After commit c018f5fd29 Fenrir is being switched over to go. If you do not want to be part of the testing process, please switch to master.

internal/reader/changes.go

@@ -0,0 +1,112 @@
+// Fenrir console screen reader.
+// Copyright (c) 2026 Storm Dragon
+// SPDX-License-Identifier: GPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation, either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+// more details.
+//
+// You should have received a copy of the GNU General Public License along with
+// this program. If not, see <https://www.gnu.org/licenses/gpl-3.0.html>.
+
+package reader
+
+import (
+	"slices"
+	"strings"
+	"unicode"
+
+	"git.stormux.org/storm/fenrir/internal/presentation"
+	"git.stormux.org/storm/fenrir/internal/screen"
+)
+
+func changes(previous, next screen.Snapshot, cursorEcho bool) []presentation.Message {
+	// TUI navigation can move over unchanged text while a status line also
+	// changes. That status delta must not hide the newly focused row (mutt).
+	if cursorEcho && next.Y != previous.Y && strings.TrimSpace(next.Text(next.Y)) != "" && slices.Equal(previous.Line(next.Y), next.Line(next.Y)) {
+		return []presentation.Message{presentation.Line_message(next, next.Y)}
+	}
+	if slices.Equal(previous.Cells, next.Cells) {
+		if cursorEcho && next.Y != previous.Y {
+			return []presentation.Message{presentation.Line_message(next, next.Y)}
+		}
+		if cursorEcho && next.X != previous.X {
+			return []presentation.Message{presentation.Character_message(next.Line(next.Y)[next.X])}
+		}
+		return nil
+	}
+	// Match a scroll as one shift so old lines aren't read a second time.
+	// Find the first non-space cell once. Successively shorter overlaps
+	// cannot be meaningful scroll matches once they contain only whitespace.
+	// Avoid converting each candidate overlap into a whole-screen string.
+	firstText := slices.IndexFunc(next.Cells, func(cell rune) bool { return !unicode.IsSpace(cell) })
+	for shift := 1; shift < next.Rows && firstText >= 0 && firstText < (next.Rows-shift)*next.Cols; shift++ {
+		if !slices.Equal(previous.Cells[shift*next.Cols:], next.Cells[:(next.Rows-shift)*next.Cols]) {
+			continue
+		}
+		var result []presentation.Message
+		for row := next.Rows - shift; row < next.Rows; row++ {
+			if text := next.Text(row); strings.TrimSpace(text) != "" {
+				result = append(result, presentation.Message{Text: text})
+			}
+		}
+		return result
+	}
+	var changedRows []int
+	for row := 0; row < next.Rows; row++ {
+		if !slices.Equal(previous.Line(row), next.Line(row)) {
+			changedRows = append(changedRows, row)
+		}
+	}
+	scrollStart, scrollEnd := 0, 0
+	if len(changedRows) > 1 {
+		scrollStart, scrollEnd = screen.Scrolled_overlap(previous, next)
+		kept := changedRows[:0]
+		for _, row := range changedRows {
+			if row < scrollStart || row >= scrollEnd {
+				kept = append(kept, row)
+			}
+		}
+		changedRows = kept
+	}
+	if len(changedRows) == 1 && scrollStart == scrollEnd {
+		row := changedRows[0]
+		before, after := previous.Line(row), next.Line(row)
+		if next.Y == previous.Y && next.Y == row && next.X < previous.X && previous.X-next.X <= 4 && len([]rune(next.Text(row))) < len([]rune(previous.Text(row))) {
+			removed := before[next.X:previous.X]
+			if len(removed) == 1 {
+				return []presentation.Message{presentation.Character_message(removed[0])}
+			}
+			return []presentation.Message{{Text: string(removed)}}
+		}
+		start := 0
+		for start < min(len(before), len(after)) && before[start] == after[start] {
+			start++
+		}
+		endBefore, endAfter := len(before), len(after)
+		for endBefore > start && endAfter > start && before[endBefore-1] == after[endAfter-1] {
+			endBefore--
+			endAfter--
+		}
+		inserted := after[start:endAfter]
+		if len(inserted) != 0 && strings.TrimSpace(string(inserted)) != "" {
+			if len(inserted) == 1 {
+				return []presentation.Message{presentation.Character_message(inserted[0])}
+			}
+			return []presentation.Message{{Text: string(inserted)}}
+		}
+	}
+	var result []presentation.Message
+	for _, row := range changedRows {
+		if text := next.Text(row); strings.TrimSpace(text) != "" {
+			result = append(result, presentation.Message{Text: text})
+		}
+	}
+	return result
+}