import * as _ from "lodash";
import { EventFired } from "../HandleEvent";
import { HandlerContext } from "../HandlerContext";
import { HandlerResult } from "../HandlerResult";
import {
    Arg,
    CommandInvocation,
} from "../internal/invoker/Payload";
import { Automations } from "../internal/metadata/metadata";
import {
    CommandHandlerMetadata,
    EventHandlerMetadata,
} from "../metadata/automationMetadata";
import { AutomationServer } from "./AutomationServer";

export const NoEventHandlersError = "NO_EVENT_HANDLERS";
export function noEventHandlersWereFound(result: HandlerResult) {
    return result.code !== 0 && !!result.message && result.message.startsWith(NoEventHandlersError);
}

/**
 * Support for implementing an automation server.
 */
export abstract class AbstractAutomationServer implements AutomationServer {

    public abstract automations: Automations;

    public invokeCommand(payload: CommandInvocation, ctx: HandlerContext): Promise<HandlerResult> {
        const h = this.validateCommandInvocation(payload);
        return this.invokeCommandHandler(payload, h, ctx);
    }

    public onEvent(payload: EventFired<any>, ctx: HandlerContext): Promise<HandlerResult[]> {
        const h = this.automations.events.filter(eh => eh.subscriptionName === payload.extensions.operationName);
        if (!h || h.length === 0) {
            throw new Error(`${NoEventHandlersError}: No event handler with name '${payload.extensions.operationName}'` +
                `: Known event handlers are '${this.automations.events.map(e => e.name)}'`);
        } else {
            return Promise.all(h.map(eh => this.invokeEventHandler(payload, eh, ctx)));
        }
    }

    public validateCommandInvocation(payload: CommandInvocation): CommandHandlerMetadata {
        const handler = this.automations.commands.find(h => h.name === payload.name);
        if (!handler) {
            throw new Error(`No command handler with name '${payload.name}'` +
                `: Known command handlers are '${this.automations.commands.map(c => c.name)}'`);
        }
        handler.parameters.forEach(p => {
            const payloadValue: Arg = payload.args ?
                payload.args.find(a => a.name === p.name) : undefined;
            if (!payloadValue || _.isNil(payloadValue.value)) {
                if (p.required && p.default_value === undefined) {
                    throw new Error(`Parameter '${p.name}' required but missing in invocation to '${handler.name}'`);
                }
            } else {
                // We have a parameter. Validate it
                if (p.pattern && payloadValue.value.toString().match(new RegExp(p.pattern)) === null) {
                    throw new Error(`Parameter '${p.name}' value of '${payloadValue.value}'` +
                        ` invalid in invocation to '${handler.name}' with pattern '${p.pattern}'`);
                }
            }
        });
        return handler;
    }

    protected abstract invokeCommandHandler(payload: CommandInvocation, h: CommandHandlerMetadata,
                                            ctx: HandlerContext): Promise<HandlerResult>;

    protected abstract invokeEventHandler(payload: EventFired<any>, h: EventHandlerMetadata,
                                          ctx: HandlerContext): Promise<HandlerResult>;

}