require('packer').startup(function(use) 
  --packer
  use 'wbthomason/packer.nvim'

  --lsp
  use 'neovim/nvim-lspconfig'

  --auto complete
  use 'hrsh7th/cmp-nvim-lsp'
  use 'hrsh7th/cmp-buffer'
  use 'hrsh7th/cmp-path'
  use 'hrsh7th/cmp-cmdline'
  use 'hrsh7th/nvim-cmp'
  --
  use 'hrsh7th/cmp-vsnip'
  use 'hrsh7th/vim-vsnip'
  vim.opt.completeopt = { "menu", "menuone", "noselect" }
end)

local has_words_before = function()
  local line, col = unpack(vim.api.nvim_win_get_cursor(0))
  return col ~= 0 and vim.api.nvim_buf_get_lines(0, line - 1, line, true)[1]:sub(col, col):match("%s") == nil
end

local feedkey = function(key, mode)
  vim.api.nvim_feedkeys(vim.api.nvim_replace_termcodes(key, true, true, true), mode, true)
end


local cmp = require('cmp')

cmp.setup({
  snippet = {
    expand = function(args)
      vim.fn["vsnip#anonymous"](args.body) -- For `vsnip` users.
    end,
  },
  mapping = {
    -- ['<CR>'] = cmp.mapping.confirm({ select = true }), -- Accept currently selected item. Set `select` to `false` to only confirm explicitly selected items.
    ["<Tab>"] = cmp.mapping(function(fallback)
      if cmp.visible() then
        cmp.select_next_item()
      elseif vim.fn["vsnip#available"](1) == 1 then
        feedkey("<Plug>(vsnip-expand-or-jump)", "")
      elseif has_words_before() then
        cmp.complete()
      else
        fallback() -- The fallback function sends a already mapped key. In this case, it's probably `<Tab>`.
      end
    end, { "i", "s" }),
    ["<S-Tab>"] = cmp.mapping(function()
      if cmp.visible() then
        cmp.select_prev_item()
      elseif vim.fn["vsnip#jumpable"](-1) == 1 then
        feedkey("<Plug>(vsnip-jump-prev)", "")
      end
    end, { "i", "s" }),
  },
  sources = cmp.config.sources({
    { name = 'nvim_lsp' },
    { name = 'vsnip' }, -- For vsnip users.
  }, {
    { name = 'buffer' },
  })
})


local capabilities = require('cmp_nvim_lsp').default_capabilities() --nvim-cmp

local on_attach = function(client, bufnr)
  local function buf_set_keymap(...) vim.api.nvim_buf_set_keymap(bufnr, ...) end
  local function buf_set_option(...) vim.api.nvim_buf_set_option(bufnr, ...) end

  buf_set_option('omnifunc', 'v:lua.vim.lsp.omnifunc')
end

-- Setup lspconfig.
local nvim_lsp = require('lspconfig')

-- setup languages 
-- GoLang
nvim_lsp['gopls'].setup{
  cmd = {'gopls'},
  -- on_attach = on_attach,
  capabilities = capabilities,
  settings = {
    gopls = {
      experimentalPostfixCompletions = true,
      analyses = {
        unusedparams = true,
        shadow = true,
      },
      staticcheck = true,
    },
  },
  init_options = {
    usePlaceholders = true,
  }
}

vim.opt.completeopt = "menu,menuone,noinsert"

require("packer").startup({{
	{ "wbthomason/packer.nvim" },

	{ "hrsh7th/nvim-cmp" },
	{ "hrsh7th/cmp-buffer" },
	{ "hrsh7th/cmp-nvim-lua" },
	{ "hrsh7th/cmp-nvim-lsp" },
	{ "hrsh7th/cmp-nvim-lsp-signature-help" },
	{ "hrsh7th/cmp-path" },
	{ "neovim/nvim-lspconfig" },
	{ "L3MON4D3/LuaSnip" },
	{ "saadparwaiz1/cmp_luasnip" },
	{ "simrat39/rust-tools.nvim" },
}, config = {}})

-- Setup cmp
local cmp = require("cmp")
cmp.setup({
	mapping = cmp.mapping.preset.insert({ -- Preset: ^n, ^p, ^y, ^e, you know the drill..
		["<C-d>"] = cmp.mapping.scroll_docs(-4),
		["<C-f>"] = cmp.mapping.scroll_docs(4),
	}),
	snippet = {
		expand = function(args)
			require("luasnip").lsp_expand(args.body)
		end,
	},
	sources = cmp.config.sources({
		{ name = "nvim_lsp" },
		{ name = "nvim_lsp_signature_help" },
		{ name = "nvim_lua" },
		{ name = "luasnip" },
		{ name = "path" },
	}, {
		{ name = "buffer", keyword_length = 3 },
	}),
})

-- Setup buffer-local keymaps / options for LSP buffers
local capabilities = require("cmp_nvim_lsp").update_capabilities(vim.lsp.protocol.make_client_capabilities())
local lsp_attach = function(client, buf)
	-- Example maps, set your own with vim.api.nvim_buf_set_keymap(buf, "n", <lhs>, <rhs>, { desc = <desc> })
	-- or a plugin like which-key.nvim
	-- <lhs>        <rhs>                        <desc>
	-- "K"          vim.lsp.buf.hover            "Hover Info"
	-- "<leader>qf" vim.diagnostic.setqflist     "Quickfix Diagnostics"
	-- "[d"         vim.diagnostic.goto_prev     "Previous Diagnostic"
	-- "]d"         vim.diagnostic.goto_next     "Next Diagnostic"
	-- "<leader>e"  vim.diagnostic.open_float    "Explain Diagnostic"
	-- "<leader>ca" vim.lsp.buf.code_action      "Code Action"
	-- "<leader>cr" vim.lsp.buf.rename           "Rename Symbol"
	-- "<leader>fs" vim.lsp.buf.document_symbol  "Document Symbols"
	-- "<leader>fS" vim.lsp.buf.workspace_symbol "Workspace Symbols"
	-- "<leader>gq" vim.lsp.buf.formatting_sync  "Format File"

	vim.api.nvim_buf_set_option(buf, "formatexpr", "v:lua.vim.lsp.formatexpr()")
	vim.api.nvim_buf_set_option(buf, "omnifunc", "v:lua.vim.lsp.omnifunc")
	vim.api.nvim_buf_set_option(buf, "tagfunc", "v:lua.vim.lsp.tagfunc")
end

-- Setup rust_analyzer via rust-tools.nvim
require("rust-tools").setup({
	server = {
		capabilities = capabilities,
		on_attach = lsp_attach,
	}
})

-- Keymaps for Luasnip
local ls = require("luasnip")
vim.keymap.set({ "i", "s" }, "<C-k>", function()
	if ls.expand_or_jumpable() then
		ls.expand_or_jump()
	end
end, { silent = true })

vim.keymap.set({ "i", "s" }, "<C-j>", function()
	if ls.jumpable(-1) then
		ls.jump(-1)
	end
end, { silent = true })

vim.keymap.set("i", "<C-l>", function()
	if ls.choice_active() then
		ls.change_choice(1)
	end
end)