package repository

import (
	"context"
	"fmt"
)

const lessonReorderSortBump int32 = 1_000_000

// ReorderExamPrepCatalogCourses sets sort_order to 1..n for all catalog course rows (transactional).
func (s *Store) ReorderExamPrepCatalogCourses(ctx context.Context, orderedIDs []int64) error {
	tx, err := s.conn.Begin(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = tx.Rollback(ctx) }()
	for i, id := range orderedIDs {
		tag, err := tx.Exec(ctx, `
UPDATE exam_prep.catalog_courses
SET sort_order = $1,
    updated_at = CURRENT_TIMESTAMP
WHERE id = $2`, int32(i+1), id)
		if err != nil {
			return err
		}
		if tag.RowsAffected() == 0 {
			return fmt.Errorf("exam prep catalog course id %d not found", id)
		}
	}
	return tx.Commit(ctx)
}

// ReorderExamPrepUnitsInCatalogCourse sets sort_order to 1..n for units under catalogCourseID.
func (s *Store) ReorderExamPrepUnitsInCatalogCourse(ctx context.Context, catalogCourseID int64, orderedIDs []int64) error {
	tx, err := s.conn.Begin(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = tx.Rollback(ctx) }()
	for i, id := range orderedIDs {
		tag, err := tx.Exec(ctx, `
UPDATE exam_prep.units
SET sort_order = $1,
    updated_at = CURRENT_TIMESTAMP
WHERE id = $2
  AND catalog_course_id = $3`, int32(i+1), id, catalogCourseID)
		if err != nil {
			return err
		}
		if tag.RowsAffected() == 0 {
			return fmt.Errorf("unit id %d not in catalog course %d", id, catalogCourseID)
		}
	}
	return tx.Commit(ctx)
}

// ReorderExamPrepUnitModulesInUnit sets sort_order to 1..n for modules under unitID.
func (s *Store) ReorderExamPrepUnitModulesInUnit(ctx context.Context, unitID int64, orderedIDs []int64) error {
	tx, err := s.conn.Begin(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = tx.Rollback(ctx) }()
	for i, id := range orderedIDs {
		tag, err := tx.Exec(ctx, `
UPDATE exam_prep.unit_modules
SET sort_order = $1,
    updated_at = CURRENT_TIMESTAMP
WHERE id = $2
  AND unit_id = $3`, int32(i+1), id, unitID)
		if err != nil {
			return err
		}
		if tag.RowsAffected() == 0 {
			return fmt.Errorf("module id %d not in unit %d", id, unitID)
		}
	}
	return tx.Commit(ctx)
}

// ReorderExamPrepUnitModuleLessonsInUnitModule sets sort_order to 1..n under unitModuleID.
// Uses an intermediate bump so UNIQUE (unit_module_id, sort_order) is never violated mid-reorder.
func (s *Store) ReorderExamPrepUnitModuleLessonsInUnitModule(ctx context.Context, unitModuleID int64, orderedIDs []int64) error {
	tx, err := s.conn.Begin(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = tx.Rollback(ctx) }()

	if _, err := tx.Exec(ctx, `
UPDATE exam_prep.unit_module_lessons
SET sort_order = sort_order + $1,
    updated_at = CURRENT_TIMESTAMP
WHERE unit_module_id = $2`, lessonReorderSortBump, unitModuleID); err != nil {
		return err
	}

	for i, id := range orderedIDs {
		tag, err := tx.Exec(ctx, `
UPDATE exam_prep.unit_module_lessons
SET sort_order = $1,
    updated_at = CURRENT_TIMESTAMP
WHERE id = $2
  AND unit_module_id = $3`, int32(i+1), id, unitModuleID)
		if err != nil {
			return err
		}
		if tag.RowsAffected() == 0 {
			return fmt.Errorf("lesson id %d not in exam prep module %d", id, unitModuleID)
		}
	}
	return tx.Commit(ctx)
}