local M = {}

local GOLDEN_RATIO_CONJUGATE = 0.618033988749895

--- This is totally not AI generated and I definitely know what this all means, trust me bro!
---@param str string
---@return number
local function hash(str)
  local h = 2166136261
  for i = 1, #str do
    h = bit.bxor(h, string.byte(str, i))
    h = (h * 16777619) % 2 ^ 32
  end
  return h
end

---@param hue number
---@param sat number
---@param light number
---@return string
local function hsl_to_hex(hue, sat, light)
  local h = hue / 60
  local c = (1 - math.abs(2 * light - 1)) * sat
  local x = c * (1 - math.abs(h % 2 - 1))
  local m = light - c / 2

  local r, g, b
  if h < 1 then
    r, g, b = c, x, 0
  elseif h < 2 then
    r, g, b = x, c, 0
  elseif h < 3 then
    r, g, b = 0, c, x
  elseif h < 4 then
    r, g, b = 0, x, c
  elseif h < 5 then
    r, g, b = x, 0, c
  else
    r, g, b = c, 0, x
  end

  return string.format(
    "#%02x%02x%02x",
    math.floor((r + m) * 255),
    math.floor((g + m) * 255),
    math.floor((b + m) * 255)
  )
end

--- Returns a stable "golden ratio" color from a given string, in hex format.
---@param str string
---@param sat number
---@param light number
---@return string
function M.stable_from_string(str, sat, light)
  local hue = ((hash(str) * GOLDEN_RATIO_CONJUGATE) % 1) * 360
  return hsl_to_hex(hue, sat, light)
end

---@type jjannotate.Config.ResolvedPalette
local palette_dark = {
  fg = { sat = 0.6, light = 0.7 },
  fg_bold = { sat = 0.75, light = 0.75 },
  bg = { sat = 0.25, light = 0.125 },
}

---@type jjannotate.Config.ResolvedPalette
local palette_light = {
  fg = { sat = 0.35, light = 0.35 },
  fg_bold = { sat = 0.5, light = 0.3 },
  bg = { sat = 0.25, light = 0.925 },
}

M.palette_dark = palette_dark
M.palette_light = palette_light

---@param x number
---@param min number
---@param max number
---@return number
local function clamp(x, min, max) return math.min(math.max(x, min), max) end

---@param base jjannotate.Config.ResolvedPalette
---@param multiplier jjannotate.Config.Palette.Color
---@return jjannotate.Config.ResolvedPalette
local function apply_multiplier(base, multiplier)
  return vim.tbl_map(
    function(color)
      return {
        sat = clamp(color.sat * multiplier.sat, 0, 1),
        light = clamp(color.light * multiplier.light, 0, 1),
      }
    end,
    base
  ) --[[@as jjannotate.Config.ResolvedPalette]]
end

---@param palette jjannotate.Config.Palette
---@return jjannotate.Config.ResolvedPalette
function M.resolve_palette(palette)
  if palette == "auto" then return vim.o.background == "dark" and palette_dark or palette_light end
  if palette.auto then
    local base = vim.o.background == "dark" and palette_dark or palette_light
    local m = palette.multiplier or { sat = 1, light = 1 }
    return apply_multiplier(base, m)
  end
  return palette --[[@as jjannotate.Config.ResolvedPalette]]
end

return M