import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { z } from 'zod';
import type { ServerContext } from '../../context.ts';
import { germanDay, isCalendarDate, schoolToday } from '../../core/dates.ts';
import {
	filterNotes,
	NoteNotFound,
	noteSections,
	noteSubjects,
	normalizeRelative,
	readNoteAt,
	readNotes,
	writeNote,
	type NoteDoc,
} from '../../core/notes.ts';
import { heading, joinSections, matchesAll, tokenize } from '../../core/text.ts';
import { failure, text, toToolError } from './result.ts';

/**
 * The user's own lesson notes.
 *
 * Registered only when NOTES_DIR is set, on the same principle as the untis_*
 * tools: a note tool with nowhere to read from can only ever fail, and a model
 * offered one will keep trying it.
 *
 * These are the only tools in this server that write anything, and what they
 * write is the user's own notes directory — never Schulcloud, which stays
 * read-only in the strict sense the invariant in CLAUDE.md describes. The write
 * is bounded by the same two functions the file mirror uses: every path
 * component is reduced by `safeComponent` and the result is checked by
 * `resolveWithin`, so a title of `../../.ssh/authorized_keys` becomes a
 * filename and not a path.
 */

const READ_ONLY = { readOnlyHint: true, destructiveHint: false, idempotentHint: true, openWorldHint: false };

/** Notes listed before the tool starts summarising instead of listing. */
const MAX_LISTED = 200;

const dateArgument = z
	.string()
	.regex(/^\d{4}-\d{2}-\d{2}$/, 'Use YYYY-MM-DD.')
	.describe('A date as YYYY-MM-DD.');

export function registerNoteTools(server: McpServer, context: ServerContext): void {
	const root = context.config.notesDir;
	if (!root) return;

	server.registerTool(
		'list_notes',
		{
			title: 'My lesson notes',
			description:
				"The user's own notes from lessons — what they wrote down themselves, which is neither in Schulcloud " +
				'nor in WebUntis and is often the only record of what a teacher actually said. **Read these before ' +
				'answering anything about what was covered in class, and before preparing for a test**: they say what ' +
				'was emphasised, which the uploaded material does not. Filter by subject ("Deutsch", "LF07") or by ' +
				'date to get the lessons around a topic — a note is often a whole school day with a heading per ' +
				'lesson, so the subject filter looks at those headings too. Returns titles and a preview; get_note ' +
				'opens one. search finds notes by their contents as well, and names the lesson it matched in.',
			inputSchema: {
				subject: z
					.string()
					.optional()
					.describe('Only notes for this subject, matched as a fragment. The user\'s own wording, not a course id.'),
				since: dateArgument.optional().describe('Only notes from this day onwards.'),
				until: dateArgument.optional().describe('Only notes up to and including this day.'),
				query: z
					.string()
					.optional()
					.describe('Only notes whose title, subject or tags contain every word given. For full text, use search.'),
				limit: z.number().int().min(1).max(MAX_LISTED).default(50).describe('Maximum notes to list.'),
			},
			annotations: READ_ONLY,
		},
		async ({ subject, since, until, query, limit }) => {
			const unreal = [since, until].filter((value): value is string => Boolean(value) && !isCalendarDate(value!));
			if (unreal.length > 0) return failure(`Not a date in the calendar: ${unreal.join(', ')}. Use YYYY-MM-DD.`);
			try {
				const all = await readNotes(root);
				if (all.length === 0) return text(emptyStore(root, context.config.notesWritable));

				const terms = query ? tokenize(query) : [];
				const matched = filterNotes(all, { subject, since, until }).filter(
					(note) =>
						terms.length === 0 ||
						matchesAll([note.title, ...noteSubjects(note), note.tags.join(' ')].join(' '), terms),
				);
				if (matched.length === 0) {
					return text(
						`None of the ${all.length} note(s) match${describeFilter({ subject, since, until, query })}. ` +
							'Drop a filter, or use search to look inside the text.',
					);
				}
				return text(
					joinSections([
						heading(2, `Notizen (${Math.min(limit, matched.length)} of ${matched.length})`),
						matched.slice(0, limit).map(listLine).join('\n'),
						matched.length > limit ? `_${matched.length - limit} more — narrow it down with subject or since._` : undefined,
					]),
				);
			} catch (error) {
				return toToolError(error, 'read the notes directory');
			}
		},
	);

	server.registerTool(
		'get_note',
		{
			title: 'Read one note',
			description:
				'The full text of one of the user\'s own notes, by the path list_notes and search print. Quote from it ' +
				'the way you would quote a course file — it is a primary source for what happened in the lesson.',
			inputSchema: {
				path: z
					.string()
					.min(1)
					.describe('The note\'s path, e.g. "Deutsch/2026-09-15 Erörterung.md", exactly as it was listed.'),
			},
			annotations: READ_ONLY,
		},
		async ({ path }) => {
			// A search hit inside a day's note carries `<path>#2`; opening the note
			// is the right answer, so the anchor is dropped rather than 404ing on a
			// filename nobody has.
			const wanted = normalizeRelative(path).replace(/#\d+$/, '');
			try {
				return text(renderNote(await readNoteAt(root, wanted)));
			} catch (error) {
				if (error instanceof NoteNotFound) {
					return failure(
						`There is no note at "${wanted}". Paths come from list_notes or search and include the folder and ` +
							'the .md ending.',
					);
				}
				return toToolError(error, `read the note "${wanted}"`);
			}
		},
	);

	if (!context.config.notesWritable) return;

	server.registerTool(
		'add_note',
		{
			title: 'Write a lesson note',
			description:
				'Saves a note into the user\'s own notes, so it is there next time — during a lesson ("halte fest, ' +
				'dass …"), or when writing up what was just discussed. Give the subject as the user says it ' +
				'("Deutsch", "LF07") and the day the lesson was on; both are what makes the note findable later. ' +
				'Pass append=true to add to the note already written for that subject and day rather than starting a ' +
				'second one — that is the right choice during a lesson. This writes **only** to the notes directory; ' +
				'it cannot change anything in Schulcloud or WebUntis. Do not use it to store things the user did not ' +
				'ask to keep.',
			inputSchema: {
				title: z.string().min(1).max(200).describe('A short title — the topic of the lesson, not a sentence.'),
				text: z.string().min(1).describe('The note itself, as Markdown. Write it in the language the user used.'),
				subject: z
					.string()
					.max(80)
					.optional()
					.describe('Subject as the user names it, e.g. "Deutsch" or "LF07". Becomes the folder.'),
				date: dateArgument.optional().describe('The day of the lesson. Defaults to today.'),
				tags: z.array(z.string().max(40)).max(12).optional().describe('Optional keywords, e.g. ["klausur"].'),
				courseId: z
					.string()
					.optional()
					.describe('The Schulcloud course id, when it is known — it links the note to the course in search.'),
				append: z
					.boolean()
					.default(false)
					.describe('Add to an existing note for that subject and day instead of creating another one.'),
			},
			// Writes — to the notes directory, and to nothing else.
			annotations: { readOnlyHint: false, destructiveHint: false, idempotentHint: false, openWorldHint: false },
		},
		async ({ title, text: body, subject, date, tags, courseId, append }) => {
			if (date && !isCalendarDate(date)) return failure(`Not a date in the calendar: ${date}. Use YYYY-MM-DD.`);
			try {
				const { note, appended } = await writeNote(root, {
					title,
					text: body,
					date: date ?? schoolToday(),
					...(subject ? { subject } : {}),
					...(courseId ? { courseId } : {}),
					...(tags && tags.length > 0 ? { tags } : {}),
					source: 'add_note',
					append,
				});
				return text(
					joinSections([
						`${appended ? 'Added to' : 'Saved'} **${note.title}** — \`${note.path}\``,
						'_It is searchable after the next refresh_index; get_note reads it now._',
					]),
				);
			} catch (error) {
				return toToolError(error, `save the note "${title}"`);
			}
		},
	);
}

// --- formatting ----------------------------------------------------------

function listLine(note: NoteDoc): string {
	const when = note.date ? germanDay(note.date) : 'ohne Datum';
	const subjects = noteSubjects(note);
	const where = subjects.length > 0 ? ` · ${subjects.join(', ')}` : '';
	const tags = note.tags.length > 0 ? ` · ${note.tags.map((tag) => `#${tag}`).join(' ')}` : '';
	// For a day's note the lessons are the useful preview; for a single piece of
	// prose the first line is.
	const sections = noteSections(note);
	const preview = sections.length > 0 ? `${sections.length} Stunde(n)` : firstLine(note.text);
	return [`- **${note.title}** — ${when}${where}${tags} \`${note.path}\``, preview ? `  ${preview}` : undefined]
		.filter(Boolean)
		.join('\n');
}

function renderNote(note: NoteDoc): string {
	const subjects = noteSubjects(note);
	const facts = [
		note.date ? `Datum: ${germanDay(note.date)}` : undefined,
		subjects.length > 0 ? `${subjects.length > 1 ? 'Fächer' : 'Fach'}: ${subjects.join(', ')}` : undefined,
		note.tags.length > 0 ? `Tags: ${note.tags.join(', ')}` : undefined,
		note.courseId ? `Kurs: \`${note.courseId}\`` : undefined,
	].filter(Boolean);
	return joinSections([
		heading(2, note.title),
		facts.length > 0 ? `_${facts.join(' · ')}_` : undefined,
		note.text || '_This note is empty._',
		`_Own note: \`${note.path}\`_`,
	]);
}

function firstLine(body: string): string | undefined {
	const line = body
		.split('\n')
		.map((entry) => entry.replace(/^#+\s*/, '').trim())
		.find((entry) => entry.length > 0);
	if (!line) return undefined;
	return line.length > 160 ? `${line.slice(0, 157)}…` : line;
}

function describeFilter(filter: { subject?: string; since?: string; until?: string; query?: string }): string {
	const parts = [
		filter.subject ? `subject "${filter.subject}"` : undefined,
		filter.query ? `"${filter.query}"` : undefined,
		filter.since ? `from ${germanDay(filter.since)}` : undefined,
		filter.until ? `to ${germanDay(filter.until)}` : undefined,
	].filter(Boolean);
	return parts.length > 0 ? ` ${parts.join(', ')}` : '';
}

/**
 * The empty case, which is the normal one on a fresh install.
 *
 * It says where the directory is because the usual next step is to put files
 * there by hand or with the import script, not to call a tool.
 */
function emptyStore(root: string, writable: boolean): string {
	return joinSections([
		`There are no notes yet. The notes directory is \`${root}\`.`,
		writable
			? 'Notes are Markdown files; add_note writes one, and anything dropped in that directory is picked up too.'
			: 'This server was started with NOTES_READONLY, so notes have to be put there by hand or synced in.',
	]);
}