/**
 * Fast string building with minimum heap allocations.
 *
 * License:
 *   This Source Code Form is subject to the terms of
 *   the Mozilla Public License, v. 2.0. If a copy of
 *   the MPL was not distributed with this file, You
 *   can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Authors:
 *   Vladimir Panteleev <ae@cy.md>
 */

module ae.utils.textout;

import ae.utils.appender;

// **************************************************************************

/// Resolves to `true` when `T` can accept strings via `.put`.
template isStringSink(T)
{
	enum isStringSink = is(typeof(T.init.put("Test")));
}
deprecated alias IsStringSink = isStringSink;

// **************************************************************************

/// Appender instantiations for building strings.
alias FastAppender!(immutable(char)) StringBuilder; /// Immutable (single-use) variant.
alias FastAppender!           char   StringBuffer ; /// Reusable variant.

static assert(isStringSink!StringBuilder);
static assert(isStringSink!StringBuffer);

unittest
{
	StringBuilder sb;
	sb.put("Hello", ' ', "world!");
	assert(sb.get() == "Hello world!");
}

unittest
{
	StringBuilder sb;
	foreach (n; 0..4096)
		sb.put("Hello", " ", "world!");
	string s;
	foreach (n; 0..4096)
		s ~= "Hello world!";
	assert(sb.get() == s);
}

// **************************************************************************

/// Output range which writes to a static buffer.
struct StaticBuf(T, size_t size)
{
	T[size] buf; /// The buffer.
	size_t pos; /// Current position.
	void put(T v) { buf[pos++] = v; } ///
	void put(in T[] v) { buf[pos..pos+v.length] = v[]; pos+=v.length; } ///
	inout(T)[] data() inout { return buf[0..pos]; } /// Retrieve what was written so far.
}

// **************************************************************************

/// Sink which simply counts how much data is written to it.
struct CountingWriter(T)
{
	size_t count; /// Number of elements written.

	void put(T v) { count++; } ///
	void put(in T[] v) { count += v.length; } ///
}

// **************************************************************************

/// Sink which simply copies data to a pointer and advances it.
/// No reallocation, no bounds check - unsafe.
struct BlindWriter(T)
{
	T* ptr; /// Write target.

	void put(T v)
	{
		*ptr++ = v;
	} ///

	void put(in T[] v)
	{
		import core.stdc.string;
		memcpy(ptr, v.ptr, v.length*T.sizeof);
		ptr += v.length;
	} ///
}

static assert(isStringSink!(BlindWriter!char));

version(unittest) import ae.utils.time;

unittest
{
	import std.datetime;

	char[64] buf;
	auto writer = BlindWriter!char(buf.ptr);

	auto time = SysTime(DateTime(2010, 7, 4, 7, 6, 12), UTC());
	putTime(writer, time, TimeFormats.ISO8601);
	auto timeStr = buf[0..writer.ptr-buf.ptr];
	assert(timeStr == "2010-07-04T07:06:12+0000", timeStr.idup);
}

// **************************************************************************

/// Calls putter to count the length of the output, allocates a buffer of
/// that size, and then calls putter a second time to write to the buffer.
/// Returns the buffer.

template countCopy(T)
{
	T[] countCopy(Putter)(Putter putter)
	{
		CountingWriter!T counter;
		putter(&counter);

		T[] buf = new T[counter.count];

		BlindWriter!T writer;
		writer.ptr = buf.ptr;
		putter(&writer);
		assert(writer.ptr == buf.ptr + buf.length);

		return buf;
	}
}

version(none) // Method alias binding
T[] countCopy(T, alias putter)()
{
	CountingWriter!T counter;
	putter(&counter);

	T[] buf = new T[counter.count];

	BlindWriter!T writer;
	writer.ptr = buf.ptr;
	putter(&writer);
	assert(writer.ptr = buf.ptr + buf.length);

	return buf;
} /// ditto

// **************************************************************************

/// Default implementation of put for dchars
void put(S)(ref S sink, dchar c)
	if (isStringSink!S)
{
	import std.utf;
	char[4] buf;
	auto size = encode(buf, c);
	sink.put(buf[0..size]);
}

unittest
{
	StringBuilder sb;
	put(sb, 'Я');
	assert(sb.get() == "Я");
}

import std.traits;
import ae.utils.text : toDec, decimalSize;

/// Default implementation of put for numbers (uses decimal ASCII)
void put(S, N)(ref S sink, N n)
	if (isStringSink!S && is(N : long) && !isSomeChar!N)
{
	sink.putDecimal(n);
}

/// Write a number `n` in decimal to `sink`.
void putDecimal(S, N)(ref S sink, N n)
{
	char[decimalSize!N] buf = void;
	sink.put(toDec(n, buf));
}

unittest
{
	void test(N)(N n)
	{
		import std.conv;
		StringBuilder sb;
		put(sb, n);
		assert(sb.get() == text(n), sb.get() ~ "!=" ~ text(n));
	}

	test(0);
	test(1);
	test(-1);
	test(0xFFFFFFFFFFFFFFFFLU);
}