feat: input validators

lua/input-form/validators.lua

@@ -0,0 +1,139 @@
+--- Validators for form inputs.
+---
+--- A validator is a function `fun(value): string|nil`. It receives the
+--- current input value and returns a non-empty error message string when
+--- invalid, or `nil` / `""` when valid.
+---
+--- This module exposes factory functions for common validators plus a
+--- `chain` combinator that runs several validators in order and returns the
+--- first error.
+---
+---@tag input-form.validators
+
+local M = {}
+
+--- Require the field to have a non-empty value.
+---@param msg string|nil Override error message.
+---@return function
+function M.non_empty(msg)
+  msg = msg or "This field is required"
+  return function(value)
+    if value == nil then
+      return msg
+    end
+    if type(value) == "string" and value == "" then
+      return msg
+    end
+    return nil
+  end
+end
+
+--- Require the value's length to be at least `n` characters.
+---@param n integer
+---@param msg string|nil
+---@return function
+function M.min_length(n, msg)
+  return function(value)
+    local s = type(value) == "string" and value or tostring(value or "")
+    if vim.fn.strchars(s) < n then
+      return msg or ("Must be at least " .. n .. " characters")
+    end
+    return nil
+  end
+end
+
+--- Require the value's length to be at most `n` characters.
+---@param n integer
+---@param msg string|nil
+---@return function
+function M.max_length(n, msg)
+  return function(value)
+    local s = type(value) == "string" and value or tostring(value or "")
+    if vim.fn.strchars(s) > n then
+      return msg or ("Must be at most " .. n .. " characters")
+    end
+    return nil
+  end
+end
+
+--- Require the value to match a Lua pattern.
+---@param pattern string Lua pattern (not PCRE).
+---@param msg string|nil
+---@return function
+function M.matches(pattern, msg)
+  return function(value)
+    local s = type(value) == "string" and value or tostring(value or "")
+    if not s:match(pattern) then
+      return msg or "Invalid format"
+    end
+    return nil
+  end
+end
+
+--- Require the value to parse as a number.
+---@param msg string|nil
+---@return function
+function M.is_number(msg)
+  return function(value)
+    if value == nil or value == "" or tonumber(value) == nil then
+      return msg or "Must be a number"
+    end
+    return nil
+  end
+end
+
+--- Require the value to be one of the given choices (useful for text inputs
+--- that must match a fixed allowlist; select inputs should use their
+--- `options` list instead).
+---@param choices table List of allowed values.
+---@param msg string|nil
+---@return function
+function M.one_of(choices, msg)
+  return function(value)
+    for _, c in ipairs(choices) do
+      if c == value then
+        return nil
+      end
+    end
+    return msg or "Value is not allowed"
+  end
+end
+
+--- Wrap a predicate `fun(value): boolean` as a validator.
+---@param predicate function
+---@param msg string Error message to return when the predicate is false.
+---@return function
+function M.custom(predicate, msg)
+  return function(value)
+    if predicate(value) then
+      return nil
+    end
+    return msg
+  end
+end
+
+--- Combine multiple validators. Runs them in order and returns the first
+--- non-empty error. Accepts either a list table or a varargs list.
+---@param ... function|table
+---@return function
+function M.chain(...)
+  local validators = { ... }
+  if
+    #validators == 1
+    and type(validators[1]) == "table"
+    and type(validators[1][1]) == "function"
+  then
+    validators = validators[1]
+  end
+  return function(value)
+    for _, v in ipairs(validators) do
+      local err = v(value)
+      if err and err ~= "" then
+        return err
+      end
+    end
+    return nil
+  end
+end
+
+return M