/**
 * Graph ledger store (W4; vision §1, contracts.ts "v1 emission").
 *
 * Five append-only JSONL ledgers at config.LEDGER_FILES:
 *   nodes.jsonl     GraphNode        — one line per graph node
 *   edges.jsonl     GraphEdge        — one line per edge ASSERTION (a second
 *                                      session asserting the same (from,to,type)
 *                                      appends another line; reads merge)
 *   events.jsonl    LedgerEvent      — quiz outcomes + taught events
 *   mappings.jsonl  NodeMapping      — the naive-union identity map:
 *                                      (chatId, treeNodeId) → graphNodeId
 *   sessions.jsonl  SessionCheckpoint— emission checkpoints (foldedAt)
 *
 * data/graph/* is exclusively this store's (the legacy V0 scaffold lives in
 * data/legacy-graph). Reads are strict against the contracts.ts shapes:
 * corrupt lines are skipped, never guessed at — the ledgers are the source of
 * truth and everything else is derived (src/core/graph.ts).
 *
 * Same idioms as src/store/chats.ts: sync fs, tiny records, no framework.
 */

import * as fs from "node:fs";
import * as path from "node:path";
import { randomBytes } from "node:crypto";
import { LEDGER_FILES } from "../../config.ts";
import type { GraphEdge, GraphNode, LedgerEvent, LedgerEventKind } from "../core/contracts.ts";

/** The naive-union identity map line: a chat's tree node → graph node. */
export interface NodeMapping {
	chatId: string;
	treeNodeId: string;
	graphNodeId: string;
}

/** sessions.jsonl line — the emission checkpoint for one chat. */
export interface SessionCheckpoint {
	chatId: string;
	/** The chat record's `updatedAt` at the time of the fold. */
	foldedAt: string;
}

/** "n_" + nanoid-like (contracts.ts GraphNode.id). */
export function newGraphNodeId(): string {
	return `n_${randomBytes(6).toString("hex")}`;
}

// ─── JSONL primitives ────────────────────────────────────────────────────────

function appendLine<T>(file: string, record: T): void {
	fs.mkdirSync(path.dirname(file), { recursive: true });
	fs.appendFileSync(file, `${JSON.stringify(record)}\n`, "utf-8");
}

function readRawLines(file: string): unknown[] {
	let raw: string;
	try {
		raw = fs.readFileSync(file, "utf-8");
	} catch {
		return []; // no ledger yet — nothing has ever been emitted
	}
	const out: unknown[] = [];
	for (const line of raw.split("\n")) {
		const trimmed = line.trim();
		if (trimmed.length === 0) continue;
		try {
			out.push(JSON.parse(trimmed));
		} catch {
			// Corrupt line: skip rather than fail the whole read — a torn
			// append must never take the home graph down with it.
		}
	}
	return out;
}

function isRecord(v: unknown): v is Record<string, unknown> {
	return typeof v === "object" && v !== null;
}

const isString = (v: unknown): v is string => typeof v === "string";

/** Strict shape guards — anything not matching a W4 ledger shape is skipped. */
function readValid<T>(file: string, isValid: (v: unknown) => v is T): T[] {
	return readRawLines(file).filter(isValid);
}

const isGraphNode = (v: unknown): v is GraphNode =>
	isRecord(v) &&
	isString(v.id) &&
	isString(v.statement) &&
	Array.isArray(v.aliases) &&
	(v.kind === "truth" || v.kind === "misconception") &&
	isString(v.createdAt);

const EDGE_TYPES = ["requires", "supports"] as const;

const isGraphEdge = (v: unknown): v is GraphEdge =>
	isRecord(v) &&
	isString(v.from) &&
	isString(v.to) &&
	(EDGE_TYPES as readonly string[]).includes(v.type as string) &&
	Array.isArray(v.provenance) &&
	v.provenance.every(isString);

const EVENT_KINDS: readonly LedgerEventKind[] = [
	"probe-correct",
	"probe-miss",
	"dont-know",
	"misconception-signaled",
	"taught",
	"check-correct",
	"check-incorrect",
];

const isLedgerEvent = (v: unknown): v is LedgerEvent =>
	isRecord(v) &&
	(v.nodeId === null || isString(v.nodeId)) &&
	(EVENT_KINDS as readonly string[]).includes(v.kind as string) &&
	isString(v.chatId) &&
	isString(v.at);

const isNodeMapping = (v: unknown): v is NodeMapping =>
	isRecord(v) && isString(v.chatId) && isString(v.treeNodeId) && isString(v.graphNodeId);

const isCheckpoint = (v: unknown): v is SessionCheckpoint =>
	isRecord(v) && isString(v.chatId) && isString(v.foldedAt);

// ─── typed ledger access ─────────────────────────────────────────────────────

export const graphLedgers = {
	appendNode(node: GraphNode): void {
		appendLine(LEDGER_FILES.nodes, node);
	},
	/** Raw node lines in append order (ids are unique — no merging needed). */
	readNodes(): GraphNode[] {
		return readValid(LEDGER_FILES.nodes, isGraphNode);
	},

	/** Append one edge ASSERTION; readers merge lines by (from,to,type). */
	appendEdge(edge: GraphEdge): void {
		appendLine(LEDGER_FILES.edges, edge);
	},
	readEdges(): GraphEdge[] {
		return readValid(LEDGER_FILES.edges, isGraphEdge);
	},

	appendEvent(event: LedgerEvent): void {
		appendLine(LEDGER_FILES.events, event);
	},
	readEvents(): LedgerEvent[] {
		return readValid(LEDGER_FILES.events, isLedgerEvent);
	},

	appendMapping(mapping: NodeMapping): void {
		appendLine(LEDGER_FILES.mappings, mapping);
	},
	readMappings(): NodeMapping[] {
		return readValid(LEDGER_FILES.mappings, isNodeMapping);
	},

	appendCheckpoint(checkpoint: SessionCheckpoint): void {
		appendLine(LEDGER_FILES.sessions, checkpoint);
	},
	readCheckpoints(): SessionCheckpoint[] {
		return readValid(LEDGER_FILES.sessions, isCheckpoint);
	},
};