import { ConsoleLogger } from '@nestjs/common';
import { Subject } from 'rxjs';

export type LogEntry = {
    timestamp: string;
    level: 'log' | 'error' | 'warn' | 'debug' | 'verbose';
    context: string;
    message: string;
};

// Singleton — created once in main.ts, accessed by the SSE controller
// via LogStreamService.instance. NestJS DI isn't available at bootstrap
// time (the logger is created before the container), so we use a static
// instance instead of @Injectable().
export class LogStreamService extends ConsoleLogger {
    static readonly instance = new LogStreamService();
    readonly logSubject = new Subject<LogEntry>();
    private readonly buffer: LogEntry[] = [];
    private static readonly MAX_BUFFER = 500;

    getRecentLogs(limit = 200): LogEntry[] {
        return this.buffer.slice(-limit);
    }

    private emit(level: LogEntry['level'], message: unknown, context?: string) {
        const entry: LogEntry = {
            timestamp: new Date().toISOString(),
            level,
            context: context ?? this.context ?? '',
            message: typeof message === 'string' ? message : JSON.stringify(message),
        };
        this.buffer.push(entry);
        if (this.buffer.length > LogStreamService.MAX_BUFFER) this.buffer.shift();
        this.logSubject.next(entry);
    }

    log(message: unknown, context?: string) {
        super.log(message, context);
        this.emit('log', message, context);
    }

    error(message: unknown, stack?: string, context?: string) {
        super.error(message, stack, context);
        this.emit('error', message, context);
    }

    warn(message: unknown, context?: string) {
        super.warn(message, context);
        this.emit('warn', message, context);
    }

    debug(message: unknown, context?: string) {
        super.debug(message, context);
        this.emit('debug', message, context);
    }

    verbose(message: unknown, context?: string) {
        super.verbose(message, context);
        this.emit('verbose', message, context);
    }
}