use anyhow::{anyhow, bail, Context as _, Error, Result};
use serde::{Deserialize, Serialize};
use serde_json::de::Deserializer;
use serenity::{
    all::{
        CommandDataOptionValue, CommandInteraction, CommandOptionType, CommandType, Member, RoleId,
    },
    builder::{
        CreateButton, CreateCommand, CreateCommandOption, CreateInteractionResponse,
        CreateInteractionResponseMessage,
    },
    client::Context,
    model::Permissions,
};
use sqlx::SqlitePool;
use std::process::Stdio;
use tokio::{io::AsyncWriteExt, process::Command};

use crate::utils::EnumAsArray;

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct DiscocamlConfig {
    pub command: Vec<String>,
    pub role: RoleId,
}

#[derive(Debug, PartialEq, Serialize)]
pub struct DiscocamlRequest {
    pub expr: String,
    pub command: DiscocamlCommand,
}

#[derive(Debug, PartialEq, Serialize)]
pub enum DiscocamlCommand {
    Roundtrip,
}

/// A response outputted by the discocaml subprocess as a JSON string.
///
/// ```
/// # use lambo::{commands::discocaml::*, utils::EnumAsArray};
/// # use serde::Deserialize;
/// # use serde_json::Deserializer;
///
/// let example = r#"
/// [ "Expr"
/// , { "expr": "1 + 2"
///   }
/// ]
/// "#;
/// let expected = DiscocamlResponse::Expr(DiscocamlResponseExpr {
///     expr: "1 + 2".to_string(),
/// });
///
/// let mut de = Deserializer::from_str(&example);
/// let out = DiscocamlResponse::deserialize(EnumAsArray(&mut de)).unwrap();
/// de.end().unwrap();
///
/// assert_eq!(out, expected);
/// ```
#[derive(Debug, Deserialize, PartialEq)]
#[serde(deny_unknown_fields)]
pub enum DiscocamlResponse {
    Expr(DiscocamlResponseExpr),
    Error(String),
}

#[derive(Debug, Deserialize, PartialEq)]
#[serde(deny_unknown_fields)]
pub struct DiscocamlResponseExpr {
    pub expr: String,
}

pub fn command() -> CreateCommand {
    CreateCommand::new("discocaml")
        .kind(CommandType::ChatInput)
        .default_member_permissions(Permissions::empty())
        .dm_permission(true)
        .description("Sends this expression to the disco!")
        .add_option(
            CreateCommandOption::new(
                CommandOptionType::String,
                "expr",
                "The expression to operate on.",
            )
            .required(true),
        )
}

async fn check_permissions(config: &DiscocamlConfig, member: &Option<Box<Member>>) -> Result<()> {
    if let Some(member) = member {
        if !member.roles.contains(&config.role) {
            bail!("This command can only be used by <@&{}>.", config.role)
        }
        Ok(())
    } else {
        bail!("This command cannot be used in DMs.")
    }
}

async fn respond_with_error(ctx: &Context, command: &CommandInteraction, err: &Error) {
    let msg = CreateInteractionResponseMessage::new().content(format!(":no_entry_sign: {}", err));
    if let Err(err) = command
        .create_response(ctx, CreateInteractionResponse::Message(msg))
        .await
    {
        log::error!(
            "failed to respond to command that failed permissions check: {:?}",
            err
        )
    }
}

pub async fn run_discocaml(
    config: &DiscocamlConfig,
    req: &DiscocamlRequest,
) -> Result<DiscocamlResponseExpr> {
    let mut child = Command::new(&config.command[0])
        .args(&config.command)
        .stdin(Stdio::piped())
        .stdout(Stdio::piped())
        .kill_on_drop(true)
        .spawn()
        .context("failed to start discocaml")?;

    let mut stdin = child.stdin.take().unwrap();
    let req = serde_json::to_string(req).context("failed to serialize request to discocaml")?;
    stdin
        .write_all(req.as_bytes())
        .await
        .context("failed to write request to discocaml")?;
    stdin
        .shutdown()
        .await
        .context("failed to close pipe to discocaml")?;
    drop(stdin);
    drop(req);

    let output = child
        .wait_with_output()
        .await
        .context("failed to wait for discocaml to complete")?;
    if !output.status.success() {
        bail!("discocaml exited with non-zero status {:?}", output.status)
    }

    let mut de = Deserializer::from_slice(&output.stdout);
    let out = DiscocamlResponse::deserialize(EnumAsArray(&mut de))
        .context("failed to parse response from discocaml")?;
    de.end()
        .context("failed to parse response from discocaml")?;

    match out {
        DiscocamlResponse::Expr(expr) => Ok(expr),
        DiscocamlResponse::Error(err) => bail!("got an error from discocaml: {:?}", err),
    }
}

fn make_response_message(expr: &DiscocamlResponseExpr) -> CreateInteractionResponseMessage {
    // TODO: Real escaping
    CreateInteractionResponseMessage::new()
        .content(format!("```ocaml\n{}\n```", expr.expr))
        .button(CreateButton::new("step-cbv").label("Step (CBV)"))
        .button(CreateButton::new("step-cbn").label("Step (CBN)"))
        .button(CreateButton::new("run-cbv").label("Run (CBV)"))
        .button(CreateButton::new("run-cbn").label("Run (CBN)"))
        .button(CreateButton::new("draw-tree").label("Draw Tree"))
}

pub async fn handle_command(
    ctx: &Context,
    config: &DiscocamlConfig,
    _db: &SqlitePool,
    command: &CommandInteraction,
) -> Result<()> {
    // Check that the required role was present.
    if let Err(err) = check_permissions(config, &command.member).await {
        respond_with_error(ctx, command, &err).await;
        return Err(err.context("permissions check failed"));
    }

    // Parse the expression out.
    let mut expr = None;
    for option in &command.data.options {
        match (&option.name as &str, &option.value) {
            ("expr", CommandDataOptionValue::String(value)) => expr = Some(value),
            _ => {
                let err = anyhow!("unknown option {:?}", option);
                respond_with_error(ctx, command, &err).await;
                return Err(err);
            }
        }
    }
    let expr = if let Some(expr) = expr {
        expr
    } else {
        let err = anyhow!("missing option {:?}", "expr");
        respond_with_error(ctx, command, &err).await;
        return Err(err);
    };

    // Round-trip the expression through discocaml.
    let req = DiscocamlRequest {
        expr: expr.to_string(),
        command: DiscocamlCommand::Roundtrip,
    };
    let res = match run_discocaml(config, &req).await {
        Ok(res) => res,
        Err(err) => {
            respond_with_error(ctx, command, &err).await;
            return Err(err.context("failed to run discocaml"));
        }
    };

    // Respond with the expression and the buttons.
    command
        .create_response(
            &ctx,
            CreateInteractionResponse::Message(make_response_message(&res)),
        )
        .await
        .context("failed to respond")
}