// 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/>.

use instructions;
use std::fmt;

/// Stack trait with VM-friendly API
pub trait Stack<T> {
    /// Returns `Stack[len(Stack) - no_from_top]`
    fn peek(&self, no_from_top: usize) -> &T;
    /// Swaps Stack[len(Stack)] and Stack[len(Stack) - no_from_top]
    fn swap_with_top(&mut self, no_from_top: usize);
    /// Returns true if Stack has at least `no_of_elems` elements
    fn has(&self, no_of_elems: usize) -> bool;
    /// Get element from top and remove it from Stack. Panics if stack is empty.
    fn pop_back(&mut self) -> T;
    /// Get (up to `instructions::MAX_NO_OF_TOPICS`) elements from top and remove them from Stack. Panics if stack is empty.
    fn pop_n(&mut self, no_of_elems: usize) -> &[T];
    /// Add element on top of the Stack
    fn push(&mut self, elem: T);
    /// Get number of elements on Stack
    fn size(&self) -> usize;
    /// Returns all data on stack.
    fn peek_top(&self, no_of_elems: usize) -> &[T];
}

pub struct VecStack<S> {
    stack: Vec<S>,
    logs: [S; instructions::MAX_NO_OF_TOPICS],
}

impl<S: Copy> VecStack<S> {
    pub fn with_capacity(capacity: usize, zero: S) -> Self {
        VecStack {
            stack: Vec::with_capacity(capacity),
            logs: [zero; instructions::MAX_NO_OF_TOPICS],
        }
    }
}

impl<S: fmt::Display> Stack<S> for VecStack<S> {
    fn peek(&self, no_from_top: usize) -> &S {
        &self.stack[self.stack.len() - no_from_top - 1]
    }

    fn swap_with_top(&mut self, no_from_top: usize) {
        let len = self.stack.len();
        self.stack.swap(len - no_from_top - 1, len - 1);
    }

    fn has(&self, no_of_elems: usize) -> bool {
        self.stack.len() >= no_of_elems
    }

    fn pop_back(&mut self) -> S {
        self.stack
            .pop()
            .expect("instruction validation prevents from popping too many items; qed")
    }

    fn pop_n(&mut self, no_of_elems: usize) -> &[S] {
        assert!(no_of_elems <= instructions::MAX_NO_OF_TOPICS);

        for i in 0..no_of_elems {
            self.logs[i] = self.pop_back();
        }
        &self.logs[0..no_of_elems]
    }

    fn push(&mut self, elem: S) {
        self.stack.push(elem);
    }

    fn size(&self) -> usize {
        self.stack.len()
    }

    fn peek_top(&self, no_from_top: usize) -> &[S] {
        assert!(
            self.stack.len() >= no_from_top,
            "peek_top asked for more items than exist."
        );
        &self.stack[self.stack.len() - no_from_top..self.stack.len()]
    }
}
