setup

#!/bin/sh
# Visible names in home/ map to dotfiles in $HOME; shell entrypoints stay local.
set -eu

case "${1:-}" in
'') ;;
-h | --help)
    printf '%s\n' 'Usage: ./setup' \
        'Links home/ files into $HOME, replacing existing files and symlinks.' \
        'Shell entrypoints are appended once. Software is installed separately.'
    exit 0
    ;;
*)
    printf '%s\n' 'Usage: ./setup' >&2
    exit 2
    ;;
esac

repo_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
mkdir -p "$HOME"
target_home=$(CDPATH= cd -- "$HOME" && pwd)
case "$target_home/" in
"$repo_dir/"*)
    printf '%s\n' 'HOME must be outside the repository.' >&2
    exit 1
    ;;
esac

find "$repo_dir/home" -type f | sort | while IFS= read -r source; do
    relative=${source#"$repo_dir/home/"}
    # Only the first component gains a dot: config/nvim -> .config/nvim.
    target=$target_home/.$relative
    case "$relative" in
    bashrc | profile | zshrc) target=$target_home/.config/shell/$relative ;;
    esac

    # Do not follow directory links into an old checkout or another config tree.
    parent=${target%/*}
    while [ "$parent" != "$target_home" ]; do
        if [ -L "$parent" ]; then
            printf 'Directory symlink needs manual migration: %s\n' "$parent" >&2
            exit 1
        fi
        parent=${parent%/*}
    done
    mkdir -p "${target%/*}"

    if [ -L "$target" ] && [ "$(readlink "$target")" = "$source" ]; then
        continue
    fi
    # rm -f deliberately refuses to remove an actual directory.
    rm -f "$target"
    ln -s "$source" "$target"
    printf 'LINK  %s\n' "$target"

done

# Keep writable machine entrypoints separate from repository configuration.
for shell_file in bashrc profile zshrc; do
    target=$target_home/.$shell_file
    if [ -L "$target" ]; then
        temporary=$(mktemp "$target.setup.XXXXXX")
        if [ -f "$target" ]; then cat "$target" >"$temporary"; fi
        mv -f "$temporary" "$target"
    fi
    touch "$target"
    loader='.'
    if [ "$shell_file" = zshrc ]; then loader=source; fi
    {
        printf '%s "$HOME/.config/shell/%s"\n' "$loader" "$shell_file"
        printf '[ -f "$HOME/.%s.local" ] && %s "$HOME/.%s.local"\n' "$shell_file" "$loader" "$shell_file"
    } | while IFS= read -r line; do
        if ! grep -Fqx -- "$line" "$target"; then
            printf '\n%s\n' "$line" >>"$target"
        fi
    done
    printf 'LOAD  %s\n' "$target"
done