local config = require("github_theme.config")
local palette = require("github_theme.palette")
local highlights = require("github_theme.highlights")

local M = {
  _config = config.merge(),
}

local function hex_to_rgb(color)
  local red, green, blue = color:match("^#(%x%x)(%x%x)(%x%x)$")
  if not red then
    return nil
  end

  return tonumber(red, 16), tonumber(green, 16), tonumber(blue, 16)
end

local function normalize_color(color, alpha_base)
  if type(color) ~= "string" or color == "NONE" then
    return color
  end

  local red, green, blue, alpha = color:match("^#(%x%x)(%x%x)(%x%x)(%x%x)$")
  if not red then
    return color:upper()
  end

  local base_red, base_green, base_blue = hex_to_rgb(alpha_base)
  local opacity = tonumber(alpha, 16) / 255
  local source_red = tonumber(red, 16)
  local source_green = tonumber(green, 16)
  local source_blue = tonumber(blue, 16)

  local function blend(source, base)
    return math.floor((source * opacity) + (base * (1 - opacity)) + 0.5)
  end

  return string.format(
    "#%02X%02X%02X",
    blend(source_red, base_red),
    blend(source_green, base_green),
    blend(source_blue, base_blue)
  )
end

local function normalize_override(spec)
  local normalized = {}

  for key, value in pairs(spec) do
    if (key == "fg" or key == "bg" or key == "sp") and value == false then
      normalized[key] = "NONE"
    else
      normalized[key] = value
    end
  end

  return normalized
end

local function apply_highlights(groups, alpha_base)
  for group, spec in pairs(groups) do
    if spec.link then
      vim.api.nvim_set_hl(0, group, spec)
    else
      vim.api.nvim_set_hl(0, group, {
        fg = normalize_color(spec.fg, alpha_base),
        bg = normalize_color(spec.bg, alpha_base),
        sp = normalize_color(spec.sp, alpha_base),
        bold = spec.bold,
        italic = spec.italic,
        underline = spec.underline,
        undercurl = spec.undercurl,
        underdouble = spec.underdouble,
        underdotted = spec.underdotted,
        underdashed = spec.underdashed,
        strikethrough = spec.strikethrough,
        reverse = spec.reverse,
        standout = spec.standout,
        nocombine = spec.nocombine,
        default = spec.default,
        ctermfg = spec.ctermfg,
        ctermbg = spec.ctermbg,
        cterm = spec.cterm,
        force = spec.force,
      })
    end
  end
end

local function apply_terminal_colors(palette_values)
  vim.g.terminal_color_0 = palette_values.ansi_black
  vim.g.terminal_color_1 = palette_values.ansi_red
  vim.g.terminal_color_2 = palette_values.ansi_green
  vim.g.terminal_color_3 = palette_values.ansi_yellow
  vim.g.terminal_color_4 = palette_values.ansi_blue
  vim.g.terminal_color_5 = palette_values.ansi_magenta
  vim.g.terminal_color_6 = palette_values.ansi_cyan
  vim.g.terminal_color_7 = palette_values.ansi_white
  vim.g.terminal_color_8 = palette_values.ansi_bright_black
  vim.g.terminal_color_9 = palette_values.ansi_bright_red
  vim.g.terminal_color_10 = palette_values.ansi_bright_green
  vim.g.terminal_color_11 = palette_values.ansi_bright_yellow
  vim.g.terminal_color_12 = palette_values.ansi_bright_blue
  vim.g.terminal_color_13 = palette_values.ansi_bright_magenta
  vim.g.terminal_color_14 = palette_values.ansi_bright_cyan
  vim.g.terminal_color_15 = palette_values.ansi_bright_white
end

function M.setup(opts)
  M._config = config.merge(opts)
  return M._config
end

function M.load(variant)
  local active_config = M._config or config.merge()
  local theme = palette.get(variant, active_config)
  local groups = highlights.build(theme.palette, active_config)

  for group, spec in pairs(active_config.highlights or {}) do
    groups[group] = vim.tbl_deep_extend("force", groups[group] or {}, normalize_override(spec))
  end

  vim.o.background = theme.is_dark and "dark" or "light"
  vim.cmd("highlight clear")

  if vim.fn.exists("syntax_on") == 1 then
    vim.cmd("syntax reset")
  end

  vim.g.colors_name = variant

  apply_highlights(groups, theme.palette.bg ~= "NONE" and theme.palette.bg or (theme.is_dark and "#0D1117" or "#FFFFFF"))
  apply_terminal_colors(theme.palette)

  return theme
end

return M