken::InvalidByte { .. } => {
                    panic!("scope token contains invalid byte")
                }
            }
        }

        Self(compact_str::CompactString::new_inline(value))
    }

    const fn const_validate(s: &str) -> Result<(), InvalidScopeToken> {
        if s.is_empty() {
            return Err(InvalidScopeToken::EmptyString);
        }

        let mut idx = 0;
        let b = s.as_bytes();
        let mut invalid = None;
        while idx < b.len() {
            let c = b[idx];
            if c <= 0x20 || c == 0x22 || c == 0x5C || 0x7F <= c {
                invalid = Some((idx, c));
            }
            idx += 1;
        }

        if let Some((position, value)) = invalid {
            Err(InvalidScopeToken::InvalidByte { position, value })
        } else {
            Ok(())
        }
    }
}

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
#[serde(untagged)]
enum ScopeDto {
    String(String),
    Array(Vec<ScopeToken>),
}

impl TryFrom<Option<ScopeDto>> for Scope {
    type Error = InvalidScopeToken;

    fn try_from(dto: Option<ScopeDto>) -> Result<Self, Self::Error> {
        if let Some(dto) = dto {
            match dto {
                ScopeDto::String(s) => Self::try_from(s),
                ScopeDto::Array(arr) => Ok(arr.into_iter().collect()),
            }
        } else {
            Ok(Self::empty())
        }
    }
}

impl From<Scope> for ScopeDto {
    fn from(s: Scope) -> Self {
        ScopeDto::String(s.to_string())
    }
}

/// An OAuth2 (or OIDC) Scope defining a set of access permissions
#[derive(Clone, Debug, PartialEq, Eq, Deserialize, Serialize)]
#[serde(try_from = "Option<ScopeDto>", into = "ScopeDto")]
#[must_use]
pub struct Scope(ScopeInner);

impl Default for Scope {
    fn default() -> Self {
        Self::empty()
    }
}

#[derive(Clone, Debug, PartialEq, Eq)]
enum ScopeInner {
    Empty,
    Single(ScopeToken),
    Multiple(BTreeSet<ScopeToken>),
}

impl Scope {
    /// Produces an empty scope
    #[inline]
    pub const fn empty() -> Self {
        Self(ScopeInner::Empty)
    }

    /// Constructs a new scope from a single scope token
    #[inline]
    pub const fn single(scope_token: ScopeToken) -> Self {
        Self(ScopeInner::Single(scope_token))
    }

    /// Adds an additional scope token
    #[inline]
    pub fn and(self, scope_token: ScopeToken) -> Self {
        match self.0 {
            ScopeInner::Empty => Self::single(scope_token),
            ScopeInner::Single(existing) => {
                let mut set = BTreeSet::new();
                set.insert(existing);
                set.insert(scope_token);
                Self(ScopeInner::Multiple(set))
            }
            ScopeInner::Multiple(mut set) => {
                set.insert(scope_token);
                Self(ScopeInner::Multiple(set))
            }
        }
    }

    /// Constructs a scope from an iterator of scope tokens
    #[inline]
    pub fn from_scope_tokens<I>(scope_tokens: I) -> Self
    where
        I: IntoIterator<Item = ScopeToken>,
    {
        Self::from_iter(scope_tokens)
    }

    /// Adds a scope token to the scope
    #[inline]
    pub fn insert(&mut self, scope_token: ScopeToken) {
        let this = std::mem::replace(self, Self::empty());
        *self = this.and(scope_token);
    }

    /// Produces an iterator of the scope tokens in this set
    #[inline]
    pub fn iter(&self) -> impl Iterator<Item = &ScopeTokenRef> {
        self.into_iter()
    }

    /// Checks to see whether this scope contains all of
    /// the scope tokens in `subset`.
    #[inline]
    #[must_use]
    pub fn contains_all(&self, subset: &Scope) -> bool {
        match (&self.0, &subset.0) {
            (ScopeInner::Empty, ScopeInner::Empty) => true,
            (ScopeInner::Empty, _) => false,
            (_, ScopeInner::Empty) => true,
            (ScopeInner::Single(left), ScopeInner::Single(right)) => left == right,
            (ScopeInner::Single(_), ScopeInner::Multiple(_)) => false,
            (ScopeInner::Multiple(set), ScopeInner::Single(token)) => set.contains(token),
            (ScopeInner::Multiple(superset), ScopeInner::Multiple(subset)) => {
                superset.is_superset(subset)
            }
        }
    }

    /// The number of scope tokens
    #[inline]
    #[must_use]
    pub fn len(&self) -> usize {
        match &self.0 {
            ScopeInner::Empty => 0,
            ScopeInner::Single(_) => 1,
            ScopeInner::Multiple(set) => set.len(),
        }
    }

    /// Whether this scope has any scope tokens at all
    #[inline]
    #[must_use]
    pub const fn is_empty(&self) -> bool {
        matches!(self.0, ScopeInner::Empty)
    }
}

impl fmt::Display for Scope {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        use std::fmt::Write;

        let mut iter = self.iter();
        let first = iter.next();
        if let Some(first) = first {
            fmt::Display::fmt(first, &mut *f)?;
        }

        for token in iter {
            f.write_char(' ')?;
            fmt::Display::fmt(token, &mut *f)?;
        }

        Ok(())
    }
}

impl IntoIterator for Scope {
    type Item = ScopeToken;
    type IntoIter = IntoIter;

    #[inline]
    fn into_iter(self) -> Self::IntoIter {
        match self {
            Scope(ScopeInner::Empty) => IntoIter {
                inner: IntoIterInner::Empty,
            },
            Scope(ScopeInner::Single(token)) => IntoIter {
                inner: IntoIterInner::Single(iter::once(token)),
            },
            Scope(ScopeInner::Multiple(set)) => IntoIter {
                inner: IntoIterInner::Multiple(set.into_iter()),
            },
        }
    }
}

/// An iterator over the tokens in a scope
#[derive(Debug)]
pub struct IntoIter {
    inner: IntoIterInner,
}

#[derive(Debug)]
enum IntoIterInner {
    Empty,
    Single(iter::Once<ScopeToken>),
    Multiple(btree_set::IntoIter<ScopeToken>),
}

impl Iterator for IntoIter {
    type Item = ScopeToken;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        match &mut self.inner {
            IntoIterInner::Empty => None,
            IntoIterInner::Single(token) => token.next(),
            IntoIterInner::Multiple(set) => set.next(),
        }
    }
}

/// An iterator over a set of borrowed scope tokens
#[derive(Clone, Debug)]
pub struct Iter<'a> {
    inner: IterInner<'a>,
}

#[derive(Clone, Debug)]
enum IterInner<'a> {
    Empty,
    Single(iter::Once<&'a ScopeToken>),
    Multiple(btree_set::Iter<'a, ScopeToken>),
}

impl<'a> Iterator for Iter<'a> {
    type Item = &'a ScopeTokenRef;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        match &mut self.inner {
            IterInner::Empty => None,
            IterInner::Single(token) => token.next().map(AsRef::as_ref),
            IterInner::Multiple(set) => set.next().map(AsRef::as_ref),
        }
    }
}

impl<'a> IntoIterator for &'a Scope {
    type Item = &'a ScopeTokenRef;
    type IntoIter = Iter<'a>;

    #[inline]
    fn into_iter(self) -> Self::IntoIter {
        Iter {
            inner: match &self.0 {
                ScopeInner::Empty => IterInner::Empty,
                ScopeInner::Single(token) => IterInner::Single(iter::once(token)),
                ScopeInner::Multiple(set) => IterInner::Multiple(set.iter()),
            },
        }
    }
}

impl<S> Extend<S> for Scope
where
    S: Into<ScopeToken>,
{
    fn extend<I>(&mut self, iter: I)
    where
        I: IntoIterator<Item = S>,
    {
        for token in iter {
            self.insert(token.into());
        }
    }
}

impl<S> FromIterator<S> for Scope
where
    S: Into<ScopeToken>,
{
    #[inline]
    fn from_iter<I>(iter: I) -> Self
    where
        I: IntoIterator<Item = S>,
    {
        let mut set = Self::empty();
        set.extend(iter);
        set
    }
}

impl From<ScopeToken> for Scope {
    #[inline]
    fn from(t: ScopeToken) -> Self {
        Self::single(t)
    }
}

impl TryFrom<&'_ str> for Scope {
    type Error = InvalidScopeToken;

    #[inline]
    fn try_from(s: &str) -> Result<Self, Self::Error> {
        s.split_whitespace().map(ScopeToken::try_from).collect()
    }
}

impl TryFrom<String> for Scope {
    type Error = InvalidScopeToken;

    #[inline]
    fn try_from(s: String) -> Result<Self, Self::Error> {
        Self::try_from(s.as_str())
    }
}

impl FromStr for Scope {
    type Err = InvalidScopeToken;

    #[inline]
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Self::try_from(s)
    }
}

/// A convenience structure for payloads where the user only cares about the
/// scope and other basic claims
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct BasicClaimsWithScope {
    /// The basic claims
    #[serde(flatten)]
    pub basic: jwt::BasicClaims,

    /// The `scope` claim
    pub scope: Scope,
}

impl jwt::CoreClaims for BasicClaimsWithScope {
    #[inline]
    fn nbf(&self) -> Option<UnixTime> {
        self.basic.nbf()
    }

    #[inline]
    fn exp(&self) -> Option<UnixTime> {
        self.basic.exp()
    }

    #[inline]
    fn aud(&self) -> &jwt::Audiences {
        self.basic.aud()
    }

    #[inline]
    fn iss(&self) -> Option<&jwt::IssuerRef> {
        self.basic.iss()
    }

    #[inline]
    fn sub(&self) -> Option<&jwt::SubjectRef> {
        self.basic.sub()
    }
}

/// Indicates that the type has an OAuth2 (or OIDC) scope claim
pub trait HasScope {
    /// OAuth2 (or OIDC) scope
    ///
    /// Scope claimed by the underlying token, generally in the `scope`
    /// claim.
    fn scope(&self) -> &Scope;
}

impl HasScope for BasicClaimsWithScope {
    #[inline]
    fn scope(&self) -> &Scope {
        &self.scope
    }
}

impl HasScope for Scope {
    #[inline]
    fn scope(&self) -> &Scope {
        self
    }
}

/// Construct a scope from a list of tokens.
///
/// ```
/// use aliri_oauth2::scope;
///
/// let scope = scope!["users.read", "users.update", "users.list"];
/// ```
///
/// This is equivalent to the following:
///
/// ```
/// use aliri_oauth2::{scope, Scope};
///
/// let scope = Scope::empty()
///     .and(scope::ScopeToken::from_static("users.read"))
///     .and(scope::ScopeToken::from_static("users.update"))
///     .and(scope::ScopeToken::from_static("users.list"));
/// ```
///
/// # Panics
///
/// This macro will attempt to convert all the passed in string literals into tokens
/// using [`ScopeToken::from_static`] which will panic if any are invalid.
///
/// ```should_panic
/// use aliri_oauth2::scope;
///
/// let scope = scope!["users read", "users.update", "users.list"];
/// ```
///
/// # Errors
///
/// If the values passed in are not literals, then the tokens will be parsed
/// at runtime, and any errors will be propagated back to the caller.
///
/// ```
/// use aliri_oauth2::scope;
///
/// let scope = scope![String::from("users.read")].unwrap();
/// assert!(scope![String::from("users read")].is_err());
/// ```
#[macro_export]
macro_rules! scope {
    ($($token:literal),+ $(,)?) => {
        {
            $crate::Scope::empty()
            $(
                .and($crate::scope::ScopeToken::from_static($token))
            )+
        }
    };
    ($($token:expr),+ $(,)?) => {
        {
            let __f = || -> Result<$crate::Scope, $crate::scope::InvalidScopeToken> {
                ::core::result::Result::Ok(
                    $crate::Scope::empty()
                    $(
                        .and(::core::convert::TryFrom::try_from($token)?)
                    )+
                )
            };

            __f()
        }
    };
    () => {
        $crate::Scope::empty()
    }
}

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

    #[test]
    fn owned_handles_valid() {
        let x = ScopeToken::from_static("https://crates.io/scopes/publish:crate");
        assert_eq!(x.as_str(), "https://crates.io/scopes/publish:crate");
    }

    #[test]
    fn owned_rejects_empty() {
        let x = ScopeToken::try_from("");
        assert!(matches!(x, Err(InvalidScopeToken::EmptyString)));
    }

    #[test]
    fn owned_rejects_invalid_quote() {
        let x = ScopeToken::try_from("https://crates.io/scopes/\"publish:crate\"");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn owned_rejects_invalid_control() {
        let x = ScopeToken::try_from("https://crates.io/scopes/\tpublish:crate");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn owned_rejects_invalid_backslash() {
        let x = ScopeToken::try_from("https://crates.io/scopes/\\publish:crate");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn owned_rejects_invalid_delete() {
        let x = ScopeToken::try_from("https://crates.io/scopes/\x7Fpublish:crate");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn owned_rejects_invalid_non_ascii() {
        let x = ScopeToken::try_from("https://crates.io/scopes/¿publish:crate");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn owned_rejects_invalid_emoji() {
        let x = ScopeToken::try_from("https://crates.io/scopes/🪤publish:crate");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn ref_handles_valid() {
        let x = ScopeTokenRef::from_static("https://crates.io/scopes/publish:crate");
        assert_eq!(x.as_str(), "https://crates.io/scopes/publish:crate");
    }

    #[test]
    fn ref_rejects_empty() {
        let x = ScopeTokenRef::from_str("");
        assert!(matches!(x, Err(InvalidScopeToken::EmptyString)));
    }

    #[test]
    fn ref_rejects_invalid_quote() {
        let x = ScopeTokenRef::from_str("https://crates.io/scopes/\"publish:crate\"");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn ref_rejects_invalid_control() {
        let x = ScopeTokenRef::from_str("https://crates.io/scopes/\tpublish:crate");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn ref_rejects_invalid_backslash() {
        let x = ScopeTokenRef::from_str("https://crates.io/scopes/\\publish:crate");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn ref_rejects_invalid_delete() {
        let x = ScopeTokenRef::from_str("https://crates.io/scopes/\x7Fpublish:crate");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn ref_rejects_invalid_non_ascii() {
        let x = ScopeTokenRef::from_str("https://crates.io/scopes/¿publish:crate");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn ref_rejects_invalid_emoji() {
        let x = ScopeTokenRef::from_str("https://crates.io/scopes/🪤publish:crate");
        assert!(matches!(x, Err(InvalidScopeToken::InvalidByte { .. })));
    }

    #[test]
    fn scope_to_string() {
        let scope: String = scope!["test1", "test2", "test3"].to_string();
        assert_eq!(scope.len(), 17);
        assert!(scope.contains("test1"));
        assert!(scope.contains("test2"));
        assert!(scope.contains("test3"));
        assert_eq!(&scope[5..6], " ");
        assert_eq!(&scope[11..12], " ");
    }
}
