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--[[
(c) Copyright 2013 Ondrej Fafejta <fafejtao@gmail.com>
https://github.com/fafejtao/pmxChords
]]--
--
-- Chords transposition class
--
ChordsTr = {} -- the table representing the class, which will double as the metatable for the instances
ChordsTr.__index = ChordsTr -- failed table lookups on the instances should fallback to the class table, to get methods
setmetatable(
ChordsTr,
{
__call = function (cls, ...)
return cls.new(...)
end,
})
--
-- global constants
--
ChordsTr.CHORDS_BEGIN="\\ch."
ChordsTr.CHORDS_END=".\\"
ChordsTr.BASE_CHORDS_ARR= { -- lua is indexing from 1 I need from 0 ...
[0] = "C",
[1] = "Cs",
[2] = "D",
[3] = "Ef",
[4] = "E",
[5] = "F",
[6] = "Fs",
[7] = "G",
[8] = "Af",
[9] = "A",
[10] = "Bf",
[11] = "B"
}
--
-- Create instance of chords transposition class
-- params iSig input signature e.g. -1 - F major
-- oSig output signature e.g. 2 - D major
--
function ChordsTr.new(iSig, oSig)
local self = setmetatable({}, ChordsTr)
self.trMap = ChordsTr.__createTransposeMap(oSig - iSig)
return self
end
--
-- Core of transposition.
-- Prepare map of transposed chords.
-- Key is input base chord and value is output base chord.
--
function ChordsTr.__createTransposeMap(sigDiff)
local size = 12
local halfTones = (sigDiff * 7) % size
if (halfTones < 0 ) then
halfTones = halfTones + size
end
-- generate transpose map of base chords ...
local res = {}
local i
for i = 0, size - 1, 1 do
local key = ChordsTr.BASE_CHORDS_ARR[i]
local trIdx = (i + halfTones) % size;
res[key] = ChordsTr.BASE_CHORDS_ARR[trIdx]
end
return res
end
--
-- transpose one line.
-- Find each chords in line and transpose it into output signature.
-- return transposed line.
--
function ChordsTr:lineTranspose(line)
local pos = 0;
local trLine = "" -- transposed line (result)
while true do
local i = string.find(line, ChordsTr.CHORDS_BEGIN, pos)
if i == nil then
trLine = trLine .. string.sub(line, pos)
break
end
i = i + 3 -- move after \ch.
trLine = trLine .. string.sub(line, pos, i) -- append non chord string into result
pos = string.find(line, ChordsTr.CHORDS_END, i)
if pos == nil then -- TODO check correctly end of chords ... e.g. check wrong line (first chord is not finished correctly): \ch.C. c \ch.G7.\ b
io.stderr:write("End of chords was not found!\n")
os.exit(-1)
end
chord = string.sub(line, i + 1, pos - 1)
trLine=trLine .. self:doTranspose(chord)
end
return trLine
end
--
-- do transpose of one chord.
--
function ChordsTr:doTranspose(chord)
local base, alt = ChordsTr.splitChord(chord)
return self.trMap[base]..alt
end
--
-- Split chord into two part: base chord and chord alteration.
-- e.g. Fsm7 - base chord is Fs, alteration is m7
--
function ChordsTr.splitChord(chord)
if(chord.len == 1) then
return chord, ""
end
local secondChar = string.sub(chord, 2, 2)
if (secondChar == 's' or secondChar == 'f' ) then
return chord.sub(chord, 1, 2), chord.sub(chord, 3)
else
return chord.sub(chord, 1, 1), chord.sub(chord, 2)
end
end
--
-- end of ChordsTr class
--
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