use crate::ion_data::{IonEq, IonOrd};
use crate::result::decoding_error;
use crate::{IonResult, SymbolRef};
use std::borrow::Borrow;
use std::cmp::Ordering;
use std::fmt::{Display, Formatter};
use std::hash::{Hash, Hasher};
use std::sync::Arc;

/// Stores or points to the text of a given [Symbol].
#[derive(Debug, Eq)]
enum SymbolText {
    // This Symbol refers to a string in the symbol table
    Shared(Arc<str>),
    // This Symbol owns its own text
    Owned(String),
    // This Symbol is equivalent to SID zero (`$0`)
    Unknown,
}

impl SymbolText {
    fn text(&self) -> Option<&str> {
        let text = match self {
            SymbolText::Shared(s) => s.as_ref(),
            SymbolText::Owned(s) => s.as_str(),
            SymbolText::Unknown => return None,
        };
        Some(text)
    }
}

impl Hash for SymbolText {
    fn hash<H: Hasher>(&self, state: &mut H) {
        match self {
            SymbolText::Shared(text) => text.hash(state),
            SymbolText::Owned(text) => text.hash(state),
            SymbolText::Unknown => 0.hash(state),
        }
    }
}

impl Clone for SymbolText {
    fn clone(&self) -> Self {
        match self {
            SymbolText::Owned(text) => SymbolText::Owned(text.to_owned()),
            SymbolText::Shared(text) => SymbolText::Shared(Arc::clone(text)),
            SymbolText::Unknown => SymbolText::Unknown,
        }
    }
}

impl PartialEq<Self> for SymbolText {
    fn eq(&self, other: &Self) -> bool {
        self.cmp(other) == Ordering::Equal
    }
}

impl PartialOrd<Self> for SymbolText {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for SymbolText {
    fn cmp(&self, other: &Self) -> Ordering {
        match (self.text(), other.text()) {
            // If both Symbols have known text, delegate the comparison to their text.
            (Some(s1), Some(s2)) => s1.cmp(s2),
            // Otherwise, $0 (unknown text) is treated as 'less than' known text
            (Some(_), None) => Ordering::Greater,
            (None, Some(_)) => Ordering::Less,
            (None, None) => Ordering::Equal,
        }
    }
}

/// The text of a fully resolved field name, annotation, or symbol value. If the symbol has known
/// text (that is: the symbol is not `$0`), it will be stored as either a `String` or a shared
/// reference to text in a symbol table.
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone)]
pub struct Symbol {
    text: SymbolText,
}

impl Symbol {
    pub fn owned<I: Into<String>>(text: I) -> Symbol {
        Symbol {
            text: SymbolText::Owned(text.into()),
        }
    }

    pub fn shared(text: Arc<str>) -> Symbol {
        Symbol {
            text: SymbolText::Shared(text),
        }
    }

    pub fn unknown_text() -> Symbol {
        Symbol {
            text: SymbolText::Unknown,
        }
    }

    /// Converts this symbol into a shared one
    pub(crate) fn into_shared(self) -> Symbol {
        match self.text {
            SymbolText::Shared(text) => Symbol::shared(text),
            SymbolText::Owned(text) => Symbol::shared(text.into()),
            SymbolText::Unknown => Symbol::unknown_text(),
        }
    }

    pub fn text(&self) -> Option<&str> {
        self.text.text()
    }

    pub fn text_or_error(&self) -> IonResult<&str> {
        match self.text() {
            Some(text) => Ok(text),
            None => decoding_error("symbol has unknown text"),
        }
    }
}

impl IonEq for Symbol {
    fn ion_eq(&self, other: &Self) -> bool {
        self == other
    }
}

impl IonOrd for Symbol {
    fn ion_cmp(&self, other: &Self) -> Ordering {
        self.cmp(other)
    }
}

// We cannot use a blanket impl for AsRef<str> as that would prevent us from
// optimizing the From<String> case, a conversion which can be performed
// without cloning.

impl From<&str> for Symbol {
    fn from(text: &str) -> Self {
        Symbol::owned(text)
    }
}

impl From<String> for Symbol {
    fn from(text: String) -> Self {
        Symbol::owned(text)
    }
}

impl From<&String> for Symbol {
    fn from(text: &String) -> Self {
        text.as_str().into()
    }
}

impl<'a> From<&'a Symbol> for Symbol {
    fn from(text: &'a Symbol) -> Self {
        text.clone()
    }
}

impl<'a> From<SymbolRef<'a>> for Symbol {
    fn from(symbol_ref: SymbolRef<'a>) -> Self {
        symbol_ref.to_owned()
    }
}

impl Display for Symbol {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        match self.text() {
            None => write!(f, "$0"),
            Some(text) => write!(f, "'{text}'"),
        }
    }
}

impl<A: AsRef<str>> PartialEq<A> for Symbol {
    fn eq(&self, other: &A) -> bool {
        self.text()
            // If the symbol has known text, compare it to the provide text
            .map(|t| t == other.as_ref())
            // If there's no text, it's definitely not equivalent to the provided text
            .unwrap_or(false)
    }
}

impl PartialEq<Symbol> for String {
    fn eq(&self, other: &Symbol) -> bool {
        other.text().map(|t| t == self.as_str()).unwrap_or(false)
    }
}

impl PartialEq<Symbol> for &str {
    fn eq(&self, other: &Symbol) -> bool {
        other.text().map(|t| &t == self).unwrap_or(false)
    }
}

// Note that this method panics if the Symbol has unknown text! This is unfortunate but is required
// in order to allow a HashMap<Symbol, _> to do lookups with a &str instead of a &Symbol
impl Borrow<str> for Symbol {
    fn borrow(&self) -> &str {
        self.text()
            .expect("cannot borrow a &str from a Symbol with unknown text")
    }
}

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

    #[test]
    fn ordering_and_eq() {
        let mut symbols = vec![
            Symbol::owned("foo"),
            Symbol::shared(Arc::from("bar")),
            Symbol::shared(Arc::from("baz")),
            Symbol::owned("quux"),
        ];
        // Sort the list to demonstrate that our Ord implementation works.
        symbols.as_mut_slice().sort();
        // Equality testing doesn't depend on what kind of Symbol it is, just the text.
        // We can compare the sorted version of the vec above to this one and it will
        // be considered equal.
        let expected = vec![
            Symbol::owned("bar"),
            Symbol::owned("baz"),
            Symbol::owned("foo"),
            Symbol::owned("quux"),
        ];
        assert_eq!(symbols, expected)
    }
}