package gudusoft.gsqlparser.resolver2.inference;

import gudusoft.gsqlparser.nodes.TParseTreeNode;

/**
 * Represents a piece of evidence for column inference.
 *
 * <p>Evidence is collected from various sources in the SQL statement:
 * - Column references in WHERE clauses
 * - JOIN conditions
 * - SELECT list expressions
 * - INSERT statements (column lists)
 * - etc.
 *
 * <p>Each piece of evidence has a confidence weight that contributes
 * to the overall inference confidence.
 *
 * <p>Example:
 * <pre>
 * SELECT t1.* FROM t1 WHERE t1.id = 100
 *                              ^^
 * Evidence: "id" exists in t1 (from WHERE clause, high confidence)
 * </pre>
 */
public class InferenceEvidence {

    /** The inferred column name */
    private final String columnName;

    /** The table name this evidence relates to */
    private final String tableName;

    /** Type of evidence */
    private final EvidenceType evidenceType;

    /** Confidence weight [0.0, 1.0] */
    private final double confidence;

    /** Source AST node that provides this evidence */
    private final TParseTreeNode sourceNode;

    /** Description of how this evidence was obtained */
    private final String description;

    public InferenceEvidence(
            String columnName,
            String tableName,
            EvidenceType evidenceType,
            double confidence,
            TParseTreeNode sourceNode,
            String description) {
        this.columnName = columnName;
        this.tableName = tableName;
        this.evidenceType = evidenceType;
        this.confidence = Math.max(0.0, Math.min(1.0, confidence));
        this.sourceNode = sourceNode;
        this.description = description;
    }

    public String getColumnName() {
        return columnName;
    }

    public String getTableName() {
        return tableName;
    }

    public EvidenceType getEvidenceType() {
        return evidenceType;
    }

    public double getConfidence() {
        return confidence;
    }

    public TParseTreeNode getSourceNode() {
        return sourceNode;
    }

    public String getDescription() {
        return description;
    }

    /**
     * Create evidence from a qualified column reference.
     * Example: WHERE t1.id = 100
     */
    public static InferenceEvidence fromQualifiedReference(
            String columnName,
            String tableName,
            TParseTreeNode sourceNode) {
        return new InferenceEvidence(
            columnName,
            tableName,
            EvidenceType.QUALIFIED_REFERENCE,
            0.95,  // High confidence - explicit table reference
            sourceNode,
            "Qualified column reference: " + tableName + "." + columnName
        );
    }

    /**
     * Create evidence from an unqualified column reference.
     * Example: WHERE id = 100 (when only one table in scope)
     */
    public static InferenceEvidence fromUnqualifiedReference(
            String columnName,
            String tableName,
            TParseTreeNode sourceNode,
            int tableCount) {
        double confidence = tableCount == 1 ? 0.8 : 0.5;  // Lower if ambiguous
        return new InferenceEvidence(
            columnName,
            tableName,
            EvidenceType.UNQUALIFIED_REFERENCE,
            confidence,
            sourceNode,
            "Unqualified column reference: " + columnName + " (tables in scope: " + tableCount + ")"
        );
    }

    /**
     * Create evidence from a JOIN condition.
     * Example: JOIN t2 ON t1.id = t2.t1_id
     */
    public static InferenceEvidence fromJoinCondition(
            String columnName,
            String tableName,
            TParseTreeNode sourceNode) {
        return new InferenceEvidence(
            columnName,
            tableName,
            EvidenceType.JOIN_CONDITION,
            0.9,  // Very high confidence - explicit relationship
            sourceNode,
            "JOIN condition: " + tableName + "." + columnName
        );
    }

    /**
     * Create evidence from SELECT list.
     * Example: SELECT t1.name, t1.age FROM t1
     */
    public static InferenceEvidence fromSelectList(
            String columnName,
            String tableName,
            TParseTreeNode sourceNode) {
        return new InferenceEvidence(
            columnName,
            tableName,
            EvidenceType.SELECT_LIST,
            0.85,
            sourceNode,
            "SELECT list column: " + tableName + "." + columnName
        );
    }

    /**
     * Create evidence from INSERT statement column list.
     * Example: INSERT INTO t1 (id, name) VALUES (...)
     */
    public static InferenceEvidence fromInsertColumns(
            String columnName,
            String tableName,
            TParseTreeNode sourceNode) {
        return new InferenceEvidence(
            columnName,
            tableName,
            EvidenceType.INSERT_COLUMN_LIST,
            1.0,  // Perfect confidence - explicit column definition
            sourceNode,
            "INSERT column list: " + columnName
        );
    }

    /**
     * Create evidence from UPDATE statement.
     * Example: UPDATE t1 SET name = 'value'
     */
    public static InferenceEvidence fromUpdateSet(
            String columnName,
            String tableName,
            TParseTreeNode sourceNode) {
        return new InferenceEvidence(
            columnName,
            tableName,
            EvidenceType.UPDATE_SET,
            0.95,
            sourceNode,
            "UPDATE SET: " + columnName
        );
    }

    @Override
    public String toString() {
        return String.format("Evidence[%s.%s, type=%s, conf=%.2f]",
            tableName, columnName, evidenceType, confidence);
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (!(obj instanceof InferenceEvidence)) return false;
        InferenceEvidence other = (InferenceEvidence) obj;
        return columnName.equals(other.columnName) &&
               tableName.equals(other.tableName) &&
               evidenceType == other.evidenceType;
    }

    @Override
    public int hashCode() {
        int result = columnName.hashCode();
        result = 31 * result + tableName.hashCode();
        result = 31 * result + evidenceType.hashCode();
        return result;
    }
}