import type { Database } from "bun:sqlite";
import { createHash } from "node:crypto";
import { inflateSync } from "node:zlib";
import type { ReleaseRecord } from "../bucket/repo.ts";
import { mirrorState } from "./store.ts";

export type Save = {
	id: string;
	parent: string;
	message: string;
	created_at: number;
	machine: string;
	agent: string;
	session: string;
	is_checkpoint: boolean;
};

export type FileEntry = { path: string; hash: string; executable: boolean; size: number };

/** The saves that touched each path up to one save, oldest first; `line` is every one of
 * them in line order. */
export type Touches = { line: Save[]; byPath: Map<string, Save[]> };

export type RepoStats = { saves: number; lines: number; language: string; updated: number | null };

const SAVE_COLUMNS = `id, COALESCE(parent, '') AS parent, message, created_at, machine,
	COALESCE(agent, '') AS agent, COALESCE(session, '') AS session, is_checkpoint = 1 AS is_checkpoint`;
const LINE_COLUMNS =
	"line.id, line.parent, line.message, line.created_at, line.machine, line.agent, line.session, line.is_checkpoint, line.n";
const ID_PREFIX = /^[0-9a-f]{6,12}$/;

// Checkpoints are working marks, not history (§21.4): every list and count below leaves them out.
const NOT_CHECKPOINT = "is_checkpoint = 0";

export function headId(db: Database): string | null {
	return mirrorState(db, "head");
}

/** A page of saves, newest first. Rows land oldest first, so rowid is the order of the line. */
export function history(db: Database, limit: number, offset: number): Save[] {
	return db
		.query<Save, [number, number]>(
			`SELECT ${SAVE_COLUMNS} FROM saves WHERE ${NOT_CHECKPOINT} ORDER BY rowid DESC LIMIT ? OFFSET ?`,
		)
		.all(limit, offset)
		.map(asSave);
}

/** Every save, oldest first, for the timeline. */
export function timeline(db: Database): Save[] {
	return db
		.query<Save, []>(`SELECT ${SAVE_COLUMNS} FROM saves WHERE ${NOT_CHECKPOINT} ORDER BY rowid`)
		.all()
		.map(asSave);
}

/** The save a unique prefix of 6–12 hex characters names (§6.1), or null when none or
 * several do. */
export function saveByPrefix(db: Database, prefix: string): Save | null {
	if (!ID_PREFIX.test(prefix)) return null;
	// A migrated save's whole six-character ID can also begin a twelve-character one.
	const exact = db
		.query<Save, [string]>(`SELECT ${SAVE_COLUMNS} FROM saves WHERE id = ?`)
		.get(prefix);
	if (exact) return asSave(exact);
	const rows = db
		.query<Save, [string]>(`SELECT ${SAVE_COLUMNS} FROM saves WHERE id LIKE ? || '%' LIMIT 2`)
		.all(prefix);
	return rows.length === 1 ? asSave(rows[0] as Save) : null;
}

/** The nearest ancestor that is not a checkpoint: the parent a visitor can see (§21.4). */
export function visibleParent(db: Database, save: Save): Save | null {
	for (let id = save.parent; id !== ""; ) {
		const parent = saveByPrefix(db, id);
		if (!parent?.is_checkpoint) return parent;
		id = parent.parent;
	}
	return null;
}

/** The reason a save is flagged, or null when it isn't: its newest flag or clear event wins (§10.1). */
export function flagReason(db: Database, saveId: string): string | null {
	const row = db
		.query<{ kind: string; reason: string }, [string]>(
			`SELECT kind, COALESCE(reason, '') AS reason FROM events
			WHERE save_id = ? AND kind IN ('flag', 'clear') ORDER BY created_at DESC, id DESC LIMIT 1`,
		)
		.get(saveId);
	return row?.kind === "flag" ? row.reason : null;
}

/** How many strip events have landed: events are append-only, so this only ever grows. */
/**
 * What a save's tarball depends on besides the save: the strips landed, and the hidden paths and
 * epoch the mirror was built with. A change to any of them names a new key, so an old tarball is
 * never looked up again, whatever a late write or a failed cleanup leaves behind.
 */
export function tarballGeneration(db: Database): string {
	const built = `${mirrorState(db, "hidden") ?? ""}\n${mirrorState(db, "epoch") ?? ""}`;
	return `${stripCount(db)}-${createHash("sha256").update(built).digest("hex").slice(0, 12)}`;
}

function stripCount(db: Database): number {
	return db.query<{ n: number }, []>("SELECT COUNT(*) AS n FROM events WHERE kind = 'strip'").get()
		?.n as number;
}

export function filesAt(db: Database, saveId: string): FileEntry[] {
	return db
		.query<FileEntry, [string]>(
			`SELECT f.path, f.hash, f.executable = 1 AS executable, o.size FROM save_files f
			JOIN objects o ON o.hash = f.hash WHERE f.save_id = ? ORDER BY f.path`,
		)
		.all(saveId)
		.map((file) => ({ ...file, executable: Boolean(file.executable) }));
}

export function fileAt(db: Database, saveId: string, path: string): FileEntry | null {
	const file = db
		.query<FileEntry, [string, string]>(
			`SELECT f.path, f.hash, f.executable = 1 AS executable, o.size FROM save_files f
			JOIN objects o ON o.hash = f.hash WHERE f.save_id = ? AND f.path = ?`,
		)
		.get(saveId, path);
	return file ? { ...file, executable: Boolean(file.executable) } : null;
}

export function objectBytes(db: Database, hash: string): Uint8Array<ArrayBuffer> | null {
	const row = db
		.query<{ data: Uint8Array }, [string]>("SELECT data FROM objects WHERE hash = ?")
		.get(hash);
	return row ? new Uint8Array(inflateSync(row.data)) : null;
}

export function repoStats(db: Database): RepoStats {
	const row = db
		.query<{ saves: number; updated: number | null }, []>(
			`SELECT COUNT(*) AS saves, MAX(created_at) AS updated FROM saves WHERE ${NOT_CHECKPOINT}`,
		)
		.get() ?? { saves: 0, updated: null };
	return {
		saves: row.saves,
		updated: row.updated,
		lines: Number(mirrorState(db, "lines") ?? 0),
		language: mirrorState(db, "language") ?? "",
	};
}

/**
 * Which saves touched each path on the line up to `saveId` (§21.5's detail panel). A save touched a path when
 * the path was added, changed or removed against the save before it; checkpoints are skipped, so a
 * change first recorded by a checkpoint counts at the next real save.
 */
export function fileTouches(db: Database, saveId: string): Touches {
	const rows = db
		.query<Save & { path: string; n: number }, { at: string }>(
			`WITH line AS (
				SELECT ${SAVE_COLUMNS}, LAG(id) OVER (ORDER BY rowid) AS prev, rowid AS n FROM saves
				WHERE ${NOT_CHECKPOINT} AND rowid <= (SELECT rowid FROM saves WHERE id = $at)
			)
			SELECT ${LINE_COLUMNS}, f.path FROM line JOIN save_files f ON f.save_id = line.id
			LEFT JOIN save_files p ON p.save_id = line.prev AND p.path = f.path
			WHERE p.hash IS NOT f.hash OR p.executable IS NOT f.executable
			UNION ALL
			SELECT ${LINE_COLUMNS}, p.path FROM line JOIN save_files p ON p.save_id = line.prev
			WHERE NOT EXISTS (SELECT 1 FROM save_files f WHERE f.save_id = line.id AND f.path = p.path)
			ORDER BY n`,
		)
		.all({ at: saveId });
	const saves = new Map<string, Save>();
	const byPath = new Map<string, Save[]>();
	for (const { path, n: _, ...row } of rows) {
		const save = saves.get(row.id) ?? asSave(row);
		saves.set(save.id, save);
		const touched = byPath.get(path);
		if (touched) touched.push(save);
		else byPath.set(path, [save]);
	}
	return { line: [...saves.values()], byPath };
}

/** Lines per language at the newest real save, most first, vendored code left out as in the header's language. */
export function languageLines(db: Database): [string, number][] {
	return JSON.parse(mirrorState(db, "languages") ?? "[]") as [string, number][];
}

/** Every distinct object (unique file contents) a real save refers to, at any point in history. */
export function objectHashes(db: Database): string[] {
	// From `objects`, probing save_files_hash: every save lists its whole tree, so a DISTINCT over
	// save_files reads saves × files rows (1.4 s for 1,083 saves on Tylee).
	return db
		.query<{ hash: string }, []>(
			`SELECT o.hash
			 FROM objects o
			 WHERE EXISTS (
				SELECT 1
				FROM save_files f
				JOIN saves s ON s.id = f.save_id
				WHERE f.hash = o.hash
				AND s.${NOT_CHECKPOINT}
			 )`,
		)
		.all()
		.map((row) => row.hash);
}

/** Every release record the bucket holds, in no particular order. */
export function releaseRecords(db: Database): ReleaseRecord[] {
	return db
		.query<{ record: string }, []>("SELECT record FROM releases")
		.all()
		.map((row) => JSON.parse(row.record) as ReleaseRecord);
}

function asSave(row: Save): Save {
	return { ...row, is_checkpoint: Boolean(row.is_checkpoint) };
}