import {
	type PullRequestTarget,
	type ReviewOptions,
	THINKING_LEVELS,
	type ThinkingLevel,
} from "./types.ts";

const PR_URL = /^https:\/\/github\.com\/([^/]+)\/([^/]+)\/pull\/(\d+)\/?$/;

function tokenize(input: string): string[] {
	const tokens: string[] = [];
	let token = "";
	let quote: "'" | '"' | undefined;
	let escaping = false;

	for (const character of input) {
		if (escaping) {
			token += character;
			escaping = false;
			continue;
		}
		if (character === "\\") {
			escaping = true;
			continue;
		}
		if (quote) {
			if (character === quote) quote = undefined;
			else token += character;
			continue;
		}
		if (character === "'" || character === '"') {
			quote = character;
			continue;
		}
		if (/\s/.test(character)) {
			if (token) {
				tokens.push(token);
				token = "";
			}
			continue;
		}
		token += character;
	}

	if (escaping) throw new Error("Argument list ends with an incomplete escape");
	if (quote) throw new Error("Argument list contains an unterminated quote");
	if (token) tokens.push(token);
	return tokens;
}

function parseTarget(value: string): PullRequestTarget {
	if (/^[1-9]\d*$/.test(value))
		return { kind: "number", number: Number(value) };
	const match = PR_URL.exec(value);
	if (match) {
		return {
			kind: "url",
			url: value.replace(/\/$/, ""),
			owner: match[1],
			repo: match[2],
			number: Number(match[3]),
		};
	}
	throw new Error(`Invalid pull request target: ${value}`);
}

export function parseArguments(input: string): ReviewOptions {
	const tokens = tokenize(input);
	let target: PullRequestTarget | undefined;
	let comment = false;
	let model: string | undefined;
	let thinking: ThinkingLevel | undefined;

	for (let index = 0; index < tokens.length; index++) {
		const token = tokens[index];
		if (token === "--comment") {
			if (comment) throw new Error("Duplicate --comment flag");
			comment = true;
			continue;
		}
		if (token === "--model") {
			if (model) throw new Error("Duplicate --model flag");
			model = tokens[++index];
			if (!model || model.startsWith("--"))
				throw new Error("--model requires a value");
			continue;
		}
		if (token === "--thinking") {
			if (thinking) throw new Error("Duplicate --thinking flag");
			const value = tokens[++index];
			if (!value || !THINKING_LEVELS.includes(value as ThinkingLevel)) {
				throw new Error(
					`--thinking requires one of: ${THINKING_LEVELS.join(", ")}`,
				);
			}
			thinking = value as ThinkingLevel;
			continue;
		}
		if (token.startsWith("--")) throw new Error(`Unknown flag: ${token}`);
		if (target) throw new Error("Only one pull request target may be provided");
		target = parseTarget(token);
	}

	return { target: target ?? { kind: "current" }, comment, model, thinking };
}