module deflate

import encoding.binary
import hash.adler32
import hash.crc32

pub type ChunkCallback = fn (chunk []u8, userdata voidptr) int

// CompressFormat selects the output container around the RFC 1951 payload.
pub enum CompressFormat {
    zlib
    gzip
    raw_deflate
}

@[params]
pub struct CompressParams {
pub:
    format CompressFormat = .zlib
}

pub struct RawInflateResult {
pub:
    decoded  []u8
    consumed int
}

pub struct ZlibHeader {
pub:
    payload_start int = 2
}

pub struct GzipHeader {
pub mut:
    flags             u8
    payload_start     int
    extra             []u8
    filename          []u8
    comment           []u8
    modification_time u32
    operating_system  u8
}

// validate_zlib_header validates a RFC 1950 zlib header.
@[direct_array_access]
pub fn validate_zlib_header(data []u8) !ZlibHeader {
    if data.len < 6 {
        return error('invalid zlib stream: too short')
    }
    if data[0] & 0x0f != 8 {
        return error('invalid zlib stream: unsupported compression method')
    }
    if (u32(data[0]) * 256 + u32(data[1])) % 31 != 0 {
        return error('invalid zlib stream: bad header checksum')
    }
    if data[1] & 0x20 != 0 {
        return error('invalid zlib stream: preset dictionary not supported')
    }
    return ZlibHeader{}
}

// validate_gzip_header validates a RFC 1952 gzip header and returns parsed fields.
@[direct_array_access]
pub fn validate_gzip_header(data []u8) !GzipHeader {
    if data.len < 18 {
        return error('invalid gzip stream: too short')
    }
    if data[0] != 0x1f || data[1] != 0x8b {
        return error('invalid gzip stream: bad magic')
    }
    if data[2] != 8 {
        return error('invalid gzip stream: unsupported compression method')
    }
    flg := data[3]
    if flg & 0xe0 != 0 {
        return error('invalid gzip stream: reserved flags set')
    }
    mut header := GzipHeader{
        flags:             flg
        payload_start:     10
        modification_time: binary.little_endian_u32_at(data, 4)
        operating_system:  data[9]
    }
    if flg & 0x04 != 0 {
        if header.payload_start + 2 > data.len {
            return error('invalid gzip stream: truncated extra')
        }
        xlen := int(u32(data[header.payload_start]) | u32(data[header.payload_start + 1]) << 8)
        header.payload_start += 2
        if header.payload_start + xlen > data.len {
            return error('invalid gzip stream: truncated extra')
        }
        header.extra = data[header.payload_start..header.payload_start + xlen]
        header.payload_start += xlen
    }
    if flg & 0x08 != 0 {
        for header.payload_start < data.len && data[header.payload_start] != 0 {
            header.filename << data[header.payload_start]
            header.payload_start++
        }
        header.payload_start++
    }
    if flg & 0x10 != 0 {
        for header.payload_start < data.len && data[header.payload_start] != 0 {
            header.comment << data[header.payload_start]
            header.payload_start++
        }
        header.payload_start++
    }
    if flg & 0x02 != 0 {
        if header.payload_start + 2 > data.len {
            return error('invalid gzip stream: truncated fhcrc')
        }
        expected_crc16 := u16(data[header.payload_start]) | (u16(data[header.payload_start + 1]) << 8)
        actual_crc16 := u16(crc32.sum(data[..header.payload_start]) & 0xffff)
        if actual_crc16 != expected_crc16 {
            return error('invalid gzip stream: header crc16 mismatch')
        }
        header.payload_start += 2
    }
    if header.payload_start + 8 > data.len {
        return error('invalid gzip stream: truncated payload')
    }
    return header
}

// compress compresses data as zlib, gzip, or raw DEFLATE.
pub fn compress(data []u8, format CompressParams) ![]u8 {
    return match format.format {
        .zlib { compress_zlib(data) }
        .gzip { compress_gzip(data) }
        .raw_deflate { deflate_compress_fixed(data)! }
    }
}

pub fn compress_zlib(data []u8) ![]u8 {
    payload := deflate_compress_fixed(data)!
    cksum := adler32.sum(data)
    mut out := []u8{cap: 2 + payload.len + 4}
    out << u8(0x78) // CMF: CM=8 deflate, CINFO=7 (32K window)
    out << u8(0x9c) // FLG: default compression, FCHECK satisfies (CMF*256+FLG)%31==0
    out << payload
    out << binary.big_endian_get_u32(cksum)
    return out
}

// compress_gzip compresses data into a gzip stream (RFC 1952).
pub fn compress_gzip(data []u8) ![]u8 {
    payload := deflate_compress_fixed(data)!
    mut out := []u8{cap: 10 + payload.len + 8}
    // 10-byte gzip header: ID1 ID2 CM FLG MTIME(4) XFL OS
    out << [u8(0x1f), 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff]
    out << payload
    out << binary.little_endian_get_u32(crc32.sum(data))
    out << binary.little_endian_get_u32(u32(data.len))
    return out
}

// compress_raw compresses data to a raw RFC 1951 DEFLATE stream.
pub fn compress_raw(data []u8) ![]u8 {
    return deflate_compress_fixed(data)!
}

// decompress decompresses a zlib (RFC 1950), gzip (RFC 1952), or raw DEFLATE (RFC 1951) stream.
// The format is auto-detected.
pub fn decompress(data []u8) ![]u8 {
    if data.len >= 2 {
        // gzip magic: 0x1f 0x8b
        if data[0] == 0x1f && data[1] == 0x8b {
            return decompress_gzip(data)
        }
        // zlib: CM=8 and header checksum passes
        if data[0] & 0x0f == 8 && (u32(data[0]) * 256 + u32(data[1])) % 31 == 0 {
            return decompress_zlib(data)
        }
    }
    // raw DEFLATE
    return inflate(data)
}

// decompress_zlib decompresses a zlib stream (RFC 1950).
// It returns the decompressed bytes in a new array.
pub fn decompress_zlib(data []u8) ![]u8 {
    header := validate_zlib_header(data)!
    payload := data[header.payload_start..data.len - 4]
    expected := binary.big_endian_u32_at(data, data.len - 4)
    res := inflate_with_consumed(payload)!
    if res.consumed != payload.len {
        return error('invalid zlib stream: trailing data before adler32')
    }
    decoded := res.decoded
    if adler32.sum(decoded) != expected { return error('invalid zlib stream: adler32 mismatch') }
    return decoded
}

// decompress_gzip decompresses a gzip stream (RFC 1952).
// It returns the decompressed bytes in a new array.
pub fn decompress_gzip(data []u8) ![]u8 {
    header := validate_gzip_header(data)!
    payload := data[header.payload_start..data.len - 8]
    expected_crc := binary.little_endian_u32_at(data, data.len - 8)
    expected_size := binary.little_endian_u32_at(data, data.len - 4)
    res := inflate_with_consumed(payload)!
    if res.consumed != payload.len {
        return error('invalid gzip stream: trailing data before trailer')
    }
    decoded := res.decoded
    if crc32.sum(decoded) != expected_crc {
        return error('invalid gzip stream: crc32 mismatch')
    }
    if u32(decoded.len) != expected_size {
        return error('invalid gzip stream: size mismatch')
    }
    return decoded
}

// decompress_raw_with_consumed decompresses raw RFC 1951 DEFLATE data and tracks consumed bytes.
pub fn decompress_raw_with_consumed(data []u8) !RawInflateResult {
    res := inflate_with_consumed(data)!
    return RawInflateResult{
        decoded:  res.decoded
        consumed: res.consumed
    }
}

// decompress_with_callback decompresses a zlib/gzip/raw stream (RFC 1950, RFC 1952) using a callback for chunked delivery.
// The callback receives chunks of decompressed data and should return the chunk length to continue, or 0 to abort.
// Returns the total decompressed length.
pub fn decompress_with_callback(data []u8, cb ChunkCallback, userdata voidptr) !int {
    if data.len >= 2 {
        // gzip magic: 0x1f 0x8b
        if data[0] == 0x1f && data[1] == 0x8b {
            return decompress_gzip_with_callback(data, cb, userdata)
        }
        // zlib: CM=8 and header checksum passes
        if data[0] & 0x0f == 8 && (u32(data[0]) * 256 + u32(data[1])) % 31 == 0 {
            return decompress_zlib_with_callback(data, cb, userdata)
        }
    }
    // raw DEFLATE
    res := inflate_with_callback(data, cb, userdata)!
    return res.delivered
}

fn decompress_zlib_with_callback(data []u8, cb ChunkCallback, userdata voidptr) !int {
    header := validate_zlib_header(data)!
    payload := data[header.payload_start..data.len - 4]
    expected := binary.big_endian_u32_at(data, data.len - 4)
    res := inflate_with_callback(payload, cb, userdata)!
    if res.aborted {
        return res.delivered
    }
    if res.consumed != payload.len {
        return error('invalid zlib stream: trailing data before adler32')
    }
    if adler32.sum(res.decoded) != expected {
        return error('invalid zlib stream: adler32 mismatch')
    }
    return res.delivered
}

fn decompress_gzip_with_callback(data []u8, cb ChunkCallback, userdata voidptr) !int {
    header := validate_gzip_header(data)!
    payload := data[header.payload_start..data.len - 8]
    expected_crc := binary.little_endian_u32_at(data, data.len - 8)
    expected_size := binary.little_endian_u32_at(data, data.len - 4)
    res := inflate_with_callback(payload, cb, userdata)!
    if res.aborted {
        return res.delivered
    }
    if res.consumed != payload.len {
        return error('invalid gzip stream: trailing data before trailer')
    }
    if crc32.sum(res.decoded) != expected_crc {
        return error('invalid gzip stream: crc32 mismatch')
    }
    if u32(res.decoded.len) != expected_size {
        return error('invalid gzip stream: size mismatch')
    }
    return res.delivered
}

fn bit_reverse(v u32, n int) u32 {
    mut r := u32(0)
    mut val := v
    for _ in 0 .. n {
        r = (r << 1) | (val & 1)
        val >>= 1
    }
    return r
}