Add completions for lftp (#1113)

[lftp](https://lftp.yar.ru/) is the program which I use when I need to
copy many files at once via SSH. Though having `FTP` in the name, it
supports more protocols than just FTP.

This PR provides auto-completion for the "site" argument. Source of
sites are:
- SSH aliases (for SFTP and FISH protocols).
- LFTP's bookmarks.


![image](https://github.com/user-attachments/assets/4c6c5876-069b-454c-9e49-5e43c9061a52)

custom-completions/lftp/README.md

@@ -0,0 +1,31 @@
+# LFTP completions
+
+[`LFTP`](https://lftp.yar.ru/) is a file transfer program supporting many protocols (FTP, HTTP, SFTP, FISH, TORRENT). It is shell-like, reliable and can transfer several files in parallel.
+
+## Install completion script
+
+### Method 1: Use from Git repo
+
+- `git clone https://github.com/nushell/nu_scripts.git`
+
+- Add this to `$nu.config-path` file.
+
+  ```nu
+  source repo/custom-completions/lftp/lftp-completions.nu
+  ```
+
+### Method 2: Selectively copy
+
+
+- Copy the _lftp-completions.nu_ to Nu standard place.
+
+  ```nu
+  cp custom-completions/lftp/lftp-completions.nu ($nu.data-dir | path join 'completions')
+  ```
+
+- Open `$nu.config-path` file and add this:
+
+  ```nu
+  source lftp-completions.nu
+  ```
+

custom-completions/lftp/lftp-completions.nu

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+# nu-version: 0.102.0
+
+module lftp-completion-utils {
+    def extract-host []: list<string> -> record<name: string, addr: string> {
+        # Host is a list of lines, like:
+        # ╭───┬──────────────────────────────╮
+        # │ 0 │ Host quanweb                 │
+        # │ 1 │     User quan                │
+        # │ 2 │     Hostname quan.hoabinh.vn │
+        # │ 3 │     # ProxyJump farmb-omz    │
+        # │ 4 │                              │
+        # ╰───┴──────────────────────────────╯
+        let host = $in
+        let $first_line = try { $host | first | str trim } catch { null }
+        # Don't accept blocks like "Host *"
+        if ($first_line | is-empty) or '*' in $first_line {
+            null
+        } else {
+            let name = $first_line |  split row -r '\s+' | get 1
+            # May not contain hostname
+            match ($host | slice 1.. | find -ir '^\s*Hostname\s') {
+                [] => null,
+                $addr => { name: $name, addr: ($addr | str trim | split row -n 2 -r '\s+' | get 1) }
+            }
+        }
+    }
+
+    # Process a SSH config file
+    export def process []: string -> record<hosts: list<record<name: string, addr: string>>, includes: list<string>> {
+        let lines = $in | lines
+        # Get 'Include' lines
+        let include_lines = $lines | find -n -ir '^Include\s' | str trim | each { $in | split row -n 2 -r '\s+' | get 1 | str trim -c '"'}
+        # Find "Host" blocks
+        let marks = $lines | enumerate | find -n -ir '^Host\s'
+        let mark_indices = $marks | get index | append ($lines | length)
+        let hosts = $mark_indices | window 2 | each {|w| $lines | slice $w.0..<($w.1) }
+        {
+            hosts: ($hosts | each { $in | extract-host }),
+            includes: $include_lines
+        }
+    }
+
+    export def get-ssh-sites []: nothing -> table<value: string, description: string> {
+      let files = [
+          '/etc/ssh/ssh_config',
+          '~/.ssh/config'
+      ] | filter {|file| $file | path exists }
+
+
+      let first_result: record<hosts: list<record<name: string, addr: string>>, includes: list<string>> = $files | par-each {|file|
+          let folder = $file | path expand | path dirname
+          let r = $file | open --raw | process
+          $r | update includes { each {|f| $folder | path join $f } }
+      } | reduce {|it| merge deep $it --strategy=append }
+
+      let $includes: list<string> = $first_result.includes | each {|f|
+          if '*' in $f {
+              glob $f
+          } else if ($f | path exists) {
+              [$f]
+          } else []
+      } | flatten
+
+      # Process include files
+      let included_hosts: list<record<name: string, addr: string>> = (if ($includes | is-empty) { [] } else {
+          let second_result = $includes | par-each {|p| $p | open --raw | process } | reduce {|it| merge deep $it --strategy=append }
+          $second_result.hosts
+      })
+
+      let hosts = $first_result.hosts ++ $included_hosts
+      $hosts | each {|h| [$"sftp://($h.name)" $"fish://($h.name)"] | wrap value | insert description $h.addr } | flatten
+    }
+
+    export def get-bookmark-sites []: nothing -> table<value: string, description: string> {
+      const FILE_PATH = '~/.local/share/lftp/bookmarks' | path expand
+      let sites = open --raw $FILE_PATH | lines | split column -n 2 -r \s+ value description
+      $sites | update value { $"bm:($in)" }
+    }
+}
+
+
+def "nu-complete lftp-site" [] {
+  use lftp-completion-utils get-ssh-sites
+  use lftp-completion-utils get-bookmark-sites
+  get-ssh-sites | append (get-bookmark-sites)
+}
+
+export extern 'lftp' [
+  -c: string                             # Execute the commands and exit
+  -d                                     # Switch on debugging mode
+  -e: string                             # Execute the command just after selecting
+  -p: int                                # Use the port for connection
+  -u: string                             # Use the user/password for authentication
+  --norc                                 # Don't execute rc files from the home directory
+  --help                                 # Print the help and exit
+  --version                              # Print lftp version and exit
+  site?: string@"nu-complete lftp-site"  # Host name, URL or bookmark name
+]