use std::collections::HashMap;

use chrono::Utc;
use sea_orm::{
    ActiveModelTrait, ColumnTrait, ConnectionTrait, DatabaseBackend, EntityTrait, PaginatorTrait,
    QueryFilter, Set, Statement, TransactionTrait,
};
use uuid::Uuid;

use crate::dto::{CompleteTaskReq, DelegateTaskReq, TaskResp};
use crate::engine::executor::FlowExecutor;
use crate::engine::parser;
use crate::entity::{process_definition, process_instance, task};
use crate::error::{WorkflowError, WorkflowResult};
use erp_core::audit::AuditLog;
use erp_core::audit_service;
use erp_core::events::EventBus;
use erp_core::types::Pagination;

/// 任务服务。
pub struct TaskService;

impl TaskService {
    /// 查询当前用户的待办任务。
    pub async fn list_pending(
        tenant_id: Uuid,
        assignee_id: Uuid,
        pagination: &Pagination,
        db: &sea_orm::DatabaseConnection,
    ) -> WorkflowResult<(Vec<TaskResp>, u64)> {
        let paginator = task::Entity::find()
            .filter(task::Column::TenantId.eq(tenant_id))
            .filter(task::Column::AssigneeId.eq(assignee_id))
            .filter(task::Column::Status.eq("pending"))
            .filter(task::Column::DeletedAt.is_null())
            .paginate(db, pagination.limit());

        let total = paginator
            .num_items()
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?;

        let page_index = pagination.page.unwrap_or(1).saturating_sub(1);
        let models = paginator
            .fetch_page(page_index)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?;

        let mut resps = Vec::new();
        for m in &models {
            let mut resp = Self::model_to_resp(m);
            // 附加实例信息
            if let Some(inst) = process_instance::Entity::find_by_id(m.instance_id)
                .one(db)
                .await
                .ok()
                .flatten()
            {
                resp.business_key = inst.business_key;
                if let Some(def) = process_definition::Entity::find_by_id(inst.definition_id)
                    .one(db)
                    .await
                    .ok()
                    .flatten()
                {
                    resp.definition_name = Some(def.name);
                }
            }
            resps.push(resp);
        }

        Ok((resps, total))
    }

    /// 查询当前用户的已办任务。
    pub async fn list_completed(
        tenant_id: Uuid,
        assignee_id: Uuid,
        pagination: &Pagination,
        db: &sea_orm::DatabaseConnection,
    ) -> WorkflowResult<(Vec<TaskResp>, u64)> {
        let paginator = task::Entity::find()
            .filter(task::Column::TenantId.eq(tenant_id))
            .filter(task::Column::AssigneeId.eq(assignee_id))
            .filter(task::Column::Status.is_in(["completed", "approved", "rejected", "delegated"]))
            .filter(task::Column::DeletedAt.is_null())
            .paginate(db, pagination.limit());

        let total = paginator
            .num_items()
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?;

        let page_index = pagination.page.unwrap_or(1).saturating_sub(1);
        let models = paginator
            .fetch_page(page_index)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?;

        let mut resps = Vec::new();
        for m in &models {
            let mut resp = Self::model_to_resp(m);
            if let Some(inst) = process_instance::Entity::find_by_id(m.instance_id)
                .one(db)
                .await
                .ok()
                .flatten()
            {
                resp.business_key = inst.business_key;
                if let Some(def) = process_definition::Entity::find_by_id(inst.definition_id)
                    .one(db)
                    .await
                    .ok()
                    .flatten()
                {
                    resp.definition_name = Some(def.name);
                }
            }
            resps.push(resp);
        }

        Ok((resps, total))
    }

    /// 完成任务：更新任务状态 + 推进 token。
    pub async fn complete(
        id: Uuid,
        tenant_id: Uuid,
        operator_id: Uuid,
        req: &CompleteTaskReq,
        db: &sea_orm::DatabaseConnection,
        event_bus: &EventBus,
    ) -> WorkflowResult<TaskResp> {
        let task_model = task::Entity::find_by_id(id)
            .one(db)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?
            .filter(|t| t.tenant_id == tenant_id && t.deleted_at.is_none())
            .ok_or_else(|| WorkflowError::NotFound(format!("任务不存在: {id}")))?;

        if task_model.status != "pending" {
            return Err(WorkflowError::InvalidState(
                "任务状态不是 pending，无法完成".to_string(),
            ));
        }

        // 验证操作者是当前处理人
        if task_model.assignee_id != Some(operator_id) {
            return Err(WorkflowError::InvalidState(
                "只有当前处理人才能完成任务".to_string(),
            ));
        }

        let instance_id = task_model.instance_id;
        let token_id = task_model.token_id;

        // 获取流程定义和流程图
        let instance = process_instance::Entity::find_by_id(instance_id)
            .one(db)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?
            .filter(|i| i.tenant_id == tenant_id && i.deleted_at.is_none())
            .ok_or_else(|| WorkflowError::NotFound(format!("流程实例不存在: {instance_id}")))?;

        let definition = process_definition::Entity::find_by_id(instance.definition_id)
            .one(db)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?
            .filter(|d| d.tenant_id == tenant_id && d.deleted_at.is_none())
            .ok_or_else(|| {
                WorkflowError::NotFound(format!("流程定义不存在: {}", instance.definition_id))
            })?;

        if instance.status != "running" {
            return Err(WorkflowError::InvalidState(format!(
                "流程实例状态不是 running: {}",
                instance.status
            )));
        }

        let nodes: Vec<crate::dto::NodeDef> = serde_json::from_value(definition.nodes.clone())
            .map_err(|e| WorkflowError::InvalidDiagram(format!("节点数据无效: {e}")))?;
        let edges: Vec<crate::dto::EdgeDef> = serde_json::from_value(definition.edges.clone())
            .map_err(|e| WorkflowError::InvalidDiagram(format!("连线数据无效: {e}")))?;
        let graph = parser::parse_and_validate(&nodes, &edges)?;

        // 准备变量（从 req.form_data 中提取）
        let mut variables = HashMap::new();
        if let Some(form) = &req.form_data
            && let Some(obj) = form.as_object()
        {
            for (k, v) in obj {
                variables.insert(k.clone(), v.clone());
            }
        }

        // 在事务中更新任务 + 推进 token
        let now = Utc::now();
        let outcome = req.outcome.clone();
        let form_data = req.form_data.clone();
        db.transaction::<_, (), WorkflowError>(|txn| {
            let graph = graph.clone();
            let variables = variables.clone();
            let task_model = task_model.clone();
            Box::pin(async move {
                // 更新任务状态
                let current_version = task_model.version;
                let mut active: task::ActiveModel = task_model.clone().into();
                active.status = Set("completed".to_string());
                active.outcome = Set(Some(outcome));
                active.form_data = Set(form_data);
                active.completed_at = Set(Some(now));
                active.version = Set(current_version + 1);
                active.updated_at = Set(now);
                active.updated_by = Set(operator_id);
                active
                    .update(txn)
                    .await
                    .map_err(|e| WorkflowError::Validation(e.to_string()))?;

                // 推进 token
                FlowExecutor::advance(token_id, instance_id, tenant_id, &graph, &variables, txn)
                    .await?;

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

        event_bus
            .publish(
                erp_core::events::DomainEvent::new(
                    "task.completed",
                    tenant_id,
                    serde_json::json!({
                        "task_id": id,
                        "instance_id": instance_id,
                        "started_by": instance.started_by,
                        "outcome": req.outcome,
                    }),
                ),
                db,
            )
            .await;

        audit_service::record(
            AuditLog::new(tenant_id, Some(operator_id), "task.complete", "task")
                .with_resource_id(id),
            db,
        )
        .await;

        // 重新查询任务
        let updated = task::Entity::find_by_id(id)
            .one(db)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?
            .ok_or_else(|| WorkflowError::NotFound(format!("任务不存在: {id}")))?;

        Ok(Self::model_to_resp(&updated))
    }

    /// 委派任务给其他人。
    pub async fn delegate(
        id: Uuid,
        tenant_id: Uuid,
        operator_id: Uuid,
        req: &DelegateTaskReq,
        db: &sea_orm::DatabaseConnection,
    ) -> WorkflowResult<TaskResp> {
        let task_model = task::Entity::find_by_id(id)
            .one(db)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?
            .filter(|t| t.tenant_id == tenant_id && t.deleted_at.is_none())
            .ok_or_else(|| WorkflowError::NotFound(format!("任务不存在: {id}")))?;

        if task_model.status != "pending" {
            return Err(WorkflowError::InvalidState(
                "任务状态不是 pending，无法委派".to_string(),
            ));
        }

        // 验证操作者是当前处理人
        if task_model.assignee_id != Some(operator_id) {
            return Err(WorkflowError::InvalidState(
                "只有当前处理人才能委派任务".to_string(),
            ));
        }

        // 验证目标用户属于同一租户（使用 raw SQL 避免跨模块依赖 erp-auth）
        let result = db.query_one(Statement::from_sql_and_values(
            DatabaseBackend::Postgres,
            "SELECT EXISTS(SELECT 1 FROM users WHERE id = $1 AND tenant_id = $2 AND deleted_at IS NULL AND status = 'active') AS ok",
            [req.delegate_to.into(), tenant_id.into()],
        ))
        .await
        .map_err(|e| WorkflowError::Validation(e.to_string()))?;

        let target_ok = result
            .and_then(|r| r.try_get::<bool>("", "ok").ok())
            .unwrap_or(false);

        if !target_ok {
            return Err(WorkflowError::Validation(
                "委派目标用户不存在或不属于当前租户".to_string(),
            ));
        }

        let current_version = task_model.version;
        let mut active: task::ActiveModel = task_model.into();
        active.assignee_id = Set(Some(req.delegate_to));
        active.version = Set(current_version + 1);
        active.updated_at = Set(Utc::now());
        active.updated_by = Set(operator_id);

        let updated = active
            .update(db)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?;

        audit_service::record(
            AuditLog::new(tenant_id, Some(operator_id), "task.delegate", "task")
                .with_resource_id(id),
            db,
        )
        .await;

        Ok(Self::model_to_resp(&updated))
    }

    /// 创建任务记录（由执行引擎调用）。
    #[allow(clippy::too_many_arguments)]
    pub async fn create_task(
        instance_id: Uuid,
        tenant_id: Uuid,
        token_id: Uuid,
        node_id: &str,
        node_name: Option<&str>,
        assignee_id: Option<Uuid>,
        candidate_groups: Option<Vec<String>>,
        db: &sea_orm::DatabaseConnection,
    ) -> WorkflowResult<Uuid> {
        let id = Uuid::now_v7();
        let now = Utc::now();
        let system_user = Uuid::nil();

        let model = task::ActiveModel {
            id: Set(id),
            tenant_id: Set(tenant_id),
            instance_id: Set(instance_id),
            token_id: Set(token_id),
            node_id: Set(node_id.to_string()),
            node_name: Set(node_name.map(|s| s.to_string())),
            assignee_id: Set(assignee_id),
            candidate_groups: Set(
                candidate_groups.map(|g| serde_json::to_value(g).unwrap_or_default())
            ),
            status: Set("pending".to_string()),
            outcome: Set(None),
            form_data: Set(None),
            due_date: Set(None),
            completed_at: Set(None),
            created_at: Set(now),
            updated_at: Set(now),
            created_by: Set(system_user),
            updated_by: Set(system_user),
            deleted_at: Set(None),
            version: Set(1),
        };
        model
            .insert(db)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?;

        Ok(id)
    }

    /// 认领任务：将 pending 状态的任务分配给当前用户。
    ///
    /// 适用于 candidate_groups 群组任务池中的任务，用户主动认领后
    /// 任务状态变为 in_progress，assignee_id 设置为认领用户。
    pub async fn claim(
        id: Uuid,
        tenant_id: Uuid,
        user_id: Uuid,
        db: &sea_orm::DatabaseConnection,
    ) -> WorkflowResult<TaskResp> {
        let task_model = task::Entity::find_by_id(id)
            .one(db)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?
            .filter(|t| t.tenant_id == tenant_id && t.deleted_at.is_none())
            .ok_or_else(|| WorkflowError::NotFound(format!("任务不存在: {id}")))?;

        if task_model.status != "pending" {
            return Err(WorkflowError::InvalidState(format!(
                "任务状态不是 pending（当前状态: {}），无法认领",
                task_model.status
            )));
        }

        let current_version = task_model.version;
        let mut active: task::ActiveModel = task_model.into();
        active.assignee_id = Set(Some(user_id));
        active.status = Set("in_progress".to_string());
        active.version = Set(current_version + 1);
        active.updated_at = Set(Utc::now());
        active.updated_by = Set(user_id);

        let updated = active
            .update(db)
            .await
            .map_err(|e| WorkflowError::Validation(e.to_string()))?;

        audit_service::record(
            AuditLog::new(tenant_id, Some(user_id), "task.claim", "task").with_resource_id(id),
            db,
        )
        .await;

        Ok(Self::model_to_resp(&updated))
    }

    fn model_to_resp(m: &task::Model) -> TaskResp {
        TaskResp {
            id: m.id,
            instance_id: m.instance_id,
            token_id: m.token_id,
            node_id: m.node_id.clone(),
            node_name: m.node_name.clone(),
            assignee_id: m.assignee_id,
            candidate_groups: m.candidate_groups.clone(),
            status: m.status.clone(),
            outcome: m.outcome.clone(),
            form_data: m.form_data.clone(),
            due_date: m.due_date,
            completed_at: m.completed_at,
            created_at: m.created_at,
            definition_name: None,
            business_key: None,
            version: m.version,
        }
    }
}