use std::collections::BTreeMap;
use std::sync::{Arc, Mutex};
use std::time::Instant;

use chrono::Utc;
use picloud_shared::{
    ScriptValidator, SdkCallCx, Services, TriggerEvent, ValidatedScript, ValidationError,
    SDK_VERSION,
};
use rhai::{Dynamic, Engine as RhaiEngine, EvalAltResult, Map, Module, Scope, AST};
use serde_json::Value as Json;

use crate::module_resolver::{
    extract_imports, new_module_cache, validate_module_source, ModuleCache, PicloudModuleResolver,
};
use crate::sandbox::Limits;
use crate::sdk;
use crate::sdk::bridge::{dynamic_to_json, json_to_dynamic};
use crate::types::{
    ExecError, ExecRequest, ExecResponse, ExecStats, InvocationType, LogEntry, LogLevel,
};

/// Default capacity for the module cache. Sized assuming a small fleet
/// of distinct modules per process; can be overridden via
/// `PICLOUD_MODULE_CACHE_SIZE`.
const DEFAULT_MODULE_CACHE_SIZE: usize = 512;

/// Preconfigured Rhai engine with sandbox limits applied and the SDK
/// `Services` bundle attached.
///
/// One `Engine` is constructed at process startup and reused across
/// invocations. `execute` is **synchronous** — it owns the per-call
/// scope and log buffer. Wall-clock timeouts and offloading off the
/// async runtime belong to the caller (orchestrator-core's
/// `LocalExecutorClient` wraps this with `spawn_blocking` + `timeout`).
///
/// The `Services` bundle is empty in v1.1.0; subsequent v1.1.x PRs add
/// service handles (KV, docs, …) and `sdk::register_all` wires them
/// into each per-call Rhai engine.
pub struct Engine {
    limits: Limits,
    services: Services,
    /// v1.1.3: shared compiled-module cache. Per-key
    /// `(app_id, name)`; invalidated lazily by `updated_at` mismatch
    /// at resolver time.
    module_cache: Arc<ModuleCache>,
}

impl Engine {
    #[must_use]
    pub fn new(limits: Limits, services: Services) -> Self {
        let cap = std::env::var("PICLOUD_MODULE_CACHE_SIZE")
            .ok()
            .and_then(|s| s.parse::<usize>().ok())
            .unwrap_or(DEFAULT_MODULE_CACHE_SIZE);
        Self::with_module_cache_capacity(limits, services, cap)
    }

    /// Explicit capacity for tests that exercise LRU eviction.
    #[must_use]
    pub fn with_module_cache_capacity(
        limits: Limits,
        services: Services,
        module_cache_capacity: usize,
    ) -> Self {
        Self {
            limits,
            services,
            module_cache: new_module_cache(module_cache_capacity),
        }
    }

    #[must_use]
    pub fn limits(&self) -> &Limits {
        &self.limits
    }

    /// Shared compiled-module cache. Exposed so tests can introspect
    /// the cache state (length, contents) under a Mutex lock.
    #[must_use]
    pub fn module_cache(&self) -> &Arc<ModuleCache> {
        &self.module_cache
    }

    /// Parse-only validation for endpoint scripts. Surfaced at script-
    /// upload time so syntax errors are caught before the first
    /// invocation. Returns the script's literal-path `import "<name>"`
    /// declarations so the repo can populate the dep-graph table.
    pub fn validate(&self, source: &str) -> Result<ValidatedScript, ExecError> {
        // Validation uses a fresh `RhaiEngine` without service hooks
        // attached — modules are only resolved at execute() time, so
        // the resolver during validate is intentionally Dummy (no DB
        // access here; we just need the parser).
        let engine = build_engine(self.limits, None);
        extract_imports(&engine, source).map_err(ExecError::Parse)
    }

    /// Module-shape validation (v1.1.3). Compiles, rejects any top-
    /// level statement that isn't `fn`/`const`/`import`, and returns
    /// the declared imports.
    pub fn validate_module(&self, source: &str) -> Result<ValidatedScript, ExecError> {
        let engine = build_engine(self.limits, None);
        validate_module_source(&engine, source).map_err(ExecError::Parse)
    }

    /// Compile `source` to a reusable AST. Lets callers (the
    /// orchestrator's script cache) compile once and execute many
    /// times against the same AST.
    pub fn compile(&self, source: &str) -> Result<Arc<AST>, ExecError> {
        let engine = build_engine(self.limits, None);
        engine
            .compile(source)
            .map(Arc::new)
            .map_err(|e| ExecError::Parse(e.to_string()))
    }

    /// Execute `source` against `req`. Op-budget protection comes from
    /// Rhai's `set_max_operations`; wall-clock enforcement is the
    /// caller's responsibility. Per-script sandbox overrides on the
    /// request replace the engine's defaults field-by-field; the
    /// manager already clamped them against the admin ceiling.
    pub fn execute(&self, source: &str, req: ExecRequest) -> Result<ExecResponse, ExecError> {
        let effective_limits = self.limits.with_overrides(&req.sandbox_overrides);
        // Compile inline so the source-only path stays available for
        // tests and one-off callers that don't pre-cache an AST.
        let engine_for_compile = build_engine(effective_limits, None);
        let ast = engine_for_compile
            .compile(source)
            .map(Arc::new)
            .map_err(|e| ExecError::Parse(e.to_string()))?;
        self.execute_ast(&ast, req)
    }

    /// v1.1.3: execute a pre-compiled AST. The orchestrator's script
    /// cache hands compiled ASTs in directly; this path skips the
    /// per-call compile.
    pub fn execute_ast(&self, ast: &Arc<AST>, req: ExecRequest) -> Result<ExecResponse, ExecError> {
        let effective_limits = self.limits.with_overrides(&req.sandbox_overrides);
        let logs: Arc<Mutex<Vec<LogEntry>>> = Arc::new(Mutex::new(Vec::new()));
        let mut engine = build_engine(effective_limits, Some(logs.clone()));

        // Per-call context handed to every stateful SDK service via the
        // `sdk::register_all` hook. The Arc lets future service closures
        // capture cheap clones of the cx for use at script-call time.
        let cx = Arc::new(SdkCallCx {
            app_id: req.app_id,
            script_id: req.script_id,
            principal: req.principal.clone(),
            execution_id: req.execution_id,
            request_id: req.request_id,
            trigger_depth: req.trigger_depth,
            root_execution_id: req.root_execution_id,
            is_dead_letter_handler: req.is_dead_letter_handler,
            event: req.event.clone(),
        });
        // v1.1.3: replace the no-op `DummyModuleResolver` build_engine
        // installed with the real per-call resolver. The resolver owns
        // `cx.clone()` so cross-app isolation derives from this exact
        // call's context, not from any script-passed argument.
        let resolver = PicloudModuleResolver::new(
            self.services.modules.clone(),
            cx.clone(),
            self.module_cache.clone(),
            effective_limits.module_import_depth_max,
        );
        engine.set_module_resolver(resolver);
        sdk::register_all(&mut engine, &self.services, cx);

        let mut scope = Scope::new();
        scope.push_constant("ctx", build_ctx_map(&req));

        let started = Instant::now();
        let value: Dynamic = engine
            .eval_ast_with_scope(&mut scope, ast.as_ref())
            .map_err(map_eval_error)?;
        let duration = started.elapsed();

        let logs = Arc::try_unwrap(logs).map_or_else(
            |arc| arc.lock().map(|g| g.clone()).unwrap_or_default(),
            |m| m.into_inner().unwrap_or_default(),
        );

        let (status_code, headers, body) = parse_response(value)?;

        Ok(ExecResponse {
            status_code,
            headers,
            body,
            logs,
            stats: ExecStats {
                duration_ms: u64::try_from(duration.as_millis()).unwrap_or(u64::MAX),
                operations: 0,
            },
        })
    }
}

impl ScriptValidator for Engine {
    fn validate(&self, source: &str) -> Result<ValidatedScript, ValidationError> {
        Engine::validate(self, source).map_err(|e| match e {
            ExecError::Parse(msg) => ValidationError::Syntax(msg),
            other => ValidationError::Syntax(other.to_string()),
        })
    }

    fn validate_module(&self, source: &str) -> Result<ValidatedScript, ValidationError> {
        Engine::validate_module(self, source).map_err(|e| match e {
            ExecError::Parse(msg) => ValidationError::ModuleShape(msg),
            other => ValidationError::ModuleShape(other.to_string()),
        })
    }
}

// ----------------------------------------------------------------------------
// Engine construction
// ----------------------------------------------------------------------------

fn build_engine(limits: Limits, logs: Option<Arc<Mutex<Vec<LogEntry>>>>) -> RhaiEngine {
    let mut engine = RhaiEngine::new();

    engine.set_max_operations(limits.max_operations);
    engine.set_max_string_size(limits.max_string_size);
    engine.set_max_array_size(limits.max_array_size);
    engine.set_max_map_size(limits.max_map_size);
    engine.set_max_call_levels(limits.max_call_levels);
    engine.set_max_expr_depths(limits.max_expr_depth, limits.max_expr_depth);

    // Reject `import` — scripts cannot pull external modules.
    engine.set_module_resolver(rhai::module_resolvers::DummyModuleResolver);

    // Rhai's built-in `print` and `debug` map to stdout/stderr by
    // default; we never want scripts dumping there directly. Disable
    // them so scripts route all output through `log::*` instead.
    engine.disable_symbol("print");

    if let Some(logs) = logs {
        engine.register_static_module("log", build_log_module(logs).into());
    }

    // Stateless utility modules — regex::/random::/time::/json::/base64::/
    // hex::/url::. Always registered, including in the parse-only validate
    // path, so script authors get consistent surface in both phases.
    sdk::stdlib::register_stdlib(&mut engine);

    engine
}

fn build_log_module(logs: Arc<Mutex<Vec<LogEntry>>>) -> Module {
    let mut module = Module::new();
    register_log_fn(&mut module, "trace", LogLevel::Trace, &logs);
    register_log_fn(&mut module, "info", LogLevel::Info, &logs);
    register_log_fn(&mut module, "warn", LogLevel::Warn, &logs);
    register_log_fn(&mut module, "error", LogLevel::Error, &logs);
    // No `log::debug` — `debug` is a Rhai reserved keyword. Use
    // `log::trace` for sub-info-level diagnostics.
    module
}

fn register_log_fn(
    module: &mut Module,
    name: &str,
    level: LogLevel,
    logs: &Arc<Mutex<Vec<LogEntry>>>,
) {
    // Single-argument form: `log::info("message")`.
    let logs_single = logs.clone();
    module.set_native_fn(name, move |msg: &str| {
        push_log(&logs_single, level, msg, None);
        Ok::<_, Box<EvalAltResult>>(())
    });

    // Two-argument form: `log::info("message", #{ user: 42 })`.
    let logs_struct = logs.clone();
    module.set_native_fn(name, move |msg: &str, data: Dynamic| {
        let json = dynamic_to_json(&data);
        push_log(&logs_struct, level, msg, Some(json));
        Ok::<_, Box<EvalAltResult>>(())
    });
}

fn push_log(logs: &Arc<Mutex<Vec<LogEntry>>>, level: LogLevel, message: &str, data: Option<Json>) {
    if let Ok(mut g) = logs.lock() {
        g.push(LogEntry {
            timestamp: Utc::now(),
            level,
            message: message.to_string(),
            data,
        });
    }
}

// ----------------------------------------------------------------------------
// ctx construction
// ----------------------------------------------------------------------------

fn build_ctx_map(req: &ExecRequest) -> Map {
    let mut ctx = Map::new();
    ctx.insert("sdk_version".into(), SDK_VERSION.into());
    ctx.insert("execution_id".into(), req.execution_id.to_string().into());
    ctx.insert("script_id".into(), req.script_id.to_string().into());
    ctx.insert("script_name".into(), req.script_name.clone().into());
    ctx.insert("request_id".into(), req.request_id.to_string().into());
    ctx.insert(
        "invocation_type".into(),
        invocation_type_str(req.invocation_type).into(),
    );

    let mut request = Map::new();
    request.insert("path".into(), req.path.clone().into());

    let mut headers = Map::new();
    for (k, v) in &req.headers {
        headers.insert(k.clone().into(), v.clone().into());
    }
    request.insert("headers".into(), headers.into());

    request.insert("body".into(), json_to_dynamic(req.body.clone()));

    // SDK 1.1 additions — route-captured params, query string, prefix
    // tail. Empty when not applicable so scripts can always read them.
    let mut params = Map::new();
    for (k, v) in &req.params {
        params.insert(k.clone().into(), v.clone().into());
    }
    request.insert("params".into(), params.into());

    let mut query = Map::new();
    for (k, v) in &req.query {
        query.insert(k.clone().into(), v.clone().into());
    }
    request.insert("query".into(), query.into());

    request.insert("rest".into(), req.rest.clone().into());

    ctx.insert("request".into(), request.into());

    // Triggered invocations: surface the originating event as
    // `ctx.event`. Direct ingress (HTTP request, manual run) leaves
    // the key absent so scripts can test `if "event" in ctx`.
    if let Some(event) = req.event.as_ref() {
        ctx.insert("event".into(), trigger_event_to_dynamic(event));
    }

    ctx
}

/// Convert a `TriggerEvent` into the `ctx.event` Rhai shape defined in
/// `docs/v1.1.x-design-notes.md` §4 (the dead-letter sub-shape) and
/// §2/blueprint §9 (KV). Each variant becomes a Rhai map with a
/// `source` discriminant plus per-source fields.
#[allow(clippy::too_many_lines)]
fn trigger_event_to_dynamic(event: &TriggerEvent) -> Dynamic {
    let mut m = Map::new();
    m.insert("source".into(), event.source().into());
    match event {
        TriggerEvent::Kv {
            op,
            collection,
            key,
            value,
        } => {
            m.insert("op".into(), op.as_str().into());
            let mut kv_map = Map::new();
            kv_map.insert("collection".into(), collection.clone().into());
            kv_map.insert("key".into(), key.clone().into());
            kv_map.insert(
                "value".into(),
                value.clone().map_or(Dynamic::UNIT, json_to_dynamic),
            );
            m.insert("kv".into(), kv_map.into());
        }
        TriggerEvent::Docs {
            op,
            collection,
            id,
            data,
            prev_data,
        } => {
            m.insert("op".into(), op.as_str().into());
            let mut docs_map = Map::new();
            docs_map.insert("collection".into(), collection.clone().into());
            docs_map.insert("id".into(), id.clone().into());
            docs_map.insert(
                "data".into(),
                data.clone().map_or(Dynamic::UNIT, json_to_dynamic),
            );
            docs_map.insert(
                "prev_data".into(),
                prev_data.clone().map_or(Dynamic::UNIT, json_to_dynamic),
            );
            m.insert("docs".into(), docs_map.into());
        }
        TriggerEvent::Cron {
            schedule,
            timezone,
            scheduled_at,
            fired_at,
        } => {
            // `ctx.event.op` is always "tick" for cron (the only op a
            // schedule produces). Mirrors the docs/v1.1.x-design-notes
            // §7 shape.
            m.insert("op".into(), "tick".into());
            let mut cron_map = Map::new();
            cron_map.insert("schedule".into(), schedule.clone().into());
            cron_map.insert("timezone".into(), timezone.clone().into());
            cron_map.insert("scheduled_at".into(), scheduled_at.to_rfc3339().into());
            cron_map.insert("fired_at".into(), fired_at.to_rfc3339().into());
            m.insert("cron".into(), cron_map.into());
        }
        TriggerEvent::Files {
            op,
            collection,
            id,
            name,
            content_type,
            size,
            checksum,
            prev,
        } => {
            m.insert("op".into(), op.as_str().into());
            let mut files_map = Map::new();
            files_map.insert("collection".into(), collection.clone().into());
            files_map.insert("id".into(), id.clone().into());
            files_map.insert("name".into(), name.clone().into());
            files_map.insert("content_type".into(), content_type.clone().into());
            files_map.insert(
                "size".into(),
                i64::try_from(*size).unwrap_or(i64::MAX).into(),
            );
            files_map.insert("checksum".into(), checksum.clone().into());
            files_map.insert(
                "prev".into(),
                prev.clone().map_or(Dynamic::UNIT, json_to_dynamic),
            );
            m.insert("files".into(), files_map.into());
        }
        TriggerEvent::DeadLetter {
            dead_letter_id,
            original,
            attempts,
            last_error,
            trigger_id,
            script_id,
            first_attempt_at,
            last_attempt_at,
        } => {
            let mut dl = Map::new();
            dl.insert("id".into(), dead_letter_id.to_string().into());
            dl.insert("original".into(), trigger_event_to_dynamic(original));
            dl.insert("attempts".into(), i64::from(*attempts).into());
            dl.insert("last_error".into(), last_error.clone().into());
            dl.insert(
                "trigger_id".into(),
                trigger_id
                    .map(|id| Dynamic::from(id.to_string()))
                    .unwrap_or(Dynamic::UNIT),
            );
            dl.insert(
                "script_id".into(),
                script_id
                    .map(|id| Dynamic::from(id.to_string()))
                    .unwrap_or(Dynamic::UNIT),
            );
            dl.insert(
                "first_attempt_at".into(),
                first_attempt_at.to_rfc3339().into(),
            );
            dl.insert(
                "last_attempt_at".into(),
                last_attempt_at.to_rfc3339().into(),
            );
            m.insert("dead_letter".into(), dl.into());
        }
    }
    m.into()
}

fn invocation_type_str(it: InvocationType) -> &'static str {
    match it {
        InvocationType::Http => "http",
        InvocationType::Function => "function",
        InvocationType::Scheduled => "scheduled",
    }
}

// ----------------------------------------------------------------------------
// Response parsing
// ----------------------------------------------------------------------------

fn parse_response(value: Dynamic) -> Result<(u16, BTreeMap<String, String>, Json), ExecError> {
    // Convention: a Map with a `statusCode` field is the structured shape.
    // Anything else is treated as a 200 response with the value as body.
    if value.is_map() {
        if let Some(map) = value.clone().try_cast::<Map>() {
            if map.contains_key("statusCode") {
                return parse_structured_response(map);
            }
        }
    }
    Ok((200, BTreeMap::new(), dynamic_to_json(&value)))
}

fn parse_structured_response(map: Map) -> Result<(u16, BTreeMap<String, String>, Json), ExecError> {
    let status_dyn = map
        .get("statusCode")
        .ok_or_else(|| ExecError::InvalidResponse("missing statusCode".into()))?;
    let status_code: i64 = status_dyn
        .as_int()
        .map_err(|_| ExecError::InvalidResponse("statusCode must be an integer".into()))?;
    let status_code = u16::try_from(status_code)
        .map_err(|_| ExecError::InvalidResponse("statusCode out of HTTP range".into()))?;

    let mut headers: BTreeMap<String, String> = BTreeMap::new();
    if let Some(h) = map.get("headers") {
        if let Some(h_map) = h.clone().try_cast::<Map>() {
            for (k, v) in h_map {
                headers.insert(k.to_string(), v.to_string());
            }
        }
    }

    let body = map.get("body").map_or(Json::Null, dynamic_to_json);

    Ok((status_code, headers, body))
}

// ----------------------------------------------------------------------------
// Error mapping
// ----------------------------------------------------------------------------

fn map_eval_error(err: Box<EvalAltResult>) -> ExecError {
    match *err {
        EvalAltResult::ErrorTooManyOperations(_) => ExecError::OperationBudgetExceeded,
        EvalAltResult::ErrorParsing(parse_err, _) => ExecError::Parse(parse_err.to_string()),
        other => ExecError::Runtime(other.to_string()),
    }
}