/*!
This module defines the core of the miette protocol: a series of types and traits
that you can implement to get access to miette's (and related library's) full
reporting and such features.
*/

use std::{fmt::Display, sync::Arc};

use crate::MietteError;

/**
Adds rich metadata to your Error that can be used by [DiagnosticReporter] to print
really nice and human-friendly error messages.
*/
pub trait Diagnostic: std::error::Error {
    /// Unique diagnostic code that can be used to look up more information
    /// about this Diagnostic. Ideally also globally unique, and documented in
    /// the toplevel crate's documentation for easy searching. Rust path
    /// format (`foo::bar::baz`) is recommended, but more classic codes like
    /// `E0123` or Enums will work just fine.
    fn code(&self) -> &(dyn Display);

    /// Diagnostic severity. This may be used by [DiagnosticReporter]s to change the
    /// display format of this diagnostic.
    ///
    /// If `None`, reporters should treat this as [Severity::Error]
    fn severity(&self) -> Option<Severity> {
        None
    }

    /// Additional help text related to this Diagnostic. Do you have any
    /// advice for the poor soul who's just run into this issue?
    fn help(&self) -> Option<&(dyn Display)> {
        None
    }

    /// Additional contextual snippets. This is typically used for adding
    /// marked-up source file output the way compilers often do.
    fn snippets(&self) -> Option<Box<dyn Iterator<Item = DiagnosticSnippet>>> {
        None
    }
}

impl std::error::Error for Box<dyn Diagnostic> {}

impl<T: Diagnostic + Send + Sync + 'static> From<T>
    for Box<dyn Diagnostic + Send + Sync + 'static>
{
    fn from(diag: T) -> Self {
        Box::new(diag)
    }
}

impl<T: Diagnostic + Send + Sync + 'static> From<T> for Box<dyn Diagnostic + Send + 'static> {
    fn from(diag: T) -> Self {
        Box::<dyn Diagnostic + Send + Sync>::from(diag)
    }
}

impl<T: Diagnostic + Send + Sync + 'static> From<T> for Box<dyn Diagnostic + 'static> {
    fn from(diag: T) -> Self {
        Box::<dyn Diagnostic + Send + Sync>::from(diag)
    }
}

/**
Protocol for [Diagnostic] handlers, which are responsible for actually printing out Diagnostics.

Blatantly based on [EyreHandler](https://docs.rs/eyre/0.6.5/eyre/trait.EyreHandler.html) (thanks, Jane!)
*/
pub trait DiagnosticReporter: core::any::Any + Send + Sync {
    /// Define the report format.
    fn debug(
        &self,
        diagnostic: &(dyn Diagnostic),
        f: &mut core::fmt::Formatter<'_>,
    ) -> core::fmt::Result;

    /// Override for the `Display` format.
    fn display(
        &self,
        diagnostic: &(dyn Diagnostic),
        f: &mut core::fmt::Formatter<'_>,
    ) -> core::fmt::Result {
        write!(f, "{}", diagnostic)?;
        Ok(())
    }
}

/**
[Diagnostic] severity. Intended to be used by [DiagnosticReporter] to change the
way different Diagnostics are displayed.
*/
#[derive(Copy, Clone, Debug)]
pub enum Severity {
    /// Critical failure. The program cannot continue.
    Error,
    /// Warning. Please take note.
    Warning,
    /// Just some help. Here's how you could be doing it better.
    Advice,
}

/**
Represents a readable source of some sort.

This trait is able to support simple Source types like [String]s, as well
as more involved types like indexes into centralized `SourceMap`-like types,
file handles, and even network streams.

If you can read it, you can source it,
and it's not necessary to read the whole thing--meaning you should be able to
support Sources which are gigabytes or larger in size.
*/
pub trait Source: std::fmt::Debug + Send + Sync + 'static {
    /// Read the bytes for a specific span from this Source.
    fn read_span<'a>(
        &'a self,
        span: &SourceSpan,
    ) -> Result<Box<dyn SpanContents + 'a>, MietteError>;
}

/**
Contents of a [Source] covered by [SourceSpan].

Includes line and column information to optimize highlight calculations.
*/
pub trait SpanContents {
    /// Reference to the data inside the associated span, in bytes.
    fn data(&self) -> &[u8];
    /// The 0-indexed line in the associated [Source] where the data begins.
    fn line(&self) -> usize;
    /// The 0-indexed column in the associated [Source] where the data begins,
    /// relative to `line`.
    fn column(&self) -> usize;
}

/**
Basic implementation of the [SpanContents] trait, for convenience.
*/
#[derive(Clone, Debug)]
pub struct MietteSpanContents<'a> {
    /// Data from a [Source], in bytes.
    data: &'a [u8],
    // The 0-indexed line where the associated [SourceSpan] _starts_.
    line: usize,
    // The 0-indexed column where the associated [SourceSpan] _starts_.
    column: usize,
}

impl<'a> MietteSpanContents<'a> {
    /// Make a new [MietteSpanContents] object.
    pub fn new(data: &'a [u8], line: usize, column: usize) -> MietteSpanContents<'a> {
        MietteSpanContents { data, line, column }
    }
}

impl<'a> SpanContents for MietteSpanContents<'a> {
    fn data(&self) -> &[u8] {
        self.data
    }
    fn line(&self) -> usize {
        self.line
    }
    fn column(&self) -> usize {
        self.column
    }
}

/**
A snippet from a [Source] to be displayed with a message and possibly some highlights.
 */
#[derive(Clone, Debug)]
pub struct DiagnosticSnippet {
    /// Explanation of this specific diagnostic snippet.
    pub message: Option<String>,
    /// The "filename" for this snippet.
    pub source_name: String,
    /// A [Source] that can be used to read the actual text of a source.
    pub source: Arc<dyn Source>,
    /// The primary [SourceSpan] where this diagnostic is located.
    pub context: SourceSpan,
    /// Additional [SourceSpan]s that mark specific sections of the span, for
    /// example, to underline specific text within the larger span. They're
    /// paired with labels that should be applied to those sections.
    pub highlights: Option<Vec<(String, SourceSpan)>>,
}

/**
Span within a [Source] with an associated message.
*/
#[derive(Clone, Debug)]
pub struct SourceSpan {
    /// The start of the span.
    pub start: SourceOffset,
    /// The (exclusive) end of the span.
    pub end: SourceOffset,
}

impl SourceSpan {
    pub fn new(start: SourceOffset, end: SourceOffset) -> Self {
        assert!(
            start.offset() <= end.offset(),
            "Starting offset must come before the end offset."
        );
        Self { start, end }
    }

    pub fn len(&self) -> usize {
        self.end.offset() - self.start.offset() + 1
    }

    pub fn is_empty(&self) -> bool {
        self.start.offset() == self.end.offset()
    }
}

/**
"Raw" type for the byte offset from the beginning of a [Source].
*/
pub type ByteOffset = usize;

/**
Newtype that represents the [ByteOffset] from the beginning of a [Source]
*/
#[derive(Clone, Copy, Debug)]
pub struct SourceOffset(ByteOffset);

impl SourceOffset {
    /// Actual byte offset.
    pub fn offset(&self) -> ByteOffset {
        self.0
    }
}

impl From<ByteOffset> for SourceOffset {
    fn from(bytes: ByteOffset) -> Self {
        SourceOffset(bytes)
    }
}