//! Discord Gateway/Webhook channel for IronClaw.
//!
//! This WASM component implements the channel interface for handling Discord
//! interactions via webhooks and sending messages back to Discord.
//!
//! # Features
//!
//! - URL verification for Discord interactions
//! - Slash command handling
//! - Message event parsing (@mentions, DMs)
//! - Thread support for conversations
//! - Response posting via Discord Web API
//! - Automatic message truncation (> 2000 chars)
//!
//! # Security
//!
//! - Signature validation is handled by the host (webhook secrets)
//! - Bot token is injected by host during HTTP requests
//! - WASM never sees raw credentials

wit_bindgen::generate!({
    world: "sandboxed-channel",
    path: "../../wit/channel.wit",
});

use serde::{Deserialize, Serialize};

use exports::near::agent::channel::{
    AgentResponse, ChannelConfig, Guest, HttpEndpointConfig, IncomingHttpRequest,
    OutgoingHttpResponse, StatusUpdate,
};
use near::agent::channel_host::{self, EmittedMessage};

/// Discord interaction wrapper.
#[derive(Debug, Deserialize)]
struct DiscordInteraction {
    /// Interaction type (1=Ping, 2=ApplicationCommand, 3=MessageComponent)
    #[serde(rename = "type")]
    interaction_type: u8,

    /// Interaction ID
    id: String,

    /// Application ID
    application_id: String,

    /// Guild ID (if in server)
    #[allow(dead_code)] // Part of API payload, currently unused
    guild_id: Option<String>,

    /// Channel ID
    channel_id: Option<String>,

    /// Member info (if in server)
    member: Option<DiscordMember>,

    /// User info (if DM)
    user: Option<DiscordUser>,

    /// Command data (for slash commands)
    data: Option<DiscordCommandData>,

    /// Message (for component interactions)
    message: Option<DiscordMessage>,

    /// Token for responding
    token: String,
}

#[derive(Debug, Deserialize, Clone)]
struct DiscordMember {
    user: DiscordUser,
    #[allow(dead_code)] // Part of API payload, currently unused
    nick: Option<String>,
}

#[derive(Debug, Deserialize, Clone)]
struct DiscordUser {
    id: String,
    username: String,
    global_name: Option<String>,
}

#[derive(Debug, Deserialize, Clone)]
struct DiscordCommandData {
    #[allow(dead_code)] // Part of API payload, currently unused
    id: String,
    name: String,
    options: Option<Vec<DiscordCommandOption>>,
}

#[derive(Debug, Deserialize, Clone)]
struct DiscordCommandOption {
    name: String,
    value: serde_json::Value,
}

#[derive(Debug, Deserialize, Clone)]
struct DiscordMessage {
    #[allow(dead_code)] // Part of API payload, currently unused
    id: String,
    content: String,
    channel_id: String,
    #[allow(dead_code)] // Part of API payload, currently unused
    author: DiscordUser,
}

/// Metadata stored with emitted messages for response routing.
#[derive(Debug, Serialize, Deserialize)]
struct DiscordMessageMetadata {
    /// Discord channel ID
    channel_id: String,

    /// Interaction ID for followups
    interaction_id: String,

    /// Interaction token for responding
    token: String,

    /// Application ID
    application_id: String,

    /// Thread ID (for forum threads)
    thread_id: Option<String>,
}

/// Workspace path for persisting owner_id across WASM callbacks.
const OWNER_ID_PATH: &str = "state/owner_id";
/// Workspace path for persisting dm_policy across WASM callbacks.
const DM_POLICY_PATH: &str = "state/dm_policy";
/// Workspace path for persisting allow_from (JSON array) across WASM callbacks.
const ALLOW_FROM_PATH: &str = "state/allow_from";
/// Channel name for pairing store (used by pairing host APIs).
const CHANNEL_NAME: &str = "discord";

/// Channel configuration from capabilities file.
#[derive(Debug, Deserialize)]
struct DiscordConfig {
    #[serde(default)]
    #[allow(dead_code)]
    require_signature_verification: bool,
    #[serde(default)]
    owner_id: Option<String>,
    #[serde(default)]
    dm_policy: Option<String>,
    #[serde(default)]
    allow_from: Option<Vec<String>>,
}

struct DiscordChannel;

impl Guest for DiscordChannel {
    fn on_start(config_json: String) -> Result<ChannelConfig, String> {
        let config: DiscordConfig = serde_json::from_str(&config_json)
            .map_err(|e| format!("Failed to parse config: {}", e))?;

        channel_host::log(channel_host::LogLevel::Info, "Discord channel starting");

        // Persist owner_id so subsequent callbacks can read it
        if let Some(ref owner_id) = config.owner_id {
            let _ = channel_host::workspace_write(OWNER_ID_PATH, owner_id);
            channel_host::log(
                channel_host::LogLevel::Info,
                &format!("Owner restriction enabled: user {}", owner_id),
            );
        } else {
            let _ = channel_host::workspace_write(OWNER_ID_PATH, "");
        }

        // Persist dm_policy and allow_from for DM pairing
        let dm_policy = config.dm_policy.as_deref().unwrap_or("pairing");
        let _ = channel_host::workspace_write(DM_POLICY_PATH, dm_policy);

        let allow_from_json = serde_json::to_string(&config.allow_from.unwrap_or_default())
            .unwrap_or_else(|_| "[]".to_string());
        let _ = channel_host::workspace_write(ALLOW_FROM_PATH, &allow_from_json);

        Ok(ChannelConfig {
            display_name: "Discord".to_string(),
            http_endpoints: vec![HttpEndpointConfig {
                path: "/webhook/discord".to_string(),
                methods: vec!["POST".to_string()],
                require_secret: true,
            }],
            poll: None,
        })
    }

    fn on_http_request(req: IncomingHttpRequest) -> OutgoingHttpResponse {
        let body_str = match std::str::from_utf8(&req.body) {
            Ok(s) => s,
            Err(_) => {
                return json_response(400, serde_json::json!({"error": "Invalid UTF-8 body"}));
            }
        };

        let interaction: DiscordInteraction = match serde_json::from_str(body_str) {
            Ok(i) => i,
            Err(e) => {
                channel_host::log(
                    channel_host::LogLevel::Error,
                    &format!("Failed to parse Discord interaction: {}", e),
                );
                return json_response(400, serde_json::json!({"error": "Invalid interaction"}));
            }
        };

        match interaction.interaction_type {
            // Ping - Discord verification
            1 => {
                channel_host::log(channel_host::LogLevel::Info, "Responding to Discord ping");
                json_response(200, serde_json::json!({"type": 1}))
            }

            // Application Command (slash command)
            2 => {
                if handle_slash_command(&interaction) {
                    json_response(200, serde_json::json!({"type": 5}))
                } else {
                    // Permission denied — ephemeral response
                    json_response(
                        200,
                        serde_json::json!({
                            "type": 4,
                            "data": {
                                "content": "You are not authorized to use this bot.",
                                "flags": 64
                            }
                        }),
                    )
                }
            }

            // Message Component (buttons, selects)
            3 => {
                if let Some(ref message) = interaction.message {
                    handle_message_component(&interaction, message);
                }
                json_response(200, serde_json::json!({"type": 6}))
            }

            _ => {
                channel_host::log(
                    channel_host::LogLevel::Warn,
                    &format!(
                        "Unknown Discord interaction type: {}",
                        interaction.interaction_type
                    ),
                );
                json_response(200, serde_json::json!({"type": 6}))
            }
        }
    }

    fn on_poll() {}

    fn on_respond(response: AgentResponse) -> Result<(), String> {
        let metadata: DiscordMessageMetadata = serde_json::from_str(&response.metadata_json)
            .map_err(|e| format!("Failed to parse metadata: {}", e))?;

        // Use webhook endpoint for followup
        let url = format!(
            "https://discord.com/api/v10/webhooks/{}/{}",
            metadata.application_id, metadata.token
        );

        // Truncate content to 2000 characters to comply with Discord limits
        let content = truncate_message(&response.content);

        let mut payload = serde_json::json!({
            "content": content,
        });

        // Check for embeds in metadata
        if let Ok(meta_json) = serde_json::from_str::<serde_json::Value>(&response.metadata_json) {
            if let Some(embeds) = meta_json.get("embeds") {
                payload["embeds"] = embeds.clone();
            }
        }

        let payload_bytes =
            serde_json::to_vec(&payload).map_err(|e| format!("Failed to serialize: {}", e))?;

        let headers = serde_json::json!({
            "Content-Type": "application/json"
        });

        let result = channel_host::http_request(
            "POST",
            &url,
            &headers.to_string(),
            Some(&payload_bytes),
            None,
        );

        match result {
            Ok(http_response) => {
                if http_response.status >= 200 && http_response.status < 300 {
                    channel_host::log(channel_host::LogLevel::Debug, "Posted followup to Discord");
                    Ok(())
                } else {
                    let body_str = String::from_utf8_lossy(&http_response.body);
                    Err(format!(
                        "Discord API error: {} - {}",
                        http_response.status, body_str
                    ))
                }
            }
            Err(e) => Err(format!("HTTP request failed: {}", e)),
        }
    }

    fn on_status(_update: StatusUpdate) {}

    fn on_broadcast(_user_id: String, _response: AgentResponse) -> Result<(), String> {
        Err("broadcast not yet implemented for Discord channel".to_string())
    }

    fn on_shutdown() {
        channel_host::log(
            channel_host::LogLevel::Info,
            "Discord channel shutting down",
        );
    }
}

/// Returns true if the message was emitted, false if permission denied.
fn handle_slash_command(interaction: &DiscordInteraction) -> bool {
    let user = interaction
        .member
        .as_ref()
        .map(|m| &m.user)
        .or(interaction.user.as_ref());
    let user_id = user.map(|u| u.id.clone()).unwrap_or_default();
    let user_name = user
        .map(|u| {
            u.global_name
                .as_ref()
                .filter(|s| !s.is_empty())
                .unwrap_or(&u.username)
                .clone()
        })
        .unwrap_or_default();

    // DM if no guild member context (only direct user field set)
    let is_dm = interaction.member.is_none();

    // Permission check
    if !check_sender_permission(
        &user_id,
        Some(&user_name),
        is_dm,
        Some(&PairingReplyCtx {
            application_id: interaction.application_id.clone(),
            token: interaction.token.clone(),
        }),
    ) {
        return false;
    }

    let channel_id = interaction.channel_id.clone().unwrap_or_default();

    let command_name = interaction
        .data
        .as_ref()
        .map(|d| d.name.clone())
        .unwrap_or_default();
    let options = interaction.data.as_ref().and_then(|d| d.options.clone());

    let content = if let Some(opts) = options {
        let opt_str = opts
            .iter()
            .map(|o| format!("{}: {}", o.name, o.value))
            .collect::<Vec<_>>()
            .join(", ");
        format!("/{} {}", command_name, opt_str)
    } else {
        format!("/{}", command_name)
    };

    let metadata = DiscordMessageMetadata {
        channel_id: channel_id.clone(),
        interaction_id: interaction.id.clone(),
        token: interaction.token.clone(),
        application_id: interaction.application_id.clone(),
        thread_id: None,
    };

    let metadata_json = match serde_json::to_string(&metadata) {
        Ok(json) => json,
        Err(e) => {
            channel_host::log(
                channel_host::LogLevel::Error,
                &format!("Failed to serialize metadata: {}", e),
            );
            let url = format!(
                "https://discord.com/api/v10/webhooks/{}/{}",
                interaction.application_id, interaction.token
            );
            let payload = serde_json::json!({
                "content": "❌ Internal Error: Failed to process command metadata.",
                "flags": 64
            });
            let _ = channel_host::http_request(
                "POST",
                &url,
                &serde_json::json!({"Content-Type": "application/json"}).to_string(),
                Some(&serde_json::to_vec(&payload).unwrap_or_default()),
                None,
            );
            return true; // Error, but not a permission denial
        }
    };

    channel_host::emit_message(&EmittedMessage {
        user_id,
        user_name: Some(user_name),
        content,
        thread_id: None,
        metadata_json,
        attachments: vec![],
    });
    true
}

fn handle_message_component(interaction: &DiscordInteraction, message: &DiscordMessage) {
    let user = interaction
        .member
        .as_ref()
        .map(|m| &m.user)
        .or(interaction.user.as_ref());
    let user_id = user.map(|u| u.id.clone()).unwrap_or_default();
    let user_name = user
        .map(|u| {
            u.global_name
                .as_ref()
                .filter(|s| !s.is_empty())
                .unwrap_or(&u.username)
                .clone()
        })
        .unwrap_or_default();

    let is_dm = interaction.member.is_none();
    if !check_sender_permission(&user_id, Some(&user_name), is_dm, None) {
        return;
    }

    let channel_id = message.channel_id.clone();

    let metadata = DiscordMessageMetadata {
        channel_id: channel_id.clone(),
        interaction_id: interaction.id.clone(),
        token: interaction.token.clone(),
        application_id: interaction.application_id.clone(),
        thread_id: None,
    };

    let metadata_json = match serde_json::to_string(&metadata) {
        Ok(json) => json,
        Err(e) => {
            channel_host::log(
                channel_host::LogLevel::Error,
                &format!("Failed to serialize metadata: {}", e),
            );
            return; // Don't emit message if metadata can't be serialized
        }
    };

    channel_host::emit_message(&EmittedMessage {
        user_id,
        user_name: Some(user_name),
        content: format!("[Button clicked] {}", message.content),
        thread_id: None,
        metadata_json,
        attachments: vec![],
    });
}

// ============================================================================
// Permission & Pairing
// ============================================================================

/// Context needed to send a pairing reply via Discord webhook followup.
struct PairingReplyCtx {
    application_id: String,
    token: String,
}

/// Check if a sender is permitted to interact with the bot.
/// Returns true if allowed, false if denied (pairing reply sent if applicable).
fn check_sender_permission(
    user_id: &str,
    username: Option<&str>,
    is_dm: bool,
    reply_ctx: Option<&PairingReplyCtx>,
) -> bool {
    // 1. Owner check (highest priority, applies to all contexts)
    let owner_id = channel_host::workspace_read(OWNER_ID_PATH).filter(|s| !s.is_empty());
    if let Some(ref owner) = owner_id {
        if user_id != owner {
            channel_host::log(
                channel_host::LogLevel::Debug,
                &format!(
                    "Dropping interaction from non-owner user {} (owner: {})",
                    user_id, owner
                ),
            );
            return false;
        }
        return true;
    }

    // 2. DM policy (only for DMs when no owner_id)
    if !is_dm {
        return true; // Guild interactions bypass DM policy
    }

    let dm_policy =
        channel_host::workspace_read(DM_POLICY_PATH).unwrap_or_else(|| "pairing".to_string());

    if dm_policy == "open" {
        return true;
    }

    // 3. Build merged allow list: config allow_from + pairing store
    let mut allowed: Vec<String> = channel_host::workspace_read(ALLOW_FROM_PATH)
        .and_then(|s| serde_json::from_str(&s).ok())
        .unwrap_or_default();

    if let Ok(store_allowed) = channel_host::pairing_read_allow_from(CHANNEL_NAME) {
        allowed.extend(store_allowed);
    }

    // 4. Check sender against allow list
    let is_allowed = allowed.contains(&"*".to_string())
        || allowed.contains(&user_id.to_string())
        || username.is_some_and(|u| allowed.contains(&u.to_string()));

    if is_allowed {
        return true;
    }

    // 5. Not allowed — handle by policy
    if dm_policy == "pairing" {
        let meta = serde_json::json!({
            "user_id": user_id,
            "username": username,
        })
        .to_string();

        match channel_host::pairing_upsert_request(CHANNEL_NAME, user_id, &meta) {
            Ok(result) => {
                channel_host::log(
                    channel_host::LogLevel::Info,
                    &format!(
                        "Pairing request for user {}: code {}",
                        user_id, result.code
                    ),
                );
                if result.created {
                    if let Some(ctx) = reply_ctx {
                        let _ = send_pairing_reply(ctx, &result.code);
                    }
                }
            }
            Err(e) => {
                channel_host::log(
                    channel_host::LogLevel::Error,
                    &format!("Pairing upsert failed: {}", e),
                );
            }
        }
    }
    false
}

/// Send a pairing code as an ephemeral Discord followup message.
fn send_pairing_reply(ctx: &PairingReplyCtx, code: &str) -> Result<(), String> {
    let url = format!(
        "https://discord.com/api/v10/webhooks/{}/{}",
        ctx.application_id, ctx.token
    );

    let payload = serde_json::json!({
        "content": format!(
            "To pair with this bot, run: `ironclaw pairing approve discord {}`",
            code
        ),
        "flags": 64 // Ephemeral — only visible to the sender
    });

    let payload_bytes =
        serde_json::to_vec(&payload).map_err(|e| format!("Failed to serialize: {}", e))?;

    let headers = serde_json::json!({"Content-Type": "application/json"});

    let result = channel_host::http_request(
        "POST",
        &url,
        &headers.to_string(),
        Some(&payload_bytes),
        None,
    );

    match result {
        Ok(response) if response.status >= 200 && response.status < 300 => Ok(()),
        Ok(response) => {
            let body_str = String::from_utf8_lossy(&response.body);
            Err(format!(
                "Discord API error: {} - {}",
                response.status, body_str
            ))
        }
        Err(e) => Err(format!("HTTP request failed: {}", e)),
    }
}

fn json_response(status: u16, value: serde_json::Value) -> OutgoingHttpResponse {
    let body = serde_json::to_vec(&value).unwrap_or_default();
    let headers = serde_json::json!({"Content-Type": "application/json"});

    OutgoingHttpResponse {
        status,
        headers_json: headers.to_string(),
        body,
    }
}

export!(DiscordChannel);

fn truncate_message(content: &str) -> String {
    if content.len() <= 2000 {
        content.to_string()
    } else {
        let max_bytes = 1990;
        let cutoff = content
            .char_indices()
            .map(|(i, c)| i + c.len_utf8())
            .take_while(|&end| end <= max_bytes)
            .last()
            .unwrap_or(0);
        let mut truncated = content[..cutoff].to_string();
        truncated.push_str("\n... (truncated)");
        truncated
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_truncate_message() {
        let short = "Hello world";
        assert_eq!(truncate_message(short), short);

        let long = "a".repeat(2005);
        let truncated = truncate_message(&long);
        assert_eq!(truncated.len(), 2006); // 1990 + 16 chars suffix
        assert!(truncated.ends_with("\n... (truncated)"));

        // Test with multibyte characters (Euro sign is 3 bytes)
        // 1000 chars * 3 bytes = 3000 bytes
        let multi = "€".repeat(1000);
        let truncated_multi = truncate_message(&multi);

        // 1990 bytes limit. 1990 / 3 = 663 with remainder 1.
        // Should truncate at 663 chars (1989 bytes).
        // Suffix is 16 bytes. Total: 1989 + 16 = 2005 bytes.
        assert!(truncated_multi.len() <= 2006);
        assert!(truncated_multi.len() >= 2006 - 4); // Allow for max utf8 char width variance
        assert!(truncated_multi.ends_with("\n... (truncated)"));

        let content_part = &truncated_multi[..truncated_multi.len() - 16];
        assert!(content_part.chars().all(|c| c == '€'));
    }

    #[test]
    fn test_metadata_serialization() {
        let metadata = DiscordMessageMetadata {
            channel_id: "123".into(),
            interaction_id: "456".into(),
            token: "abc".into(),
            application_id: "789".into(),
            thread_id: None,
        };
        let json = serde_json::to_string(&metadata).unwrap();
        let parsed: DiscordMessageMetadata = serde_json::from_str(&json).unwrap();
        assert_eq!(parsed.channel_id, "123");
        assert_eq!(parsed.interaction_id, "456");
    }

    #[test]
    fn test_parse_slash_command_interaction() {
        // Verify that a slash command interaction deserializes correctly.
        let json = r#"{
            "type": 2,
            "id": "int_1",
            "application_id": "app_1",
            "channel_id": "ch_1",
            "member": {
                "user": {
                    "id": "user_1",
                    "username": "testuser",
                    "global_name": "Test User"
                }
            },
            "data": {
                "id": "cmd_1",
                "name": "ask",
                "options": [
                    {"name": "question", "value": "What is rust?"}
                ]
            },
            "token": "token_abc"
        }"#;

        let interaction: DiscordInteraction = serde_json::from_str(json).unwrap();
        assert_eq!(interaction.interaction_type, 2);
        assert!(interaction.data.is_some());
    }
}