use std::borrow::{Borrow, Cow};
use std::hash::{Hash, Hasher};
use std::os::raw::c_void;
use std::string::String as StdString;
use std::{fmt, slice, str};

#[cfg(feature = "serialize")]
use {
    serde::ser::{Serialize, Serializer},
    std::result::Result as StdResult,
};

use crate::error::{Error, Result};
use crate::types::LuaRef;

/// Handle to an internal Lua string.
///
/// Unlike Rust strings, Lua strings may not be valid UTF-8.
#[derive(Clone)]
pub struct String<'lua>(pub(crate) LuaRef<'lua>);

/// Owned handle to an internal Lua string.
///
/// The owned handle holds a *strong* reference to the current Lua instance.
/// Be warned, if you place it into a Lua type (eg. [`UserData`] or a Rust callback), it is *very easy*
/// to accidentally cause reference cycles that would prevent destroying Lua instance.
///
/// [`UserData`]: crate::UserData
#[cfg(feature = "unstable")]
#[cfg_attr(docsrs, doc(cfg(feature = "unstable")))]
#[derive(Clone)]
pub struct OwnedString(pub(crate) crate::types::LuaOwnedRef);

#[cfg(feature = "unstable")]
impl OwnedString {
    /// Get borrowed handle to the underlying Lua string.
    #[cfg_attr(feature = "send", allow(unused))]
    pub const fn to_ref(&self) -> String {
        String(self.0.to_ref())
    }
}

impl<'lua> String<'lua> {
    /// Unsafe because we omit type checks.
    #[inline]
    pub unsafe fn from_ref(r: LuaRef<'lua>) -> Self {
        Self(r)
    }

    pub fn as_raw_ref(&self) -> &LuaRef<'lua> {
        &self.0
    }

    /// Get a `&str` slice if the Lua string is valid UTF-8.
    ///
    /// # Examples
    ///
    /// ```
    /// # use mlua::{Lua, Result, String};
    /// # fn main() -> Result<()> {
    /// # let lua = Lua::new();
    /// let globals = lua.globals();
    ///
    /// let version: String = globals.get("_VERSION")?;
    /// assert!(version.to_str()?.contains("Lua"));
    ///
    /// let non_utf8: String = lua.load(r#"  "test\255"  "#).eval()?;
    /// assert!(non_utf8.to_str().is_err());
    /// # Ok(())
    /// # }
    /// ```
    #[inline]
    pub fn to_str(&self) -> Result<&str> {
        str::from_utf8(self.as_bytes()).map_err(|e| Error::FromLuaConversionError {
            from: "string",
            to: "&str",
            message: Some(e.to_string()),
        })
    }

    /// Converts this string to a [`Cow<str>`].
    ///
    /// Any non-Unicode sequences are replaced with [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD].
    ///
    /// [U+FFFD]: std::char::REPLACEMENT_CHARACTER
    ///
    /// # Examples
    ///
    /// ```
    /// # use mlua::{Lua, Result};
    /// # fn main() -> Result<()> {
    /// let lua = Lua::new();
    ///
    /// let s = lua.create_string(b"test\xff")?;
    /// assert_eq!(s.to_string_lossy(), "test\u{fffd}");
    /// # Ok(())
    /// # }
    /// ```
    #[inline]
    pub fn to_string_lossy(&self) -> Cow<'_, str> {
        StdString::from_utf8_lossy(self.as_bytes())
    }

    /// Get the bytes that make up this string.
    ///
    /// The returned slice will not contain the terminating nul byte, but will contain any nul
    /// bytes embedded into the Lua string.
    ///
    /// # Examples
    ///
    /// ```
    /// # use mlua::{Lua, Result, String};
    /// # fn main() -> Result<()> {
    /// # let lua = Lua::new();
    /// let non_utf8: String = lua.load(r#"  "test\255"  "#).eval()?;
    /// assert!(non_utf8.to_str().is_err());    // oh no :(
    /// assert_eq!(non_utf8.as_bytes(), &b"test\xff"[..]);
    /// # Ok(())
    /// # }
    /// ```
    #[inline]
    pub fn as_bytes(&self) -> &[u8] {
        let nulled = self.as_bytes_with_nul();
        &nulled[..nulled.len() - 1]
    }

    /// Get the bytes that make up this string, including the trailing nul byte.
    pub fn as_bytes_with_nul(&self) -> &[u8] {
        let ref_thread = self.0.lua.ref_thread();
        unsafe {
            mlua_debug_assert!(
                ffi::lua_type(ref_thread, self.0.index) == ffi::LUA_TSTRING,
                "string ref is not string type"
            );

            let mut size = 0;
            // This will not trigger a 'm' error, because the reference is guaranteed to be of
            // string type
            let data = ffi::lua_tolstring(ref_thread, self.0.index, &mut size);

            slice::from_raw_parts(data as *const u8, size + 1)
        }
    }

    /// Converts the string to a generic C pointer.
    ///
    /// There is no way to convert the pointer back to its original value.
    ///
    /// Typically this function is used only for hashing and debug information.
    #[inline]
    pub fn to_pointer(&self) -> *const c_void {
        self.0.to_pointer()
    }

    /// Convert this handle to owned version.
    #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
    #[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
    #[inline]
    pub fn into_owned(self) -> OwnedString {
        OwnedString(self.0.into_owned())
    }
}

impl<'lua> fmt::Debug for String<'lua> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let bytes = self.as_bytes();
        // Check if the string is valid utf8
        if let Ok(s) = str::from_utf8(bytes) {
            return s.fmt(f);
        }

        // Format as bytes
        write!(f, "b\"")?;
        for &b in bytes {
            // https://doc.rust-lang.org/reference/tokens.html#byte-escapes
            match b {
                b'\n' => write!(f, "\\n")?,
                b'\r' => write!(f, "\\r")?,
                b'\t' => write!(f, "\\t")?,
                b'\\' | b'"' => write!(f, "\\{}", b as char)?,
                b'\0' => write!(f, "\\0")?,
                // ASCII printable
                0x20..=0x7e => write!(f, "{}", b as char)?,
                _ => write!(f, "\\x{b:02x}")?,
            }
        }
        write!(f, "\"")?;

        Ok(())
    }
}

impl<'lua> AsRef<[u8]> for String<'lua> {
    fn as_ref(&self) -> &[u8] {
        self.as_bytes()
    }
}

impl<'lua> Borrow<[u8]> for String<'lua> {
    fn borrow(&self) -> &[u8] {
        self.as_bytes()
    }
}

// Lua strings are basically &[u8] slices, so implement PartialEq for anything resembling that.
//
// This makes our `String` comparable with `Vec<u8>`, `[u8]`, `&str`, `String` and `mlua::String`
// itself.
//
// The only downside is that this disallows a comparison with `Cow<str>`, as that only implements
// `AsRef<str>`, which collides with this impl. Requiring `AsRef<str>` would fix that, but limit us
// in other ways.
impl<'lua, T> PartialEq<T> for String<'lua>
where
    T: AsRef<[u8]> + ?Sized,
{
    fn eq(&self, other: &T) -> bool {
        self.as_bytes() == other.as_ref()
    }
}

impl<'lua> Eq for String<'lua> {}

impl<'lua> Hash for String<'lua> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.as_bytes().hash(state);
    }
}

#[cfg(feature = "serialize")]
impl<'lua> Serialize for String<'lua> {
    fn serialize<S>(&self, serializer: S) -> StdResult<S::Ok, S::Error>
    where
        S: Serializer,
    {
        match self.to_str() {
            Ok(s) => serializer.serialize_str(s),
            Err(_) => serializer.serialize_bytes(self.as_bytes()),
        }
    }
}

// Additional shortcuts
#[cfg(feature = "unstable")]
impl OwnedString {
    /// Get a `&str` slice if the Lua string is valid UTF-8.
    ///
    /// This is a shortcut for [`String::to_str()`].
    #[inline]
    pub fn to_str(&self) -> Result<&str> {
        let s = self.to_ref();
        // Reattach lifetime to &self
        unsafe { std::mem::transmute(s.to_str()) }
    }

    /// Get the bytes that make up this string.
    ///
    /// This is a shortcut for [`String::as_bytes()`].
    #[inline]
    pub fn as_bytes(&self) -> &[u8] {
        let s = self.to_ref();
        // Reattach lifetime to &self
        unsafe { std::mem::transmute(s.as_bytes()) }
    }
}

#[cfg(feature = "unstable")]
impl fmt::Debug for OwnedString {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.to_ref().fmt(f)
    }
}

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

    static_assertions::assert_not_impl_any!(String: Send);
}