Attempt to make a slice-able forward range.

filerange.d

module filerange;

import std.algorithm;
import std.array;
import std.conv;
import std.exception;
import std.file;
import std.range;
import std.stdio;

enum size = 4;

struct FileRange {
private:
	size_t index;
	string buff;
	File.ByChunk chunks;
public:
	static auto opCall(File file) {
		FileRange fr;
		fr.chunks = file.byChunk(size);
		fr.prime();
		return fr;
	}

	auto empty() {
		return buff.length == index;
	}

	auto popFront() {
		index++;
		if(index > buff.length - size/2 && !chunks.empty) {
			prime();
		}
	}

	auto save() {
		FileRange fr;
		fr.chunks = chunks;
		fr.buff = buff;
		return fr;
	}

	auto front() {
		return buff[index..$].front;
	}

	auto length() {
		return buff.length;
	}

	private void prime() {
		buff ~= cast(string)chunks.front.idup;
		chunks.popFront();
	}

	auto opSlice(size_t x, size_t y) {
		FileRange fr;
		fr.chunks = chunks;
		if(y == buff.length)
			fr.buff = buff[x+index..y];
		else
			fr.buff = buff[x+index..y+index];
		return fr;
	}

	auto opAssign(FileRange fr) {
		chunks = fr.chunks;
		index = fr.index;
		buff = fr.buff;
	}

	auto opOpAssign(string op)(FileRange fr) if(op == "~") {
		chunks = fr.chunks;
		buff ~= fr.buff;
	}
}

struct InputFileRange {
private:
	string buff;
	File.ByChunk chunks;
public:
	static auto opCall(File file) {
		FileRange fr;
		fr.chunks = file.byChunk(4096);
		fr.prime();
		return fr;
	}

	auto empty() {
		return buff.length == 0;
	}

	auto popFront() {
		buff.popFront();
		if(buff.length < 2048 && !chunks.empty) {
			prime();
		}
	}

	auto front() {
		return buff.front;
	}

	private void prime() {
		buff ~= cast(string)chunks.front.idup;
		chunks.popFront();
	}
}