qedit/ui/textedit.go

package ui

import (
	"fmt"
	"math"
	"strconv"
	"strings"
	"unicode/utf8"

	"github.com/fivemoreminix/diesel/ui/buffer"
	"github.com/gdamore/tcell/v2"
)

// A Selection represents a region of the buffer to be selected for text editing
// purposes. It is asserted that the start position is less than the end position.
// The start and end are inclusive. If the EndCol of a Region is one more than the
// last column of a line, then it points to the line delimiter at the end of that
// line. It is understood that as a Region spans multiple lines, those connecting
// line-delimiters are included, as well.
type Region struct {
	StartLine, StartCol int
	EndLine, EndCol     int
}

// TextEdit is a field for line-based editing. It features syntax highlighting
// tools, is autocomplete ready, and contains the various information about
// content being edited.
type TextEdit struct {
	Buffer      buffer.Buffer
	LineNumbers bool   // Whether to render line numbers (and therefore the column)
	Dirty       bool   // Whether the buffer has been edited
	UseHardTabs bool   // When true, tabs are '\t'
	TabSize     int    // How many spaces to indent by
	IsCRLF      bool   // Whether the file's line endings are CRLF (\r\n) or LF (\n)
	FilePath    string // Will be empty if the file has not been saved yet

	screen           *tcell.Screen // We keep our own reference to the screen for cursor purposes.
	x, y             int
	width, height    int
	focused          bool
	curx, cury       int // Zero-based: cursor points before the character at that position.
	prevCurCol       int // Previous maximum column the cursor was at, when the user pressed left or right
	scrollx, scrolly int // X and Y offset of view, known as scroll

	selection  Region // Selection: selectMode determines if it should be used
	selectMode bool   // Whether the user is actively selecting text

	Theme *Theme
}

// New will initialize the buffer using the given 'contents'. If the 'filePath' or 'FilePath' is empty,
// it can be assumed that the TextEdit has no file association, or it is unsaved.
func NewTextEdit(screen *tcell.Screen, filePath string, contents []byte, theme *Theme) *TextEdit {
	te := &TextEdit{
		Buffer:      nil,
		LineNumbers: true,
		UseHardTabs: true,
		TabSize:     4,
		FilePath:    filePath,
		screen:      screen,
		Theme:       theme,
	}
	te.SetContents(contents)
	return te
}

// SetContents applies the string to the internal buffer of the TextEdit component.
// The string is determined to be either CRLF or LF based on line-endings.
func (t *TextEdit) SetContents(contents []byte) {
	var i int
loop:
	for i < len(contents) {
		switch contents[i] {
		case '\n':
			t.IsCRLF = false
			break loop
		case '\r':
			// We could check for a \n after, but what's the point?
			t.IsCRLF = true
			break loop
		}
		_, size := utf8.DecodeRune(contents[i:])
		i += size
	}

	t.Buffer = buffer.NewRopeBuffer(contents)
}

// GetLineDelimiter returns "\r\n" for a CRLF buffer, or "\n" for an LF buffer.
func (t *TextEdit) GetLineDelimiter() string {
	if t.IsCRLF {
		return "\r\n"
	} else {
		return "\n"
	}
}

// Changes a file's line delimiters. If `crlf` is true, then line delimiters are replaced
// with Windows CRLF (\r\n). If `crlf` is false, then line delimtiers are replaced with Unix
// LF (\n). The TextEdit `IsCRLF` variable is updated with the new value.
func (t *TextEdit) ChangeLineDelimiters(crlf bool) {
	t.IsCRLF = crlf
	t.Dirty = true
	// line delimiters are constructed with String() function
	// TODO: ^ not true anymore ^
	panic("Cannot ChangeLineDelimiters")
}

// Delete with `forwards` false will backspace, destroying the character before the cursor,
// while Delete with `forwards` true will delete the character after (or on) the cursor.
// In insert mode, forwards is always true.
func (t *TextEdit) Delete(forwards bool) {
	t.Dirty = true

	if t.selectMode { // If text is selected, delete the whole selection
		t.cury, t.curx = t.Buffer.ClampLineCol(t.selection.EndLine, t.selection.EndCol)
		t.selectMode = false // Disable selection and prevent infinite loop

		// Delete the region
		t.Buffer.Remove(t.selection.StartLine, t.selection.StartCol, t.selection.EndLine, t.selection.EndCol)
		t.SetLineCol(t.selection.StartLine, t.selection.StartCol) // Set cursor to start of region

		return
	}

	if forwards { // Delete the character after the cursor
		// If the cursor is not at the end of the last line...
		if t.cury < t.Buffer.Lines()-1 || t.curx < t.Buffer.RunesInLine(t.cury) {
			t.Buffer.Remove(t.cury, t.curx, t.cury, t.curx) // Remove character at cursor
		}
	} else { // Delete the character before the cursor
		// If the cursor is not at the first column of the first line...
		if t.cury > 0 || t.curx > 0 {
			t.CursorLeft() // Back up to that character
			t.Buffer.Remove(t.cury, t.curx, t.cury, t.curx) // Remove character at cursor
		}
	}
}

// Writes `contents` at the cursor position. Line delimiters and tab character supported.
// Any other control characters will be printed. Overwrites any active selection.
func (t *TextEdit) Insert(contents string) {
	t.Dirty = true

	if t.selectMode { // If there is a selection...
		// Go to and delete the selection
		t.Delete(true) // The parameter doesn't matter with selection
	}

	runes := []rune(contents)
	for i := 0; i < len(runes); i++ {
		ch := runes[i]
		switch ch {
		case '\r':
			// If the character after is a \n, then it is a CRLF
			if i+1 < len(runes) && runes[i+1] == '\n' {
				i++ // Consume '\n' after
				t.Buffer.Insert(t.cury, t.curx, []byte{'\n'})
				t.SetLineCol(t.cury+1, 0) // Go to the start of that new line
			}
		case '\n':
			t.Buffer.Insert(t.cury, t.curx, []byte{'\n'})
			t.SetLineCol(t.cury+1, 0) // Go to the start of that new line
		case '\b':
			t.Delete(false) // Delete the character before the cursor
		case '\t':
			if !t.UseHardTabs { // If this file does not use hard tabs...
				// Insert spaces
				spaces := strings.Repeat(" ", t.TabSize)
				t.Buffer.Insert(t.cury, t.curx, []byte(spaces))
				t.SetLineCol(t.cury, t.curx+len(spaces)) // Advance the cursor
				break
			}
			fallthrough // Append the \t character
		default:
			// Insert character into line
			t.Buffer.Insert(t.cury, t.curx, []byte(string(ch)))
			t.SetLineCol(t.cury, t.curx+1) // Advance the cursor
		}
	}
	t.prevCurCol = t.curx
}

// getTabCountInLineAtCol returns tabs in the given line, before the column position,
// if hard tabs are enabled. If hard tabs are not enabled, the function returns zero.
// Multiply returned tab count by TabSize to get the offset produced by tabs.
// Col must be a valid column position in the given line. Maybe call clampLineCol before
// this function.
func (t *TextEdit) getTabCountInLineAtCol(line, col int) int {
	if t.UseHardTabs {
		return t.Buffer.Count(line, 0, line, col, []byte{'\t'})
	}
	return 0
}

// GetLineCol returns (line, col) of the cursor. Zero is origin for both.
func (t *TextEdit) GetLineCol() (int, int) {
	return t.cury, t.curx
}

// SetLineCol sets the cursor line and column position. Zero is origin for both.
// If `line` is out of bounds, `line` will be clamped to the closest available line.
// If `col` is out of bounds, `col` will be clamped to the closest column available for the line.
// Will scroll the TextEdit just enough to see the line the cursor is at.
func (t *TextEdit) SetLineCol(line, col int) {
	line, col = t.Buffer.ClampLineCol(line, col)

	// Handle hard tabs
	tabOffset := t.getTabCountInLineAtCol(line, col) * (t.TabSize-1) // Offset for the current line from hard tabs (temporary; purely visual)

	// Scroll the screen when going to lines out of view
	if line >= t.scrolly+t.height-1 { // If the new line is below view...
		t.scrolly = line - t.height + 1 // Scroll just enough to view that line
	} else if line < t.scrolly { // If the new line is above view
		t.scrolly = line
	}

	columnWidth := t.getColumnWidth()

	// Scroll the screen horizontally when going to columns out of view
	if col+tabOffset >= t.scrollx+(t.width-columnWidth-1) { // If the new column is right of view
		t.scrollx = (col + tabOffset) - (t.width - columnWidth) + 1 // Scroll just enough to view that column
	} else if col+tabOffset < t.scrollx { // If the new column is left of view
		t.scrollx = col + tabOffset // Scroll left enough to view that column
	}

	if t.scrollx < 0 {
		panic("oops")
	}

	t.cury, t.curx = line, col
	if t.focused && !t.selectMode {
		(*t.screen).ShowCursor(t.x+columnWidth+col+tabOffset-t.scrollx, t.y+line-t.scrolly)
	} else {
		(*t.screen).HideCursor()
	}
}

// CursorUp moves the cursor up a line.
func (t *TextEdit) CursorUp() {
	if t.cury <= 0 { // If the cursor is at the first line...
		t.SetLineCol(t.cury, 0) // Go to beginning
	} else {
		line, col := t.Buffer.ClampLineCol(t.cury-1, t.prevCurCol)
		if t.UseHardTabs { // When using hard tabs, subtract offsets produced by tabs
			tabOffset := t.getTabCountInLineAtCol(line, col) * (t.TabSize - 1)
			col -= tabOffset // We still count each \t in the col
		}
		t.SetLineCol(line, col)
	}
}

// CursorDown moves the cursor down a line.
func (t *TextEdit) CursorDown() {
	if t.cury >= t.Buffer.Lines()-1 { // If the cursor is at the last line...
		t.SetLineCol(t.cury, math.MaxInt32) // Go to end of current line
	} else {
		line, col := t.Buffer.ClampLineCol(t.cury+1, t.prevCurCol)
		if t.UseHardTabs {
			tabOffset := t.getTabCountInLineAtCol(line, col) * (t.TabSize - 1)
			col -= tabOffset // We still count each \t in the col
		}
		t.SetLineCol(line, col) // Go to line below
	}
}

// CursorLeft moves the cursor left a column.
func (t *TextEdit) CursorLeft() {
	if t.curx <= 0 && t.cury != 0 { // If we are at the beginning of the current line...
		t.SetLineCol(t.cury-1, math.MaxInt32) // Go to end of line above
	} else {
		t.SetLineCol(t.cury, t.curx-1)
	}
	tabOffset := t.getTabCountInLineAtCol(t.cury, t.curx) * (t.TabSize - 1)
	t.prevCurCol = t.curx + tabOffset
}

// CursorRight moves the cursor right a column.
func (t *TextEdit) CursorRight() {
	// If we are at the end of the current line,
	// and not at the last line...
	if t.curx >= t.Buffer.RunesInLine(t.cury) && t.cury < t.Buffer.Lines()-1 {
		t.SetLineCol(t.cury+1, 0) // Go to beginning of line below
	} else {
		t.SetLineCol(t.cury, t.curx+1)
	}
	tabOffset := t.getTabCountInLineAtCol(t.cury, t.curx) * (t.TabSize - 1)
	t.prevCurCol = t.curx + tabOffset
}

// getColumnWidth returns the width of the line numbers column if it is present.
func (t *TextEdit) getColumnWidth() int {
	columnWidth := 0
	if t.LineNumbers {
		// Set columnWidth to max count of line number digits
		columnWidth = Max(2, len(strconv.Itoa(t.Buffer.Lines()))) // Column has minimum width of 2
	}
	return columnWidth
}

// GetSelectedBytes returns a byte slice of the region of the buffer that is currently selected.
// If the returned string is empty, then nothing was selected. The slice returned may or may not
// be a copy of the buffer, so do not write to it.
func (t *TextEdit) GetSelectedBytes() []byte {
	if t.selectMode {
		return t.Buffer.Slice(t.selection.StartLine, t.selection.StartCol, t.selection.EndLine, t.selection.EndCol)
	}
	return []byte{}
}

// Draw renders the TextEdit component.
func (t *TextEdit) Draw(s tcell.Screen) {
	columnWidth := t.getColumnWidth()
	bufferLines := t.Buffer.Lines()

	textEditStyle := t.Theme.GetOrDefault("TextEdit")
	selectedStyle := t.Theme.GetOrDefault("TextEditSelected")
	columnStyle := t.Theme.GetOrDefault("TextEditColumn")

	DrawRect(s, t.x, t.y, t.width, t.height, ' ', textEditStyle) // Fill background

	var tabStr string
	if t.UseHardTabs {
		// Only call strings.Repeat once for each draw in hard tab files
		tabStr = strings.Repeat(" ", t.TabSize)
	}

	for lineY := t.y; lineY < t.y+t.height; lineY++ { // For each line we can draw...
		line := lineY + t.scrolly - t.y // The line number being drawn (starts at zero)

		lineNumStr := ""

		if line < bufferLines { // Only index buffer if we are within it...
			lineNumStr = strconv.Itoa(line + 1) // Line number as a string

			lineStr := string(t.Buffer.Line(line)) // Line to be drawn
			if t.UseHardTabs {
				lineStr = strings.ReplaceAll(lineStr, "\t", tabStr)
			}

			lineRunes := []rune(lineStr) // TODO: something more efficient here
			if len(lineRunes) >= t.scrollx { // If some of the line is visible at our horizontal scroll...
				lineRunes = lineRunes[t.scrollx:] // Trim left side of string we cannot see

				if len(lineRunes) >= t.width-columnWidth { // If that trimmed line continues out of view to the right...
					lineRunes = lineRunes[:t.width-columnWidth] // Trim right side of string we cannot see
				}

				// If the current line is part of a selected region...
				if t.selectMode && line >= t.selection.StartLine && line <= t.selection.EndLine {
					selStartIdx := t.scrollx
					if line == t.selection.StartLine { // If the selection begins somewhere in the line...
						// Account for hard tabs
						tabCount := t.getTabCountInLineAtCol(line, t.selection.StartCol)
						selStartIdx = t.selection.StartCol + tabCount*(t.TabSize-1) - t.scrollx
					}
					selEndIdx := len(lineRunes) - t.scrollx - 1 // used inclusively
					if line == t.selection.EndLine {        // If the selection ends somewhere in the line...
						tabCount := t.getTabCountInLineAtCol(line, t.selection.EndCol)
						selEndIdx = t.selection.EndCol - 1 + tabCount*(t.TabSize-1) - t.scrollx
					}

					// NOTE: a special draw function just for selections. Should combine this with ordinary draw
					currentStyle := textEditStyle
					for i := 0; i < t.width-columnWidth; i++ { // For each column we can draw
						if i == selStartIdx {
							currentStyle = selectedStyle // begin drawing selected
						} else if i > selEndIdx {
							currentStyle = textEditStyle // reset style
						}

						r := ' '                // Rune to draw
						if i < len(lineRunes) { // While we're drawing the line
							r = lineRunes[i]
						}

						s.SetContent(t.x+columnWidth+i, lineY, r, nil, currentStyle)
					}
				} else {
					DrawStr(s, t.x+columnWidth, lineY, string(lineRunes), textEditStyle) // Draw line
				}
			}
		}

		columnStr := fmt.Sprintf("%s%s", strings.Repeat(" ", columnWidth-len(lineNumStr)), lineNumStr) // Right align line number

		DrawStr(s, t.x, lineY, columnStr, columnStyle) // Draw column
	}

	// Update cursor
	t.SetLineCol(t.cury, t.curx)
}

// SetFocused sets whether the TextEdit is focused. When focused, the cursor is set visible
// and its position is updated on every event.
func (t *TextEdit) SetFocused(v bool) {
	t.focused = v
	if v {
		t.SetLineCol(t.cury, t.curx)
	} else {
		(*t.screen).HideCursor()
	}
}

func (t *TextEdit) SetTheme(theme *Theme) {
	t.Theme = theme
}

// GetPos gets the position of the TextEdit.
func (t *TextEdit) GetPos() (int, int) {
	return t.x, t.y
}

// SetPos sets the position of the TextEdit.
func (t *TextEdit) SetPos(x, y int) {
	t.x, t.y = x, y
}

func (t *TextEdit) GetMinSize() (int, int) {
	return 0, 0
}

// GetSize gets the size of the TextEdit.
func (t *TextEdit) GetSize() (int, int) {
	return t.width, t.height
}

// SetSize sets the size of the TextEdit.
func (t *TextEdit) SetSize(width, height int) {
	t.width, t.height = width, height
}

// HandleEvent allows the TextEdit to handle `event` if it chooses, returns
// whether the TextEdit handled the event.
func (t *TextEdit) HandleEvent(event tcell.Event) bool {
	switch ev := event.(type) {
	case *tcell.EventKey:
		switch ev.Key() {
		// Cursor movement
		case tcell.KeyUp:
			if ev.Modifiers() == tcell.ModShift {
				if !t.selectMode {
					t.selection.StartLine, t.selection.StartCol = t.cury, t.curx
					t.selection.EndLine, t.selection.EndCol = t.cury, t.curx
					t.selectMode = true
				} else {
					prevCurX, prevCurY := t.curx, t.cury
					t.CursorUp()
					// Grow the selection in the correct direction
					if prevCurY <= t.selection.StartLine && prevCurX <= t.selection.StartCol {
						t.selection.StartLine, t.selection.StartCol = t.cury, t.curx
					} else {
						t.selection.EndLine, t.selection.EndCol = t.cury, t.curx
					}
				}
			} else {
				t.selectMode = false
				t.CursorUp()
			}
		case tcell.KeyDown:
			if ev.Modifiers() == tcell.ModShift {
				if !t.selectMode {
					t.selection.StartLine, t.selection.StartCol = t.cury, t.curx
					t.selection.EndLine, t.selection.EndCol = t.cury, t.curx
					t.selectMode = true
				} else {
					prevCurX, prevCurY := t.curx, t.cury
					t.CursorDown()
					if prevCurY >= t.selection.EndLine && prevCurX >= t.selection.EndCol {
						t.selection.EndLine, t.selection.EndCol = t.cury, t.curx
					} else {
						t.selection.StartLine, t.selection.StartCol = t.cury, t.curx
					}
				}
			} else {
				t.selectMode = false
				t.CursorDown()
			}
		case tcell.KeyLeft:
			if ev.Modifiers() == tcell.ModShift {
				if !t.selectMode {
					t.CursorLeft() // We want the character to the left to be selected only (think insert)
					t.selection.StartLine, t.selection.StartCol = t.cury, t.curx
					t.selection.EndLine, t.selection.EndCol = t.cury, t.curx
					t.selectMode = true
				} else {
					prevCurX, prevCurY := t.curx, t.cury
					t.CursorLeft()
					if prevCurY == t.selection.StartLine && prevCurX == t.selection.StartCol { // We are moving the start...
						t.selection.StartLine, t.selection.StartCol = t.cury, t.curx
					} else {
						t.selection.EndLine, t.selection.EndCol = t.cury, t.curx
					}
				}
			} else {
				t.selectMode = false
				t.CursorLeft()
			}
		case tcell.KeyRight:
			if ev.Modifiers() == tcell.ModShift {
				if !t.selectMode { // If we are not already selecting...
					// Reset the selection to cursor pos
					t.selection.StartLine, t.selection.StartCol = t.cury, t.curx
					t.selection.EndLine, t.selection.EndCol = t.cury, t.curx
					t.selectMode = true
				} else {
					prevCurX, prevCurY := t.curx, t.cury
					t.CursorRight() // Advance the cursor
					if prevCurY == t.selection.EndLine && prevCurX == t.selection.EndCol {
						t.selection.EndLine, t.selection.EndCol = t.cury, t.curx
					} else {
						t.selection.StartLine, t.selection.StartCol = t.cury, t.curx
					}
				}
			} else {
				t.selectMode = false
				t.CursorRight()
			}
		case tcell.KeyHome:
			t.SetLineCol(t.cury, 0)
			t.prevCurCol = t.curx
		case tcell.KeyEnd:
			t.SetLineCol(t.cury, math.MaxInt32) // Max column
			t.prevCurCol = t.curx
		case tcell.KeyPgUp:
			t.SetLineCol(t.scrolly-t.height, t.curx) // Go a page up
			t.prevCurCol = t.curx
		case tcell.KeyPgDn:
			t.SetLineCol(t.scrolly+t.height*2-1, t.curx) // Go a page down
			t.prevCurCol = t.curx

		// Deleting
		case tcell.KeyBackspace:
			fallthrough
		case tcell.KeyBackspace2:
			t.Delete(false)
		case tcell.KeyDelete:
			t.Delete(true)

		// Other control
		case tcell.KeyTab:
			t.Insert("\t") // (can translate to four spaces)
		case tcell.KeyEnter:
			t.Insert("\n")

		// Inserting
		case tcell.KeyRune:
			t.Insert(string(ev.Rune())) // Insert rune
		default:
			return false
		}
		return true
	}
	return false
}