Lua add metadata and settings reading helper module

Adds example scripts for reading track metadata + dumping albumart
and rockbox settings

settings are now stored as a table of strings rather than a table of tables
as it saves ~15 kb of ram without adding much complexity

Change-Id: I611c312b2a60ab96e595e4710b17aedbd6c0689b

apps/plugins/lua/include_lua/rbsettings.lua

@@ -0,0 +1,164 @@
+--[[ Lua rb settings reader
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2019 William Wilgus
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+]]
+
+rb.settings = rb.settings or {}
+
+local var = {offset = 1, size = 2, type = 3, fields = 3}
+
+local function bytesLE_n(str)
+    str = str or ""
+    local tbyte={str:byte(1, -1)}
+    local bpos, num = 1, 0
+    for k = 1,#tbyte do -- (k = #t, 1, -1 for BE)
+        num = num + tbyte[k] * bpos
+        bpos = bpos * 256 --1<<8
+    end
+    return num
+end
+
+local function get_var_fields(s_var)
+    -- converts member string into table
+    -- var = {offset, size, "type"}
+    s_var = s_var or ""
+    local o, s, t = string.match(s_var, "(0x%x+),%s*(%d+),%s*(.+)")
+    local tvar = {o, s, t}
+
+    return #tvar == var.fields and tvar or nil
+end
+
+local function format_val(val, var_type)
+    local ret, num
+    if var_type == nil then
+        return nil
+    elseif var_type == "str" then
+        -- stop at first null byte, return nil if str doesn't exist
+        return val and string.match(val, "^%Z+") or nil
+    end
+
+    num = bytesLE_n(val)
+    if string.find(var_type, "^b") then
+        if(num <= 0) then
+            ret = false
+        else
+            ret = true
+        end
+    elseif string.find(var_type, "^u_[cil]") then
+        -- Lua integers are signed so we need to do a bit of extra processing
+        ret = (string.format("%u", num))
+    else
+        ret = num
+    end
+
+    return ret
+end
+
+local function dump_struct(t_settings, t_struct, n_elems, t_var)
+    --Internal function dumps structs
+    local tdata = {}
+
+    local function struct_get_elem(v, elem_offset)
+        local val, offset, tvar1
+        tvar1 = get_var_fields(v)
+        offset = t_var[var.offset] + tvar1[var.offset] + elem_offset
+        val = t_settings(offset, tvar1[var.size])
+        return format_val(val, tvar1[var.type])
+    end
+
+    if n_elems > 0 then
+        -- Array of structs, struct[elems];
+        local elemsize = (t_var[var.size] / n_elems)
+        for i = 0, n_elems - 1 do
+            tdata[i] = tdata[i] or {}
+            for k1, v1 in pairs(t_struct) do
+                tdata[i][k1] = struct_get_elem(v1, (elemsize * i))
+            end
+        end
+    else
+        -- single struct, struct;
+        for k1, v1 in pairs(t_struct) do
+            tdata[k1] = struct_get_elem(v1, 0)
+        end
+    end
+    return tdata
+end
+
+local function get_array_elems(var_type)
+    --extract the number of elements, returns 0 if not found
+    local elems = string.match(var_type,".*%[(%d+)%]")
+    return tonumber(elems) or 0
+end
+
+local function get_struct_name(var_type)
+    --extract the name of a struct, returns nil if not found
+    return string.match(var_type,"^s_([^%[%]%s]+)")
+end
+
+function rb.settings.read(s_settings, s_var, s_groupname)
+    local data, val
+    local tvar = get_var_fields(s_var)
+    if tvar == nil then return nil end
+
+    local elems = get_array_elems(tvar[var.type])
+    local structname = get_struct_name(tvar[var.type])
+
+    local tsettings = rb[s_settings]
+    if not tsettings then error(s_settings .. " does not exist") end
+
+    if structname and rb[s_groupname] then
+        return dump_struct(tsettings, rb[s_groupname][structname], elems, tvar)
+    end
+
+    local voffset, vsize, vtype = tvar[var.offset], tvar[var.size], tvar[var.type]
+    if elems > 0 then
+        -- Arrays of values, val[elems];
+        data = {}
+        local elemsize = (vsize / elems)
+
+        for i = 0, elems - 1 do
+            val = tsettings(voffset + (elemsize * i), elemsize)
+            data[i] = format_val(val, vtype)
+        end
+    else
+        -- Single value, val;
+        if vtype == "ptr_char" then -- (**char)
+            vtype = "str"
+            val = tsettings(voffset, vsize, nil, true)
+        else
+            val = tsettings(voffset, vsize)
+        end
+        data = format_val(val, vtype)
+    end
+    return data
+end
+
+function rb.settings.dump(s_settings, s_groupname, s_structname, t_output)
+    t_output = t_output or {}
+    local tgroup = rb[s_groupname]
+    s_structname = s_structname or s_settings
+    for k, v in pairs(tgroup[s_structname]) do
+        t_output[k] = rb.settings.read(s_settings, v, s_groupname)
+    end
+    return t_output
+end
+
+return true