/// 拼图图片生成的默认反向提示词。
///
/// 这里单独收口拼图图片提示词，避免图片生成链路、候选图持久化和 DashScope 请求编排
/// 混在同一个脚本里，后续调画风或资产约束时只需要改这一处。
pub(crate) const PUZZLE_DEFAULT_NEGATIVE_PROMPT: &str =
    "低清晰度，低质量，文字水印，畸形构图，过度模糊，重复肢体，画面脏污";

/// wan2.2 / wan2.1 文生图旧协议的正向 prompt 上限。
///
/// 中文注释：DashScope 旧 text2image 接口会把超长 prompt 判成请求参数不合法，
/// 所以这里先在拼图提示词模块内压缩，保证固定玩法约束不会被用户长描述挤掉。
pub(crate) const PUZZLE_TEXT_TO_IMAGE_PROMPT_MAX_CHARS: usize = 500;

const PUZZLE_IMAGE_LEVEL_NAME_MAX_CHARS: usize = 40;
const PUZZLE_IMAGE_PROMPT_FALLBACK: &str = "清晰、有辨识度的拼图画面";

/// 根据拼图关卡名和陶泥儿主输入构造最终发给图片模型的提示词。
pub(crate) fn build_puzzle_image_prompt(level_name: &str, prompt: &str) -> String {
    let level_name =
        truncate_puzzle_prompt_segment(level_name.trim(), PUZZLE_IMAGE_LEVEL_NAME_MAX_CHARS);
    let prompt = prompt.trim();
    let prompt = if prompt.is_empty() {
        PUZZLE_IMAGE_PROMPT_FALLBACK
    } else {
        prompt
    };
    let template_chars = build_puzzle_image_prompt_text(level_name.as_str(), "")
        .chars()
        .count();
    let prompt_max_chars = PUZZLE_TEXT_TO_IMAGE_PROMPT_MAX_CHARS.saturating_sub(template_chars);
    let prompt = truncate_puzzle_prompt_segment(prompt, prompt_max_chars);
    let image_prompt = build_puzzle_image_prompt_text(level_name.as_str(), prompt.as_str());

    debug_assert!(
        image_prompt.chars().count() <= PUZZLE_TEXT_TO_IMAGE_PROMPT_MAX_CHARS,
        "puzzle image prompt should fit DashScope wan2.2 limit"
    );
    image_prompt
}

fn build_puzzle_image_prompt_text(_level_name: &str, prompt: &str) -> String {
    format!(
        concat!(
            "请生成一张高清插画。",
            "画面主体：{prompt}。",
            "画面要求：1:1",
            "主体要清晰集中，前中后景层次明确，局部细节丰富但不要杂乱，",
            "避免文字、水印、边框和 UI 元素。"
        ),
        prompt = prompt,
    )
}

fn truncate_puzzle_prompt_segment(value: &str, max_chars: usize) -> String {
    if value.chars().count() <= max_chars {
        return value.to_string();
    }

    const MARKER: &str = "...";
    if max_chars <= MARKER.chars().count() {
        return value.chars().take(max_chars).collect();
    }

    let keep_chars = max_chars - MARKER.chars().count();
    format!(
        "{}{MARKER}",
        value.chars().take(keep_chars).collect::<String>()
    )
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn build_puzzle_image_prompt_keeps_puzzle_asset_constraints() {
        let prompt = build_puzzle_image_prompt("雨夜神庙", "猫咪在发光遗迹前寻找线索");

        assert!(prompt.contains("猫咪在发光遗迹前寻找线索"));
        assert!(prompt.contains("1:1"));
        assert!(prompt.contains("主体要清晰集中"));
        assert!(prompt.contains("避免文字、水印、边框和 UI 元素"));
    }

    #[test]
    fn build_puzzle_image_prompt_trims_long_user_description_for_wan22() {
        let long_level_name = "雨夜神庙".repeat(20);
        let long_description =
            "发光遗迹、猫咪、漂浮碎片、雨水反光、远处灯塔、适合拼图切块。".repeat(50);
        let prompt = build_puzzle_image_prompt(long_level_name.as_str(), long_description.as_str());

        assert!(prompt.chars().count() <= PUZZLE_TEXT_TO_IMAGE_PROMPT_MAX_CHARS);
        assert!(prompt.contains("1:1"));
        assert!(prompt.contains("主体要清晰集中"));
        assert!(prompt.contains("避免文字、水印、边框和 UI 元素"));
    }

    #[test]
    fn default_negative_prompt_blocks_text_and_low_quality_assets() {
        assert!(PUZZLE_DEFAULT_NEGATIVE_PROMPT.contains("低清晰度"));
        assert!(PUZZLE_DEFAULT_NEGATIVE_PROMPT.contains("文字水印"));
    }
}