MAX_BODY_CHARS = 8000


def build_assist_messages(
    body: str, target_section: str, instruction: str, whole_doc: bool = False
) -> list[dict]:
    """Build Ollama messages for writing assist.

    When whole_doc=True, the model revises the entire document.
    When whole_doc=False (section mode), the full body is provided as read-only
    context and 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)"

    if whole_doc:
        system_content = (
            "You are a writing assistant. Revise the document per the instruction. "
            "Output ONLY the complete revised document. Preserve all structure and "
            "content not addressed by the instruction. "
            "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"--- Document ---\n{truncated_body}\n--- End Document ---\n\n"
            f"Instruction: {instruction}"
        )
    else:
        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},
    ]