/**
 * CSV Validation utilities
 * Checks for required fields and data quality
 */

export interface ValidationResult {
    isValid: boolean;
    errors: string[];
    warnings: string[];
}

export interface FieldValidation {
    found: boolean;
    fieldName?: string;
    nonNullCount: number;
    nonZeroCount: number;
    totalRows: number;
}

/**
 * Validate CSV structure and required fields
 * @param data - Parsed CSV data array
 * @returns Validation result with errors and warnings
 */
export function validateCSV(data: any[]): ValidationResult {
    const errors: string[] = [];
    const warnings: string[] = [];

    if (!data || data.length === 0) {
        errors.push('CSV file is empty or contains no valid data rows.');
        return { isValid: false, errors, warnings };
    }

    const totalRows = data.length;

    // Required fields validation
    const dateField = validateField(data, ['Date', 'Activity Date', 'date']);
    const timeField = validateField(data, ['Time', 'Duration', 'Moving Time', 'Elapsed Time']);
    const activityTypeField = validateField(data, ['Activity Type', 'Type', 'Sport']);

    // Check required fields
    if (!dateField.found) {
        errors.push('Missing required field: "Date". Expected column names: Date, Activity Date, or date.');
    } else if (dateField.nonNullCount === 0) {
        errors.push(`Field "${dateField.fieldName}" has no valid values (all rows are empty or "--").`);
    } else if (dateField.nonNullCount < totalRows) {
        warnings.push(`Field "${dateField.fieldName}": ${totalRows - dateField.nonNullCount} out of ${totalRows} rows have missing dates.`);
    }

    if (!timeField.found) {
        errors.push('Missing required field: "Time" or "Duration". Expected column names: Time, Duration, Moving Time, or Elapsed Time.');
    } else if (timeField.nonNullCount === 0) {
        errors.push(`Field "${timeField.fieldName}" has no valid values (all rows are empty or "--").`);
    } else if (timeField.nonNullCount < totalRows) {
        warnings.push(`Field "${timeField.fieldName}": ${totalRows - timeField.nonNullCount} out of ${totalRows} rows have missing duration.`);
    }

    if (!activityTypeField.found) {
        errors.push('Missing required field: "Activity Type". Expected column names: Activity Type, Type, or Sport.');
    } else if (activityTypeField.nonNullCount === 0) {
        errors.push(`Field "${activityTypeField.fieldName}" has no valid values (all rows are empty or "--").`);
    }

    // Optional but important fields validation
    const distanceField = validateField(data, ['Distance', 'distance']);
    const normalizedPowerField = validateFieldByPrefix(data, 'Normalized Power');

    // Distance warnings
    if (!distanceField.found) {
        warnings.push('Optional field "Distance" is missing. Distance-based ACWR chart will be empty.');
    } else if (distanceField.nonZeroCount === 0) {
        warnings.push('Field "Distance" exists but all values are 0 or empty. Distance-based ACWR chart will be empty.');
    } else if (distanceField.nonZeroCount < totalRows * 0.5) {
        warnings.push(`Field "Distance": Only ${distanceField.nonZeroCount} out of ${totalRows} activities have distance values.`);
    }

    // Power/TSS warnings
    const tssField = validateFieldByPrefix(data, 'Training Stress Score');

    if (!normalizedPowerField.found && !tssField.found) {
        warnings.push('Neither "Normalized Power" nor "Training Stress Score" fields found. TSS will be calculated using default FTP (343W). Ensure activities have Normalized Power data for accurate TSS calculation.');
    } else if (normalizedPowerField.found && normalizedPowerField.nonZeroCount === 0) {
        warnings.push('Field "Normalized Power" exists but all values are 0 or empty. TSS calculation may be limited.');
    } else if (normalizedPowerField.found && normalizedPowerField.nonZeroCount < totalRows * 0.3) {
        warnings.push(`Field "Normalized Power": Only ${normalizedPowerField.nonZeroCount} out of ${totalRows} activities have power data. TSS-based ACWR will have limited data.`);
    }

    // Summary
    if (errors.length === 0 && warnings.length === 0) {
        warnings.push(`✓ CSV validation passed. Successfully found ${totalRows} activities with all required fields.`);
    }

    return {
        isValid: errors.length === 0,
        errors,
        warnings,
    };
}

/**
 * Validate a field by checking multiple possible column names
 */
function validateField(data: any[], possibleNames: string[]): FieldValidation {
    for (const name of possibleNames) {
        if (data[0] && name in data[0]) {
            const nonNullCount = data.filter(row => {
                const value = row[name];
                return value && value !== '--' && value !== '';
            }).length;

            const nonZeroCount = data.filter(row => {
                const value = row[name];
                if (!value || value === '--' || value === '') return false;
                const parsed = parseFloat(value);
                return !isNaN(parsed) && parsed !== 0;
            }).length;

            return {
                found: true,
                fieldName: name,
                nonNullCount,
                nonZeroCount,
                totalRows: data.length,
            };
        }
    }

    return {
        found: false,
        nonNullCount: 0,
        nonZeroCount: 0,
        totalRows: data.length,
    };
}

/**
 * Validate a field by checking if any column name starts with a prefix
 */
function validateFieldByPrefix(data: any[], prefix: string): FieldValidation {
    if (!data[0]) {
        return {
            found: false,
            nonNullCount: 0,
            nonZeroCount: 0,
            totalRows: data.length,
        };
    }

    const fieldName = Object.keys(data[0]).find(key => key.startsWith(prefix));

    if (!fieldName) {
        return {
            found: false,
            nonNullCount: 0,
            nonZeroCount: 0,
            totalRows: data.length,
        };
    }

    const nonNullCount = data.filter(row => {
        const value = row[fieldName];
        return value && value !== '--' && value !== '';
    }).length;

    const nonZeroCount = data.filter(row => {
        const value = row[fieldName];
        if (!value || value === '--' || value === '') return false;
        const parsed = parseFloat(value);
        return !isNaN(parsed) && parsed !== 0;
    }).length;

    return {
        found: true,
        fieldName,
        nonNullCount,
        nonZeroCount,
        totalRows: data.length,
    };
}