From 9d5437bcaec37489728aeaed6406da82ecccea76 Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Fri, 27 Mar 2026 16:23:26 +0100
Subject: [PATCH 01/14] Add commands

---
 plugin/decipher.lua    | 155 +++++++++++++++++++++++++++++++++++++++++
 tests/minimal_init.lua |   1 +
 tests/plugin_spec.lua  |  34 +++++++++
 3 files changed, 190 insertions(+)
 create mode 100644 plugin/decipher.lua
 create mode 100644 tests/plugin_spec.lua

diff --git a/plugin/decipher.lua b/plugin/decipher.lua
new file mode 100644
index 0000000..70714e4
--- /dev/null
+++ b/plugin/decipher.lua
@@ -0,0 +1,155 @@
+---@alias decipher.CommandPreviewFunc fun(
+---options: vim.api.keyset.create_user_command.command_args,
+---ns_id: integer,
+---preview_buffer: integer): integer
+
+---@param arg_lead   string
+---@param cmdline    string
+---@param cursor_pos integer
+local function command_complete(arg_lead, cmdline, cursor_pos)
+    if #arg_lead > 0 and vim.startswith("preview", arg_lead) then
+        return { "preview=true", "preview=false" }
+    end
+
+    return require("decipher").supported_codecs()
+end
+
+---@param args string
+---@return string[], string[], string[], string[]
+local function parse_command_args(args)
+    local decipher = require("decipher")
+    local codecs, options, unrecognised_args, errors = {}, {}, {}, {}
+    local supported_codecs = decipher.supported_codecs()
+
+    for _, arg in ipairs(vim.split(args, " ", { plain = true, trimempty = true })) do
+        ---@type string?
+        local preview_match = arg:match("preview=(%S+)")
+
+        if preview_match then
+            if preview_match ~= "true" and preview_match ~= "false" then
+                table.insert(errors, "Invalid value for option 'preview', expected 'true' or 'false'")
+            else
+                options.preview = preview_match == "true"
+            end
+        elseif vim.tbl_contains(supported_codecs, arg) then
+            table.insert(codecs, arg)
+        else
+            table.insert(unrecognised_args, arg)
+        end
+    end
+
+    return codecs, options, unrecognised_args, errors
+end
+
+---@param codecs string[]
+---@param unrecognised_args string[]
+---@param errors string[]
+local function process_command_args(codecs, unrecognised_args, errors)
+    if #codecs > 1 then
+        error("Multiple valid codecs given, specify only one")
+    end
+
+    if #errors > 0 then
+        error(("Found one or more errors: %s"):format(vim.fn.join(errors, ", ")))
+    end
+
+    if #unrecognised_args > 0 then
+        error(("One or more unrecognised arguments: %s"):format(vim.fn.join(unrecognised_args, ", ")))
+    end
+end
+
+---@param codec_func_name string
+---@return decipher.CommandPreviewFunc
+local function create_preview_func(codec_func_name)
+    return function(options, ns_id, preview_buffer)
+        local buffer = vim.api.nvim_get_current_buf()
+        local region = require("decipher.selection").get_selection("visual")
+        local codecs, _ = parse_command_args(options.args)
+
+        if #codecs == 0 then
+            return 0
+        end
+
+        local text = vim.api.nvim_buf_get_text(
+            buffer,
+            region.start.lnum - 1,
+            region.start.col - 1,
+            region["end"].lnum - 1,
+            region["end"].col,
+            {}
+        )
+
+        local codec_value = require("decipher")[codec_func_name](codecs[1], text[1])
+
+        vim.api.nvim_buf_set_text(
+            buffer,
+            region.start.lnum - 1,
+            region.start.col - 1,
+            region["end"].lnum - 1,
+            region["end"].col,
+            { codec_value }
+        )
+
+        vim.hl.range(
+            buffer,
+            ns_id,
+            "Title",
+            { region.start.lnum - 1, region.start.col - 1 },
+            { region["end"].lnum - 1, region.start.col - 1 + #codec_value }
+        )
+
+        if preview_buffer then
+            local lines = vim.api.nvim_buf_get_lines(buffer, region.start.lnum - 1, region["end"].lnum, true)
+
+            vim.api.nvim_buf_set_lines(preview_buffer, 0, -1, false, lines)
+            vim.hl.range(preview_buffer, ns_id, "Title", { 0, region.start.col - 1 }, { -1, region["end"].col - 1 + #codec_value })
+        end
+
+        return 2
+    end
+end
+
+vim.api.nvim_create_user_command("DecipherVersion", function()
+    local v = require("decipher").version()
+    vim.cmd.echo("'" .. v .. "'")
+end, { nargs = 0 })
+
+vim.api.nvim_create_user_command("DecipherEncode", function(args)
+    local codecs, options, unrecognised_args, errors = parse_command_args(args.args)
+
+    process_command_args(codecs, unrecognised_args, errors)
+
+    local decipher = require("decipher")
+    vim.print(vim.inspect(require("decipher.selection").get_visual_selection()))
+    if #codecs == 0 then
+        decipher.encode_selection_prompt(options)
+    else
+        decipher.encode_selection(codecs[1], options)
+    end
+end, {
+    range = true,
+    nargs = "?",
+    complete = command_complete,
+    desc = "Encode a visual selection",
+    preview = create_preview_func("encode"),
+})
+
+vim.api.nvim_create_user_command("DecipherDecode", function(args)
+    local codecs, options, unrecognised_args, errors = parse_command_args(args.args)
+
+    process_command_args(codecs, unrecognised_args, errors)
+
+    local decipher = require("decipher")
+
+    if #codecs == 0 then
+        decipher.decode_selection_prompt(options)
+    else
+        decipher.decode_selection(codecs[1], options)
+    end
+end, {
+    range = true,
+    nargs = "?",
+    complete = command_complete,
+    desc = "Decode a visual selection",
+    preview = create_preview_func("decode"),
+})
diff --git a/tests/minimal_init.lua b/tests/minimal_init.lua
index fb62299..3470249 100644
--- a/tests/minimal_init.lua
+++ b/tests/minimal_init.lua
@@ -1,4 +1,5 @@
 vim.opt.rtp:append(".")
 vim.opt.rtp:append("~/.local/share/nvim/lazy/plenary.nvim")
 
+vim.cmd.runtime({ "plugin/decipher.lua", bang = true })
 vim.cmd.runtime({ "plugin/plenary.vim", bang = true })
diff --git a/tests/plugin_spec.lua b/tests/plugin_spec.lua
new file mode 100644
index 0000000..75eb188
--- /dev/null
+++ b/tests/plugin_spec.lua
@@ -0,0 +1,34 @@
+local vader = require("decipher.util.vader")
+
+local given, normal, expect = vader.given, vader.normal, vader.expect
+
+describe("commands", function()
+    it("runs DecipherVersion", function()
+        assert.are.same(vim.fn.exists(":DecipherVersion"), 2)
+
+        local output = vim.fn.execute("DecipherVersion", "")
+        local version = vim.split(output, "\n", { plain = true, trimempty = true })[1]
+
+        assert.are.same(version, "3.0.0") -- TODO: Match instead?
+    end)
+
+    it("runs DecipherEncode", function()
+        assert.are.same(vim.fn.exists(":DecipherEncode"), 2)
+
+        given({ "light work" }, function(context)
+            normal("gg0vg_<esc>")
+            vim.cmd("DecipherEncode base64")
+            expect({ "bGlnaHQgd29yaw==" })
+        end)
+    end)
+
+    it("runs DecipherDecode", function()
+        assert.are.same(vim.fn.exists(":DecipherDecode"), 2)
+
+        given({ "bGlnaHQgd29yaw==" }, function(context)
+            normal("gg0vg_<esc>")
+            vim.cmd("DecipherDecode base64")
+            expect({ "light work" })
+        end)
+    end)
+end)

From ad8320335fde32952a3d97a67048f3f383152c96 Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Fri, 27 Mar 2026 16:23:38 +0100
Subject: [PATCH 02/14] Minor type fixes

---
 lua/decipher/init.lua | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lua/decipher/init.lua b/lua/decipher/init.lua
index e1ef5bc..692ad48 100644
--- a/lua/decipher/init.lua
+++ b/lua/decipher/init.lua
@@ -26,7 +26,7 @@ function decipher.version()
     return decipher_version
 end
 
----@return decipher.Codecs[] a list of the names of supported codecs
+---@return decipher.Codecs[] # a list of the names of supported codecs
 function decipher.supported_codecs()
     return codecs.supported()
 end
@@ -34,7 +34,7 @@ end
 ---@param codec_name decipher.CodecArg
 ---@param value string
 ---@param func_key "encode" | "decode"
----@return string | nil
+---@return string?
 local function handle_codec(codec_name, value, func_key)
     local codec = codecs.get(codec_name)
 
@@ -53,14 +53,14 @@ end
 
 ---@param codec_name decipher.CodecArg
 ---@param value string value to encode
----@return string | nil the encoded value or nil if encoding failed
+---@return string? the encoded value or nil if encoding failed
 function decipher.encode(codec_name, value)
     return handle_codec(codec_name, value, "encode")
 end
 
 ---@param codec_name decipher.CodecArg
 ---@param value string value to decode
----@return string | nil the decoded value or nil if decoding failed
+---@return string? the decoded value or nil if decoding failed
 function decipher.decode(codec_name, value)
     return handle_codec(codec_name, value, "decode")
 end

From 343f56df9f27560e40d29ebea7a314673d618014 Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Fri, 27 Mar 2026 20:09:33 +0100
Subject: [PATCH 03/14] Remove print statement

---
 plugin/decipher.lua | 1 -
 1 file changed, 1 deletion(-)

diff --git a/plugin/decipher.lua b/plugin/decipher.lua
index 70714e4..07a186d 100644
--- a/plugin/decipher.lua
+++ b/plugin/decipher.lua
@@ -120,7 +120,6 @@ vim.api.nvim_create_user_command("DecipherEncode", function(args)
     process_command_args(codecs, unrecognised_args, errors)
 
     local decipher = require("decipher")
-    vim.print(vim.inspect(require("decipher.selection").get_visual_selection()))
     if #codecs == 0 then
         decipher.encode_selection_prompt(options)
     else

From 9f09e52ae2acb7dd8bfdaeb34e805dab634fe1f2 Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Fri, 27 Mar 2026 22:01:18 +0100
Subject: [PATCH 04/14] Add tests for invalid command arguments

---
 tests/plugin_spec.lua | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/tests/plugin_spec.lua b/tests/plugin_spec.lua
index 75eb188..acf5954 100644
--- a/tests/plugin_spec.lua
+++ b/tests/plugin_spec.lua
@@ -22,6 +22,36 @@ describe("commands", function()
         end)
     end)
 
+    it("handles invalid options for 'preview'", function()
+        local ok, err = pcall(vim.fn.execute, "DecipherEncode preview=nope", "")
+
+        assert.is_false(ok)
+
+        ---@diagnostic disable-next-line: undefined-field
+        assert.has_match(
+            "Found one or more errors: Invalid value for option 'preview', expected 'true' or 'false'",
+            err
+        )
+    end)
+
+    it("handles more than one codec", function()
+        local ok, err = pcall(vim.fn.execute, "DecipherEncode base64 base32", "")
+
+        assert.is_false(ok)
+
+        ---@diagnostic disable-next-line: undefined-field
+        assert.has_match("Multiple valid codecs given, specify only one", err)
+    end)
+
+    it("handles unknown arguments", function()
+        local ok, err = pcall(vim.fn.execute, "DecipherEncode nope preview=true", "")
+
+        assert.is_false(ok)
+
+        ---@diagnostic disable-next-line: undefined-field
+        assert.has_match("One or more unrecognised arguments: nope", err)
+    end)
+
     it("runs DecipherDecode", function()
         assert.are.same(vim.fn.exists(":DecipherDecode"), 2)
 

From 40879e0180c4288fb6645bca379c1005d225fb0b Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Fri, 27 Mar 2026 23:00:43 +0100
Subject: [PATCH 05/14] Match on version in test instead

---
 tests/plugin_spec.lua | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tests/plugin_spec.lua b/tests/plugin_spec.lua
index acf5954..da5614a 100644
--- a/tests/plugin_spec.lua
+++ b/tests/plugin_spec.lua
@@ -9,7 +9,8 @@ describe("commands", function()
         local output = vim.fn.execute("DecipherVersion", "")
         local version = vim.split(output, "\n", { plain = true, trimempty = true })[1]
 
-        assert.are.same(version, "3.0.0") -- TODO: Match instead?
+        ---@diagnostic disable-next-line: undefined-field
+        assert.has_match("^%d+%.%d+%.%d+$", version)
     end)
 
     it("runs DecipherEncode", function()

From 85d9733afb991d6f5d570090d3a7601f8d781c53 Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Fri, 27 Mar 2026 23:01:15 +0100
Subject: [PATCH 06/14] Minor refactor

---
 plugin/decipher.lua | 42 +++++++++++++-----------------------------
 1 file changed, 13 insertions(+), 29 deletions(-)

diff --git a/plugin/decipher.lua b/plugin/decipher.lua
index 07a186d..fbe7e45 100644
--- a/plugin/decipher.lua
+++ b/plugin/decipher.lua
@@ -62,50 +62,34 @@ end
 ---@return decipher.CommandPreviewFunc
 local function create_preview_func(codec_func_name)
     return function(options, ns_id, preview_buffer)
-        local buffer = vim.api.nvim_get_current_buf()
-        local region = require("decipher.selection").get_selection("visual")
         local codecs, _ = parse_command_args(options.args)
 
         if #codecs == 0 then
             return 0
         end
 
-        local text = vim.api.nvim_buf_get_text(
-            buffer,
-            region.start.lnum - 1,
-            region.start.col - 1,
-            region["end"].lnum - 1,
-            region["end"].col,
-            {}
-        )
+        local buffer = vim.api.nvim_get_current_buf()
+        local region = require("decipher.selection").get_selection("visual")
+        local start_lnum, end_lnum = region.start.lnum - 1, region["end"].lnum - 1
+        local start_col, end_col = region.start.col - 1, region["end"].col - 1
+
+        local text = vim.api.nvim_buf_get_text(buffer, start_lnum, start_col, end_lnum, end_col, {})
 
         local codec_value = require("decipher")[codec_func_name](codecs[1], text[1])
 
-        vim.api.nvim_buf_set_text(
-            buffer,
-            region.start.lnum - 1,
-            region.start.col - 1,
-            region["end"].lnum - 1,
-            region["end"].col,
-            { codec_value }
-        )
-
-        vim.hl.range(
-            buffer,
-            ns_id,
-            "Title",
-            { region.start.lnum - 1, region.start.col - 1 },
-            { region["end"].lnum - 1, region.start.col - 1 + #codec_value }
-        )
+        -- Set preview text and highlight in buffer
+        vim.api.nvim_buf_set_text(buffer, start_lnum, start_col, end_lnum, end_col + 1, { codec_value })
+        vim.hl.range(buffer, ns_id, "Title", { start_lnum, start_col }, { end_lnum, start_col + #codec_value })
 
+        -- Set preview text and highlight in preview buffer if enabled
         if preview_buffer then
-            local lines = vim.api.nvim_buf_get_lines(buffer, region.start.lnum - 1, region["end"].lnum, true)
+            local lines = vim.api.nvim_buf_get_lines(buffer, start_lnum, end_lnum, true)
 
             vim.api.nvim_buf_set_lines(preview_buffer, 0, -1, false, lines)
-            vim.hl.range(preview_buffer, ns_id, "Title", { 0, region.start.col - 1 }, { -1, region["end"].col - 1 + #codec_value })
+            vim.hl.range(preview_buffer, ns_id, "Title", { 0, start_col - 1 }, { -1, end_col - 1 + #codec_value })
         end
 
-        return 2
+        return 2 -- TODO: Double-check
     end
 end
 

From 6dea36c6ce239979cd8b2d037e31b88bf0b47760 Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Sun, 19 Apr 2026 15:42:55 +0200
Subject: [PATCH 07/14] Add documentation

---
 README.md        | 24 ++++++++++++++++++++++++
 doc/decipher.txt | 29 +++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/README.md b/README.md
index 83bd4c8..2241946 100644
--- a/README.md
+++ b/README.md
@@ -19,6 +19,8 @@
 
 - [Installing](#installing)
 - [Setup](#setup)
+- [Commands](#commands)
+- [JSON view](#json-view)
 - [Example keymaps](#example-keymaps)
 - [Supported Codecs](#supported-codecs)
     - [base32](#base32)
@@ -100,6 +102,28 @@ require("decipher").setup({
 })
 ```
 
+## Commands 
+
+### `DecipherVersion`
+
+Prints the current version
+
+### `[range]DecipherEncode [options]`
+
+Encode the selected visual range or the last visual selection with the codec
+given on the command line. Prompts for a codec if not given. Also takes an
+option for previewing i.e. `preview=true|false`.
+
+Example: `:'<,'>DecipherEncode crockford preview=false`
+
+### `[range]DecipherDecode [options]`
+
+Decode the selected visual range or the last visual selection with the codec
+given on the command line. Prompts for a codec if not given. Also takes an
+option for previewing i.e. `preview=true|false`.
+
+Example: `:'<,'>DecipherDecode base64 preview=true`
+
 ## JSON view
 
 ### Applying
diff --git a/doc/decipher.txt b/doc/decipher.txt
index 4bb5299..bbcf5d7 100644
--- a/doc/decipher.txt
+++ b/doc/decipher.txt
@@ -19,6 +19,7 @@ decipher                                                              *decipher*
   Setup ....................................................... |decipher.setup|
   Types ....................................................... |decipher.types|
   Functions ............................................... |decipher.functions|
+  Commands ................................................. |decipher.commands|
   Mappings ................................................. |decipher.mappings|
   Motions ................................................... |decipher.motions|
   Highlights ............................................. |decipher.highlights|
@@ -213,6 +214,34 @@ decode_motion_prompt({options})                  *decipher.decode_motion_prompt*
     Parameters:  
       • {options}    (`decipher.Options`) Options to use
 
+==============================================================================
+Commands                                                     *decipher.commands*
+
+:DecipherVersion                                              *:DecipherVersion*
+                 Prints the current version
+
+:[range]DecipherEncode [options]                               *:DecipherEncode*
+                                Encode the selected visual range or the last
+                                visual selection with the codec given on the
+                                command line. Prompts for a codec if not
+                                given. Also takes an option for previewing
+                                i.e. `preview=true|false`.
+
+                                Example:
+                                >
+                                :'<,'>DecipherEncode crockford preview=false
+
+:[range]DecipherDecode [options]                               *:DecipherDecode*
+                                Decode the selected visual range or the last
+                                visual selection with the codec given on the
+                                command line. Prompts for a codec if not
+                                given. Also takes an option for previewing
+                                i.e. `preview=true|false`.
+
+                                Example:
+                                >
+                                :'<,'>DecipherDecode base64 preview=true
+
 ==============================================================================
 Mappings                                                     *decipher.mappings*
 

From e22d1dcae0617e9a58d01d2edd3f8aac12085249 Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Sun, 19 Apr 2026 15:45:18 +0200
Subject: [PATCH 08/14] Simplify command argument completion

---
 plugin/decipher.lua | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/plugin/decipher.lua b/plugin/decipher.lua
index fbe7e45..8e990a1 100644
--- a/plugin/decipher.lua
+++ b/plugin/decipher.lua
@@ -3,15 +3,17 @@
 ---ns_id: integer,
 ---preview_buffer: integer): integer
 
+local command_arguments
+
 ---@param arg_lead   string
 ---@param cmdline    string
 ---@param cursor_pos integer
 local function command_complete(arg_lead, cmdline, cursor_pos)
-    if #arg_lead > 0 and vim.startswith("preview", arg_lead) then
-        return { "preview=true", "preview=false" }
+    if not command_arguments then
+        command_arguments = vim.list_extend({ "preview=true", "preview=false" }, require("decipher").supported_codecs())
     end
 
-    return require("decipher").supported_codecs()
+    return command_arguments
 end
 
 ---@param args string

From c9861a76229993513cb766aeaa7da0aa00ad6b30 Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Sun, 26 Apr 2026 22:19:17 +0200
Subject: [PATCH 09/14] Mention command previewing

---
 README.md        | 4 ++++
 doc/decipher.txt | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/README.md b/README.md
index 2241946..dcddb8b 100644
--- a/README.md
+++ b/README.md
@@ -114,6 +114,8 @@ Encode the selected visual range or the last visual selection with the codec
 given on the command line. Prompts for a codec if not given. Also takes an
 option for previewing i.e. `preview=true|false`.
 
+The command supports command previewing, see `:h 'inccommand'`.
+
 Example: `:'<,'>DecipherEncode crockford preview=false`
 
 ### `[range]DecipherDecode [options]`
@@ -122,6 +124,8 @@ Decode the selected visual range or the last visual selection with the codec
 given on the command line. Prompts for a codec if not given. Also takes an
 option for previewing i.e. `preview=true|false`.
 
+The command supports command previewing, see `:h 'inccommand'`.
+
 Example: `:'<,'>DecipherDecode base64 preview=true`
 
 ## JSON view
diff --git a/doc/decipher.txt b/doc/decipher.txt
index bbcf5d7..99cd082 100644
--- a/doc/decipher.txt
+++ b/doc/decipher.txt
@@ -227,6 +227,9 @@ Commands                                                     *decipher.commands*
                                 given. Also takes an option for previewing
                                 i.e. `preview=true|false`.
 
+                                The command supports command previewing, see
+                                |'inccommand'|.
+
                                 Example:
                                 >
                                 :'<,'>DecipherEncode crockford preview=false
@@ -238,6 +241,9 @@ Commands                                                     *decipher.commands*
                                 given. Also takes an option for previewing
                                 i.e. `preview=true|false`.
 
+                                The command supports command previewing, see
+                                |'inccommand'|.
+
                                 Example:
                                 >
                                 :'<,'>DecipherDecode base64 preview=true

From 17286cc584acd1ac1cb9d089e466db3f00710afc Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Sat, 2 May 2026 13:01:27 +0200
Subject: [PATCH 10/14] Minor fixes

---
 README.md           | 2 +-
 doc/decipher.txt    | 2 +-
 plugin/decipher.lua | 9 ++++++---
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index dcddb8b..22c7ce6 100644
--- a/README.md
+++ b/README.md
@@ -106,7 +106,7 @@ require("decipher").setup({
 
 ### `DecipherVersion`
 
-Prints the current version
+Prints the current version.
 
 ### `[range]DecipherEncode [options]`
 
diff --git a/doc/decipher.txt b/doc/decipher.txt
index 99cd082..1838622 100644
--- a/doc/decipher.txt
+++ b/doc/decipher.txt
@@ -218,7 +218,7 @@ decode_motion_prompt({options})                  *decipher.decode_motion_prompt*
 Commands                                                     *decipher.commands*
 
 :DecipherVersion                                              *:DecipherVersion*
-                 Prints the current version
+                 Prints the current version.
 
 :[range]DecipherEncode [options]                               *:DecipherEncode*
                                 Encode the selected visual range or the last
diff --git a/plugin/decipher.lua b/plugin/decipher.lua
index 8e990a1..71f4233 100644
--- a/plugin/decipher.lua
+++ b/plugin/decipher.lua
@@ -3,11 +3,13 @@
 ---ns_id: integer,
 ---preview_buffer: integer): integer
 
+---@type string[]?
 local command_arguments
 
 ---@param arg_lead   string
 ---@param cmdline    string
 ---@param cursor_pos integer
+---@return string[]
 local function command_complete(arg_lead, cmdline, cursor_pos)
     if not command_arguments then
         command_arguments = vim.list_extend({ "preview=true", "preview=false" }, require("decipher").supported_codecs())
@@ -64,7 +66,7 @@ end
 ---@return decipher.CommandPreviewFunc
 local function create_preview_func(codec_func_name)
     return function(options, ns_id, preview_buffer)
-        local codecs, _ = parse_command_args(options.args)
+        local codecs, _, _, _ = parse_command_args(options.args)
 
         if #codecs == 0 then
             return 0
@@ -96,8 +98,8 @@ local function create_preview_func(codec_func_name)
 end
 
 vim.api.nvim_create_user_command("DecipherVersion", function()
-    local v = require("decipher").version()
-    vim.cmd.echo("'" .. v .. "'")
+    local version = require("decipher").version()
+    vim.cmd.echo("'" .. version .. "'")
 end, { nargs = 0 })
 
 vim.api.nvim_create_user_command("DecipherEncode", function(args)
@@ -106,6 +108,7 @@ vim.api.nvim_create_user_command("DecipherEncode", function(args)
     process_command_args(codecs, unrecognised_args, errors)
 
     local decipher = require("decipher")
+
     if #codecs == 0 then
         decipher.encode_selection_prompt(options)
     else

From af764f6b3c5ac3b47776c07a7f6856e460f84176 Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Sat, 16 May 2026 21:44:42 +0200
Subject: [PATCH 11/14] Fix command preview

---
 lua/decipher/init.lua |  2 ++
 plugin/decipher.lua   | 28 ++++++++++++++++++++--------
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/lua/decipher/init.lua b/lua/decipher/init.lua
index 692ad48..b6d97d5 100644
--- a/lua/decipher/init.lua
+++ b/lua/decipher/init.lua
@@ -227,6 +227,8 @@ function decipher.setup(user_config)
 
     config.setup(user_config)
     ui.float.setup()
+
+    vim.cmd([[hi default link DecipherCommandPreview Title]])
 end
 
 return decipher
diff --git a/plugin/decipher.lua b/plugin/decipher.lua
index 71f4233..fe72b9b 100644
--- a/plugin/decipher.lua
+++ b/plugin/decipher.lua
@@ -62,7 +62,7 @@ local function process_command_args(codecs, unrecognised_args, errors)
     end
 end
 
----@param codec_func_name string
+---@param codec_func_name "encode" | "decode"
 ---@return decipher.CommandPreviewFunc
 local function create_preview_func(codec_func_name)
     return function(options, ns_id, preview_buffer)
@@ -76,24 +76,36 @@ local function create_preview_func(codec_func_name)
         local region = require("decipher.selection").get_selection("visual")
         local start_lnum, end_lnum = region.start.lnum - 1, region["end"].lnum - 1
         local start_col, end_col = region.start.col - 1, region["end"].col - 1
+        local text = vim.api.nvim_buf_get_text(buffer, start_lnum, start_col, end_lnum, end_col + 1, {})
+        local ok, result = pcall(require("decipher")[codec_func_name], codecs[1], table.concat(text, "\n"))
 
-        local text = vim.api.nvim_buf_get_text(buffer, start_lnum, start_col, end_lnum, end_col, {})
+        if not ok then
+            return 0
+        end
 
-        local codec_value = require("decipher")[codec_func_name](codecs[1], text[1])
+        local new_lines = vim.split(result, "\r?\n")
+        local new_end_lnum = end_lnum + #new_lines - 1
+        local new_end_col = #new_lines[#new_lines]
+
+        if codec_func_name == "decode" and #new_lines == 1 then
+            -- If there is only one decoded line offset the new end column by
+            -- the original start column
+            new_end_col = start_col + new_end_col
+        end
 
         -- Set preview text and highlight in buffer
-        vim.api.nvim_buf_set_text(buffer, start_lnum, start_col, end_lnum, end_col + 1, { codec_value })
-        vim.hl.range(buffer, ns_id, "Title", { start_lnum, start_col }, { end_lnum, start_col + #codec_value })
+        vim.api.nvim_buf_set_text(buffer, start_lnum, start_col, end_lnum, end_col + 1, new_lines)
+        vim.hl.range(buffer, ns_id, "DecipherCommandPreview", { start_lnum, start_col }, { new_end_lnum, new_end_col })
 
         -- Set preview text and highlight in preview buffer if enabled
         if preview_buffer then
-            local lines = vim.api.nvim_buf_get_lines(buffer, start_lnum, end_lnum, true)
+            local lines = vim.api.nvim_buf_get_lines(buffer, start_lnum, new_end_lnum + 1, true)
 
             vim.api.nvim_buf_set_lines(preview_buffer, 0, -1, false, lines)
-            vim.hl.range(preview_buffer, ns_id, "Title", { 0, start_col - 1 }, { -1, end_col - 1 + #codec_value })
+            vim.hl.range(preview_buffer, ns_id, "DecipherCommandPreview", { 0, start_col }, { #new_lines, new_end_col })
         end
 
-        return 2 -- TODO: Double-check
+        return 2
     end
 end
 

From fdb5220823c8f221cb74548f3612e4aae587ec5b Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Sat, 16 May 2026 21:49:36 +0200
Subject: [PATCH 12/14] Pass options instead of 5 arguments

---
 lua/decipher/init.lua | 42 +++++++++++++++++++++++++++++++-----------
 1 file changed, 31 insertions(+), 11 deletions(-)

diff --git a/lua/decipher/init.lua b/lua/decipher/init.lua
index b6d97d5..957d36b 100644
--- a/lua/decipher/init.lua
+++ b/lua/decipher/init.lua
@@ -19,6 +19,13 @@ decipher.codec = codecs.codec
 ---@field selection_type decipher.SelectionType
 ---@field codec_type "encode" | "decode"
 
+---@class decipher.SetTextRegionOptions
+---@field codec_name string
+---@field codec_type "encode" | "decode"
+---@field status boolean
+---@field value string
+---@field selection_type decipher.SelectionType
+
 ---@alias decipher.CodecArg string | decipher.Codecs
 
 ---@return string
@@ -96,24 +103,31 @@ local function open_float_handler(codec_name, status, value, selection_type, cod
 end
 
 --- Handler for setting a text region to a value
----@param codec_name string
----@param status boolean
----@param value string
----@param selection_type decipher.SelectionType
----@diagnostic disable-next-line:unused-local
-local function set_text_region_handler(codec_name, status, value, selection_type)
-    if not status then
-        notifications.error(("%s: %s"):format(codec_name, value))
+---@param options decipher.SetTextRegionOptions
+local function set_text_region_handler(options)
+    local value = options.value
+
+    if not options.status then
+        notifications.error(("%s: %s"):format(options.codec_name, value))
         return
     end
 
     if value == nil then
-        notifications.codec_not_found("Codec not found: " .. codec_name)
+        notifications.codec_not_found("Codec not found: " .. options.codec_name)
         return
     end
 
+    ---@type string[]
+    local lines
+
+    if options.codec_type == "decode" then
+        lines = vim.split(value, "\r?\n")
+    else
+        lines = { value }
+    end
+
     -- Escape the string since you cannot set lines in a buffer if it contains newlines
-    selection.set_text(0, selection_type, str_utils.escape_newlines({ value }))
+    selection.set_text(0, options.selection_type, str_utils.escape_newlines(lines))
 end
 
 --- Process a codec action
@@ -134,7 +148,13 @@ local function process_codec(codec_name, codec_func, selection_type, codec_type,
     if do_preview then
         open_float_handler(_codec_name, status, value, selection_type, codec_type)
     else
-        set_text_region_handler(_codec_name, status, value, selection_type)
+        set_text_region_handler({
+            codec_name = _codec_name,
+            status = status,
+            value = value,
+            selection_type = selection_type,
+            codec_type = codec_type,
+        })
     end
 end
 

From 698e890dc5d21bb4d23cca916f02809e5a41cc75 Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Sat, 16 May 2026 22:34:07 +0200
Subject: [PATCH 13/14] Do not show preview if there are invalid command args

---
 plugin/decipher.lua | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/plugin/decipher.lua b/plugin/decipher.lua
index fe72b9b..c02ae47 100644
--- a/plugin/decipher.lua
+++ b/plugin/decipher.lua
@@ -66,9 +66,10 @@ end
 ---@return decipher.CommandPreviewFunc
 local function create_preview_func(codec_func_name)
     return function(options, ns_id, preview_buffer)
-        local codecs, _, _, _ = parse_command_args(options.args)
+        local codecs, _, unrecognised_args, errors = parse_command_args(options.args)
 
-        if #codecs == 0 then
+        if #codecs ~= 1 or #unrecognised_args > 0 or #errors > 0 then
+            -- Do not show preview
             return 0
         end
 
@@ -80,6 +81,7 @@ local function create_preview_func(codec_func_name)
         local ok, result = pcall(require("decipher")[codec_func_name], codecs[1], table.concat(text, "\n"))
 
         if not ok then
+            -- Do not show preview
             return 0
         end
 

From e1930558e0046a43ba1df8928e4bb9ec6e092dab Mon Sep 17 00:00:00 2001
From: MisanthropicBit <proximity.dev@proton.me>
Date: Sat, 16 May 2026 22:36:13 +0200
Subject: [PATCH 14/14] Add DecipherCommandPreview to doc

---
 doc/decipher.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/doc/decipher.txt b/doc/decipher.txt
index 1838622..538e647 100644
--- a/doc/decipher.txt
+++ b/doc/decipher.txt
@@ -292,6 +292,10 @@ Highlights                                                 *decipher.highlights*
   Highlight group for the title of the floating window preview. Defaults to
   *Title*.
 
+*DecipherCommandPreview*
+  Highlight group used in command previews for the encoded/decoded text.
+  Defaults to *Title*.
+
 ==============================================================================
 Codecs                                                         *decipher.codecs*