//! Rhai scripting runtime for board objects.
//!
//! [`ScriptHost`] owns the Rhai [`Engine`], the compiled scripts referenced by a
//! board's objects, and a persistent per-object [`Scope`]. It drives the optional
//! lifecycle hooks on each scripted object:
//!
//! - `init(me, state)` — run once after the whole map is loaded (see [`ScriptHost::run_init`]).
//! - `tick(me, state, dt)` — run every frame with the elapsed seconds (see [`ScriptHost::run_tick`]).
//! - `bump(me, dir)` — run when a solid (the player, an object, or a pushed crate) presses into this
//!   object's cell, with the [`Direction`] the bump came *from*; see [`ScriptHost::run_bump`].
//! - `grab(me, state)` — run when the player walks onto a `grab` object; see [`ScriptHost::run_grab`].
//!   Typically adds a stat + `die()`s.
//!
//! | Name | Type | Description |
//! |---|---|---|
//! | `Registry` | `Registry` | Board-scoped key→value store persisting across board transitions. |
//!
//! Direction and color constants are registered as a global Rhai module and
//! are visible to all functions at any call depth, including Rhai-to-Rhai calls:
//!
//! | Name | Type | Description |
//! |---|---|---|
//! | `North`/`South`/`East`/`West` | `Direction` | Cardinal directions. |
//! | `Black`..`White` | `String` | 16 EGA/VGA color hex strings. |
//!
//! ## Write functions
//!
//! `move(dir)`, `delay(secs)`, `now()`, `set_tile(n)`, `log(msg)`, `say(msg)`,
//! `set_fg(fg)`, `set_bg(bg)`, `set_color(fg, bg)`, `set_tag(target, tag, present)`,
//! `send(target_id, fn_name [, arg])`, `teleport(id, x, y)`, `push(x, y, dir)`,
//! `shift([[x, y], …])`, `alter_gems(n)`, `alter_health(dh)`, `set_key(color, present)`, `die()`

use crate::action::{Action, BoardAction, ScrollLine, SendArg, MOVE_COST};
use crate::game::SAY_DURATION;
use crate::log::LogLine;
use crate::map_file::parse_color;
use crate::object_def::ObjectDef;
use crate::utils::{Direction, ErrorSink, Hook, ObjectId};
use rhai::{
    Array, CallFnOptions, Dynamic, Engine, ImmutableString, Module, NativeCallContext,
    Scope, AST,
};
use std::collections::{HashMap, HashSet};
use crate::api::board::BoardRef;
use crate::api::object_info::ObjectInfo;
use crate::api::player::PlayerWithPos;
use crate::api::queue::ObjQueue;
use crate::api::registry::Registry;
use crate::glyph::Glyph;
use crate::keys::Keyring;
use crate::player::PlayerRef;

/// Types which can be registered to be sent to Rhai
pub trait Registerable {
    /// Register this type and relevant getters / setters with a Rhai engine
    fn register(engine: &mut Engine, error_sink: ErrorSink);
}

/// A compiled script plus which lifecycle hooks it defines.
struct CompiledScript {
    ast: AST,
    has_init: bool,
    has_tick: bool,
    has_bump: bool,
    has_grab: bool,
}

impl CompiledScript {
    pub fn has(&self, hook: Hook) -> bool {
        match hook {
            Hook::Init => self.has_init,
            Hook::Tick => self.has_tick,
            Hook::Grab => self.has_grab,
            Hook::Bump => self.has_bump
        }
    }
}

/// The compile-key for an object's script: the object's `script_name` — a
/// world-pool name for a named script, or a synthetic `BUILTIN_*` name set by
/// [`Board::expand_builtin_archetypes`](crate::board::Board::expand_builtin_archetypes)
/// for an expanded built-in (so identical built-ins share one compiled AST,
/// while the source still comes from `builtin_script`). `None` if the object has
/// no script.
fn script_key(obj: &ObjectDef) -> Option<String> {
    obj.script_name.clone()
}

// ── ScriptHost ────────────────────────────────────────────────────────────────

/// Owns the Rhai engine and per-object script state for a board.
pub struct ScriptHost {
    engine: Engine,
    scripts: HashMap<String, CompiledScript>,
    scopes: HashMap<ObjectId, Scope<'static>>,
    errors: ErrorSink,
    board: BoardRef
}

impl ScriptHost {
    /// Builds a host for the board behind `board_cell`: registers the full script API,
    /// compiles every script referenced by an object (once each), and creates a fresh
    /// scope and output queue per scripted object. Compile errors and references to
    /// unknown scripts are queued onto the error sink; no script is run here.
    ///
    /// `scripts` is the world-level script pool (script name → Rhai source); it is
    /// read only during construction and not retained afterward.
    pub fn new(board_ref: BoardRef, player: PlayerRef, script_sources: &HashMap<String, String>) -> Self {
        let errors = ErrorSink::new();
        let mut scopes = HashMap::new();

        let mut engine = Engine::new();

        PlayerWithPos::register(&mut engine, errors.clone());
        Keyring::register(&mut engine, errors.clone());
        BoardRef::register(&mut engine, errors.clone());
        ObjectInfo::register(&mut engine, errors.clone());
        Glyph::register(&mut engine, errors.clone());
        ObjQueue::register(&mut engine, errors.clone());
        Registry::register(&mut engine, errors.clone());

        register_write_api(&mut engine, board_ref.clone());
        register_global_constants(&mut engine, board_ref.clone(), player.clone());

        let board = board_ref.borrow();

        // Compile each referenced script once, keyed by `script_key` (the object's
        // `script_name`: a world-pool name for named scripts, or a synthetic
        // `BUILTIN_*` name for built-ins so identical ones share one AST). The
        // source for a built-in still comes from its embedded `builtin_script`.
        let mut scripts: HashMap<String, CompiledScript> = HashMap::new();
        let mut failed: HashSet<String> = HashSet::new();
        for obj in board.objects.values() {
            let Some(key) = script_key(obj) else {
                continue;
            };
            if scripts.contains_key(&key) || failed.contains(&key) {
                continue;
            }
            // Source: the embedded built-in, or a lookup in the world script pool.
            let source: &str = if let Some(src) = obj.builtin_script {
                src
            } else {
                match script_sources.get(&key) {
                    Some(src) => src,
                    None => {
                        failed.insert(key.clone());
                        errors.error(format!("object references unknown script '{key}'"));
                        continue;
                    }
                }
            };
            match engine.compile(source) {
                Ok(ast) => {
                    let defines = |n: &str, params: usize| {
                        ast.iter_functions()
                            .any(|f| f.name == n && f.params.len() == params)
                    };
                    scripts.insert(
                        key,
                        CompiledScript {
                            has_init: defines("init", 1),
                            has_tick: defines("tick", 2),
                            has_bump: defines("bump", 2),
                            has_grab: defines("grab", 1),
                            ast,
                        },
                    );
                }
                Err(err) => {
                    failed.insert(key.clone());
                    errors.error(format!("script '{key}' failed to compile: {err}"));
                }
            }
        }

        // One runtime per object whose script compiled.
        for (&id, obj) in board.objects.iter() {
            let Some(key) = script_key(obj) else {
                continue;
            };
            if !scripts.contains_key(&key) {
                continue;
            }
            scopes.insert(id, Scope::new());
        }

        drop(board);
        Self {
            engine,
            scripts,
            errors,
            scopes,
            board: board_ref
        }
    }

    /// Runs the `tick(me, dt)` hook on one object and returns the actions it
    /// drained (see [`run_hook_on_one`](ScriptHost::run_hook_on_one)).
    pub(crate) fn run_tick_on(&mut self, id: ObjectId, dt: f64) -> Vec<BoardAction> {
        self.run_hook_on(Hook::Tick, id, dt)
    }

    /// Runs the `init(me)` hook on one object and returns the actions it drained.
    pub(crate) fn run_init_on(&mut self, id: ObjectId) -> Vec<BoardAction> {
        self.run_hook_on(Hook::Init, id, 0.0)
    }

    /// Runs `hook` on the single object `id` and returns the actions it drained.
    ///
    /// The `dt` arg is only meaningful for `Tick` (it becomes the hook's `dt`
    /// parameter and paces the object's delay draining); pass `0.0` otherwise.
    pub(crate) fn run_hook_on(&mut self, hook: Hook, id: ObjectId, dt: f64) -> Vec<BoardAction> {
        let arg = match hook {
            Hook::Tick => Some(Dynamic::from(dt)),
            _ => None,
        };
        self.run_hook_on_one(hook, id, arg, dt)
    }

    /// Calls one lifecycle `hook` on object `id` (if the script defines it), then
    /// drains that object's ready actions into a fresh `Vec` and returns them —
    /// [`GameState`](crate::game::GameState) applies them immediately, before the
    /// next object runs, so each object sees the board state its actions run against.
    fn run_hook_on_one(&mut self, hook: Hook, id: ObjectId, arg: Option<Dynamic>, dt: f64) -> Vec<BoardAction> {
        let mut actions = Vec::new();
        if let Some(mut info) = ObjectInfo::from_id(id, self.board.clone()) {
            if let Some(script_key) = info.script_name.as_ref()
                && let Some(script) = self.scripts.get(script_key)
                && let Some(scope) = self.scopes.get_mut(&id) {

                if script.has(hook) {
                    let mut args = vec![Dynamic::from(info.clone())];
                    if let Some(d) = arg { args.push(d) }

                    // Call this with opts tagging this call as our id. The write API will read
                    // that to find what queue to emit events to
                    if let Err(err) = self.engine.call_fn_with_options::<()>(
                        CallFnOptions::default().with_tag(id as i64),
                        scope,
                        &script.ast,
                        hook.to_str(),
                        args,
                    ) {
                        self.errors.error(format!("script '{}' {} error: {err}", script_key, hook));
                    }
                }
                // Run the drain regardless of if we have the hook, otherwise
                // things with no tick will never advance past a delay
                info.drain(&mut actions, dt)
            }
        } else {
            unreachable!("Object not found");
        }
        actions
    }

    /// Calls `bump(dir)` on the object with [`ObjectId`] `id`, if it defines the
    /// hook, and returns the actions it drained. `dir` is the [`Direction`] the
    /// bump came *from* (it points from the bumped object toward the bumper).
    pub(crate) fn run_bump(&mut self, id: ObjectId, dir: Direction) -> Vec<BoardAction> {
        self.run_hook_on_one(Hook::Bump, id, Some(Dynamic::from(dir)), 0.0)
    }

    /// Calls `grab()` on the object with [`ObjectId`] `object_id`, if it defines the
    /// hook, and returns the actions it drained.
    ///
    /// Fired when the player walks onto a grab object (see
    /// [`GameState`](crate::game::GameState)). The hook typically increments a
    /// player stat and removes the object via `die()`.
    pub(crate) fn run_grab(&mut self, object_id: ObjectId) -> Vec<BoardAction> {
        self.run_hook_on_one(Hook::Grab, object_id, None, 0.0)
    }

    /// Calls the named function on the object with [`ObjectId`] `target_id`.
    ///
    /// What we pass depends on arity, in this order:
    /// - If it has arity 2, we pass `[ObjectInfo, arg]`
    /// - If it has arity 1, we pass the ObjectInfo alone
    /// - If it has arity 0, we pass nothing
    ///
    /// In cases where the arg isn't provided but we have the arity, we pass `Dynamic::UNIT`.
    /// Returns the actions the call drained.
    pub(crate) fn run_send(&mut self, id: ObjectId, fn_name: &str, arg: SendArg) -> Vec<BoardAction> {
        let mut actions = Vec::new();
        if let Some(mut info) = ObjectInfo::from_id(id, self.board.clone()) {
            if let Some(script_key) = info.script_name.as_ref()
                && let Some(script) = self.scripts.get(script_key)
                && let Some(scope) = self.scopes.get_mut(&id) {

                // Find the function:
                let arities: HashSet<_> = script.ast.iter_functions().filter_map(|f| {
                    if f.name == fn_name {
                        Some(f.params.len())
                    } else {
                        None
                    }
                }).collect();

                // If it's not there at all, just bail:
                if arities.is_empty() {
                    self.errors.error(format!("script '{}' send({}) error: function not found", script_key, fn_name));
                    return actions;
                }

                // Assemble the args
                let mut args = vec![];
                if arities.contains(&2) {
                    args.push(Dynamic::from(info.clone()));
                    args.push(arg.into());
                } else if arities.contains(&1) {
                    args.push(Dynamic::from(info.clone()));
                }

                // Call this with opts tagging this call as our id. The write API will read
                // that to find what queue to emit events to
                if let Err(err) = self.engine.call_fn_with_options::<()>(
                    CallFnOptions::default().with_tag(id as i64),
                    scope,
                    &script.ast,
                    fn_name,
                    args,
                ) {
                    self.errors.error(format!("script '{}' send({}) error: {err}", script_key, fn_name));
                }
                info.drain(&mut actions, 0.0)
            }
        } else {
            unreachable!("Object id not found, tried to send");
        }
        actions
    }

    /// Removes and returns the errors collected since the last drain.
    pub fn take_errors(&mut self) -> Vec<LogLine> {
        self.errors.take()
    }
}

// ── Write API ─────────────────────────────────────────────────────────────────

fn register_write_api(engine: &mut Engine, board: BoardRef) {
    engine.register_type_with_name::<Direction>("Direction");
    // Rhai does not auto-derive comparison for custom types, so register `==`/`!=`
    // to let scripts test the `bump` direction (e.g. `if dir == West { … }`).
    engine.register_fn("==", |a: Direction, b: Direction| a == b);
    engine.register_fn("!=", |a: Direction, b: Direction| a != b);
    // Let a Direction interpolate/print as its name (e.g. in `log(`from ${dir}`)`).
    let dir_name = |d: Direction| match d {
        Direction::North => "North",
        Direction::South => "South",
        Direction::East => "East",
        Direction::West => "West",
    };
    engine.register_fn("to_string", dir_name);
    engine.register_fn("to_debug", dir_name);
    // Expose the unit-step components so scripts can turn a direction into a cell
    // offset (e.g. the bumper's cell is `(me.x + dir.dx, me.y + dir.dy)`).
    engine.register_get("dx", |d: &mut Direction| d.dx());
    engine.register_get("dy", |d: &mut Direction| d.dy());

    // move(dir): enqueue a Move followed by a rate-limiting Delay.
    let b = board.clone();
    engine.register_fn("move", move |ctx: NativeCallContext, dir: Direction| {
        let src = source_of(&ctx);
        if let Some(def) = b.borrow_mut().objects.get_mut(&src) {
            def.queue.act(Action::Move(dir));
            def.queue.delay(MOVE_COST);
        }
    });

    let b = board.clone();
    engine.register_fn("delay", move |ctx: NativeCallContext, dt: Dynamic| {
        let src = source_of(&ctx);
        if let Some(def) = b.borrow_mut().objects.get_mut(&src)
            && let Ok(dt) = dt.as_float() {
            def.queue.delay(dt);
        }
    });

    let b = board.clone();
    engine.register_fn("now", move |ctx: NativeCallContext| {
        let src = source_of(&ctx);
        if let Some(def) = b.borrow_mut().objects.get_mut(&src) {
            def.queue.now()
        }
    });

    let b = board.clone();
    engine.register_fn("set_tile", move |ctx: NativeCallContext, tile: i64| {
        emit(&b, source_of(&ctx), Action::SetTile(tile as u32));
    });

    // alter_gems(n): change the player's gem count (negative subtracts; clamped at 0).
    let b = board.clone();
    engine.register_fn("alter_gems", move |ctx: NativeCallContext, n: i64| {
        emit(&b, source_of(&ctx), Action::AddGems(n));
    });

    // alter_health(dh): change the player's health by dh (clamped to [0, max_health]).
    let b = board.clone();
    engine.register_fn("alter_health", move |ctx: NativeCallContext, dh: i64| {
        emit(&b, source_of(&ctx), Action::AlterHealth(dh));
    });

    // set_key(color, present): give (true) or take (false) the named key color.
    let b = board.clone();
    engine.register_fn(
        "set_key",
        move |ctx: NativeCallContext, color: ImmutableString, present: bool| {
            emit(&b, source_of(&ctx), Action::SetKey(color.into(), present));
        },
    );

    // die(): remove the calling object from the board.
    let b = board.clone();
    engine.register_fn("die", move |ctx: NativeCallContext| {
        emit(&b, source_of(&ctx), Action::Die);
    });

    let b = board.clone();
    engine.register_fn(
        "log",
        move |ctx: NativeCallContext, msg: ImmutableString| {
            let id = source_of(&ctx);
            emit(&b, id, Action::Log(LogLine::raw(msg.to_string())));
        },
    );

    let b = board.clone();
    engine.register_fn(
        "say",
        move |ctx: NativeCallContext, msg: ImmutableString| {
            emit(
                &b,
                source_of(&ctx),
                Action::Say(msg.to_string(), SAY_DURATION),
            );
        },
    );
    let b = board.clone();
    engine.register_fn(
        "say",
        move |ctx: NativeCallContext, msg: ImmutableString, dur: f64| {
            emit(&b, source_of(&ctx), Action::Say(msg.to_string(), dur));
        },
    );

    // scroll(lines): open a full-screen scrollable overlay. Each element of `lines`
    // is either a plain string (text) or a 2-element array [choice_key, display_text].
    let b = board.clone();
    engine.register_fn("scroll", move |ctx: NativeCallContext, arr: Array| {
        let lines = arr
            .into_iter()
            .filter_map(|item| {
                if let Ok(s) = item.clone().into_string() {
                    Some(ScrollLine::Text(s))
                } else {
                    let pair: Vec<Dynamic> = item.into_array().ok()?;
                    if pair.len() == 2 {
                        let choice = pair[0].clone().into_string().ok()?;
                        let display = pair[1].clone().into_string().ok()?;
                        Some(ScrollLine::Choice { choice, display })
                    } else {
                        None
                    }
                }
            })
            .collect();
        emit(&b, source_of(&ctx), Action::Scroll(lines));
    });

    let b = board.clone();
    engine.register_fn(
        "set_tag",
        move |ctx: NativeCallContext, target: i64, tag: ImmutableString, present: bool| {
            emit(&b, source_of(&ctx), Action::SetTag { target: target as ObjectId, tag: tag.to_string(), present })
        }
    );

    let b = board.clone();
    engine.register_fn(
        "set_tag",
        move |ctx: NativeCallContext, target: ObjectId, tag: ImmutableString, present: bool| {
            emit(&b, source_of(&ctx), Action::SetTag { target, tag: tag.to_string(), present })
        }
    );

    // set_fg(fg): change foreground color only.
    let b = board.clone();
    engine.register_fn(
        "set_fg",
        move |ctx: NativeCallContext, fg: ImmutableString| {
            emit(
                &b,
                source_of(&ctx),
                Action::SetColor {
                    fg: Some(parse_color(fg.as_str())),
                    bg: None,
                },
            );
        },
    );

    // set_bg(bg): change background color only.
    let b = board.clone();
    engine.register_fn(
        "set_bg",
        move |ctx: NativeCallContext, bg: ImmutableString| {
            emit(
                &b,
                source_of(&ctx),
                Action::SetColor {
                    fg: None,
                    bg: Some(parse_color(bg.as_str())),
                },
            );
        },
    );

    // set_color(fg, bg): change both colors.
    let b = board.clone();
    engine.register_fn(
        "set_color",
        move |ctx: NativeCallContext, fg: ImmutableString, bg: ImmutableString| {
            emit(
                &b,
                source_of(&ctx),
                Action::SetColor {
                    fg: Some(parse_color(fg.as_str())),
                    bg: Some(parse_color(bg.as_str())),
                },
            );
        },
    );

    // send(target, fn_name): call a named function on another object.
    let b = board.clone();
    engine.register_fn(
        "send",
        move |ctx: NativeCallContext, target: i64, name: ImmutableString| {
            emit(
                &b,
                source_of(&ctx),
                Action::Send {
                    target: target as ObjectId,
                    fn_name: name.to_string(),
                    arg: SendArg::None,
                },
            );
        },
    );

    // send(target, fn_name, arg): same, with an optional string or number argument.
    let b = board.clone();
    engine.register_fn(
        "send",
        move |ctx: NativeCallContext, target: i64, name: ImmutableString, arg: Dynamic| {
            emit(
                &b,
                source_of(&ctx),
                Action::Send {
                    target: target as ObjectId,
                    fn_name: name.to_string(),
                    arg: arg.into(),
                },
            );
        },
    );

    // teleport(target, x, y): move object `target` to an arbitrary cell (pass your
    // own `me.id` to move yourself; `target == -1` moves the player). Zero time
    // cost. Blocked (with an error logged at resolve time) if that entity is solid
    // and the destination already holds a different solid occupant.
    let b = board.clone();
    engine.register_fn("teleport", move |ctx: NativeCallContext, target: i64, x: i64, y: i64| {
        emit(&b, source_of(&ctx), Action::Teleport { target, x, y });
    });

    // push(x, y, dir): shove the pushable chain at (x, y) one step in dir. Acts on
    // arbitrary cells, not the caller, and adds no delay (zero time cost).
    let b = board.clone();
    engine.register_fn(
        "push",
        move |ctx: NativeCallContext, x: i64, y: i64, dir: Direction| {
            emit(&b, source_of(&ctx), Action::Push { x, y, dir, });
        }
    );

    // shift([[x, y], ...): Emits a shift action which moves the contents of each given cell in
    // a loop (the last cell is moved to the first coord). Doesn't move things that aren't pushable,
    // and won't move anything into a cell that's not vacant (or vacated by this shift).
    let b = board.clone();
    engine.register_fn("shift", move |ctx: NativeCallContext, arr: Array| {
        let src = source_of(&ctx);
        match read_coord_array(&arr) {
            Ok(pairs) => emit(&b, src, Action::Shift(pairs)),
            Err(_) => emit(&b, src, Action::Log(LogLine::error("shift: each entry must be [x, y]".to_string())))
        }
    });
}

/// Read a `Vec<(i32, i32)>` from a Rhai array, to receive a list of coordinates from a script.
/// Returns Err if the array isn't `[[x, y], ...]`
fn read_coord_array(arr: &Array) -> Result<Vec<(i64, i64)>, ()> {
    let mut pairs = Vec::new();
    for elem in arr {
        let coords: Option<Vec<i64>> = elem.read_lock::<Array>().and_then(|inner| {
            inner.iter().map(|v| v.as_int().ok()).collect()
        });
        if let Some(coords) = coords && coords.len() == 2 {
            pairs.push((coords[0], coords[1]))
        } else {
            return Err(());
        }
    }
    Ok(pairs)
}

// ── Scope construction & global constants ─────────────────────────────────────

/// Registers direction and color constants as a global Rhai module so they are
/// visible to every function at any call depth, including Rhai-to-Rhai calls.
/// (Scope-level constants are only visible to the top-level function Rust calls.)
fn register_global_constants(engine: &mut Engine, board: BoardRef, player: PlayerRef) {
    let mut m = Module::new();
    m.set_var("Board", board.clone());
    m.set_var("Player", PlayerWithPos(player.clone(), board));
    m.set_var("North", Direction::North);
    m.set_var("South", Direction::South);
    m.set_var("East", Direction::East);
    m.set_var("West", Direction::West);
    // 16 EGA/VGA color constants as "#RRGGBB" strings, from the shared palette table
    // (the single source of truth, also used by the editor's color picker).
    for (name, c) in crate::colors::NAMED_COLORS {
        m.set_var(name, format!("#{:02X}{:02X}{:02X}", c.r, c.g, c.b));
    }
    engine.register_global_module(m.into());
}

/// Appends `action` to the output queue of the object identified by `source`.
fn emit(board: &BoardRef, source: ObjectId, action: Action) {
    if let Some(def) = board.borrow_mut().objects.get_mut(&source) {
        def.queue.act(action);
    }
}

/// Reads the issuing object's [`ObjectId`] from the call tag.
fn source_of(ctx: &NativeCallContext) -> ObjectId {
    ctx.tag()
        .and_then(|t| t.as_int().ok())
        .and_then(|n| ObjectId::try_from(n).ok())
        .unwrap_or(0)
}