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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package flate

import (
        "io"
        "math"
        "strconv"
)

const (
        // The largest offset code.
        offsetCodeCount = 30

        // The special code used to mark the end of a block.
        endBlockMarker = 256

        // The first length code.
        lengthCodesStart = 257

        // The number of codegen codes.
        codegenCodeCount = 19
        badCode          = 255
)

// The number of extra bits needed by length code X - LENGTH_CODES_START.
var lengthExtraBits = []int8{
        /* 257 */ 0, 0, 0,
        /* 260 */ 0, 0, 0, 0, 0, 1, 1, 1, 1, 2,
        /* 270 */ 2, 2, 2, 3, 3, 3, 3, 4, 4, 4,
        /* 280 */ 4, 5, 5, 5, 5, 0,
}

// The length indicated by length code X - LENGTH_CODES_START.
var lengthBase = []uint32{
        0, 1, 2, 3, 4, 5, 6, 7, 8, 10,
        12, 14, 16, 20, 24, 28, 32, 40, 48, 56,
        64, 80, 96, 112, 128, 160, 192, 224, 255,
}

// offset code word extra bits.
var offsetExtraBits = []int8{
        0, 0, 0, 0, 1, 1, 2, 2, 3, 3,
        4, 4, 5, 5, 6, 6, 7, 7, 8, 8,
        9, 9, 10, 10, 11, 11, 12, 12, 13, 13,
        /* extended window */
        14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20,
}

var offsetBase = []uint32{
        /* normal deflate */
        0x000000, 0x000001, 0x000002, 0x000003, 0x000004,
        0x000006, 0x000008, 0x00000c, 0x000010, 0x000018,
        0x000020, 0x000030, 0x000040, 0x000060, 0x000080,
        0x0000c0, 0x000100, 0x000180, 0x000200, 0x000300,
        0x000400, 0x000600, 0x000800, 0x000c00, 0x001000,
        0x001800, 0x002000, 0x003000, 0x004000, 0x006000,

        /* extended window */
        0x008000, 0x00c000, 0x010000, 0x018000, 0x020000,
        0x030000, 0x040000, 0x060000, 0x080000, 0x0c0000,
        0x100000, 0x180000, 0x200000, 0x300000,
}

// The odd order in which the codegen code sizes are written.
var codegenOrder = []uint32{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}

type huffmanBitWriter struct {
        w io.Writer
        // Data waiting to be written is bytes[0:nbytes]
        // and then the low nbits of bits.
        bits            uint32
        nbits           uint32
        bytes           [64]byte
        nbytes          int
        literalFreq     []int32
        offsetFreq      []int32
        codegen         []uint8
        codegenFreq     []int32
        literalEncoding *huffmanEncoder
        offsetEncoding  *huffmanEncoder
        codegenEncoding *huffmanEncoder
        err             error
}

type WrongValueError struct {
        name  string
        from  int32
        to    int32
        value int32
}

func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
        return &huffmanBitWriter{
                w:               w,
                literalFreq:     make([]int32, maxLit),
                offsetFreq:      make([]int32, offsetCodeCount),
                codegen:         make([]uint8, maxLit+offsetCodeCount+1),
                codegenFreq:     make([]int32, codegenCodeCount),
                literalEncoding: newHuffmanEncoder(maxLit),
                offsetEncoding:  newHuffmanEncoder(offsetCodeCount),
                codegenEncoding: newHuffmanEncoder(codegenCodeCount),
        }
}

func (err WrongValueError) Error() string {
        return "huffmanBitWriter: " + err.name + " should belong to [" + strconv.FormatInt(int64(err.from), 10) + ";" +
                strconv.FormatInt(int64(err.to), 10) + "] but actual value is " + strconv.FormatInt(int64(err.value), 10)
}

func (w *huffmanBitWriter) flushBits() {
        if w.err != nil {
                w.nbits = 0
                return
        }
        bits := w.bits
        w.bits >>= 16
        w.nbits -= 16
        n := w.nbytes
        w.bytes[n] = byte(bits)
        w.bytes[n+1] = byte(bits >> 8)
        if n += 2; n >= len(w.bytes) {
                _, w.err = w.w.Write(w.bytes[0:])
                n = 0
        }
        w.nbytes = n
}

func (w *huffmanBitWriter) flush() {
        if w.err != nil {
                w.nbits = 0
                return
        }
        n := w.nbytes
        if w.nbits > 8 {
                w.bytes[n] = byte(w.bits)
                w.bits >>= 8
                w.nbits -= 8
                n++
        }
        if w.nbits > 0 {
                w.bytes[n] = byte(w.bits)
                w.nbits = 0
                n++
        }
        w.bits = 0
        _, w.err = w.w.Write(w.bytes[0:n])
        w.nbytes = 0
}

func (w *huffmanBitWriter) writeBits(b, nb int32) {
        w.bits |= uint32(b) << w.nbits
        if w.nbits += uint32(nb); w.nbits >= 16 {
                w.flushBits()
        }
}

func (w *huffmanBitWriter) writeBytes(bytes []byte) {
        if w.err != nil {
                return
        }
        n := w.nbytes
        if w.nbits == 8 {
                w.bytes[n] = byte(w.bits)
                w.nbits = 0
                n++
        }
        if w.nbits != 0 {
                w.err = InternalError("writeBytes with unfinished bits")
                return
        }
        if n != 0 {
                _, w.err = w.w.Write(w.bytes[0:n])
                if w.err != nil {
                        return
                }
        }
        w.nbytes = 0
        _, w.err = w.w.Write(bytes)
}

// RFC 1951 3.2.7 specifies a special run-length encoding for specifying
// the literal and offset lengths arrays (which are concatenated into a single
// array).  This method generates that run-length encoding.
//
// The result is written into the codegen array, and the frequencies
// of each code is written into the codegenFreq array.
// Codes 0-15 are single byte codes. Codes 16-18 are followed by additional
// information.  Code badCode is an end marker
//
//  numLiterals      The number of literals in literalEncoding
//  numOffsets       The number of offsets in offsetEncoding
func (w *huffmanBitWriter) generateCodegen(numLiterals int, numOffsets int) {
        for i := range w.codegenFreq {
                w.codegenFreq[i] = 0
        }
        // Note that we are using codegen both as a temporary variable for holding
        // a copy of the frequencies, and as the place where we put the result.
        // This is fine because the output is always shorter than the input used
        // so far.
        codegen := w.codegen // cache
        // Copy the concatenated code sizes to codegen.  Put a marker at the end.
        copy(codegen[0:numLiterals], w.literalEncoding.codeBits)
        copy(codegen[numLiterals:numLiterals+numOffsets], w.offsetEncoding.codeBits)
        codegen[numLiterals+numOffsets] = badCode

        size := codegen[0]
        count := 1
        outIndex := 0
        for inIndex := 1; size != badCode; inIndex++ {
                // INVARIANT: We have seen "count" copies of size that have not yet
                // had output generated for them.
                nextSize := codegen[inIndex]
                if nextSize == size {
                        count++
                        continue
                }
                // We need to generate codegen indicating "count" of size.
                if size != 0 {
                        codegen[outIndex] = size
                        outIndex++
                        w.codegenFreq[size]++
                        count--
                        for count >= 3 {
                                n := 6
                                if n > count {
                                        n = count
                                }
                                codegen[outIndex] = 16
                                outIndex++
                                codegen[outIndex] = uint8(n - 3)
                                outIndex++
                                w.codegenFreq[16]++
                                count -= n
                        }
                } else {
                        for count >= 11 {
                                n := 138
                                if n > count {
                                        n = count
                                }
                                codegen[outIndex] = 18
                                outIndex++
                                codegen[outIndex] = uint8(n - 11)
                                outIndex++
                                w.codegenFreq[18]++
                                count -= n
                        }
                        if count >= 3 {
                                // count >= 3 && count <= 10
                                codegen[outIndex] = 17
                                outIndex++
                                codegen[outIndex] = uint8(count - 3)
                                outIndex++
                                w.codegenFreq[17]++
                                count = 0
                        }
                }
                count--
                for ; count >= 0; count-- {
                        codegen[outIndex] = size
                        outIndex++
                        w.codegenFreq[size]++
                }
                // Set up invariant for next time through the loop.
                size = nextSize
                count = 1
        }
        // Marker indicating the end of the codegen.
        codegen[outIndex] = badCode
}

func (w *huffmanBitWriter) writeCode(code *huffmanEncoder, literal uint32) {
        if w.err != nil {
                return
        }
        w.writeBits(int32(code.code[literal]), int32(code.codeBits[literal]))
}

// Write the header of a dynamic Huffman block to the output stream.
//
//  numLiterals  The number of literals specified in codegen
//  numOffsets   The number of offsets specified in codegen
//  numCodegens  The number of codegens used in codegen
func (w *huffmanBitWriter) writeDynamicHeader(numLiterals int, numOffsets int, numCodegens int, isEof bool) {
        if w.err != nil {
                return
        }
        var firstBits int32 = 4
        if isEof {
                firstBits = 5
        }
        w.writeBits(firstBits, 3)
        w.writeBits(int32(numLiterals-257), 5)
        w.writeBits(int32(numOffsets-1), 5)
        w.writeBits(int32(numCodegens-4), 4)

        for i := 0; i < numCodegens; i++ {
                value := w.codegenEncoding.codeBits[codegenOrder[i]]
                w.writeBits(int32(value), 3)
        }

        i := 0
        for {
                var codeWord int = int(w.codegen[i])
                i++
                if codeWord == badCode {
                        break
                }
                // The low byte contains the actual code to generate.
                w.writeCode(w.codegenEncoding, uint32(codeWord))

                switch codeWord {
                case 16:
                        w.writeBits(int32(w.codegen[i]), 2)
                        i++
                        break
                case 17:
                        w.writeBits(int32(w.codegen[i]), 3)
                        i++
                        break
                case 18:
                        w.writeBits(int32(w.codegen[i]), 7)
                        i++
                        break
                }
        }
}

func (w *huffmanBitWriter) writeStoredHeader(length int, isEof bool) {
        if w.err != nil {
                return
        }
        var flag int32
        if isEof {
                flag = 1
        }
        w.writeBits(flag, 3)
        w.flush()
        w.writeBits(int32(length), 16)
        w.writeBits(int32(^uint16(length)), 16)
}

func (w *huffmanBitWriter) writeFixedHeader(isEof bool) {
        if w.err != nil {
                return
        }
        // Indicate that we are a fixed Huffman block
        var value int32 = 2
        if isEof {
                value = 3
        }
        w.writeBits(value, 3)
}

func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
        if w.err != nil {
                return
        }
        for i := range w.literalFreq {
                w.literalFreq[i] = 0
        }
        for i := range w.offsetFreq {
                w.offsetFreq[i] = 0
        }

        n := len(tokens)
        tokens = tokens[0 : n+1]
        tokens[n] = endBlockMarker

        for _, t := range tokens {
                switch t.typ() {
                case literalType:
                        w.literalFreq[t.literal()]++
                case matchType:
                        length := t.length()
                        offset := t.offset()
                        w.literalFreq[lengthCodesStart+lengthCode(length)]++
                        w.offsetFreq[offsetCode(offset)]++
                }
        }

        // get the number of literals
        numLiterals := len(w.literalFreq)
        for w.literalFreq[numLiterals-1] == 0 {
                numLiterals--
        }
        // get the number of offsets
        numOffsets := len(w.offsetFreq)
        for numOffsets > 0 && w.offsetFreq[numOffsets-1] == 0 {
                numOffsets--
        }
        if numOffsets == 0 {
                // We haven't found a single match. If we want to go with the dynamic encoding,
                // we should count at least one offset to be sure that the offset huffman tree could be encoded.
                w.offsetFreq[0] = 1
                numOffsets = 1
        }

        w.literalEncoding.generate(w.literalFreq, 15)
        w.offsetEncoding.generate(w.offsetFreq, 15)

        storedBytes := 0
        if input != nil {
                storedBytes = len(input)
        }
        var extraBits int64
        var storedSize int64 = math.MaxInt64
        if storedBytes <= maxStoreBlockSize && input != nil {
                storedSize = int64((storedBytes + 5) * 8)
                // We only bother calculating the costs of the extra bits required by
                // the length of offset fields (which will be the same for both fixed
                // and dynamic encoding), if we need to compare those two encodings
                // against stored encoding.
                for lengthCode := lengthCodesStart + 8; lengthCode < numLiterals; lengthCode++ {
                        // First eight length codes have extra size = 0.
                        extraBits += int64(w.literalFreq[lengthCode]) * int64(lengthExtraBits[lengthCode-lengthCodesStart])
                }
                for offsetCode := 4; offsetCode < numOffsets; offsetCode++ {
                        // First four offset codes have extra size = 0.
                        extraBits += int64(w.offsetFreq[offsetCode]) * int64(offsetExtraBits[offsetCode])
                }
        }

        // Figure out smallest code.
        // Fixed Huffman baseline.
        var size = int64(3) +
                fixedLiteralEncoding.bitLength(w.literalFreq) +
                fixedOffsetEncoding.bitLength(w.offsetFreq) +
                extraBits
        var literalEncoding = fixedLiteralEncoding
        var offsetEncoding = fixedOffsetEncoding

        // Dynamic Huffman?
        var numCodegens int

        // Generate codegen and codegenFrequencies, which indicates how to encode
        // the literalEncoding and the offsetEncoding.
        w.generateCodegen(numLiterals, numOffsets)
        w.codegenEncoding.generate(w.codegenFreq, 7)
        numCodegens = len(w.codegenFreq)
        for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
                numCodegens--
        }
        dynamicHeader := int64(3+5+5+4+(3*numCodegens)) +
                w.codegenEncoding.bitLength(w.codegenFreq) +
                int64(extraBits) +
                int64(w.codegenFreq[16]*2) +
                int64(w.codegenFreq[17]*3) +
                int64(w.codegenFreq[18]*7)
        dynamicSize := dynamicHeader +
                w.literalEncoding.bitLength(w.literalFreq) +
                w.offsetEncoding.bitLength(w.offsetFreq)

        if dynamicSize < size {
                size = dynamicSize
                literalEncoding = w.literalEncoding
                offsetEncoding = w.offsetEncoding
        }

        // Stored bytes?
        if storedSize < size {
                w.writeStoredHeader(storedBytes, eof)
                w.writeBytes(input[0:storedBytes])
                return
        }

        // Huffman.
        if literalEncoding == fixedLiteralEncoding {
                w.writeFixedHeader(eof)
        } else {
                w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
        }
        for _, t := range tokens {
                switch t.typ() {
                case literalType:
                        w.writeCode(literalEncoding, t.literal())
                        break
                case matchType:
                        // Write the length
                        length := t.length()
                        lengthCode := lengthCode(length)
                        w.writeCode(literalEncoding, lengthCode+lengthCodesStart)
                        extraLengthBits := int32(lengthExtraBits[lengthCode])
                        if extraLengthBits > 0 {
                                extraLength := int32(length - lengthBase[lengthCode])
                                w.writeBits(extraLength, extraLengthBits)
                        }
                        // Write the offset
                        offset := t.offset()
                        offsetCode := offsetCode(offset)
                        w.writeCode(offsetEncoding, offsetCode)
                        extraOffsetBits := int32(offsetExtraBits[offsetCode])
                        if extraOffsetBits > 0 {
                                extraOffset := int32(offset - offsetBase[offsetCode])
                                w.writeBits(extraOffset, extraOffsetBits)
                        }
                        break
                default:
                        panic("unknown token type: " + string(t))
                }
        }
}