link

#!/bin/sh

# shellcheck shell=sh

CLONE_DIR=$(
  cd "$(dirname "$0")" || exit 1
  pwd
)

in_path() { command -v "$1" 1>/dev/null; }

DST_DIR="$HOME/bin"
mkdir -p "$DST_DIR"

for PAIR in "bash,#!/usr/bin/env bash" "sh,#!/usr/bin/env sh" "py,#!/usr/bin/env python3"; do
  SUFFIX=${PAIR%,*}
  SHEBANG_LINE=${PAIR#*,}
  SHEBANG_PATH=${PAIR#*\#\!}
  SHEBANG_PATH=${SHEBANG_PATH% *}
  if ! in_path "$SHEBANG_PATH"; then
    echo "Warning: Skipping ALL '*.$SUFFIX' files as '$SHEBANG_PATH' isn't in \$PATH" >&2
    continue
  fi

  for SRC_PATH in "$CLONE_DIR/"*."$SUFFIX"; do
    [ ! -f "$SRC_PATH" ] && echo "No *.$SUFFIX files" >&2 && continue

    NOSUFFIX_NAME=$(basename "$SRC_PATH")
    NOSUFFIX_NAME=${NOSUFFIX_NAME%%."$SUFFIX"}
    SCRIPT="$(dirname "$SRC_PATH")/.$(basename "$SRC_PATH")"

    if ! [ -x "$SRC_PATH" ]; then
      echo "Warning: Skipping non executable '$SRC_PATH'" >&2
      continue
    fi

    if [ "$(head -n 1 "$SRC_PATH")" != "$SHEBANG_LINE" ]; then
      echo "Warning: Skipping '$SRC_PATH' as it has a malformed or missing shebang" >&2
      continue
    fi

    DST_PATH="$DST_DIR/$NOSUFFIX_NAME"

    if [ -e "$DST_PATH" ]; then
      if [ "$(stat -c '%d:%i' "$SRC_PATH")" = "$(stat -c '%d:%i' "$DST_PATH")" ]; then
        continue
      elif
        diff -q "$SRC_PATH" "$DST_PATH" >/dev/null 2>&1
      then
        echo "Note: Replacing '$DST_PATH' with a link (same content)" >&2
        rm -fv "$DST_PATH"
      else
        echo "Warning: Skipping link as '$SRC_PATH' differs from '$DST_PATH'" >&2
        continue
      fi
    fi

    if [ -z "$MSG_SHOWN" ]; then
      echo "Linking files from $CLONE_DIR to $DST_DIR..." >&2
      MSG_SHOWN='true'
    fi

    if [ -e "$SCRIPT" ]; then
      "$SCRIPT" && ln -v "$SRC_PATH" "$DST_PATH"
    else
      ln -v "$SRC_PATH" "$DST_PATH"
    fi
  done
done