use core::fmt;
use core::marker::PhantomData;
use core::mem::take;

use crate::alloc::{self, Vec};
use crate::ast::{Span, Spanned};
use crate::compile;
#[cfg(feature = "std")]
use crate::compile::FileSourceLoader as DefaultSourceLoader;
#[cfg(not(feature = "std"))]
use crate::compile::NoopSourceLoader as DefaultSourceLoader;
use crate::compile::{CompileVisitor, Located, MetaError, Options, Pool, SourceLoader};
use crate::runtime::unit::{DefaultStorage, UnitEncoder};
use crate::runtime::Unit;
use crate::{Context, Diagnostics, SourceId, Sources};

/// Error raised when we failed to load sources.
///
/// Look at the passed in [Diagnostics] instance for details.
#[derive(Default, Debug)]
#[non_exhaustive]
pub struct BuildError {
    kind: BuildErrorKind,
}

impl From<alloc::Error> for BuildError {
    fn from(error: alloc::Error) -> Self {
        Self {
            kind: BuildErrorKind::Alloc(error),
        }
    }
}

#[derive(Default, Debug)]
enum BuildErrorKind {
    #[default]
    Default,
    Alloc(alloc::Error),
}

impl fmt::Display for BuildError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match &self.kind {
            BuildErrorKind::Default => write!(
                f,
                "Failed to build rune sources (see diagnostics for details)"
            ),
            BuildErrorKind::Alloc(error) => error.fmt(f),
        }
    }
}

cfg_std! {
    impl std::error::Error for BuildError {
        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
            match &self.kind {
                BuildErrorKind::Alloc(error) => Some(error),
                _ => None,
            }
        }
    }
}

/// Entry point to building [Sources] of Rune using the default unit storage.
///
/// Uses the [Source::name](crate::Source::name) when generating diagnostics to
/// reference the file.
///
/// # Examples
///
/// Note: these must be built with the `emit` feature enabled (default) to give
/// access to `rune::termcolor`.
///
/// ```
/// use rune::termcolor::{ColorChoice, StandardStream};
/// use rune::{Context, Source, Vm};
/// use std::sync::Arc;
///
/// let context = Context::with_default_modules()?;
/// let runtime = Arc::new(context.runtime()?);
///
/// let mut sources = rune::Sources::new();
///
/// sources.insert(Source::new("entry", r#"
/// pub fn main() {
///     println("Hello World");
/// }
/// "#)?)?;
///
/// let mut diagnostics = rune::Diagnostics::new();
///
/// let result = rune::prepare(&mut sources)
///     .with_context(&context)
///     .with_diagnostics(&mut diagnostics)
///     .build();
///
/// if !diagnostics.is_empty() {
///     let mut writer = StandardStream::stderr(ColorChoice::Always);
///     diagnostics.emit(&mut writer, &sources)?;
/// }
///
/// let unit = result?;
/// let unit = Arc::new(unit);
/// let vm = Vm::new(runtime, unit);
/// # Ok::<_, rune::support::Error>(())
/// ```
pub fn prepare(sources: &mut Sources) -> Build<'_, DefaultStorage> {
    prepare_with(sources)
}

/// Prepare with a custom unit storage.
pub fn prepare_with<S>(sources: &mut Sources) -> Build<'_, S>
where
    S: UnitEncoder,
{
    Build {
        sources,
        context: None,
        diagnostics: None,
        options: None,
        visitors: Vec::new(),
        source_loader: None,
        _unit_storage: PhantomData,
    }
}

/// High level helper for setting up a build of Rune sources into a [Unit].
pub struct Build<'a, S> {
    sources: &'a mut Sources,
    context: Option<&'a Context>,
    diagnostics: Option<&'a mut Diagnostics>,
    options: Option<&'a Options>,
    visitors: Vec<&'a mut dyn compile::CompileVisitor>,
    source_loader: Option<&'a mut dyn SourceLoader>,
    _unit_storage: PhantomData<S>,
}

/// Wraps a collection of CompileVisitor
struct CompileVisitorGroup<'a> {
    visitors: Vec<&'a mut dyn compile::CompileVisitor>,
}

impl<'a> compile::CompileVisitor for CompileVisitorGroup<'a> {
    fn register_meta(&mut self, meta: compile::MetaRef<'_>) -> Result<(), MetaError> {
        for v in self.visitors.iter_mut() {
            v.register_meta(meta)?;
        }

        Ok(())
    }

    fn visit_meta(
        &mut self,
        location: &dyn Located,
        meta: compile::MetaRef<'_>,
    ) -> Result<(), MetaError> {
        for v in self.visitors.iter_mut() {
            v.visit_meta(location, meta)?;
        }

        Ok(())
    }

    fn visit_variable_use(
        &mut self,
        source_id: SourceId,
        var_span: &dyn Spanned,
        span: &dyn Spanned,
    ) -> Result<(), MetaError> {
        for v in self.visitors.iter_mut() {
            v.visit_variable_use(source_id, var_span, span)?;
        }

        Ok(())
    }

    fn visit_mod(&mut self, location: &dyn Located) -> Result<(), MetaError> {
        for v in self.visitors.iter_mut() {
            v.visit_mod(location)?;
        }

        Ok(())
    }

    fn visit_doc_comment(
        &mut self,
        location: &dyn Located,
        item: &compile::Item,
        hash: crate::Hash,
        doc: &str,
    ) -> Result<(), MetaError> {
        for v in self.visitors.iter_mut() {
            v.visit_doc_comment(location, item, hash, doc)?;
        }

        Ok(())
    }

    fn visit_field_doc_comment(
        &mut self,
        location: &dyn Located,
        item: &compile::Item,
        hash: crate::Hash,
        field: &str,
        doc: &str,
    ) -> Result<(), MetaError> {
        for v in self.visitors.iter_mut() {
            v.visit_field_doc_comment(location, item, hash, field, doc)?;
        }

        Ok(())
    }
}

impl<'a, S> Build<'a, S> {
    /// Modify the current [Build] to use the given [Context] while building.
    ///
    /// If unspecified the empty context constructed with [Context::new] will be
    /// used. Since this counts as building without a context,
    /// [Vm::without_context][crate::runtime::Vm] can be used when running the
    /// produced [Unit].
    #[inline]
    pub fn with_context(mut self, context: &'a Context) -> Self {
        self.context = Some(context);
        self
    }

    /// Modify the current [Build] to use the given [Diagnostics] collection.
    #[inline]
    pub fn with_diagnostics(mut self, diagnostics: &'a mut Diagnostics) -> Self {
        self.diagnostics = Some(diagnostics);
        self
    }

    /// Modify the current [Build] to use the given [Options].
    #[inline]
    pub fn with_options(mut self, options: &'a Options) -> Self {
        self.options = Some(options);
        self
    }

    /// Modify the current [Build] to configure the given [CompileVisitor].
    ///
    /// A compile visitor allows for custom collecting of compile-time metadata.
    /// Like if you want to collect every function that is discovered in the
    /// project.
    #[inline]
    pub fn with_visitor(mut self, visitor: &'a mut dyn CompileVisitor) -> alloc::Result<Self> {
        self.visitors.try_push(visitor)?;
        Ok(self)
    }

    /// Modify the current [Build] to configure the given [SourceLoader].
    ///
    /// Source loaders are used to determine how sources are loaded externally
    /// from the current file (as is neede when a module is imported).
    #[inline]
    pub fn with_source_loader(mut self, source_loader: &'a mut dyn SourceLoader) -> Self {
        self.source_loader = Some(source_loader);
        self
    }

    /// Build a [`Unit`] with the current configuration.
    pub fn build(mut self) -> Result<Unit<S>, BuildError>
    where
        S: Default + UnitEncoder,
    {
        let default_context;

        let context = match self.context.take() {
            Some(context) => context,
            None => {
                default_context = Context::new();
                &default_context
            }
        };

        let mut unit = compile::UnitBuilder::default();

        let prelude = if context.has_default_modules() {
            compile::Prelude::with_default_prelude()?
        } else {
            compile::Prelude::default()
        };

        let mut default_diagnostics;

        let diagnostics = match self.diagnostics.take() {
            Some(diagnostics) => diagnostics,
            None => {
                default_diagnostics = Diagnostics::new();
                &mut default_diagnostics
            }
        };

        let default_options;

        let options = match self.options.take() {
            Some(options) => options,
            None => {
                default_options = Options::default();
                &default_options
            }
        };

        let mut default_visitors;
        let visitors = match self.visitors.is_empty() {
            true => {
                default_visitors = CompileVisitorGroup {
                    visitors: Vec::new(),
                };
                &mut default_visitors
            }
            false => {
                let v = take(&mut self.visitors);
                default_visitors = CompileVisitorGroup { visitors: v };

                &mut default_visitors
            }
        };

        let mut default_source_loader;

        let source_loader = match self.source_loader.take() {
            Some(source_loader) => source_loader,
            None => {
                default_source_loader = DefaultSourceLoader::default();
                &mut default_source_loader
            }
        };

        let mut pool = Pool::new()?;
        let mut unit_storage = S::default();

        compile::compile(
            &mut unit,
            &prelude,
            self.sources,
            &mut pool,
            context,
            visitors,
            diagnostics,
            source_loader,
            options,
            &mut unit_storage,
        )?;

        if diagnostics.has_error() {
            return Err(BuildError::default());
        }

        if options.link_checks {
            unit.link(context, diagnostics)?;
        }

        if diagnostics.has_error() {
            return Err(BuildError::default());
        }

        match unit.build(Span::empty(), unit_storage) {
            Ok(unit) => Ok(unit),
            Err(error) => {
                diagnostics.error(SourceId::empty(), error)?;
                Err(BuildError::default())
            }
        }
    }
}