#!/usr/bin/env zsh

local AUTHOR_NAME=$(git config --get user.name)
local UPSTREAM=origin/master
local ENDPOINT
export seqno

fail() { echo "$1" >&2; exit 1 }

usage() {
  cat >&2 <<EOF
$0: a zsh developer's add-X-Seq-and-ChangeLog script

Usage: $0 NUMBER

Will prefix NUMBER to the log message of each local commit not yet
in $UPSTREAM, and amend the commit with a ChangeLog entry.  The following
formats are accepted for NUMBER: '42', 'users/42', 'unposted'.

Prerequisite: git must have been compiled with PCRE support.
EOF
  exit ${1:-1}
}

## Require a recent zsh
if [[ $( (){ shift -p; echo $# } arg1 arg2 arg3 ) -ne 2 ]]; then
  fail "This script requires a zsh supporting 'shift -p'"
fi

## Argument parsing
if [[ $# -ne 1 ]] ||
   [[ $1 != (<30000->*|users/<->|unposted) ]] ||
   [[ $(git log -1 --pretty=%cn) != *"${AUTHOR_NAME}"* ]] ||
   false
then
  usage
fi

seqno=$1

## Validate worktree state
if [[ -n "`git status --porcelain ChangeLog`" ]]; then
  fail "ChangeLog has local mods"
fi

if ! git merge-base --is-ancestor $UPSTREAM HEAD; then
  fail "'$UPSTREAM' must be an ancestor of HEAD, but isn't"
fi

## Set ENDPOINT to oldest commit such that $ENDPOINT..HEAD consists of commits
## by $AUTHOR_NAME that don't touch ChangeLog.

# We can't just 'git log --not --committer=$AUTHOR_NAME', since the --not is silently ignored.
# Hence we use --perl-regexp, even though it requires PCRE.
[[ $AUTHOR_NAME == *'\'* ]] && fail "bobby tables"
ENDPOINT=$(git log --perl-regexp --committer='^(?!\Q'$AUTHOR_NAME'\E)' -1 --pretty=%H)
() { 
  local arg
  # Arguments are youngest-to-oldest, so:
  while (( $# )); do
    arg=$argv[-1]
    if [[ $(git diff --name-only $arg^..$arg) != *ChangeLog* ]]; then
      ENDPOINT=$argv[-1]
      return
    fi
    shift -p
  done
} $(git rev-list $ENDPOINT..HEAD)

## Main body
seqno=$seqno \
  GIT_EDITOR='true' git rebase -i $ENDPOINT^ --exec \
    "$0-internal"