feat(themes): add automatic theme for nvim-base16 colorschemes(#597)

THEMES.md

@@ -46,6 +46,18 @@ load ayu_light when background=light and ayu_dark when background=dark
 But if `g:ayuprefermirage` exists, it will load ayu_mirage instead when
 `background=dark`.
 
+### base16
+
+This theme will automatically uses colors defined by your colorscheme using [RRethy/nvim-base16](https://github.com/RRethy/nvim-base16)] plugin.
+The following example is using the `tomorrow-night` colorscheme:
+
+<p>
+<img width='700' src='https://user-images.githubusercontent.com/11501572/156889654-3dedc9a1-e7a5-4cbe-b219-2a97499cf1d2.png'/>
+<img width='700' src='https://user-images.githubusercontent.com/11501572/156889648-93bf3ce8-064d-4ac0-8415-20d6ef87c60b.png'/>
+<img width='700' src='https://user-images.githubusercontent.com/11501572/156889624-c97fc3ae-d642-41ba-b39a-f9a72ff8b15e.png'/>
+<img width='700' src='https://user-images.githubusercontent.com/11501572/156889566-17066e95-7f85-4bfd-8178-c4a34beab453.png'/>
+</p>
+
 ### codedark
 <p>
 <img width='700' src='https://user-images.githubusercontent.com/41551030/108648568-dff4c980-74bb-11eb-9d16-b68ac68f2ab2.png'/>

lua/lualine/themes/auto.lua

@@ -5,6 +5,11 @@ local loader = require('lualine.utils.loader')
 
 local color_name = vim.g.colors_name
 if color_name then
+  -- All base16 colorschemes share the same theme
+  if 'base16' == color_name:sub(1, 6) then
+    color_name = 'base16'
+  end
+
   -- Check if there's a theme for current colorscheme
   -- If there is load that instead of genarating a new one
   local ok, theme = pcall(loader.load_theme, color_name)

lua/lualine/themes/base16.lua

@@ -0,0 +1,92 @@
+local modules = require('lualine_require').lazy_require({ notices = 'lualine.utils.notices' })
+
+local function add_notice(notice)
+  modules.notices.add_notice('theme(base16): ' .. notice)
+end
+
+local function setup(colors)
+  local theme = {
+    normal = {
+      a = { fg = colors.bg, bg = colors.normal },
+      b = { fg = colors.light_fg, bg = colors.alt_bg },
+      c = { fg = colors.fg, bg = colors.bg },
+    },
+    replace = {
+      a = { fg = colors.bg, bg = colors.replace },
+      b = { fg = colors.light_fg, bg = colors.alt_bg },
+    },
+    insert = {
+      a = { fg = colors.bg, bg = colors.insert },
+      b = { fg = colors.light_fg, bg = colors.alt_bg },
+    },
+    visual = {
+      a = { fg = colors.bg, bg = colors.visual },
+      b = { fg = colors.light_fg, bg = colors.alt_bg },
+    },
+    inactive = {
+      a = { fg = colors.dark_fg, bg = colors.bg },
+      b = { fg = colors.dark_fg, bg = colors.bg },
+      c = { fg = colors.dark_fg, bg = colors.bg },
+    },
+  }
+
+  theme.command = theme.normal
+  theme.terminal = theme.insert
+
+  return theme
+end
+
+local function setup_default()
+  return setup {
+    bg       = '#282a2e',
+    alt_bg   = '#373b41',
+    dark_fg  = '#969896',
+    fg       = '#b4b7b4',
+    light_fg = '#c5c8c6',
+    normal   = '#81a2be',
+    insert   = '#b5bd68',
+    visual   = '#b294bb',
+    replace  = '#de935f',
+  }
+end
+
+local function setup_base16()
+  local loaded, base16 = pcall(require, 'base16-colorscheme')
+
+  if not loaded then
+    add_notice(
+      'nvim-base16 is not currently present in your runtimepath, make sure it is properly installed,'
+      .. ' fallback to default colors.'
+    )
+
+    return nil
+  end
+
+  if not base16.colors and not vim.env.BASE16_THEME then
+    add_notice(
+      'nvim-base16 is not loaded yet, you should update your configuration to load it before lualine'
+      .. ' so that the colors from your colorscheme can be used, fallback to "tomorrow-night" theme.'
+    )
+  elseif not base16.colors and not base16.colorschemes[vim.env.BASE16_THEME] then
+    add_notice(
+      'The colorscheme "%s" defined by the environment variable "BASE16_THEME" is not handled by'
+      .. ' nvim-base16, fallback to "tomorrow-night" theme.'
+    )
+  end
+
+  local colors = base16.colors or base16.colorschemes[vim.env.BASE16_THEME or 'tomorrow-night']
+
+  return setup {
+    bg        = colors.base01,
+    alt_bg    = colors.base02,
+    dark_fg   = colors.base03,
+    fg        = colors.base04,
+    light_fg  = colors.base05,
+    normal    = colors.base0D,
+    insert    = colors.base0B,
+    visual    = colors.base0E,
+    replace   = colors.base09,
+  }
+end
+
+return setup_base16() or setup_default()