'use strict';

// ------------------------------------------------------------------
// Definitions
// ------------------------------------------------------------------

// Use symbols for the names of the instructions
// Unsure if this helps in any way over strings, but I feel it neater

// +++++ → {type: add, value: 5}
// Can have offset property
const add = Symbol('add');
// > → {type: moveHead, value: 1}
const moveHead = Symbol('moveHead');
// . → {type: writeByte}
// Can have offset property
const writeByte = Symbol('writeByte');
// , → {type: readByte}
// Can have offset property
const readByte = Symbol('readByte');
// [-] → {type: loop, contents: [{type: add, value: -1}]}
// Can have isBalanced property
const loop = Symbol('loop');

// [-] → {type: clear}
// Can have offset property
const clear = Symbol('clear');

// [>+>++<<-] → {type: move, changes: Map { 0 → -1, 1 → 1, 2 → 2 }}
const multiply = Symbol('multiply');

// {type: jumpIfZero, target: 5}
const jumpIfZero = Symbol('jumpIfZero');
// {type: jumpIfNonZero, target: 2}
const jumpIfNonZero = Symbol('jumpIfNonZero');

// : → {type: writeInt}
// Can have offset property
const writeInt = Symbol('writeInt');
// ; → {type: readInt}
// Can have offset property
const readInt = Symbol('readInt');
// # → {type: breakPoint}
const breakPoint = Symbol('breakPoint');

class ParsingError extends Error {}

class UnknownIRError extends Error {}

// ------------------------------------------------------------------
// Parsing
// ------------------------------------------------------------------

// (string, bool) → [commandObjects]
// enableExtensions contols whether commands :;# are recognized
// May throw ParsingError
function parse(program, enableExtensions = true) {
	// (string, int, bool) → {parsed: [commandObjects], lastIndex: int}
	// index is the index of the next character to consume
	// inLoop tells whether we're parsing a loop or the top level
	// lastIndex is the last index the function consumed
	function constructTree(program, index = 0, inLoop = false) {
		let commands = [];

		// Move this out of the loop body since we need to return
		// the index of the last character we parsed
		let i = index;
		for(;;) {
			if(i >= program.length) {
				// If we're parsing a loop, we have a
				// missing ]
				// If we're parsing the top level, this is
				// where we should exit
				if(inLoop) {
					throw new ParsingError('Missing ]');
				} else {
					break;
				}
				i++;

			} else if(program[i] == ']') {
				// If we're parsing a loop, this is where we
				// should exit
				// If we're parsing the top level, we have a
				// missing [
				if(inLoop) {
					break;
				} else {
					throw new ParsingError('Missing [');
				}
				i++;

			} else if(program[i] == '+' || program[i] == '-') {
				// Fold a run of +s and -s into one node
				let value = 0;
				for(; i < program.length; i++) {
					if(program[i] == '+') {
						value++;
					} else if(program[i] == '-') {
						value--;
					} else {
						// Reached end of the run
						break;
					}
				}

				// Only add the command is value is not 0
				if(value != 0) {
					commands.push({type: add, value: value});
				}
				// i is not incremented, since it already
				// points to a location containig a char we
				// have not yet handled

			} else if(program[i] == '<' || program[i] == '>') {
				// Fold a run of <s and >s into one node
				let value = 0;
				for(; i < program.length; i++) {
					if(program[i] == '>') {
						value++;
					} else if(program[i] == '<') {
						value--;
					} else {
						// Reached end of the run
						break;
					}
				}

				// Only add the command is value is not 0
				if(value != 0) {
					commands.push({type: moveHead, value: value});
				}
				// see +/- for why we don't increment i

			} else if(program[i] == '.') {
				commands.push({type: writeByte});
				i++;

			} else if(program[i] == ',') {
				commands.push({type: readByte});
				i++;

			} else if(program[i] == '[') {
				// Parse a loop. This is done by calling the
				// same parser function recursively
				// Due to this the loop appears as one node
				// in the parsed result
				let {parsed, lastIndex} = constructTree(
					program, // Same program data
					i + 1, // Start at the next char
					true // We're parsing a loop
				);
				commands.push({type: loop, contents: parsed});
				// Since lastIndex was consumed by the inner
				// function, we don't want to consume it a
				// second time
				i = lastIndex + 1;

			} else if(program[i] == ':' && enableExtensions) {
				commands.push({type: writeInt});
				i++;

			} else if(program[i] == ';' && enableExtensions) {
				commands.push({type: readInt});
				i++;

			} else if(program[i] == '#' && enableExtensions) {
				commands.push({type: breakPoint});
				i++;

			} else {
				// All others characters are comments,
				// ignore them
				i++;
			}
		}

		return {parsed: commands, lastIndex: i};
	}

	// We only care about the parsed contents, since under normal
	// operarion we only get out of the loop if we've reached the end
	// of the program
	let {parsed} = constructTree(program);
	return parsed;
}

// ([commandObjects/offsetCommandObjects/flatCommandObjects]) → str
function prettifyIR(ir) {
	// ([commandObjects/offsetCommandObjectsflatCommandObjects], string) → str
	function worker(ir, indent = '') {
		let lines = [];

		for(let i = 0; i < ir.length; i++) {
			let command = ir[i];

			let line = `${indent}${i} `;
			if(command.type == add) {
				line += `add ${command.value}`;
				if('offset' in command) {
					line += ` (${command.offset})`;
				}
				lines.push(line);
			} else if(command.type == moveHead) {
				line += `moveHead ${command.value}`;
				lines.push(line);
			} else if(command.type == writeByte) {
				line += 'writeByte';
				if('offset' in command) {
					line += ` (${command.offset})`;
				}
				lines.push(line);
			} else if(command.type == readByte) {
				line += 'readByte';
				if('offset' in command) {
					line += ` (${command.offset})`;
				}
				lines.push(line);
			} else if(command.type == loop) {
				line += 'loop';
				if('isBalanced' in command) {
					line += ` (balanced: ${command.isBalanced})`;
				}
				lines.push(line);
				lines = lines.concat(worker(command.contents, indent + '  '));
			} else if(command.type == clear) {
				line += 'clear';
				if('offset' in command) {
					line += ` (${command.offset})`;
				}
				lines.push(line);
			} else if(command.type == multiply) {
				let changes = [];
				for(let [offset, value] of command.changes.entries()) {
					changes.push(`${offset}: ${value}`);
				}
				line += `multiply ${changes.join(', ')}`;
				lines.push(line);
			} else if(command.type == jumpIfZero) {
				line += `jumpIfZero ${command.target}`;
				lines.push(line);
			} else if(command.type == jumpIfNonZero) {
				line += `jumpIfNonZero ${command.target}`;
				lines.push(line);
			} else if(command.type == writeInt) {
				line += 'writeInt';
				if('offset' in command) {
					line += ` (${command.offset})`;
				}
				lines.push(line);
			} else if(command.type == readInt) {
				line += 'readInt';
				if('offset' in command) {
					line += ` (${command.offset})`;
				}
				lines.push(line);
			} else if(command.type == breakPoint) {
				line += 'breakPoint';
				lines.push(line);
			} else {
				line += `unknown ${command.type.toString()}`;
				lines.push(line);
			}
		}

		return lines
	}
	return worker(ir).join('\n');
}

// ------------------------------------------------------------------
// Optimization passes
// ------------------------------------------------------------------

// ([commandObjects]) → [commandObjects]
function joinAdjacentOps(parsed) {
	// ([commandObjects], commandType) → [commandObjects]
	function worker(parsed, type) {
		let optimized = [];

		let prevOfType = false, value = 0;
		for(let command of parsed) {
			if(prevOfType && command.type == type) {
				// Update value, don't add to optimized yet
				value += command.value;
			} else if(!prevOfType && command.type == type) {
				// Start of a possible run of commands
				prevOfType = true;
				value = command.value;
			} else {
				// If a run has ended, add it to optimized
				// However, skip it if value is 0
				if(prevOfType && value != 0) {
					optimized.push({type: type, value: value});
				}

				// Add the command for this round
				if(command.type == loop) {
					// Recurse
					optimized.push({type: loop,
						contents: worker(
							command.contents,
							type)});
				} else {
					optimized.push(command);
				}
				prevOfType = false;
			}
		}
		// Did we end with a command of given type
		if(prevOfType) {
			// Yes, add it to optimized (unless value is 0)
			if(value != 0) {
				optimized.push({type: type, value: value});
			}
		}

		return optimized;
	}

	return worker(worker(parsed, moveHead), add);
}

// ([commandObjects]) → [commandObjects]
function transformClearLoops(parsed) {
	let optimized = [];

	for(let command of parsed) {
		// Only match loops like [-] or [+]
		let isClearLoop = command.type == loop &&
			command.contents.length == 1 &&
			command.contents[0].type == add &&
			(command.contents[0].value == 1 ||
			command.contents[0].value == -1);
		if(isClearLoop) {
			optimized.push({type: clear});
		} else if(command.type == loop) {
			// Run for inner loops
			optimized.push({type: loop,
				contents: transformClearLoops(command.contents)});
		} else {
			optimized.push(command);
		}
	}

	return optimized;
}

// ([commandObjects]) → [offsetCommandObjects]
function addOffsetProperties(parsed) {
	// ([commandObjects]) → {offsetted: [offsetCommandObjects], isBalanced: bool}
	function worker(parsed) {
		let offsetted = [];
		let isBalanced = true;
		let headChange = 0;

		let offset = 0;
		for(let command of parsed) {
			if(command.type == add) {
				offsetted.push({type: add,
					value: command.value,
					offset: offset});
			} else if(command.type == moveHead) {
				offset += command.value;
			} else if(command.type == writeByte) {
				offsetted.push({type: writeByte,
					offset: offset});
			} else if(command.type == readByte) {
				offsetted.push({type: readByte,
					offset: offset});
			} else if(command.type == clear) {
				offsetted.push({type: clear,
					offset: offset});
			} else if(command.type == loop) {
				// A loop should be self-contained
				// If offset is not 0, add a moveHead
				if(offset != 0) {
					offsetted.push({type: moveHead,
						value: offset});
					// Mark we've moved the head
					headChange += offset;
				}
				offset = 0;

				// Run optimization on the loop
				let result = worker(command.contents);
				// We're only balanced if our loops are
				isBalanced = isBalanced && result.isBalanced;
				offsetted.push({type: loop,
					contents: result.offsetted,
					isBalanced: result.isBalanced});
				// headChange's value becomes invalid if the
				// loop is not balanced. However, we only
				// care about its value when figuring out
				// our isBalanced, which will be forced to
				// false if any inner loop is not balanced
			} else if(command.type == writeInt) {
				offsetted.push({type: writeInt,
					offset: offset});
			} else if(command.type == readInt) {
				offsetted.push({type: readInt,
					offset: offset});
			} else if(command.type == breakPoint) {
				// A breakpoint should have the tape head
				// where it would be without the offsets
				// If offset is not 0, add a moveHead
				if(offset != 0) {
					offsetted.push({type: moveHead,
						value: offset});
					// Mark we've moved the head
					headChange += offset;
				}
				offset = 0;

				// Add the breakpoint
				offsetted.push({type: breakPoint});
			} else {
				throw new UnknownIRError(
					`Unknown command ${command.type.toString()}`);
			}
		}

		// We need to move the tape head in the end anyways, so
		// generate moveHead is offseet is not 0
		if(offset != 0) {
			offsetted.push({type: moveHead,
				value: offset});
		}

		// We're only balanced if relative to start of the loop ends
		// up as 0
		isBalanced = isBalanced && offset + headChange == 0;

		return {offsetted, isBalanced};
	}

	return worker(parsed).offsetted;
}

// ([offsetCommandObjects]) → [offsetCommandObjects]
function transformMultiplyLoops(offsetted) {
	let optimized = [];

	for(let command of offsetted) {
		let isMultiplyLoop = false;
		// Not necessarily a multiply loop, since multiply loops,
		// in addition to being balanced loops with only adds,
		// also decrement / increment the cell under tape head
		// by one. However, these are loops we can run through the
		// next processing step, and we can drop unfit ones after
		// that
		let maybeMultiplyLoop = command.type == loop &&
			command.isBalanced &&
			command.contents.every(x => x.type == add);

		// TODO: Change this to use a Proxy thingie
		let changes = new Map();
		if(maybeMultiplyLoop) {
			for(let addition of command.contents) {
				// We already know all of these are adds
				if(!changes.has(addition.offset)) {
					changes.set(addition.offset, 0);
				}

				let current = changes.get(addition.offset);
				changes.set(addition.offset,
					current + addition.value);
			}

			// Did we actually have a multiply loop?
			isMultiplyLoop = changes.has(0) &&
				(changes.get(0) == 1 ||
					changes.get(0) == -1);
		}

		if(isMultiplyLoop) {
			// If changes[0] is 1, we are dealing with
			// a loop of the type [>-<+], which is
			// (except for run time) same as [>+<-].
			// Transform former into latter
			if(changes.get(0) == 1) {
				for(let [offset, value] of changes.entries()) {
					changes.set(offset, -value);
				}
			}

			optimized.push({type: multiply,
				changes: changes});
		} else if(command.type == loop) {
			// Recurse
			optimized.push({type: loop,
				contents: transformMultiplyLoops(command.contents),
				balanced: command.balanced});
		} else {
			// Pass through
			optimized.push(command);
		}
	}

	return optimized;
}

// ([offsetCommandObjects]) → [flatCommandObjects]
function flattenLoops(offsetted) {
	// ([offsetCommandObjects], int) → [flatCommandObjects]
	// prevLength tells length of the flattened program up until now
	function worker(offsetted, prevLength = 0) {
		let flattened = [];

		for(let command of offsetted) {
			if(command.type == loop) {
				// flattened.length is the index of the next
				// command in out flattened
				// flattened.length + prevLength is the
				// index of it in the resulting combined
				// flattened
				// Since this should be the index of the
				// start of the loop body we want to point
				// after the next command, which is going
				// to be the jump
				let startIndex = flattened.length +
					prevLength + 1;

				let loopBody = worker(command.contents,
					startIndex // length = index of next
				);

				// startIndex + loopBody.length is the index
				// of the next command after the loop body
				// The command after it is going to be the
				// jump back to the start of the body, so we
				// want to point to the command after it
				let endIndex = startIndex +
					loopBody.length + 1;

				// Add the first jump
				flattened.push({type: jumpIfZero,
					target: endIndex});

				// Add the loop body
				flattened = flattened.concat(loopBody);

				// Add the second loop
				flattened.push({type: jumpIfNonZero,
					target: startIndex});
			} else {
				flattened.push(command);
			}
		}

		return flattened;
	}

	return worker(offsetted);
}

// ([commandObjects]) → [flatCommandObjects]
function optimize(parsed) {
	const optimizations = [
		joinAdjacentOps,
		transformClearLoops,
		addOffsetProperties,
		transformMultiplyLoops,
		flattenLoops
	]
	return optimizations.reduce((IR, optimization) =>
		optimization(IR), parsed);
}

// ------------------------------------------------------------------
// Virtual machine
// ------------------------------------------------------------------

// ([flatCommandObject], [int], int/null) → girVMState
// onEof tells what to set the cell to in case of EOF, or if it null to keep
// the same value
function newVM(program, input, onEof = 0) {
	return {
		// Initial state for the machine
		program: program,
		ip: 0,

		memory: new Map(),
		tapeHead: 0,

		input: input,
		output: [],

		// Configuration
		onEof: onEof
	};
}

// (girVMState, int/null) → {state: girVMState, complete: bool, cycles: int,
//                      intParseFailed: bool, breakPointReached: bool,
//                      lastIndex: int/null}
// complete is set to true is the program completed its execution
// cycles is the number of cycles the VM ran
// intParseFailed is true is parseInt failed to read a valid number
// breakPointReached is true if a breakPoint command was executed
// lastIndex tells the last memory index accessed by the VM
// If maxCycles is null, the program runs until completion
function runVM(state, maxCycles = null) {
	// (int) → int
	function readMemory(index) {
		// Return 0 if index doesn't exist
		if(memory.has(index)) {
			return memory.get(index);
		} else {
			return 0;
		}
	}

	let program = state.program;
	let ip = state.ip;

	// Create a copy of the memory, since we're going to modify it
	// TODO: Make memory into a Proxied thing that returns 0 if it
	// doesn't have the requested cell
	let memory = new Map(state.memory.entries());
	let tapeHead = state.tapeHead;

	// Create copies of input and output, since we might modify them
	let input = state.input.slice();
	let output = state.output.slice();

	// Flags we want to return
	let complete = false;
	let intParseFailed = false;
	let breakPointReached = false;

	// Debug features
	let lastIndex = null;

	let cycle = 0;
	for(; maxCycles === null || cycle < maxCycles; cycle++) {
		// Exit the loop if we run to the end of the program
		if(ip >= program.length) {
			// Program completed
			complete = true;
			break;
		}

		let command = program[ip];

		// Calculate the index into the array of the cell we're
		// accessing
		let index = tapeHead;
		switch(command.type) {
			case add:
			case writeByte:
			case readByte:
			case clear:
			case writeInt:
			case readInt:
				// These have an offset property, add it
				index += command.offset;
		}
		lastIndex = index;

		// Run the command
		switch(command.type) {
			case add:
				let old = readMemory(index);
				memory.set(index, (command.value + old) & 0xFF);

				ip++;
				break;

			case moveHead:
				tapeHead += command.value;
				// Set lastIndex to the new tape head
				// position. Technically we do not access
				// the cell, but otherwise it will point
				// to the cell we were in previously, so
				// this allows better debugging
				lastIndex = tapeHead;

				ip++;
				break;

			case writeByte:
				output.push(readMemory(index));
				ip++;
				break;

			case readByte:
				// Have we reached EOF?
				if(input.length == 0) {
					// Yes
					// If state.onEof is null, don't
					// change the value
					// If it's something else, set the
					// cell to that
					if(state.onEof !== null) {
						memory.set(index,
							state.onEof & 0xff);
					}
				} else {
					// No, return character
					memory.set(index, input.shift());
				}
				ip++;
				break;

			case clear:
				memory.set(index, 0);
				ip++;
				break;

			case multiply:
				if(command.changes.get(0) != -1) {
					throw new UnknownIRError(
						`multiply where change for 0 is ${command.changes.get(0)}`);
				}

				let multiplier = readMemory(index);

				for(let [offset, change] of command.changes.entries()) {
					let index = tapeHead + offset;
					let old = readMemory(index);
					let value = old + multiplier * change;
					memory.set(index, value & 0xff);
				}

				ip++;
				break;

			case jumpIfZero:
				if(readMemory(index) == 0) {
					ip = command.target;
				} else {
					ip++;
				}
				break;

			case jumpIfNonZero:
				if(readMemory(index) != 0) {
					ip = command.target;
				} else {
					ip++;
				}
				break;

			case writeInt:
				let outputStr = readMemory(index).toString();
				output.push(...encodeUTF8(outputStr))
				ip++;
				break;

			case readInt:
				// Skip any spaces in front
				while(input.length > 0 && input[0] == 0x20) {
					input.shift();
				}

				let number = 0;

				// Read digits
				let consumedInput = false;
				while(input.length > 0 &&
					input[0] >= 0x30 &&
					input[0] <= 0x39) {
					let digit = input.shift() - 0x30;
					number = number * 10 + digit;
					consumedInput = true;
				}

				// Did we read anything
				if(consumedInput) {
					// Yes, clamp value to [0, 255] and
					// set cell to it
					number = Math.max(
						Math.min(number, 255),
						0);
					memory.set(index, number);
				} else if(input.length == 0) {
					// No, but there was an EOF
					// If state.onEof is null, don't
					// change the value
					// If it's something else, set the
					// cell to that
					if(state.onEof !== null) {
						memory.set(index,
							state.onEof & 0xff);
					}
				} else {
					// No, and there wasn't an EOF, so
					// signal an error
					intParseFailed = true;
				}

				ip++;
				break;

			case breakPoint:
				breakPointReached = true;

				ip++;
				break;

			default:
				// Unknown command type
				throw new UnknownIRError(
					`Unknown command ${command.type.toString()}`);
		}

		// Since can't use 'break' from a switch(), do it here
		if(intParseFailed || breakPointReached) {
			break;
		}
	}

	let newState = {
		program,
		ip,

		memory,
		tapeHead,

		input,
		output
	};

	return {state: newState, complete: complete, cycles: cycle,
		intParseFailed: intParseFailed,
		breakPointReached: breakPointReached,
		lastIndex: lastIndex};
}

// ------------------------------------------------------------------
// UTF-8
// ------------------------------------------------------------------

// string → [int]
function encodeUTF8(string) {
	let encoded = [];

	for(let character of string) {
		let codepoint = character.codePointAt(0);

		if(codepoint < 0x80) {
			// 0xxxxxxx
			encoded.push(codepoint);
		} else if(codepoint < 0x0800) {
			// 110xxxxx 10xxxxxx
			let b1 = codepoint >> 6 | 0b11000000;
			let b2 = codepoint & 0b00111111 | 0b10000000;
			encoded.push(b1);
			encoded.push(b2);
		} else if(codepoint < 0x10000) {
			// 1110xxxx 10xxxxxx 10xxxxxx
			let b1 = codepoint >> 12 | 0b11100000;
			let b2 = codepoint >> 6 & 0b00111111 | 0b10000000;
			let b3 = codepoint & 0b00111111 | 0b10000000;
			encoded.push(b1);
			encoded.push(b2);
			encoded.push(b3);
		} else {
			// 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
			let b1 = codepoint >> 18 | 0b11110000;
			let b2 = codepoint >> 12 & 0b00111111 | 0b10000000;
			let b3 = codepoint >> 6 & 0b00111111 | 0b10000000;
			let b4 = codepoint & 0b00111111 | 0b10000000;
			encoded.push(b1);
			encoded.push(b2);
			encoded.push(b3);
			encoded.push(b4);
		}
	}

	return encoded;
}

// [int] → string
function decodeUTF8(encoded) {
	let codePoints = [];

	for(let i = 0; i < encoded.length;) {
		let codePoint = 0;

		let firstByte = encoded[i];
		i++;

		let toRead = null;
		// Determine number of continuation bytes to read and
		// decode the first byte into codePoint
		// Since we'll do the shifts later, we just mask here
		if(firstByte >> 7 == 0) {
			// 0xxxxxxx
			toRead = 0;
			codePoint = firstByte;
		} else if(firstByte >> 5 == 0b110) {
			// 110xxxxx 10xxxxxx
			toRead = 1;
			codePoint = firstByte & 0b00011111;
		} else if(firstByte >> 4 == 0b1110) {
			// 1110xxxx 10xxxxxx 10xxxxxx
			toRead = 2;
			codePoint = firstByte & 0b00001111;
		} else if(firstByte >> 3 == 0b11110) {
			// 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
			toRead = 3;
			codePoint = firstByte & 0b00000111;
		} else {
			// Illegal sequence, push replacement char
			codePoints.push(0xFFFD);
			continue;
		}

		for(; toRead > 0 && i < encoded.length; toRead--) {
			let continuationByte = encoded[i];
			i++;

			// Check that we have a valid continuation byte
			if(continuationByte >> 6 == 0b10) {
				// We do, add its contents to codePoint
				codePoint = codePoint << 6 |
					continuationByte & 0b00111111;
			} else {
				// We don't, break out of the loop
				break;
			}
		}

		// Did we read all required continuation bytes?
		if(toRead == 0) {
			// We did, add the codepoint to the array
			codePoints.push(codePoint);
		} else {
			// We didn't, push replacement char
			codePoints.push(0xFFFD);
		}
	}

	// Convert to a string
	let decoded = codePoints.map(x => String.fromCodePoint(x)).join('');

	return decoded;
}

// ------------------------------------------------------------------
// User-facing functions
// ------------------------------------------------------------------

// (string, bool) → [flatCommandObjects]
function compile(program, enableExtensions = true) {
	return optimize(parse(program, enableExtensions));
}

exports.compile = compile;
exports.prettifyIR = prettifyIR;
exports.newVM = newVM;
exports.runVM = runVM;
exports.encodeUTF8 = encodeUTF8;
exports.decodeUTF8 = decodeUTF8;