package api

import (
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/google/uuid"

	"work-queue-api/internal/model"
)

const timeLayout = time.RFC3339

var terminalStatuses = map[string]bool{"completed": true, "failed": true, "cancelled": true}

var validTransitions = map[string]map[string]bool{
	"queued":      {"dispatched": true, "cancelled": true},
	"dispatched":  {"in_progress": true, "cancelled": true},
	"in_progress": {"blocked": true, "completed": true, "failed": true},
	"blocked":     {"in_progress": true, "failed": true, "completed": true},
	"completed":   {},
	"failed":      {},
	"cancelled":   {},
}

type createWorkRequest struct {
	ProjectID     *string         `json:"project_id"`
	Type          string          `json:"type"`
	Description   string          `json:"description"`
	Payload       json.RawMessage `json:"payload"`
	Priority      *int            `json:"priority"`
	AssignedAgent *string         `json:"assigned_agent"`
	CreatedBy     *string         `json:"created_by"`
}

type patchWorkRequest struct {
	Status        *string `json:"status"`
	Outcome       *string `json:"outcome"`
	Notes         *string `json:"notes"`
	AssignedAgent *string `json:"assigned_agent"`
}

func (s *Server) handleCreateWork(w http.ResponseWriter, r *http.Request) {
	var req createWorkRequest
	if err := decodeJSON(r, &req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json body")
		return
	}
	if req.Type == "" || req.Description == "" {
		writeError(w, http.StatusBadRequest, "type and description are required")
		return
	}
	priority := 3
	if req.Priority != nil {
		priority = *req.Priority
	}
	if priority < 1 || priority > 5 {
		writeError(w, http.StatusBadRequest, "priority must be between 1 and 5")
		return
	}
	if req.ProjectID != nil {
		if _, err := s.fetchProject(*req.ProjectID); err == sql.ErrNoRows {
			writeError(w, http.StatusBadRequest, "project_id does not exist")
			return
		} else if err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
	}

	now := nowUTC()
	item := model.WorkItem{
		ID:            uuid.NewString(),
		ProjectID:     req.ProjectID,
		Type:          req.Type,
		Description:   req.Description,
		Priority:      priority,
		Status:        "queued",
		AssignedAgent: req.AssignedAgent,
		CreatedBy:     req.CreatedBy,
		CreatedAt:     now,
		UpdatedAt:     now,
	}
	payloadText := nullablePayload(req.Payload)
	if len(req.Payload) > 0 {
		_ = json.Unmarshal(req.Payload, &item.Payload)
	}

	_, err := s.db.Exec(`INSERT INTO work_items (id, project_id, type, description, payload, priority, status, assigned_agent, created_by, created_at, updated_at, completed_at, outcome, notes)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, NULL, NULL, NULL)`,
		item.ID, item.ProjectID, item.Type, item.Description, payloadText, item.Priority, item.Status, item.AssignedAgent, item.CreatedBy,
		item.CreatedAt.Format(timeLayout), item.UpdatedAt.Format(timeLayout),
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}

	writeJSON(w, http.StatusCreated, item)
}

func (s *Server) handleListWork(w http.ResponseWriter, r *http.Request) {
	query := `SELECT id, project_id, type, description, payload, priority, status, assigned_agent, created_by, created_at, updated_at, completed_at, outcome, notes FROM work_items`
	var where []string
	var args []any

	if status := r.URL.Query().Get("status"); status != "" {
		where = append(where, "status = ?")
		args = append(args, status)
	}
	if agent := r.URL.Query().Get("agent"); agent != "" {
		where = append(where, "assigned_agent = ?")
		args = append(args, agent)
	}
	if projectID := r.URL.Query().Get("project_id"); projectID != "" {
		where = append(where, "project_id = ?")
		args = append(args, projectID)
	}
	if since := r.URL.Query().Get("since"); since != "" {
		if _, err := time.Parse(timeLayout, since); err != nil {
			writeError(w, http.StatusBadRequest, "since must be ISO8601/RFC3339")
			return
		}
		where = append(where, "created_at > ?")
		args = append(args, since)
	}
	if len(where) > 0 {
		query += " WHERE " + strings.Join(where, " AND ")
	}
	if r.URL.Query().Get("since") != "" {
		query += " ORDER BY created_at ASC"
	} else {
		query += " ORDER BY priority ASC, created_at ASC"
	}

	rows, err := s.db.Query(query, args...)
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}
	defer rows.Close()

	var items []model.WorkItem
	for rows.Next() {
		item, err := scanWorkItem(rows)
		if err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		items = append(items, item)
	}

	writeJSON(w, http.StatusOK, items)
}

func (s *Server) handleGetWork(w http.ResponseWriter, r *http.Request) {
	item, err := s.fetchWorkItem(chi.URLParam(r, "id"))
	if err == sql.ErrNoRows {
		writeError(w, http.StatusNotFound, "work item not found")
		return
	}
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}

	logs, err := s.fetchDispatchLogs(item.ID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}
	item.DispatchLog = logs

	writeJSON(w, http.StatusOK, item)
}

func (s *Server) handlePatchWork(w http.ResponseWriter, r *http.Request) {
	id := chi.URLParam(r, "id")
	item, err := s.fetchWorkItem(id)
	if err == sql.ErrNoRows {
		writeError(w, http.StatusNotFound, "work item not found")
		return
	}
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}

	var req patchWorkRequest
	if err := decodeJSON(r, &req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json body")
		return
	}

	if req.AssignedAgent != nil {
		item.AssignedAgent = req.AssignedAgent
	}
	if req.Notes != nil {
		item.Notes = req.Notes
	}

	if req.Status != nil {
		if err := applyStatusTransition(&item, *req.Status, req.Outcome, req.Notes); err != nil {
			writeError(w, http.StatusBadRequest, err.Error())
			return
		}
	}
	item.UpdatedAt = nowUTC()

	if err := s.persistPatchedWork(item, req.Status); err != nil {
		if isUniqueConstraint(err) {
			writeError(w, http.StatusConflict, "agent already has an in_progress work item")
			return
		}
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}

	writeJSON(w, http.StatusOK, item)
}

func (s *Server) handleDeleteWork(w http.ResponseWriter, r *http.Request) {
	item, err := s.fetchWorkItem(chi.URLParam(r, "id"))
	if err == sql.ErrNoRows {
		writeError(w, http.StatusNotFound, "work item not found")
		return
	}
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}
	if item.Status != "queued" && item.Status != "dispatched" {
		writeError(w, http.StatusBadRequest, "only queued or dispatched items can be cancelled")
		return
	}
	outcome := "cancelled"
	if err := applyStatusTransition(&item, "cancelled", &outcome, nil); err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}
	item.UpdatedAt = nowUTC()

	if err := s.persistPatchedWork(item, ptr("cancelled")); err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}

	w.WriteHeader(http.StatusNoContent)
}

func applyStatusTransition(item *model.WorkItem, nextStatus string, outcome *string, notes *string) error {
	nextStatus = strings.TrimSpace(nextStatus)
	if !validTransitions[item.Status][nextStatus] {
		return fmt.Errorf("invalid status transition: %s -> %s", item.Status, nextStatus)
	}
	if item.Status == "queued" && nextStatus == "dispatched" && item.AssignedAgent == nil {
		return errors.New("assigned_agent is required for queued -> dispatched")
	}
	if nextStatus == "blocked" && (notes == nil || strings.TrimSpace(*notes) == "") {
		return errors.New("notes are required when status is blocked")
	}
	if (nextStatus == "completed" || nextStatus == "failed" || nextStatus == "cancelled") && outcome == nil {
		return errors.New("outcome is required for terminal statuses")
	}
	if nextStatus == "completed" && *outcome != "success" {
		return errors.New("completed requires outcome=success")
	}
	if nextStatus == "failed" && *outcome != "failed" {
		return errors.New("failed requires outcome=failed")
	}
	if nextStatus == "cancelled" && *outcome != "cancelled" {
		return errors.New("cancelled requires outcome=cancelled")
	}

	item.Status = nextStatus
	if terminalStatuses[nextStatus] {
		now := nowUTC()
		item.CompletedAt = &now
		item.Outcome = outcome
	} else {
		item.CompletedAt = nil
		item.Outcome = nil
	}
	return nil
}

func (s *Server) persistPatchedWork(item model.WorkItem, requestedStatus *string) error {
	tx, err := s.db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	_, err = tx.Exec(`UPDATE work_items
		SET project_id = ?, type = ?, description = ?, payload = ?, priority = ?, status = ?, assigned_agent = ?, created_by = ?, created_at = ?, updated_at = ?, completed_at = ?, outcome = ?, notes = ?
		WHERE id = ?`,
		item.ProjectID, item.Type, item.Description, marshalPayload(item.Payload), item.Priority, item.Status, item.AssignedAgent, item.CreatedBy,
		item.CreatedAt.Format(timeLayout), item.UpdatedAt.Format(timeLayout), formatNullTime(item.CompletedAt), item.Outcome, item.Notes, item.ID,
	)
	if err != nil {
		return err
	}

	if requestedStatus != nil && *requestedStatus == "dispatched" {
		_, err = tx.Exec(`INSERT INTO dispatch_log (id, work_item_id, dispatched_at, agent, completed_at, outcome) VALUES (?, ?, ?, ?, NULL, NULL)`,
			uuid.NewString(), item.ID, item.UpdatedAt.Format(timeLayout), deref(item.AssignedAgent),
		)
		if err != nil {
			return err
		}
	}
	if requestedStatus != nil && terminalStatuses[*requestedStatus] {
		_, err = tx.Exec(`UPDATE dispatch_log SET completed_at = ?, outcome = ? WHERE work_item_id = ? AND completed_at IS NULL`,
			formatNullTime(item.CompletedAt), item.Outcome, item.ID,
		)
		if err != nil {
			return err
		}
	}

	return tx.Commit()
}

func (s *Server) fetchWorkItem(id string) (model.WorkItem, error) {
	row := s.db.QueryRow(`SELECT id, project_id, type, description, payload, priority, status, assigned_agent, created_by, created_at, updated_at, completed_at, outcome, notes FROM work_items WHERE id = ?`, id)
	return scanWorkItem(row)
}

func (s *Server) fetchDispatchLogs(workItemID string) ([]model.DispatchLog, error) {
	rows, err := s.db.Query(`SELECT id, work_item_id, dispatched_at, agent, completed_at, outcome FROM dispatch_log WHERE work_item_id = ? ORDER BY dispatched_at ASC`, workItemID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var logs []model.DispatchLog
	for rows.Next() {
		var log model.DispatchLog
		var dispatchedAt, completedAt sql.NullString
		var outcome sql.NullString
		if err := rows.Scan(&log.ID, &log.WorkItemID, &dispatchedAt, &log.Agent, &completedAt, &outcome); err != nil {
			return nil, err
		}
		log.DispatchedAt, err = time.Parse(timeLayout, dispatchedAt.String)
		if err != nil {
			return nil, err
		}
		if completedAt.Valid {
			parsed, err := time.Parse(timeLayout, completedAt.String)
			if err != nil {
				return nil, err
			}
			log.CompletedAt = &parsed
		}
		if outcome.Valid {
			log.Outcome = &outcome.String
		}
		logs = append(logs, log)
	}
	return logs, rows.Err()
}

func scanProject(scanner interface{ Scan(dest ...any) error }) (model.Project, error) {
	var project model.Project
	var externalRef sql.NullString
	var createdAt, updatedAt string
	if err := scanner.Scan(&project.ID, &project.Name, &externalRef, &createdAt, &updatedAt); err != nil {
		return project, err
	}
	if externalRef.Valid {
		project.ExternalRef = &externalRef.String
	}
	var err error
	project.CreatedAt, err = time.Parse(timeLayout, createdAt)
	if err != nil {
		return project, err
	}
	project.UpdatedAt, err = time.Parse(timeLayout, updatedAt)
	return project, err
}

func scanWorkItem(scanner interface{ Scan(dest ...any) error }) (model.WorkItem, error) {
	var item model.WorkItem
	var projectID, payload, assignedAgent, createdBy, completedAt, outcome, notes sql.NullString
	var createdAt, updatedAt string
	if err := scanner.Scan(&item.ID, &projectID, &item.Type, &item.Description, &payload, &item.Priority, &item.Status, &assignedAgent, &createdBy, &createdAt, &updatedAt, &completedAt, &outcome, &notes); err != nil {
		return item, err
	}
	if projectID.Valid {
		item.ProjectID = &projectID.String
	}
	if payload.Valid && payload.String != "" {
		var decoded any
		if err := json.Unmarshal([]byte(payload.String), &decoded); err == nil {
			item.Payload = decoded
		}
	}
	if assignedAgent.Valid {
		item.AssignedAgent = &assignedAgent.String
	}
	if createdBy.Valid {
		item.CreatedBy = &createdBy.String
	}
	if notes.Valid {
		item.Notes = &notes.String
	}
	var err error
	item.CreatedAt, err = time.Parse(timeLayout, createdAt)
	if err != nil {
		return item, err
	}
	item.UpdatedAt, err = time.Parse(timeLayout, updatedAt)
	if err != nil {
		return item, err
	}
	if completedAt.Valid {
		parsed, err := time.Parse(timeLayout, completedAt.String)
		if err != nil {
			return item, err
		}
		item.CompletedAt = &parsed
	}
	if outcome.Valid {
		item.Outcome = &outcome.String
	}
	return item, nil
}

func nullablePayload(payload json.RawMessage) any {
	if len(payload) == 0 {
		return nil
	}
	return string(payload)
}

func marshalPayload(payload any) any {
	if payload == nil {
		return nil
	}
	bytes, err := json.Marshal(payload)
	if err != nil {
		return nil
	}
	return string(bytes)
}

func formatNullTime(t *time.Time) any {
	if t == nil {
		return nil
	}
	return t.Format(timeLayout)
}

func ptr(s string) *string { return &s }
func deref(s *string) string {
	if s == nil {
		return ""
	}
	return *s
}

func isUniqueConstraint(err error) bool {
	if err == nil {
		return false
	}
	return strings.Contains(strings.ToLower(err.Error()), "unique constraint failed")
}