// 班级服务 — 创建班级、加入班级、班级查询

use chrono::{Months, Utc};
use sea_orm::{
    ActiveModelTrait, ColumnTrait, DatabaseConnection, EntityTrait, QueryFilter,
    Set, TransactionTrait,
};
use uuid::Uuid;

use crate::dto::{ClassMemberResp, ClassResp, ResetClassCodeResp};
use crate::entity::{class_member, school_class};
use crate::error::{DiaryError, DiaryResult};
use erp_core::events::{DomainEvent, EventBus};

use crate::event::DiaryEvent;

/// 班级服务 — 6 位码生成、过期控制、成员管理
pub struct ClassService;

impl ClassService {
    /// 创建班级（老师）
    ///
    /// 生成 6 位随机班级码，设置过期时间（6 个月后），
    /// 自动将老师加入 class_members。
    pub async fn create_class(
        tenant_id: Uuid,
        teacher_id: Uuid,
        name: String,
        school_name: Option<String>,
        db: &DatabaseConnection,
        event_bus: &EventBus,
    ) -> DiaryResult<ClassResp> {
        let now = Utc::now();
        let id = Uuid::now_v7();

        // 生成唯一班级码（最多重试 10 次）
        let class_code = Self::generate_unique_code(db).await?;

        // 过期时间：6 个月后
        let expires_at = now.checked_add_months(Months::new(6));

        // 事务：创建班级 + 老师自动加入（原子操作，保证一致性）
        let inserted_class = db
            .transaction::<_, school_class::Model, DiaryError>(|txn| {
                Box::pin(async move {
                    let class_model = school_class::ActiveModel {
                        id: Set(id),
                        tenant_id: Set(tenant_id),
                        name: Set(name),
                        school_name: Set(school_name),
                        teacher_id: Set(teacher_id),
                        class_code: Set(class_code),
                        member_count: Set(1), // 老师自动计入
                        is_active: Set(true),
                        expires_at: Set(expires_at),
                        created_at: Set(now),
                        updated_at: Set(now),
                        created_by: Set(teacher_id),
                        updated_by: Set(teacher_id),
                        deleted_at: Set(None),
                        version: Set(1),
                    };
                    let inserted = class_model.insert(txn).await?;

                    let member_model = class_member::ActiveModel {
                        class_id: Set(id),
                        user_id: Set(teacher_id),
                        tenant_id: Set(tenant_id),
                        role: Set("teacher".to_string()),
                        nickname: Set(None),
                        joined_at: Set(now),
                        created_at: Set(now),
                        updated_at: Set(now),
                        created_by: Set(teacher_id),
                        updated_by: Set(teacher_id),
                        deleted_at: Set(None),
                        version: Set(1),
                    };
                    member_model.insert(txn).await?;

                    Ok(inserted)
                })
            })
            .await?;

        // 发布 ClassCreated 事件
        event_bus
            .publish(
                DiaryEvent::ClassCreated {
                    class_id: id,
                    teacher_id,
                }
                .to_domain_event(tenant_id),
                db,
            )
            .await;

        Ok(class_model_to_resp(inserted_class))
    }

    /// 加入班级（学生通过班级码）
    ///
    /// 验证班级码有效性和过期状态，检查是否已是成员，
    /// 创建 class_member 记录并更新 member_count。
    /// 包含 Redis 错误锁定：连续 5 次错误后锁定 30 分钟。
    pub async fn join_class(
        tenant_id: Uuid,
        user_id: Uuid,
        class_code: String,
        nickname: Option<String>,
        db: &DatabaseConnection,
        redis: Option<&redis::Client>,
        event_bus: &EventBus,
    ) -> DiaryResult<ClassResp> {
        let now = Utc::now();
        let lock_key = format!("class_code_attempts:{user_id}");

        // 0. 检查错误锁定
        if let Some(redis_client) = redis {
            if let Ok(mut conn) = redis_client.get_multiplexed_async_connection().await {
                let attempts: i64 = redis::cmd("GET")
                    .arg(&lock_key)
                    .query_async(&mut conn)
                    .await
                    .unwrap_or(0);

                if attempts >= 5 {
                    let ttl: i64 = redis::cmd("TTL")
                        .arg(&lock_key)
                        .query_async(&mut conn)
                        .await
                        .unwrap_or(1800);
                    let lockout_minutes = (ttl.max(0) as u32 / 60).max(1);
                    return Err(DiaryError::ClassCodeLocked { lockout_minutes });
                }
            }
        }

        // 1. 查找班级码对应的班级
        let class_model = school_class::Entity::find()
            .filter(school_class::Column::ClassCode.eq(&class_code))
            .filter(school_class::Column::TenantId.eq(tenant_id))
            .filter(school_class::Column::DeletedAt.is_null())
            .one(db)
            .await?;

        // 班级码无效 → 增加错误计数
        let class_model = match class_model {
            Some(m) => m,
            None => {
                Self::increment_fail_count(redis, &lock_key).await;
                return Err(DiaryError::InvalidClassCode);
            }
        };

        // 2. 检查班级是否激活
        if !class_model.is_active {
            Self::increment_fail_count(redis, &lock_key).await;
            return Err(DiaryError::BadRequest("班级已停用".to_string()));
        }

        // 3. 检查是否过期
        if let Some(expires) = class_model.expires_at {
            if now > expires {
                Self::increment_fail_count(redis, &lock_key).await;
                return Err(DiaryError::ClassCodeExpired);
            }
        }

        let class_id = class_model.id;

        // 4. 检查是否已是成员
        let existing = class_member::Entity::find()
            .filter(class_member::Column::ClassId.eq(class_id))
            .filter(class_member::Column::UserId.eq(user_id))
            .filter(class_member::Column::DeletedAt.is_null())
            .one(db)
            .await?;

        if existing.is_some() {
            return Err(DiaryError::BadRequest("已是班级成员".to_string()));
        }

        // 5. 事务：创建成员记录 + 更新 member_count（原子操作）
        let current_count = class_model.member_count;
        let current_version = class_model.version;
        let updated_class = db
            .transaction::<_, school_class::Model, DiaryError>(|txn| {
                Box::pin(async move {
                    let member_model = class_member::ActiveModel {
                        class_id: Set(class_id),
                        user_id: Set(user_id),
                        tenant_id: Set(tenant_id),
                        role: Set("student".to_string()),
                        nickname: Set(nickname),
                        joined_at: Set(now),
                        created_at: Set(now),
                        updated_at: Set(now),
                        created_by: Set(user_id),
                        updated_by: Set(user_id),
                        deleted_at: Set(None),
                        version: Set(1),
                    };
                    member_model.insert(txn).await?;

                    let mut active_class: school_class::ActiveModel = class_model.into();
                    active_class.member_count = Set(current_count + 1);
                    active_class.updated_at = Set(now);
                    active_class.version = Set(current_version + 1);
                    let updated = active_class.update(txn).await?;

                    Ok(updated)
                })
            })
            .await?;

        // 7. 成功加入 → 清除错误计数
        if let Some(redis_client) = redis {
            if let Ok(mut conn) = redis_client.get_multiplexed_async_connection().await {
                let _: () = redis::cmd("DEL")
                    .arg(&lock_key)
                    .query_async(&mut conn)
                    .await
                    .unwrap_or(());
            }
        }

        // 8. 发布 StudentJoinedClass 事件
        event_bus
            .publish(
                DiaryEvent::StudentJoinedClass {
                    class_id,
                    student_id: user_id,
                }
                .to_domain_event(tenant_id),
                db,
            )
            .await;

        Ok(class_model_to_resp(updated_class))
    }

    /// 增加班级码验证失败计数（Redis INCR + 30分钟过期）
    async fn increment_fail_count(redis: Option<&redis::Client>, lock_key: &str) {
        if let Some(redis_client) = redis {
            if let Ok(mut conn) = redis_client.get_multiplexed_async_connection().await {
                let _: i64 = redis::cmd("INCR")
                    .arg(lock_key)
                    .query_async(&mut conn)
                    .await
                    .unwrap_or(0);
                // 设置 30 分钟过期（仅在第一次失败时设置，后续 INCR 不重置 TTL）
                let ttl: i64 = redis::cmd("TTL")
                    .arg(lock_key)
                    .query_async(&mut conn)
                    .await
                    .unwrap_or(-1);
                if ttl == -1 {
                    // key 存在但没有过期时间 → 设置 30 分钟
                    let _: () = redis::cmd("EXPIRE")
                        .arg(lock_key)
                        .arg(1800i64)
                        .query_async(&mut conn)
                        .await
                        .unwrap_or(());
                }
            }
        }
    }

    /// 获取班级详情
    pub async fn get_class(
        tenant_id: Uuid,
        class_id: Uuid,
        db: &DatabaseConnection,
    ) -> DiaryResult<ClassResp> {
        let model = school_class::Entity::find()
            .filter(school_class::Column::Id.eq(class_id))
            .filter(school_class::Column::TenantId.eq(tenant_id))
            .filter(school_class::Column::DeletedAt.is_null())
            .one(db)
            .await?
            .ok_or_else(|| DiaryError::NotFound(format!("班级 {} 不存在", class_id)))?;

        Ok(class_model_to_resp(model))
    }

    /// 获取班级成员列表
    pub async fn list_members(
        tenant_id: Uuid,
        class_id: Uuid,
        db: &DatabaseConnection,
    ) -> DiaryResult<Vec<ClassMemberResp>> {
        let members = class_member::Entity::find()
            .filter(class_member::Column::ClassId.eq(class_id))
            .filter(class_member::Column::TenantId.eq(tenant_id))
            .filter(class_member::Column::DeletedAt.is_null())
            .all(db)
            .await?;

        Ok(members.into_iter().map(member_model_to_resp).collect())
    }

    /// 获取我加入的班级列表
    pub async fn my_classes(
        tenant_id: Uuid,
        user_id: Uuid,
        db: &DatabaseConnection,
    ) -> DiaryResult<Vec<ClassResp>> {
        // 先查用户所在的班级 ID
        let memberships = class_member::Entity::find()
            .filter(class_member::Column::UserId.eq(user_id))
            .filter(class_member::Column::TenantId.eq(tenant_id))
            .filter(class_member::Column::DeletedAt.is_null())
            .all(db)
            .await?;

        let class_ids: Vec<Uuid> = memberships.iter().map(|m| m.class_id).collect();

        if class_ids.is_empty() {
            return Ok(vec![]);
        }

        let classes = school_class::Entity::find()
            .filter(school_class::Column::Id.is_in(class_ids))
            .filter(school_class::Column::TenantId.eq(tenant_id))
            .filter(school_class::Column::DeletedAt.is_null())
            .filter(school_class::Column::IsActive.eq(true))
            .all(db)
            .await?;

        Ok(classes.into_iter().map(class_model_to_resp).collect())
    }

    /// 获取租户下所有班级（管理端用）
    ///
    /// 仅限管理员/老师角色调用，返回租户内所有未删除的班级。
    pub async fn list_all_classes(
        tenant_id: Uuid,
        db: &DatabaseConnection,
    ) -> DiaryResult<Vec<ClassResp>> {
        let classes = school_class::Entity::find()
            .filter(school_class::Column::TenantId.eq(tenant_id))
            .filter(school_class::Column::DeletedAt.is_null())
            .all(db)
            .await?;

        Ok(classes.into_iter().map(class_model_to_resp).collect())
    }

    /// 更新班级信息（老师）
    ///
    /// 仅班级创建者（teacher_id）可修改班级名称和学校名称。
    /// 使用乐观锁防止并发冲突。
    pub async fn update_class(
        tenant_id: Uuid,
        user_id: Uuid,
        class_id: Uuid,
        name: Option<String>,
        school_name: Option<String>,
        version: i32,
        db: &DatabaseConnection,
    ) -> DiaryResult<ClassResp> {
        let model = school_class::Entity::find()
            .filter(school_class::Column::Id.eq(class_id))
            .filter(school_class::Column::TenantId.eq(tenant_id))
            .filter(school_class::Column::DeletedAt.is_null())
            .one(db)
            .await?
            .ok_or_else(|| DiaryError::NotFound(format!("班级 {} 不存在", class_id)))?;

        // 仅班级创建者可编辑
        if model.teacher_id != user_id {
            return Err(DiaryError::Forbidden);
        }

        // 乐观锁校验
        if model.version != version {
            return Err(DiaryError::VersionConflict {
                local: version,
                server: model.version,
            });
        }

        let now = Utc::now();
        let mut active: school_class::ActiveModel = model.into();
        if let Some(n) = name {
            if n.trim().is_empty() {
                return Err(DiaryError::Validation("班级名称不能为空".to_string()));
            }
            active.name = Set(n);
        }
        if let Some(s) = school_name {
            active.school_name = Set(Some(s));
        }
        active.updated_at = Set(now);
        active.updated_by = Set(user_id);
        active.version = Set(version + 1);

        let updated = active.update(db).await?;
        Ok(class_model_to_resp(updated))
    }

    /// 停用班级（老师）
    ///
    /// 将班级设为停用状态，学生将无法通过班级码加入。
    /// 已在班内的学生仍可查看班级内容。
    pub async fn deactivate_class(
        tenant_id: Uuid,
        user_id: Uuid,
        class_id: Uuid,
        db: &DatabaseConnection,
        event_bus: &EventBus,
    ) -> DiaryResult<ClassResp> {
        let model = school_class::Entity::find()
            .filter(school_class::Column::Id.eq(class_id))
            .filter(school_class::Column::TenantId.eq(tenant_id))
            .filter(school_class::Column::DeletedAt.is_null())
            .one(db)
            .await?
            .ok_or_else(|| DiaryError::NotFound(format!("班级 {} 不存在", class_id)))?;

        // 仅班级创建者可停用
        if model.teacher_id != user_id {
            return Err(DiaryError::Forbidden);
        }

        if !model.is_active {
            return Err(DiaryError::BadRequest("班级已处于停用状态".to_string()));
        }

        let now = Utc::now();
        let current_version = model.version;
        let mut active: school_class::ActiveModel = model.into();
        active.is_active = Set(false);
        active.updated_at = Set(now);
        active.updated_by = Set(user_id);
        active.version = Set(current_version + 1);
        let updated = active.update(db).await?;

        // 发布 ClassDeactivated 事件
        event_bus
            .publish(
                DomainEvent::new(
                    "diary.class.deactivated",
                    tenant_id,
                    serde_json::json!({
                        "class_id": class_id,
                        "teacher_id": user_id,
                    }),
                ),
                db,
            )
            .await;

        Ok(class_model_to_resp(updated))
    }

    /// 重置班级码（老师）
    ///
    /// 生成新的 6 位班级码，旧码立即失效。
    /// CLAUDE.md 要求："老师可随时重置"。
    pub async fn reset_class_code(
        tenant_id: Uuid,
        user_id: Uuid,
        class_id: Uuid,
        db: &DatabaseConnection,
    ) -> DiaryResult<ResetClassCodeResp> {
        let model = school_class::Entity::find()
            .filter(school_class::Column::Id.eq(class_id))
            .filter(school_class::Column::TenantId.eq(tenant_id))
            .filter(school_class::Column::DeletedAt.is_null())
            .one(db)
            .await?
            .ok_or_else(|| DiaryError::NotFound(format!("班级 {} 不存在", class_id)))?;

        // 仅班级创建者可重置班级码
        if model.teacher_id != user_id {
            return Err(DiaryError::Forbidden);
        }

        let new_code = Self::generate_unique_code(db).await?;
        let now = Utc::now();
        let current_version = model.version;

        let mut active: school_class::ActiveModel = model.into();
        active.class_code = Set(new_code.clone());
        // 重置过期时间为 6 个月
        active.expires_at = Set(now.checked_add_months(Months::new(6)));
        active.updated_at = Set(now);
        active.updated_by = Set(user_id);
        active.version = Set(current_version + 1);
        active.update(db).await?;

        Ok(ResetClassCodeResp {
            class_id,
            new_class_code: new_code,
        })
    }

    /// 生成唯一班级码（重试最多 10 次）
    async fn generate_unique_code(db: &DatabaseConnection) -> DiaryResult<String> {
        for _ in 0..10 {
            let code = generate_class_code();
            let exists = school_class::Entity::find()
                .filter(school_class::Column::ClassCode.eq(&code))
                .one(db)
                .await?
                .is_some();

            if !exists {
                return Ok(code);
            }
        }
        Err(DiaryError::Internal("无法生成唯一班级码".to_string()))
    }
}

/// 生成 6 位字母数字混合班级码（62^6 ≈ 568 亿种组合）
///
/// CLAUDE.md 要求"6 位字母数字混合（62^6 ≈ 568 亿种组合）"。
/// 使用 UUID v7 后 8 字节（随机部分）作为熵源，映射到 [0-9A-Za-z] 字符集。
/// 前 8 字节含时间戳，同毫秒内重复概率高，因此只用后 8 字节。
fn generate_class_code() -> String {
    const CHARSET: &[u8] = b"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
    let bytes = *Uuid::now_v7().as_bytes();
    let mut code = String::with_capacity(6);
    // UUID v7: bytes[0..8] = 时间戳, bytes[8..16] = 随机部分
    // 从随机部分取 6 个字节，避免同毫秒碰撞
    for i in 0..6 {
        code.push(CHARSET[(bytes[8 + i] as usize) % CHARSET.len()] as char);
    }
    code
}

/// school_class::Model -> ClassResp
fn class_model_to_resp(model: school_class::Model) -> ClassResp {
    ClassResp {
        id: model.id,
        name: model.name,
        school_name: model.school_name,
        teacher_id: model.teacher_id,
        class_code: model.class_code,
        member_count: model.member_count,
        is_active: model.is_active,
    }
}

/// class_member::Model -> ClassMemberResp
fn member_model_to_resp(model: class_member::Model) -> ClassMemberResp {
    ClassMemberResp {
        user_id: model.user_id,
        role: model.role,
        nickname: model.nickname,
        joined_at: model.joined_at,
    }
}

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

    // ===== 班级码生成测试 =====

    #[test]
    fn generate_class_code_is_6_chars() {
        let code = generate_class_code();
        assert_eq!(code.len(), 6, "班级码必须是 6 位");
    }

    #[test]
    fn generate_class_code_is_alphanumeric() {
        let code = generate_class_code();
        assert!(
            code.chars().all(|c| c.is_ascii_alphanumeric()),
            "班级码必须全部是字母数字"
        );
    }

    #[test]
    fn generate_class_code_is_unique() {
        let codes: std::collections::HashSet<String> = (0..100)
            .map(|_| generate_class_code())
            .collect();
        // 100 个码应该全部不同（概率上几乎确定）
        assert!(codes.len() > 90, "生成的班级码应该高度唯一");
    }

    // ===== 错误映射测试 =====

    #[test]
    fn invalid_class_code_error() {
        let err = DiaryError::InvalidClassCode;
        assert!(err.to_string().contains("无效"));
    }

    #[test]
    fn class_code_expired_error() {
        let err = DiaryError::ClassCodeExpired;
        assert!(err.to_string().contains("过期"));
    }

    #[test]
    fn class_code_locked_error() {
        let err = DiaryError::ClassCodeLocked {
            lockout_minutes: 30,
        };
        assert!(err.to_string().contains("30"));
    }
}