set main_checkout ~/dev
set worktree_root ~/worktrees/dev
set base_branch main
set remote origin

function __devtree_usage --no-scope-shadowing
    echo "usage: devtree <command> [args]" >&2
    echo "commands:" >&2
    echo "  new <branch>       create a branch worktree from main and cd into it" >&2
    echo "  cd <branch>        cd into an existing worktree" >&2
    echo "  list               list worktrees" >&2
    echo "  sync [<branch>]    fast-forward main, then rebase branch onto main" >&2
    echo "  sync --all         fast-forward main, then rebase clean topic worktrees onto main" >&2
    echo "  remove <branch>    remove a clean worktree, keeping the branch" >&2
    echo "  prune [--dry-run]  prune worktree metadata and stale merged local branches" >&2
end

function __devtree_path_for_branch --no-scope-shadowing --argument-names branch
    set current_path ""
    for line in (git -C $main_checkout worktree list --porcelain)
        if string match -q 'worktree *' -- $line
            set current_path (string replace 'worktree ' '' -- $line)
        else if test "$line" = "branch refs/heads/$branch"
            echo $current_path
            return 0
        end
    end

    return 1
end

function __devtree_checked_out_branches --no-scope-shadowing
    for line in (git -C $main_checkout worktree list --porcelain)
        if string match -q 'branch refs/heads/*' -- $line
            string replace 'branch refs/heads/' '' -- $line
        end
    end
end

function __devtree_update_main --no-scope-shadowing
    if not test -d $main_checkout/.git
        echo "devtree: main checkout not found at $main_checkout" >&2
        return 1
    end

    set dirty_lines (git -C $main_checkout status --porcelain)
    if test (count $dirty_lines) -gt 0
        echo "devtree: refusing to update dirty main checkout: $main_checkout" >&2
        return 1
    end

    git -C $main_checkout fetch --prune $remote
    or return $status

    git -C $main_checkout switch $base_branch
    or return $status

    git -C $main_checkout merge --ff-only $remote/$base_branch
end

function __devtree_sync_branch --no-scope-shadowing --argument-names branch
    if test "$branch" = "$base_branch"
        echo "$branch: already updated"
        return 0
    end

    set path (__devtree_path_for_branch $branch)
    if test -z "$path"
        echo "devtree: no worktree found for branch '$branch'" >&2
        return 1
    end

    set dirty_lines (git -C $path status --porcelain)
    if test (count $dirty_lines) -gt 0
        echo "$branch: skipped: dirty ($path)"
        return 0
    end

    echo "$branch: rebasing onto $base_branch"
    git -C $path rebase $base_branch
end

if test (count $argv) -eq 0
    __devtree_usage
    return 2
end

set command $argv[1]
set args $argv[2..-1]

switch $command
    case new
        if test (count $args) -ne 1
            echo "usage: devtree new <branch>" >&2
            return 2
        end

        set branch $args[1]
        set path $worktree_root/(string replace -a / __ $branch)

        if git -C $main_checkout show-ref --verify --quiet refs/heads/$branch
            echo "devtree: branch already exists: $branch" >&2
            return 1
        end

        if test -e $path
            echo "devtree: worktree path already exists: $path" >&2
            return 1
        end

        __devtree_update_main
        or return $status

        mkdir -p $worktree_root
        or return $status

        git -C $main_checkout worktree add -b $branch $path $base_branch
        or return $status

        cd $path

    case cd
        if test (count $args) -ne 1
            echo "usage: devtree cd <branch>" >&2
            return 2
        end

        set path (__devtree_path_for_branch $args[1])
        if test -z "$path"
            echo "devtree: no worktree found for branch '$args[1]'" >&2
            return 1
        end

        cd $path

    case list
        if test (count $args) -ne 0
            echo "usage: devtree list" >&2
            return 2
        end

        git -C $main_checkout worktree list

    case sync
        if test (count $args) -gt 1
            echo "usage: devtree sync [<branch>]" >&2
            echo "       devtree sync --all" >&2
            return 2
        end

        __devtree_update_main
        or return $status

        if test (count $args) -eq 1; and test "$args[1]" = --all
            set current_path ""
            set branches
            for line in (git -C $main_checkout worktree list --porcelain)
                if string match -q 'worktree *' -- $line
                    set current_path (string replace 'worktree ' '' -- $line)
                else if string match -q 'branch refs/heads/*' -- $line
                    set branch (string replace 'branch refs/heads/' '' -- $line)
                    if test "$branch" != "$base_branch"
                        set --append branches $branch
                    end
                end
            end

            for branch in $branches
                __devtree_sync_branch $branch
                or return $status
            end
        else
            if test (count $args) -eq 1
                set branch $args[1]
            else
                git rev-parse --show-toplevel >/dev/null 2>&1
                or begin
                    echo "devtree: run 'devtree sync' from a git checkout, or pass a branch" >&2
                    return 2
                end

                set branch (git branch --show-current)
                if test -z "$branch"
                    echo "devtree: could not determine the current branch" >&2
                    return 2
                end
            end

            __devtree_sync_branch $branch
        end

    case remove
        if test (count $args) -ne 1
            echo "usage: devtree remove <branch>" >&2
            return 2
        end

        set branch $args[1]
        if test "$branch" = "$base_branch"
            echo "devtree: refusing to remove $base_branch" >&2
            return 1
        end

        set path (__devtree_path_for_branch $branch)
        if test -z "$path"
            echo "devtree: no worktree found for branch '$branch'" >&2
            return 1
        end

        set dirty_lines (git -C $path status --porcelain)
        if test (count $dirty_lines) -gt 0
            echo "devtree: refusing to remove dirty worktree: $path" >&2
            return 1
        end

        git -C $main_checkout worktree remove $path

    case prune
        set dry_run false
        if test (count $args) -gt 1
            echo "usage: devtree prune [--dry-run]" >&2
            return 2
        else if test (count $args) -eq 1
            if test "$args[1]" = --dry-run
                set dry_run true
            else
                echo "usage: devtree prune [--dry-run]" >&2
                return 2
            end
        end

        git -C $main_checkout worktree prune
        or return $status

        git -C $main_checkout fetch --prune $remote
        or return $status

        set checked_out (__devtree_checked_out_branches)
        for line in (git -C $main_checkout for-each-ref --format='%(refname:short)|%(upstream:track)' refs/heads)
            set parts (string split '|' -- $line)
            set branch $parts[1]
            set upstream_track $parts[2]

            if test "$branch" = "$base_branch"
                continue
            end

            if contains -- $branch $checked_out
                continue
            end

            if not string match -q '*gone*' -- $upstream_track
                continue
            end

            if not git -C $main_checkout merge-base --is-ancestor $branch $base_branch
                echo "$branch: skipped: not merged into $base_branch"
                continue
            end

            if test "$dry_run" = true
                echo "$branch: would delete"
            else
                git -C $main_checkout branch -d $branch
                or return $status
            end
        end

    case '*'
        echo "devtree: unknown command: $command" >&2
        __devtree_usage
        return 2
end