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go-watch/README.md

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Go Watch

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A change detection server that can notify through various services written in Go

Intro

GoWatch works through filters, a filter performs operations on the input it recieves.
Here is an example of a 'Watch' that calculates the lowest and average price of 4090s on NewEgg and notifies the user if the lowest price changed:
NewEgg 4090

Note that everything, including scheduling/storing/notifying, is a filter.

Schedule is a cron filter with a '@every 15m' value, so this will run every 15 minutes.

NewEgg Fetch is a Get URL filter with a 'https://www.newegg.com/p/pl?N=100007709&d=4090&isdeptsrh=1&PageSize=96' value, it's output will be the HTTP response.

Select Price is a CSS filter with the value '.item-container .item-action strong[class!="item-buying-choices-price"]' value, it's output will be the html elements containing the prices.
An alternative filter type could've been the XPath filter.

Sanitize is a Replace filter, using a regular expression ('[^0-9]') it removes anything that's not a number.

Avg is an Average filter, it calculates the average value of its inputs.

Min is a Minimum filter, it calculates the minimum value of its inputs.

Store Avg and Store Min are Store filters, they store its input values in the database.

Diff is a Different Then Last filter, only passing on the inputs that are different then the last value stored in the database.

Notify is a Notify filter, if there are any inputs to this filter, it will execute a template and send the result to a user defined 'notifier' (Telegram/Discord/Matrix/etc).

Filters

Cron

Get URL

CSS

XPath

Replace

Store

Notify

Math

Average

Minimum

Condition

Different Then Last

type script compilation

tsc static/*.ts --lib es2020,dom --watch --downlevelIteration

Dependencies

The following libaries are used in Go-Watch: