// Copyright 2023 by Sergey S. Chernov.
//
// 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 std::iter::Iterator;
use std::usize;

const V0LIMIT: u64 = 1u64 << 6;
const V1LIMIT: u64 = 1u64 << 14;
const V2LIMIT: u64 = 1u64 << 22;

/// Numeric value convertible to Unsigned 64 bit to be used
/// with [BipackSink#put_unsigned] compressed format. It is implemented fir usize
/// and u* types already.
pub trait IntoU64 {
    fn into_u64(self) -> u64;
}

macro_rules! into_u64 {
    ($($type:ident),*) => {
        $(impl IntoU64 for $type {
            fn into_u64(self) -> u64 {
                self as u64
            }
        })*
    };
}

into_u64!(u8, u16, u32, usize, u64);

/// Data sink to encode bipack binary format.
///
/// To implement just override [BipackSink::put_u8] and optionally [BipackSink::put_fixed_bytes].
///
/// Note that the sink is not returning errors, unlike [crate::bipack_source::BipackSource].
/// It is supposed that the sink has unlimited
/// size for the context of data it is used for. This is practical. For the case of overflow-aware
/// sink you can create one that ignores extra data when overflow is detected and report it
/// somehow, but for encoding it does not worth effort (data size could be estimated in advance).
pub trait BipackSink {
    fn put_u8(self: &mut Self, data: u8);

    fn put_fixed_bytes(self: &mut Self, data: &[u8]) {
        for b in data { self.put_u8(*b); }
    }

    fn put_var_bytes(self: &mut Self, data: &[u8]) {
        self.put_unsigned(data.len());
        self.put_fixed_bytes(data);
    }

    fn put_str(self: &mut Self, str: &str) {
        self.put_var_bytes(str.as_bytes());
    }

    fn put_u16(self: &mut Self, mut value: u16) {
        let mut result = [0u8; 2];
        for i in (0..result.len()).rev() {
            result[i] = value as u8;
            value = value >> 8;
        }
        self.put_fixed_bytes(&result);
    }

    fn put_u32(self: &mut Self, mut value: u32) {
        let mut result = [0u8; 4];
        for i in (0..result.len()).rev() {
            result[i] = value as u8;
            value = value >> 8;
        }
        self.put_fixed_bytes(&result);
    }
    fn put_u64(self: &mut Self, mut value: u64) {
        let mut result = [0u8; 8];
        for i in (0..result.len()).rev() {
            result[i] = value as u8;
            value = value >> 8;
        }
        self.put_fixed_bytes(&result);
    }

    fn put_i64(self: &mut Self, value: i64) {
        self.put_u64(value as u64)
    }
    fn put_i32(self: &mut Self, value: i32) {
        self.put_u32(value as u32)
    }
    fn put_i16(self: &mut Self, value: i16) {
        self.put_u16(value as u16)
    }
    fn put_i8(self: &mut Self, value: i8) {
        self.put_u8(value as u8)
    }

    /// Put unsigned value to compressed variable-length format, `Smartint` in the bipack
    /// terms. This format is used to store size of variable-length binaries and strings.
    /// Use [crate::bipack_source::BipackSource::get_unsigned] to unpack it.
    fn put_unsigned<T: IntoU64>(self: &mut Self, number: T) {
        let value = number.into_u64();
        let mut encode_seq = |ty: u8, bytes: &[u64]| {
            if bytes.len() == 0 { self.put_u8(0); } else {
                if bytes[0] as u64 > V0LIMIT { panic!("first byte is too big (internal error)"); }
                self.put_u8((ty & 0x03) | ((bytes[0] as u8) << 2));
                for i in 1..bytes.len() {
                    self.put_u8(bytes[i] as u8);
                }
            }
        };

        if value < V0LIMIT {
            encode_seq(0, &[value]);
        } else if value < V1LIMIT {
            encode_seq(1, &[value & 0x3F, value >> 6]);
        } else if value < V2LIMIT {
            encode_seq(2, &[value & 0x3f, value >> 6, value >> 14]);
        } else {
            encode_seq(3, &[value & 0x3f, value >> 6, value >> 14]);
            self.put_var_unsigned(value >> 22);
        }
    }

    /// Put variable-length encoded integer value. it is packed just like variable-length
    /// unsigned value except that LSB (bit 0) is used as negative number flag (when set,
    /// the encoded number is negative).
    ///
    /// Note that for really big number using [BipackSink::put_i64] could be more effective
    /// than the variable-length.
    fn put_signed(self: &mut Self, val: i64) {
        let (neg, val) = if val < 0 { (1, -val) } else { (0, val) };
        self.put_unsigned( (neg as u64) | ((val as u64) << 1) );
    }

    fn put_var_unsigned(self: &mut Self, value: u64) {
        let mut rest = value;
        loop {
            let x = rest & 127;
            rest = rest >> 7;
            if rest > 0 {
                self.put_u8((x | 0x80) as u8);
            } else {
                self.put_u8(x as u8)
            }
            if rest == 0 { break; }
        }
    }
}


impl BipackSink for Vec<u8> {
    fn put_u8(self: &mut Self, data: u8) {
        self.push(data);
    }
}