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/*
 * Copyright 2020 Fluence Labs Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use super::air;
use super::lexer::AIRLexer;
use super::lexer::AirPos;
use super::lexer::Token;
use super::ParserError;
use crate::ast::Instruction;
use crate::parser::VariableValidator;
use air::AIRParser;

use codespan_reporting::diagnostic::{Diagnostic, Label};
use codespan_reporting::files::SimpleFiles;
use codespan_reporting::term;
use codespan_reporting::term::termcolor::{Buffer, ColorChoice, StandardStream};
use lalrpop_util::{ErrorRecovery, ParseError};

// caching parser to improve instantiation time
thread_local!(static PARSER: AIRParser = AIRParser::new());

/// Parse AIR `source_code` to `Box<Instruction>`
#[tracing::instrument(skip_all)]
pub fn parse(air_script: &str) -> Result<Box<Instruction<'_>>, String> {
    let mut files = SimpleFiles::new();
    let file_id = files.add("script.air", air_script);

    PARSER.with(|parser| {
        let mut errors: Vec<ErrorRecovery<AirPos, Token<'_>, ParserError>> = Vec::new();
        let lexer = AIRLexer::new(air_script);
        let mut validator = VariableValidator::new();
        let result = parser.parse(air_script, &mut errors, &mut validator, lexer);

        let validator_errors = validator.finalize();
        errors.extend(validator_errors);

        match result {
            Ok(r) if errors.is_empty() => Ok(r),
            Ok(_) => Err(report_errors(file_id, files, errors)),
            Err(error) => Err(report_errors(
                file_id,
                files,
                vec![ErrorRecovery {
                    error,
                    dropped_tokens: vec![],
                }],
            )),
        }
    })
}

fn report_errors(
    file_id: usize,
    files: SimpleFiles<&str, &str>,
    errors: Vec<ErrorRecovery<AirPos, Token<'_>, ParserError>>,
) -> String {
    let labels = errors_to_labels(file_id, errors);
    let diagnostic = Diagnostic::error().with_labels(labels);

    // Write to stderr
    let writer = StandardStream::stderr(ColorChoice::Auto);
    let config = codespan_reporting::term::Config::default();
    term::emit(&mut writer.lock(), &config, &files, &diagnostic).expect("term emit to stderr");

    // Return as a string
    let mut buffer = Buffer::no_color();
    term::emit(&mut buffer, &config, &files, &diagnostic).expect("term emit to buffer");
    String::from_utf8_lossy(buffer.as_slice())
        .as_ref()
        .to_string()
}

fn errors_to_labels(
    file_id: usize,
    errors: Vec<ErrorRecovery<AirPos, Token<'_>, ParserError>>,
) -> Vec<Label<usize>> {
    errors
        .into_iter()
        .map(|err| match err.error {
            ParseError::UnrecognizedToken {
                token: (start, _, end),
                expected,
            } => Label::primary(file_id, start.into()..end.into())
                .with_message(format!("expected {}", pretty_expected(expected))),
            ParseError::InvalidToken { location } => {
                Label::primary(file_id, location.into()..(location + 1).into())
                    .with_message("unexpected token")
            }
            ParseError::ExtraToken {
                token: (start, _, end),
            } => Label::primary(file_id, start.into()..end.into()).with_message("extra token"),
            ParseError::UnrecognizedEOF { location, expected } => {
                Label::primary(file_id, location.into()..(location + 1).into())
                    .with_message(format!("expected {}", pretty_expected(expected)))
            }
            ParseError::User { error } => parser_error_to_label(file_id, error),
        })
        .collect()
}

fn pretty_expected(expected: Vec<String>) -> String {
    if expected.is_empty() {
        "<nothing>".to_string()
    } else {
        expected.join(" or ")
    }
}

fn parser_error_to_label(file_id: usize, error: ParserError) -> Label<usize> {
    let span = error.span();
    Label::primary(file_id, span.left.into()..span.right.into()).with_message(error.to_string())
}