noob-components/packages/base/data/list-table-v2/usePretextColumnWidths.ts

/**
 * usePretextColumnWidths
 *
 * Computes flex-based column width parameters using pretext text measurement.
 * - flexBasis: mean (μ) of measured widths + padding
 * - flexGrow/flexShrink: derived from variance (σ²)
 * - minWidth: max(μ - 2*σ, 50) + padding
 * - maxWidth: unconstrained by default
 *
 * User can override any parameter via column definition.
 */
import { computed, type Ref } from "vue";
import { measureShrinkWrapWidth } from "./measureText";
import type { ListTableColumn } from "./types";

const DEFAULT_FONT = "14px Inter, sans-serif";
const DEFAULT_HEADER_FONT = "bold 14px Inter, sans-serif";
const DEFAULT_PADDING = 16;
const CELL_PADDING = DEFAULT_PADDING * 2; // left + right
const MAX_WIDTH = Number.POSITIVE_INFINITY;
const MIN_BASE_WIDTH = 50;
const MIN_AUTO_FLEX = 1.1;
const MAX_AUTO_FLEX = 2;

export interface ColumnFlexConfig {
  key: string;
  flexBasis: number;
  flexGrow: number;
  flexShrink: number;
  minWidth: number;
  maxWidth: number;
  measuredMean: number;
  measuredVariance: number;
  measuredSampleCount: number;
}

/**
 * Sample rows evenly distributed across the dataset.
 * Takes first, last, and evenly spaced rows in between.
 */
function sampleRows<T>(data: T[], sampleSize: number): T[] {
  if (data.length <= sampleSize) return data;
  const result: T[] = [];
  const step = (data.length - 1) / (sampleSize - 1);
  for (let i = 0; i < sampleSize; i++) {
    result.push(data[Math.round(i * step)]);
  }
  return result;
}

/**
 * Compute mean and variance of an array of numbers
 */
function computeStats(widths: number[]): { mean: number; variance: number } {
  if (widths.length === 0) return { mean: 0, variance: 0 };

  const mean = widths.reduce((sum, w) => sum + w, 0) / widths.length;
  const variance = widths.reduce((sum, w) => sum + Math.pow(w - mean, 2), 0) / widths.length;

  return { mean, variance };
}

/**
 * Derive flexGrow/flexShrink from variance score
 * varianceScore = min(1, σ / (μ * 0.5))
 * flex = 1.1 + varianceScore * 0.9  → range [1.1, 2.0]
 */
function varianceToFlex(mean: number, variance: number): number {
  if (mean <= 0) return MIN_AUTO_FLEX;
  const stdDev = Math.sqrt(variance);
  const varianceScore = Math.min(1, stdDev / (mean * 0.5));
  return MIN_AUTO_FLEX + varianceScore * (MAX_AUTO_FLEX - MIN_AUTO_FLEX);
}

/**
 * Compute actual column widths using a flexbox-inspired distribution algorithm.
 * - First, compute raw flex widths based on available space
 * - Then, enforce minWidth/maxWidth constraints iteratively
 * - If constraints cause overflow, reduce widths proportionally while respecting mins
 */
export function computeFlexWidths(configs: ColumnFlexConfig[], containerWidth: number): number[] {
  if (!configs.length || containerWidth <= 0) {
    return configs.map(() => 0);
  }

  // Calculate total flex basis
  const totalFlexBasis = configs.reduce((sum, c) => sum + c.flexBasis, 0);

  if (totalFlexBasis === 0) {
    // Edge case: all zero bases - distribute evenly
    const evenWidth = containerWidth / configs.length;
    return configs.map((c) => clamp(evenWidth, c.minWidth, c.maxWidth));
  }

  // Calculate raw flex widths
  let widths = computeRawFlexWidths(configs, containerWidth, totalFlexBasis);

  // Apply min/max constraints iteratively until stable
  // This handles the case where clamping some columns causes others to overflow
  for (let iteration = 0; iteration < 10; iteration++) {
    // Apply constraints
    widths = widths.map((w, i) => clamp(w, configs[i].minWidth, configs[i].maxWidth));

    const totalWidth = widths.reduce((sum, w) => sum + w, 0);

    if (totalWidth <= containerWidth) {
      // Fits! Distribute remaining space proportionally based on flexGrow
      const remaining = containerWidth - totalWidth;
      if (remaining > 0) {
        const totalFlexGrow = configs.reduce((sum, c) => sum + c.flexGrow * c.flexBasis, 0);
        if (totalFlexGrow > 0) {
          widths = widths.map((w, i) => {
            const growAmount = ((configs[i].flexGrow * configs[i].flexBasis) / totalFlexGrow) * remaining;
            return w + growAmount;
          });
        }
      }
      break;
    }

    // Overflow - need to reduce widths that are above their minimums
    const overflow = totalWidth - containerWidth;

    // Calculate how much each column can be reduced (only those above minWidth)
    const reducible = widths.map((w, i) => Math.max(0, w - configs[i].minWidth));
    const totalReducible = reducible.reduce((sum, r) => sum + r, 0);

    if (totalReducible === 0) {
      // All at minimum - force even distribution
      const evenWidth = containerWidth / configs.length;
      widths = configs.map((c) => clamp(evenWidth, c.minWidth, c.maxWidth));
      break;
    }

    // Reduce proportionally based on how much each column can be reduced
    widths = widths.map((w, i) => {
      const reduction = (reducible[i] / totalReducible) * overflow;
      return Math.max(w - reduction, configs[i].minWidth);
    });
  }

  // Final clamp
  widths = widths.map((w, i) => clamp(w, configs[i].minWidth, configs[i].maxWidth));

  return widths;
}

/**
 * Compute raw flex widths without min/max constraints
 */
function computeRawFlexWidths(configs: ColumnFlexConfig[], containerWidth: number, totalFlexBasis: number): number[] {
  const availableSpace = containerWidth - totalFlexBasis;

  if (availableSpace === 0) {
    return configs.map((c) => c.flexBasis);
  }

  if (availableSpace > 0) {
    // Grow phase: distribute extra space proportionally by flexGrow * flexBasis
    const totalGrowFactor = configs.reduce((sum, c) => sum + c.flexGrow * c.flexBasis, 0);
    if (totalGrowFactor === 0) {
      return configs.map((c) => c.flexBasis);
    }
    return configs.map((c) => {
      const growAmount = ((c.flexGrow * c.flexBasis) / totalGrowFactor) * availableSpace;
      return c.flexBasis + growAmount;
    });
  } else {
    // Shrink phase: remove space proportionally by flexShrink * flexBasis
    const totalShrinkFactor = configs.reduce((sum, c) => sum + c.flexShrink * c.flexBasis, 0);
    if (totalShrinkFactor === 0) {
      // No shrink - distribute loss evenly
      const evenShrink = -availableSpace / configs.length;
      return configs.map((c) => Math.max(0, c.flexBasis - evenShrink));
    }
    return configs.map((c) => {
      const shrinkAmount = ((c.flexShrink * c.flexBasis) / totalShrinkFactor) * -availableSpace;
      return Math.max(0, c.flexBasis - shrinkAmount);
    });
  }
}

function clamp(value: number, min: number, max: number): number {
  return Math.max(min, Math.min(max, value));
}

export function usePretextColumnWidths<T>(
  data: Ref<T[]>,
  columns: Ref<ListTableColumn<T>[]>,
  containerWidth: Ref<number>,
  options?: {
    font?: string;
    headerFont?: string;
    sampleSize?: number;
    formatCellValue?: (row: T, col: ListTableColumn<T>) => string;
  }
) {
  const font = options?.font ?? DEFAULT_FONT;
  const headerFont = options?.headerFont ?? DEFAULT_HEADER_FONT;
  const sampleSize = options?.sampleSize ?? 100;
  const formatCellValue = options?.formatCellValue;

  const computedConfigs = computed<ColumnFlexConfig[]>(() => {
    if (!columns.value.length) return [];

    const sampled = sampleRows(data.value, sampleSize);
    const configs: ColumnFlexConfig[] = [];

    for (const col of columns.value) {
      const colKey = String(col.key);

      // User overrides (convert string values to numbers)
      const userFlexGrow = col.flexGrow;
      const userFlexShrink = col.flexShrink;
      const userFlexBasis = col.flexBasis !== undefined && col.flexBasis !== "auto" ? Number(col.flexBasis) : undefined;
      const userMinWidth = col.minWidth !== undefined ? Number(col.minWidth) : undefined;
      const userMaxWidth =
        col.maxWidth !== undefined && Number.isFinite(Number(col.maxWidth)) ? Number(col.maxWidth) : undefined;

      // Measure header width
      const headerText = col.name || col.i18n || colKey;
      const headerWidth = measureShrinkWrapWidth(headerText, headerFont) + CELL_PADDING;

      // Measure sampled cell widths
      const cellWidths: number[] = [];
      for (const row of sampled) {
        const rawValue = (row as any)[col.dataKey || colKey];
        const cellText = formatCellValue?.(row, col) ?? (rawValue == null ? "" : String(rawValue));
        if (cellText) {
          const w = measureShrinkWrapWidth(cellText, font) + CELL_PADDING;
          cellWidths.push(w);
        }
      }

      // Include header in stats
      const allWidths = [headerWidth, ...cellWidths];
      const { mean, variance } = computeStats(allWidths);

      // Derived values
      const flexBasis = userFlexBasis ?? mean;
      const minWidth = userMinWidth
        ? Number(userMinWidth)
        : Math.max(mean - 2 * Math.sqrt(variance), MIN_BASE_WIDTH) + CELL_PADDING;
      const maxWidth = userMaxWidth ?? MAX_WIDTH;
      const flexGrow = userFlexGrow ?? varianceToFlex(mean, variance);
      const flexShrink = userFlexShrink ?? varianceToFlex(mean, variance);

      configs.push({
        key: colKey,
        flexBasis,
        flexGrow,
        flexShrink,
        minWidth,
        maxWidth,
        measuredMean: mean,
        measuredVariance: variance,
        measuredSampleCount: allWidths.length,
      });
    }

    return configs;
  });

  // Total flex basis (sum of all flexBasis values)
  const totalFlexBasis = computed(() => computedConfigs.value.reduce((sum, c) => sum + c.flexBasis, 0));

  // Actual column widths computed using flexbox algorithm
  const columnWidths = computed(() => computeFlexWidths(computedConfigs.value, containerWidth.value));

  return {
    computedConfigs,
    totalFlexBasis,
    columnWidths,
  };
}