use alloc::{
    collections::BTreeMap,
    string::{String, ToString},
    sync::Arc,
    vec::Vec,
};

use super::*;

// SOURCE ID
// ================================================================================================

/// A [SourceId] represents the index/identifier associated with a unique source file in a
/// [SourceManager] implementation.
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct SourceId(u32);

impl Default for SourceId {
    fn default() -> Self {
        Self::UNKNOWN
    }
}

impl SourceId {
    pub const UNKNOWN: Self = Self(u32::MAX);

    /// Create a new [SourceId] from a `u32` value, but assert if the value is reserved
    pub fn new(id: u32) -> Self {
        assert_ne!(id, u32::MAX, "u32::MAX is a reserved value for SourceId::default()/UNKNOWN");

        Self(id)
    }

    /// Create a new [SourceId] from a raw `u32` value
    #[inline(always)]
    pub const fn new_unchecked(id: u32) -> Self {
        Self(id)
    }

    #[inline(always)]
    pub const fn to_usize(self) -> usize {
        self.0 as usize
    }

    #[inline(always)]
    pub const fn to_u32(self) -> u32 {
        self.0
    }

    pub const fn is_unknown(&self) -> bool {
        self.0 == u32::MAX
    }
}

impl TryFrom<usize> for SourceId {
    type Error = ();

    #[inline]
    fn try_from(id: usize) -> Result<Self, Self::Error> {
        match u32::try_from(id) {
            Ok(n) if n < u32::MAX => Ok(Self(n)),
            _ => Err(()),
        }
    }
}

// SOURCE MANAGER
// ================================================================================================

/// The set of errors which may be raised by a [SourceManager]
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum SourceManagerError {
    /// A [SourceId] was provided to a [SourceManager] which was allocated by a different
    /// [SourceManager]
    #[error("attempted to use an invalid source id")]
    InvalidSourceId,
    /// An attempt was made to read content using invalid byte indices
    #[error("attempted to read content out of bounds")]
    InvalidBounds,
    /// An attempt to load a source file failed due to an I/O error
    #[cfg(feature = "std")]
    #[error(transparent)]
    LoadFailed(#[from] std::io::Error),
}

pub trait SourceManager {
    /// Returns true if `file` is managed by this source manager
    fn is_manager_of(&self, file: &SourceFile) -> bool {
        match self.get(file.id()) {
            Ok(found) => core::ptr::addr_eq(Arc::as_ptr(&found), file),
            Err(_) => false,
        }
    }
    /// Copies `file` into this source manager (if not already managed by this manager).
    ///
    /// The returned source file is guaranteed to be owned by this manager.
    fn copy_into(&self, file: &SourceFile) -> Arc<SourceFile> {
        if let Ok(found) = self.get(file.id()) {
            if core::ptr::addr_eq(Arc::as_ptr(&found), file) {
                return found;
            }
        }
        self.load_from_raw_parts(file.name(), file.content().clone())
    }
    /// Load the given `content` into this [SourceManager] with `name`
    fn load(&self, name: &str, content: String) -> Arc<SourceFile> {
        let name = Arc::from(name.to_string().into_boxed_str());
        let content = SourceContent::new(Arc::clone(&name), content.into_boxed_str());
        self.load_from_raw_parts(name, content)
    }
    /// Load content into this [SourceManager] from raw [SourceFile] components
    fn load_from_raw_parts(&self, name: Arc<str>, content: SourceContent) -> Arc<SourceFile>;
    /// Get the [SourceFile] corresponding to `id`
    fn get(&self, id: SourceId) -> Result<Arc<SourceFile>, SourceManagerError>;
    /// Get the most recent [SourceFile] whose path is `path`
    fn get_by_path(&self, path: &str) -> Option<Arc<SourceFile>> {
        self.find(path).and_then(|id| self.get(id).ok())
    }
    /// Search for a source file named `name`, and return its [SourceId] if found.
    fn find(&self, name: &str) -> Option<SourceId>;
    /// Convert a [FileLineCol] to an equivalent [SourceSpan], if the referenced file is available
    fn file_line_col_to_span(&self, loc: FileLineCol) -> Option<SourceSpan>;
    /// Convert a [SourceSpan] to an equivalent [FileLineCol], if the span is valid
    fn file_line_col(&self, span: SourceSpan) -> Result<FileLineCol, SourceManagerError>;
    /// Convert a [Location] to an equivalent [SourceSpan], if the referenced file is available
    fn location_to_span(&self, loc: Location) -> Option<SourceSpan>;
    /// Convert a [SourceSpan] to an equivalent [Location], if the span is valid
    fn location(&self, span: SourceSpan) -> Result<Location, SourceManagerError>;
    /// Get the source associated with `id` as a string slice
    fn source(&self, id: SourceId) -> Result<&str, SourceManagerError>;
    /// Get the source corresponding to `span` as a string slice
    fn source_slice(&self, span: SourceSpan) -> Result<&str, SourceManagerError>;
}

impl<T: ?Sized + SourceManager> SourceManager for Arc<T> {
    #[inline(always)]
    fn is_manager_of(&self, file: &SourceFile) -> bool {
        (**self).is_manager_of(file)
    }
    #[inline(always)]
    fn copy_into(&self, file: &SourceFile) -> Arc<SourceFile> {
        (**self).copy_into(file)
    }
    #[inline(always)]
    fn load(&self, name: &str, content: String) -> Arc<SourceFile> {
        (**self).load(name, content)
    }
    #[inline(always)]
    fn load_from_raw_parts(&self, name: Arc<str>, content: SourceContent) -> Arc<SourceFile> {
        (**self).load_from_raw_parts(name, content)
    }
    #[inline(always)]
    fn get(&self, id: SourceId) -> Result<Arc<SourceFile>, SourceManagerError> {
        (**self).get(id)
    }
    #[inline(always)]
    fn get_by_path(&self, path: &str) -> Option<Arc<SourceFile>> {
        (**self).get_by_path(path)
    }
    #[inline(always)]
    fn find(&self, name: &str) -> Option<SourceId> {
        (**self).find(name)
    }
    #[inline(always)]
    fn file_line_col_to_span(&self, loc: FileLineCol) -> Option<SourceSpan> {
        (**self).file_line_col_to_span(loc)
    }
    #[inline(always)]
    fn file_line_col(&self, span: SourceSpan) -> Result<FileLineCol, SourceManagerError> {
        (**self).file_line_col(span)
    }
    #[inline(always)]
    fn location_to_span(&self, loc: Location) -> Option<SourceSpan> {
        (**self).location_to_span(loc)
    }
    #[inline(always)]
    fn location(&self, span: SourceSpan) -> Result<Location, SourceManagerError> {
        (**self).location(span)
    }
    #[inline(always)]
    fn source(&self, id: SourceId) -> Result<&str, SourceManagerError> {
        (**self).source(id)
    }
    #[inline(always)]
    fn source_slice(&self, span: SourceSpan) -> Result<&str, SourceManagerError> {
        (**self).source_slice(span)
    }
}

#[cfg(feature = "std")]
pub trait SourceManagerExt: SourceManager {
    /// Load the content of `path` into this [SourceManager], using the given path as the source
    /// name.
    fn load_file(&self, path: &std::path::Path) -> Result<Arc<SourceFile>, SourceManagerError> {
        let name = path.to_string_lossy();
        if let Some(existing) = self.get_by_path(name.as_ref()) {
            return Ok(existing);
        }

        let name = Arc::from(name.into_owned().into_boxed_str());
        let content = std::fs::read_to_string(path)
            .map(|s| SourceContent::new(Arc::clone(&name), s.into_boxed_str()))
            .map_err(SourceManagerError::LoadFailed)?;

        Ok(self.load_from_raw_parts(name, content))
    }
}

#[cfg(feature = "std")]
impl<T: ?Sized + SourceManager> SourceManagerExt for T {}

// DEFAULT SOURCE MANAGER
// ================================================================================================

use crate::utils::sync::RwLock;

#[derive(Default)]
pub struct DefaultSourceManager(RwLock<DefaultSourceManagerImpl>);
impl Clone for DefaultSourceManager {
    fn clone(&self) -> Self {
        let manager = self.0.read();
        Self(RwLock::new(manager.clone()))
    }
}

#[derive(Default, Clone)]
struct DefaultSourceManagerImpl {
    files: Vec<Arc<SourceFile>>,
    names: BTreeMap<Arc<str>, SourceId>,
}

impl DefaultSourceManagerImpl {
    fn insert(&mut self, name: Arc<str>, content: SourceContent) -> Arc<SourceFile> {
        // If we have previously inserted the same content with `name`, return the previously
        // inserted source id
        if let Some(file) = self.names.get(&name).copied().and_then(|id| {
            let file = &self.files[id.to_usize()];
            if file.as_str() == content.as_str() {
                Some(Arc::clone(file))
            } else {
                None
            }
        }) {
            return file;
        }
        let id = SourceId::try_from(self.files.len())
            .expect("system limit: source manager has exhausted its supply of source ids");
        let file = Arc::new(SourceFile::from_raw_parts(id, content));
        self.files.push(Arc::clone(&file));
        file
    }

    fn get(&self, id: SourceId) -> Result<Arc<SourceFile>, SourceManagerError> {
        self.files
            .get(id.to_usize())
            .cloned()
            .ok_or(SourceManagerError::InvalidSourceId)
    }

    fn get_by_path(&self, path: &str) -> Option<Arc<SourceFile>> {
        self.find(path).and_then(|id| self.get(id).ok())
    }

    fn find(&self, name: &str) -> Option<SourceId> {
        self.names.get(name).copied()
    }

    fn file_line_col_to_span(&self, loc: FileLineCol) -> Option<SourceSpan> {
        let file = self
            .names
            .get(&loc.path)
            .copied()
            .and_then(|id| self.files.get(id.to_usize()))?;
        file.line_column_to_span(loc.line, loc.column)
    }

    fn file_line_col(&self, span: SourceSpan) -> Result<FileLineCol, SourceManagerError> {
        self.files
            .get(span.source_id().to_usize())
            .ok_or(SourceManagerError::InvalidSourceId)
            .map(|file| file.location(span))
    }

    fn location_to_span(&self, loc: Location) -> Option<SourceSpan> {
        let file = self
            .names
            .get(&loc.path)
            .copied()
            .and_then(|id| self.files.get(id.to_usize()))?;

        let max_len = ByteIndex::from(file.as_str().len() as u32);
        if loc.start >= max_len || loc.end > max_len {
            return None;
        }

        Some(SourceSpan::new(file.id(), loc.start..loc.end))
    }

    fn location(&self, span: SourceSpan) -> Result<Location, SourceManagerError> {
        self.files
            .get(span.source_id().to_usize())
            .ok_or(SourceManagerError::InvalidSourceId)
            .map(|file| Location::new(file.name(), span.start(), span.end()))
    }
}

impl SourceManager for DefaultSourceManager {
    fn load_from_raw_parts(&self, name: Arc<str>, content: SourceContent) -> Arc<SourceFile> {
        let mut manager = self.0.write();
        manager.insert(name, content)
    }

    fn get(&self, id: SourceId) -> Result<Arc<SourceFile>, SourceManagerError> {
        let manager = self.0.read();
        manager.get(id)
    }

    fn get_by_path(&self, path: &str) -> Option<Arc<SourceFile>> {
        let manager = self.0.read();
        manager.get_by_path(path)
    }

    fn find(&self, name: &str) -> Option<SourceId> {
        let manager = self.0.read();
        manager.find(name)
    }

    fn file_line_col_to_span(&self, loc: FileLineCol) -> Option<SourceSpan> {
        let manager = self.0.read();
        manager.file_line_col_to_span(loc)
    }

    fn file_line_col(&self, span: SourceSpan) -> Result<FileLineCol, SourceManagerError> {
        let manager = self.0.read();
        manager.file_line_col(span)
    }

    fn location_to_span(&self, loc: Location) -> Option<SourceSpan> {
        let manager = self.0.read();
        manager.location_to_span(loc)
    }

    fn location(&self, span: SourceSpan) -> Result<Location, SourceManagerError> {
        let manager = self.0.read();
        manager.location(span)
    }

    fn source(&self, id: SourceId) -> Result<&str, SourceManagerError> {
        let manager = self.0.read();
        let ptr = manager
            .files
            .get(id.to_usize())
            .ok_or(SourceManagerError::InvalidSourceId)
            .map(|file| file.as_str() as *const str)?;
        drop(manager);
        // SAFETY: Because the lifetime of the returned reference is bound to the manager, and
        // because we can only ever add files, not modify/remove them, this is safe. Exclusive
        // access to the manager does _not_ mean exclusive access to the contents of previously
        // added source files
        Ok(unsafe { &*ptr })
    }

    fn source_slice(&self, span: SourceSpan) -> Result<&str, SourceManagerError> {
        self.source(span.source_id())?
            .get(span.into_slice_index())
            .ok_or(SourceManagerError::InvalidBounds)
    }
}