feat(tui): FILES sidebar panel with click-to-select and file drill-in

internal/tui/file_view.go

@@ -0,0 +1,251 @@
+// file_view.go is the drill-in view for a touched file, opened from the FILES
+// sidebar section (files_panel.go). It reuses the subchat pattern: while
+// active, the chat column's body swaps to this file's content — the sidebar,
+// composer, and scroll engine keep working unchanged (transcriptBodyItems is
+// the single source the viewport, renderer, and hit-testers all read, so
+// swapping there keeps every consumer consistent). Two modes:
+//
+//	diff (default) — the file's edit cards from this session, full-depth
+//	full           — the file as it stands on disk, syntax highlighted, with
+//	                 gutter markers on the lines this session's diffs added
+//
+// d/f switch modes (with an empty composer), Esc returns to the chat at the
+// scroll position it was left at.
+package tui
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// fileViewMaxLines caps the full-file mode so a giant generated file can't
+// freeze a render; the tail collapses into a "… N more lines" trailer.
+const fileViewMaxLines = 4000
+
+const (
+	fileViewDiff = iota
+	fileViewFull
+)
+
+// fileViewState manages the drill-in view for a touched file. When active, the
+// transcript body swaps to the file's diff/content instead of the chat rows.
+type fileViewState struct {
+	active bool
+	path   string // workspace-relative, as carried by changedFiles
+	mode   int    // fileViewDiff | fileViewFull
+	// parentScrollOffset preserves the chat scroll position so closing the view
+	// returns to the same spot (mirrors subchatState).
+	parentScrollOffset int
+}
+
+// openFileView activates the drill-in for path in diff mode. Opening from an
+// already-open view (clicking another FILES row) keeps the original saved chat
+// scroll position rather than saving the file view's own offset as "parent".
+// Re-opening the file that is ALREADY being viewed is a no-op: a stray
+// re-click must not bounce the user from full mode back to diff or reset
+// their scroll position.
+func (m model) openFileView(path string) model {
+	if m.fileView.active && m.fileView.path == path {
+		return m
+	}
+	if !m.fileView.active {
+		m.fileView.parentScrollOffset = m.chatScrollOffset
+	}
+	m.fileView.active = true
+	m.fileView.path = path
+	m.fileView.mode = fileViewDiff
+	// A file only the git sweep knows about (bash/subagent mutation) has no edit
+	// cards to stack — open straight on the full file instead of a placeholder.
+	if len(m.fileViewResultRows()) == 0 {
+		m.fileView.mode = fileViewFull
+	}
+	m.chatScrollOffset = 0
+	m = m.clearHover() // bodyY numbering differs between the file body and the chat
+	return m
+}
+
+// exitFileView deactivates the view and restores the chat scroll position.
+func (m model) exitFileView() model {
+	if !m.fileView.active {
+		return m
+	}
+	m.chatScrollOffset = m.fileView.parentScrollOffset
+	m.fileView = fileViewState{}
+	m = m.clearHover()
+	return m
+}
+
+// setFileViewMode switches diff/full, resetting the scroll to the bottom-anchored
+// start since the two bodies have unrelated heights.
+func (m model) setFileViewMode(mode int) model {
+	if !m.fileView.active || m.fileView.mode == mode {
+		return m
+	}
+	m.fileView.mode = mode
+	m.chatScrollOffset = 0
+	return m
+}
+
+// fileViewNavBar renders the single-line header shown in place of the pinned
+// title bar while the view is active: the path plus the key hints. One line
+// exactly, so every scrollableTranscriptFrame computed against it agrees with
+// the title bar's geometry.
+func (m model) fileViewNavBar(width int) string {
+	mode := "diff"
+	other := "f full"
+	if m.fileView.mode == fileViewFull {
+		mode = "full"
+		other = "d diff"
+	}
+	left := zeroTheme.accent.Render("← "+truncatePathLeft(m.fileView.path, maxInt(8, width/2))) +
+		zeroTheme.faint.Render("  ·  "+mode)
+	right := zeroTheme.faint.Render(other + " · esc back")
+	return fitStyledLine(joinHeaderLine(left, right, width), width)
+}
+
+// fileViewBodyItems builds the body items the transcript machinery renders
+// while the view is active — one pre-rendered block, so scrolling and height
+// accounting flow through the exact same path as chat rows.
+func (m model) fileViewBodyItems(width int) []transcriptBodyItem {
+	var block string
+	if m.fileView.mode == fileViewFull {
+		block = m.renderFileViewFull(width)
+	} else {
+		block = m.renderFileViewDiff(width)
+	}
+	return []transcriptBodyItem{transcriptBlockBodyItem(transcriptBodyItemRow, -1, block)}
+}
+
+// fileViewResultRows returns the transcript's tool-result rows that touched the
+// viewed file, in chronological order.
+func (m model) fileViewResultRows() []transcriptRow {
+	var rows []transcriptRow
+	for _, row := range m.transcript {
+		if row.kind != rowToolResult {
+			continue
+		}
+		for _, p := range row.changedFiles {
+			if p == m.fileView.path {
+				rows = append(rows, row)
+				break
+			}
+		}
+	}
+	return rows
+}
+
+// renderFileViewDiff renders the session's edits to the file as its full-depth
+// tool cards (bodyCap 0, the detailed-view depth), stacked chronologically —
+// the same cards the chat shows, so the diffs read identically in both places.
+func (m model) renderFileViewDiff(width int) string {
+	rows := m.fileViewResultRows()
+	if len(rows) == 0 {
+		return zeroTheme.faint.Render("No recorded edits for this file in this session.")
+	}
+	rc := buildRowContext(m.transcript)
+	opts := cardRenderOptions{bodyCap: 0, cwd: m.cwd}
+	var b strings.Builder
+	for i, row := range rows {
+		if i > 0 {
+			b.WriteString("\n\n")
+		}
+		if len(rows) > 1 {
+			b.WriteString(zeroTheme.faint.Render(fmt.Sprintf("edit %d of %d", i+1, len(rows))))
+			b.WriteString("\n")
+		}
+		b.WriteString(m.renderRowModeUncached(row, width, rc, opts))
+	}
+	return b.String()
+}
+
+// renderFileViewFull renders the file as it currently stands on disk, syntax
+// highlighted, with a line-number gutter and an accent ▎ marker on the lines
+// this session's diffs added (matched by exact text — an approximation that
+// tolerates later drift; a stale marker just doesn't highlight).
+func (m model) renderFileViewFull(width int) string {
+	target := m.fileView.path
+	if !filepath.IsAbs(target) {
+		target = filepath.Join(m.cwd, target)
+	}
+	// Stream the read and stop at the cap: os.ReadFile would load a multi-GB
+	// file wholesale before any truncation, which is the exact render freeze
+	// fileViewMaxLines exists to prevent.
+	file, err := os.Open(target)
+	if err != nil {
+		return zeroTheme.faint.Render("Could not read file: " + err.Error())
+	}
+	defer file.Close()
+	var lines []string
+	truncated := false
+	scanner := bufio.NewScanner(file)
+	scanner.Buffer(make([]byte, 0, 64*1024), 16*1024*1024)
+	for scanner.Scan() {
+		if len(lines) == fileViewMaxLines {
+			truncated = true
+			break
+		}
+		lines = append(lines, scanner.Text())
+	}
+	if err := scanner.Err(); err != nil {
+		if len(lines) == 0 {
+			return zeroTheme.faint.Render("Could not read file: " + err.Error())
+		}
+		truncated = true // e.g. a single over-long line mid-file: show what we have
+	}
+
+	changed := m.fileViewChangedLines()
+	gutterW := len(fmt.Sprintf("%d", len(lines)))
+	textBudget := maxInt(8, width-gutterW-3) // gutter + space + marker column
+	// Highlight with an effectively-infinite measure so the highlighter never
+	// wraps — output lines stay 1:1 with file lines and the gutter numbering
+	// can't desync. Each line is then truncated to the column budget below.
+	display, ok := highlightCodeForPath(lines, m.fileView.path, 1<<20, nil)
+	if !ok || len(display) != len(lines) {
+		display = lines // no lexer for this path: render plain
+	}
+
+	var b strings.Builder
+	for i, line := range display {
+		line = fitStyledLine(line, textBudget)
+		if i > 0 {
+			b.WriteString("\n")
+		}
+		marker := " "
+		if changed[strings.TrimSpace(lines[i])] {
+			marker = zeroTheme.accent.Render("▎")
+		}
+		b.WriteString(zeroTheme.faintest.Render(fmt.Sprintf("%*d ", gutterW, i+1)))
+		b.WriteString(marker)
+		b.WriteString(line)
+	}
+	if truncated {
+		// No exact remaining-line count: computing one would require reading the
+		// rest of the file, defeating the bounded read above.
+		b.WriteString("\n")
+		b.WriteString(zeroTheme.faint.Render(fmt.Sprintf("… more lines (file truncated at %d for display)", len(lines))))
+	}
+	return b.String()
+}
+
+// fileViewChangedLines collects the trimmed text of every line the session's
+// diffs ADDED to the viewed file, for the full-mode gutter markers. Very short
+// lines ("}", "return", ")") are skipped: text-matching them would mark every
+// unrelated occurrence across the file, which misleads far more than a missing
+// marker on a brace line ever could.
+func (m model) fileViewChangedLines() map[string]bool {
+	changed := map[string]bool{}
+	for _, row := range m.fileViewResultRows() {
+		for _, line := range strings.Split(row.detail, "\n") {
+			if !strings.HasPrefix(line, "+") || strings.HasPrefix(line, "+++") {
+				continue
+			}
+			if text := strings.TrimSpace(strings.TrimPrefix(line, "+")); len(text) >= 4 {
+				changed[text] = true
+			}
+		}
+	}
+	return changed
+}