git-base

#!/usr/bin/tclsh

set la ""
set ia ""
foreach val $argv {

	if { $val == "--/" } {
		set la ""
		continue
	}

	if { [string range $val 0 1] == "--" } {
		set la [string range $val 2 end]
		set ::options($la) ""
		continue
	}

	if { $la != "" } {
		lappend ::options($la) $val
		continue
	}

	# If not for-option and not option, then free args.
	lappend ia $val
}

if { [llength $ia] > 1 } {
	"Usage: git base \[branch\] <options...>"
	exit 1
}

proc option {name {default ""}} {
	if {[info exists ::options($name)]} {
		return $::options($name)
	}

	return $default
}

set mbranch $ia

if {$mbranch == ""} {
	set mbranch [exec git branch --show-current]
	if {$mbranch == ""} {
		puts stderr "ERROR: Detached head state. The branch must be explicitly specified"
		exit 1
	}
}

set refloginfo [exec git reflog show $mbranch {--pretty=format:%H %gd {%D}}]

set all_remotes [exec git remote]

set reflogdata ""

foreach i [split $refloginfo \n] {
	lassign $i hid refmark branchinfo
	lassign [split $refmark @] mbr ord

	set brlist [split $branchinfo ,]

	set markhead ""

	set sidebr ""
	foreach b $brlist {
		set b [string trim $b]
		lassign [regexp -inline {([^ ]*) -> ([^ ]*)} $b] unu hd br
		if {$unu != ""} {
			if {$hd == "HEAD"} {
				set markhead "="
			}
		} else {
			set br $b
		}

		if { [string range $br 0 4] == "tag: " } {
			set br "" ;# ignore tags
		}

		set isrem 0
		# Now check if the branch is remote
		set brparts [file split $br]
		if {[llength $brparts] > 1} {
			# Name with slash; check if the first part is remote.
			# If so, it's a remote branch
			set rname [lindex $brparts 0]
			if {$rname == "remotes" || $rname in $all_remotes} {
				set isrem 1
			}
		}

		if {!$isrem && $sidebr == ""} {
			set sidebr $br
		}
	}

	lappend reflogdata $hid ${markhead}$sidebr
}

# May check the parent information, if necessary:

#set parents [exec git rev-list --parents -n 5 $headcommit]

# foreach l [split $parents \n] {
# 	puts "\[[lindex $l 0]\] -> [lrange $l 1 end]"
# }

# Display - for debugging

# Note: with --all, all other options are ignored, except debug
set is_debug [expr {[option debug -] != "-"}]

if {[option all -] != "-"} {
	# Walk through the list, skip those that have
	# the head branch (= in the name) or no branch info.
	# Display all others, in the right order.

	set first 1
	foreach {hid br} $reflogdata {
		if {$first} {
			# Skip the very first entry, it's the branch's head.
			set first 0
			continue
		}
		if {$br == ""} {
			continue
		}

		if {$is_debug} {
			puts "$hid : $br"
		} else {
			puts $hid
		}
	}
	exit 0
}

if {$is_debug} {
	foreach {hid br} $reflogdata {

		if {$br == ""} {
			puts "$hid (continued)"
		} else {
			puts "$hid : $br"
		}
	}
	exit 0
}


# Search for the first found with branch marker, just not head.
set first [option first -]
if {$first != "-"} {

	set first 1
	foreach {hid br} $reflogdata {
		if {$first} {
			# Skip the very first entry, it's the branch's head.
			set first 0
			continue
		}
		if {$br == ""} {
			continue
		}

		puts $hid
		exit 0
	}

	puts stderr "NOTE: no commit found merged from '$reqbase'"
	exit 0
}

set reqbase [option off]

# This option defines, which branch is considered the parent branch.
# If defined, this branch will be searched in the list. Otherwise first
# found will be considered the direct base.

# If not, look at the BOTTOM of the list to see if you have the first branch
# (default mode)
if {$reqbase == ""} {
	set reqbase [lindex $reflogdata end] 
	if {$reqbase == ""} {
		set hdbr [lindex $reflogdata 1]
		if {[string index $hdbr 0] == "="} {
			set hdbr [string range $hdbr 1 end]
		} else {
			set hdbr "(unknown)"
		}

		puts stderr "NOTE: No draw-off information found for '$mbranch' walking from '$hdbr'"
		exit 1
	}
}

# Just in case, read the reflog information from this name.
set reqbase_reflog [exec git reflog show $reqbase --pretty=format:%H]

set first 1
foreach {hid br} $reflogdata {
	if {$first} {
		# Skip the very first entry, it's the branch's head.
		set first 0
		continue
	}
	if {$br == ""} {
		# Check that maybe this hash is in the reqbase reflog
		# XXX CHECK ITS CHILD COMMIT, NOT IT ITSELF!
		if {$hid in $reqbase_reflog} {
			set br $reqbase
		} else {
			continue
		}
	}

	if {$br == $reqbase} {
		puts $hid
		exit 0
	}
}
puts stderr "NOTE: no commit found merged from '$reqbase'"
exit 0