/*
 Cargo KConfig - KConfig parser
 Copyright (C) 2022  Sjoerd van Leent

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*/

//! This file contains the source lexer, which behaves like a regular lexer,
//! but inserts the contents of source files indicated by the "source ..."
//! directive.

use std::fmt::Display;

use super::{
    structs::{Keyword, Lexicon, Token},
    LexerBase,
};
use crate::parse_string;

/// The source lexer allows the source directive to be used to load
/// additional sources as part of the (currently) loaded Kconfig file.
pub struct SourceLexer<LB>
where
    LB: LexerBase,
{
    /// This stack is composed of the name of the stream and the lexer
    /// belonging to the stream. If the lexer has been depleted, it will
    /// be removed from the stack.
    stack: Vec<Table<LB>>,

    /// The source function takes the name of the source and returns a new
    /// lexer.
    source_function: fn(&str) -> Result<LB, String>,

    /// The resolve_name_function resolves the name of the source
    /// to a canonical name understood by the system. This is primarily
    /// used to discover source recursion (which wouldn't end).
    canonical_name_function: fn(&str) -> String,
}

struct Table<LB>
where
    LB: LexerBase,
{
    stream_name: String,
    lexer: LB,
}

/// Provides a basic error message when the source function for one
/// or the other reason fails.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Error {
    msg: String,
}

impl Error {
    /// Creates a new error from a source function, and allows it to
    /// be passed as part of the source lexer error conditions.
    pub fn new(s: &str) -> Error {
        Error { msg: s.to_string() }
    }
}

impl Display for Error {
    /// Formats the error
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{}", self.msg)
    }
}

impl<LB> SourceLexer<LB>
where
    LB: LexerBase,
{
    /// Creates a new source lexer, given the stream's name. This will
    /// create the first source_function call, to actually load the
    /// stream.
    pub fn new(
        stream_name: &str,
        source_function: fn(&str) -> Result<LB, String>,
        canonical_name_function: fn(&str) -> String,
    ) -> Result<Self, Error> {
        match (source_function)(stream_name) {
            Ok(lexer) => Ok(Self {
                stack: vec![Table {
                    stream_name: stream_name.to_string(),
                    lexer: lexer,
                }],
                source_function,
                canonical_name_function,
            }),
            Err(s) => {
                Err(Error::new(&s))
            }
        }
    }
}

impl<LB> LexerBase for SourceLexer<LB>
where
    LB: LexerBase,
{
    fn next_token(&mut self) -> super::structs::Token {
        let last = self.stack.last_mut();
        match last {
            Some(table) => {
                let token = table.lexer.next_token();
                match token.term() {
                    Lexicon::EOT => {
                        self.stack.pop();
                        token
                    }
                    Lexicon::Keyword(k) => match k {
                        Keyword::Source => {
                            // read the next token, which should be a string,
                            // pointing to the stream to read.
                            let token = table.lexer.next_token();
                            match token.term() {
                                Lexicon::String(stream_name) => {
                                    let stream_name = match parse_string(&stream_name) {
                                        Ok(s) => s,
                                        Err(e) => {
                                            return Token::create(
                                                Lexicon::Error(e),
                                                token.column(),
                                                token.line(),
                                                &token.raw(),
                                            )
                                        }
                                    };
                                    let canonical_name =
                                        (self.canonical_name_function)(&stream_name);
                                    // Verify whether the the stream_name
                                    // does not already exist in the stack and creates
                                    // a circular load.
                                    for needle in &self.stack {
                                        if needle.stream_name.eq(&canonical_name) {
                                            return Token::create(
                                                Lexicon::Error(
                                                    "Circular source detected, abort load"
                                                        .to_string(),
                                                ),
                                                token.column(),
                                                token.line(),
                                                &token.raw(),
                                            );
                                        }
                                    }

                                    match (self.source_function)(&stream_name) {
                                        Ok(lb) => {
                                            let t = Table {
                                                stream_name: canonical_name,
                                                lexer: lb,
                                            };
        
                                            self.stack.push(t);
                                            self.next_token()
                                        },
                                        Err(s) => {
                                            Token::create(Lexicon::Error(s), token.column(), token.line(), &token.raw())
                                        }
                                    }
                                }
                                _ => Token::create(
                                    Lexicon::Error(
                                        "Expected string indicating source file or stream"
                                            .to_string(),
                                    ),
                                    token.column(),
                                    token.line(),
                                    &token.raw(),
                                ),
                            }
                        }
                        _ => token,
                    },
                    _ => token,
                }
            }
            None => Token::create(Lexicon::EOT, 0, 0, &""),
        }
    }

    fn current_stream(&self) -> Option<String> {
        let last = self.stack.last();
        match last {
            Some(table) => Some(table.stream_name.to_string()),
            _ => None,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::super::Lexer;
    use super::super::LexerBase;
    use super::*;

    #[test]
    fn test_keywords() {
        let mut l = SourceLexer::<Lexer<&[u8]>>::new(
            "foo",
            |stream_name| {
                if stream_name == "foo" {
                    let s = &mut "mainmenu config menuconfig choice endchoice menu endmenu if endif bool def_bool \
                                  tristate def_tristate string hex int default depends on select imply visible range prompt comment".as_bytes();
                    Ok(Lexer::create(s))
                } else {
                    Err("Error".to_owned())
                }
            },
            |stream_name| stream_name.to_string(),
        ).unwrap();
        assert_eq!(Lexicon::Keyword(Keyword::Mainmenu), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Config), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Menuconfig), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Choice), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Endchoice), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Menu), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Endmenu), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::If), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Endif), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Bool), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::DefBool), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Tristate), l.next_token().term());
        assert_eq!(
            Lexicon::Keyword(Keyword::DefTristate),
            l.next_token().term()
        );
        assert_eq!(Lexicon::Keyword(Keyword::String), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Hex), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Int), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Default), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Depends), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::On), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Select), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Imply), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Visible), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Range), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Prompt), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Comment), l.next_token().term());
        assert_eq!(Lexicon::EOT, l.next_token().term());
    }

    #[test]
    fn test_keywords_sub_lexer() {
        let mut l = SourceLexer::<Lexer<&[u8]>>::new(
            "foo",
            |stream_name| {
                if stream_name == "foo" {
                    let s = &mut "source \"bar\"".as_bytes();
                    Ok(Lexer::create(s))
                } else if stream_name == "bar" {
                    let s = &mut "mainmenu config menuconfig choice endchoice menu endmenu if endif bool def_bool \
                                  tristate def_tristate string hex int default depends on select imply visible range prompt comment".as_bytes();
                    Ok(Lexer::create(s))
                } else {
                    Err("Error".to_owned())
                }
            },
            |stream_name| stream_name.to_string(),
        ).unwrap();
        assert_eq!(Lexicon::Keyword(Keyword::Mainmenu), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Config), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Menuconfig), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Choice), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Endchoice), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Menu), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Endmenu), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::If), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Endif), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Bool), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::DefBool), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Tristate), l.next_token().term());
        assert_eq!(
            Lexicon::Keyword(Keyword::DefTristate),
            l.next_token().term()
        );
        assert_eq!(Lexicon::Keyword(Keyword::String), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Hex), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Int), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Default), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Depends), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::On), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Select), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Imply), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Visible), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Range), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Prompt), l.next_token().term());
        assert_eq!(Lexicon::Keyword(Keyword::Comment), l.next_token().term());
        assert_eq!(Lexicon::EOT, l.next_token().term());
    }

    #[test]
    fn test_error_wrong_syntax() {
        let mut l = SourceLexer::<Lexer<&[u8]>>::new(
            "foo",
            |stream_name| {
                if stream_name == "foo" {
                    let s = &mut "source bla".as_bytes();
                    Ok(Lexer::create(s))
                } else {
                    Err("Error".to_owned())
                }
            },
            |stream_name| stream_name.to_string(),
        ).unwrap();

        let is_error = if let Lexicon::Error(_) = l.next_token().term() {
            true
        } else {
            false
        };
        assert_eq!(is_error, true);
    }

    #[test]
    fn test_error_circular_syntax() {
        let mut l = SourceLexer::<Lexer<&[u8]>>::new(
            "foo",
            |stream_name| {
                if stream_name == "foo" {
                    let s = &mut "source \"bar\"".as_bytes();
                    Ok(Lexer::create(s))
                } else if stream_name == "bar" {
                    let s = &mut "source \"foo\"".as_bytes();
                    Ok(Lexer::create(s))
                } else {
                    Err("Error".to_owned())
                }
            },
            |stream_name| stream_name.to_string(),
        ).unwrap();

        let is_error = if let Lexicon::Error(_) = l.next_token().term() {
            true
        } else {
            false
        };
        assert_eq!(is_error, true);
    }
}