#!/bin/sh

# Copyright 2022 Loïc Cerf (lcerf@dcc.ufmg.br)

# 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 3 of the License, or (at
# your option) any later version.

# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.

if [ -z "$1" -o "$1" = "-h" -o "$1" = "--help" ]
then
    printf "Usage: $0 max_char_per_line [file.srt]...

Approximately-evenly break too-long lines in .srt subtitles into lines
of at most max_char_per_line (> 1) characters (except for single
words) and always have at most two lines on the screen.
"
    exit
fi

max=$1
shift
sed -e 's/\b\([nd][eao]\) /\1~/g' -e 's/\b\([aeiouyAEIOUY]\) /\1~/g' "$@" | awk -v max=$max '
function after_last_punct() {
    if (NF > 3) {
        next_NF = NF - 1
        for (after = $next_NF " " $NF; --next_NF != 1 && $next_NF !~ /[[:punct:]]$/; after = $next_NF " " after);
        if (next_NF != 1)
            return after }
    next_NF = 0
    return $0 }

function after_intermediary_punct() {
    if (NF > 2) {
        next_NF = NF
        for (after = $NF; --next_NF != 1 && $next_NF !~ /[[:punct:]]$/; after = $next_NF " " after);
        if (next_NF != 1)
            return after }
    next_NF = 0
    return $0 }

/^ *[0-9:,.]* *-->/ {
    print
    next }

{
    for (out = after_last_punct(); NF; ) {
        soft_min = (length * (1 - 1 / max) + 1) / max
        if (soft_min != int(soft_min))
            soft_min = int(soft_min) + 1
        soft_min = (length + 1) / soft_min - 1
        l = length(after_last_punct())
        NF = next_NF
        for (l += length(after_intermediary_punct()); NF && ++l <= soft_min; l += length(after_intermediary_punct())) {
            out = after_intermediary_punct() " " out
            NF = next_NF }
        if (NF) {
            if (l <= max) {
                out = after_intermediary_punct() " " out
                NF = next_NF }
            out = after_last_punct() "\n" out } }
    print out }' | awk -v max=$max '
/^ *[0-9:,.]* *-->/ {
    print
    next }

{
    for (out = $NF; NF; ) {
        soft_min = (length * (1 - 1 / max) + 1) / max
        if (soft_min != int(soft_min))
            soft_min = int(soft_min) + 1
        soft_min = (length + 1) / soft_min - 1
        for (l = length($NF) + length($--NF); NF && ++l <= soft_min; l += length($--NF))
            out = $NF " " out
        if (NF) {
            if (l <= max) {
                out = $NF " " out
                --NF }
            out = $NF "\n" out } }
    print out }' | LC_ALL=C awk -F \\n -v RS='' '
function to_sec(t) {
    n = split(t, hms, /:/)
    sub(/,/, ".", hms[n])
    return hms[n] + 60 * hms[--n] + 3600 * hms[--n] }

function print_time() {
    h = int(time / 3600)
    m = int((time - 3600 * h) / 60)
    s = sprintf("%02.3f", time - 3600 * h - 60 * m)
    sub(/\./, ",", s)
    printf "%02d:%02d:%s", h, m, s }

function print_cue(duration) {
    print ++nb
    print_time()
    printf " --> "
    time += duration
    print_time() }

{
    for (; $NF == ""; --NF);
    split($2, interval, /-->/)
    time = to_sec(interval[1])
    duration = (to_sec(interval[2]) - time) / (length - length($1) - length($2) - 1)
    for (i = 3; i < NF; ++i) {
        print_cue((length($i) + length($(i + 1)) + 2) * duration)
        print "\n" $i "\n" $++i "\n" } }

i == NF {
    print_cue((length($i) + 1) * duration)
    print "\n" $i "\n" }' | sed -e 's/\b\([nd][eao]\)~/\1 /g' -e 's/\b\([aeiouyAEIOUY]\)~/\1 /g'