use crate::*;

macro_rules! def_peek_seek(($peek:ident, $seek:ident, $seek_start:ident, $seek_length:ident)=>{
    /// Find a slice corrensponding to a syntax token.
    pub const fn $peek (source: &str) -> DslPerhaps<&str> {
        match $seek(source) {
            Ok(Some((start, length))) => Ok(Some(str_range(source, start, start + length))),
            Ok(None) => Ok(None),
            Err(e) => Err(e)
        }
    }
    /// Find a start and length corresponding to a syntax token.
    pub const fn $seek (source: &str) -> DslPerhaps<(usize, usize)> {
        match $seek_start(source) {
            Ok(Some(start)) => match $seek_length(str_from(source, start)) {
                Ok(Some(length)) => Ok(Some((start, length))),
                Ok(None) => Ok(None),
                Err(e) => Err(e),
            },
            Ok(None) => Ok(None),
            Err(e) => Err(e)
        }
    }
});

def_peek_seek!(exp_peek, exp_seek, exp_seek_start, exp_seek_length);
pub const fn is_exp_start (c: char) -> bool { c == '(' }
pub const fn is_exp_end (c: char) -> bool { c == ')' }
pub const fn exp_seek_start (mut source: &str) -> DslPerhaps<usize> {
    for_each!((i, c) in char_indices(source) => if is_exp_start(c) {
        return Ok(Some(i))
    } else if !is_whitespace(c) {
        return Err(Unexpected(c))
    });
    Ok(None)
}
pub const fn exp_seek_length (mut source: &str) -> DslPerhaps<usize> {
    let mut depth = 0;
    for_each!((i, c) in char_indices(source) => if is_exp_start(c) {
        depth += 1;
    } else if is_exp_end(c) {
        if depth == 0 {
            return Err(Unexpected(c))
        } else if depth == 1 {
            return Ok(Some(i + 1))
        } else {
            depth -= 1;
        }
    });
    Err(Incomplete)
}

def_peek_seek!(sym_peek,  sym_seek,  sym_seek_start,  sym_seek_length);
pub const fn is_sym_start (c: char) -> bool { matches!(c, ':'|'@') }
pub const fn is_sym_char (c: char) -> bool { matches!(c, 'a'..='z'|'A'..='Z'|'0'..='9'|'-') }
pub const fn is_sym_end (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t'|')') }
pub const fn sym_seek_start (mut source: &str) -> DslPerhaps<usize> {
    for_each!((i, c) in char_indices(source) => if is_sym_start(c) {
        return Ok(Some(i))
    } else if !is_whitespace(c) {
        return Err(Unexpected(c))
    });
    Ok(None)
}
pub const fn sym_seek_length (mut source: &str) -> DslPerhaps<usize> {
    for_each!((i, c) in char_indices(source) => if is_sym_end(c) {
        return Ok(Some(i))
    } else if !is_sym_char(c) {
        return Err(Unexpected(c))
    });
    Ok(Some(source.len()))
}

def_peek_seek!(key_peek,  key_seek,  key_seek_start,  key_seek_length);
pub const fn is_key_start (c: char) -> bool { matches!(c, '/'|('a'..='z')) }
pub const fn is_key_char (c: char) -> bool { matches!(c, 'a'..='z'|'0'..='9'|'-'|'/') }
pub const fn is_key_end (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t'|')') }
pub const fn key_seek_start (mut source: &str) -> DslPerhaps<usize> {
    for_each!((i, c) in char_indices(source) => if is_key_start(c) {
        return Ok(Some(i))
    } else if !is_whitespace(c) {
        return Err(Unexpected(c))
    });
    Ok(None)
}
pub const fn key_seek_length (mut source: &str) -> DslPerhaps<usize> {
    for_each!((i, c) in char_indices(source) => if is_key_end(c) {
        return Ok(Some(i))
    } else if !is_key_char(c) {
        return Err(Unexpected(c))
    });
    Ok(Some(source.len()))
}

def_peek_seek!(text_peek, text_seek, text_seek_start, text_seek_length);
pub const fn is_text_start (c: char) -> bool { matches!(c, '"') }
pub const fn is_text_end (c: char) -> bool { matches!(c, '"') }
pub const fn text_seek_start (mut source: &str) -> DslPerhaps<usize> {
    for_each!((i, c) in char_indices(source) => if is_text_start(c) {
        return Ok(Some(i))
    } else if !is_whitespace(c) {
        return Err(Unexpected(c))
    });
    Ok(None)
}
pub const fn text_seek_length (mut source: &str) -> DslPerhaps<usize> {
    for_each!((i, c) in char_indices(source) => if is_text_end(c) { return Ok(Some(i)) });
    Ok(None)
}

def_peek_seek!(num_peek,  num_seek,  num_seek_start,  num_seek_length);
pub const fn num_seek_start (mut source: &str) -> DslPerhaps<usize> {
    for_each!((i, c) in char_indices(source) => if is_digit(c) {
        return Ok(Some(i));
    } else if !is_whitespace(c) {
        return Err(Unexpected(c))
    });
    Ok(None)
}
pub const fn num_seek_length (mut source: &str) -> DslPerhaps<usize> {
    for_each!((i, c) in char_indices(source) => if is_num_end(c) {
        return Ok(Some(i))
    } else if !is_digit(c) {
        return Err(Unexpected(c))
    });
    Ok(None)
}
pub const fn is_digit (c: char) -> bool { matches!(c, '0'..='9') }
pub const fn is_num_end (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t'|')') }
pub const fn to_number <D: Dsl> (digits: &str) -> Result<usize, DslError> {
    let mut iter = char_indices(digits);
    let mut value = 0;
    while let Some(((_, c), next)) = iter.next() {
        match to_digit(c) {
            Ok(digit) => value = 10 * value + digit,
            Err(e) => return Err(e),
        }
        iter = next;
    }
    Ok(value)
}
pub const fn to_digit (c: char) -> Result<usize, DslError> {
    Ok(match c {
        '0' => 0, '1' => 1, '2' => 2, '3' => 3, '4' => 4,
        '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9,
        _ => return Err(Unexpected(c))
    })
}

pub const fn peek (mut src: &str) -> DslPerhaps<&str> {
    Ok(Some(match () {
        _ if let Ok(Some(exp))  = exp_peek(src) => exp,
        _ if let Ok(Some(sym))  = sym_peek(src) => sym,
        _ if let Ok(Some(key))  = key_peek(src) => key,
        _ if let Ok(Some(num))  = num_peek(src) => num,
        _ if let Ok(Some(text)) = text_peek(src) => text,
        _ => {
            for_each!((i, c) in char_indices(src) => if !is_whitespace(c) {
                return Err(Unexpected(c))
            });
            return Ok(None)
        }
    }))
}

pub const fn seek (mut src: &str) -> DslPerhaps<(usize, usize)> {
    Ok(Some(match () {
        _ if let Ok(Some(exp))  = exp_seek(src) => exp,
        _ if let Ok(Some(sym))  = sym_seek(src) => sym,
        _ if let Ok(Some(key))  = key_seek(src) => key,
        _ if let Ok(Some(num))  = num_seek(src) => num,
        _ if let Ok(Some(text)) = text_seek(src) => text,
        _ => {
            for_each!((i, c) in char_indices(src) => if !is_whitespace(c) {
                return Err(Unexpected(c))
            });
            return Ok(None)
        }
    }))
}

pub const fn is_whitespace (c: char) -> bool {
    matches!(c, ' '|'\n'|'\r'|'\t')
}