package ui

import (
	"fmt"
	"math"
	"strconv"
	"strings"

	"github.com/gdamore/tcell/v2"
)

// 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 {
	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

	buffer           []string      // TODO: replace line-based buffer with gap buffer
	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

	Theme *Theme
}

// New will initialize the buffer using the given string `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, contents string, theme *Theme) *TextEdit {
	te := &TextEdit{
		LineNumbers: true,
		UseHardTabs: true,
		TabSize:     4,
		FilePath:    filePath,
		buffer:      nil,
		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 string) {
loop:
	for _, r := range contents {
		switch r {
		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
		}
	}

	delimiter := "\n"
	if t.IsCRLF {
		delimiter = "\r\n"
	}

	t.buffer = strings.Split(contents, delimiter) // Split contents into lines
}

func (t *TextEdit) String() string {
	delimiter := "\n"
	if t.IsCRLF {
		delimiter = "\r\n"
	}
	return strings.Join(t.buffer, delimiter)
}

// 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
	// line delimiters are constructed with String() function
}

// 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) {
	// TODO: deleting through lines
	if forwards { // Delete the character after the cursor
		if t.curx < len(t.buffer[t.cury]) { // If the cursor is not at the end of the line...
			lineRunes := []rune(t.buffer[t.cury])
			copy(lineRunes[t.curx:], lineRunes[t.curx+1:]) // Shift runes at cursor + 1 left
			lineRunes = lineRunes[:len(lineRunes)-1]       // Shrink line length
			t.buffer[t.cury] = string(lineRunes)           // Reassign line
		} else { // If the cursor is at the end of the line...
			if t.cury < len(t.buffer)-1 { // And the cursor is not at the last line...
				oldLineIdx := t.cury + 1
				curLineRunes := []rune(t.buffer[t.cury])
				oldLineRunes := []rune(t.buffer[oldLineIdx])
				curLineRunes = append(curLineRunes, oldLineRunes...) // Append runes from deleted line to current line
				t.buffer[t.cury] = string(curLineRunes)              // Update the current line with the new runes

				copy(t.buffer[oldLineIdx:], t.buffer[oldLineIdx+1:]) // Shift lines below the old line up
				t.buffer = t.buffer[:len(t.buffer)-1]                // Shrink buffer by one line
			}
		}
	} else { // Delete the character before the cursor
		if t.curx > 0 { // If the cursor is not at the beginning of the line...
			lineRunes := []rune(t.buffer[t.cury])
			copy(lineRunes[t.curx-1:], lineRunes[t.curx:]) // Shift runes at cursor left
			lineRunes = lineRunes[:len(lineRunes)-1]       // Shrink line length
			t.buffer[t.cury] = string(lineRunes)           // Reassign line

			t.SetLineCol(t.cury, t.curx-1) // Shift cursor left
		} else { // If the cursor is at the beginning of the line...
			if t.cury > 0 { // And the cursor is not at the first line...
				oldLineIdx := t.cury
				t.SetLineCol(t.cury-1, len(t.buffer[t.cury-1])) // Cursor goes to the end of the above line
				curLineRunes := []rune(t.buffer[t.cury])
				oldLineRunes := []rune(t.buffer[oldLineIdx])
				curLineRunes = append(curLineRunes, oldLineRunes...) // Append the old line to the current line
				t.buffer[t.cury] = string(curLineRunes)              // Update the current line to the new runes

				copy(t.buffer[oldLineIdx:], t.buffer[oldLineIdx+1:]) // Shift lines below the old line up
				t.buffer = t.buffer[:len(t.buffer)-1]                // Shrink buffer by one line
			}
		}
	}
}

// Writes `contents` at the cursor position. Line delimiters and tab character supported.
// Any other control characters will be printed.
func (t *TextEdit) Insert(contents string) {
	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++
				t.insertNewLine()
			}
		case '\n':
			t.insertNewLine()
		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 := []rune(strings.Repeat(" ", t.TabSize))
				spacesLen := len(spaces)

				lineRunes := []rune(t.buffer[t.cury])
				lineRunes = append(lineRunes, spaces...)
				copy(lineRunes[t.curx+spacesLen:], lineRunes[t.curx:]) // Shift runes at cursor to the right
				copy(lineRunes[t.curx:], spaces)                       // Copy spaces into the gap

				t.buffer[t.cury] = string(lineRunes) // Reassign the line

				t.SetLineCol(t.cury, t.curx+spacesLen) // Advance the cursor
				break
			}
			fallthrough // Append the \t character
		default:
			// Insert character into line
			lineRunes := []rune(t.buffer[t.cury])
			lineRunes = append(lineRunes, ch)              // Extend the length of the string
			copy(lineRunes[t.curx+1:], lineRunes[t.curx:]) // Shift runes at cursor to the right
			lineRunes[t.curx] = ch

			t.buffer[t.cury] = string(lineRunes) // Reassign the line

			t.SetLineCol(t.cury, t.curx+1) // Advance the cursor
		}
	}
}

// insertNewLine inserts a line break at the cursor and sets the cursor position to the first
// column of that new line. Text before the cursor on the current line remains on that line,
// text at or after the cursor on the current line is moved to the new line.
func (t *TextEdit) insertNewLine() {
	lineRunes := []rune(t.buffer[t.cury]) // A slice of runes of the old line
	movedRunes := lineRunes[t.curx:]      // A slice of the old line containing runes to be moved
	newLineRunes := make([]rune, len(movedRunes))
	copy(newLineRunes, movedRunes)                // Copy old runes to new line
	t.buffer[t.cury] = string(lineRunes[:t.curx]) // Shrink old line's length

	t.buffer = append(t.buffer, "")                // Increment buffer length
	copy(t.buffer[t.cury+2:], t.buffer[t.cury+1:]) // Shift lines after current line down
	t.buffer[t.cury+1] = string(newLineRunes)      // Assign the new line

	t.SetLineCol(t.cury+1, 0) // Go to start of new line
}

// 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) {
	// Clamp the line input
	if line < 0 {
		line = 0
	} else if len := len(t.buffer); line >= len { // If new line is beyond the length of the buffer...
		line = len - 1 // Change that line to be the end of the buffer, instead
	}

	lineRunes := []rune(t.buffer[line])

	// Clamp the column input
	if col < 0 {
		col = 0
	} else if len := len(lineRunes); col > len {
		col = len
	}

	// Handle hard tabs
	tabOffset := 0     // Offset for the current column (temporary; purely visual)
	if t.UseHardTabs { // If the file is encoded as tabs, not spaces...
		tabOffset = (t.TabSize - 1) * strings.Count(string(lineRunes[0:col]), "\t") // Shift the cursor for tabs (they are rendered as spaces)
	}

	// 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
	}

	t.cury, t.curx = line, col
	if t.focused {
		columnWidth := t.getColumnWidth()
		(*t.screen).ShowCursor(t.x+columnWidth+col+tabOffset, t.y+line-t.scrolly)
	}
}

// CursorUp moves the cursor up a line.
func (t *TextEdit) CursorUp() {
	t.SetLineCol(t.cury-1, t.prevCurCol)
}

// CursorDown moves the cursor down a line.
func (t *TextEdit) CursorDown() {
	if t.cury >= len(t.buffer)-1 { // If the cursor is at the last line...
		t.SetLineCol(t.cury, len(t.buffer[t.cury])) // Go to end of current line
	} else {
		t.SetLineCol(t.cury+1, t.prevCurCol) // 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)
	}
	t.prevCurCol = t.curx
}

// 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 >= len([]rune(t.buffer[t.cury])) && t.cury < len(t.buffer)-1 {
		t.SetLineCol(t.cury+1, 0) // Go to beginning of line below
	} else {
		t.SetLineCol(t.cury, t.curx+1)
	}
	t.prevCurCol = t.curx
}

// 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(len(t.buffer)))) // Column has minimum width of 2
	}
	return columnWidth
}

// Draw renders the TextEdit component.
func (t *TextEdit) Draw(s tcell.Screen) {
	columnWidth := t.getColumnWidth()
	bufferLen := len(t.buffer)

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

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

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

			var lineStr string // Line to be drawn
			if t.UseHardTabs {
				lineStr = strings.ReplaceAll(t.buffer[line], "\t", strings.Repeat(" ", t.TabSize))
			} else {
				lineStr = t.buffer[line]
			}

			DrawStr(s, t.x+columnWidth, lineY, lineStr, 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:
			t.CursorUp()
		case tcell.KeyDown:
			t.CursorDown()
		case tcell.KeyLeft:
			t.CursorLeft()
		case tcell.KeyRight:
			t.CursorRight()
		case tcell.KeyHome:
			t.SetLineCol(t.cury, 0)
		case tcell.KeyEnd:
			t.SetLineCol(t.cury, len(t.buffer[t.cury]))
		case tcell.KeyPgUp:
			t.SetLineCol(t.scrolly - t.height, t.curx) // Go a page up
		case tcell.KeyPgDn:
			t.SetLineCol(t.scrolly + t.height*2 - 1, t.curx) // Go a page down

		// 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.insertNewLine()

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