// Copyright 2024 The Wuffs Authors.
//
// 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.
//
// SPDX-License-Identifier: Apache-2.0 OR MIT

// --------

// The Lzip file format specification is at
// https://www.nongnu.org/lzip/manual/lzip_manual.html#File-format

use "std/crc32"
use "std/lzma"

pub status "#bad checksum"
pub status "#bad footer"
pub status "#bad header"
pub status "#truncated input"

pub const DECODER_DST_HISTORY_RETAIN_LENGTH_MAX_INCL_WORST_CASE : base.u64 = 0
pub const DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE               : base.u64 = 0xFFFF_FFFF + 273

pub struct decoder? implements base.io_transformer(
        ignore_checksum : base.bool,

        dsize_have : base.u64,
        ssize_have : base.u64,

        util : base.utility,
) + (
        crc32 : crc32.ieee_hasher,
        lzma  : lzma.decoder,
)

pub func decoder.get_quirk(key: base.u32) base.u64 {
    if (args.key == base.QUIRK_IGNORE_CHECKSUM) and this.ignore_checksum {
        return 1
    }
    return 0
}

pub func decoder.set_quirk!(key: base.u32, value: base.u64) base.status {
    if args.key == base.QUIRK_IGNORE_CHECKSUM {
        this.ignore_checksum = args.value > 0
        return ok
    }
    return base."#unsupported option"
}

pub func decoder.dst_history_retain_length() base.optional_u63 {
    return this.lzma.dst_history_retain_length()
}

pub func decoder.workbuf_len() base.range_ii_u64 {
    return this.lzma.workbuf_len()
}

pub func decoder.transform_io?(dst: base.io_writer, src: base.io_reader, workbuf: slice base.u8) {
    var status : base.status

    while true {
        status =? this.do_transform_io?(dst: args.dst, src: args.src, workbuf: args.workbuf)
        if (status == base."$short read") and args.src.is_closed() {
            return "#truncated input"
        }
        yield? status
    }
}

pri func decoder.do_transform_io?(dst: base.io_writer, src: base.io_reader, workbuf: slice base.u8) {
    var c8            : base.u8
    var c32           : base.u32
    var c64           : base.u64
    var dmark         : base.u64
    var smark         : base.u64
    var status        : base.status
    var checksum_want : base.u32
    var checksum_have : base.u32
    var size_want     : base.u64

    while.outer true {
        // Read the magic number and version number.
        //
        // Some of the test/3pdata/xzsuite/good*v0*.lz files have a 0x00
        // version number (instead of 0x01). We reject those, just like
        // /usr/bin/lzip does and as per the Lzip spec.
        c64 = args.src.read_u40le_as_u64?()
        if c64 <> 'LZIP\x01'le {
            return "#bad header"
        }

        // Read the dictionary size.
        c8 = args.src.read_u8?()
        status = this.lzma.set_quirk!(
                key: lzma.QUIRK_FORMAT_EXTENSION,
                value: 0x01 | ((c8 as base.u64) << 8))
        if not status.is_ok() {
            if status == base."#bad argument" {
                return "#bad header"
            }
            return status
        }

        // Decode LZMA.
        //
        // Re lzma.QUIRK_ALLOW_NON_ZERO_INITIAL_BYTE, as exercised by
        // test/3pdata/xzsuite/lzip-testsuite/fox6_mark.lz, the LZMA spec says
        // that the decoder must check that the byte is zero, but the Lzip spec
        // says that the byte "must be ignored by the range decoder".
        this.ssize_have = 0
        this.dsize_have = 0
        this.lzma.set_quirk!(key: lzma.QUIRK_ALLOW_NON_ZERO_INITIAL_BYTE, value: 1)
        while true {
            dmark = args.dst.mark()
            smark = args.src.mark()
            status =? this.lzma.transform_io?(dst: args.dst, src: args.src, workbuf: args.workbuf)
            this.ssize_have ~mod+= args.src.count_since(mark: smark)
            this.dsize_have ~mod+= args.dst.count_since(mark: dmark)

            if not this.ignore_checksum {
                this.crc32.update!(x: args.dst.since(mark: dmark))
            }

            if status.is_ok() {
                break
            }
            yield? status
        }

        // Check the checksum.
        checksum_want = args.src.read_u32le?()
        if not this.ignore_checksum {
            checksum_have = this.crc32.checksum_u32()
            if checksum_have <> checksum_want {
                return "#bad checksum"
            }
        }

        // Check the uncompressed size.
        size_want = args.src.read_u64le?()
        if this.dsize_have <> size_want {
            return "#bad footer"
        }

        // Check the compressed size, which includes 6 bytes of header and 20
        // bytes of footer. Per the spec, it's also capped at 2 PiB.
        size_want = args.src.read_u64le?()
        if (size_want < 26) or (0x8_0000_0000_0000 < size_want) {
            return "#bad footer"
        } else if this.ssize_have <> (size_want - 26) {
            return "#bad footer"
        }

        // Reset state and continue the outer loop, if not at EOF and it looks
        // like there's another LZIP-encoded chunk.
        while args.src.length() < 4,
                post args.src.length() >= 4,
        {
            if args.src.is_closed() {
                break.outer
            }
            yield? base."$short read"
        }
        c32 = args.src.peek_u32le()
        if c32 <> 'LZIP'le {
            break.outer
        }
        this.crc32.reset!()
        this.lzma.reset!()
    }.outer
}