// Copyright Mozilla Foundation. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use super::*;
use crate::handles::*;
use crate::variant::*;

pub struct Utf16Decoder {
    lead_surrogate: u16, // If non-zero and pending_bmp == false, a pending lead surrogate
    lead_byte: Option<u8>,
    be: bool,
    pending_bmp: bool, // if true, lead_surrogate is actually pending BMP
}

impl Utf16Decoder {
    pub fn new(big_endian: bool) -> VariantDecoder {
        VariantDecoder::Utf16(Utf16Decoder {
            lead_surrogate: 0,
            lead_byte: None,
            be: big_endian,
            pending_bmp: false,
        })
    }

    pub fn additional_from_state(&self) -> usize {
        1 + if self.lead_byte.is_some() { 1 } else { 0 }
            + if self.lead_surrogate == 0 { 0 } else { 2 }
    }

    pub fn max_utf16_buffer_length(&self, byte_length: usize) -> Option<usize> {
        checked_add(
            1,
            checked_div(byte_length.checked_add(self.additional_from_state()), 2),
        )
    }

    pub fn max_utf8_buffer_length_without_replacement(&self, byte_length: usize) -> Option<usize> {
        checked_add(
            1,
            checked_mul(
                3,
                checked_div(byte_length.checked_add(self.additional_from_state()), 2),
            ),
        )
    }

    pub fn max_utf8_buffer_length(&self, byte_length: usize) -> Option<usize> {
        checked_add(
            1,
            checked_mul(
                3,
                checked_div(byte_length.checked_add(self.additional_from_state()), 2),
            ),
        )
    }

    decoder_functions!(
        {
            if self.pending_bmp {
                match dest.check_space_bmp() {
                    Space::Full(_) => {
                        return (DecoderResult::OutputFull, 0, 0);
                    }
                    Space::Available(destination_handle) => {
                        destination_handle.write_bmp(self.lead_surrogate);
                        self.pending_bmp = false;
                        self.lead_surrogate = 0;
                    }
                }
            }
        },
        {
            // This is the fast path. The rest runs only at the
            // start and end for partial sequences.
            if self.lead_byte.is_none() && self.lead_surrogate == 0 {
                if let Some((read, written)) = if self.be {
                    dest.copy_utf16_from::<BigEndian>(&mut source)
                } else {
                    dest.copy_utf16_from::<LittleEndian>(&mut source)
                } {
                    return (DecoderResult::Malformed(2, 0), read, written);
                }
            }
        },
        {
            debug_assert!(!self.pending_bmp);
            if self.lead_surrogate != 0 || self.lead_byte.is_some() {
                // We need to check space without intent to write in order to
                // make sure that there is space for the replacement character.
                match dest.check_space_bmp() {
                    Space::Full(_) => {
                        return (DecoderResult::OutputFull, 0, 0);
                    }
                    Space::Available(_) => {
                        if self.lead_surrogate != 0 {
                            self.lead_surrogate = 0;
                            match self.lead_byte {
                                None => {
                                    return (
                                        DecoderResult::Malformed(2, 0),
                                        src_consumed,
                                        dest.written(),
                                    );
                                }
                                Some(_) => {
                                    self.lead_byte = None;
                                    return (
                                        DecoderResult::Malformed(3, 0),
                                        src_consumed,
                                        dest.written(),
                                    );
                                }
                            }
                        }
                        debug_assert!(self.lead_byte.is_some());
                        self.lead_byte = None;
                        return (DecoderResult::Malformed(1, 0), src_consumed, dest.written());
                    }
                }
            }
        },
        {
            match self.lead_byte {
                None => {
                    self.lead_byte = Some(b);
                    continue;
                }
                Some(lead) => {
                    self.lead_byte = None;
                    let code_unit = if self.be {
                        u16::from(lead) << 8 | u16::from(b)
                    } else {
                        u16::from(b) << 8 | u16::from(lead)
                    };
                    let high_bits = code_unit & 0xFC00u16;
                    if high_bits == 0xD800u16 {
                        // high surrogate
                        if self.lead_surrogate != 0 {
                            // The previous high surrogate was in
                            // error and this one becomes the new
                            // pending one.
                            self.lead_surrogate = code_unit as u16;
                            return (
                                DecoderResult::Malformed(2, 2),
                                unread_handle.consumed(),
                                destination_handle.written(),
                            );
                        }
                        self.lead_surrogate = code_unit;
                        continue;
                    }
                    if high_bits == 0xDC00u16 {
                        // low surrogate
                        if self.lead_surrogate == 0 {
                            return (
                                DecoderResult::Malformed(2, 0),
                                unread_handle.consumed(),
                                destination_handle.written(),
                            );
                        }
                        destination_handle.write_surrogate_pair(self.lead_surrogate, code_unit);
                        self.lead_surrogate = 0;
                        continue;
                    }
                    // bmp
                    if self.lead_surrogate != 0 {
                        // The previous high surrogate was in
                        // error and this code unit becomes a
                        // pending BMP character.
                        self.lead_surrogate = code_unit;
                        self.pending_bmp = true;
                        return (
                            DecoderResult::Malformed(2, 2),
                            unread_handle.consumed(),
                            destination_handle.written(),
                        );
                    }
                    destination_handle.write_bmp(code_unit);
                    continue;
                }
            }
        },
        self,
        src_consumed,
        dest,
        source,
        b,
        destination_handle,
        unread_handle,
        check_space_astral
    );
}

// Any copyright to the test code below this comment is dedicated to the
// Public Domain. http://creativecommons.org/publicdomain/zero/1.0/

#[cfg(all(test, feature = "alloc"))]
mod tests {
    use super::super::testing::*;
    use super::super::*;

    fn decode_utf_16le(bytes: &[u8], expect: &str) {
        decode_without_padding(UTF_16LE, bytes, expect);
    }

    fn decode_utf_16be(bytes: &[u8], expect: &str) {
        decode_without_padding(UTF_16BE, bytes, expect);
    }

    fn encode_utf_16le(string: &str, expect: &[u8]) {
        encode(UTF_16LE, string, expect);
    }

    fn encode_utf_16be(string: &str, expect: &[u8]) {
        encode(UTF_16BE, string, expect);
    }

    #[test]
    fn test_utf_16_decode() {
        decode_utf_16le(b"", "");
        decode_utf_16be(b"", "");

        decode_utf_16le(b"\x61\x00\x62\x00", "\u{0061}\u{0062}");
        decode_utf_16be(b"\x00\x61\x00\x62", "\u{0061}\u{0062}");

        decode_utf_16le(b"\xFE\xFF\x00\x61\x00\x62", "\u{0061}\u{0062}");
        decode_utf_16be(b"\xFF\xFE\x61\x00\x62\x00", "\u{0061}\u{0062}");

        decode_utf_16le(b"\x61\x00\x62", "\u{0061}\u{FFFD}");
        decode_utf_16be(b"\x00\x61\x00", "\u{0061}\u{FFFD}");

        decode_utf_16le(b"\x3D\xD8\xA9", "\u{FFFD}");
        decode_utf_16be(b"\xD8\x3D\xDC", "\u{FFFD}");

        decode_utf_16le(b"\x3D\xD8\xA9\xDC\x03\x26", "\u{1F4A9}\u{2603}");
        decode_utf_16be(b"\xD8\x3D\xDC\xA9\x26\x03", "\u{1F4A9}\u{2603}");

        decode_utf_16le(b"\xA9\xDC\x03\x26", "\u{FFFD}\u{2603}");
        decode_utf_16be(b"\xDC\xA9\x26\x03", "\u{FFFD}\u{2603}");

        decode_utf_16le(b"\x3D\xD8\x03\x26", "\u{FFFD}\u{2603}");
        decode_utf_16be(b"\xD8\x3D\x26\x03", "\u{FFFD}\u{2603}");

        // The \xFF makes sure that the parts before and after have different alignment
        let long_le = b"\x00\x00\x00\x00\x00\x00\x00\x00\x3D\xD8\xA9\xDC\x00\x00\x00\x00\x00\x00\x00\x00\x3D\xD8\x00\x00\x00\x00\x00\x00\x00\x00\xA9\xDC\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x3D\xD8\xFF\x00\x00\x00\x00\x00\x00\x00\x00\x3D\xD8\xA9\xDC\x00\x00\x00\x00\x00\x00\x00\x00\x3D\xD8\x00\x00\x00\x00\x00\x00\x00\x00\xA9\xDC\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x3D\xD8";
        let long_be = b"\x00\x00\x00\x00\x00\x00\x00\x00\xD8\x3D\xDC\xA9\x00\x00\x00\x00\x00\x00\x00\x00\xD8\x3D\x00\x00\x00\x00\x00\x00\x00\x00\xDC\xA9\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xD8\x3D\xFF\x00\x00\x00\x00\x00\x00\x00\x00\xD8\x3D\xDC\xA9\x00\x00\x00\x00\x00\x00\x00\x00\xD8\x3D\x00\x00\x00\x00\x00\x00\x00\x00\xDC\xA9\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xD8\x3D";
        let long_expect = "\x00\x00\x00\x00\u{1F4A9}\x00\x00\x00\x00\u{FFFD}\x00\x00\x00\x00\u{FFFD}\x00\x00\x00\x00\x00\x00\x00\x00\u{FFFD}";
        decode_utf_16le(&long_le[..long_le.len() / 2], long_expect);
        decode_utf_16be(&long_be[..long_be.len() / 2], long_expect);
        decode_utf_16le(&long_le[long_le.len() / 2 + 1..], long_expect);
        decode_utf_16be(&long_be[long_be.len() / 2 + 1..], long_expect);
    }

    #[test]
    fn test_utf_16_encode() {
        // Empty
        encode_utf_16be("", b"");
        encode_utf_16le("", b"");

        // Encodes as UTF-8
        assert_eq!(UTF_16LE.new_encoder().encoding(), UTF_8);
        assert_eq!(UTF_16BE.new_encoder().encoding(), UTF_8);
        encode_utf_16le("\u{1F4A9}\u{2603}", "\u{1F4A9}\u{2603}".as_bytes());
        encode_utf_16be("\u{1F4A9}\u{2603}", "\u{1F4A9}\u{2603}".as_bytes());
    }

    #[test]
    fn test_utf_16be_decode_one_by_one() {
        let input = b"\x00\x61\x00\xE4\x26\x03\xD8\x3D\xDC\xA9";
        let mut output = [0u16; 20];
        let mut decoder = UTF_16BE.new_decoder();
        for b in input.chunks(1) {
            assert_eq!(b.len(), 1);
            let needed = decoder.max_utf16_buffer_length(b.len()).unwrap();
            let (result, read, _, had_errors) =
                decoder.decode_to_utf16(b, &mut output[..needed], false);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, 1);
            assert!(!had_errors);
        }
    }

    #[test]
    fn test_utf_16le_decode_one_by_one() {
        let input = b"\x61\x00\xE4\x00\x03\x26\x3D\xD8\xA9\xDC";
        let mut output = [0u16; 20];
        let mut decoder = UTF_16LE.new_decoder();
        for b in input.chunks(1) {
            assert_eq!(b.len(), 1);
            let needed = decoder.max_utf16_buffer_length(b.len()).unwrap();
            let (result, read, _, had_errors) =
                decoder.decode_to_utf16(b, &mut output[..needed], false);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, 1);
            assert!(!had_errors);
        }
    }

    #[test]
    fn test_utf_16be_decode_three_at_a_time() {
        let input = b"\x00\xE4\x26\x03\xD8\x3D\xDC\xA9\x00\x61\x00\xE4";
        let mut output = [0u16; 20];
        let mut decoder = UTF_16BE.new_decoder();
        for b in input.chunks(3) {
            assert_eq!(b.len(), 3);
            let needed = decoder.max_utf16_buffer_length(b.len()).unwrap();
            let (result, read, _, had_errors) =
                decoder.decode_to_utf16(b, &mut output[..needed], false);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, b.len());
            assert!(!had_errors);
        }
    }

    #[test]
    fn test_utf_16le_decode_three_at_a_time() {
        let input = b"\xE4\x00\x03\x26\x3D\xD8\xA9\xDC\x61\x00\xE4\x00";
        let mut output = [0u16; 20];
        let mut decoder = UTF_16LE.new_decoder();
        for b in input.chunks(3) {
            assert_eq!(b.len(), 3);
            let needed = decoder.max_utf16_buffer_length(b.len()).unwrap();
            let (result, read, _, had_errors) =
                decoder.decode_to_utf16(b, &mut output[..needed], false);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, b.len());
            assert!(!had_errors);
        }
    }

    #[test]
    fn test_utf_16le_decode_bom_prefixed_split_byte_pair() {
        let mut output = [0u16; 20];
        let mut decoder = UTF_16LE.new_decoder();
        {
            let needed = decoder.max_utf16_buffer_length(1).unwrap();
            let (result, read, written, had_errors) =
                decoder.decode_to_utf16(b"\xFF", &mut output[..needed], false);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, 1);
            assert_eq!(written, 0);
            assert!(!had_errors);
        }
        {
            let needed = decoder.max_utf16_buffer_length(1).unwrap();
            let (result, read, written, had_errors) =
                decoder.decode_to_utf16(b"\xFD", &mut output[..needed], true);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, 1);
            assert_eq!(written, 1);
            assert!(!had_errors);
            assert_eq!(output[0], 0xFDFF);
        }
    }

    #[test]
    fn test_utf_16be_decode_bom_prefixed_split_byte_pair() {
        let mut output = [0u16; 20];
        let mut decoder = UTF_16BE.new_decoder();
        {
            let needed = decoder.max_utf16_buffer_length(1).unwrap();
            let (result, read, written, had_errors) =
                decoder.decode_to_utf16(b"\xFE", &mut output[..needed], false);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, 1);
            assert_eq!(written, 0);
            assert!(!had_errors);
        }
        {
            let needed = decoder.max_utf16_buffer_length(1).unwrap();
            let (result, read, written, had_errors) =
                decoder.decode_to_utf16(b"\xFD", &mut output[..needed], true);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, 1);
            assert_eq!(written, 1);
            assert!(!had_errors);
            assert_eq!(output[0], 0xFEFD);
        }
    }

    #[test]
    fn test_utf_16le_decode_bom_prefix() {
        let mut output = [0u16; 20];
        let mut decoder = UTF_16LE.new_decoder();
        {
            let needed = decoder.max_utf16_buffer_length(1).unwrap();
            let (result, read, written, had_errors) =
                decoder.decode_to_utf16(b"\xFF", &mut output[..needed], true);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, 1);
            assert_eq!(written, 1);
            assert!(had_errors);
            assert_eq!(output[0], 0xFFFD);
        }
    }

    #[test]
    fn test_utf_16be_decode_bom_prefix() {
        let mut output = [0u16; 20];
        let mut decoder = UTF_16BE.new_decoder();
        {
            let needed = decoder.max_utf16_buffer_length(1).unwrap();
            let (result, read, written, had_errors) =
                decoder.decode_to_utf16(b"\xFE", &mut output[..needed], true);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, 1);
            assert_eq!(written, 1);
            assert!(had_errors);
            assert_eq!(output[0], 0xFFFD);
        }
    }

    #[test]
    fn test_utf_16le_decode_near_end() {
        let mut output = [0u8; 4];
        let mut decoder = UTF_16LE.new_decoder();
        {
            let (result, read, written, had_errors) =
                decoder.decode_to_utf8(&[0x03], &mut output[..], false);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, 1);
            assert_eq!(written, 0);
            assert!(!had_errors);
            assert_eq!(output[0], 0x0);
        }
        {
            let (result, read, written, had_errors) =
                decoder.decode_to_utf8(&[0x26, 0x03, 0x26], &mut output[..], false);
            assert_eq!(result, CoderResult::OutputFull);
            assert_eq!(read, 1);
            assert_eq!(written, 3);
            assert!(!had_errors);
            assert_eq!(output[0], 0xE2);
            assert_eq!(output[1], 0x98);
            assert_eq!(output[2], 0x83);
            assert_eq!(output[3], 0x00);
        }
    }

    #[test]
    fn test_utf_16be_decode_near_end() {
        let mut output = [0u8; 4];
        let mut decoder = UTF_16BE.new_decoder();
        {
            let (result, read, written, had_errors) =
                decoder.decode_to_utf8(&[0x26], &mut output[..], false);
            assert_eq!(result, CoderResult::InputEmpty);
            assert_eq!(read, 1);
            assert_eq!(written, 0);
            assert!(!had_errors);
            assert_eq!(output[0], 0x0);
        }
        {
            let (result, read, written, had_errors) =
                decoder.decode_to_utf8(&[0x03, 0x26, 0x03], &mut output[..], false);
            assert_eq!(result, CoderResult::OutputFull);
            assert_eq!(read, 1);
            assert_eq!(written, 3);
            assert!(!had_errors);
            assert_eq!(output[0], 0xE2);
            assert_eq!(output[1], 0x98);
            assert_eq!(output[2], 0x83);
            assert_eq!(output[3], 0x00);
        }
    }
}