{%- for message in messages %}
    {#-- Validate role is a stringified integer --#}
    {%- if not message['role'] is string or not message['role'].isdigit() %}
        {{- raise_exception("The role must be an integer or a stringified integer (e.g. '0') designating the speaker id") }}
    {%- endif %}

    {#-- Validate content is a list --#}
    {%- set content = message['content'] %}
    {%- if content is not iterable or content is string %}
        {{- raise_exception("The content must be a list") }}
    {%- endif %}

    {#-- Collect content types --#}
    {%- set content_types = content | map(attribute='type') | list %}
    {%- set is_last = loop.last %}

    {#-- Last message validation --#}
    {%- if is_last %}
        {%- if 'text' not in content_types %}
            {{- raise_exception("The last message must include one item of type 'text'") }}
        {%- elif (content_types | select('equalto', 'text') | list | length > 1) or (content_types | select('equalto', 'audio') | list | length > 1) %}
            {{- raise_exception("At most two items are allowed in the last message: one 'text' and one 'audio'") }}
        {%- endif %}

    {#-- All other messages validation --#}
    {%- else %}
        {%- if content_types | select('equalto', 'text') | list | length != 1
              or content_types | select('equalto', 'audio') | list | length != 1 %}
            {{- raise_exception("Each message (except the last) must contain exactly one 'text' and one 'audio' item") }}
        {%- elif content_types | reject('in', ['text', 'audio']) | list | length > 0 %}
            {{- raise_exception("Only 'text' and 'audio' types are allowed in content") }}
        {%- endif %}
    {%- endif %}
{%- endfor %}

{%- for message in messages %}
    {{- bos_token }}
    {{- '[' + message['role'] + ']' }}
    {{- message['content'][0]['text'] }}
    {{- eos_token }}
    {%- if message['content']|length > 1 %}
        {{- '<|AUDIO|><|audio_eos|>' }}
    {%- endif %}
{%- endfor %}