vim9script

def GetMatch(base: string, line: string, add_base: bool): list<any>
    var s = base
    while stridx(line, s) == -1
        s = strpart(s, 1)
        if strlen(s) == 0
            return [0, ""] # vim ignores these
        endif
    endwhile
    const idx = stridx(line, s)
    const slen = strlen(s)
    if add_base
        return [slen, base .. strpart(line, idx + slen)]
    else
        return [slen, strpart(line, idx + slen)]
    endif
enddef

def LineSuffixCompl(findstart: bool, base: string): any
    if findstart
        return 0
    endif
    return  getbufinfo()
        ->map( (_, buf) => getbufline(buf["bufnr"], 1, "$"))
        ->flattennew()
        ->sort()
        ->uniq()
        ->map( (_, v) => GetMatch(base, v, v:true) )
        ->sort( (x, y) => y[0] - x[0] )
        ->map( (_, v) => v[1] )
enddef

def DoLSCmpl(): string
    const base = getline('.')
    const lines = getbufinfo()
        ->map( (_, buf) => getbufline(buf["bufnr"], 1, "$"))
        ->flattennew()
        ->sort()
        ->uniq()
        ->map( (_, v) => GetMatch(base, v, v:false) )
        ->sort( (x, y) => y[0] - x[0] )
        ->map( (_, v) => v[1] )

    complete(col('.'), lines)
    return ''
enddef

# inoremap <C-X><C-L> <C-R>=<SID>DoLSCmpl()<CR>

set completefunc=LineSuffixCompl