use alloc::borrow::Cow;
use alloc::string::String;
use core::iter;

use crate::{maybe_small, Error, Function, InlinedFunction, ResUnit};

/// A source location.
pub struct Location<'a> {
    /// The file name.
    pub file: Option<&'a str>,
    /// The line number.
    pub line: Option<u32>,
    /// The column number.
    ///
    /// A value of `Some(0)` indicates the left edge.
    pub column: Option<u32>,
}

/// A function frame.
pub struct Frame<'ctx, R: gimli::Reader> {
    /// The DWARF unit offset corresponding to the DIE of the function.
    pub dw_die_offset: Option<gimli::UnitOffset<R::Offset>>,
    /// The name of the function.
    pub function: Option<FunctionName<R>>,
    /// The source location corresponding to this frame.
    pub location: Option<Location<'ctx>>,
}

/// An iterator over function frames.
pub struct FrameIter<'ctx, R>(FrameIterState<'ctx, R>)
where
    R: gimli::Reader;

enum FrameIterState<'ctx, R>
where
    R: gimli::Reader,
{
    Empty,
    Location(Option<Location<'ctx>>),
    Frames(FrameIterFrames<'ctx, R>),
}

struct FrameIterFrames<'ctx, R>
where
    R: gimli::Reader,
{
    unit: &'ctx ResUnit<R>,
    sections: &'ctx gimli::Dwarf<R>,
    function: &'ctx Function<R>,
    inlined_functions: iter::Rev<maybe_small::IntoIter<&'ctx InlinedFunction<R>>>,
    next: Option<Location<'ctx>>,
}

impl<'ctx, R> FrameIter<'ctx, R>
where
    R: gimli::Reader + 'ctx,
{
    pub(crate) fn new_empty() -> Self {
        FrameIter(FrameIterState::Empty)
    }

    pub(crate) fn new_location(location: Location<'ctx>) -> Self {
        FrameIter(FrameIterState::Location(Some(location)))
    }

    pub(crate) fn new_frames(
        unit: &'ctx ResUnit<R>,
        sections: &'ctx gimli::Dwarf<R>,
        function: &'ctx Function<R>,
        inlined_functions: maybe_small::Vec<&'ctx InlinedFunction<R>>,
        location: Option<Location<'ctx>>,
    ) -> Self {
        FrameIter(FrameIterState::Frames(FrameIterFrames {
            unit,
            sections,
            function,
            inlined_functions: inlined_functions.into_iter().rev(),
            next: location,
        }))
    }

    /// Advances the iterator and returns the next frame.
    #[allow(clippy::should_implement_trait)]
    pub fn next(&mut self) -> Result<Option<Frame<'ctx, R>>, Error> {
        let frames = match &mut self.0 {
            FrameIterState::Empty => return Ok(None),
            FrameIterState::Location(location) => {
                // We can't move out of a mutable reference, so use `take` instead.
                let location = location.take();
                self.0 = FrameIterState::Empty;
                return Ok(Some(Frame {
                    dw_die_offset: None,
                    function: None,
                    location,
                }));
            }
            FrameIterState::Frames(frames) => frames,
        };

        let loc = frames.next.take();
        let func = match frames.inlined_functions.next() {
            Some(func) => func,
            None => {
                let frame = Frame {
                    dw_die_offset: Some(frames.function.dw_die_offset),
                    function: frames.function.name.clone().map(|name| FunctionName {
                        name,
                        language: frames.unit.lang,
                    }),
                    location: loc,
                };
                self.0 = FrameIterState::Empty;
                return Ok(Some(frame));
            }
        };

        let mut next = Location {
            file: None,
            line: if func.call_line != 0 {
                Some(func.call_line)
            } else {
                None
            },
            column: if func.call_column != 0 {
                Some(func.call_column)
            } else {
                None
            },
        };
        if let Some(call_file) = func.call_file {
            if let Some(lines) = frames.unit.parse_lines(frames.sections)? {
                next.file = lines.file(call_file);
            }
        }
        frames.next = Some(next);

        Ok(Some(Frame {
            dw_die_offset: Some(func.dw_die_offset),
            function: func.name.clone().map(|name| FunctionName {
                name,
                language: frames.unit.lang,
            }),
            location: loc,
        }))
    }
}

#[cfg(feature = "fallible-iterator")]
impl<'ctx, R> fallible_iterator::FallibleIterator for FrameIter<'ctx, R>
where
    R: gimli::Reader + 'ctx,
{
    type Item = Frame<'ctx, R>;
    type Error = Error;

    #[inline]
    fn next(&mut self) -> Result<Option<Frame<'ctx, R>>, Error> {
        self.next()
    }
}

/// A function name.
pub struct FunctionName<R: gimli::Reader> {
    /// The name of the function.
    pub name: R,
    /// The language of the compilation unit containing this function.
    pub language: Option<gimli::DwLang>,
}

impl<R: gimli::Reader> FunctionName<R> {
    /// The raw name of this function before demangling.
    pub fn raw_name(&self) -> Result<Cow<'_, str>, Error> {
        self.name.to_string_lossy()
    }

    /// The name of this function after demangling (if applicable).
    pub fn demangle(&self) -> Result<Cow<'_, str>, Error> {
        self.raw_name().map(|x| demangle_auto(x, self.language))
    }
}

/// Demangle a symbol name using the demangling scheme for the given language.
///
/// Returns `None` if demangling failed or is not required.
#[allow(unused_variables)]
pub fn demangle(name: &str, language: gimli::DwLang) -> Option<String> {
    match language {
        #[cfg(feature = "rustc-demangle")]
        gimli::DW_LANG_Rust => rustc_demangle::try_demangle(name)
            .ok()
            .as_ref()
            .map(|x| format!("{:#}", x)),
        #[cfg(feature = "cpp_demangle")]
        gimli::DW_LANG_C_plus_plus
        | gimli::DW_LANG_C_plus_plus_03
        | gimli::DW_LANG_C_plus_plus_11
        | gimli::DW_LANG_C_plus_plus_14 => cpp_demangle::Symbol::new(name)
            .ok()
            .and_then(|x| x.demangle(&Default::default()).ok()),
        _ => None,
    }
}

/// Apply 'best effort' demangling of a symbol name.
///
/// If `language` is given, then only the demangling scheme for that language
/// is used.
///
/// If `language` is `None`, then heuristics are used to determine how to
/// demangle the name. Currently, these heuristics are very basic.
///
/// If demangling fails or is not required, then `name` is returned unchanged.
pub fn demangle_auto(name: Cow<'_, str>, language: Option<gimli::DwLang>) -> Cow<'_, str> {
    match language {
        Some(language) => demangle(name.as_ref(), language),
        None => demangle(name.as_ref(), gimli::DW_LANG_Rust)
            .or_else(|| demangle(name.as_ref(), gimli::DW_LANG_C_plus_plus)),
    }
    .map(Cow::from)
    .unwrap_or(name)
}