//! An in-process engine session that answers the control-channel methods itself.

use std::sync::Arc;

use serde_json::{Value, json};
use vectorcraft_engine::file_access::{self, AutomationRoots};
use vectorcraft_engine::{Session, UiRequest, ViewInfo};
use vectorcraft_geom::Point;
use vectorcraft_render::Renderer;
use vectorcraft_tools::{Mods, PointerEvent, PointerKind, TOOL_GROUPS, ToolKey};

use crate::backend::Backend;

/// Headless backend: a [`Session`] plus a CPU [`Renderer`] for screenshots and PNG export.
pub struct Headless {
    pub session: Session,
    pub renderer: Renderer,
    /// View state handed to tools (zoom 1, smart guides on).
    pub view: ViewInfo,
    /// The folders its methods may read and write (`--automation-read-root`,
    /// `--automation-write-root`); `None`: anywhere.
    roots: Option<Arc<AutomationRoots>>,
}

impl Default for Headless {
    fn default() -> Self {
        Self::new()
    }
}

/// Commands the desktop app adds on top of the engine; the headless backend implements them too so
/// `run_command` behaves the same in both modes.
const HOST_COMMANDS: &[(&str, &str, &str)] = &[
    ("file.open", "Open…", "{path} open any readable file (see document.formats) as a new document; templates open untitled"),
    (
        "file.save",
        "Save",
        "{path?, format?, options?, svg?: {…SVG options}} = document.save: .vectorcraft, .ai (a PDF that reopens editable), .pdf, .svg or .svgz (default: the document's own path and format)",
    ),
    ("file.export", "Export…", "{path?, format?, artboard?, range?, scale?, …} = document.export (no path → dataBase64)"),
    (
        "file.exportForScreens",
        "Export for Screens…",
        "{folder?, zip?, artboards? | range? | fullDocument? | assets?, includeBleed?, subfolders?, preset?, formats?, settings?, prefix?} = document.exportForScreens (no folder → the files, or one zip, as dataBase64)",
    ),
    ("tool.select", "Select Tool", "{tool} e.g. selection, directSelection, pen, rectangle, ellipse, polygon, star, lineSegment"),
    (
        "tool.setOption",
        "Tool Option",
        "{key, value} | {values: {key: value…}}, tool?: id (default: the active tool) → the tool's options (`{}` reads them); kept options last across tool switches",
    ),
];

fn s<'a>(p: &'a Value, k: &str) -> Option<&'a str> {
    p.get(k).and_then(Value::as_str)
}

pub(crate) fn pointer_kind(k: &str) -> Option<PointerKind> {
    Some(match k {
        "down" => PointerKind::Down,
        "drag" => PointerKind::Drag,
        "up" => PointerKind::Up,
        "move" => PointerKind::Move,
        "doubleclick" | "dblclick" => PointerKind::DoubleClick,
        _ => return None,
    })
}

fn tool_key(name: &str) -> Option<ToolKey> {
    Some(match name.to_ascii_lowercase().as_str() {
        "enter" | "return" => ToolKey::Enter,
        "esc" | "escape" => ToolKey::Escape,
        "backspace" => ToolKey::Backspace,
        "delete" => ToolKey::Delete,
        "up" | "arrowup" => ToolKey::Up,
        "down" | "arrowdown" => ToolKey::Down,
        "left" | "arrowleft" => ToolKey::Left,
        "right" | "arrowright" => ToolKey::Right,
        "[" | "bracketleft" | "openbracket" => ToolKey::BracketLeft,
        "]" | "bracketright" | "closebracket" => ToolKey::BracketRight,
        "tab" => ToolKey::Tab,
        k if k.len() == 1 => ToolKey::Digit(k.parse().ok()?),
        _ => return None,
    })
}

/// Does a shortcut like `Cmd+Shift+]` match `key` + `mods`?
fn shortcut_matches(shortcut: &str, key: &str, mods: Mods) -> bool {
    let parts: Vec<&str> = shortcut.split('+').collect();
    let Some((k, ms)) = parts.split_last() else { return false };
    let has = |m: &str| ms.iter().any(|x| x.eq_ignore_ascii_case(m));
    k.eq_ignore_ascii_case(key)
        && has("cmd") == mods.cmd
        && has("shift") == mods.shift
        && (has("alt") || has("option")) == mods.alt
        && has("ctrl") == mods.ctrl
}

impl Headless {
    /// A session with no document (the first `file.new` / `app.open` creates one).
    pub fn new() -> Self {
        Self { session: Session::new(), renderer: Renderer::new(), view: ViewInfo::default(), roots: None }
    }

    /// Confine the files every method reads and writes to `roots` ([`file_access`]).
    pub fn with_automation_roots(mut self, roots: Option<Arc<AutomationRoots>>) -> Self {
        self.roots = roots;
        self
    }

    /// A session with a fresh default (Letter) document, ready to draw into.
    pub fn with_document() -> Self {
        let mut h = Self::new();
        h.ensure_document();
        h
    }

    /// Create a default document when none is open.
    pub fn ensure_document(&mut self) {
        if self.session.active().is_none()
            && let Err(e) = self.session.execute("file.new", &json!({}))
        {
            log::error!("file.new failed: {e}");
        }
    }

    fn exec(&mut self, id: &str, params: &Value) -> Result<Value, String> {
        match id {
            "file.open" => self.open(params),
            "file.save" => self.save(params),
            "file.export" => self.export(params),
            "file.exportForScreens" => self.session.execute("document.exportForScreens", params).map_err(|e| e.to_string()),
            "tool.select" => self.select_tool(params),
            "tool.setOption" => self.session.set_tool_option_cmd(params),
            _ => self.session.execute(id, params).map_err(|e| e.to_string()),
        }
    }

    fn commands(&self) -> Value {
        let mut v: Vec<Value> = self.session.commands().into_iter().map(|c| serde_json::to_value(c).unwrap_or_default()).collect();
        for (id, label, params) in HOST_COMMANDS {
            v.push(json!({"id": id, "label": label, "menu": [], "shortcut": null, "params": params, "enabled": true, "host": true}));
        }
        Value::Array(v)
    }

    fn select_tool(&mut self, p: &Value) -> Result<Value, String> {
        let t = s(p, "tool").ok_or("missing `tool`")?;
        if vectorcraft_tools::tool_info(t).is_none() {
            return Err(format!("unknown tool `{t}` (see ui.tool.list)"));
        }
        self.session.select_tool(t, self.view).map_err(|e| e.to_string())?;
        Ok(json!({"tool": self.session.tool_id()}))
    }

    fn apply_ui_requests(&mut self, reqs: Vec<UiRequest>, out: &mut Vec<Value>) -> Result<(), String> {
        for r in reqs {
            match r {
                UiRequest::SwitchTool(t) => {
                    self.session.select_tool(&t, self.view).map_err(|e| e.to_string())?;
                }
                UiRequest::Dialog(k, p) => out.push(json!({"dialog": k, "params": p})),
                UiRequest::Status(msg) => out.push(json!({"status": msg})),
            }
        }
        Ok(())
    }

    fn pointer(&mut self, p: &Value) -> Result<Value, String> {
        let events = p.get("events").and_then(Value::as_array).ok_or("missing `events`")?;
        let base: Mods = p.get("mods").and_then(|m| serde_json::from_value(m.clone()).ok()).unwrap_or_default();
        self.ensure_document();
        let mut requests = vec![];
        for e in events {
            let kind = s(e, "kind").unwrap_or("");
            let kind = pointer_kind(kind).ok_or_else(|| format!("unknown pointer kind `{kind}` (down|drag|up|move|doubleclick)"))?;
            if s(e, "space") == Some("screen") {
                return Err("screen-space pointer events need the desktop app; use document coordinates".into());
            }
            let x = e.get("x").and_then(Value::as_f64).ok_or("pointer event needs numeric `x`")?;
            let y = e.get("y").and_then(Value::as_f64).ok_or("pointer event needs numeric `y`")?;
            let mods = e.get("mods").and_then(|m| serde_json::from_value(m.clone()).ok()).unwrap_or(base);
            let ev = PointerEvent { kind, pos: Point::new(x, y), mods, pressure: PointerEvent::json_pressure(e) };
            let reqs = self.session.pointer(&ev, self.view).map_err(|e| e.to_string())?;
            self.apply_ui_requests(reqs, &mut requests)?;
            let hold = PointerEvent::json_hold(e);
            if hold > 0.0 {
                let reqs = self.session.tool_tick(hold, self.view).map_err(|e| e.to_string())?;
                self.apply_ui_requests(reqs, &mut requests)?;
            }
        }
        let sel = self.session.active().map(|d| d.selection.objects.iter().map(|i| i.0).collect::<Vec<_>>()).unwrap_or_default();
        let key = self.session.active().and_then(|d| d.selection.key).map(|k| k.0);
        Ok(json!({"selection": sel, "key": key, "tool": self.session.tool_id(), "requests": requests}))
    }

    fn key(&mut self, p: &Value) -> Result<Value, String> {
        let key = s(p, "key").ok_or("missing `key`")?;
        let b = |n: &str| p.get(n).and_then(Value::as_bool).unwrap_or(false);
        let mods = Mods { shift: b("shift"), alt: b("alt"), cmd: b("cmd"), ctrl: b("ctrl"), ..Mods::default() };
        let tk = tool_key(key);
        // A busy tool (pen path in progress, shape being dragged) gets its keys first, as do keys
        // the tool claims (the Gradient tool's selected stop takes Delete and the arrows).
        if let Some(k) = tk
            && (self.session.tool_busy() || self.session.tool_claims_key(k, self.view))
        {
            let mut out = vec![];
            let reqs = self.session.tool_key(k, mods, self.view).map_err(|e| e.to_string())?;
            self.apply_ui_requests(reqs, &mut out)?;
            return Ok(json!({"handledBy": "tool", "requests": out}));
        }
        if let Some(c) = vectorcraft_engine::command_specs().iter().find(|c| c.shortcut.is_some_and(|sc| shortcut_matches(sc, key, mods))) {
            let r = self.exec(c.id, &json!({}))?;
            return Ok(json!({"handledBy": "command", "command": c.id, "result": r}));
        }
        if let Some(t) = TOOL_GROUPS.iter().flat_map(|g| g.iter()).find(|t| t.shortcut.is_some_and(|sc| shortcut_matches(sc, key, mods))) {
            self.session.select_tool(t.id, self.view).map_err(|e| e.to_string())?;
            return Ok(json!({"handledBy": "tool.select", "tool": t.id}));
        }
        // Backspace clears the selection as Delete does (as in the desktop app).
        if tk == Some(ToolKey::Backspace) && mods == Mods::default() && self.session.active().is_some_and(|d| !d.selection.is_empty()) {
            let r = self.exec("edit.clear", &json!({}))?;
            return Ok(json!({"handledBy": "command", "command": "edit.clear", "result": r}));
        }
        if let Some(k) = tk {
            let mut out = vec![];
            let reqs = self.session.tool_key(k, mods, self.view).map_err(|e| e.to_string())?;
            self.apply_ui_requests(reqs, &mut out)?;
            return Ok(json!({"handledBy": "tool", "requests": out}));
        }
        Err(format!("no headless binding for key `{key}`"))
    }

    fn render(&mut self, p: &Value) -> Result<Value, String> {
        let st = self.session.active().ok_or("no document")?;
        let doc = st.doc.clone();
        let idx = p.get("artboard").and_then(Value::as_u64).unwrap_or(0) as usize;
        let r = doc.artboards.get(idx).map(|a| a.rect).ok_or("no such artboard")?;
        let scale = p.get("scale").and_then(Value::as_f64).unwrap_or(1.0).clamp(0.01, 16.0);
        vectorcraft_render::raster_size(r, scale)?;
        let img = self.renderer.render_region(&doc, r, scale, true);
        let png = img.to_png()?;
        let mut out = json!({"width": img.width, "height": img.height});
        match s(p, "path") {
            Some(path) => {
                file_access::check_write(path)?;
                vectorcraft_format::write_atomic(std::path::Path::new(path), &png).map_err(|e| format!("write {path}: {e}"))?;
                out["path"] = json!(path);
                // `data: true` asks for the image as well as the file.
                if p.get("data").and_then(Value::as_bool) == Some(true) {
                    out["pngBase64"] = json!(vectorcraft_format::base64_encode(&png));
                }
            }
            None => out["pngBase64"] = json!(vectorcraft_format::base64_encode(&png)),
        }
        Ok(out)
    }

    /// `app.open {path}`: any readable file as a new active document (`document.open`).
    pub fn open(&mut self, p: &Value) -> Result<Value, String> {
        let path = s(p, "path").ok_or("missing `path`")?;
        self.session.execute("document.open", &json!({"path": path})).map_err(|e| e.to_string())
    }

    /// `app.save {path?, format?, options?}`: `document.save` (by default the document's own path and
    /// format); remembers the path and clears the dirty flag.
    pub fn save(&mut self, p: &Value) -> Result<Value, String> {
        let st = self.session.active().ok_or("no document")?;
        if s(p, "path").is_none() && st.path.is_none() {
            return Err("missing `path` (document was never saved)".into());
        }
        self.session.execute("document.save", p).map_err(|e| e.to_string())
    }

    /// `app.export {path?, format?, …}`: `document.export` (format defaults to the path's extension).
    pub fn export(&mut self, p: &Value) -> Result<Value, String> {
        self.session.execute("document.export", p).map_err(|e| e.to_string())
    }
}

impl Backend for Headless {
    fn call(&mut self, method: &str, params: Value) -> Result<Value, String> {
        let roots = self.roots.clone();
        file_access::confine(roots.as_ref(), || self.answer(method, &params))
    }

    fn has_ui(&self) -> bool {
        false
    }

    fn describe(&self) -> String {
        "headless".into()
    }
}

impl Headless {
    /// One control-channel method ([`Backend::call`]).
    fn answer(&mut self, method: &str, p: &Value) -> Result<Value, String> {
        match method {
            "engine.execute" | "ui.menu.invoke" | "command" => {
                let id = s(p, "command").or(s(p, "id")).ok_or("missing `command`")?.to_string();
                let params = match p.get("params") {
                    None | Some(Value::Null) => json!({}),
                    Some(v) => v.clone(),
                };
                self.exec(&id, &params)
            }
            "engine.commands" => Ok(self.commands()),
            "document.inspect" => self.exec("document.inspect", p),
            "document.node" => self.exec("document.node", p),
            "document.json" => self.exec("document.json", &json!({})),
            "ui.tool.select" => self.select_tool(p),
            "ui.tool.list" => Ok(serde_json::to_value(TOOL_GROUPS).unwrap_or_default()),
            "ui.pointer" => self.pointer(p),
            "ui.key" => self.key(p),
            "ui.render" | "ui.screenshot" => self.render(p),
            "app.open" => self.open(p),
            "app.save" => self.save(p),
            "app.export" => self.export(p),
            "app.quit" => Ok(Value::Null),
            m if m.starts_with("ui.") => {
                Err(format!("`{m}` needs the desktop app (start `vectorcraft --control 7979` and use `vectorcraft-cli mcp --connect`)"))
            }
            other => Err(format!("unknown method `{other}`")),
        }
    }
}