package editor

import (
	"strings"
	"testing"

	"git.gophernest.net/azpect/TextEditor/internal/core"
)

// =============================================================================
// yy (Yank Line / DoublePress) Tests
// =============================================================================

func TestYankLineBasic(t *testing.T) {
	t.Run("yy yanks current line to register", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.LinewiseRegister {
			t.Errorf("register type = %v, want LinewiseRegister", reg.Type)
		}
		if len(reg.Content) != 1 {
			t.Errorf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "line 1" {
			t.Errorf("register content[0] = %q, want 'line 1'", reg.Content[0])
		}
	})

	t.Run("yy does not modify buffer", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 1, Col: 0}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 3 {
			t.Errorf("LineCount() = %d, want 3", m.ActiveBuffer().LineCount())
		}
		if m.ActiveBuffer().Lines[0].String() != "line 1" {
			t.Errorf("Line(0) = %q, want 'line 1'", m.ActiveBuffer().Lines[0].String())
		}
		if m.ActiveBuffer().Lines[1].String() != "line 2" {
			t.Errorf("Line(1) = %q, want 'line 2'", m.ActiveBuffer().Lines[1].String())
		}
		if m.ActiveBuffer().Lines[2].String() != "line 3" {
			t.Errorf("Line(2) = %q, want 'line 3'", m.ActiveBuffer().Lines[2].String())
		}
	})

	t.Run("yy does not move cursor", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 1, Col: 3}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)
		if m.ActiveWindow().Cursor.Line != 1 {
			t.Errorf("CursorY() = %d, want 1", m.ActiveWindow().Cursor.Line)
		}
		if m.ActiveWindow().Cursor.Col != 3 {
			t.Errorf("CursorX() = %d, want 3", m.ActiveWindow().Cursor.Col)
		}
	})

	t.Run("yy from middle of file", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"first", "second", "third", "fourth"}),
			WithCursorPos(core.Position{Line: 2, Col: 0}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)
		reg, _ := m.GetRegister('"')
		if reg.Content[0] != "third" {
			t.Errorf("register content[0] = %q, want 'third'", reg.Content[0])
		}
	})

	t.Run("yy at last line", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "last line"}),
			WithCursorPos(core.Position{Line: 2, Col: 0}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)
		reg, _ := m.GetRegister('"')
		if reg.Content[0] != "last line" {
			t.Errorf("register content[0] = %q, want 'last line'", reg.Content[0])
		}
	})
}

func TestYankLineWithCount(t *testing.T) {
	t.Run("2yy yanks two lines", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3", "line 4"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "2", "y", "y")

		m := getFinalModel(t, tm)
		reg, _ := m.GetRegister('"')
		if len(reg.Content) != 2 {
			t.Errorf("register content length = %d, want 2", len(reg.Content))
		}
		if reg.Content[0] != "line 1" {
			t.Errorf("register content[0] = %q, want 'line 1'", reg.Content[0])
		}
		if reg.Content[1] != "line 2" {
			t.Errorf("register content[1] = %q, want 'line 2'", reg.Content[1])
		}
	})

	t.Run("3yy yanks three lines", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"a", "b", "c", "d", "e"}),
			WithCursorPos(core.Position{Line: 1, Col: 0}),
		)
		sendKeys(tm, "3", "y", "y")

		m := getFinalModel(t, tm)
		reg, _ := m.GetRegister('"')
		if len(reg.Content) != 3 {
			t.Errorf("register content length = %d, want 3", len(reg.Content))
		}
		if reg.Content[0] != "b" {
			t.Errorf("register content[0] = %q, want 'b'", reg.Content[0])
		}
		if reg.Content[1] != "c" {
			t.Errorf("register content[1] = %q, want 'c'", reg.Content[1])
		}
		if reg.Content[2] != "d" {
			t.Errorf("register content[2] = %q, want 'd'", reg.Content[2])
		}
	})

	t.Run("yy with count overflow clamps to available lines", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 1, Col: 0}),
		)
		sendKeys(tm, "1", "0", "y", "y") // 10yy but only 2 lines available

		m := getFinalModel(t, tm)
		reg, _ := m.GetRegister('"')
		if len(reg.Content) != 2 {
			t.Errorf("register content length = %d, want 2 (clamped)", len(reg.Content))
		}
		if reg.Content[0] != "line 2" {
			t.Errorf("register content[0] = %q, want 'line 2'", reg.Content[0])
		}
		if reg.Content[1] != "line 3" {
			t.Errorf("register content[1] = %q, want 'line 3'", reg.Content[1])
		}
	})

	t.Run("yy with count does not modify buffer", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "3", "y", "y")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 3 {
			t.Errorf("LineCount() = %d, want 3", m.ActiveBuffer().LineCount())
		}
	})
}

func TestYankLineEdgeCases(t *testing.T) {
	t.Run("yy on empty line", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "", "line 3"}),
			WithCursorPos(core.Position{Line: 1, Col: 0}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)
		reg, _ := m.GetRegister('"')
		if len(reg.Content) != 1 {
			t.Errorf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "" {
			t.Errorf("register content[0] = %q, want ''", reg.Content[0])
		}
	})

	t.Run("yy on single line buffer", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"only line"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)
		reg, _ := m.GetRegister('"')
		if reg.Content[0] != "only line" {
			t.Errorf("register content[0] = %q, want 'only line'", reg.Content[0])
		}
	})

	t.Run("yy preserves whitespace", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"    indented", "\ttabbed", "  spaces  "}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "3", "y", "y")

		m := getFinalModel(t, tm)
		reg, _ := m.GetRegister('"')
		if reg.Content[0] != "    indented" {
			t.Errorf("register content[0] = %q, want '    indented'", reg.Content[0])
		}
		if reg.Content[1] != "\ttabbed" {
			t.Errorf("register content[1] = %q, want '\\ttabbed'", reg.Content[1])
		}
		if reg.Content[2] != "  spaces  " {
			t.Errorf("register content[2] = %q, want '  spaces  '", reg.Content[2])
		}
	})
}

// =============================================================================
// Yank with Linewise Motions (yj, yk, yG, ygg) - TDD Tests
// =============================================================================

func TestYankWithLinewiseMotions(t *testing.T) {
	t.Run("yj yanks current line and line below", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "j")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.LinewiseRegister {
			t.Errorf("register type = %v, want LinewiseRegister", reg.Type)
		}
		if len(reg.Content) != 2 {
			t.Fatalf("register content length = %d, want 2", len(reg.Content))
		}
		if reg.Content[0] != "line 1" {
			t.Errorf("register content[0] = %q, want 'line 1'", reg.Content[0])
		}
		if reg.Content[1] != "line 2" {
			t.Errorf("register content[1] = %q, want 'line 2'", reg.Content[1])
		}
	})

	t.Run("yk yanks current line and line above", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 1, Col: 0}),
		)
		sendKeys(tm, "y", "k")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.LinewiseRegister {
			t.Errorf("register type = %v, want LinewiseRegister", reg.Type)
		}
		if len(reg.Content) != 2 {
			t.Fatalf("register content length = %d, want 2", len(reg.Content))
		}
		if reg.Content[0] != "line 1" {
			t.Errorf("register content[0] = %q, want 'line 1'", reg.Content[0])
		}
		if reg.Content[1] != "line 2" {
			t.Errorf("register content[1] = %q, want 'line 2'", reg.Content[1])
		}
	})

	t.Run("yG yanks from cursor to end of file", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3", "line 4"}),
			WithCursorPos(core.Position{Line: 1, Col: 0}),
		)
		sendKeys(tm, "y", "G")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.LinewiseRegister {
			t.Errorf("register type = %v, want LinewiseRegister", reg.Type)
		}
		if len(reg.Content) != 3 {
			t.Fatalf("register content length = %d, want 3", len(reg.Content))
		}
		if reg.Content[0] != "line 2" {
			t.Errorf("register content[0] = %q, want 'line 2'", reg.Content[0])
		}
		if reg.Content[2] != "line 4" {
			t.Errorf("register content[2] = %q, want 'line 4'", reg.Content[2])
		}
	})

	t.Run("ygg yanks from cursor to beginning of file", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3", "line 4"}),
			WithCursorPos(core.Position{Line: 2, Col: 0}),
		)
		sendKeys(tm, "y", "g", "g")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.LinewiseRegister {
			t.Errorf("register type = %v, want LinewiseRegister", reg.Type)
		}
		if len(reg.Content) != 3 {
			t.Fatalf("register content length = %d, want 3", len(reg.Content))
		}
		if reg.Content[0] != "line 1" {
			t.Errorf("register content[0] = %q, want 'line 1'", reg.Content[0])
		}
		if reg.Content[2] != "line 3" {
			t.Errorf("register content[2] = %q, want 'line 3'", reg.Content[2])
		}
	})

	t.Run("y2j yanks current and next two lines", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"a", "b", "c", "d", "e"}),
			WithCursorPos(core.Position{Line: 1, Col: 0}),
		)
		sendKeys(tm, "y", "2", "j")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if len(reg.Content) != 3 {
			t.Fatalf("register content length = %d, want 3", len(reg.Content))
		}
		if reg.Content[0] != "b" {
			t.Errorf("register content[0] = %q, want 'b'", reg.Content[0])
		}
		if reg.Content[1] != "c" {
			t.Errorf("register content[1] = %q, want 'c'", reg.Content[1])
		}
		if reg.Content[2] != "d" {
			t.Errorf("register content[2] = %q, want 'd'", reg.Content[2])
		}
	})

	t.Run("yj does not move cursor", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 0, Col: 3}),
		)
		sendKeys(tm, "y", "j")

		m := getFinalModel(t, tm)
		if m.ActiveWindow().Cursor.Line != 0 {
			t.Errorf("CursorY() = %d, want 0", m.ActiveWindow().Cursor.Line)
		}
	})

	t.Run("yG does not modify buffer", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "G")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 3 {
			t.Errorf("LineCount() = %d, want 3", m.ActiveBuffer().LineCount())
		}
	})
}

// =============================================================================
// Yank with Charwise Motions (yw, ye, yb, y$, y0) - TDD Tests
// =============================================================================

func TestYankWithCharwiseMotions(t *testing.T) {
	t.Run("yw yanks word under cursor", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "w")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.CharwiseRegister {
			t.Errorf("register type = %v, want CharwiseRegister", reg.Type)
		}
		// yw includes trailing space
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "hello " {
			t.Errorf("register content = %q, want 'hello '", reg.Content[0])
		}
	})

	t.Run("ye yanks to end of word (exclusive)", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "e")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.CharwiseRegister {
			t.Errorf("register type = %v, want CharwiseRegister", reg.Type)
		}
		// ye is inclusive of last char
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "hello" {
			t.Errorf("register content = %q, want 'hello'", reg.Content[0])
		}
	})

	t.Run("yb yanks backward word", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 6}), // on 'w'
		)
		sendKeys(tm, "y", "b")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.CharwiseRegister {
			t.Errorf("register type = %v, want CharwiseRegister", reg.Type)
		}
		// yb from 'w' back to start of 'hello'
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "hello " {
			t.Errorf("register content = %q, want 'hello '", reg.Content[0])
		}
	})

	t.Run("y$ yanks to end of line", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 6}), // on 'w'
		)
		sendKeys(tm, "y", "$")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.CharwiseRegister {
			t.Errorf("register type = %v, want CharwiseRegister", reg.Type)
		}
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "world" {
			t.Errorf("register content = %q, want 'world'", reg.Content[0])
		}
	})

	t.Run("y0 yanks to beginning of line", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 6}), // on 'w'
		)
		sendKeys(tm, "y", "0")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.CharwiseRegister {
			t.Errorf("register type = %v, want CharwiseRegister", reg.Type)
		}
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "hello " {
			t.Errorf("register content = %q, want 'hello '", reg.Content[0])
		}
	})

	t.Run("y_ yanks to first non-whitespace", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"    hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 10}), // on 'w'
		)
		sendKeys(tm, "y", "_")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.CharwiseRegister {
			t.Errorf("register type = %v, want CharwiseRegister", reg.Type)
		}
		// From 'w' back to 'h' (first non-ws)
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "hello " {
			t.Errorf("register content = %q, want 'hello '", reg.Content[0])
		}
	})

	t.Run("y2w yanks two words", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"one two three four"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "2", "w")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "one two " {
			t.Errorf("register content = %q, want 'one two '", reg.Content[0])
		}
	})

	t.Run("yw does not move cursor", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "w")

		m := getFinalModel(t, tm)
		if m.ActiveWindow().Cursor.Col != 0 {
			t.Errorf("CursorX() = %d, want 0", m.ActiveWindow().Cursor.Col)
		}
	})

	t.Run("yw does not modify buffer", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "w")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().Lines[0].String() != "hello world" {
			t.Errorf("Line(0) = %q, want 'hello world'", m.ActiveBuffer().Lines[0].String())
		}
	})
}

// =============================================================================
// Visual Mode Yank Tests - TDD Tests
// =============================================================================

func TestYankVisualCharwise(t *testing.T) {
	t.Run("v selection then y yanks selected text", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "v", "l", "l", "l", "l", "y") // select "hello"

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.CharwiseRegister {
			t.Errorf("register type = %v, want CharwiseRegister", reg.Type)
		}
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "hello" {
			t.Errorf("register content = %q, want 'hello'", reg.Content[0])
		}
	})

	t.Run("v selection across lines yanks with newlines", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2"}),
			WithCursorPos(core.Position{Line: 0, Col: 3}),
		)
		sendKeys(tm, "v", "j", "l", "l", "y") // select "e 1\nlin"

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.CharwiseRegister {
			t.Errorf("register type = %v, want CharwiseRegister", reg.Type)
		}
		// Multi-line charwise yank
		if len(reg.Content) < 1 {
			t.Fatal("register content empty, expected multi-line selection")
		}
	})

	t.Run("visual yank exits visual mode", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "v", "l", "l", "y")

		m := getFinalModel(t, tm)
		if m.Mode() != core.NormalMode {
			t.Errorf("Mode() = %v, want NormalMode", m.Mode())
		}
	})

	t.Run("visual yank does not modify buffer", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "v", "l", "l", "l", "l", "y")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().Lines[0].String() != "hello world" {
			t.Errorf("Line(0) = %q, want 'hello world'", m.ActiveBuffer().Lines[0].String())
		}
	})
}

func TestYankVisualLinewise(t *testing.T) {
	t.Run("V selection then y yanks entire lines", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "V", "j", "y") // select lines 1 and 2

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.LinewiseRegister {
			t.Errorf("register type = %v, want LinewiseRegister", reg.Type)
		}
		if len(reg.Content) != 2 {
			t.Fatalf("register content length = %d, want 2", len(reg.Content))
		}
		if reg.Content[0] != "line 1" {
			t.Errorf("register content[0] = %q, want 'line 1'", reg.Content[0])
		}
		if reg.Content[1] != "line 2" {
			t.Errorf("register content[1] = %q, want 'line 2'", reg.Content[1])
		}
	})

	t.Run("V on single line then y yanks that line", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "V", "y")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.LinewiseRegister {
			t.Errorf("register type = %v, want LinewiseRegister", reg.Type)
		}
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "line 1" {
			t.Errorf("register content[0] = %q, want 'line 1'", reg.Content[0])
		}
	})

	t.Run("V selection upward yanks in correct order", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 2, Col: 0}),
		)
		sendKeys(tm, "V", "k", "y") // select from line 3 upward to line 2

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if len(reg.Content) != 2 {
			t.Fatalf("register content length = %d, want 2", len(reg.Content))
		}
		// Order should be top-to-bottom regardless of selection direction
		if reg.Content[0] != "line 2" {
			t.Errorf("register content[0] = %q, want 'line 2'", reg.Content[0])
		}
		if reg.Content[1] != "line 3" {
			t.Errorf("register content[1] = %q, want 'line 3'", reg.Content[1])
		}
	})

	t.Run("visual line yank exits visual mode", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "V", "y")

		m := getFinalModel(t, tm)
		if m.Mode() != core.NormalMode {
			t.Errorf("Mode() = %v, want NormalMode", m.Mode())
		}
	})
}

func TestYankVisualBlock(t *testing.T) {
	t.Run("ctrl+v selection then y yanks block", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"abcdef", "ghijkl", "mnopqr"}),
			WithCursorPos(core.Position{Line: 0, Col: 1}),
		)
		sendKeys(tm, "ctrl+v", "j", "j", "l", "l", "y") // select 3x3 block starting at col 1

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if reg.Type != core.BlockwiseRegister {
			t.Errorf("register type = %v, want BlockwiseRegister", reg.Type)
		}
		// Block should contain "bcd", "hij", "nop"
		if len(reg.Content) != 3 {
			t.Fatalf("register content length = %d, want 3", len(reg.Content))
		}
		if reg.Content[0] != "bcd" {
			t.Errorf("register content[0] = %q, want 'bcd'", reg.Content[0])
		}
		if reg.Content[1] != "hij" {
			t.Errorf("register content[1] = %q, want 'hij'", reg.Content[1])
		}
		if reg.Content[2] != "nop" {
			t.Errorf("register content[2] = %q, want 'nop'", reg.Content[2])
		}
	})

	t.Run("visual block yank exits visual mode", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"abcd", "efgh"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "ctrl+v", "j", "l", "y")

		m := getFinalModel(t, tm)
		if m.Mode() != core.NormalMode {
			t.Errorf("Mode() = %v, want NormalMode", m.Mode())
		}
	})

	t.Run("visual block yank with uneven line lengths", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"abcdefgh", "ij", "klmnop"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "ctrl+v", "j", "j", "l", "l", "l", "y") // 4-wide block

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		// Short line should be padded or truncated based on implementation
		if len(reg.Content) != 3 {
			t.Fatalf("register content length = %d, want 3", len(reg.Content))
		}
	})
}

// =============================================================================
// Register Behavior Tests
// =============================================================================

func TestYankRegisterBehavior(t *testing.T) {
	t.Run("yy updates register 0 and unnamed register", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)

		// Check unnamed register
		unnamed, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if len(unnamed.Content) == 0 {
			t.Fatal("unnamed register is empty")
		}
		if unnamed.Content[0] != "line 1" {
			t.Errorf("unnamed register = %q, want 'line 1'", unnamed.Content[0])
		}

		// Check register 0
		reg0, ok := m.GetRegister('0')
		if !ok {
			t.Fatal("register 0 not found")
		}
		if len(reg0.Content) == 0 {
			t.Fatal("register 0 is empty")
		}
		if reg0.Content[0] != "line 1" {
			t.Errorf("register 0 = %q, want 'line 1'", reg0.Content[0])
		}
	})

	t.Run("multiple yanks shift numbered registers", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"first", "second", "third"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "y") // yank "first"
		sendKeys(tm, "j")
		sendKeys(tm, "y", "y") // yank "second"

		m := getFinalModel(t, tm)

		// Most recent yank should be in 0 and unnamed
		reg0, ok := m.GetRegister('0')
		if !ok {
			t.Fatal("register 0 not found")
		}
		if len(reg0.Content) == 0 {
			t.Fatal("register 0 is empty")
		}
		if reg0.Content[0] != "second" {
			t.Errorf("register 0 = %q, want 'second'", reg0.Content[0])
		}

		// Previous yank should shift to register 1
		reg1, ok := m.GetRegister('1')
		if !ok {
			t.Fatal("register 1 not found")
		}
		if len(reg1.Content) == 0 {
			t.Fatal("register 1 is empty")
		}
		if reg1.Content[0] != "first" {
			t.Errorf("register 1 = %q, want 'first'", reg1.Content[0])
		}
	})

	t.Run("yank then paste uses correct content", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"original", "to copy"}),
			WithCursorPos(core.Position{Line: 1, Col: 0}),
		)
		sendKeys(tm, "y", "y") // yank "to copy"
		sendKeys(tm, "k")      // move up
		sendKeys(tm, "p")      // paste

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 3 {
			t.Errorf("LineCount() = %d, want 3", m.ActiveBuffer().LineCount())
		}
		if m.ActiveBuffer().Lines[1].String() != "to copy" {
			t.Errorf("Line(1) = %q, want 'to copy'", m.ActiveBuffer().Lines[1].String())
		}
	})
}

// =============================================================================
// Edge Cases and Special Scenarios
// =============================================================================

func TestYankEdgeCases(t *testing.T) {
	t.Run("yy on whitespace-only line", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "    ", "line 3"}),
			WithCursorPos(core.Position{Line: 1, Col: 0}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if len(reg.Content) == 0 {
			t.Fatal("register is empty")
		}
		if reg.Content[0] != "    " {
			t.Errorf("register content = %q, want '    '", reg.Content[0])
		}
	})

	t.Run("yw at end of line", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello"}),
			WithCursorPos(core.Position{Line: 0, Col: 4}), // on 'o'
		)
		sendKeys(tm, "y", "w")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		// At end of line, yw should yank just the last character
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "o" {
			t.Errorf("register content = %q, want 'o'", reg.Content[0])
		}
	})

	t.Run("y$ at beginning of line yanks entire line content", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "$")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "hello world" {
			t.Errorf("register content = %q, want 'hello world'", reg.Content[0])
		}
	})

	t.Run("y0 at beginning of line yanks nothing", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "0")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		// At col 0, y0 should yank empty string
		if len(reg.Content) != 1 {
			t.Fatalf("register content length = %d, want 1", len(reg.Content))
		}
		if reg.Content[0] != "" {
			t.Errorf("register content = %q, want ''", reg.Content[0])
		}
	})

	t.Run("yy on very long line", func(t *testing.T) {
		longLine := strings.Repeat("a", 1000)
		tm := newTestModel(t,
			WithLines([]string{longLine}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if len(reg.Content) == 0 {
			t.Fatal("register is empty")
		}
		if len(reg.Content[0]) != 1000 {
			t.Errorf("register content length = %d, want 1000", len(reg.Content[0]))
		}
	})

	t.Run("yy with special characters", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello\tworld", "foo\nbar"}), // tab and embedded newline
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "y")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		if len(reg.Content) == 0 {
			t.Fatal("register is empty")
		}
		if reg.Content[0] != "hello\tworld" {
			t.Errorf("register content = %q, want 'hello\\tworld'", reg.Content[0])
		}
	})
}

// =============================================================================
// Visual Yank → Paste Round-Trip Tests
// =============================================================================

func TestVisualYankPasteRoundTrip(t *testing.T) {
	t.Run("visual charwise yank then paste single line", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		// Select "hello", yank it, move to end, paste
		sendKeys(tm, "v", "l", "l", "l", "l", "y", "$", "p")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().Lines[0].String() != "hello worldhello" {
			t.Errorf("Line(0) = %q, want 'hello worldhello'", m.ActiveBuffer().Lines[0].String())
		}
	})

	t.Run("visual charwise yank then paste before", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 6}), // on 'w'
		)
		// Select "world", yank it, go to start, paste before
		sendKeys(tm, "v", "$", "y", "0", "P")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().Lines[0].String() != "worldhello world" {
			t.Errorf("Line(0) = %q, want 'worldhello world'", m.ActiveBuffer().Lines[0].String())
		}
	})

	t.Run("visual line yank then paste", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		// V yank line 1, go to line 2, paste
		sendKeys(tm, "V", "y", "j", "p")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 4 {
			t.Errorf("LineCount() = %d, want 4", m.ActiveBuffer().LineCount())
		}
		if m.ActiveBuffer().Lines[2].String() != "line 1" {
			t.Errorf("Line(2) = %q, want 'line 1'", m.ActiveBuffer().Lines[2].String())
		}
	})

	t.Run("visual line yank multiple lines then paste", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3", "line 4"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		// V select lines 1-2, yank, go to end, paste
		sendKeys(tm, "V", "j", "y", "G", "p")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 6 {
			t.Errorf("LineCount() = %d, want 6", m.ActiveBuffer().LineCount())
		}
		if m.ActiveBuffer().Lines[4].String() != "line 1" {
			t.Errorf("Line(4) = %q, want 'line 1'", m.ActiveBuffer().Lines[4].String())
		}
		if m.ActiveBuffer().Lines[5].String() != "line 2" {
			t.Errorf("Line(5) = %q, want 'line 2'", m.ActiveBuffer().Lines[5].String())
		}
	})

	t.Run("visual line yank then paste before", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 2, Col: 0}),
		)
		// V yank line 3, go to line 1, paste before
		sendKeys(tm, "V", "y", "g", "g", "P")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 4 {
			t.Errorf("LineCount() = %d, want 4", m.ActiveBuffer().LineCount())
		}
		if m.ActiveBuffer().Lines[0].String() != "line 3" {
			t.Errorf("Line(0) = %q, want 'line 3'", m.ActiveBuffer().Lines[0].String())
		}
		if m.ActiveBuffer().Lines[1].String() != "line 1" {
			t.Errorf("Line(1) = %q, want 'line 1'", m.ActiveBuffer().Lines[1].String())
		}
	})

	t.Run("yy then p duplicates line below", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"original", "other"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		sendKeys(tm, "y", "y", "p")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 3 {
			t.Errorf("LineCount() = %d, want 3", m.ActiveBuffer().LineCount())
		}
		if m.ActiveBuffer().Lines[0].String() != "original" {
			t.Errorf("Line(0) = %q, want 'original'", m.ActiveBuffer().Lines[0].String())
		}
		if m.ActiveBuffer().Lines[1].String() != "original" {
			t.Errorf("Line(1) = %q, want 'original'", m.ActiveBuffer().Lines[1].String())
		}
		if m.ActiveBuffer().Lines[2].String() != "other" {
			t.Errorf("Line(2) = %q, want 'other'", m.ActiveBuffer().Lines[2].String())
		}
	})

	t.Run("yy then P duplicates line above", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"original", "other"}),
			WithCursorPos(core.Position{Line: 1, Col: 0}),
		)
		sendKeys(tm, "y", "y", "P")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 3 {
			t.Errorf("LineCount() = %d, want 3", m.ActiveBuffer().LineCount())
		}
		if m.ActiveBuffer().Lines[0].String() != "original" {
			t.Errorf("Line(0) = %q, want 'original'", m.ActiveBuffer().Lines[0].String())
		}
		if m.ActiveBuffer().Lines[1].String() != "other" {
			t.Errorf("Line(1) = %q, want 'other'", m.ActiveBuffer().Lines[1].String())
		}
		if m.ActiveBuffer().Lines[2].String() != "other" {
			t.Errorf("Line(2) = %q, want 'other'", m.ActiveBuffer().Lines[2].String())
		}
	})

	t.Run("yw then p pastes word after cursor", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		// yw yanks "hello ", move to end of world, paste
		sendKeys(tm, "y", "w", "$", "p")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().Lines[0].String() != "hello worldhello " {
			t.Errorf("Line(0) = %q, want 'hello worldhello '", m.ActiveBuffer().Lines[0].String())
		}
	})

	t.Run("ye then p pastes word after cursor", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello world"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		// ye yanks "hello" (inclusive), move to end of line, paste
		sendKeys(tm, "y", "e", "$", "p")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().Lines[0].String() != "hello worldhello" {
			t.Errorf("Line(0) = %q, want 'hello worldhello'", m.ActiveBuffer().Lines[0].String())
		}
	})

	t.Run("visual select partial word yank then paste", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"abcdefgh"}),
			WithCursorPos(core.Position{Line: 0, Col: 2}), // on 'c'
		)
		// Select "cde", yank, go to end, paste
		sendKeys(tm, "v", "l", "l", "y", "$", "p")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().Lines[0].String() != "abcdefghcde" {
			t.Errorf("Line(0) = %q, want 'abcdefghcde'", m.ActiveBuffer().Lines[0].String())
		}
	})

	t.Run("visual yank empty selection does nothing", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"hello"}),
			WithCursorPos(core.Position{Line: 0, Col: 2}),
		)
		// Enter visual mode then immediately yank (single char)
		sendKeys(tm, "v", "y")

		m := getFinalModel(t, tm)
		reg, ok := m.GetRegister('"')
		if !ok {
			t.Fatal("unnamed register not found")
		}
		// Should have yanked single char 'l'
		if len(reg.Content) != 1 || reg.Content[0] != "l" {
			t.Errorf("register content = %q, want 'l'", reg.Content)
		}
	})

	t.Run("dd then p moves deleted line down", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		// dd deletes line 1, p pastes it below cursor (now on line 2)
		sendKeys(tm, "d", "d", "p")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 3 {
			t.Errorf("LineCount() = %d, want 3", m.ActiveBuffer().LineCount())
		}
		if m.ActiveBuffer().Lines[0].String() != "line 2" {
			t.Errorf("Line(0) = %q, want 'line 2'", m.ActiveBuffer().Lines[0].String())
		}
		if m.ActiveBuffer().Lines[1].String() != "line 1" {
			t.Errorf("Line(1) = %q, want 'line 1'", m.ActiveBuffer().Lines[1].String())
		}
		if m.ActiveBuffer().Lines[2].String() != "line 3" {
			t.Errorf("Line(2) = %q, want 'line 3'", m.ActiveBuffer().Lines[2].String())
		}
	})

	t.Run("2yy then 2p pastes twice", func(t *testing.T) {
		tm := newTestModel(t,
			WithLines([]string{"line 1", "line 2", "line 3"}),
			WithCursorPos(core.Position{Line: 0, Col: 0}),
		)
		// 2yy yanks lines 1-2, 2p pastes them twice after current line
		sendKeys(tm, "2", "y", "y", "2", "p")

		m := getFinalModel(t, tm)
		if m.ActiveBuffer().LineCount() != 7 {
			t.Errorf("LineCount() = %d, want 7", m.ActiveBuffer().LineCount())
		}
		// Original + 2 copies of 2 lines = 3 + 4 = 7
		if m.ActiveBuffer().Lines[1].String() != "line 1" {
			t.Errorf("Line(1) = %q, want 'line 1'", m.ActiveBuffer().Lines[1].String())
		}
		if m.ActiveBuffer().Lines[2].String() != "line 2" {
			t.Errorf("Line(2) = %q, want 'line 2'", m.ActiveBuffer().Lines[2].String())
		}
		if m.ActiveBuffer().Lines[3].String() != "line 1" {
			t.Errorf("Line(3) = %q, want 'line 1'", m.ActiveBuffer().Lines[3].String())
		}
		if m.ActiveBuffer().Lines[4].String() != "line 2" {
			t.Errorf("Line(4) = %q, want 'line 2'", m.ActiveBuffer().Lines[4].String())
		}
	})
}