#!/usr/bin/env bash
#> Play audio through one or more sinks together using a virtual output.
#> Usage: sound-merge [<sink name, index, or quoted exact description> ...]
#> Without arguments, select outputs with Tab in fzf, then Enter to merge.
#> Example: sound-merge "Jabra Elite 10" "Tronsmart Sounfii NC 2"
function sound-merge {
    if ! command -v pactl >/dev/null 2>&1 || ! command -v jq >/dev/null 2>&1; then
        printf '%s\n' 'sound-merge: pactl and jq are required.' >&2
        return 1
    fi

    local sinks target matches count name names='[]' slaves
    if ! sinks=$(pactl --format=json list sinks); then
        printf '%s\n' 'sound-merge: could not list sinks.' >&2
        return 1
    fi
    if [ "$#" -eq 0 ]; then
        if ! command -v fzf >/dev/null 2>&1; then
            printf '%s\n' 'sound-merge: fzf is required for interactive selection.' >&2
            return 1
        fi
        local choices selected
        if ! choices=$(printf '%s\n' "$sinks" | jq -r '
            .[] | select(.name != "sound_merge") | [.name, .description] | join("\t")
        '); then
            printf '%s\n' 'sound-merge: could not read sink information.' >&2
            return 1
        fi
        [ -n "$choices" ] || return 0
        selected=$(printf '%s\n' "$choices" | fzf --multi \
            --prompt="Select audio outputs: " --delimiter=$'\t' --with-nth=2 \
            --header="Tab: select outputs · Enter: merge · Esc: cancel") || return 0
        [ -n "$selected" ] || return 0
        while IFS=$'\t' read -r name target; do
            names=$(printf '%s\n' "$names" | jq -c --arg name "$name" '. + [$name] | unique')
        done <<< "$selected"
    fi
    for target in "$@"; do
        if ! matches=$(printf '%s\n' "$sinks" | jq -c --arg target "$target" '
            [.[] | select(.name == $target or (.index | tostring) == $target
                or .description == $target)]
        '); then
            printf '%s\n' 'sound-merge: could not read sink information.' >&2
            return 1
        fi
        count=$(printf '%s\n' "$matches" | jq 'length')
        if [ "$count" -ne 1 ]; then
            printf 'sound-merge: sink %s matched %s outputs; use an exact, unique name or index.\n' "$target" "$count" >&2
            return 1
        fi
        name=$(printf '%s\n' "$matches" | jq -r '.[0].name')
        if [ "$name" = sound_merge ]; then
            printf '%s\n' 'sound-merge: the merged sink cannot be one of its own targets.' >&2
            return 1
        fi
        names=$(printf '%s\n' "$names" | jq -c --arg name "$name" '. + [$name] | unique')
    done
    slaves=$(printf '%s\n' "$names" | jq -r 'join(",")')

    local owner modules module='' existing_slaves='' inputs input_ids input failed=0 created=0
    owner=$(printf '%s\n' "$sinks" | jq -r '.[] | select(.name == "sound_merge") | .owner_module')
    if [ -n "$owner" ]; then
        if ! modules=$(pactl --format=json list modules); then
            printf '%s\n' 'sound-merge: could not list modules.' >&2
            return 1
        fi
        # Only the module explicitly owning our fixed sink name may be unloaded.
        if ! module=$(printf '%s\n' "$modules" | jq -r --arg owner "$owner" '
            .[] | select((.index | tostring) == $owner and .name == "module-combine-sink")
            | select((.argument // "") | test("(^|[[:space:]])sink_name=sound_merge([[:space:]]|$)"))
            | .index
        '); then
            printf '%s\n' 'sound-merge: could not read module information.' >&2
            return 1
        fi
        if [ -z "$module" ]; then
            printf '%s\n' 'sound-merge: sound_merge already exists and is not owned by this helper; leaving it untouched.' >&2
            return 1
        fi
        existing_slaves=$(printf '%s\n' "$modules" | jq -r --arg module "$module" '
            .[] | select((.index | tostring) == $module)
            | (try ((.argument // "") | capture("(^|[[:space:]])slaves=(?<slaves>[^[:space:]]+)").slaves) catch "")
            | split(",") | unique | join(",")
        ')
    fi

    # Gather stream IDs before changing anything, so query failures leave audio alone.
    if ! inputs=$(pactl --format=json list sink-inputs) ||
        ! input_ids=$(printf '%s\n' "$inputs" | jq -r '.[].index'); then
        printf '%s\n' 'sound-merge: could not list playing streams.' >&2
        return 1
    fi
    if [ -n "$module" ] && [ "$existing_slaves" != "$slaves" ]; then
        if ! pactl unload-module "$module"; then
            printf '%s\n' 'sound-merge: could not replace the previous merged sink.' >&2
            return 1
        fi
        module=''
    fi
    if [ -z "$module" ]; then
        if ! module=$(pactl load-module module-combine-sink sink_name=sound_merge \
            "slaves=$slaves" "sink_properties=\"device.description='Merged audio outputs'\""); then
            printf '%s\n' 'sound-merge: could not create the merged sink.' >&2
            return 1
        fi
        created=1
    fi
    if ! pactl set-default-sink sound_merge; then
        printf '%s\n' 'sound-merge: could not select the merged sink.' >&2
        if [ "$created" -eq 1 ]; then
            if ! pactl unload-module "$module"; then
                printf 'sound-merge: cleanup failed; module %s remains loaded.\n' "$module" >&2
            fi
        fi
        return 1
    fi
    while IFS= read -r input; do
        [ -n "$input" ] || continue
        if ! pactl move-sink-input "$input" sound_merge; then
            printf 'sound-merge: could not move stream %s to the merged sink.\n' "$input" >&2
            failed=1
        fi
    done <<< "$input_ids"
    [ "$failed" -eq 0 ] || return 1
    printf 'Audio output: Merged audio outputs (%s)\n' "$slaves"
}