Created Gateway: developing new one (markdown)

Gateway:-developing-new-one.md

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+How to develop a new gateway?
+
+## Step-by step list
+
+- [ ] Create a new catalog in [`/bridge` folder](https://github.com/42wim/matterbridge/tree/master/bridge) and a main file named after the bridge you are creating, such as `whatsapp.go`
+- [ ] Implement a [`Bridger` interface](https://github.com/42wim/matterbridge/blob/2cfd880cdb0df29771bf8f31df8d990ab897889d/bridge/bridge.go#L11-L16)
+- [ ] [`gitter`](https://github.com/42wim/matterbridge/blob/master/bridge/gitter/gitter.go) is a relatively simple bridge that you might use as a reference to adapt
+- [ ] Mention your bridge exists in [`/gateway/bridgemap/bridgemap.go`](https://github.com/42wim/matterbridge/blob/master/gateway/bridgemap/bridgemap.go)
+- [ ] Divide functionality in several files, as it is done for [slack](https://github.com/42wim/matterbridge/tree/master/bridge)
+  - `yourbridge.go` with main struct and implementation of the `Bridger` interface
+  - `handlers.go` with handling messages incoming to Bridge
+  - `helpers.go` for all the misc fucntions and helpers
+- [ ] While sending the message to the bridge make sure that you set the `config.Message.Channel` field to channel as it is mentioned in the config file.
+- [ ] Minimal set of features is sending and receiving text messages working.
+- [ ] Documentation
+  - [ ] Add a [sample configuration](https://github.com/42wim/matterbridge/commit/6372d599b1ca2497aa49142d10496f345041b678#diff-0fcc5f77f08a4f4106d2da34c4dcd133) of your bridge to `matterbridge.toml.sample` and explain all the custom options
+  - [ ] Add your bridge to README
+  - [ ] Document all exported functions
+- [ ] Run `golint` and `goimports` and clean the code
+- [ ] Run `go mod vendor` to pull in all the vendor code
+- [ ] Send a PR
+
+## Features
+
+Below is a feature list that you might copy to your issue.
+
+Features:
+- [ ] Connect to external service
+- [ ] Get all active chats
+- [ ] Check if chosen channels exist exgternally
+- [ ] Connect to chosen channel
+- [ ] Show nicknames in external service
+- [ ] Show nicknames in relayed messages
+- [ ] Test if multiple channels are working
+- [ ] Show profile pictures from your bridge in relayed messages
+- [ ] Show profile picture in your bridge
+- [ ] Handle reply/thread messages
+- [ ] Handle notifications 
+- [ ] Create a channel if it doesn't exist
+- [ ] Sync channel metadata (name, topic, etc.)
+- [ ] Document settings in `matterbridge.toml.sample`
+- [ ] Document bridge in README
+- [ ] Explain setting up the bridge process for users in the wiki
+- [ ] Add screenshots from your bridge in the wiki
+- [ ] Document code
+
+Handle messages
+- [ ] text from the bridge
+- [ ] text to the bridge
+- [ ] image
+- [ ] audio
+- [ ] video
+- [ ] contacts?
+- [ ] any other?