gen-chains

#!/bin/env bash

set -e -o pipefail

# max number of pipeline stages
readonly N=16

# parameter check
if [ -z "$1" ]
then
	echo >&2 "[error] $(basename "$0"): file name is not specified"
	exit 1
fi

# redirect
exec 1>"$1"

# header
echo "// Code generated by $(basename "$0") tool. DO NOT EDIT.

package $GOPACKAGE"

# Chain2
echo '// Chain2 composes 2 pipeline stages into one.
func Chain2[A, B, C any](s1 Stage[A, B], s2 Stage[B, C]) Stage[A, C] {
	return func(src Gen[A], yield func(C) error) error {
		return s2(Bind(src, s1), yield)
	}
}
'

readonly letters='ABCDEFGHIJKLMOPQRSTUVWXYZ'

for (( i=3; i<=N; i++ ))
do
	# comment
	echo "// Chain${i} composes ${i} pipeline stages into one."

	# function signature start
	echo -n "func Chain${i}[A, B, C"

	# template parameter list
	for (( j=3; j<=i; j++ ))
	do
		echo -n ", ${letters:j:1}"
	done

	# function parameters start
	echo -n " any](s1 Stage[A, B], s2 Stage[B, C]"

	# function parameters
	for (( j=3; j<=i; j++ ))
	do
		echo -n ", s${j} Stage[${letters:((j-1)):1}, ${letters:j:1}]"
	done

	# end of function signature
	echo ") Stage[A, ${letters:i:1}] {"

	# implementation start
	echo -n -e "\treturn Chain2(Chain$((i-1))(s1, s2"

	# implementation chain
	for (( j=3; j<i; j++ ))
	do
		echo -n ", s${j}"
	done

	# implementation end
	echo -e "), s${i})\n}"
done

# and finally
goimports -w "$1" >/dev/null