| 1 | package sheets |
| 2 | |
| 3 | import ( |
| 4 | "math" |
| 5 | "strconv" |
| 6 | |
| 7 | "amadan.net/oficina/sheets/internal/sheets/store" |
| 8 | ) |
| 9 | |
| 10 | // aaFloor is WCAG 2.2's contrast minimum for normal-size text: 4.5:1. |
| 11 | const aaFloor = 4.5 |
| 12 | |
| 13 | // maxWarnedCells bounds the list a page names. Somebody importing a |
| 14 | // heavily formatted file does not need four hundred cell references; |
| 15 | // they need to know it happened and where to start. |
| 16 | const maxWarnedCells = 12 |
| 17 | |
| 18 | // contrastRatio is WCAG 2.x relative luminance, (L1+0.05)/(L2+0.05). |
| 19 | // |
| 20 | // Written here rather than borrowed: rastrillo has this computation, |
| 21 | // but only inside ui/contrast_test.go, and a _test.go file exports |
| 22 | // nothing to another package. Copying twenty lines of a published |
| 23 | // standard beats vendoring a test file or waiting for an upstream |
| 24 | // export — and the constants below are the standard's, checkable |
| 25 | // against it rather than against us. |
| 26 | func contrastRatio(a, b string) (float64, bool) { |
| 27 | la, ok := relativeLuminance(a) |
| 28 | if !ok { |
| 29 | return 0, false |
| 30 | } |
| 31 | lb, ok := relativeLuminance(b) |
| 32 | if !ok { |
| 33 | return 0, false |
| 34 | } |
| 35 | if la < lb { |
| 36 | la, lb = lb, la |
| 37 | } |
| 38 | return (la + 0.05) / (lb + 0.05), true |
| 39 | } |
| 40 | |
| 41 | // relativeLuminance parses an 8-char ARGB or 6-char RGB hex and returns |
| 42 | // WCAG relative luminance. The alpha channel is ignored: a fill in a |
| 43 | // spreadsheet is composited over the sheet, and treating a translucent |
| 44 | // fill as opaque overstates rather than understates the risk, which is |
| 45 | // the safe direction for a warning. |
| 46 | func relativeLuminance(hex string) (float64, bool) { |
| 47 | switch len(hex) { |
| 48 | case 8: |
| 49 | hex = hex[2:] |
| 50 | case 6: |
| 51 | default: |
| 52 | return 0, false |
| 53 | } |
| 54 | channel := func(s string) (float64, bool) { |
| 55 | v, err := strconv.ParseUint(s, 16, 8) |
| 56 | if err != nil { |
| 57 | return 0, false |
| 58 | } |
| 59 | c := float64(v) / 255 |
| 60 | if c <= 0.04045 { |
| 61 | return c / 12.92, true |
| 62 | } |
| 63 | return math.Pow((c+0.055)/1.055, 2.4), true |
| 64 | } |
| 65 | r, okR := channel(hex[0:2]) |
| 66 | g, okG := channel(hex[2:4]) |
| 67 | b, okB := channel(hex[4:6]) |
| 68 | if !okR || !okG || !okB { |
| 69 | return 0, false |
| 70 | } |
| 71 | return 0.2126*r + 0.7152*g + 0.0722*b, true |
| 72 | } |
| 73 | |
| 74 | // lowContrast reports whether a format's AUTHORED pair fails AA. |
| 75 | // |
| 76 | // Both halves must be present. A fill on its own cannot fail: our own |
| 77 | // ink comes from the theme, and that pairing is one this app controls |
| 78 | // and gates elsewhere. What can fail is a fill and an ink that both |
| 79 | // arrived in somebody's file — which is not hypothetical, since Excel |
| 80 | // ships #9C6500 on #FFEB9C at 4.12:1 as a conditional-formatting |
| 81 | // preset (spec §11.1). |
| 82 | // |
| 83 | // It reports, and nothing acts on it beyond telling a person. Spec |
| 84 | // §11.1 ruled that we render an imported file as authored: silently |
| 85 | // correcting it would lie about the document. The obligation is |
| 86 | // surfacing, not overriding. |
| 87 | func lowContrast(f *store.Format) bool { |
| 88 | if f == nil || f.FillHex == "" || f.InkHex == "" { |
| 89 | return false |
| 90 | } |
| 91 | ratio, ok := contrastRatio(f.FillHex, f.InkHex) |
| 92 | if !ok { |
| 93 | return false |
| 94 | } |
| 95 | return ratio < aaFloor |
| 96 | } |
| 97 | |
| 98 | // warnedCells lists the A1 references in a window whose imported |
| 99 | // colours fail AA, newest window first and capped. |
| 100 | func warnedCells(h *store.Handle, idx posIndex, rows, cols int) []string { |
| 101 | coords, err := h.Cells() |
| 102 | if err != nil { |
| 103 | return nil |
| 104 | } |
| 105 | var refs []string |
| 106 | for _, c := range coords { |
| 107 | r, okR := idx.rowPos[c.RowID] |
| 108 | col, okC := idx.colPos[c.ColID] |
| 109 | if !okR || !okC || r >= rows || col >= cols { |
| 110 | continue |
| 111 | } |
| 112 | if !lowContrast(h.Format(c.RowID, c.ColID)) { |
| 113 | continue |
| 114 | } |
| 115 | if len(refs) == maxWarnedCells { |
| 116 | return append(refs, "…") |
| 117 | } |
| 118 | refs = append(refs, colLabel(col)+strconv.Itoa(r+1)) |
| 119 | } |
| 120 | return refs |
| 121 | } |
| 122 | |
amadan