breakpilot-lehrer/admin-lehrer/components/ocr-overlay/useSlideWordPositions.ts

import { useEffect, useState } from 'react'
import type { GridCell } from '@/app/(admin)/ai/ocr-overlay/types'

export interface WordPosition {
  xPct: number
  wPct: number
  text: string
  fontRatio: number
}

/**
 * "Slide from left" positioning algorithm.
 *
 * Takes ALL recognised words per cell and slides them left-to-right across
 * the row's dark-pixel projection until each word "locks" onto its ink.
 *
 * Font size: fontRatio = 1.0 for all tokens.  The renderer computes the
 * actual font size as medianCellHeightPx * fontRatio * fontScale, which
 * matches the fallback rendering exactly.  The user controls size via the
 * font-scale slider.
 *
 * Position: each token's x-position is found by sliding a cursor from left
 * to right and looking for dark-pixel coverage.  Token width (wPct) is
 * computed from canvas measureText proportional to the median cell height,
 * giving visually correct character widths.
 *
 * Guarantees: no words dropped, no complex matching rules needed.
 */
export function useSlideWordPositions(
  imageUrl: string,
  cells: GridCell[],
  active: boolean,
  rotation: 0 | 180 = 0,
): Map<string, WordPosition[]> {
  const [result, setResult] = useState<Map<string, WordPosition[]>>(new Map())

  useEffect(() => {
    if (!active || cells.length === 0 || !imageUrl) return

    const img = new Image()
    img.crossOrigin = 'anonymous'
    img.onload = () => {
      const imgW = img.naturalWidth
      const imgH = img.naturalHeight

      const canvas = document.createElement('canvas')
      canvas.width = imgW
      canvas.height = imgH
      const ctx = canvas.getContext('2d')
      if (!ctx) return

      if (rotation === 180) {
        ctx.translate(imgW, imgH)
        ctx.rotate(Math.PI)
        ctx.drawImage(img, 0, 0)
        ctx.setTransform(1, 0, 0, 1, 0, 0)
      } else {
        ctx.drawImage(img, 0, 0)
      }

      // --- Compute median cell height in image pixels ---
      const cellHeights = cells
        .filter(c => c.bbox_pct && c.bbox_pct.h > 0)
        .map(c => Math.round(c.bbox_pct.h / 100 * imgH))
        .sort((a, b) => a - b)
      const medianCh = cellHeights.length > 0
        ? cellHeights[Math.floor(cellHeights.length / 2)]
        : 30

      // The renderer computes: fontSize = medianCellHeightPx * fontRatio * fontScale
      // With fontRatio=1.0 and fontScale=0.7 (default), that's 70% of median cell height.
      // We need to know how wide each token is at THAT rendered font size,
      // expressed in image pixels.
      //
      // The rendered container is reconWidth px wide = imgW image pixels.
      // So 1 image pixel = reconWidth/imgW display pixels.
      // Rendered font size (display px) = medianCellHeightPx_display * 1.0 * fontScale
      // medianCellHeightPx_display = medianCh * (reconWidth / imgW)
      // So rendered font = medianCh * (reconWidth/imgW) * fontScale
      // In image-pixel units: medianCh * fontScale
      //
      // measureText at refFontSize=40 gives pixel widths.
      // Scale from refFontSize → actual image-pixel font size:
      const refFontSize = 40
      const fontFam = "'Liberation Sans', Arial, sans-serif"
      ctx.font = `${refFontSize}px ${fontFam}`

      // Approximate rendered font size in image pixels.
      // fontScale default is 0.7 but we don't know it here.
      // Use 0.7 as approximation — the slide positions will still be correct
      // because we only use this for relative token widths (proportional).
      const approxFontScale = 0.7
      const renderedFontImgPx = medianCh * approxFontScale
      const measureScale = renderedFontImgPx / refFontSize

      const positions = new Map<string, WordPosition[]>()

      for (const cell of cells) {
        if (!cell.bbox_pct || !cell.text) continue

        // --- Cell rectangle in image pixels ---
        let cx: number, cy: number
        const cw = Math.round(cell.bbox_pct.w / 100 * imgW)
        const ch = Math.round(cell.bbox_pct.h / 100 * imgH)

        if (rotation === 180) {
          cx = Math.round((100 - cell.bbox_pct.x - cell.bbox_pct.w) / 100 * imgW)
          cy = Math.round((100 - cell.bbox_pct.y - cell.bbox_pct.h) / 100 * imgH)
        } else {
          cx = Math.round(cell.bbox_pct.x / 100 * imgW)
          cy = Math.round(cell.bbox_pct.y / 100 * imgH)
        }
        if (cw <= 0 || ch <= 0) continue
        if (cx < 0) cx = 0
        if (cy < 0) cy = 0
        if (cx + cw > imgW || cy + ch > imgH) continue

        // --- Dark-pixel projection ---
        const imageData = ctx.getImageData(cx, cy, cw, ch)
        const proj = new Float32Array(cw)
        for (let y = 0; y < ch; y++) {
          for (let x = 0; x < cw; x++) {
            const idx = (y * cw + x) * 4
            const lum = 0.299 * imageData.data[idx] + 0.587 * imageData.data[idx + 1] + 0.114 * imageData.data[idx + 2]
            if (lum < 128) proj[x]++
          }
        }

        const threshold = Math.max(1, ch * 0.03)

        // Binary ink mask
        const ink = new Uint8Array(cw)
        for (let x = 0; x < cw; x++) {
          ink[x] = proj[x] >= threshold ? 1 : 0
        }

        if (rotation === 180) {
          ink.reverse()
        }

        // --- Tokens ---
        const tokens = cell.text.split(/\s+/).filter(Boolean)
        if (tokens.length === 0) continue

        // Token widths in image pixels at the approximate rendered font size
        const tokenWidthsPx = tokens.map(t =>
          Math.max(4, Math.round(ctx.measureText(t).width * measureScale))
        )
        const spaceWidthPx = Math.max(2, Math.round(ctx.measureText(' ').width * measureScale))

        // --- Slide each token left-to-right ---
        const wordPos: WordPosition[] = []
        let cursor = 0

        for (let ti = 0; ti < tokens.length; ti++) {
          const tokenW = tokenWidthsPx[ti]

          // Find first x from cursor where ≥20% of span has ink
          const coverageNeeded = Math.max(1, Math.round(tokenW * 0.20))
          let bestX = cursor

          const searchLimit = Math.max(cursor, cw - tokenW)

          for (let x = cursor; x <= searchLimit; x++) {
            let inkCount = 0
            const spanEnd = Math.min(x + tokenW, cw)
            for (let dx = 0; dx < spanEnd - x; dx++) {
              inkCount += ink[x + dx]
            }
            if (inkCount >= coverageNeeded) {
              bestX = x
              break
            }
            // Safety: don't scan more than 40% of cell width past cursor
            if (x > cursor + cw * 0.4 && ti > 0) {
              bestX = cursor
              break
            }
          }

          // Clamp to cell bounds
          if (bestX + tokenW > cw) {
            bestX = Math.max(0, cw - tokenW)
          }

          wordPos.push({
            xPct: cell.bbox_pct.x + (bestX / cw) * cell.bbox_pct.w,
            wPct: (tokenW / cw) * cell.bbox_pct.w,
            text: tokens[ti],
            fontRatio: 1.0,
          })

          // Advance cursor: past this token + space
          cursor = bestX + tokenW + spaceWidthPx
        }

        if (wordPos.length > 0) {
          positions.set(cell.cell_id, wordPos)
        }
      }

      setResult(positions)
    }
    img.src = imageUrl
  }, [active, cells, imageUrl, rotation])

  return result
}