// Copyright 2018 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

use "std/crc32"
use "std/deflate"

pub status "#bad checksum"
pub status "#bad compression method"
pub status "#bad encoding flags"
pub status "#bad header"
pub status "#truncated input"

pub const DECODER_DST_HISTORY_RETAIN_LENGTH_MAX_INCL_WORST_CASE : base.u64 = 0

// TODO: reference deflate.DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE.
pub const DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE : base.u64 = 1

pub struct decoder? implements base.io_transformer(
        ignore_checksum : base.bool,
        checksum        : crc32.ieee_hasher,

        flate : deflate.decoder,

        util : base.utility,
)

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.util.make_optional_u63(has_value: true, value: 0)
}

pub func decoder.workbuf_len() base.range_ii_u64 {
    return this.util.make_range_ii_u64(
            min_incl: DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE,
            max_incl: DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE)
}

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 flags               : base.u8
    var xlen                : base.u16
    var mark                : base.u64
    var checksum_have       : base.u32
    var decoded_length_have : base.u32
    var status              : base.status
    var checksum_want       : base.u32
    var decoded_length_want : base.u32

    // Read the header.
    c8 = args.src.read_u8?()
    if c8 <> 0x1F {
        return "#bad header"
    }
    c8 = args.src.read_u8?()
    if c8 <> 0x8B {
        return "#bad header"
    }
    c8 = args.src.read_u8?()
    if c8 <> 0x08 {
        return "#bad compression method"
    }
    flags = args.src.read_u8?()
    // TODO: API for returning the header's MTIME field.
    args.src.skip_u32?(n: 6)

    // Handle FEXTRA.
    if (flags & 0x04) <> 0 {
        xlen = args.src.read_u16le?()
        args.src.skip_u32?(n: xlen as base.u32)
    }

    // Handle FNAME.
    //
    // TODO: API for returning the header's FNAME field. This might require
    // converting ISO 8859-1 to UTF-8. We may also want to cap the UTF-8
    // filename length to NAME_MAX, which is 255.
    if (flags & 0x08) <> 0 {
        while true {
            c8 = args.src.read_u8?()
            if c8 == 0 {
                break
            }
        }
    }

    // Handle FCOMMENT.
    if (flags & 0x10) <> 0 {
        while true {
            c8 = args.src.read_u8?()
            if c8 == 0 {
                break
            }
        }
    }

    // Handle FHCRC.
    if (flags & 0x02) <> 0 {
        args.src.skip_u32?(n: 2)
    }

    // Reserved flags bits must be zero.
    if (flags & 0xE0) <> 0 {
        return "#bad encoding flags"
    }

    // Decode and checksum the DEFLATE-encoded payload.
    while true {
        mark = args.dst.mark()
        status =? this.flate.transform_io?(dst: args.dst, src: args.src, workbuf: args.workbuf)
        if not this.ignore_checksum {
            checksum_have = this.checksum.update_u32!(x: args.dst.since(mark: mark))
            decoded_length_have ~mod+= (args.dst.count_since(mark: mark) & 0xFFFF_FFFF) as base.u32
        }
        if status.is_ok() {
            break
        }
        yield? status
    }
    checksum_want = args.src.read_u32le?()
    decoded_length_want = args.src.read_u32le?()
    if (not this.ignore_checksum) and
            ((checksum_have <> checksum_want) or (decoded_length_have <> decoded_length_want)) {
        return "#bad checksum"
    }
}