add `nerv.print_usage(options)`

2 files changed, 67 insertions, 17 deletions

diff --git a/nerv/init.lua b/nerv/init.lua
index fdfd531..d72d8b8 100644
--- a/nerv/init.lua
+++ b/nerv/init.lua
@@ -173,6 +173,23 @@ function nerv.include(filename)
 end
 
 --- Parse the command-line options and arguments
+-- @param argv the argrument list to parsed
+-- @param options The specification of options, should be a list of tables,
+-- each one for exactly one available option, say `v`, with `v[1]`, `v[2]`,
+-- `v[3]` indicating the full name of the option, the short form of the option
+-- (when it is a boolean option) and the type of the value controlled by the
+-- option. `default` and `desc` keys can also be specified to set the default
+-- value and description of the option.
+--
+-- An example of specification:
+-- {{"aaa", "a", "bool", default = false, desc = "an option called aaa"},
+-- {"bbb", "b", "bool", default = true, desc = "bbb is set to be true if --bbb=no does not present"},
+-- {"ccc", nil, "int", default = 0, desc = "ccc expects an integeral value"}}`
+--
+-- @return args, opts The non-option arguments and parsed options. `opts` is
+-- again a list of tables, each of which corresponds to one table in parameter
+-- `options`. The parsed value could be accessed by `opts["aaa"].val` (which is
+-- `true` if "--aaa" or "-a" is specified).
 function nerv.parse_args(argv, options)
     local is_opt_exp = "^[-](.*)$"
     local sim_opt_exp = "^[-]([a-z]+)$"
@@ -190,14 +207,14 @@ function nerv.parse_args(argv, options)
             v[3] == nil then
             err()
         end
-        opt_full = v[1]
-        opt_short = v[2]
-        opt_type = v[3]
+        local opt_full = v[1]
+        local opt_short = v[2]
+        local opt_type = v[3]
         local opt_meta = {type = opt_type,
                             desc = v.desc or "",
                             val = v.default}
         if opt_short ~= nil then
-            if type(opt_short) ~= "string" then err() end
+            if type(opt_short) ~= "string" or #opt_short ~= 1 then err() end
             if opt_type ~= "bool" then
                 nerv.error("only boolean option could have short form")
             end
@@ -275,6 +292,40 @@ function nerv.parse_args(argv, options)
     return args, opts
 end
 
+--- Print usage information of the command-line options
+-- @param options the list of options used in `parse_args`
+function nerv.print_usage(options)
+    local full_maxlen = 0
+    local type_maxlen = 0
+    local default_maxlen = 0
+    for _, v in ipairs(options) do
+        local opt_full = v[1]
+        local opt_short = v[2]
+        local opt_type = v[3]
+        full_maxlen = math.max(full_maxlen, #opt_full or 0)
+        type_maxlen = math.max(full_maxlen, #opt_type or 0)
+        default_maxlen = math.max(full_maxlen, #tostring(v.default) or 0)
+    end
+    local function pattern_gen()
+        return string.format("\t%%-%ds\t%%-2s\t%%-%ds\t%%-%ds\t%%s\n",
+                            full_maxlen, type_maxlen, default_maxlen)
+    end
+    nerv.printf("\n")
+    nerv.printf(pattern_gen(), "Option", "Abbr.", "Type", "Default", "Desc.")
+    for _, v in ipairs(options) do
+        local opt_full = v[1]
+        local opt_short = v[2]
+        local opt_type = v[3]
+        nerv.printf(pattern_gen(),
+                    (opt_full and '--' .. opt_full) or "",
+                    (opt_short and '-' .. opt_short) or "",
+                    opt_type,
+                    v.default or "",
+                    v.desc or "")
+    end
+    nerv.printf("\n")
+end
+
 -- the following lines trigger the initialization of basic modules
 
 nerv.include('matrix/init.lua')
diff --git a/nerv/test/parse_args.lua b/nerv/test/parse_args.lua
index 7146c3b..0d280a1 100644
--- a/nerv/test/parse_args.lua
+++ b/nerv/test/parse_args.lua
@@ -1,16 +1,15 @@
-args, opts = nerv.parse_args(
-                    {"arg1", "arg2", "-abcd", "arg3",
-                    "--hehe", "--oh=no", "--uid=43",
-                    "highfive", "--str=hello"},
+local options = {{"abandon", "a", "bool", default = false, desc = "abandon your belief"},
+                 {"bullshit", "b", "bool", default = false, desc = "start to bullshit"},
+                 {"cheat", "c", "bool", default = false, desc = "try to cheat"},
+                 {"delete", "d", "bool", default = false, desc = "remove everything"},
+                 {"hehe", "h", "bool", default = false, desc = "233333"},
+                 {"oh", "o", "bool", default = true, desc = "oh yes!"},
+                 {"uid", nil, "int", desc = "user uid"},
+                 {"str", nil, "string", desc = "test string"}}
 
-                    {{"abandon", "a", "bool", default = false, desc = "abandon your belief"},
-                    {"bullshit", "b", "bool", default = false, desc = "start to bullshit"},
-                    {"cheat", "c", "bool", default = false, desc = "try to cheat"},
-                    {"delete", "d", "bool", default = false, desc = "remove everything"},
-                    {"hehe", "h", "bool", default = false, desc = "233333"},
-                    {"oh", "o", "bool", default = true, desc = "oh yes!"},
-                    {"uid", nil, "int", desc = "user uid"},
-                    {"str", nil, "string", desc = "test string"}}
-            )
+args, opts = nerv.parse_args({"arg1", "arg2", "-abcd", "arg3",
+                                "--hehe", "--oh=no", "--uid=43",
+                                "highfive", "--str=hello"}, options)
 
+nerv.print_usage(options)
 print(table.tostring(args), table.tostring(opts))