#!/bin/bash
# see several paragraphs below for more on the choice of shell interpreter.

# ml is a mail reading interface for mh(1).  the design is that of
# a thin wrapper (this script) which uses 'less' for message
# display, and mh commands for doing the real work.
#
# this script was completely and utterly inspired by a message
# posted by Ralph Corderoy to the nmh developer's list, describing
# his similar, unpublished, script:
#   http://lists.nongnu.org/archive/html/nmh-workers/2012-02/msg00148.html
#
# see the usage() and help() functions, below, for more detail.	 (or
# use 'ml -?' for usage, and '?' within ml for help.)
#
# ml creates its own lesskeys map file the first time you run it,
# called ~/Mail/ml_lesskeymap.
#
# there are a number of places where i let ml invoke my own wrapper
# scripts to do something mh-like.  these wrappers do things like
# provide safe(r) message deletion, select among repl formats, etc.
# all of these can be easily changed -- see the do_xxxx() functions.
# all are assumed to operate on mh-style message specifications, and
# on 'cur' by default.
#
# this script uses the sequences 'ml', 'mldel', 'mlspam', 'mlunr',
# 'mlkeep', and 'mlrepl'.  it also manipulates the user's Unseen-sequence.
#
# the shell dialect used is very conservative.  dash (debian's
# /bin/sh), bash, ksh, and solaris /bin/sh will all work, and probably
# the current bsd /bin/sh variants as well, with very slightly
# improved function in bash or ksh.  the only non-posix shell feature
# used is an argument to "read".  search for the function ask_init()
# for more detail.
#
# paul fox, pgf@foxharp.boston.ma.us, february 2012
# ------------


create_lesskey_map()
{
    # the lesskey(1) bindings that cause less to work well with ml are:
    lesskey -o $lesskeymap -- - <<-EOF
	\^	quit \^
	\?	quit \?
	E	quit E
	H	quit H
	J	quit J
	n	quit n
	K	quit K
	P	quit P
	p	quit p
	Q	quit Q
	q	quit q
	R	quit R
	S	quit S
	U	quit U
	V	quit V
	X	quit X
	d	quit d
	f	quit f
	r	quit r
	s	quit s
	u	quit u
	i	quit i

	# \40 maps the space char, to force the last page to start at
	# the end of prev page, rather than lining up with bottom of
	# screen.
	\40	    forw-screen-force
EOF

}


#
# the functions named do_xxxx() are the ones that are most ripe for
# customization.  feel free to nuke my personal preferences.
#

do_rmm()
{
    # d "$@" ; return   # pgf's private alias
    rmm "$@"
}

do_spamremove()
{
    # spam "$@" ; return	  # pgf's private alias
    refile +spambucket "$@"    # you're on your own
}

do_reply()
{
    # rf "$@" ; return	# pgf's private alias
    repl "$@"
}

do_replyall()
{
    # R "$@" ; return   # pgf's private alias
    repl -cc to -cc cc "$@"
}

do_forw()
{
    # f "$@" ; return   # pgf's private alias
    forw "$@"
}

do_edit()
{
    ${VISUAL:-${EDITOR:-vi}} $(mhpath cur)
}

do_urlview()
{
    urlview $(mhpath cur)
}

do_viewhtml()
{
    echo 'mhshow-show-text/html: ' \
	  ' %p/usr/bin/lynx -force_html '%F' -dump | less' \
	> /tmp/ml-mhshow-html$$

    MHSHOW=/tmp/ml-mhshow-html$$ \
    LC_ALL=C \
	mhshow -type text/html "$@"

    rm -f /tmp/ml-mhshow-html$$
}

do_sort()
{
    # the intent is to apply some sort of thread/date ordering.
    # be sure no sequences have been started
    verify_empty "Sorting requires starting over." mldel || return
    verify_empty "Sorting requires starting over." mlspam || return
    verify_empty "Sorting requires starting over." mlunr || return

    # sort by date, then by subject, to get, to get subject-major,
    # date-minor ordering
    sortm ml
    sortm -textfield subject ml
}



usage()
{
    cat <<EOF >&2
usage: $me [ msgs | -s | -a ]
  $me will present the specified 'msgs' (any valid MH message
    specification).  With no arguments, messages will come from
    the '$ml_unseen_seq' sequence.
  Use "$me -s" to get the status of sequences used internally by $me, or
    "$me -a" to apply previous results (shouldn't usually be needed).
  Use ? when in less to display help for '$me'.
EOF
    exit 1
}

help()
{

    less -c <<EOF



    "ml" takes an MH message specification as argument.
    If none is specified, ml will operate on the sequence named "$ml_unseen_seq".

    Messages are repeatedly displayed using 'less', which mostly
    behaves as usual.  less is configured with some special key
    bindings which cause it to quit with special exit codes.  These
    in turn cause ml to execute distinct commands: they might cause
    ml to display the next message, to mark the current message as
    spam, to quit, etc.

    The special key bindings within less are:

    ?	display this help (in a separate 'less' invocation)

    ^      show first message
    n,J	   show next message
    p,P,K  show previous message

    d	mark message for later deletion, by adding to sequence 'mldel'.
    s	mark message for later spam training, by adding to sequence 'mlspam'.
    u	mark message to remain "unread", by adding to sequence 'mlunr'.
    U	undo, i.e., remove it from any of 'mldel', 'mlspam', and 'mlunr'.

    r	compose a reply
    R	compose a reply to all message recipients
    f	forward the current message

    S	sort the messages, by subject and date
    H	render html from the message
    V	run 'urlview' on the message
    E	edit the raw message file

    q	quit.  The 'mlunr' sequence will be added back to '$ml_unseen_seq',
	    messages in the 'mldel' are deleted, and those in 'mlspam'
	    are dealt with accordingly.  Any messages that were read,
	    but not deleted or marked as spam will be left in the
	    'mlkeep' sequence.  If ml dies unexpectedly (or the 'Q'
	    command is used instead of 'q'), "ml -a" (see below) can
	    be used to apply the changes that would have been made.

    Q,X exit.  Useful if you want to "start over".  The '$ml_unseen_seq'
	    sequence will be restored to its previous state, and the
	    current message list is preserved to 'mlprev'.  No other
	    message processing is done.

    Any other command which causes less to quit will simply display
    the next message.  ('q', for instance)

    ml recognizes three special commandline arguments:
      "ml -s"  will report the status of the sequences ml uses, which is
		handy after quitting with 'X', for example.
      "ml -a"  will apply the changes indicated by the user -- messages
		in the 'mldel' sequence are deleted, messages in the
		'mlspam' sequence are trained and marked as spam, and
		the 'mlunr' sequence is added to the '$ml_unseen_seq'
		sequence.
      "ml -k"  will recreate the ml_lesskey file used by ml when running
		less.  ml will usually handle this automatically.

EOF
}

normal_quit()
{
    apply_changes
    mark -sequence ml -delete all 2>/dev/null
    exit
}

ask_init()
{
    # if "read -n 1" gives an error message, it's unsupported,
    # so don't use it -- the user will need to hit <enter>.
    # this test works on dash, bash, ksh, and a recent solaris
    # /bin/sh, but fails on zsh.
    no_immed=$(read -n 1 < /dev/null 2>&1)
}

ask()
{
    immed=;

    if [ "$1" = -i ]
    then
	test "$no_immed" || immed="-n 1"
	shift
    fi
    echo -n "${1}? [N/y] "
    read $immed a
    case $a in
    [Yy]*) return 0 ;;
    *) return 1 ;;
    esac

}

# ensure the given sequence is empty
verify_empty()
{
    pre="$1"
    seq=$2
    if pick $seq:first >/dev/null 2>&1
    then
	echo $pre
	if ask "Non-empty '$seq' sequence found, okay to continue"
	then
	    mark -sequence $seq -delete all 2>/dev/null
	else
	    return 1
	fi
    fi
    return 0
}

# safely return the (non-zero) length of given sequence, with error if empty
seq_count()
{
    msgs=$(pick $1 2>/dev/null) || return 1
    echo "$msgs" | wc -l
}

# move 'ml' to 'mlprev'
preserve_ml_seq()
{
    mark -sequence mlprev -zero -add ml 2>/dev/null
    mark -sequence ml -delete all 2>/dev/null
}

# restore the unseen sequence to its value on entry
restore_unseen()
{
    mark -sequence $ml_unseen_seq -add saveunseen 2>/dev/null
}

# add the message to just one of the special sequences.
markit()
{
    case $1 in
    mlkeep)  # this is really an undo, since it restores default action
	mark -add -sequence mlkeep cur
	mark -delete -sequence mlspam cur 2>/dev/null
	mark -delete -sequence mldel cur 2>/dev/null
	mark -delete -sequence mlunr cur 2>/dev/null
	;;
    mlspam)
	mark -delete -sequence mlkeep cur 2>/dev/null
	mark -add -sequence mlspam cur
	mark -delete -sequence mldel cur 2>/dev/null
	mark -delete -sequence mlunr cur 2>/dev/null
	;;
    mldel)
	mark -delete -sequence mlkeep cur 2>/dev/null
	mark -delete -sequence mlspam cur 2>/dev/null
	mark -add -sequence mldel cur
	mark -delete -sequence mlunr cur 2>/dev/null
	;;
    mlunr)
	mark -delete -sequence mlkeep cur 2>/dev/null
	mark -delete -sequence mlspam cur 2>/dev/null
	mark -delete -sequence mldel cur 2>/dev/null
	mark -add -sequence mlunr cur
	;;
    mlrepl) # this sequence only affects the displayed header of the message.
	mark -add -sequence mlrepl cur
	;;
    esac
}

# emit an informational header at the top of each message.
header()
{
    local msg=$1

    this_mess="${BOLD}Message $folder:$msg${NORMAL}"

    # get index of current message
    mindex=$(echo "$ml_contents" | grep -xn $msg)
    mindex=${mindex%:*}

    # are we on the first or last or only messages?
    if [ $ml_len != 1 ]
    then
	if [ $mindex = 1 ]
	then
	    mindex="${BOLD}FIRST${NORMAL}"
	elif [ $mindex = $ml_len ]
	then
	    mindex="${BOLD}LAST${NORMAL}"
	fi
    fi
    position="($mindex of $ml_len)"

    # have we done anything to this message?
    r=; s=;
    if pick mlrepl 2>/dev/null | grep -qx $msg
    then
	r="${BLUE}Replied ${NORMAL}"
    fi
    if pick mldel 2>/dev/null | grep -qx $msg
    then
	s="${RED}Deleted ${NORMAL}"
    elif pick mlspam 2>/dev/null | grep -qx $msg
    then
	s="${RED}Spam ${NORMAL}"
    elif pick mlunr 2>/dev/null | grep -qx $msg
    then
	s="${RED}Unread ${NORMAL}"
    fi
    status=${r}${s}

    # show progress for whole ml run (how many deleted, etc.)
    scnt=$(seq_count mlspam)
    dcnt=$(seq_count mldel)
    ucnt=$(seq_count mlunr)
    others="${scnt:+$scnt spam }${dcnt:+$dcnt deleted }${ucnt:+$ucnt marked unread}"
    others="${others:+[$others]}"

    statusline="$this_mess $position $status $others"

    echo $statusline

}

# emit the header again
footer()
{
    echo "-----------"
    echo "$statusline"
}

# make the Subject: and From: headers stand out
colorize()
{
    sed \
	-e 's/^\(Subject: *\)\(.*\)/\1'"$RED"'\2'"$NORMAL"'/' \
	-e 's/^\(From: *\)\(.*\)/\1'"$BLUE"'\2'"$NORMAL"'/' # 2>/dev/null
}

cleanup()
{
    # the first replacement gets rid of the default header that
    # show emits with every message -- we provide our own.
    # for the second:  i think the 'Press <return> text is a bug in
    # mhl.  there's no reason to display this message when not
    # actually pausing for <return> to be pressed.
    sed -e '1s/^(Message .*)$/---------/' \
	-e 's/Press <return> to show content\.\.\.//'
}

# this is the where the message is displayed, using less
show_msg()
{
    local nmsg
    local which=$1


    # only (re)set $msg if pick succeeds
    if nmsg=$(pick ml:$which 2>/dev/null)
    then
	msg=$nmsg
	viewcount=0
    else
	# do we keep hitting the same message?
	: $(( viewcount += 1 ))
	if [ $viewcount -gt 2 ]
	then
	    if ask -i "See message $msg yet again"
	    then
		viewcount=0
	    else
		normal_quit
	    fi
	fi
    fi

    (
	header $msg
	Mail=$(mhpath +)
	export NMH_NON_INTERACTIVE=1
	export MHSHOW=$Mail/mhn.noshow
	mhshow $msg |
		cleanup |
		colorize
	footer
    ) | LESS=miXcR less $lesskeyfileopt
    return $?	# return less' exit code
}

# bad things would happen if we were to keep going after the current
# folder has been changed from another shell.
check_current_folder()
{
    curfold=$(folder -fast)
    if [ "$curfold" != "$folder" ]  # danger, will robinson!!
    then
	echo "Current folder has changed to '$curfold'!"
	echo "Answering 'no' will discard changes, and exit."
	if ask "Switch back to '$folder'"
	then
	    folder +$folder
	else
	    restore_unseen
	    preserve_ml_seq
	    exit
	fi
    fi
}

loop()
{
    local nextmsg

    nextmsg=first
    while :
    do
	check_current_folder

	show_msg $nextmsg
	cmd=$?		# save the less exit code

	check_current_folder

	# by default, stay on the same message
	nextmsg=cur

	case $cmd in

	# help
	$_ques) help
		;;

	# dispatch
	$_d) markit mldel
	     ##nextmsg=next
	     ;;
	$_s) markit mlspam
	     ##nextmsg=next
	     ;;
	$_u) markit mlunr
	     ##nextmsg=next
	     ;;
	$_U) markit mlkeep
	     ##nextmsg=next
	     ;;

	# send mail
	$_r) do_reply
	     markit mlrepl
	     #nextmsg=cur
	     ;;
	$_R) do_replyall
	     markit mlrepl
	     #nextmsg=cur
	     ;;
	$_f) do_forw
	     markit mlrepl
	     #nextmsg=cur
	     ;;

	# special viewers
	$_H) do_viewhtml
	     #nextmsg=cur
	     ;;
	$_V) do_urlview
	     #nextmsg=cur
	     ;;
	$_E) do_edit
	     #nextmsg=cur
	     ;;
	$_i) show_status | less -c
	     #nextmsg=cur
	     ;;

	# quitting
	$_q) normal_quit
	     ;;

	$_X|$_Q) restore_unseen
	     preserve_ml_seq
	     exit
	     ;;

	# other
	$_S) do_sort
	     nextmsg=first
	     ;;

	# navigation
	$_up) nextmsg=first
	     ;;

	$_K) nextmsg=prev
	     ;;
	$_p|$_P) nextmsg=prev
	     ;;
	$_n|$_J) nextmsg=next
	     ;;
	*)   nextmsg=next
	     ;;

	esac
    done
}

# summarize ml's internal sequences, for "ml -s"
show_status()
{
    echo Folder: $folder
    for s in mlspam mldel mlrepl mlunr
    do
	#pick $s:first >/dev/null 2>&1 || continue
	case $s in
	mlrepl) echo "Have attempted a reply: (sequence $s)" ;;
	mldel) echo "Will delete: (sequence $s)" ;;
	mlspam) echo "Will mark as spam: (sequence $s)" ;;
	mlunr) echo "Will mark as unseen: (sequence $s)" ;;
	# mlkeep) echo "Will leave as seen: (sequence $s)" ;;
	esac
	scan $s 2>/dev/null || echo '       none'
    done
}

apply_changes()
{
    if cnt=$(seq_count mlspam)
    then
	echo "Marking $cnt messages as spam."
	do_spamremove mlspam
    fi

    if cnt=$(seq_count mldel)
    then
	echo "Removing $cnt messages."
	do_rmm mldel
    fi

    if cnt=$(seq_count mlunr)
    then
	echo "Marking $cnt messages unread."
	mark -add -sequence $ml_unseen_seq mlunr 2>/dev/null
	mark -sequence mlunr -delete all
    fi

    if cnt=$(seq_count mlkeep)
    then
	echo "Keeping $cnt messages in sequence 'mlkeep':"
	scan mlkeep
    fi
}

# decimal to character mappings.  lesskeys lets you specify exit codes
# from less as ascii characters, but the shell really wants them to be
# numeric, in decimal.	these definitions let you do "quit S" in
# lesskeys, and then check against $_S here in the shell.
char_init()
{
    _A=65; _B=66; _C=67; _D=68; _E=69; _F=70; _G=71; _H=72; _I=73;
    _J=74; _K=75; _L=76; _M=77; _N=78; _O=79; _P=80; _Q=81; _R=82;
    _S=83; _T=84; _U=85; _V=86; _W=87; _X=88; _Y=89; _Z=90;

    _a=97; _b=98; _c=99; _d=100; _e=101; _f=102; _g=103; _h=104; _i=105;
    _j=106; _k=107; _l=108; _m=109; _n=110; _o=111; _p=112; _q=113; _r=114;
    _s=115; _t=116; _u=117; _v=118; _w=119; _x=120; _y=121; _z=122;

    _up=94; _ques=63;
}

color_init()
{
    RED="$(printf \\033[1\;31m)"
    GREEN="$(printf \\033[1\;32m)"
    YELLOW="$(printf \\033[1\;33m)"
    BLUE="$(printf \\033[1\;34m)"
    PURPLE="$(printf \\033[1\;35m)"
    CYAN="$(printf \\033[1\;36m)"
    BOLD="$(printf \\033[1m)"
    NORMAL="$(printf \\033[m)"
    ESC="$(printf \\033)"
}


# in-line execution starts here

set -u	  # be defensive

me=${0##*/}

folder=$(folder -fast)
lesskeymap=$(mhpath +)/ml_lesskeymap
lesskeyfileopt="--lesskey-file=$lesskeymap"

if [ ! -f $lesskeymap -o $0 -nt $lesskeymap ]
then
    create_lesskey_map
fi

ml_unseen_seq=$(mhparam Unseen-Sequence)
: ${ml_unseen_seq:=unseen}  # default to "unseen"

# check arguments
case ${1:-} in
    -s) show_status;		exit ;;	  # "ml -s"
    -a) apply_changes;		exit ;;	  # "ml -a"
    -k) create_lesskey_map;	 exit ;;   # "ml -k"  (should be automatic)
    -*) usage			     ;;	  # "ml -?"
    "") starting_seq=$ml_unseen_seq  ;;	  # "ml"
     *) starting_seq="$*"	     ;;	  # "ml picked ..."
esac


# if sequence ml isn't empty, another instance may be running
verify_empty "Another instance of ml may be running." ml || exit

# gather any user message specifications into the sequence 'ml'
if ! mark -sequence ml -zero -add $starting_seq	 >/dev/null 2>&1
then
    echo "No messages (or message sequence) specified."
    exit 1
fi

# uncomment for debug
# exec 2>/tmp/ml.log; set -x

# get the full list of messages, and count them
ml_contents=$(pick ml)
ml_len=$(echo "$ml_contents" | wc -l)

# if these aren't empty, we might not have "ml a"pplied changes from
# a previous invocation, so warn.
verify_empty "You might want to run 'ml -a'." mldel || exit
verify_empty "You might want to run 'ml -a'." mlspam || exit
verify_empty "You might want to run 'ml -a'." mlunr || exit

mark -sequence mlrepl -delete all 2>/dev/null

# initialize 'mlkeep' to 'ml', since we assume all undeleted non-spam
# messages will be kept.
mark -zero -sequence mlkeep ml

# save a copy of the unseen sequence, for restore if 'X' is used to quit.
mark -zero -sequence saveunseen $ml_unseen_seq

ask_init

char_init
color_init

loop