Module:Mgsub

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-- <nowiki>
--------------------------------------------------------------------------------
-- Multiline global substitution:
-- Like mw.ustring.gsub, but '^' and '$' match the beginning and end of each
-- line, respectively.
--------------------------------------------------------------------------------
local checkType = require('libraryUtil').checkType
local checkTypeMulti = require('Dev:CheckTypeMulti')

-- Reduce table lookups
local uGsub = mw.ustring.gsub

return function (s, pttrn, repl, n)
    checkType('Dev:Mgsub', 1, s, 'string')
    checkType('Dev:Mgsub', 2, pttrn, 'string')
    checkTypeMulti('Dev:Mgsub', 3, repl, {'function', 'table', 'string'})
    checkType('Dev:Mgsub', 4, n, 'number', true)

    -- Return the original string if no matches are allowed.
    if n and n < 1 then
        return s, 0
    end

    -- Use mw.ustring.gsub if multiline substitution does not make sense.
    if not s:find('\n') or pttrn:sub(1, 1) ~= '^' and pttrn:sub(-1) ~= '$' then
        return uGsub(s, pttrn, repl, n)
    end

    local lines = mw.text.split(s, '\n')
    local totalMatches = 0
    local remainingMatches, newMatches

    for i = 1, #lines do
        -- Stop updating lines if no more matches are allowed.
        if n and totalMatches == n then
            break
        end

        remainingMatches = n and n - totalMatches
        lines[i], newMatches = uGsub(lines[i], pttrn, repl, remainingMatches)
        totalMatches = totalMatches + newMatches
    end

    return table.concat(lines, '\n'), totalMatches
end

-- </nowiki>
-- (Add categories here.)