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locals {
  virhubconnection_map = { for k, v in module.alz_connectivity.azurerm_virtual_hub_connection.virtual_wan : v.remote_virtual_network_id => v }
  bgp_connections = {
    dev = {
      speakbrasil01 = {
        name                          = "testing-vhub-bgpconnection-speak01-dev"
        virtual_hub_id                = data.azurerm_virtual_hub.dev_brazilsouthhub.id
        peer_asn                      = 65001
        peer_ip                       = "10.240.4.52"
        virtual_network_connection_id = local.virhubconnection_map[data.terraform_remote_state.silverpeak.outputs.bs_001_vnet_id].id
      }
      speakbrasil02 = {
        name                          = "testing-vhub-bgpconnection-speak02-dev"
        virtual_hub_id                = data.azurerm_virtual_hub.dev_brazilsouthhub.id
        peer_asn                      = 65001
        peer_ip                       = "10.240.4.53"
        virtual_network_connection_id = local.virhubconnection_map[data.terraform_remote_state.silverpeak.outputs.bs_001_vnet_id].id
      }
    }
    prod = {

    }
  }
}

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what is the map function doing?
ChatGPT
The map function in the provided Terraform code is used to create a new map (key-value pairs) from an existing data structure. Here's a breakdown of how it's used:

local.virhubconnection_map is the new map being created.
module.alz_connectivity.azurerm_virtual_hub_connection.virtual_wan is the existing data structure, 
presumably a map or list of objects, from which the new map is being constructed.
The for k, v in ... syntax is a for loop that iterates over each element in the module.alz_connectivity.azurerm_virtual_hub_connection.virtual_wan. 
In each iteration, k represents the key, and v represents the value of the current element in the loop.
v.remote_virtual_network_id => v is the key-value pair being created for each element in the loop. 
The key in the new map is v.remote_virtual_network_id, and the value is the entire object v.
In essence, this map function is transforming a list or map of virtual hub connection objects into a new map where the keys are the remote_virtual_network_id of each connection, and the values are the connection objects themselves. This makes it easier to look up a connection object based on its remote_virtual_network_id.

The local.virhubconnection_map is then used later in the bgp_connections map to find the virtual network connection ID for specific virtual network IDs, as shown in the lines like:

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virtual_network_connection_id = local.virhubconnection_map[data.terraform_remote_state.silverpeak.outputs.bs_001_vnet_id].id
This line is using the local.virhubconnection_map to get the virtual network connection object that corresponds to a virtual network ID obtained from data.terraform_remote_state.silverpeak.outputs.bs_001_vnet_id, and then accessing its id property.

User
Can you make a sample out of it?
ChatGPT
Certainly! Let's create a simplified example to illustrate how the map function is used in your Terraform code.
 We'll simulate the structure of the data and show how the mapping is done.

Imagine you have a module that outputs a list of virtual hub connections. Each connection has a remote_virtual_network_id and other properties. 
We'll use this data to create a new map where the keys are these network IDs, and the values are the entire connection objects.

Here's a hypothetical example:

Initial Data (Simulated)
Suppose the module.alz_connectivity.azurerm_virtual_hub_connection.virtual_wan outputs something like this:

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[
  {
    id: "connection1",
    remote_virtual_network_id: "network1",
    // other properties...
  },
  {
    id: "connection2",
    remote_virtual_network_id: "network2",
    // other properties...
  }
]
Terraform Map Function
We want to create a map from this data where the key is remote_virtual_network_id and the value is the whole object.

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locals {
  virhubconnection_map = { for connection in module.alz_connectivity.azurerm_virtual_hub_connection.virtual_wan : connection.remote_virtual_network_id => connection }
}
Resulting Map
The local.virhubconnection_map will look like this:

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{
  "network1" = {
    id: "connection1",
    remote_virtual_network_id: "network1",
    // other properties...
  },
  "network2" = {
    id: "connection2",
    remote_virtual_network_id: "network2",
    // other properties...
  }
}
Usage in BGP Connections
You can then use this map to easily find a connection based on its remote_virtual_network_id. For example:

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virtual_network_connection_id = local.virhubconnection_map["network1"].id
This line will get the id of the connection whose remote_virtual_network_id is "network1", effectively retrieving the id of connection1 in our example.

This demonstrates the power of the map function in organizing and accessing data more efficiently in Terraform configurations.