/**
 * Buffers
 * 
 * Copyright:
 * (C) 2012-2015 Tatsuhiro Tsujikawa
 * (C) 2014-2015 Etienne Cimon
 *
 * License: 
 * Distributed under the terms of the MIT license with an additional section 1.2 of the curl/libcurl project. 
 * Consult the provided LICENSE.md file for details
 */
module libhttp2.buffers;

import libhttp2.types;
import std.algorithm : max, min;
import core.exception : onOutOfMemoryError;
import std.c.string : memcpy;
import memutils.utils;

struct Buffer
{
	/// This points to the beginning of the buffer. The effective range of buffer is [begin, end).
	ubyte* begin;
	/// This points to the memory one byte beyond the end of the buffer.
	ubyte* end;
	/// The position indicator for effective start of the buffer. pos <= last must be hold.
	ubyte* pos;
	/// The position indicator for effective one beyond of the end of the buffer. last <= end must be hold.
	ubyte* last;
	/// Mark arbitrary position in buffer [begin, end)
	ubyte* mark;
	/// true if the allocator must be secure
	bool use_secure_mem;
	/// true if the memory much be manually freed. use_secure_mem can be false if this is true
	bool zeroize_on_free;

	ubyte[] opSlice() { return pos[0 .. length]; }

	@property int length() {
		assert(last-pos >= 0);
		return cast(int)(last - pos);
	}

	@property int available() {
		return cast(int)(end - last);
	}

	@property int markAvailable() {
		return cast(int)(mark - last);
	}

	@property int capacity() {
		return cast(int)(end - begin);
	}

	@property int posOffset() {
		return cast(int)(pos - begin);
	}
	@property int offset() {
		return cast(int) (last - begin);
	}

	void shiftRight(size_t amount) {
		pos += amount;
		last += amount;
	}

	void shiftLeft(size_t amount) {
		pos -= amount;
		last -= amount;
	}

	void free()
	{
		if (!end || !begin) return;
		assert(end >= begin);
		size_t memlen = cast(size_t)((cast(void*)end) - (cast(void*)begin));
		static if (__VERSION__ >= 2067)
		{
			if (use_secure_mem) { 
				import std.c.string : memset;
				// optimization, skips freeing the entire buffer in memutils for light buffer uses
				if (capacity > 1024 && offset < capacity - capacity/128)
					memset(begin, 0, offset);
				SecureMem.free(begin[0 .. memlen]);
			}
			else 
			{
				if (zeroize_on_free)
				{
					import std.c.string : memset;
					memset(begin, 0, memlen);
				}
				Mem.free(begin[0 .. memlen]);
			}
		}
		else {
			if (zeroize_on_free || use_secure_mem)
			{
				import std.c.string : memset;
				memset(begin, 0, memlen);
			}
			Mem.free(begin[0 .. memlen]);
		}
		begin = null;
		end = null;
	}
	
	/*
	 * Extends buffer so that capacity() returns at least
	 * |new_cap|. If extensions took place, buffer pointers in |buf| will
	 * change.
	 */
	void reserve(size_t new_cap)
	{
		if (!new_cap) return;

		ubyte[] new_buf;
		size_t cap;
		
		cap = capacity;
		
		if (cap >= new_cap) {
			return;
		}
		
		new_cap = max(new_cap, cap * 2);

		static if (__VERSION__ >= 2067)
		{
			if (use_secure_mem) {
				if (begin)
					new_buf = SecureMem.realloc(begin[0 .. end - begin], new_cap);
				else
					new_buf = SecureMem.alloc!(ubyte[])(new_cap);
			}
			else {
				if (begin) {
					new_buf = Mem.realloc(begin[0 .. end - begin], new_cap);
				}
				else
					new_buf = Mem.alloc!(ubyte[])(new_cap);
			}
		}
		else {
			if (begin) {
				new_buf = Mem.realloc(begin[0 .. end - begin], new_cap);
			}
			else
				new_buf = Mem.alloc!(ubyte[])(new_cap);
		}
		ubyte* ptr = new_buf.ptr;
		
		pos = ptr + (pos - begin);
		last = ptr + (last - begin);
		mark = ptr + (mark - begin);
		begin = ptr;
		end = ptr + new_cap;
		
		return;
	}
	
	/// Resets pos, last, mark member of |buf| to buf.begin.
	void reset()
	{
		pos = last = mark = begin;
	}
	
	/*
	 * Initializes Buffer using supplied buffer |buf|. Semantically, 
	 * the application should not call *_reserve() or free() functions.
	 */
	this(ubyte[] buf) {
		begin = pos = last = mark = buf.ptr;
		end = begin + buf.length;
	}		
	
	/*
	 * Initializes the |buf| and allocates at least |initial| bytes of
	 * memory.
	 */
	this(size_t initial = 0, bool _use_secure_mem = false, bool _zeroise_on_free = false) {
		use_secure_mem = _use_secure_mem;
		zeroize_on_free = _zeroise_on_free;
		begin = null;
		end = null;
		pos = null;
		last = null;
		mark = null;
		reserve(initial);
	}

}

class Buffers {

	class Chain {
		Buffer buf;
		Chain next;
		static Chain opCall(size_t chunk_length = 0, bool _use_secure_mem = false, bool _zeroize_on_free = false)
		{
			Chain chain;
			chain = Mem.alloc!(Buffers.Chain)();
			scope(failure) Mem.free(chain);
			chain.next = null;
			chain.buf = Buffer(chunk_length, _use_secure_mem, _zeroize_on_free);
			return chain;
		}

		void free() 
		{
			buf.free();
			buf.destroy();
		}
	}

	/// Points to the first buffer
	Chain head;
	/// Buffer pointer where write occurs.
	Chain cur;
	/// The buffer capacity of each Buffer
	size_t chunk_length;
	/// The maximum number of `Chain`s
	size_t max_chunk;
	/// The number of `Chain`s allocated
	size_t chunk_used;
	/// The number of `Chain`s to keep on reset
	size_t chunk_keep;
	/// pos offset from begin in each buffers. On initialization and reset, buf.pos and buf.last are positioned at buf.begin + offset.
	size_t offset;

	/// true if the buffers were initialized with a pre-allocated ubyte[] which mustn't be freed
	bool dont_free;
	/// true if we should secure the Buffer allocations
	bool use_secure_mem;
	/// true if the Buffer allocations should be zeroized
	bool zeroize_on_free;

	/// This is the same as calling init2 with the given arguments and offset = 0.
	this(size_t _chunk_length, size_t _max_chunk, bool _use_secure_mem = false, bool _zeroize_on_free = false) {
		this(_chunk_length, _max_chunk, _max_chunk, 0, _use_secure_mem, _zeroize_on_free);
	}

	/// This is the same as calling init3 with the given arguments and chunk_keep = max_chunk.
	this(size_t _chunk_length, size_t _max_chunk, size_t _offset, bool _use_secure_mem = false, bool _zeroize_on_free = false)
	{
		this(_chunk_length, _max_chunk, _max_chunk, _offset, _use_secure_mem, _zeroize_on_free);
	}

	/**
	 * Initializes Buffers. Each buffer size is given in the
	 * |chunk_length|.  The maximum number of buffers is given in the
	 * |max_chunk|.  On reset, first |chunk_keep| buffers are kept and
	 * remaining buffers are deleted.  Each buffer will have bufs.pos and
	 * bufs.last shifted to left by |offset| bytes on creation and reset.
	 *
	 * This function allocates first buffer.  bufs.head and bufs.cur
	 * will point to the first buffer after this call.
	 */
	this(size_t _chunk_length, size_t _max_chunk, size_t _chunk_keep, size_t _offset, bool _use_secure_mem = false, bool _zeroize_on_free = false) 
	in { assert(!(_chunk_keep == 0 || _max_chunk < _chunk_keep || _chunk_length < _offset), "Invalid Arguments"); }
	body
	{
		use_secure_mem = _use_secure_mem;
		zeroize_on_free = _zeroize_on_free;
		Chain chain = Chain(_chunk_length, _use_secure_mem, _zeroize_on_free);

		offset = _offset;
		
		head = chain;
		cur = head;
		
		cur.buf.shiftRight(offset);
		
		chunk_length = _chunk_length;
		chunk_used = 1;
		max_chunk = _max_chunk;
		chunk_keep = _chunk_keep;
	}

	/*
	 * Initializes Buffers using supplied buffer |buf|.
	 * The first buffer bufs.head uses buffer |begin|.  The buffer size
	 * is fixed and no allocate extra chunk buffer is allocated.  In other
	 * words, max_chunk = chunk_keep = 1. 
	 */
	this(ubyte[] buf)
	{
		Chain chain = Chain();

		chain.next = null;
		chain.buf = Buffer(buf);

		dont_free = true;
		offset = 0;
		head = chain;
		cur = head;
		chunk_length = buf.length;
		chunk_used = 1;
		max_chunk = 1;
		chunk_keep = 1;
	}

	~this() { if (head) free(); }

	/// Frees any related resources
	void free()
	{
		Chain chain;
		Chain next_chain;
		
		if (!head) return;

		if (dont_free) {
			Mem.free(head);
			head = null;
			return;
		}
		
		for (chain = head; chain;) {
			next_chain = chain.next;
			chain.free();
			Mem.free(chain);
			chain = next_chain;
		}
		
		head = null;
	}	

	/*
	 * Reallocates internal buffer using |chunk_length|.  The max_chunk,
	 * chunk_keep and offset do not change.  After successful allocation
	 * of new buffer, previous buffers are deallocated without copying
	 * anything into new buffers.  chunk_used is reset to 1.
	 *
	 * This function returns 0 if it succeeds, or one of the following
	 * negative error codes:
	 *
	 * ErrorCode.NOMEM
	 *     Out of memory.
	 * ErrorCode.INVALID_ARGUMENT
	 *     chunk_length < offset
	 */
	void realloc(size_t _chunk_length)
	in { assert(_chunk_length >= offset, "Invalid Arguments"); }
	body {
		Chain chain = Chain(_chunk_length, use_secure_mem, zeroize_on_free);
		
		free();
		
		head = chain;
		cur = head;
		
		cur.buf.shiftRight(offset);
		
		chunk_length = _chunk_length;
		chunk_used = 1;
	}

	/*
	 * Appends the |data| of length |len| to the |bufs|. The write starts
	 * at bufs.cur.buf.last. A new buffers will be allocated to store
	 * all data.
	 *
	 * This function returns 0 if it succeeds, or one of the following
	 * negative error codes:
	 *
	 * ErrorCode.NOMEM
	 *     Out of memory.
	 * ErrorCode.BUFFER_ERROR
	 *     Out of buffer space.
	 */
	ErrorCode add(in string data)
	{
		ErrorCode rv;
		size_t nwrite;
		Buffer* buf;
		const(ubyte)* p;
		int len = cast(int)data.length;
		if (available < len) {
			return ErrorCode.BUFFER_ERROR;
		}
		
		p = cast(const(ubyte)*)data.ptr;
		
		while (len > 0) {
			buf = &cur.buf;
			
			nwrite = cast(size_t) min(buf.available, len);
			if (nwrite == 0) {
				rv = allocChain();
				if (rv != 0) {
					return rv;
				}
				continue;
			}
			memcpy(buf.last, p, nwrite);
			buf.last += nwrite;
			p += nwrite;
			len -= nwrite;
		}
		
		return ErrorCode.OK;
	}

	/*
	 * Appends a single byte |b| to the Buffers. The write starts at
	 * cur.buf.last. A new buffers will be allocated to store all
	 * data.
	 *
	 * This function returns 0 if it succeeds, or one of the following
	 * negative error codes:
	 *
	 * ErrorCode.BUFFER_ERROR
	 *     Out of buffer space.
	 */
	ErrorCode add(ubyte b)
	{
		ErrorCode rv;
		
		rv = ensureAddByte();
		if (rv != 0) 
			return rv;

		
		*cur.buf.last++ = b;
		
		return ErrorCode.OK;
	}

	/*
	 * Behaves like addb(), but this does not update
	 * buf.last pointer.
	 */
	ErrorCode addHold(ubyte b)
	{
		ErrorCode rv;
		
		rv = ensureAddByte();
		if (rv != 0) {
			return rv;
		}
		
		*cur.buf.last = b;
		
		return ErrorCode.OK;
	}

	void fastAdd(ubyte b) {
		assert(cur.buf.last+1 <= cur.buf.end);
		*cur.buf.last++ = b;
	}

	void fastAddHold(ubyte b) {
		*cur.buf.last = b;
	}
		
	/*
	 * Performs bitwise-OR of |b| at cur.buf.last. A new buffers
	 * will be allocated if necessary.
	 *
	 * This function returns 0 if it succeeds, or one of the following
	 * negative error codes:
	 *
	 * ErrorCode.NOMEM
	 *     Out of memory.
	 * ErrorCode.BUFFER_ERROR
	 *     Out of buffer space.
	 */
	ErrorCode or(ubyte b)
	{
		ErrorCode rv;
		
		rv = ensureAddByte();
		if (rv != 0) {
			return rv;
		}
		
		*cur.buf.last++ |= b;
		
		return ErrorCode.OK;
	}

	/*
	 * Behaves like orb(), but does not update buf.last
	 * pointer.
	 */
	ErrorCode orHold(ubyte b)
	{
		ErrorCode rv;
		
		rv = ensureAddByte();
		if (rv != 0) {
			return rv;
		}
		
		*cur.buf.last |= b;
		
		return ErrorCode.OK;
	}

	void fastOr(ubyte b) {
		assert(cur.buf.last+1 <= cur.buf.end);
		*cur.buf.last++ |= b;
	}

	void fastOrHold(ubyte b) {
		*cur.buf.last |= b;
	}

	/*
	 * Copies all data stored in Buffers to the contagious buffer.  This
	 * function allocates the contagious memory to store all data in
	 * Buffers and returns it.
	 */
	ubyte[] remove()
	{
		size_t len;
		Chain chain;
		Buffer* buf;
		ubyte[] res;
		Buffer resbuf;
		len = 0;
		
		for (chain = head; chain; chain = chain.next) {
			len += chain.buf.length;
		}
		if (!len) 
			res = null;
		else {
			res = Mem.alloc!(ubyte[])(len);
		}
		resbuf = Buffer(res);
		
		for (chain = head; chain; chain = chain.next) {
			buf = &chain.buf;
			
			if (resbuf.last) {
				assert(resbuf.available >= buf.length);
				memcpy(resbuf.last, buf.pos, buf.length);
				resbuf.last += buf.length;
			}
			
			buf.reset();
			chain.buf.shiftRight(offset);
		}
		
		cur = head;
		return res;
	}

	/// Fills dst with a slice of the head chain's buffer, and frees the chain if it becomes empty
	/// chunk_keep must be 1 for buffers to be emptied this way.
	ubyte[] removeOne(ubyte[] dst) 
	in { 
		assert(chunk_keep <= 1, "Cannot use removeOne with a custom keep amount set"); 
	}
	body {
		Chain chain = head;
		size_t len = min(chain.buf.length, dst.length);
		ubyte[] data = chain.buf.pos[0 .. len];
		memcpy(dst.ptr, data.ptr, len);

		chain.buf.pos += len;

		if (chain.buf.available == 0 && chain.buf.length == 0) 
		{
			if (chain.next) {
				head = chain.next;
				chain.free();
				Mem.free(chain);
				chunk_used--;
			} else {
				chain.buf.reset();
				chain.buf.shiftRight(offset);
				cur = head = chain;
			}
		}

		if (dst.length == len) 
			return dst;
		return dst[0 .. len];
	}

	// The head buffer was already read, just remove it
	void removeOne()
	in { 
		assert(chunk_keep <= 1, "Cannot use removeOne with a custom keep amount set"); 
	}
	body {
		Chain chain = head;

		if (chain.next) {
			head = chain.next;
			chain.free();
			Mem.free(chain);
			chunk_used--;
		} else {
			chain.buf.reset();
			chain.buf.shiftRight(offset);
			cur = head = chain;
		}
	}

	/*
	 * Resets Buffers and makes the buffers empty.
	 */
	void reset()
	{
		Chain chain;
		Chain ci;
		size_t k;
		
		k = chunk_keep;
		for (ci = head; ci; ci = ci.next) {
			ci.buf.reset();
			ci.buf.shiftRight(offset);
			
			if (--k == 0) {
				break;
			}
		}
		
		if (ci) {
			chain = ci.next;
			ci.next = null;
			
			for (ci = chain; ci;) {
				chain = ci.next;
				
				ci.free();
				Mem.free(ci);
				ci = chain;
			}
			
			chunk_used = chunk_keep;
		}
		
		cur = head;
	}

	/*
	 * Moves cur to cur.next.  If resulting cur is
	 * null, this function allocates new buffers and cur points to
	 * it.
	 *
	 * This function returns 0 if it succeeds, or one of the following
	 * negative error codes:
	 *
	 * ErrorCode.NOMEM
	 *     Out of memory
	 * ErrorCode.BUFFER_ERROR
	 *     Out of buffer space.
	 */
	ErrorCode advance() { return allocChain(); }

	/* Sets cur to head */
	void rewind() {
		cur = head;
	}

	
	/*
	 * Move cur, from the current position, using next member, to
	 * the last buf which has length > 0 without seeing buf
	 * which satisfies length == 0.  If cur.buf.length == 0 or cur.next is null,
	 * cur is unchanged.
	 */
	void seekLastPresent()
	{
		Chain ci;
		
		for (ci = cur; ci; ci = ci.next) {
			if (ci.buf.length == 0) {
				return;
			} else {
				cur = ci;
			}
		}
	}

	/*
	 * Returns true if cur.next is not empty.
	 */
	bool nextPresent()
	{
		Chain chain;
		
		chain = cur.next;
		
		return chain && chain.buf.length;
	}

	int curAvailable() {
		return cur.buf.available();
	}

	@property int length()
	{
		Chain ci;
		int len;
		
		len = 0;
		for (ci = head; ci; ci = ci.next) {
			len += ci.buf.length;
		}
		
		return len;
	}

	@property int available() {
		return cast(int)(cur.buf.available + (chunk_length - offset) * (max_chunk - chunk_used));

	}

private:
	ErrorCode ensureAddByte()
	{
		ErrorCode rv;
		Buffer* buf;
		
		buf = &cur.buf;
		
		if (buf.available >= 1) {
			return ErrorCode.OK;
		}
		
		rv = allocChain();
		if (rv != 0)
			return rv;		
		return ErrorCode.OK;
	}

	ErrorCode allocChain() {
		Chain chain;
		
		if (cur.next) {
			cur = cur.next;
			return ErrorCode.OK;
		}
		
		if (max_chunk == chunk_used)
			return ErrorCode.BUFFER_ERROR;

		chain = Chain(chunk_length, use_secure_mem, zeroize_on_free);
		
		LOGF("new buffer %d bytes allocated for bufs %s, used %d", chunk_length, this, chunk_used);
		
		++chunk_used;
		
		cur.next = chain;
		cur = chain;		
		cur.buf.shiftRight(offset);
		
		return ErrorCode.OK;
	}

}