refactor: improve diff handling implementation

Extract diff handling into separate class to reduce code duplication and improve
maintainability. Add custom highlighting namespace in diff class and remove
redundant code from overlay class. Add utility function for finding lines
between patterns. Improve diff accepting/showing logic with proper line number
handling.

Move highlighting setup into dedicated diff class and make overlay class more
focused. Add example for code snippet markdown links in prompts to improve
clarity.

Signed-off-by: Tomas Slusny <[email protected]>

lua/CopilotChat/chat.lua

@@ -32,6 +32,7 @@ end
 
 local Chat = class(function(self, help, on_buf_create)
   self.header_ns = vim.api.nvim_create_namespace('copilot-chat-headers')
+  self.name = 'copilot-chat'
   self.help = help
   self.on_buf_create = on_buf_create
   self.bufnr = nil
@@ -43,12 +44,12 @@ local Chat = class(function(self, help, on_buf_create)
   self.highlight_headers = true
   self.layout = nil
 
-  vim.treesitter.language.register('markdown', 'copilot-chat')
+  vim.treesitter.language.register('markdown', self.name)
 
   self.buf_create = function()
     local bufnr = vim.api.nvim_create_buf(false, true)
-    vim.api.nvim_buf_set_name(bufnr, 'copilot-chat')
-    vim.bo[bufnr].filetype = 'copilot-chat'
+    vim.api.nvim_buf_set_name(bufnr, self.name)
+    vim.bo[bufnr].filetype = self.name
     vim.bo[bufnr].syntax = 'markdown'
     vim.bo[bufnr].textwidth = 0
     local ok, parser = pcall(vim.treesitter.get_parser, bufnr, 'markdown')

lua/CopilotChat/diff.lua

@@ -0,0 +1,105 @@
+---@class CopilotChat.Diff
+---@field bufnr number
+---@field show fun(self: CopilotChat.Diff, change: string, reference: string, start_line: number?, end_line: number?, filetype: string, winnr: number)
+---@field restore fun(self: CopilotChat.Diff, winnr: number, bufnr: number)
+---@field delete fun(self: CopilotChat.Diff)
+---@field get_diff fun(self: CopilotChat.Diff): string, string, number?, number?
+
+local Overlay = require('CopilotChat.overlay')
+local utils = require('CopilotChat.utils')
+local class = utils.class
+
+local Diff = class(function(self, help, on_buf_create)
+  self.hl_ns = vim.api.nvim_create_namespace('copilot-chat-highlights')
+  vim.api.nvim_set_hl(
+    self.hl_ns,
+    '@diff.plus',
+    { bg = utils.blend_color_with_neovim_bg('DiffAdd', 20) }
+  )
+  vim.api.nvim_set_hl(
+    self.hl_ns,
+    '@diff.minus',
+    { bg = utils.blend_color_with_neovim_bg('DiffDelete', 20) }
+  )
+  vim.api.nvim_set_hl(
+    self.hl_ns,
+    '@diff.delta',
+    { bg = utils.blend_color_with_neovim_bg('DiffChange', 20) }
+  )
+
+  self.name = 'copilot-diff'
+  self.help = help
+  self.on_buf_create = on_buf_create
+  self.bufnr = nil
+  self.change = nil
+  self.reference = nil
+  self.start_line = nil
+  self.end_line = nil
+  self.filetype = nil
+
+  self.buf_create = function()
+    local bufnr = vim.api.nvim_create_buf(false, true)
+    vim.api.nvim_buf_set_name(bufnr, self.name)
+    vim.bo[bufnr].filetype = self.name
+    return bufnr
+  end
+end, Overlay)
+
+function Diff:show(change, reference, start_line, end_line, filetype, winnr)
+  self.change = change
+  self.reference = reference
+  self.start_line = start_line
+  self.end_line = end_line
+  self.filetype = filetype
+
+  self:validate()
+  vim.api.nvim_win_set_hl_ns(winnr, self.hl_ns)
+
+  -- mini.diff integration (unfinished)
+  -- local diff_found, diff = pcall(require, 'mini.diff')
+  -- if diff_found then
+  --   diff.disable(self.bufnr)
+  --   Overlay.show(self, change, filetype, winnr)
+  --
+  --   vim.b[self.bufnr].minidiff_config = {
+  --     source = {
+  --       name = self.name,
+  --       attach = function(bufnr)
+  --         diff.set_ref_text(bufnr, reference)
+  --         diff.toggle_overlay(bufnr)
+  --       end,
+  --     },
+  --   }
+  --
+  --   diff.enable(self.bufnr)
+  --   return
+  -- end
+
+  Overlay.show(
+    self,
+    tostring(vim.diff(reference, change, {
+      result_type = 'unified',
+      ignore_blank_lines = true,
+      ignore_whitespace = true,
+      ignore_whitespace_change = true,
+      ignore_whitespace_change_at_eol = true,
+      ignore_cr_at_eol = true,
+      algorithm = 'myers',
+      ctxlen = #reference,
+    })),
+    filetype,
+    winnr,
+    'diff'
+  )
+end
+
+function Diff:restore(winnr, bufnr)
+  Overlay.restore(self, winnr, bufnr)
+  vim.api.nvim_win_set_hl_ns(winnr, 0)
+end
+
+function Diff:get_diff()
+  return self.change, self.reference, self.start_line, self.end_line, self.filetype
+end
+
+return Diff