local api = vim.api
local lsp = vim.lsp

local M = {}

local function guess_filetype(path)
  local ext = path:match("^.+%.([^./\\]+)$")
  if not ext then return nil end
  ext = ext:lower()
  local map = {
    lua = "lua",
    go  = "go",
    rs  = "rust",
    js  = "javascript",
    jsx = "javascriptreact",
    ts  = "typescript",
    tsx = "typescriptreact",
    php = "php",
  }
  return map[ext]
end

local function create_scratch_buffer(path, content)
  -- Create a unique buffer name so we never clash with an existing one
  local scratch_name = string.format("chatgpt-scratch://%s#%d", path, math.random(100000, 999999))

  local bufnr = api.nvim_create_buf(false, true)
  if bufnr == 0 then
    return nil
  end

  -- Assign the unique name to the buffer
  api.nvim_buf_set_name(bufnr, scratch_name)

  -- Convert content string to lines
  local lines = {}
  for line in (content.."\n"):gmatch("(.-)\n") do
    table.insert(lines, line)
  end
  api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)

  -- Mark it as a scratch buffer
  api.nvim_buf_set_option(bufnr, "bufhidden", "wipe")
  api.nvim_buf_set_option(bufnr, "swapfile", false)

  return bufnr
end

local function attach_existing_lsp_client(bufnr, filetype)
  local clients = lsp.get_active_clients()
  if not clients or #clients == 0 then
    return nil, "No active LSP clients"
  end

  for _, client in ipairs(clients) do
    local ft_conf = client.config.filetypes or {}
    if vim.tbl_contains(ft_conf, filetype) then
      if not client.attached_buffers[bufnr] then
        vim.lsp.buf_attach_client(bufnr, client.id)
      end
      return client.id
    end
  end
  return nil, ("No active LSP client supports filetype '%s'"):format(filetype)
end

local function send_did_open(bufnr, client_id, path, filetype)
  local client = lsp.get_client_by_id(client_id)
  if not client then
    return "Invalid client ID."
  end

  local text = table.concat(api.nvim_buf_get_lines(bufnr, 0, -1, false), "\n")
  -- Even though the buffer name is unique, the LSP server sees this file as if at 'path'
  local uri = vim.uri_from_fname(path)

  local didOpenParams = {
    textDocument = {
      uri = uri,
      languageId = filetype,
      version = 0,
      text = text,
    }
  }
  client.rpc.notify("textDocument/didOpen", didOpenParams)
  return nil
end

local function send_did_change(bufnr, client_id, path)
  local client = lsp.get_client_by_id(client_id)
  if not client then return end

  local text = table.concat(api.nvim_buf_get_lines(bufnr, 0, -1, false), "\n")
  local uri = vim.uri_from_fname(path)
  local version = 1

  client.rpc.notify("textDocument/didChange", {
    textDocument = {
      uri = uri,
      version = version,
    },
    contentChanges = {
      { text = text }
    }
  })
end

-- Use vim.wait to allow the event loop to process LSP diagnostics
local function wait_for_diagnostics(bufnr, timeout_ms)
  local done = false
  local result_diags = {}

  local augrp = api.nvim_create_augroup("chatgpt_lsp_diag_"..bufnr, { clear = true })
  api.nvim_create_autocmd("DiagnosticChanged", {
    group = augrp,
    callback = function(args)
      if args.buf == bufnr then
        local diags = vim.diagnostic.get(bufnr)
        result_diags = diags
        done = true
      end
    end
  })

  vim.wait(timeout_ms, function()
    return done
  end, 50)

  pcall(api.nvim_del_augroup_by_id, augrp)
  return result_diags
end

local function diagnostics_to_string(diags)
  if #diags == 0 then
    return "No LSP diagnostics reported."
  end
  local lines = { "--- LSP Diagnostics ---" }
  for _, d in ipairs(diags) do
    local sev = vim.diagnostic.severity[d.severity] or d.severity
    lines[#lines+1] = string.format("Line %d [%s]: %s", d.lnum + 1, sev, d.message)
  end
  return table.concat(lines, "\n")
end

function M.lsp_check_file_content(path, new_content, timeout_ms)
  local filetype = guess_filetype(path) or "plaintext"

  local bufnr = create_scratch_buffer(path, new_content)
  if not bufnr then
    return "(LSP) Could not create scratch buffer."
  end

  local client_id, err = attach_existing_lsp_client(bufnr, filetype)
  if not client_id then
    api.nvim_buf_delete(bufnr, { force = true })
    return "(LSP) " .. (err or "No suitable LSP client.")
  end

  local err2 = send_did_open(bufnr, client_id, path, filetype)
  if err2 then
    api.nvim_buf_delete(bufnr, { force = true })
    return "(LSP) " .. err2
  end

  -- Optionally do a didChange with consistent URI
  send_did_change(bufnr, client_id, path)

  local diags = wait_for_diagnostics(bufnr, timeout_ms or 2000)
  local diag_str = diagnostics_to_string(diags)

  api.nvim_buf_delete(bufnr, { force = true })
  return diag_str
end

return M