# bash completion for merge-upstream-to-downstream.sh
#
# Provides Tab-completion for the script's named options and, intelligently,
# for their VALUES:
#   * remote-name options (--fork-remote/--upstream-remote/--downstream-remote)
#     complete against the git remotes of the repo containing the CWD;
#   * remote-branch options (--upstream-branch/--downstream-branch/--fork-branch)
#     complete against the branches OF THE MATCHING REMOTE — the script resolves
#     each of those to a remote (via its paired --*-remote option already on the
#     line, the MERGE_U2D_* env var, or the built-in default), so e.g.
#     `--upstream-remote eclipse --upstream-branch <Tab>` lists eclipse's branches;
#   * local-branch options (--local-*-branch) complete against local branches.
#
# Install (any one of):
#   * source it from ~/.bashrc:            source /path/to/merge-upstream-to-downstream.bash-completion
#   * or drop/symlink into the user dir:   ~/.local/share/bash-completion/completions/merge-upstream-to-downstream.sh
#   * or system-wide:                      /usr/share/bash-completion/completions/merge-upstream-to-downstream.sh
# (The last two use on-demand loading; the file's basename must match the command
#  being completed — hence the symlink name ending in .sh below.)

# Enumerate git remotes for the repo containing $PWD (empty & silent if not a repo).
__m2d_remotes() {
    git remote 2>/dev/null
}

# Enumerate branch short-names present on a given remote (arg 1), via the
# remote-tracking refs. strip=3 turns refs/remotes/<remote>/<branch> into <branch>.
__m2d_remote_branches() {
    local remote="$1"
    [ -n "$remote" ] || return 0
    git for-each-ref --format='%(refname:strip=3)' "refs/remotes/${remote}/" 2>/dev/null
}

# Enumerate local branch short-names. strip=2 turns refs/heads/<branch> into <branch>.
__m2d_local_branches() {
    git for-each-ref --format='%(refname:strip=2)' refs/heads/ 2>/dev/null
}

# Resolve which remote a given "role" (fork|upstream|downstream) points at, using
# the SAME precedence the script itself uses: an explicit --<role>-remote already
# typed on the command line > the MERGE_U2D_<ROLE>_REMOTE env var > built-in default.
# $1 = role; the current COMP_WORDS are scanned for the explicit flag.
__m2d_resolve_remote() {
    local role="$1" flag="--${1}-remote" i
    # 1) explicit flag already on the line (supports both "--flag val" and "--flag=val").
    for (( i = 1; i < COMP_CWORD; i++ )); do
        case "${COMP_WORDS[i]}" in
            "$flag")   [ $((i + 1)) -lt $COMP_CWORD ] && { printf '%s' "${COMP_WORDS[i+1]}"; return 0; } ;;
            "$flag"=*) printf '%s' "${COMP_WORDS[i]#*=}"; return 0 ;;
        esac
    done
    # 2) env var, then 3) built-in default.
    case "$role" in
        fork)       printf '%s' "${MERGE_U2D_FORK_REMOTE:-}" ;;
        upstream)   printf '%s' "${MERGE_U2D_UPSTREAM_REMOTE:-eclipse}" ;;
        downstream) printf '%s' "${MERGE_U2D_DOWNSTREAM_REMOTE:-sap}" ;;
    esac
}

_merge_upstream_to_downstream() {
    local cur prev opts
    cur="${COMP_WORDS[COMP_CWORD]}"
    prev="${COMP_WORDS[COMP_CWORD-1]}"
    opts="--fork-remote --upstream-remote --downstream-remote \
          --upstream-branch --downstream-branch --fork-branch \
          --local-upstream-branch --local-downstream-branch --local-fork-branch \
          -h --help"
    # Complete the VALUE when the previous word is an option that takes one.
    case "$prev" in
        --fork-remote|--upstream-remote|--downstream-remote)
            COMPREPLY=( $(compgen -W "$(__m2d_remotes)" -- "$cur") ); return 0 ;;
        --upstream-branch)
            COMPREPLY=( $(compgen -W "$(__m2d_remote_branches "$(__m2d_resolve_remote upstream)")" -- "$cur") ); return 0 ;;
        --downstream-branch)
            COMPREPLY=( $(compgen -W "$(__m2d_remote_branches "$(__m2d_resolve_remote downstream)")" -- "$cur") ); return 0 ;;
        --fork-branch)
            COMPREPLY=( $(compgen -W "$(__m2d_remote_branches "$(__m2d_resolve_remote fork)")" -- "$cur") ); return 0 ;;
        --local-upstream-branch|--local-downstream-branch|--local-fork-branch)
            COMPREPLY=( $(compgen -W "$(__m2d_local_branches)" -- "$cur") ); return 0 ;;
    esac
    # Otherwise complete an option NAME. compgen -W filters by "$cur", so an
    # empty cur (bare Tab right after the command) lists every option, while a
    # partial like "--fork" narrows it — and a stray non-option word yields the
    # options too rather than nothing.
    COMPREPLY=( $(compgen -W "$opts" -- "$cur") )
    return 0
}

# Register for the plain name, the .sh form, and any path invocation (./x, /abs/x).
complete -F _merge_upstream_to_downstream \
    merge-upstream-to-downstream.sh \
    ./merge-upstream-to-downstream.sh