use std::borrow::Cow;
use std::ffi::CString;

use crate::error::{Error, Result};
use crate::ffi;
use crate::function::Function;
use crate::lua::Lua;
use crate::value::{FromLuaMulti, ToLua, ToLuaMulti, Value};

#[cfg(feature = "async")]
use {futures_core::future::LocalBoxFuture, futures_util::future};

/// Trait for types [loadable by Lua] and convertible to a [`Chunk`]
///
/// [loadable by Lua]: https://www.lua.org/manual/5.4/manual.html#3.3.2
/// [`Chunk`]: crate::Chunk
pub trait AsChunk<'lua> {
    /// Returns chunk data (can be text or binary)
    fn source(&self) -> &[u8];

    /// Returns optional chunk name
    fn name(&self) -> Option<CString> {
        None
    }

    /// Returns optional chunk [environment]
    ///
    /// [environment]: https://www.lua.org/manual/5.4/manual.html#2.2
    fn env(&self, _lua: &'lua Lua) -> Result<Option<Value<'lua>>> {
        Ok(None)
    }

    /// Returns optional chunk mode (text or binary)
    fn mode(&self) -> Option<ChunkMode> {
        None
    }
}

impl<'lua, T: AsRef<[u8]> + ?Sized> AsChunk<'lua> for T {
    fn source(&self) -> &[u8] {
        self.as_ref()
    }
}

/// Returned from [`Lua::load`] and is used to finalize loading and executing Lua main chunks.
///
/// [`Lua::load`]: crate::Lua::load
#[must_use = "`Chunk`s do nothing unless one of `exec`, `eval`, `call`, or `into_function` are called on them"]
pub struct Chunk<'lua, 'a> {
    pub(crate) lua: &'lua Lua,
    pub(crate) source: Cow<'a, [u8]>,
    pub(crate) name: Option<CString>,
    pub(crate) env: Result<Option<Value<'lua>>>,
    pub(crate) mode: Option<ChunkMode>,
    #[cfg(feature = "luau")]
    pub(crate) compiler: Option<Compiler>,
}

/// Represents chunk mode (text or binary).
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum ChunkMode {
    Text,
    Binary,
}

/// Luau compiler
#[cfg(feature = "luau")]
#[derive(Clone, Copy, Debug)]
pub struct Compiler {
    optimization_level: u8,
    debug_level: u8,
    coverage_level: u8,
}

#[cfg(feature = "luau")]
impl Default for Compiler {
    fn default() -> Self {
        // Defaults are taken from luacode.h
        Compiler {
            optimization_level: 1,
            debug_level: 1,
            coverage_level: 0,
        }
    }
}

#[cfg(feature = "luau")]
impl Compiler {
    /// Creates Luau compiler instance with default options
    pub fn new() -> Self {
        Compiler::default()
    }

    /// Sets Luau compiler optimization level.
    ///
    /// Possible values:
    /// 0 - no optimization
    /// 1 - baseline optimization level that doesn't prevent debuggability (default)
    /// 2 - includes optimizations that harm debuggability such as inlining
    #[cfg(feature = "luau")]
    pub fn set_optimization_level(mut self, level: u8) -> Self {
        self.optimization_level = level;
        self
    }

    /// Sets Luau compiler debug level.
    ///
    /// Possible values:
    /// 0 - no debugging support
    /// 1 - line info & function names only; sufficient for backtraces (default)
    /// 2 - full debug info with local & upvalue names; necessary for debugger
    #[cfg(feature = "luau")]
    pub fn set_debug_level(mut self, level: u8) -> Self {
        self.debug_level = level;
        self
    }

    /// Sets Luau compiler code coverage level.
    ///
    /// Possible values:
    /// 0 - no code coverage support (default)
    /// 1 - statement coverage
    /// 2 - statement and expression coverage (verbose)
    #[cfg(feature = "luau")]
    pub fn set_coverage_level(mut self, level: u8) -> Self {
        self.coverage_level = level;
        self
    }

    /// Compiles the `source` into bytecode.
    pub fn compile(&self, source: impl AsRef<[u8]>) -> Vec<u8> {
        use std::os::raw::c_int;
        use std::ptr;

        unsafe {
            let options = ffi::lua_CompileOptions {
                optimizationLevel: self.optimization_level as c_int,
                debugLevel: self.debug_level as c_int,
                coverageLevel: self.coverage_level as c_int,
                vectorLib: ptr::null(),
                vectorCtor: ptr::null(),
                mutableGlobals: ptr::null_mut(),
            };
            ffi::luau_compile(source.as_ref(), options)
        }
    }
}

impl<'lua, 'a> Chunk<'lua, 'a> {
    /// Sets the name of this chunk, which results in more informative error traces.
    pub fn set_name<S: AsRef<[u8]> + ?Sized>(mut self, name: &S) -> Result<Chunk<'lua, 'a>> {
        let name =
            CString::new(name.as_ref().to_vec()).map_err(|e| Error::ToLuaConversionError {
                from: "&str",
                to: "string",
                message: Some(e.to_string()),
            })?;
        self.name = Some(name);
        Ok(self)
    }

    /// Sets the first upvalue (`_ENV`) of the loaded chunk to the given value.
    ///
    /// Lua main chunks always have exactly one upvalue, and this upvalue is used as the `_ENV`
    /// variable inside the chunk. By default this value is set to the global environment.
    ///
    /// Calling this method changes the `_ENV` upvalue to the value provided, and variables inside
    /// the chunk will refer to the given environment rather than the global one.
    ///
    /// All global variables (including the standard library!) are looked up in `_ENV`, so it may be
    /// necessary to populate the environment in order for scripts using custom environments to be
    /// useful.
    pub fn set_environment<V: ToLua<'lua>>(mut self, env: V) -> Result<Chunk<'lua, 'a>> {
        // Prefer to propagate errors here and wrap to `Ok`
        self.env = Ok(Some(env.to_lua(self.lua)?));
        Ok(self)
    }

    /// Sets whether the chunk is text or binary (autodetected by default).
    ///
    /// Be aware, Lua does not check the consistency of the code inside binary chunks.
    /// Running maliciously crafted bytecode can crash the interpreter.
    pub fn set_mode(mut self, mode: ChunkMode) -> Chunk<'lua, 'a> {
        self.mode = Some(mode);
        self
    }

    /// Sets Luau compiler optimization level.
    ///
    /// See [`Compiler::set_optimization_level`] for details.
    ///
    /// Requires `feature = "luau`
    #[cfg(feature = "luau")]
    pub fn set_optimization_level(mut self, level: u8) -> Self {
        self.compiler
            .get_or_insert_with(Default::default)
            .set_optimization_level(level);
        self
    }

    /// Sets Luau compiler debug level.
    ///
    /// See [`Compiler::set_debug_level`] for details.
    ///
    /// Requires `feature = "luau`
    #[cfg(feature = "luau")]
    pub fn set_debug_level(mut self, level: u8) -> Self {
        self.compiler
            .get_or_insert_with(Default::default)
            .set_debug_level(level);
        self
    }

    /// Sets Luau compiler code coverage level.
    ///
    /// See [`Compiler::set_coverage_level`] for details.
    ///
    /// Requires `feature = "luau`
    #[cfg(feature = "luau")]
    pub fn set_coverage_level(mut self, level: u8) -> Self {
        self.compiler
            .get_or_insert_with(Default::default)
            .set_coverage_level(level);
        self
    }

    /// Compiles the chunk and changes mode to binary.
    ///
    /// It does nothing if the chunk is already binary.
    #[cfg(feature = "luau")]
    #[doc(hidden)]
    pub fn compile(mut self) -> Self {
        if self.detect_mode() == ChunkMode::Text {
            let data = self
                .compiler
                .unwrap_or_default()
                .compile(self.source.as_ref());
            self.mode = Some(ChunkMode::Binary);
            self.source = Cow::Owned(data);
        }
        self
    }

    /// Execute this chunk of code.
    ///
    /// This is equivalent to calling the chunk function with no arguments and no return values.
    pub fn exec(self) -> Result<()> {
        self.call(())?;
        Ok(())
    }

    /// Asynchronously execute this chunk of code.
    ///
    /// See [`exec`] for more details.
    ///
    /// Requires `feature = "async"`
    ///
    /// [`exec`]: #method.exec
    #[cfg(feature = "async")]
    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
    pub fn exec_async<'fut>(self) -> LocalBoxFuture<'fut, Result<()>>
    where
        'lua: 'fut,
    {
        self.call_async(())
    }

    /// Evaluate the chunk as either an expression or block.
    ///
    /// If the chunk can be parsed as an expression, this loads and executes the chunk and returns
    /// the value that it evaluates to. Otherwise, the chunk is interpreted as a block as normal,
    /// and this is equivalent to calling `exec`.
    pub fn eval<R: FromLuaMulti<'lua>>(self) -> Result<R> {
        // Bytecode is always interpreted as a statement.
        // For source code, first try interpreting the lua as an expression by adding
        // "return", then as a statement. This is the same thing the
        // actual lua repl does.
        if self.detect_mode() == ChunkMode::Binary {
            self.call(())
        } else if let Ok(function) = self.to_expression() {
            function.call(())
        } else {
            self.call(())
        }
    }

    /// Asynchronously evaluate the chunk as either an expression or block.
    ///
    /// See [`eval`] for more details.
    ///
    /// Requires `feature = "async"`
    ///
    /// [`eval`]: #method.eval
    #[cfg(feature = "async")]
    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
    pub fn eval_async<'fut, R>(self) -> LocalBoxFuture<'fut, Result<R>>
    where
        'lua: 'fut,
        R: FromLuaMulti<'lua> + 'fut,
    {
        if self.detect_mode() == ChunkMode::Binary {
            self.call_async(())
        } else if let Ok(function) = self.to_expression() {
            function.call_async(())
        } else {
            self.call_async(())
        }
    }

    /// Load the chunk function and call it with the given arguments.
    ///
    /// This is equivalent to `into_function` and calling the resulting function.
    pub fn call<A: ToLuaMulti<'lua>, R: FromLuaMulti<'lua>>(self, args: A) -> Result<R> {
        self.into_function()?.call(args)
    }

    /// Load the chunk function and asynchronously call it with the given arguments.
    ///
    /// See [`call`] for more details.
    ///
    /// Requires `feature = "async"`
    ///
    /// [`call`]: #method.call
    #[cfg(feature = "async")]
    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
    pub fn call_async<'fut, A, R>(self, args: A) -> LocalBoxFuture<'fut, Result<R>>
    where
        'lua: 'fut,
        A: ToLuaMulti<'lua>,
        R: FromLuaMulti<'lua> + 'fut,
    {
        match self.into_function() {
            Ok(func) => func.call_async(args),
            Err(e) => Box::pin(future::err(e)),
        }
    }

    /// Load this chunk into a regular `Function`.
    ///
    /// This simply compiles the chunk without actually executing it.
    pub fn into_function(self) -> Result<Function<'lua>> {
        #[cfg(not(feature = "luau"))]
        let self_ = self;
        #[cfg(feature = "luau")]
        let self_ = match self.compiler {
            // We don't need to compile source if no compiler options set
            Some(_) => self.compile(),
            _ => self,
        };

        self_.lua.load_chunk(
            self_.source.as_ref(),
            self_.name.as_ref(),
            self_.env()?,
            self_.mode,
        )
    }

    fn env(&self) -> Result<Option<Value<'lua>>> {
        self.env.clone()
    }

    fn expression_source(&self) -> Vec<u8> {
        let mut buf = Vec::with_capacity(b"return ".len() + self.source.len());
        buf.extend(b"return ");
        buf.extend(self.source.as_ref());
        buf
    }

    fn to_expression(&self) -> Result<Function<'lua>> {
        // We assume that mode is Text
        let source = self.expression_source();
        // We don't need to compile source if no compiler options set
        #[cfg(feature = "luau")]
        let source = self.compiler.map(|c| c.compile(&source)).unwrap_or(source);

        self.lua
            .load_chunk(&source, self.name.as_ref(), self.env()?, None)
    }

    fn detect_mode(&self) -> ChunkMode {
        match self.mode {
            Some(mode) => mode,
            None => {
                #[cfg(not(feature = "luau"))]
                if self.source.starts_with(ffi::LUA_SIGNATURE) {
                    return ChunkMode::Binary;
                }
                #[cfg(feature = "luau")]
                if self.source[0] < b'\n' {
                    return ChunkMode::Binary;
                }
                ChunkMode::Text
            }
        }
    }
}