"use strict";

let asts = require("../asts");
let js = require("../js");
let op = require("../opcodes");
let visitor = require("../visitor");

// Generates bytecode.
//
// Instructions
// ============
//
// Stack Manipulation
// ------------------
//
//  [0] PUSH c
//
//        stack.push(consts[c]);
//
//  [1] PUSH_UNDEFINED
//
//        stack.push(undefined);
//
//  [2] PUSH_NULL
//
//        stack.push(null);
//
//  [3] PUSH_FAILED
//
//        stack.push(FAILED);
//
//  [4] PUSH_EMPTY_ARRAY
//
//        stack.push([]);
//
//  [5] PUSH_CURR_POS
//
//        stack.push(currPos);
//
//  [6] POP
//
//        stack.pop();
//
//  [7] POP_CURR_POS
//
//        currPos = stack.pop();
//
//  [8] POP_N n
//
//        stack.pop(n);
//
//  [9] NIP
//
//        value = stack.pop();
//        stack.pop();
//        stack.push(value);
//
// [10] APPEND
//
//        value = stack.pop();
//        array = stack.pop();
//        array.push(value);
//        stack.push(array);
//
// [11] WRAP n
//
//        stack.push(stack.pop(n));
//
// [12] TEXT
//
//        stack.push(input.substring(stack.pop(), currPos));
//
// Conditions and Loops
// --------------------
//
// [13] IF t, f
//
//        if (stack.top()) {
//          interpret(ip + 3, ip + 3 + t);
//        } else {
//          interpret(ip + 3 + t, ip + 3 + t + f);
//        }
//
// [14] IF_ERROR t, f
//
//        if (stack.top() === FAILED) {
//          interpret(ip + 3, ip + 3 + t);
//        } else {
//          interpret(ip + 3 + t, ip + 3 + t + f);
//        }
//
// [15] IF_NOT_ERROR t, f
//
//        if (stack.top() !== FAILED) {
//          interpret(ip + 3, ip + 3 + t);
//        } else {
//          interpret(ip + 3 + t, ip + 3 + t + f);
//        }
//
// [16] WHILE_NOT_ERROR b
//
//        while(stack.top() !== FAILED) {
//          interpret(ip + 2, ip + 2 + b);
//        }
//
// Matching
// --------
//
// [17] MATCH_ANY a, f, ...
//
//        if (input.length > currPos) {
//          interpret(ip + 3, ip + 3 + a);
//        } else {
//          interpret(ip + 3 + a, ip + 3 + a + f);
//        }
//
// [18] MATCH_STRING s, a, f, ...
//
//        if (input.substr(currPos, consts[s].length) === consts[s]) {
//          interpret(ip + 4, ip + 4 + a);
//        } else {
//          interpret(ip + 4 + a, ip + 4 + a + f);
//        }
//
// [19] MATCH_STRING_IC s, a, f, ...
//
//        if (input.substr(currPos, consts[s].length).toLowerCase() === consts[s]) {
//          interpret(ip + 4, ip + 4 + a);
//        } else {
//          interpret(ip + 4 + a, ip + 4 + a + f);
//        }
//
// [20] MATCH_REGEXP r, a, f, ...
//
//        if (consts[r].test(input.charAt(currPos))) {
//          interpret(ip + 4, ip + 4 + a);
//        } else {
//          interpret(ip + 4 + a, ip + 4 + a + f);
//        }
//
// [21] ACCEPT_N n
//
//        stack.push(input.substring(currPos, n));
//        currPos += n;
//
// [22] ACCEPT_STRING s
//
//        stack.push(consts[s]);
//        currPos += consts[s].length;
//
// [23] FAIL e
//
//        stack.push(FAILED);
//        fail(consts[e]);
//
// Calls
// -----
//
// [24] LOAD_SAVED_POS p
//
//        savedPos = stack[p];
//
// [25] UPDATE_SAVED_POS
//
//        savedPos = currPos;
//
// [26] CALL f, n, pc, p1, p2, ..., pN
//
//        value = consts[f](stack[p1], ..., stack[pN]);
//        stack.pop(n);
//        stack.push(value);
//
// Rules
// -----
//
// [27] RULE r
//
//        stack.push(parseRule(r));
//
// Failure Reporting
// -----------------
//
// [28] SILENT_FAILS_ON
//
//        silentFails++;
//
// [29] SILENT_FAILS_OFF
//
//        silentFails--;
function generateBytecode(ast) {
	let consts = [];

	function addConst(value) {
		let index = consts.indexOf(value);

		return index === -1 ? consts.push(value) - 1 : index;
	}

	function addFunctionConst(params, code) {
		return addConst(
			"function(" + params.join(", ") + ") {" + code + "}"
		);
	}

	function cloneEnv(env) {
		let clone = {};

		Object.keys(env).forEach(name => {
			clone[name] = env[name];
		});

		return clone;
	}

	function buildSequence() {
		return Array.prototype.concat.apply([], arguments);
	}

	function buildCondition(condCode, thenCode, elseCode) {
		return condCode.concat(
			[thenCode.length, elseCode.length],
			thenCode,
			elseCode
		);
	}

	function buildLoop(condCode, bodyCode) {
		return condCode.concat([bodyCode.length], bodyCode);
	}

	function buildCall(functionIndex, delta, env, sp) {
		let params = Object.keys(env).map(name => sp - env[name]);

		return [op.CALL, functionIndex, delta, params.length].concat(params);
	}

	function buildSimplePredicate(expression, negative, context) {
		return buildSequence(
			[op.PUSH_CURR_POS],
			[op.SILENT_FAILS_ON],
			generate(expression, {
				sp: context.sp + 1,
				env: cloneEnv(context.env),
				action: null
			}),
			[op.SILENT_FAILS_OFF],
			buildCondition(
				[negative ? op.IF_ERROR : op.IF_NOT_ERROR],
				buildSequence(
					[op.POP],
					[negative ? op.POP : op.POP_CURR_POS],
					[op.PUSH_UNDEFINED]
				),
				buildSequence(
					[op.POP],
					[negative ? op.POP_CURR_POS : op.POP],
					[op.PUSH_FAILED]
				)
			)
		);
	}

	function buildSemanticPredicate(code, negative, context) {
		let functionIndex = addFunctionConst(Object.keys(context.env), code);

		return buildSequence(
			[op.UPDATE_SAVED_POS],
			buildCall(functionIndex, 0, context.env, context.sp),
			buildCondition(
				[op.IF],
				buildSequence(
					[op.POP],
					negative ? [op.PUSH_FAILED] : [op.PUSH_UNDEFINED]
				),
				buildSequence(
					[op.POP],
					negative ? [op.PUSH_UNDEFINED] : [op.PUSH_FAILED]
				)
			)
		);
	}

	function buildAppendLoop(expressionCode) {
		return buildLoop(
			[op.WHILE_NOT_ERROR],
			buildSequence([op.APPEND], expressionCode)
		);
	}

	let generate = visitor.build({
		grammar(node) {
			node.rules.forEach(generate);

			node.consts = consts;
		},

		rule(node) {
			node.bytecode = generate(node.expression, {
				sp: -1,        // stack pointer
				env: { },      // mapping of label names to stack positions
				action: null   // action nodes pass themselves to children here
			});
		},

		named(node, context) {
			let nameIndex = addConst(
				"peg$otherExpectation(\"" + js.stringEscape(node.name) + "\")"
			);

			// The code generated below is slightly suboptimal because |FAIL| pushes
			// to the stack, so we need to stick a |POP| in front of it. We lack a
			// dedicated instruction that would just report the failure and not touch
			// the stack.
			return buildSequence(
				[op.SILENT_FAILS_ON],
				generate(node.expression, context),
				[op.SILENT_FAILS_OFF],
				buildCondition([op.IF_ERROR], [op.FAIL, nameIndex], [])
			);
		},

		choice(node, context) {
			function buildAlternativesCode(alternatives, context) {
				return buildSequence(
					generate(alternatives[0], {
						sp: context.sp,
						env: cloneEnv(context.env),
						action: null
					}),
					alternatives.length > 1
						? buildCondition(
							[op.IF_ERROR],
							buildSequence(
								[op.POP],
								buildAlternativesCode(alternatives.slice(1), context)
							),
							[]
						)
						: []
				);
			}

			return buildAlternativesCode(node.alternatives, context);
		},

		action(node, context) {
			let env = cloneEnv(context.env);
			let emitCall = node.expression.type !== "sequence"
                  || node.expression.elements.length === 0;
			let expressionCode = generate(node.expression, {
				sp: context.sp + (emitCall ? 1 : 0),
				env: env,
				action: node
			});
			let functionIndex = addFunctionConst(Object.keys(env), node.code);

			return emitCall
				? buildSequence(
					[op.PUSH_CURR_POS],
					expressionCode,
					buildCondition(
						[op.IF_NOT_ERROR],
						buildSequence(
							[op.LOAD_SAVED_POS, 1],
							buildCall(functionIndex, 1, env, context.sp + 2)
						),
						[]
					),
					[op.NIP]
				)
				: expressionCode;
		},

		sequence(node, context) {
			function buildElementsCode(elements, context) {
				if (elements.length > 0) {
					let processedCount = node.elements.length - elements.slice(1).length;

					return buildSequence(
						generate(elements[0], {
							sp: context.sp,
							env: context.env,
							action: null
						}),
						buildCondition(
							[op.IF_NOT_ERROR],
							buildElementsCode(elements.slice(1), {
								sp: context.sp + 1,
								env: context.env,
								action: context.action
							}),
							buildSequence(
								processedCount > 1 ? [op.POP_N, processedCount] : [op.POP],
								[op.POP_CURR_POS],
								[op.PUSH_FAILED]
							)
						)
					);
				} else {
					if (context.action) {
						let functionIndex = addFunctionConst(
							Object.keys(context.env),
							context.action.code
						);

						return buildSequence(
							[op.LOAD_SAVED_POS, node.elements.length],
							buildCall(
								functionIndex,
								node.elements.length,
								context.env,
								context.sp
							),
							[op.NIP]
						);
					} else {
						return buildSequence([op.WRAP, node.elements.length], [op.NIP]);
					}
				}
			}

			return buildSequence(
				[op.PUSH_CURR_POS],
				buildElementsCode(node.elements, {
					sp: context.sp + 1,
					env: context.env,
					action: context.action
				})
			);
		},

		labeled(node, context) {
			let env = cloneEnv(context.env);

			context.env[node.label] = context.sp + 1;

			return generate(node.expression, {
				sp: context.sp,
				env: env,
				action: null
			});
		},

		text(node, context) {
			return buildSequence(
				[op.PUSH_CURR_POS],
				generate(node.expression, {
					sp: context.sp + 1,
					env: cloneEnv(context.env),
					action: null
				}),
				buildCondition(
					[op.IF_NOT_ERROR],
					buildSequence([op.POP], [op.TEXT]),
					[op.NIP]
				)
			);
		},

		simple_and(node, context) {
			return buildSimplePredicate(node.expression, false, context);
		},

		simple_not(node, context) {
			return buildSimplePredicate(node.expression, true, context);
		},

		optional(node, context) {
			return buildSequence(
				generate(node.expression, {
					sp: context.sp,
					env: cloneEnv(context.env),
					action: null
				}),
				buildCondition(
					[op.IF_ERROR],
					buildSequence([op.POP], [op.PUSH_NULL]),
					[]
				)
			);
		},

		zero_or_more(node, context) {
			let expressionCode = generate(node.expression, {
				sp: context.sp + 1,
				env: cloneEnv(context.env),
				action: null
			});

			return buildSequence(
				[op.PUSH_EMPTY_ARRAY],
				expressionCode,
				buildAppendLoop(expressionCode),
				[op.POP]
			);
		},

		one_or_more(node, context) {
			let expressionCode = generate(node.expression, {
				sp: context.sp + 1,
				env: cloneEnv(context.env),
				action: null
			});

			return buildSequence(
				[op.PUSH_EMPTY_ARRAY],
				expressionCode,
				buildCondition(
					[op.IF_NOT_ERROR],
					buildSequence(buildAppendLoop(expressionCode), [op.POP]),
					buildSequence([op.POP], [op.POP], [op.PUSH_FAILED])
				)
			);
		},

		group(node, context) {
			return generate(node.expression, {
				sp: context.sp,
				env: cloneEnv(context.env),
				action: null
			});
		},

		semantic_and(node, context) {
			return buildSemanticPredicate(node.code, false, context);
		},

		semantic_not(node, context) {
			return buildSemanticPredicate(node.code, true, context);
		},

		rule_ref(node) {
			return [op.RULE, asts.indexOfRule(ast, node.name)];
		},

		literal(node) {
			if (node.value.length > 0) {
				let stringIndex = addConst("\""
          + js.stringEscape(
          	node.ignoreCase ? node.value.toLowerCase() : node.value
          )
          + "\""
				);
				let expectedIndex = addConst(
					"peg$literalExpectation("
            + "\"" + js.stringEscape(node.value) + "\", "
            + node.ignoreCase
            + ")"
				);

				// For case-sensitive strings the value must match the beginning of the
				// remaining input exactly. As a result, we can use |ACCEPT_STRING| and
				// save one |substr| call that would be needed if we used |ACCEPT_N|.
				return buildCondition(
					node.ignoreCase
						? [op.MATCH_STRING_IC, stringIndex]
						: [op.MATCH_STRING, stringIndex],
					node.ignoreCase
						? [op.ACCEPT_N, node.value.length]
						: [op.ACCEPT_STRING, stringIndex],
					[op.FAIL, expectedIndex]
				);
			} else {
				let stringIndex = addConst("\"\"");

				return [op.PUSH, stringIndex];
			}
		},

		class(node) {
			let regexp = "/^["
        + (node.inverted ? "^" : "")
        + node.parts.map(part =>
        	Array.isArray(part)
        		? js.regexpClassEscape(part[0])
                + "-"
                + js.regexpClassEscape(part[1])
        		: js.regexpClassEscape(part)
        ).join("")
        + "]/" + (node.ignoreCase ? "i" : "");
			let parts = "["
        + node.parts.map(part =>
        	Array.isArray(part)
        		? "[\"" + js.stringEscape(part[0]) + "\", \"" + js.stringEscape(part[1]) + "\"]"
        		: "\"" + js.stringEscape(part) + "\""
        ).join(", ")
        + "]";
			let regexpIndex = addConst(regexp);
			let expectedIndex = addConst(
				"peg$classExpectation("
          + parts + ", "
          + node.inverted + ", "
          + node.ignoreCase
          + ")"
			);

			return buildCondition(
				[op.MATCH_REGEXP, regexpIndex],
				[op.ACCEPT_N, 1],
				[op.FAIL, expectedIndex]
			);
		},

		any() {
			let expectedIndex = addConst("peg$anyExpectation()");

			return buildCondition(
				[op.MATCH_ANY],
				[op.ACCEPT_N, 1],
				[op.FAIL, expectedIndex]
			);
		}
	});

	generate(ast);
}

module.exports = generateBytecode;