package app

import (
	"fmt"
	"os"
	"strings"
)

const (
	sidebarCols = 28
	statusRows  = 1
)

// drawSidebar paints the right-rail session tree + scratchpad list.
// SPEC §4: the rail is the active session's child hierarchy on top and
// the scratchpad list (with preview) on the bottom.
//
// Implementation note: the PTY child's winsize is constrained to the
// computed main viewport, so the sidebar region is outside the child's
// cursor range. We can redraw freely without fighting the child for cells.
func (st *uiState) drawSidebar() {
	st.mu.Lock()
	palOpen := st.palette != nil
	focus := st.focusedID
	st.mu.Unlock()
	if palOpen {
		return
	}

	layout := st.layoutSnapshot()
	if !layout.sidebarVisible || layout.hostRows < 4 {
		return
	}
	left := int(layout.sidebarLeft)
	width := int(layout.sidebarWidth) - 1
	maxRow := int(layout.statusRow) - statusRows

	var b strings.Builder
	// Border column at left-1: a single vertical pipe.
	for r := 1; r <= maxRow; r++ {
		fmt.Fprintf(&b, "\x1b[%d;%dH\x1b[2m│\x1b[0m", r, left-1)
	}

	row := 1
	writeLine := func(s string, style string) {
		if row > maxRow {
			return
		}
		if len(s) > width {
			s = s[:width]
		}
		fmt.Fprintf(&b, "\x1b[%d;%dH%s%s\x1b[0m\x1b[K", row, left, style, padRight(s, width))
		row++
	}

	writeLine(" Session tree", "\x1b[1m")
	writeLine(strings.Repeat("─", width-1), "\x1b[2m")

	children := visibleSessionTree(st.sess.Children(), focus)
	if len(children) == 0 {
		writeLine(" (empty)", "\x1b[2m")
	}
	for _, c := range children {
		glyph := "◉"
		marker := "  "
		if c.ID == focus {
			marker = "▶ "
		}
		indent := ""
		if c.ParentID != "" {
			indent = "  "
		}
		line := fmt.Sprintf(" %s%s%s %s", marker, indent, glyph, c.Name)
		style := ""
		if c.ID == focus {
			style = "\x1b[1m"
		}
		writeLine(line, style)
	}

	// Scratchpads list — pick the most-recently-modified one as the
	// preview target. SPEC §4.
	var previewName string
	if row+2 <= maxRow {
		row++
		writeLine(" Scratchpads", "\x1b[1m")
		writeLine(strings.Repeat("─", width-1), "\x1b[2m")
		entries, err := st.pads.List()
		if err == nil {
			if len(entries) == 0 {
				writeLine(" (none)", "\x1b[2m")
			}
			var newest string
			var newestTS string
			for _, e := range entries {
				if e.ModifiedAt > newestTS {
					newestTS = e.ModifiedAt
					newest = e.Name
				}
			}
			previewName = newest
			for _, e := range entries {
				if row > maxRow {
					break
				}
				marker := "   "
				style := ""
				if e.Name == previewName {
					marker = " ▸ "
					style = "\x1b[1m"
				}
				writeLine(marker+e.Name, style)
			}
		}
	}

	// Preview pane at the bottom of the rail. Reserve up to 8 rows.
	if previewName != "" && row+2 <= maxRow {
		row++
		writeLine(strings.Repeat("─", width-1), "\x1b[2m")
		writeLine(" "+previewName, "\x1b[1m")
		content, _, err := st.pads.Read(previewName)
		if err == nil {
			for _, line := range strings.Split(content, "\n") {
				if row > maxRow {
					break
				}
				writeLine(" "+line, "\x1b[2m")
			}
		}
	}

	// Blank-fill any rows the rail content didn't cover so stale
	// content from a previous redraw doesn't linger.
	for row <= maxRow {
		writeLine("", "")
	}

	st.outMu.Lock()
	// Save cursor; emit the sidebar; restore.
	fmt.Fprintf(os.Stdout, "\x1b7%s\x1b8", b.String())
	st.outMu.Unlock()
}