local function highlight(group, guifg, guibg, sp, sp_color)
   local hl = {
      fg = guifg,
      bg = guibg,
      special = sp_color,
   }
   if sp ~= nil and sp ~= "none" then
      hl[sp] = true
   end
   vim.api.nvim_set_hl(0, group, hl)
end

-- Modified from https://github.com/chriskempson/base16-vim
local function apply_base16_theme(theme)
   -- Neovim terminal colours
   if vim.fn.has "nvim" then
      vim.g.terminal_color_0 = "#" .. theme.base00
      vim.g.terminal_color_1 = "#" .. theme.base08
      vim.g.terminal_color_2 = "#" .. theme.base0B
      vim.g.terminal_color_3 = "#" .. theme.base0A
      vim.g.terminal_color_4 = "#" .. theme.base0D
      vim.g.terminal_color_5 = "#" .. theme.base0E
      vim.g.terminal_color_6 = "#" .. theme.base0C
      vim.g.terminal_color_7 = "#" .. theme.base05
      vim.g.terminal_color_8 = "#" .. theme.base03
      vim.g.terminal_color_9 = "#" .. theme.base08
      vim.g.terminal_color_10 = "#" .. theme.base0B
      vim.g.terminal_color_11 = "#" .. theme.base0A
      vim.g.terminal_color_12 = "#" .. theme.base0D
      vim.g.terminal_color_13 = "#" .. theme.base0E
      vim.g.terminal_color_14 = "#" .. theme.base0C
      vim.g.terminal_color_15 = "#" .. theme.base07
      if vim.o.background == "light" then
         vim.g.terminal_color_background = "#" .. theme.base05
         vim.g.terminal_color_foreground = "#" .. theme.base0B
      else
         vim.g.terminal_color_background = "#" .. theme.base00
         vim.g.terminal_color_foreground = "#" .. theme.base0E
      end
   end

   -- TODO
   -- nvim.command "hi clear"
   -- nvim.command "syntax reset"

   -- Vim editor colors
   highlight("Normal", theme.base05, theme.base00, nil, nil)
   highlight("Bold", nil, nil, "bold", nil)
   highlight("Debug", theme.base08, nil, nil, nil)
   highlight("Directory", theme.base0D, nil, nil, nil)
   highlight("Error", theme.base00, theme.base08, nil, nil)
   highlight("ErrorMsg", theme.base08, theme.base00, nil, nil)
   highlight("Exception", theme.base08, nil, nil, nil)
   highlight("FoldColumn", theme.base0C, theme.base01, nil, nil)
   highlight("Folded", theme.base03, theme.base01, nil, nil)
   highlight("IncSearch", theme.base01, theme.base09, "none", nil)
   highlight("Italic", nil, nil, "none", nil)
   highlight("Macro", theme.base08, nil, nil, nil)
   highlight("MatchParen", nil, theme.base03, nil, nil)
   highlight("ModeMsg", theme.base0B, nil, nil, nil)
   highlight("MoreMsg", theme.base0B, nil, nil, nil)
   highlight("Question", theme.base0D, nil, nil, nil)
   highlight("Search", theme.base01, theme.base0A, nil, nil)
   highlight("Substitute", theme.base01, theme.base0A, "none", nil)
   highlight("SpecialKey", theme.base03, nil, nil, nil)
   highlight("TooLong", theme.base08, nil, nil, nil)
   highlight("Underlined", theme.base08, nil, nil, nil)
   highlight("Visual", nil, theme.base02, nil, nil)
   highlight("VisualNOS", theme.base08, nil, nil, nil)
   highlight("WarningMsg", theme.base08, nil, nil, nil)
   highlight("WildMenu", theme.base08, theme.base0A, nil, nil)
   highlight("Title", theme.base0D, nil, "none", nil)
   highlight("Conceal", theme.base0D, theme.base00, nil, nil)
   highlight("Cursor", theme.base00, theme.base05, nil, nil)
   highlight("NonText", theme.base03, nil, nil, nil)
   highlight("LineNr", theme.base03, "NONE", nil, nil)
   highlight("SignColumn", theme.base03, "NONE", nil, nil)
   highlight("StatusLine", theme.base04, "NONE", "none", nil)
   highlight("StatusLineNC", theme.base03, "NONE", "none", nil)
   highlight("VertSplit", theme.base02, "NONE", "none", nil)
   highlight("ColorColumn", nil, theme.base01, "none", nil)
   highlight("CursorColumn", nil, theme.base01, "none", nil)
   highlight("CursorLine", nil, theme.base01, "none", nil)
   highlight("CursorLineNr", theme.base04, "NONE", nil, nil)
   highlight("QuickFixLine", nil, theme.base01, "none", nil)
   highlight("PMenu", theme.base05, theme.base01, "none", nil)
   highlight("PMenuSel", theme.base01, theme.base05, nil, nil)
   highlight("TabLine", theme.base03, theme.base01, "none", nil)
   highlight("TabLineFill", theme.base03, theme.base01, "none", nil)
   highlight("TabLineSel", theme.base0B, theme.base01, "none", nil)

   -- Standard syntax highlighting
   highlight("Boolean", theme.base09, nil, nil, nil)
   highlight("Character", theme.base08, nil, nil, nil)
   highlight("Comment", theme.base03, nil, nil, nil)
   highlight("Conditional", theme.base0E, nil, nil, nil)
   highlight("Constant", theme.base08, nil, nil, nil)
   highlight("Define", theme.base0E, nil, "none", nil)
   highlight("Delimiter", theme.base0F, nil, nil, nil)
   highlight("Float", theme.base09, nil, nil, nil)
   highlight("Function", theme.base0D, nil, nil, nil)
   highlight("Identifier", theme.base08, nil, "none", nil)
   highlight("Include", theme.base0D, nil, nil, nil)
   highlight("Keyword", theme.base0E, nil, nil, nil)
   highlight("Label", theme.base0A, nil, nil, nil)
   highlight("Number", theme.base09, nil, nil, nil)
   highlight("Operator", theme.base05, nil, "none", nil)
   highlight("PreProc", theme.base0A, nil, nil, nil)
   highlight("Repeat", theme.base0A, nil, nil, nil)
   highlight("Special", theme.base0C, nil, nil, nil)
   highlight("SpecialChar", theme.base0F, nil, nil, nil)
   highlight("Statement", theme.base08, nil, nil, nil)
   highlight("StorageClass", theme.base0A, nil, nil, nil)
   highlight("String", theme.base0B, nil, nil, nil)
   highlight("Structure", theme.base0E, nil, nil, nil)
   highlight("Tag", theme.base0A, nil, nil, nil)
   highlight("Todo", theme.base0A, theme.base01, nil, nil)
   highlight("Type", theme.base0A, nil, "none", nil)
   highlight("Typedef", theme.base0A, nil, nil, nil)

   -- Diff highlighting
   highlight("DiffAdd", theme.base0B, theme.base01, nil, nil)
   highlight("DiffChange", theme.base03, theme.base01, nil, nil)
   highlight("DiffDelete", theme.base08, theme.base01, nil, nil)
   highlight("DiffText", theme.base0D, theme.base01, nil, nil)
   highlight("DiffAdded", theme.base0B, theme.base00, nil, nil)
   highlight("DiffFile", theme.base08, theme.base00, nil, nil)
   highlight("DiffNewFile", theme.base0B, theme.base00, nil, nil)
   highlight("DiffLine", theme.base0D, theme.base00, nil, nil)
   highlight("DiffRemoved", theme.base08, theme.base00, nil, nil)

   -- Git highlighting
   highlight("gitcommitOverflow", theme.base08, nil, nil, nil)
   highlight("gitcommitSummary", theme.base0B, nil, nil, nil)
   highlight("gitcommitComment", theme.base03, nil, nil, nil)
   highlight("gitcommitUntracked", theme.base03, nil, nil, nil)
   highlight("gitcommitDiscarded", theme.base03, nil, nil, nil)
   highlight("gitcommitSelected", theme.base03, nil, nil, nil)
   highlight("gitcommitHeader", theme.base0E, nil, nil, nil)
   highlight("gitcommitSelectedType", theme.base0D, nil, nil, nil)
   highlight("gitcommitUnmergedType", theme.base0D, nil, nil, nil)
   highlight("gitcommitDiscardedType", theme.base0D, nil, nil, nil)
   highlight("gitcommitBranch", theme.base09, nil, "bold", nil)
   highlight("gitcommitUntrackedFile", theme.base0A, nil, nil, nil)
   highlight("gitcommitUnmergedFile", theme.base08, nil, "bold", nil)
   highlight("gitcommitDiscardedFile", theme.base08, nil, "bold", nil)
   highlight("gitcommitSelectedFile", theme.base0B, nil, "bold", nil)

   -- Mail highlighting
   highlight("mailQuoted1", theme.base0A, nil, nil, nil)
   highlight("mailQuoted2", theme.base0B, nil, nil, nil)
   highlight("mailQuoted3", theme.base0E, nil, nil, nil)
   highlight("mailQuoted4", theme.base0C, nil, nil, nil)
   highlight("mailQuoted5", theme.base0D, nil, nil, nil)
   highlight("mailQuoted6", theme.base0A, nil, nil, nil)
   highlight("mailURL", theme.base0D, nil, nil, nil)
   highlight("mailEmail", theme.base0D, nil, nil, nil)

   -- Spelling highlighting
   highlight("SpellBad", nil, nil, "undercurl", theme.base08)
   highlight("SpellLocal", nil, nil, "undercurl", theme.base0C)
   highlight("SpellCap", nil, nil, "undercurl", theme.base0D)
   highlight("SpellRare", nil, nil, "undercurl", theme.base0E)

   -- treesitter
   highlight("TSAnnotation", theme.base0F, nil, "none", nil)
   highlight("TSAttribute", theme.base0A, nil, "none", nil)
   highlight("TSCharacter", theme.base08, nil, "none", nil)
   highlight("TSConstBuiltin", theme.base09, nil, "none", nil)
   highlight("TSConstMacro", theme.base08, nil, "none", nil)
   highlight("TSError", theme.base08, nil, "none", nil)
   highlight("TSException", theme.base08, nil, "none", nil)
   highlight("TSFloat", theme.base09, nil, "none", nil)
   highlight("TSFuncBuiltin", theme.base0D, nil, "none", nil)
   highlight("TSFuncMacro", theme.base08, nil, "none", nil)
   highlight("TSKeywordOperator", theme.base0E, nil, "none", nil)
   highlight("TSMethod", theme.base0D, nil, "none", nil)
   highlight("TSNamespace", theme.base08, nil, "none", nil)
   highlight("TSNone", theme.base05, nil, "none", nil)
   highlight("TSParameter", theme.base08, nil, "none", nil)
   highlight("TSParameterReference", theme.base05, nil, "none", nil)
   highlight("TSPunctDelimiter", theme.base0F, nil, "none", nil)
   highlight("TSPunctSpecial", theme.base05, nil, "none", nil)
   highlight("TSStringRegex", theme.base0C, nil, "none", nil)
   highlight("TSStringEscape", theme.base0C, nil, "none", nil)
   highlight("TSSymbol", theme.base0B, nil, "none", nil)
   highlight("TSTagDelimiter", theme.base0F, nil, "none", nil)
   highlight("TSText", theme.base05, nil, "none", nil)
   highlight("TSStrong", nil, nil, "bold", nil)
   highlight("TSEmphasis", theme.base09, nil, "none", nil)
   highlight("TSStrike", theme.base00, nil, "strikethrough", nil)
   highlight("TSLiteral", theme.base09, nil, "none", nil)
   highlight("TSURI", theme.base09, nil, "underline", nil)
   highlight("TSTypeBuiltin", theme.base0A, nil, "none", nil)
   highlight("TSVariableBuiltin", theme.base09, nil, "none", nil)
   highlight("TSDefinition", nil, nil, "underline", theme.base04)
   highlight("TSDefinitionUsage", nil, nil, "underline", theme.base04)
   highlight("TSCurrentScope", nil, nil, "bold", nil)

   -- TODO
   -- nvim.command 'syntax on'
end

return setmetatable({
   themes = function(name)
      name = "themes/" .. name .. "-base16"
      local present, theme_array = pcall(require, name)
      if present then
         return theme_array
      else
         error("No such base16 theme: " .. name)
      end
   end,
   apply_theme = apply_base16_theme,
   theme_from_array = function(array)
      assert(#array == 16, "base16.theme_from_array: The array length must be 16")
      local result = {}
      for i, value in ipairs(array) do
         assert(#value == 6, "base16.theme_from_array: array values must be in 6 digit hex format, e.g. 'ffffff'")
         local key = ("base%02X"):format(i - 1)
         result[key] = value
      end
      return result
   end,
}, {
   __call = function(_, ...)
      apply_base16_theme(...)
   end,
})