MAX_BODY_CHARS = 8000


def build_assist_messages(
    body: str, target_section: str, instruction: str
) -> list[dict]:
    """Build Ollama messages for section-level assist.

    The full note body (truncated) is provided as read-only context in the
    system prompt.  The target section + user instruction go in the user
    message.  The model outputs only the replacement for the target section.
    """
    truncated_body = body[:MAX_BODY_CHARS]
    if len(body) > MAX_BODY_CHARS:
        truncated_body += "\n... (truncated)"

    system_content = (
        "You are an AI writing assistant integrated into a note-taking app. "
        "The user is editing a document. The full document is shown below for context.\n\n"
        f"--- Full Document ---\n{truncated_body}\n--- End Document ---\n\n"
        "The user will give you a specific section of the document and an instruction. "
        "Output ONLY the replacement text for that section. "
        "If the target section starts with a markdown heading (e.g. ## Heading), "
        "your output MUST also start with a heading at the same level. "
        "You may revise the heading text but do not remove it. "
        "Do not include other sections, explanatory text, or markdown code fences around the output. "
        "Match the document's existing tone and style. "
        "IMPORTANT: Preserve all markdown formatting exactly — including bullet lists (- item), "
        "numbered lists (1. item), nested/indented sub-items (  - sub), bold (**text**), "
        "italic (_text_), and code blocks. Never flatten nested lists into plain text."
    )

    user_content = (
        f"--- Target Section ---\n{target_section}\n--- End Target Section ---\n\n"
        f"Instruction: {instruction}"
    )

    return [
        {"role": "system", "content": system_content},
        {"role": "user", "content": user_content},
    ]