// Copyright (c) 2016-2021 Fabian Schuiki

//! Utilities to implement diagnostics and error reporting facilities.

use crate::source::Span;
use std::fmt;

/// Print debug information. Omitted in release builds.
#[macro_export]
#[cfg(debug_assertions)]
macro_rules! debugln {
    ($($arg:tt)*) => { eprintln!("\x1B[34;1mdebug:\x1B[m {}", format!($($arg)*)); }
}

/// Print debug information. Omitted in release builds.
#[macro_export]
#[cfg(not(debug_assertions))]
macro_rules! debugln {
    ($($arg:tt)*) => {};
}

/// A handler deals with errors.
#[derive(Debug)]
pub struct Handler {}

pub static DUMMY_HANDLER: Handler = Handler {};

/// Used to emit structured error messages.
#[must_use]
#[derive(Clone, Debug)]
pub struct DiagnosticBuilder<'a> {
    pub handler: &'a Handler,
    pub message: String,
}

/// A diagnostic result type. Either carries the result `T` in the Ok variant,
/// or an assembled diagnostic in the Err variant.
pub type DiagResult<'a, T> = Result<T, DiagnosticBuilder<'a>>;

/// Emits diagnostic messages.
pub trait DiagEmitter {
    /// Emit a diagnostic message.
    fn emit(&self, diag: DiagBuilder2);
}

impl<'a, T> DiagEmitter for &'a T
where
    T: DiagEmitter + ?Sized,
{
    fn emit(&self, diag: DiagBuilder2) {
        (*self).emit(diag)
    }
}

/// Emit errors as diagnostics.
///
/// Useful if implemented on the error types returned from results. Allows these
/// results to be emitted as diagnostics on-the-fly and converted to a `()`
/// error type result.
pub trait EmitError {
    type Output;
    fn emit<C: DiagEmitter>(self, ctx: C) -> Self::Output;
}

impl<T, E: EmitError> EmitError for Result<T, E> {
    type Output = Result<T, E::Output>;
    fn emit<C: DiagEmitter>(self, ctx: C) -> Result<T, E::Output> {
        self.map_err(move |e| e.emit(ctx))
    }
}

#[must_use]
#[derive(Clone, Debug)]
pub struct DiagBuilder2 {
    pub severity: Severity,
    pub message: String,
    pub segments: Vec<DiagSegment>,
}

#[derive(Clone, Debug)]
pub enum DiagSegment {
    Span(Span),
    Note(String),
}

/// A diagnostic result type. Either carries the result `T` in the Ok variant,
/// or an assembled diagnostic in the Err variant.
pub type DiagResult2<T> = Result<T, DiagBuilder2>;

impl DiagBuilder2 {
    pub fn new<S: Into<String>>(severity: Severity, message: S) -> DiagBuilder2 {
        DiagBuilder2 {
            severity: severity,
            message: message.into(),
            segments: Vec::new(),
        }
    }

    pub fn bug<S: Into<String>>(message: S) -> DiagBuilder2 {
        DiagBuilder2::new(Severity::Bug, message)
    }

    pub fn fatal<S: Into<String>>(message: S) -> DiagBuilder2 {
        DiagBuilder2::new(Severity::Fatal, message)
    }

    pub fn error<S: Into<String>>(message: S) -> DiagBuilder2 {
        DiagBuilder2::new(Severity::Error, message)
    }

    pub fn warning<S: Into<String>>(message: S) -> DiagBuilder2 {
        DiagBuilder2::new(Severity::Warning, message)
    }

    pub fn note<S: Into<String>>(message: S) -> DiagBuilder2 {
        DiagBuilder2::new(Severity::Note, message)
    }

    pub fn segment(self, segment: DiagSegment) -> DiagBuilder2 {
        let mut segments = self.segments;
        segments.push(segment);
        DiagBuilder2 {
            segments: segments,
            ..self
        }
    }

    pub fn span<S: Into<Span>>(self, span: S) -> DiagBuilder2 {
        self.segment(DiagSegment::Span(span.into()))
    }

    pub fn add_note<S: Into<String>>(self, message: S) -> DiagBuilder2 {
        self.segment(DiagSegment::Note(message.into()))
    }

    pub fn get_severity(&self) -> Severity {
        self.severity
    }

    pub fn get_message(&self) -> &String {
        &self.message
    }

    pub fn get_segments(&self) -> &[DiagSegment] {
        &self.segments
    }
}

#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
pub enum Severity {
    Note,
    Warning,
    Error,
    Fatal,
    Bug,
}

impl Severity {
    pub fn to_str(self) -> &'static str {
        match self {
            Severity::Fatal => "fatal",
            Severity::Error => "error",
            Severity::Warning => "warning",
            Severity::Note => "note",
            Severity::Bug => "compiler bug",
        }
    }
}

impl fmt::Display for Severity {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.to_str())
    }
}

impl fmt::Display for DiagBuilder2 {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let mut colorcode = match self.get_severity() {
            Severity::Bug | Severity::Fatal | Severity::Error => "\x1B[31;1m",
            Severity::Warning => "\x1B[33;1m",
            Severity::Note => "\x1B[36;1m",
        };
        write!(
            f,
            "{}{}:\x1B[m\x1B[1m {}\x1B[m\n",
            colorcode,
            self.get_severity(),
            self.get_message()
        )?;

        for segment in &self.segments {
            match *segment {
                DiagSegment::Span(sp) => {
                    let c = sp.source.get_content();

                    // Look for the start of the line.
                    let (line, col, line_offset) = sp.begin().human();

                    // Print the line in question.
                    let text: String = c
                        .iter_from(line_offset)
                        .map(|x| x.1)
                        .take_while(|c| *c != '\n' && *c != '\r')
                        .collect();
                    write!(
                        f,
                        "  --> {}:{}:{}-{}:\n",
                        sp.source.get_path(),
                        line,
                        col,
                        col + sp.extract().len()
                    )?;
                    write!(f, "   | \n")?;
                    write!(f, "   | ")?;
                    for (mut i, c) in text.char_indices() {
                        i += line_offset;
                        if sp.begin != sp.end {
                            if i == sp.begin {
                                write!(f, "{}", colorcode)?;
                            }
                            if i == sp.end {
                                write!(f, "\x1B[m")?;
                            }
                        }
                        match c {
                            '\t' => write!(f, "    ")?,
                            c => write!(f, "{}", c)?,
                        }
                    }
                    write!(f, "\x1B[m\n")?;
                    write!(f, "   | ")?;

                    // Print the caret markers for the line in question.
                    let mut pd = ' ';
                    for (mut i, c) in text.char_indices() {
                        i += line_offset;
                        let d = if (i >= sp.begin && i < sp.end)
                            || (i == sp.begin && sp.begin == sp.end)
                        {
                            '^'
                        } else {
                            ' '
                        };
                        if d != pd {
                            write!(f, "{}", if d == ' ' { "\x1B[m" } else { colorcode })?;
                        }
                        pd = d;
                        match c {
                            '\t' => write!(f, "{}{}{}{}", d, d, d, d)?,
                            _ => write!(f, "{}", d)?,
                        }
                    }
                    write!(f, "\x1B[m\n")?;
                    colorcode = "\x1B[1m";
                }
                DiagSegment::Note(ref message) => {
                    write!(f, "   = \x1B[1mnote:\x1B[m {}\n", message)?
                }
            }
        }

        if self.get_severity() == Severity::Bug {
            write!(
                f,
                "\nYou have encountered a compiler bug. Sorry about that! We would appreciate if \
                 you open an issue [1] and describe how you triggered the bug, together with a \
                 minimal snippet of code to reproduce it. Thanks!\n"
            )?;
            write!(f, "[1]: https://github.com/fabianschuiki/moore\n")?;
        }

        Ok(())
    }
}