package sqlite

import (
	"context"
	"database/sql"
	"fmt"
	"strings"

	"github.com/steveyegge/beads/internal/types"
)

// GetReadyWork returns issues with no open blockers
// By default, shows both 'open' and 'in_progress' issues so epics/tasks
// ready to close are visible (bd-165)
func (s *SQLiteStorage) GetReadyWork(ctx context.Context, filter types.WorkFilter) ([]*types.Issue, error) {
	whereClauses := []string{}
	args := []interface{}{}

	// Default to open OR in_progress if not specified (bd-165)
	if filter.Status == "" {
		whereClauses = append(whereClauses, "i.status IN ('open', 'in_progress')")
	} else {
		whereClauses = append(whereClauses, "i.status = ?")
		args = append(args, filter.Status)
	}

	if filter.Priority != nil {
		whereClauses = append(whereClauses, "i.priority = ?")
		args = append(args, *filter.Priority)
	}

	if filter.Assignee != nil {
		whereClauses = append(whereClauses, "i.assignee = ?")
		args = append(args, *filter.Assignee)
	}

	// Build WHERE clause properly
	whereSQL := strings.Join(whereClauses, " AND ")

	// Build LIMIT clause using parameter
	limitSQL := ""
	if filter.Limit > 0 {
		limitSQL = " LIMIT ?"
		args = append(args, filter.Limit)
	}

	// Default to hybrid sort for backwards compatibility
	sortPolicy := filter.SortPolicy
	if sortPolicy == "" {
		sortPolicy = types.SortPolicyHybrid
	}
	orderBySQL := buildOrderByClause(sortPolicy)

	// Query with recursive CTE to propagate blocking through parent-child hierarchy
	// Algorithm:
	// 1. Find issues directly blocked by 'blocks' dependencies
	// 2. Recursively propagate blockage to all descendants via 'parent-child' links
	// 3. Exclude all blocked issues (both direct and transitive) from ready work
	query := fmt.Sprintf(`
		WITH RECURSIVE
		  -- Step 1: Find issues blocked directly by dependencies
		  blocked_directly AS (
		    SELECT DISTINCT d.issue_id
		    FROM dependencies d
		    JOIN issues blocker ON d.depends_on_id = blocker.id
		    WHERE d.type = 'blocks'
		      AND blocker.status IN ('open', 'in_progress', 'blocked')
		  ),

		  -- Step 2: Propagate blockage to all descendants via parent-child
		  blocked_transitively AS (
		    -- Base case: directly blocked issues
		    SELECT issue_id, 0 as depth
		    FROM blocked_directly

		    UNION ALL

		    -- Recursive case: children of blocked issues inherit blockage
		    SELECT d.issue_id, bt.depth + 1
		    FROM blocked_transitively bt
		    JOIN dependencies d ON d.depends_on_id = bt.issue_id
		    WHERE d.type = 'parent-child'
		      AND bt.depth < 50
		  )

		-- Step 3: Select ready issues (excluding all blocked)
		SELECT i.id, i.title, i.description, i.design, i.acceptance_criteria, i.notes,
		i.status, i.priority, i.issue_type, i.assignee, i.estimated_minutes,
		i.created_at, i.updated_at, i.closed_at, i.external_ref
		FROM issues i
		WHERE %s
		AND NOT EXISTS (
		SELECT 1 FROM blocked_transitively WHERE issue_id = i.id
		)
		%s
		%s
	`, whereSQL, orderBySQL, limitSQL)

	rows, err := s.db.QueryContext(ctx, query, args...)
	if err != nil {
		return nil, fmt.Errorf("failed to get ready work: %w", err)
	}
	defer func() { _ = rows.Close() }()

	return s.scanIssues(ctx, rows)
}

// GetBlockedIssues returns issues that are blocked by dependencies
func (s *SQLiteStorage) GetBlockedIssues(ctx context.Context) ([]*types.BlockedIssue, error) {
	// Use GROUP_CONCAT to get all blocker IDs in a single query (no N+1)
	rows, err := s.db.QueryContext(ctx, `
		SELECT
		    i.id, i.title, i.description, i.design, i.acceptance_criteria, i.notes,
		    i.status, i.priority, i.issue_type, i.assignee, i.estimated_minutes,
		    i.created_at, i.updated_at, i.closed_at, i.external_ref,
		    COUNT(d.depends_on_id) as blocked_by_count,
		    GROUP_CONCAT(d.depends_on_id, ',') as blocker_ids
		FROM issues i
		JOIN dependencies d ON i.id = d.issue_id
		JOIN issues blocker ON d.depends_on_id = blocker.id
		WHERE i.status IN ('open', 'in_progress', 'blocked')
		  AND d.type = 'blocks'
		  AND blocker.status IN ('open', 'in_progress', 'blocked')
		GROUP BY i.id
		ORDER BY i.priority ASC
	`)
	if err != nil {
		return nil, fmt.Errorf("failed to get blocked issues: %w", err)
	}
	defer func() { _ = rows.Close() }()

	var blocked []*types.BlockedIssue
	for rows.Next() {
		var issue types.BlockedIssue
		var closedAt sql.NullTime
		var estimatedMinutes sql.NullInt64
		var assignee sql.NullString
		var externalRef sql.NullString
		var blockerIDsStr string

		err := rows.Scan(
			&issue.ID, &issue.Title, &issue.Description, &issue.Design,
			&issue.AcceptanceCriteria, &issue.Notes, &issue.Status,
			&issue.Priority, &issue.IssueType, &assignee, &estimatedMinutes,
			&issue.CreatedAt, &issue.UpdatedAt, &closedAt, &externalRef, &issue.BlockedByCount,
			&blockerIDsStr,
		)
		if err != nil {
			return nil, fmt.Errorf("failed to scan blocked issue: %w", err)
		}

		if closedAt.Valid {
			issue.ClosedAt = &closedAt.Time
		}
		if estimatedMinutes.Valid {
			mins := int(estimatedMinutes.Int64)
			issue.EstimatedMinutes = &mins
		}
		if assignee.Valid {
			issue.Assignee = assignee.String
		}
		if externalRef.Valid {
			issue.ExternalRef = &externalRef.String
		}

		// Parse comma-separated blocker IDs
		if blockerIDsStr != "" {
			issue.BlockedBy = strings.Split(blockerIDsStr, ",")
		}

		blocked = append(blocked, &issue)
	}

	return blocked, nil
}

// buildOrderByClause generates the ORDER BY clause based on sort policy
func buildOrderByClause(policy types.SortPolicy) string {
	switch policy {
	case types.SortPolicyPriority:
		return `ORDER BY i.priority ASC, i.created_at ASC`

	case types.SortPolicyOldest:
		return `ORDER BY i.created_at ASC`

	case types.SortPolicyHybrid:
		fallthrough
	default:
		return `ORDER BY
			CASE
				WHEN datetime(i.created_at) >= datetime('now', '-48 hours') THEN 0
				ELSE 1
			END ASC,
			CASE
				WHEN datetime(i.created_at) >= datetime('now', '-48 hours') THEN i.priority
				ELSE NULL
			END ASC,
			CASE
				WHEN datetime(i.created_at) < datetime('now', '-48 hours') THEN i.created_at
				ELSE NULL
			END ASC,
			i.created_at ASC`
	}
}