Add `tabs` to `layouts`

fixes #603, fixes #349

* The layout has now a unique `tabs` section,
  that can be used, like the `parts` section,
  everything that is not inside the tabs section
  is assumed to be present on every single tab
  that is opened.

  This is a BREAKING CHANGE for people that use
  custom `layouts` already, since the `tabs` section
  is not optional - for clarity and intentionality reasons.

  The functionality to specify multiple tabs is already there,
  but is still gated behind a panic, until #621 is fixed.
  So for now one tab can be specified to load on startup.

* The `NewTab` action can optionally be bound to open
  a layout that is assumed to be in the new `tabs` section

  This is a BREAKING CHANGE for people that have the
  `NewTab` action already bound in the config file:

```
- action: [NewTab, ]
  key: [F: 5,]
```
must now be specified as:
```
- action: [NewTab: ,]
  key: [F: 5,]
```
  Optionally a layout that should be opened on the new tab can be
  specified:
```
- action: [NewTab: {
  direction: Vertical,
  parts: [ {direction: Horizontal, split_size: {Percent: 50}}, {direction: Horizontal, run: {command: {cmd: "htop"}}},],
  key: [F: 6,]
```
or:
```
- action: [NewTab: {direction: Vertical, run: {command: {cmd: "htop"} }},]
  key: [F: 7,]
```
or
```
- action: [NewTab: {
  direction: Vertical,
  parts: [ {direction: Vertical, split_size: {Percent: 25},run: {plugin: "strider" }}, {direction: Horizontal}],}, MoveFocus: Left,]
  key: [F: 8,]

```

16 files changed, 935 insertions, 26 deletions

diff --git a/zellij-utils/assets/config/default.yaml b/zellij-utils/assets/config/default.yaml
index d9090a8dc..e90b60a18 100644
--- a/zellij-utils/assets/config/default.yaml
+++ b/zellij-utils/assets/config/default.yaml
@@ -134,7 +134,7 @@ keybinds:
           key: [ Char: 'h', Left, Up, Char: 'k',]
         - action: [GoToNextTab,]
           key: [ Char: 'l', Right,Down, Char: 'j']
-        - action: [NewTab,]
+        - action: [NewTab: ,]
           key: [ Char: 'n',]
         - action: [CloseTab,]
           key: [ Char: 'x',]
diff --git a/zellij-utils/assets/layouts/default.yaml b/zellij-utils/assets/layouts/default.yaml
index 96bf1809c..39dbdc1b0 100644
--- a/zellij-utils/assets/layouts/default.yaml
+++ b/zellij-utils/assets/layouts/default.yaml
@@ -7,6 +7,8 @@ parts:
     run:
       plugin: tab-bar
   - direction: Vertical
+    tabs:
+      - direction: Vertical
   - direction: Vertical
     split_size:
       Fixed: 2
diff --git a/zellij-utils/assets/layouts/disable-status-bar.yaml b/zellij-utils/assets/layouts/disable-status-bar.yaml
index b990ba500..a0a592390 100644
--- a/zellij-utils/assets/layouts/disable-status-bar.yaml
+++ b/zellij-utils/assets/layouts/disable-status-bar.yaml
@@ -7,3 +7,5 @@ parts:
     run:
       plugin: tab-bar
   - direction: Vertical
+    tabs:
+      - direction: Vertical
diff --git a/zellij-utils/assets/layouts/strider.yaml b/zellij-utils/assets/layouts/strider.yaml
index 9bbe5772f..a39f327cf 100644
--- a/zellij-utils/assets/layouts/strider.yaml
+++ b/zellij-utils/assets/layouts/strider.yaml
@@ -7,13 +7,15 @@ parts:
     run:
       plugin: tab-bar
   - direction: Vertical
-    parts:
-      - direction: Horizontal
-        split_size:
-          Percent: 20
-        run:
-          plugin: strider
-      - direction: Horizontal
+    tabs:
+      - direction: Vertical
+        parts:
+        - direction: Horizontal
+          split_size:
+            Percent: 20
+          run:
+            plugin: strider
+        - direction: Horizontal
   - direction: Vertical
     split_size:
       Fixed: 2
diff --git a/zellij-utils/src/input/actions.rs b/zellij-utils/src/input/actions.rs
index bfd7d2559..ab711c75c 100644
--- a/zellij-utils/src/input/actions.rs
+++ b/zellij-utils/src/input/actions.rs
@@ -1,6 +1,7 @@
 //! Definition of the actions that can be bound to keys.
 
 use super::command::RunCommandAction;
+use super::layout::TabLayout;
 use crate::input::options::OnForceClose;
 use serde::{Deserialize, Serialize};
 use zellij_tile::data::InputMode;
@@ -19,7 +20,7 @@ pub enum Direction {
 // As these actions are bound to the default config, please
 // do take care when refactoring - or renaming.
 // They might need to be adjusted in the default config
-// as well `../../../assets/config/default.yaml`
+// as well `../../assets/config/default.yaml`
 /// Actions that can be bound to keys.
 #[derive(Eq, Clone, Debug, PartialEq, Deserialize, Serialize)]
 pub enum Action {
@@ -61,8 +62,8 @@ pub enum Action {
     NewPane(Option<Direction>),
     /// Close the focus pane.
     CloseFocus,
-    /// Create a new tab.
-    NewTab,
+    /// Create a new tab, optionally with a specified tab layout.
+    NewTab(Option<TabLayout>),
     /// Do nothing.
     NoOp,
     /// Go to the next tab.
diff --git a/zellij-utils/src/input/layout.rs b/zellij-utils/src/input/layout.rs
index a48c35219..713605e9c 100644
--- a/zellij-utils/src/input/layout.rs
+++ b/zellij-utils/src/input/layout.rs
@@ -17,23 +17,24 @@ use crate::{serde, serde_yaml};
 
 use serde::{Deserialize, Serialize};
 use std::path::{Path, PathBuf};
+use std::vec::Vec;
 use std::{fs::File, io::prelude::*};
 
-#[derive(Debug, Serialize, Deserialize, Clone)]
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq)]
 #[serde(crate = "self::serde")]
 pub enum Direction {
     Horizontal,
     Vertical,
 }
 
-#[derive(Debug, Serialize, Deserialize, Clone, Copy)]
+#[derive(Debug, Serialize, Deserialize, Clone, Copy, PartialEq, Eq)]
 #[serde(crate = "self::serde")]
 pub enum SplitSize {
     Percent(u8), // 1 to 100
     Fixed(u16),  // An absolute number of columns or rows
 }
 
-#[derive(Debug, Serialize, Deserialize, Clone)]
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq)]
 #[serde(crate = "self::serde")]
 pub enum Run {
     #[serde(rename = "plugin")]
@@ -42,16 +43,58 @@ pub enum Run {
     Command(RunCommand),
 }
 
-#[derive(Debug, Serialize, Deserialize, Clone)]
+// The layout struct that is ultimately used to build the layouts
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq)]
 #[serde(crate = "self::serde")]
 pub struct Layout {
     pub direction: Direction,
     #[serde(default)]
     pub parts: Vec<Layout>,
+    #[serde(default)]
+    pub tabs: Vec<TabLayout>,
+    pub split_size: Option<SplitSize>,
+    pub run: Option<Run>,
+}
+
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq)]
+#[serde(crate = "self::serde")]
+pub struct TabLayout {
+    pub direction: Direction,
+    #[serde(default)]
+    pub parts: Vec<TabLayout>,
     pub split_size: Option<SplitSize>,
     pub run: Option<Run>,
 }
 
+// Main layout struct, that carries information based on
+// position of tabs
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq)]
+#[serde(crate = "self::serde")]
+pub struct MainLayout {
+    pub pre_tab: Layout,
+    pub post_tab: Vec<Layout>,
+    pub tabs: Vec<TabLayout>,
+}
+
+impl MainLayout {
+    pub fn construct_tab_layout(&self, tab_layout: Option<TabLayout>) -> Layout {
+        if let Some(tab_layout) = tab_layout {
+            let mut pre_tab_layout = self.pre_tab.clone();
+            let post_tab_layout = &self.post_tab;
+            pre_tab_layout.merge_tab_layout(tab_layout);
+            pre_tab_layout.merge_layout_parts(post_tab_layout.to_owned());
+            pre_tab_layout
+        } else {
+            let mut pre_tab_layout = self.pre_tab.clone();
+            let post_tab_layout = &self.post_tab;
+            let default_tab_layout = TabLayout::default();
+            pre_tab_layout.merge_tab_layout(default_tab_layout);
+            pre_tab_layout.merge_layout_parts(post_tab_layout.to_owned());
+            pre_tab_layout
+        }
+    }
+}
+
 type LayoutResult = Result<Layout, ConfigError>;
 
 impl Layout {
@@ -168,6 +211,113 @@ impl Layout {
     ) -> Vec<(Layout, PositionAndSize)> {
         split_space(space, self)
     }
+
+    // Split the layout into parts that can be reassebled per tab
+    // returns the layout pre tab, the parts post tab and the tab layouts
+    pub fn split_main_and_tab_layout(&self) -> (Layout, Vec<Layout>, Vec<TabLayout>) {
+        let mut main_layout = self.clone();
+        let mut pre_tab_layout = self.clone();
+        let mut post_tab_layout = vec![];
+        let mut tabs = vec![];
+        let mut post_tab = false;
+
+        pre_tab_layout.parts.clear();
+        pre_tab_layout.tabs.clear();
+
+        if !main_layout.tabs.is_empty() {
+            tabs.append(&mut main_layout.tabs);
+            post_tab = true;
+        }
+
+        for part in main_layout.parts.drain(..) {
+            let (curr_pre_layout, mut curr_post_layout, mut curr_tabs) =
+                part.split_main_and_tab_layout();
+
+            // Leaf
+            if !post_tab && part.tabs.is_empty() {
+                pre_tab_layout.parts.push(curr_pre_layout);
+            }
+
+            // Todo: Convert into actual Error, or use the future logging system.
+            if !part.tabs.is_empty() && !part.parts.is_empty() {
+                panic!("Tabs and Parts need to be specified separately.");
+            }
+
+            // Todo: Convert into actual Error, or use the future logging system.
+            if (!part.tabs.is_empty() || !curr_tabs.is_empty()) && post_tab {
+                panic!("Only one tab section should be specified.");
+            }
+
+            // Node
+            if !part.tabs.is_empty() {
+                tabs.append(&mut part.tabs.clone());
+                post_tab = true;
+            // Node
+            } else if !curr_tabs.is_empty() {
+                tabs.append(&mut curr_tabs);
+                post_tab = true;
+            // Leaf
+            } else if post_tab {
+                    if curr_post_layout.is_empty() {
+                        let mut part_no_tab = part.clone();
+                        part_no_tab.tabs.clear();
+                        part_no_tab.parts.clear();
+                        post_tab_layout.push(part_no_tab);
+                    } else {
+                        post_tab_layout.append(&mut curr_post_layout);
+                    }
+            }
+        }
+        (pre_tab_layout, post_tab_layout, tabs)
+    }
+
+    pub fn merge_tab_layout(&mut self, tab: TabLayout) {
+        self.parts.push(tab.into());
+    }
+
+    pub fn merge_layout_parts(&mut self, mut parts: Vec<Layout>) {
+        self.parts.append(&mut parts);
+    }
+
+    pub fn construct_full_layout(&self, tab_layout: Option<TabLayout>) -> Self {
+        if let Some(tab_layout) = tab_layout {
+            let (mut pre_tab_layout, post_tab_layout, _) = self.split_main_and_tab_layout();
+            pre_tab_layout.merge_tab_layout(tab_layout);
+            pre_tab_layout.merge_layout_parts(post_tab_layout);
+            pre_tab_layout
+        } else {
+            let (mut pre_tab_layout, post_tab_layout, _) = self.split_main_and_tab_layout();
+            let default_tab_layout = TabLayout::default();
+            pre_tab_layout.merge_tab_layout(default_tab_layout);
+            pre_tab_layout.merge_layout_parts(post_tab_layout);
+            pre_tab_layout
+        }
+    }
+
+    pub fn construct_main_layout(&self) -> MainLayout {
+        let (pre_tab, post_tab, tabs) = self.split_main_and_tab_layout();
+
+        if tabs.is_empty() {
+            panic!("The layout file should have a `tabs` section specified");
+        }
+
+        if tabs.len() > 1 {
+            panic!("The layout file should have one single tab in the `tabs` section specified");
+        }
+
+        MainLayout {
+            pre_tab,
+            post_tab,
+            tabs,
+        }
+    }
+
+    fn from_vec_tab_layout(tab_layout: Vec<TabLayout>) -> Vec<Self> {
+        tab_layout
+            .iter()
+            .map(|tab_layout| Layout::from(tab_layout.to_owned()))
+            .collect()
+    }
 }
 
 fn split_space_to_parts_vertically(
@@ -322,3 +472,31 @@ fn split_space(
     }
     pane_positions
 }
+
+impl From<TabLayout> for Layout {
+    fn from(tab: TabLayout) -> Self {
+        Layout {
+            direction: tab.direction,
+            parts: Layout::from_vec_tab_layout(tab.parts),
+            tabs: vec![],
+            split_size: tab.split_size,
+            run: tab.run,
+        }
+    }
+}
+
+impl Default for TabLayout {
+    fn default() -> Self {
+        Self {
+            direction: Direction::Horizontal,
+            parts: vec![],
+            split_size: None,
+            run: None,
+        }
+    }
+}
+
+// The unit test location.
+#[cfg(test)]
+#[path = "./unit/layout_test.rs"]
+mod layout_test;
diff --git a/zellij-utils/src/input/unit/fixtures/layouts/deeply-nested-tab-layout.yaml b/zellij-utils/src/input/unit/fixtures/layouts/deeply-nested-tab-layout.yaml
new file mode 100644
index 000000000..11e5323e1
--- /dev/null
+++ b/zellij-utils/src/input/unit/fixtures/layouts/deeply-nested-tab-layout.yaml
@@ -0,0 +1,40 @@
+---
+direction: Horizontal
+parts:
+  - direction: Vertical
+    parts:
+      - direction: Horizontal
+        split_size:
+          Percent: 21
+      - direction: Vertical
+        split_size:
+          Percent: 79
+        parts:
+          - direction: Horizontal
+            split_size:
+              Percent: 22
+          - direction: Horizontal
+            split_size:
+              Percent: 78
+            parts:
+              - direction: Horizontal
+                split_size:
+                  Percent: 23
+              - direction: Vertical
+                split_size:
+                  Percent: 77
+                tabs:
+                  - direction: Horizontal
+                    split_size:
+                      Percent: 24
+    split_size:
+      Percent: 90
+  - direction: Vertical
+    split_size:
+      Percent: 15
+  - direction: Vertical
+    split_size:
+      Percent: 15
+  - direction: Vertical
+    split_size:
+      Percent: 15
diff --git a/zellij-utils/src/input/unit/fixtures/layouts/multiple-tabs-should-panic.yaml b/zellij-utils/src/input/unit/fixtures/layouts/multiple-tabs-should-panic.yaml
new file mode 100644
index 000000000..653787591
--- /dev/null
+++ b/zellij-utils/src/input/unit/fixtures/layouts/multiple-tabs-should-panic.yaml
@@ -0,0 +1,18 @@
+---
+direction: Horizontal
+parts:
+  - direction: Horizontal
+    parts:
+      - direction: Vertical
+        parts:
+          - direction: Horizontal
+            split_size:
+              Percent: 50
+          - direction: Horizontal
+            tabs:
+              - direction: Vertical
+                split_size:
+                  Percent: 50
+              - direction: Vertical
+                split_size:
+                  Percent: 50
diff --git a/zellij-utils/src/input/unit/fixtures/layouts/no-tabs-should-panic.yaml b/zellij-utils/src/input/unit/fixtures/layouts/no-tabs-should-panic.yaml
new file mode 100644
index 000000000..a67b0ff95
--- /dev/null
+++ b/zellij-utils/src/input/unit/fixtures/layouts/no-tabs-should-panic.yaml
@@ -0,0 +1,18 @@
+---
+direction: Horizontal
+parts:
+  - direction: Horizontal
+    parts:
+      - direction: Vertical
+        parts:
+          - direction: Horizontal
+            split_size:
+              Percent: 50
+          - direction: Horizontal
+            parts:
+              - direction: Vertical
+                split_size:
+                  Percent: 50
+              - direction: Vertical
+                split_size:
+                  Percent: 50
diff --git a/zellij-utils/src/input/unit/fixtures/layouts/tabs-and-parts-together-should-panic.yaml b/zellij-utils/src/input/unit/fixtures/layouts/tabs-and-parts-together-should-panic.yaml
new file mode 100644
index 000000000..1ef5a05ee
--- /dev/null
+++ b/zellij-utils/src/input/unit/fixtures/layouts/tabs-and-parts-together-should-panic.yaml
@@ -0,0 +1,25 @@
+---
+direction: Horizontal
+parts:
+  - direction: Horizontal
+    tabs:
+      - direction: Vertical
+        parts:
+          - direction: Horizontal
+            split_size:
+              Percent: 50
+          - direction: Horizontal
+            parts:
+              - direction: Vertical
+                split_size:
+                  Percent: 50
+              - direction: Vertical
+                split_size:
+                  Percent: 50
+        tabs:
+          - direction: Vertical
+            split_size:
+              Percent: 50
+          - direction: Vertical
+            split_size:
+              Percent: 50
diff --git a/zellij-utils/src/input/unit/fixtures/layouts/three-panes-with-tab-and-command.yaml b/zellij-utils/src/input/unit/fixtures/layouts/three-panes-with-tab-and-command.yaml
new file mode 100644
index 000000000..34de4291a
--- /dev/null
+++ b/zellij-utils/src/input/unit/fixtures/layouts/three-panes-with-tab-and-command.yaml
@@ -0,0 +1,32 @@
+---
+direction: Horizontal
+parts:
+  - direction: Vertical
+    split_size:
+      Fixed: 1
+    run:
+      plugin: tab-bar
+  - direction: Horizontal
+    tabs:
+      - direction: Vertical
+        parts:
+          - direction: Horizontal
+            split_size:
+              Percent: 50
+          - direction: Horizontal
+            parts:
+              - direction: Vertical
+                split_size:
+                  Percent: 50
+                run:
+                  command: {cmd: htop}
+              - direction: Vertical
+                split_size:
+                  Percent: 50
+                run:
+                  command: {cmd: htop, args: ["-C"]}
+  - direction: Vertical
+    split_size:
+      Fixed: 2
+    run:
+      plugin: status-bar
diff --git a/zellij-utils/src/input/unit/fixtures/layouts/three-panes-with-tab-and-default-plugins.yaml b/zellij-utils/src/input/unit/fixtures/layouts/three-panes-with-tab-and-default-plugins.yaml
new file mode 100644
index 000000000..a803f2916
--- /dev/null
+++ b/zellij-utils/src/input/unit/fixtures/layouts/three-panes-with-tab-and-default-plugins.yaml
@@ -0,0 +1,28 @@
+---
+direction: Horizontal
+parts:
+  - direction: Vertical
+    split_size:
+      Fixed: 1
+    run:
+      plugin: tab-bar
+  - direction: Horizontal
+    tabs:
+      - direction: Vertical
+        parts:
+          - direction: Horizontal
+            split_size:
+              Percent: 50
+          - direction: Horizontal
+            parts:
+              - direction: Vertical
+                split_size:
+                  Percent: 50
+              - direction: Vertical
+                split_size:
+                  Percent: 50
+  - direction: Vertical
+    split_size:
+      Fixed: 2
+    run:
+      plugin: status-bar
diff --git a/zellij-utils/src/input/unit/fixtures/layouts/three-panes-with-tab.yaml b/zellij-utils/src/input/unit/fixtures/layouts/three-panes-with-tab.yaml
new file mode 100644
index 000000000..e0f25b922
--- /dev/null
+++ b/zellij-utils/src/input/unit/fixtures/layouts/three-panes-with-tab.yaml
@@ -0,0 +1,18 @@
+---
+direction: Horizontal
+parts:
+  - direction: Horizontal
+    tabs:
+      - direction: Vertical
+        parts:
+          - direction: Horizontal
+            split_size:
+              Percent: 50
+          - direction: Horizontal
+            parts:
+              - direction: Vertical
+                split_size:
+                  Percent: 50
+              - direction: Vertical
+                split_size:
+                  Percent: 50
diff --git a/zellij-utils/src/input/unit/keybinds_test.rs b/zellij-utils/src/input/unit/keybinds_test.rs
index 4767fc157..e8a776d76 100644
--- a/zellij-utils/src/input/unit/keybinds_test.rs
+++ b/zellij-utils/src/input/unit/keybinds_test.rs
@@ -150,7 +150,7 @@ fn no_unbind_unbinds_none() {
 
 #[test]
 fn last_keybind_is_taken() {
-    let actions_1 = vec![Action::NoOp, Action::NewTab];
+    let actions_1 = vec![Action::NoOp, Action::NewTab(None)];
     let keyaction_1 = KeyActionFromYaml {
         action: actions_1.clone(),
         key: vec![Key::F(1), Key::Backspace, Key::Char('t')],
@@ -171,7 +171,7 @@ fn last_keybind_is_taken() {
 
 #[test]
 fn last_keybind_overwrites() {
-    let actions_1 = vec![Action::NoOp, Action::NewTab];
+    let actions_1 = vec![Action::NoOp, Action::NewTab(None)];
     let keyaction_1 = KeyActionFromYaml {
         action: actions_1.clone(),
         key: vec![Key::F(1), Key::Backspace, Key::Char('t')],
@@ -764,7 +764,7 @@ fn unbind_single_toplevel_multiple_keys_multiple_modes() {
 fn uppercase_and_lowercase_are_distinct() {
     let key_action_n = KeyActionFromYaml {
         key: vec![Key::Char('n')],
-        action: vec![Action::NewTab],
+        action: vec![Action::NewTab(None)],
     };
     let key_action_large_n = KeyActionFromYaml {
         key: vec![Key::Char('N')],
diff --git a/zellij-utils/src/input/unit/layout_test.rs b/zellij-utils/src/input/unit/layout_test.rs
new file mode 100644
index 000000000..95de356cc
--- /dev/null
+++ b/zellij-utils/src/input/unit/layout_test.rs
@@ -0,0 +1,538 @@
+use super::super::layout::*;
+
+fn layout_test_dir(layout: String) -> PathBuf {
+    let root = Path::new(env!("CARGO_MANIFEST_DIR"));
+    let layout_dir = root.join("src/input/unit/fixtures/layouts");
+    layout_dir.join(layout)
+}
+
+fn default_layout_dir(layout: String) -> PathBuf {
+    let root = Path::new(env!("CARGO_MANIFEST_DIR"));
+    let layout_dir = root.join("assets/layouts");
+    layout_dir.join(layout)
+}
+