use std::collections::BTreeSet;

use lumbridge_spike_model::PaneId as FixturePaneId;
use serde::{Deserialize, Serialize};

#[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, Ord, PartialEq, PartialOrd, Serialize)]
pub(crate) struct PanelId(u64);

impl PanelId {
    pub(crate) const fn get(self) -> u64 {
        self.0
    }
}

#[derive(Clone, Copy, Debug, Deserialize, Eq, PartialEq, Serialize)]
#[serde(rename_all = "kebab-case")]
pub(crate) enum PanelKind {
    Terminal,
    Browser,
    Markdown,
    Review,
}

impl PanelKind {
    pub(crate) const ALL: [Self; 4] = [Self::Terminal, Self::Browser, Self::Markdown, Self::Review];

    pub(crate) const fn label(self) -> &'static str {
        match self {
            Self::Terminal => "Terminal",
            Self::Browser => "Browser",
            Self::Markdown => "Markdown",
            Self::Review => "Review",
        }
    }

    pub(crate) const fn description(self) -> &'static str {
        match self {
            Self::Terminal => "A real local shell with its own runtime actor",
            // Not a web engine. There is no browser in this build; the panel
            // renders a placeholder surface and says so.
            Self::Browser => "A placeholder surface. No web engine is embedded yet",
            Self::Markdown => "Local notes, plans, and architecture",
            Self::Review => "Repository changes and approval boundaries",
        }
    }

    /// What a newly created panel is pointed at.
    ///
    /// Every one of these used to name a specific machine — this developer's,
    /// as it happens. A panel's target is whatever it was actually launched
    /// against, and a new panel has been launched against nothing but the
    /// local shell.
    const fn default_target(self) -> &'static str {
        match self {
            Self::Terminal => "local shell",
            Self::Browser => "no surface attached",
            Self::Markdown => "local document",
            Self::Review => "working tree",
        }
    }
}

#[derive(Clone, Copy, Debug, Deserialize, Eq, PartialEq, Serialize)]
#[serde(rename_all = "kebab-case")]
pub(crate) enum SeedPane {
    CodexRuntime,
    ClaudeUi,
    PiDocs,
    Architecture,
    AcpPreview,
    RuntimeReview,
}

impl SeedPane {
    pub(crate) const fn fixture_id(self) -> FixturePaneId {
        match self {
            Self::CodexRuntime => FixturePaneId::CodexRuntime,
            Self::ClaudeUi => FixturePaneId::ClaudeUi,
            Self::PiDocs => FixturePaneId::PiDocs,
            Self::Architecture => FixturePaneId::Architecture,
            Self::AcpPreview => FixturePaneId::AcpPreview,
            Self::RuntimeReview => FixturePaneId::RuntimeReview,
        }
    }
}

#[derive(Clone, Debug, Deserialize, Eq, PartialEq, Serialize)]
pub(crate) struct WorkspacePanel {
    pub(crate) id: PanelId,
    pub(crate) kind: PanelKind,
    pub(crate) title: String,
    pub(crate) target: String,
    pub(crate) attached: bool,
    pub(crate) seed: Option<SeedPane>,
}

#[derive(Clone, Debug, Deserialize, Eq, PartialEq, Serialize)]
pub(crate) struct PanelRegistry {
    schema_version: u32,
    panels: Vec<WorkspacePanel>,
    selected: PanelId,
    next_id: u64,
}

impl Default for PanelRegistry {
    fn default() -> Self {
        Self::first_run()
    }
}

impl PanelRegistry {
    /// The workspace a first run opens with.
    ///
    /// Three real local shells and nothing else. This used to seed six panes
    /// announcing "Codex · runtime / metal · Tailscale SSH", "Claude Code · UI
    /// / `MacBook` Air · local" and a Pi pane on a saved host — none of which
    /// existed. Every one was a `/bin/sh`. A pane claims a harness when one has
    /// actually been launched into it, and until then it is a terminal.
    ///
    /// Three, not one: `visible_panel_count` branches at 1100 px and 2800 px,
    /// so a single-panel default renders one pane on an ultrawide.
    pub(crate) fn first_run() -> Self {
        let seeds = [
            (PanelKind::Terminal, "Terminal 1", "local shell", None),
            (PanelKind::Terminal, "Terminal 2", "local shell", None),
            (PanelKind::Terminal, "Terminal 3", "local shell", None),
        ];
        let panels = seeds
            .into_iter()
            .enumerate()
            .map(|(index, (kind, title, target, seed))| WorkspacePanel {
                id: PanelId(index as u64 + 1),
                kind,
                title: title.to_owned(),
                target: target.to_owned(),
                attached: index < 5,
                seed,
            })
            .collect();
        Self {
            schema_version: 1,
            panels,
            selected: PanelId(1),
            next_id: 7,
        }
    }

    pub(crate) fn from_json(json: &str) -> Result<Self, String> {
        let registry: Self = serde_json::from_str(json).map_err(|error| error.to_string())?;
        registry.validate()?;
        Ok(registry)
    }

    pub(crate) fn to_json(&self) -> Result<String, String> {
        serde_json::to_string(self).map_err(|error| error.to_string())
    }

    fn validate(&self) -> Result<(), String> {
        if self.schema_version != 1 {
            return Err(format!(
                "unsupported panel snapshot version {}",
                self.schema_version
            ));
        }
        if self.panels.is_empty() || self.attached_count() == 0 {
            return Err("a workspace must retain one attached panel".to_owned());
        }
        let ids = self
            .panels
            .iter()
            .map(|panel| panel.id)
            .collect::<BTreeSet<_>>();
        if ids.len() != self.panels.len() || ids.iter().any(|id| id.get() == 0) {
            return Err("panel IDs must be unique and non-zero".to_owned());
        }
        if self
            .panel(self.selected)
            .is_none_or(|panel| !panel.attached)
        {
            return Err("the selected panel must be attached".to_owned());
        }
        let max_id = ids.iter().map(|id| id.get()).max().unwrap_or(0);
        if self.next_id <= max_id {
            return Err("the next panel ID must exceed every persisted ID".to_owned());
        }
        Ok(())
    }

    pub(crate) fn panels(&self) -> &[WorkspacePanel] {
        &self.panels
    }

    pub(crate) fn panel(&self, id: PanelId) -> Option<&WorkspacePanel> {
        self.panels.iter().find(|panel| panel.id == id)
    }

    pub(crate) fn selected(&self) -> PanelId {
        self.selected
    }

    pub(crate) fn attached_ids(&self) -> Vec<PanelId> {
        self.panels
            .iter()
            .filter(|panel| panel.attached)
            .map(|panel| panel.id)
            .collect()
    }

    pub(crate) fn detached_ids(&self) -> Vec<PanelId> {
        self.panels
            .iter()
            .filter(|panel| !panel.attached)
            .map(|panel| panel.id)
            .collect()
    }

    pub(crate) fn attached_count(&self) -> usize {
        self.panels.iter().filter(|panel| panel.attached).count()
    }

    pub(crate) fn select(&mut self, id: PanelId) -> bool {
        if self.panel(id).is_none_or(|panel| !panel.attached) || self.selected == id {
            return false;
        }
        self.selected = id;
        true
    }

    pub(crate) fn select_attached_at(&mut self, index: usize) -> bool {
        self.attached_ids()
            .get(index)
            .copied()
            .is_some_and(|id| self.select(id))
    }

    pub(crate) fn move_horizontal(&mut self, delta: isize) -> bool {
        let attached = self.attached_ids();
        let Some(position) = attached.iter().position(|id| *id == self.selected) else {
            return false;
        };
        let next = position as isize + delta;
        if next < 0 || next >= attached.len() as isize {
            return false;
        }
        self.select(attached[next as usize])
    }

    pub(crate) fn create(&mut self, kind: PanelKind) -> PanelId {
        let id = PanelId(self.next_id);
        self.next_id += 1;
        let sequence = self
            .panels
            .iter()
            .filter(|panel| panel.kind == kind)
            .count()
            + 1;
        let title = match kind {
            PanelKind::Terminal => format!("Terminal · {sequence}"),
            PanelKind::Browser => format!("Browser · {sequence}"),
            PanelKind::Markdown => format!("Notes · {sequence}"),
            PanelKind::Review => format!("Review · {sequence}"),
        };
        let selected_position = self
            .panels
            .iter()
            .position(|panel| panel.id == self.selected)
            .expect("selected panel exists");
        self.panels.insert(
            selected_position + 1,
            WorkspacePanel {
                id,
                kind,
                title,
                target: kind.default_target().to_owned(),
                attached: true,
                seed: None,
            },
        );
        self.selected = id;
        id
    }

    pub(crate) fn detach(&mut self, id: PanelId) -> bool {
        if self.attached_count() == 1 || self.panel(id).is_none_or(|panel| !panel.attached) {
            return false;
        }
        let attached_before = self.attached_ids();
        let detached_position = attached_before
            .iter()
            .position(|candidate| *candidate == id)
            .expect("attached panel appears in attached IDs");
        self.panels
            .iter_mut()
            .find(|panel| panel.id == id)
            .expect("panel exists")
            .attached = false;
        if self.selected == id {
            let remaining = self.attached_ids();
            self.selected = remaining[detached_position.min(remaining.len() - 1)];
        }
        true
    }

    pub(crate) fn attach(&mut self, id: PanelId) -> bool {
        let Some(panel) = self.panels.iter_mut().find(|panel| panel.id == id) else {
            return false;
        };
        if panel.attached {
            return false;
        }
        panel.attached = true;
        self.selected = id;
        true
    }
}

#[cfg(test)]
mod tests {
    use super::{PanelId, PanelKind, PanelRegistry};

    #[test]
    fn dynamic_panels_receive_monotonic_ids_and_insert_beside_selection() {
        let mut registry = PanelRegistry::first_run();
        let browser = registry.create(PanelKind::Browser);
        let terminal = registry.create(PanelKind::Terminal);
        assert_eq!(browser, PanelId(7));
        assert_eq!(terminal, PanelId(8));
        assert_eq!(registry.selected(), terminal);
        assert_eq!(registry.panels()[2].id, terminal);
        assert_eq!(registry.panels()[1].id, browser);
    }

    #[test]
    fn identity_and_detached_state_round_trip_without_reuse() {
        let mut registry = PanelRegistry::first_run();
        let created = registry.create(PanelKind::Markdown);
        assert!(registry.detach(created));
        let json = registry.to_json().unwrap();
        let mut restored = PanelRegistry::from_json(&json).unwrap();
        assert!(restored.detached_ids().contains(&created));
        assert_eq!(restored.create(PanelKind::Review), PanelId(8));
    }

    #[test]
    fn detach_preserves_panel_and_reattach_restores_same_identity() {
        let mut registry = PanelRegistry::first_run();
        let id = registry.create(PanelKind::Terminal);
        assert!(registry.detach(id));
        assert!(registry.panel(id).is_some());
        assert!(registry.attach(id));
        assert_eq!(registry.selected(), id);
    }

    #[test]
    fn invalid_or_empty_snapshots_are_rejected() {
        assert!(PanelRegistry::from_json("{}").is_err());
        assert!(
            PanelRegistry::from_json(
                r#"{"schema_version":1,"panels":[],"selected":1,"next_id":2}"#
            )
            .is_err()
        );
    }
}