import { Injectable } from '@nestjs/common';

@Injectable()
export class FlowVariableService {
    // Replace {{variableName}} with values from session variables
    interpolate(template: string, variables: Record<string, any>): string {
        return template.replace(/\{\{([\w.]+)\}\}/g, (match, path) => {
            // Support dot notation: {{bookingResult.appointmentId}}
            const parts = path.split('.');
            let value: any = variables;
            for (const part of parts) {
                value = value?.[part];
                if (value === undefined) return match;
            }
            if (value === null) return match;
            if (typeof value === 'object') return JSON.stringify(value);
            return String(value);
        });
    }

    // Interpolate all string values in an object
    interpolateObject(obj: Record<string, string>, variables: Record<string, any>): Record<string, any> {
        const result: Record<string, any> = {};
        for (const [key, value] of Object.entries(obj)) {
            result[key] = this.interpolate(value, variables);
        }
        return result;
    }

    // Execute expressions for SetVariableBlock
    evaluateExpression(expression: string, value: string, variables: Record<string, any>): any {
        switch (expression) {
            case 'extract_id': {
                // Extract second segment: "doc:{uuid}:{name}" → uuid, "dept:{name}" → name
                const parts = value.split(':');
                return parts.length >= 2 ? parts[1] : value;
            }
            case 'extract_datetime': {
                // Extract datetime from "slot:{doctorId}:{datetime}" → "2026-04-21T14:00:00"
                const parts = value.split(':');
                // Rejoin from index 2 onwards (datetime contains colons: 2026-04-21T14:00:00)
                return parts.length >= 3 ? parts.slice(2).join(':') : value;
            }
            case 'date_tomorrow': {
                const d = new Date(Date.now() + 86400000);
                return d.toISOString().split('T')[0];
            }
            case 'date_day_after': {
                const d = new Date(Date.now() + 2 * 86400000);
                return d.toISOString().split('T')[0];
            }
            default:
                return this.interpolate(value, variables);
        }
    }
}