import { App, TFile, TFolder } from 'obsidian';

// === Types ===

export interface HistoryEntry {
	id: string;
	timestamp: number;
	content: string;
	metadata: HistoryMetadata;
}

export interface HistoryMetadata {
	templateId: string | null;
	templateName: string | null;
	includedFiles: string[];
	includedSources: string[];
	activeNote: string | null;
	charCount: number;
	estimatedTokens: number;
	userNote?: string;
	fileHashes?: Record<string, string>;  // path -> djb2 hash
}

export interface HistorySettings {
	enabled: boolean;
	storageFolder: string;
	maxEntries: number;
	autoCleanupDays: number;
}

export const DEFAULT_HISTORY_SETTINGS: HistorySettings = {
	enabled: false,
	storageFolder: '.context-history',
	maxEntries: 50,
	autoCleanupDays: 30,
};

// === ID Generation ===

export function generateHistoryId(): string {
	return 'hist_' + Date.now().toString(36) + Math.random().toString(36).substring(2, 9);
}

// === Token Estimation ===

export function estimateTokens(text: string): number {
	// Rough estimation: ~4 characters per token for English text
	// This is a simplified heuristic, actual tokenization varies by model
	return Math.ceil(text.length / 4);
}

// === Hashing ===

export function djb2Hash(str: string): string {
	let hash = 5381;
	for (let i = 0; i < str.length; i++) {
		hash = ((hash << 5) + hash + str.charCodeAt(i)) & 0xFFFFFFFF;
	}
	return (hash >>> 0).toString(16).padStart(8, '0');
}

// === History Manager ===

export class HistoryManager {
	private app: App;
	private settings: HistorySettings;

	constructor(app: App, settings: HistorySettings) {
		this.app = app;
		this.settings = settings;
	}

	updateSettings(settings: HistorySettings) {
		this.settings = settings;
	}

	private get folderPath(): string {
		return this.settings.storageFolder;
	}

	private async ensureFolder(): Promise<TFolder | null> {
		const existing = this.app.vault.getAbstractFileByPath(this.folderPath);
		if (existing instanceof TFolder) {
			return existing;
		}

		try {
			await this.app.vault.createFolder(this.folderPath);
			return this.app.vault.getAbstractFileByPath(this.folderPath) as TFolder;
		} catch {
			return null;
		}
	}

	private getEntryFilename(entry: HistoryEntry): string {
		const date = new Date(entry.timestamp);
		const dateStr = date.toISOString().replace(/[:.]/g, '-').substring(0, 19);
		return `${dateStr}_${entry.id}.json`;
	}

	async saveEntry(
		content: string,
		metadata: Omit<HistoryMetadata, 'charCount' | 'estimatedTokens'>
	): Promise<HistoryEntry | null> {
		if (!this.settings.enabled) {
			return null;
		}

		const folder = await this.ensureFolder();
		if (!folder) {
			return null;
		}

		const entry: HistoryEntry = {
			id: generateHistoryId(),
			timestamp: Date.now(),
			content,
			metadata: {
				...metadata,
				charCount: content.length,
				estimatedTokens: estimateTokens(content),
			},
		};

		const filename = this.getEntryFilename(entry);
		const filePath = `${this.folderPath}/${filename}`;

		try {
			await this.app.vault.create(filePath, JSON.stringify(entry, null, 2));
			await this.cleanup();
			return entry;
		} catch {
			return null;
		}
	}

	async loadEntries(): Promise<HistoryEntry[]> {
		const folder = this.app.vault.getAbstractFileByPath(this.folderPath);
		if (!folder || !(folder instanceof TFolder)) {
			return [];
		}

		const entries: HistoryEntry[] = [];

		for (const file of folder.children) {
			if (file instanceof TFile && file.extension === 'json') {
				try {
					const content = await this.app.vault.read(file);
					const entry = JSON.parse(content) as HistoryEntry;
					entries.push(entry);
				} catch {
					// Skip invalid entries
				}
			}
		}

		// Sort by timestamp descending (newest first)
		entries.sort((a, b) => b.timestamp - a.timestamp);

		return entries;
	}

	async loadEntry(id: string): Promise<HistoryEntry | null> {
		const entries = await this.loadEntries();
		return entries.find(e => e.id === id) || null;
	}

	async deleteEntry(id: string): Promise<boolean> {
		const folder = this.app.vault.getAbstractFileByPath(this.folderPath);
		if (!folder || !(folder instanceof TFolder)) {
			return false;
		}

		for (const file of folder.children) {
			if (file instanceof TFile && file.name.includes(id)) {
				try {
					await this.app.vault.delete(file);
					return true;
				} catch {
					return false;
				}
			}
		}

		return false;
	}

	async updateEntryNote(id: string, userNote: string): Promise<boolean> {
		const folder = this.app.vault.getAbstractFileByPath(this.folderPath);
		if (!folder || !(folder instanceof TFolder)) {
			return false;
		}

		for (const file of folder.children) {
			if (file instanceof TFile && file.name.includes(id)) {
				try {
					const content = await this.app.vault.read(file);
					const entry = JSON.parse(content) as HistoryEntry;
					entry.metadata.userNote = userNote;
					await this.app.vault.modify(file, JSON.stringify(entry, null, 2));
					return true;
				} catch {
					return false;
				}
			}
		}

		return false;
	}

	async cleanup(): Promise<number> {
		const entries = await this.loadEntries();
		let deletedCount = 0;

		// Delete entries exceeding max count
		if (entries.length > this.settings.maxEntries) {
			const toDelete = entries.slice(this.settings.maxEntries);
			for (const entry of toDelete) {
				if (await this.deleteEntry(entry.id)) {
					deletedCount++;
				}
			}
		}

		// Delete entries older than autoCleanupDays
		if (this.settings.autoCleanupDays > 0) {
			const cutoff = Date.now() - (this.settings.autoCleanupDays * 24 * 60 * 60 * 1000);
			const remainingEntries = await this.loadEntries();

			for (const entry of remainingEntries) {
				if (entry.timestamp < cutoff) {
					if (await this.deleteEntry(entry.id)) {
						deletedCount++;
					}
				}
			}
		}

		return deletedCount;
	}

	async clearAll(): Promise<number> {
		const entries = await this.loadEntries();
		let deletedCount = 0;

		for (const entry of entries) {
			if (await this.deleteEntry(entry.id)) {
				deletedCount++;
			}
		}

		return deletedCount;
	}
}

// === Diff Utilities ===

export interface DiffResult {
	addedFiles: string[];
	removedFiles: string[];
	addedSources: string[];
	removedSources: string[];
	templateChanged: boolean;
	oldTemplate: string | null;
	newTemplate: string | null;
	charDiff: number;
	tokenDiff: number;
}

export function diffEntries(older: HistoryEntry, newer: HistoryEntry): DiffResult {
	const oldFiles = new Set(older.metadata.includedFiles);
	const newFiles = new Set(newer.metadata.includedFiles);

	const oldSources = new Set(older.metadata.includedSources);
	const newSources = new Set(newer.metadata.includedSources);

	return {
		addedFiles: newer.metadata.includedFiles.filter(f => !oldFiles.has(f)),
		removedFiles: older.metadata.includedFiles.filter(f => !newFiles.has(f)),
		addedSources: newer.metadata.includedSources.filter(s => !oldSources.has(s)),
		removedSources: older.metadata.includedSources.filter(s => !newSources.has(s)),
		templateChanged: older.metadata.templateId !== newer.metadata.templateId,
		oldTemplate: older.metadata.templateName,
		newTemplate: newer.metadata.templateName,
		charDiff: newer.metadata.charCount - older.metadata.charCount,
		tokenDiff: newer.metadata.estimatedTokens - older.metadata.estimatedTokens,
	};
}

// === Context Diff ===

export interface ContextDiffResult {
	newFiles: string[];
	modifiedFiles: string[];
	removedFiles: string[];
	unchangedFiles: string[];
	baselineTimestamp: number;
	baselineId: string;
}

export function computeContextDiff(
	currentHashes: Record<string, string>,
	baseline: HistoryEntry
): ContextDiffResult | null {
	const baseHashes = baseline.metadata.fileHashes;
	if (!baseHashes) return null;

	const newFiles: string[] = [];
	const modifiedFiles: string[] = [];
	const unchangedFiles: string[] = [];

	for (const [path, hash] of Object.entries(currentHashes)) {
		if (!(path in baseHashes)) {
			newFiles.push(path);
		} else if (baseHashes[path] !== hash) {
			modifiedFiles.push(path);
		} else {
			unchangedFiles.push(path);
		}
	}

	const currentPaths = new Set(Object.keys(currentHashes));
	const removedFiles = Object.keys(baseHashes).filter(p => !currentPaths.has(p));

	return {
		newFiles,
		modifiedFiles,
		removedFiles,
		unchangedFiles,
		baselineTimestamp: baseline.timestamp,
		baselineId: baseline.id,
	};
}

export function findBaselineWithHashes(entries: HistoryEntry[]): HistoryEntry | null {
	return entries.find(e => e.metadata.fileHashes != null) ?? null;
}

// === Formatting ===

export function formatTimestamp(timestamp: number): string {
	const date = new Date(timestamp);
	return date.toLocaleString();
}

export function formatRelativeTime(timestamp: number): string {
	const now = Date.now();
	const diff = now - timestamp;

	const minutes = Math.floor(diff / 60000);
	const hours = Math.floor(diff / 3600000);
	const days = Math.floor(diff / 86400000);

	if (minutes < 1) return 'just now';
	if (minutes < 60) return `${minutes}m ago`;
	if (hours < 24) return `${hours}h ago`;
	if (days < 7) return `${days}d ago`;

	return formatTimestamp(timestamp);
}