// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// OpenEthereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

//! Wrapper for view rlp expected to be valid with debug info

use rlp::{Decodable, DecoderError, Rlp};

/// Wrapper for trusted rlp, which is expected to be valid, for use in views
/// When created with view!, records the file and line where it was created for debugging
pub struct ViewRlp<'a> {
    /// Wrapped Rlp, expected to be valid
    pub rlp: Rlp<'a>,
    file: &'a str,
    line: u32,
}

impl<'a, 'view> ViewRlp<'a>
where
    'a: 'view,
{
    #[doc(hidden)]
    pub fn new(bytes: &'a [u8], file: &'a str, line: u32) -> Self {
        ViewRlp {
            rlp: Rlp::new(bytes),
            file,
            line,
        }
    }

    /// Returns a new instance replacing existing rlp with new rlp, maintaining debug info
    fn new_from_rlp(&self, rlp: Rlp<'a>) -> Self {
        ViewRlp {
            rlp,
            file: self.file,
            line: self.line,
        }
    }

    fn maybe_at(&self, index: usize) -> Option<ViewRlp<'a>> {
        self.rlp.at(index).map(|rlp| self.new_from_rlp(rlp)).ok()
    }

    fn expect_valid_rlp<T>(&self, r: Result<T, DecoderError>) -> T {
        r.unwrap_or_else(|e| {
            panic!(
                "View rlp is trusted and should be valid. Constructed in {} on line {}: {}",
                self.file, self.line, e
            )
        })
    }

    /// Returns rlp at the given index, panics if no rlp at that index
    pub fn at(&self, index: usize) -> ViewRlp<'a> {
        let rlp = self.expect_valid_rlp(self.rlp.at(index));
        self.new_from_rlp(rlp)
    }

    /// Returns an iterator over all rlp values
    pub fn iter(&'view self) -> ViewRlpIterator<'a, 'view> {
        self.into_iter()
    }

    /// Returns decoded value of this rlp, panics if rlp not valid
    pub fn as_val<T>(&self) -> T
    where
        T: Decodable,
    {
        self.expect_valid_rlp(self.rlp.as_val())
    }

    /// Returns decoded value at the given index, panics not present or valid at that index
    pub fn val_at<T>(&self, index: usize) -> T
    where
        T: Decodable,
    {
        self.expect_valid_rlp(self.rlp.val_at(index))
    }

    /// Returns decoded list of values, panics if rlp is invalid
    pub fn list_at<T>(&self, index: usize) -> Vec<T>
    where
        T: Decodable,
    {
        self.expect_valid_rlp(self.rlp.list_at(index))
    }

    /// Returns the number of items in the rlp, panics if it is not a list of rlp values
    pub fn item_count(&self) -> usize {
        self.expect_valid_rlp(self.rlp.item_count())
    }

    /// Returns raw rlp bytes
    pub fn as_raw(&'view self) -> &'a [u8] {
        self.rlp.as_raw()
    }
}

/// Iterator over rlp-slice list elements.
pub struct ViewRlpIterator<'a, 'view>
where
    'a: 'view,
{
    rlp: &'view ViewRlp<'a>,
    index: usize,
}

impl<'a, 'view> IntoIterator for &'view ViewRlp<'a>
where
    'a: 'view,
{
    type Item = ViewRlp<'a>;
    type IntoIter = ViewRlpIterator<'a, 'view>;

    fn into_iter(self) -> Self::IntoIter {
        ViewRlpIterator {
            rlp: self,
            index: 0,
        }
    }
}

impl<'a, 'view> Iterator for ViewRlpIterator<'a, 'view> {
    type Item = ViewRlp<'a>;

    fn next(&mut self) -> Option<ViewRlp<'a>> {
        let index = self.index;
        let result = self.rlp.maybe_at(index);
        self.index += 1;
        result
    }
}

#[macro_export]
macro_rules! view {
    ($view: ident, $bytes: expr) => {
        $view::new($crate::views::ViewRlp::new($bytes, file!(), line!()))
    };
}