use std::fmt;

use unicode_normalization::UnicodeNormalization;

/// A validated, NFC-preserving virtual filename. It is never interpreted as a URL.
#[derive(Clone, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct CanonicalPath(String);

impl CanonicalPath {
    pub fn parse(input: &str) -> Result<Self, PathDiagnostic> {
        if input.is_empty() || input.starts_with('/') || input.ends_with('/') {
            return Err(PathDiagnostic::Slash);
        }
        if input.contains('%') {
            return Err(PathDiagnostic::Percent);
        }
        if input.contains('\\') {
            return Err(PathDiagnostic::Backslash);
        }
        if input.contains('?') || input.contains('#') {
            return Err(PathDiagnostic::QueryOrFragment);
        }
        if input.chars().any(|c| c.is_control() || c == ':') {
            return Err(PathDiagnostic::ControlOrColon);
        }
        if input.nfc().collect::<String>() != input {
            return Err(PathDiagnostic::NotNfc);
        }
        for segment in input.split('/') {
            if segment.is_empty() || segment == "." || segment == ".." {
                return Err(PathDiagnostic::Segment);
            }
        }
        Ok(Self(input.to_owned()))
    }

    pub fn as_str(&self) -> &str {
        &self.0
    }

    pub fn segments(&self) -> impl Iterator<Item = &str> {
        self.0.split('/')
    }
}

impl fmt::Display for CanonicalPath {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.0.fmt(f)
    }
}

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum RootId {
    Mpd,
    Manifest,
    Models,
    Parts,
    P,
    OfficialParts,
    OfficialP,
}

impl RootId {
    pub fn as_str(self) -> &'static str {
        match self {
            Self::Mpd => "mpd",
            Self::Manifest => "manifest",
            Self::Models => "models",
            Self::Parts => "parts",
            Self::P => "p",
            Self::OfficialParts => "official-parts",
            Self::OfficialP => "official-p",
        }
    }

    pub fn case_insensitive(self) -> bool {
        !matches!(self, Self::Mpd | Self::Manifest)
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum PathDiagnostic {
    Slash,
    Percent,
    Backslash,
    QueryOrFragment,
    ControlOrColon,
    NotNfc,
    Segment,
}

#[derive(Clone, Debug, Eq, Hash, PartialEq)]
pub struct LookupEntry {
    pub root: RootId,
    pub path: CanonicalPath,
    pub target: String,
}

/// Resolve according to PM-75's fixed source precedence.
/// The maps contain already validated entries and only perform filename lookup.
pub fn resolve_precedence(
    path: &CanonicalPath,
    mpd: &[LookupEntry],
    manifest: &[LookupEntry],
    uploaded: &[LookupEntry],
    official: &[LookupEntry],
) -> Option<LookupEntry> {
    exact(path, mpd)
        .or_else(|| exact(path, manifest))
        .or_else(|| roots(path, uploaded, &[RootId::Models, RootId::Parts, RootId::P]))
        .or_else(|| roots(path, official, &[RootId::OfficialParts, RootId::OfficialP]))
}

fn exact(path: &CanonicalPath, entries: &[LookupEntry]) -> Option<LookupEntry> {
    entries.iter().find(|e| e.path == *path).cloned()
}

fn roots(path: &CanonicalPath, entries: &[LookupEntry], roots: &[RootId]) -> Option<LookupEntry> {
    roots.iter().find_map(|root| {
        entries
            .iter()
            .filter(|e| e.root == *root)
            .find(|e| {
                e.path == *path
                    || (root.case_insensitive()
                        && e.path.as_str().eq_ignore_ascii_case(path.as_str()))
            })
            .cloned()
    })
}

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

    #[test]
    fn rejects_unsafe_and_non_nfc_paths() {
        for value in [
            "",
            "/a",
            "a/",
            "a//b",
            "a/../b",
            "a/./b",
            "a%2Fb",
            "a\\b",
            "a:b",
            "a?b",
            "a#b",
            "a\u{0000}b",
        ] {
            assert!(CanonicalPath::parse(value).is_err(), "{value:?}");
        }
        assert!(CanonicalPath::parse("cafe\u{301}").is_err());
        assert_eq!(CanonicalPath::parse("café").unwrap().as_str(), "café");
    }

    #[test]
    fn precedence_and_ascii_case_policy_are_stable() {
        let path = CanonicalPath::parse("parts/3001.dat").unwrap();
        let entry = |root, target: &str| LookupEntry {
            root,
            path: path.clone(),
            target: target.into(),
        };
        let found =
            resolve_precedence(&path, &[], &[], &[entry(RootId::Models, "model")], &[]).unwrap();
        assert_eq!(found.target, "model");
        let upper = CanonicalPath::parse("PARTS/3001.DAT").unwrap();
        assert!(
            resolve_precedence(&upper, &[], &[], &[entry(RootId::Models, "model")], &[]).is_some()
        );
        let mpd = entry(RootId::Mpd, "mpd");
        assert_eq!(
            resolve_precedence(&path, &[mpd], &[], &[], &[])
                .unwrap()
                .target,
            "mpd"
        );
    }
}