--- TODO: This is implemented only for files now.
-- https://tools.ietf.org/html/rfc3986
-- https://tools.ietf.org/html/rfc2732
-- https://tools.ietf.org/html/rfc2396

local uri_decode
do
  local schar = string.char

  --- Convert hex to char
  ---@private
  local function hex_to_char(hex)
    return schar(tonumber(hex, 16))
  end
  uri_decode = function(str)
    return str:gsub('%%([a-fA-F0-9][a-fA-F0-9])', hex_to_char)
  end
end

local uri_encode
do
  local PATTERNS = {
    --- RFC 2396
    -- https://tools.ietf.org/html/rfc2396#section-2.2
    rfc2396 = "^A-Za-z0-9%-_.!~*'()",
    --- RFC 2732
    -- https://tools.ietf.org/html/rfc2732
    rfc2732 = "^A-Za-z0-9%-_.!~*'()[]",
    --- RFC 3986
    -- https://tools.ietf.org/html/rfc3986#section-2.2
    rfc3986 = "^A-Za-z0-9%-._~!$&'()*+,;=:@/",
  }
  local sbyte, tohex = string.byte
  if jit then
    tohex = require('bit').tohex
  else
    tohex = function(b)
      return string.format('%02x', b)
    end
  end

  ---@private
  local function percent_encode_char(char)
    return '%' .. tohex(sbyte(char), 2)
  end
  uri_encode = function(text, rfc)
    if not text then
      return
    end
    local pattern = PATTERNS[rfc] or PATTERNS.rfc3986
    return text:gsub('([' .. pattern .. '])', percent_encode_char)
  end
end

---@private
local function is_windows_file_uri(uri)
  return uri:match('^file:/+[a-zA-Z]:') ~= nil
end

--- Get a URI from a file path.
---@param path string Path to file
---@return string URI
local function uri_from_fname(path)
  local volume_path, fname = path:match('^([a-zA-Z]:)(.*)')
  local is_windows = volume_path ~= nil
  if is_windows then
    path = volume_path .. uri_encode(fname:gsub('\\', '/'))
  else
    path = uri_encode(path)
  end
  local uri_parts = { 'file://' }
  if is_windows then
    table.insert(uri_parts, '/')
  end
  table.insert(uri_parts, path)
  return table.concat(uri_parts)
end

local URI_SCHEME_PATTERN = '^([a-zA-Z]+[a-zA-Z0-9.+-]*):.*'
local WINDOWS_URI_SCHEME_PATTERN = '^([a-zA-Z]+[a-zA-Z0-9.+-]*):[a-zA-Z]:.*'

--- Get a URI from a bufnr
---@param bufnr number
---@return string URI
local function uri_from_bufnr(bufnr)
  local fname = vim.api.nvim_buf_get_name(bufnr)
  local volume_path = fname:match('^([a-zA-Z]:).*')
  local is_windows = volume_path ~= nil
  local scheme
  if is_windows then
    fname = fname:gsub('\\', '/')
    scheme = fname:match(WINDOWS_URI_SCHEME_PATTERN)
  else
    scheme = fname:match(URI_SCHEME_PATTERN)
  end
  if scheme then
    return fname
  else
    return uri_from_fname(fname)
  end
end

--- Get a filename from a URI
---@param uri string
---@return string filename or unchanged URI for non-file URIs
local function uri_to_fname(uri)
  local scheme = assert(uri:match(URI_SCHEME_PATTERN), 'URI must contain a scheme: ' .. uri)
  if scheme ~= 'file' then
    return uri
  end
  uri = uri_decode(uri)
  -- TODO improve this.
  if is_windows_file_uri(uri) then
    uri = uri:gsub('^file:/+', '')
    uri = uri:gsub('/', '\\')
  else
    uri = uri:gsub('^file:/+', '/')
  end
  return uri
end

--- Get the buffer for a uri.
--- Creates a new unloaded buffer if no buffer for the uri already exists.
--
---@param uri string
---@return number bufnr
local function uri_to_bufnr(uri)
  return vim.fn.bufadd(uri_to_fname(uri))
end

return {
  uri_from_fname = uri_from_fname,
  uri_from_bufnr = uri_from_bufnr,
  uri_to_fname = uri_to_fname,
  uri_to_bufnr = uri_to_bufnr,
}
-- vim:sw=2 ts=2 et