// - In the default output mode, it is paramount that the only thing written to
//   stdout is the final message (if any).
// - In --json mode, stdout must be valid JSONL, one event per line.
// For both modes, any other output must be written to stderr.
#![deny(clippy::print_stdout)]

mod cli;
mod event_processor;
mod event_processor_with_human_output;
pub mod event_processor_with_jsonl_output;
pub mod exec_events;

pub use cli::Cli;
pub use cli::Command;
pub use cli::ReviewArgs;
use codex_arg0::Arg0DispatchPaths;
use codex_cloud_requirements::cloud_requirements_loader;
use codex_core::AuthManager;
use codex_core::LMSTUDIO_OSS_PROVIDER_ID;
use codex_core::NewThread;
use codex_core::OLLAMA_OSS_PROVIDER_ID;
use codex_core::ThreadManager;
use codex_core::auth::enforce_login_restrictions;
use codex_core::check_execpolicy_for_warnings;
use codex_core::config::Config;
use codex_core::config::ConfigBuilder;
use codex_core::config::ConfigOverrides;
use codex_core::config::find_codex_home;
use codex_core::config::load_config_as_toml_with_cli_overrides;
use codex_core::config::resolve_oss_provider;
use codex_core::config_loader::ConfigLoadError;
use codex_core::config_loader::format_config_error_with_source;
use codex_core::format_exec_policy_error_with_source;
use codex_core::git_info::get_git_repo_root;
use codex_core::models_manager::collaboration_mode_presets::CollaborationModesConfig;
use codex_core::models_manager::manager::RefreshStrategy;
use codex_protocol::approvals::ElicitationAction;
use codex_protocol::config_types::SandboxMode;
use codex_protocol::protocol::AskForApproval;
use codex_protocol::protocol::Event;
use codex_protocol::protocol::EventMsg;
use codex_protocol::protocol::Op;
use codex_protocol::protocol::ReviewRequest;
use codex_protocol::protocol::ReviewTarget;
use codex_protocol::protocol::SessionSource;
use codex_protocol::protocol::SubAgentSource;
use codex_protocol::user_input::UserInput;
use codex_utils_absolute_path::AbsolutePathBuf;
use codex_utils_oss::ensure_oss_provider_ready;
use codex_utils_oss::get_default_model_for_oss_provider;
use event_processor_with_human_output::EventProcessorWithHumanOutput;
use event_processor_with_jsonl_output::EventProcessorWithJsonOutput;
use serde_json::Value;
use std::collections::HashSet;
use std::io::IsTerminal;
use std::io::Read;
use std::path::PathBuf;
use std::sync::Arc;
use supports_color::Stream;
use tokio::sync::Mutex;
use tracing::debug;
use tracing::error;
use tracing::info;
use tracing::warn;
use tracing_subscriber::EnvFilter;
use tracing_subscriber::prelude::*;
use uuid::Uuid;

use crate::cli::Command as ExecCommand;
use crate::event_processor::CodexStatus;
use crate::event_processor::EventProcessor;
use codex_core::default_client::set_default_client_residency_requirement;
use codex_core::default_client::set_default_originator;
use codex_core::find_thread_path_by_id_str;
use codex_core::find_thread_path_by_name_str;

enum InitialOperation {
    UserTurn {
        items: Vec<UserInput>,
        output_schema: Option<Value>,
    },
    Review {
        review_request: ReviewRequest,
    },
}

#[derive(Clone)]
struct ThreadEventEnvelope {
    thread_id: codex_protocol::ThreadId,
    thread: Arc<codex_core::CodexThread>,
    event: Event,
    suppress_output: bool,
}

pub async fn run_main(cli: Cli, arg0_paths: Arg0DispatchPaths) -> anyhow::Result<()> {
    if let Err(err) = set_default_originator("codex_exec".to_string()) {
        tracing::warn!(?err, "Failed to set codex exec originator override {err:?}");
    }

    let Cli {
        command,
        images,
        model: model_cli_arg,
        oss,
        oss_provider,
        config_profile,
        full_auto,
        dangerously_bypass_approvals_and_sandbox,
        cwd,
        skip_git_repo_check,
        add_dir,
        ephemeral,
        color,
        last_message_file,
        json: json_mode,
        sandbox_mode: sandbox_mode_cli_arg,
        prompt,
        output_schema: output_schema_path,
        config_overrides,
        progress_cursor,
    } = cli;

    let (_stdout_with_ansi, stderr_with_ansi) = match color {
        cli::Color::Always => (true, true),
        cli::Color::Never => (false, false),
        cli::Color::Auto => (
            supports_color::on_cached(Stream::Stdout).is_some(),
            supports_color::on_cached(Stream::Stderr).is_some(),
        ),
    };
    let cursor_ansi = if progress_cursor {
        true
    } else {
        match color {
            cli::Color::Never => false,
            cli::Color::Always => true,
            cli::Color::Auto => {
                if stderr_with_ansi || std::io::stderr().is_terminal() {
                    true
                } else {
                    match std::env::var("TERM") {
                        Ok(term) => !term.is_empty() && term != "dumb",
                        Err(_) => false,
                    }
                }
            }
        }
    };

    // Build fmt layer (existing logging) to compose with OTEL layer.
    let default_level = "error";

    // Build env_filter separately and attach via with_filter.
    let env_filter = EnvFilter::try_from_default_env()
        .or_else(|_| EnvFilter::try_new(default_level))
        .unwrap_or_else(|_| EnvFilter::new(default_level));

    let fmt_layer = tracing_subscriber::fmt::layer()
        .with_ansi(stderr_with_ansi)
        .with_writer(std::io::stderr)
        .with_filter(env_filter);

    let sandbox_mode = if full_auto {
        Some(SandboxMode::WorkspaceWrite)
    } else if dangerously_bypass_approvals_and_sandbox {
        Some(SandboxMode::DangerFullAccess)
    } else {
        sandbox_mode_cli_arg.map(Into::<SandboxMode>::into)
    };

    // Parse `-c` overrides from the CLI.
    let cli_kv_overrides = match config_overrides.parse_overrides() {
        Ok(v) => v,
        #[allow(clippy::print_stderr)]
        Err(e) => {
            eprintln!("Error parsing -c overrides: {e}");
            std::process::exit(1);
        }
    };

    let resolved_cwd = cwd.clone();
    let config_cwd = match resolved_cwd.as_deref() {
        Some(path) => AbsolutePathBuf::from_absolute_path(path.canonicalize()?)?,
        None => AbsolutePathBuf::current_dir()?,
    };

    // we load config.toml here to determine project state.
    #[allow(clippy::print_stderr)]
    let codex_home = match find_codex_home() {
        Ok(codex_home) => codex_home,
        Err(err) => {
            eprintln!("Error finding codex home: {err}");
            std::process::exit(1);
        }
    };

    #[allow(clippy::print_stderr)]
    let config_toml = match load_config_as_toml_with_cli_overrides(
        &codex_home,
        &config_cwd,
        cli_kv_overrides.clone(),
    )
    .await
    {
        Ok(config_toml) => config_toml,
        Err(err) => {
            let config_error = err
                .get_ref()
                .and_then(|err| err.downcast_ref::<ConfigLoadError>())
                .map(ConfigLoadError::config_error);
            if let Some(config_error) = config_error {
                eprintln!(
                    "Error loading config.toml:\n{}",
                    format_config_error_with_source(config_error)
                );
            } else {
                eprintln!("Error loading config.toml: {err}");
            }
            std::process::exit(1);
        }
    };

    let cloud_auth_manager = AuthManager::shared(
        codex_home.clone(),
        false,
        config_toml.cli_auth_credentials_store.unwrap_or_default(),
    );
    let chatgpt_base_url = config_toml
        .chatgpt_base_url
        .clone()
        .unwrap_or_else(|| "https://chatgpt.com/backend-api/".to_string());
    // TODO(gt): Make cloud requirements failures blocking once we can fail-closed.
    let cloud_requirements =
        cloud_requirements_loader(cloud_auth_manager, chatgpt_base_url, codex_home.clone());

    let model_provider = if oss {
        let resolved = resolve_oss_provider(
            oss_provider.as_deref(),
            &config_toml,
            config_profile.clone(),
        );

        if let Some(provider) = resolved {
            Some(provider)
        } else {
            return Err(anyhow::anyhow!(
                "No default OSS provider configured. Use --local-provider=provider or set oss_provider to one of: {LMSTUDIO_OSS_PROVIDER_ID}, {OLLAMA_OSS_PROVIDER_ID} in config.toml"
            ));
        }
    } else {
        None // No OSS mode enabled
    };

    // When using `--oss`, let the bootstrapper pick the model based on selected provider
    let model = if let Some(model) = model_cli_arg {
        Some(model)
    } else if oss {
        model_provider
            .as_ref()
            .and_then(|provider_id| get_default_model_for_oss_provider(provider_id))
            .map(std::borrow::ToOwned::to_owned)
    } else {
        None // No model specified, will use the default.
    };

    // Load configuration and determine approval policy
    let overrides = ConfigOverrides {
        model,
        review_model: None,
        config_profile,
        // Default to never ask for approvals in headless mode. Feature flags can override.
        approval_policy: Some(AskForApproval::Never),
        sandbox_mode,
        cwd: resolved_cwd,
        model_provider: model_provider.clone(),
        codex_linux_sandbox_exe: arg0_paths.codex_linux_sandbox_exe.clone(),
        main_execve_wrapper_exe: arg0_paths.main_execve_wrapper_exe.clone(),
        js_repl_node_path: None,
        js_repl_node_module_dirs: None,
        zsh_path: None,
        base_instructions: None,
        developer_instructions: None,
        personality: None,
        compact_prompt: None,
        include_apply_patch_tool: None,
        show_raw_agent_reasoning: oss.then_some(true),
        tools_web_search_request: None,
        ephemeral: ephemeral.then_some(true),
        additional_writable_roots: add_dir,
    };

    let config = ConfigBuilder::default()
        .cli_overrides(cli_kv_overrides)
        .harness_overrides(overrides)
        .cloud_requirements(cloud_requirements)
        .build()
        .await?;

    #[allow(clippy::print_stderr)]
    match check_execpolicy_for_warnings(&config.config_layer_stack).await {
        Ok(None) => {}
        Ok(Some(err)) | Err(err) => {
            eprintln!(
                "Error loading rules:\n{}",
                format_exec_policy_error_with_source(&err)
            );
            std::process::exit(1);
        }
    }

    set_default_client_residency_requirement(config.enforce_residency.value());

    if let Err(err) = enforce_login_restrictions(&config) {
        eprintln!("{err}");
        std::process::exit(1);
    }

    let otel = match std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
        codex_core::otel_init::build_provider(&config, env!("CARGO_PKG_VERSION"), None, false)
    })) {
        Ok(Ok(otel)) => otel,
        Ok(Err(e)) => {
            eprintln!("Could not create otel exporter: {e}");
            None
        }
        Err(_) => {
            eprintln!("Could not create otel exporter: panicked during initialization");
            None
        }
    };

    let otel_logger_layer = otel.as_ref().and_then(|o| o.logger_layer());

    let otel_tracing_layer = otel.as_ref().and_then(|o| o.tracing_layer());

    let _ = tracing_subscriber::registry()
        .with(fmt_layer)
        .with(otel_tracing_layer)
        .with(otel_logger_layer)
        .try_init();

    let mut event_processor: Box<dyn EventProcessor> = match json_mode {
        true => Box::new(EventProcessorWithJsonOutput::new(last_message_file.clone())),
        _ => Box::new(EventProcessorWithHumanOutput::create_with_ansi(
            stderr_with_ansi,
            cursor_ansi,
            &config,
            last_message_file.clone(),
        )),
    };
    let required_mcp_servers: HashSet<String> = config
        .mcp_servers
        .get()
        .iter()
        .filter(|(_, server)| server.enabled && server.required)
        .map(|(name, _)| name.clone())
        .collect();

    if oss {
        // We're in the oss section, so provider_id should be Some
        // Let's handle None case gracefully though just in case
        let provider_id = match model_provider.as_ref() {
            Some(id) => id,
            None => {
                error!("OSS provider unexpectedly not set when oss flag is used");
                return Err(anyhow::anyhow!(
                    "OSS provider not set but oss flag was used"
                ));
            }
        };
        ensure_oss_provider_ready(provider_id, &config)
            .await
            .map_err(|e| anyhow::anyhow!("OSS setup failed: {e}"))?;
    }

    let default_cwd = config.cwd.to_path_buf();
    let default_approval_policy = config.permissions.approval_policy.value();
    let default_sandbox_policy = config.permissions.sandbox_policy.get();
    let default_effort = config.model_reasoning_effort;
    let default_summary = config.model_reasoning_summary;

    // When --yolo (dangerously_bypass_approvals_and_sandbox) is set, also skip the git repo check
    // since the user is explicitly running in an externally sandboxed environment.
    if !skip_git_repo_check
        && !dangerously_bypass_approvals_and_sandbox
        && get_git_repo_root(&default_cwd).is_none()
    {
        eprintln!("Not inside a trusted directory and --skip-git-repo-check was not specified.");
        std::process::exit(1);
    }

    let auth_manager = AuthManager::shared(
        config.codex_home.clone(),
        true,
        config.cli_auth_credentials_store_mode,
    );
    let thread_manager = Arc::new(ThreadManager::new(
        config.codex_home.clone(),
        auth_manager.clone(),
        SessionSource::Exec,
        config.model_catalog.clone(),
        CollaborationModesConfig {
            default_mode_request_user_input: config
                .features
                .enabled(codex_core::features::Feature::DefaultModeRequestUserInput),
        },
    ));
    let default_model = thread_manager
        .get_models_manager()
        .get_default_model(&config.model, RefreshStrategy::OnlineIfUncached)
        .await;

    // Handle resume subcommand by resolving a rollout path and using explicit resume API.
    let NewThread {
        thread_id: primary_thread_id,
        thread,
        session_configured,
    } = if let Some(ExecCommand::Resume(args)) = command.as_ref() {
        let resume_path = resolve_resume_path(&config, args).await?;

        if let Some(path) = resume_path {
            thread_manager
                .resume_thread_from_rollout(config.clone(), path, auth_manager.clone())
                .await?
        } else {
            thread_manager.start_thread(config.clone()).await?
        }
    } else {
        thread_manager.start_thread(config.clone()).await?
    };
    let (initial_operation, prompt_summary) = match (command, prompt, images) {
        (Some(ExecCommand::Review(review_cli)), _, _) => {
            let review_request = build_review_request(review_cli)?;
            let summary = codex_core::review_prompts::user_facing_hint(&review_request.target);
            (InitialOperation::Review { review_request }, summary)
        }
        (Some(ExecCommand::Resume(args)), root_prompt, imgs) => {
            let prompt_arg = args
                .prompt
                .clone()
                .or_else(|| {
                    if args.last {
                        args.session_id.clone()
                    } else {
                        None
                    }
                })
                .or(root_prompt);
            let prompt_text = resolve_prompt(prompt_arg);
            let mut items: Vec<UserInput> = imgs
                .into_iter()
                .chain(args.images.into_iter())
                .map(|path| UserInput::LocalImage { path })
                .collect();
            items.push(UserInput::Text {
                text: prompt_text.clone(),
                // CLI input doesn't track UI element ranges, so none are available here.
                text_elements: Vec::new(),
            });
            let output_schema = load_output_schema(output_schema_path.clone());
            (
                InitialOperation::UserTurn {
                    items,
                    output_schema,
                },
                prompt_text,
            )
        }
        (None, root_prompt, imgs) => {
            let prompt_text = resolve_prompt(root_prompt);
            let mut items: Vec<UserInput> = imgs
                .into_iter()
                .map(|path| UserInput::LocalImage { path })
                .collect();
            items.push(UserInput::Text {
                text: prompt_text.clone(),
                // CLI input doesn't track UI element ranges, so none are available here.
                text_elements: Vec::new(),
            });
            let output_schema = load_output_schema(output_schema_path);
            (
                InitialOperation::UserTurn {
                    items,
                    output_schema,
                },
                prompt_text,
            )
        }
    };

    // Print the effective configuration and initial request so users can see what Codex
    // is using.
    event_processor.print_config_summary(&config, &prompt_summary, &session_configured);

    info!("Codex initialized with event: {session_configured:?}");

    let (tx, mut rx) = tokio::sync::mpsc::unbounded_channel::<ThreadEventEnvelope>();
    let attached_threads = Arc::new(Mutex::new(HashSet::from([primary_thread_id])));
    spawn_thread_listener(primary_thread_id, thread.clone(), tx.clone(), false);

    {
        let thread = thread.clone();
        tokio::spawn(async move {
            if tokio::signal::ctrl_c().await.is_ok() {
                tracing::debug!("Keyboard interrupt");
                // Immediately notify Codex to abort any in-flight task.
                thread.submit(Op::Interrupt).await.ok();
            }
        });
    }

    {
        let thread_manager = Arc::clone(&thread_manager);
        let attached_threads = Arc::clone(&attached_threads);
        let tx = tx.clone();
        let mut thread_created_rx = thread_manager.subscribe_thread_created();
        tokio::spawn(async move {
            loop {
                match thread_created_rx.recv().await {
                    Ok(thread_id) => {
                        if attached_threads.lock().await.contains(&thread_id) {
                            continue;
                        }
                        match thread_manager.get_thread(thread_id).await {
                            Ok(thread) => {
                                attached_threads.lock().await.insert(thread_id);
                                let suppress_output =
                                    is_agent_job_subagent(&thread.config_snapshot().await);
                                spawn_thread_listener(
                                    thread_id,
                                    thread,
                                    tx.clone(),
                                    suppress_output,
                                );
                            }
                            Err(err) => {
                                warn!("failed to attach listener for thread {thread_id}: {err}")
                            }
                        }
                    }
                    Err(tokio::sync::broadcast::error::RecvError::Lagged(_)) => {
                        warn!("thread_created receiver lagged; skipping resync");
                    }
                    Err(tokio::sync::broadcast::error::RecvError::Closed) => break,
                }
            }
        });
    }

    match initial_operation {
        InitialOperation::UserTurn {
            items,
            output_schema,
        } => {
            let task_id = thread
                .submit(Op::UserTurn {
                    items,
                    cwd: default_cwd,
                    approval_policy: default_approval_policy,
                    sandbox_policy: default_sandbox_policy.clone(),
                    model: default_model,
                    effort: default_effort,
                    summary: default_summary,
                    final_output_json_schema: output_schema,
                    collaboration_mode: None,
                    personality: None,
                })
                .await?;
            info!("Sent prompt with event ID: {task_id}");
            task_id
        }
        InitialOperation::Review { review_request } => {
            let task_id = thread.submit(Op::Review { review_request }).await?;
            info!("Sent review request with event ID: {task_id}");
            task_id
        }
    };

    // Run the loop until the task is complete.
    // Track whether a fatal error was reported by the server so we can
    // exit with a non-zero status for automation-friendly signaling.
    let mut error_seen = false;
    let mut shutdown_requested = false;
    while let Some(envelope) = rx.recv().await {
        let ThreadEventEnvelope {
            thread_id,
            thread,
            event,
            suppress_output,
        } = envelope;
        if suppress_output && should_suppress_agent_job_event(&event.msg) {
            continue;
        }
        if matches!(event.msg, EventMsg::Error(_)) {
            error_seen = true;
        }
        if shutdown_requested
            && !matches!(&event.msg, EventMsg::ShutdownComplete | EventMsg::Error(_))
        {
            continue;
        }
        if let EventMsg::ElicitationRequest(ev) = &event.msg {
            // Automatically cancel elicitation requests in exec mode.
            thread
                .submit(Op::ResolveElicitation {
                    server_name: ev.server_name.clone(),
                    request_id: ev.id.clone(),
                    decision: ElicitationAction::Cancel,
                })
                .await?;
        }
        if let EventMsg::McpStartupUpdate(update) = &event.msg
            && required_mcp_servers.contains(&update.server)
            && let codex_protocol::protocol::McpStartupStatus::Failed { error } = &update.status
        {
            error_seen = true;
            eprintln!(
                "Required MCP server '{}' failed to initialize: {error}",
                update.server
            );
            if !shutdown_requested {
                thread.submit(Op::Shutdown).await?;
                shutdown_requested = true;
            }
        }
        if thread_id != primary_thread_id && matches!(&event.msg, EventMsg::TurnComplete(_)) {
            continue;
        }
        let shutdown = event_processor.process_event(event);
        if thread_id != primary_thread_id && matches!(shutdown, CodexStatus::InitiateShutdown) {
            continue;
        }
        match shutdown {
            CodexStatus::Running => continue,
            CodexStatus::InitiateShutdown => {
                if !shutdown_requested {
                    thread.submit(Op::Shutdown).await?;
                    shutdown_requested = true;
                }
            }
            CodexStatus::Shutdown if thread_id == primary_thread_id => break,
            CodexStatus::Shutdown => continue,
        }
    }
    event_processor.print_final_output();
    if error_seen {
        std::process::exit(1);
    }

    Ok(())
}

fn spawn_thread_listener(
    thread_id: codex_protocol::ThreadId,
    thread: Arc<codex_core::CodexThread>,
    tx: tokio::sync::mpsc::UnboundedSender<ThreadEventEnvelope>,
    suppress_output: bool,
) {
    tokio::spawn(async move {
        loop {
            match thread.next_event().await {
                Ok(event) => {
                    debug!("Received event: {event:?}");

                    let is_shutdown_complete = matches!(event.msg, EventMsg::ShutdownComplete);
                    if let Err(err) = tx.send(ThreadEventEnvelope {
                        thread_id,
                        thread: Arc::clone(&thread),
                        event,
                        suppress_output,
                    }) {
                        error!("Error sending event: {err:?}");
                        break;
                    }
                    if is_shutdown_complete {
                        info!(
                            "Received shutdown event for thread {thread_id}, exiting event loop."
                        );
                        break;
                    }
                }
                Err(err) => {
                    error!("Error receiving event: {err:?}");
                    break;
                }
            }
        }
    });
}

fn is_agent_job_subagent(config: &codex_core::ThreadConfigSnapshot) -> bool {
    match &config.session_source {
        SessionSource::SubAgent(SubAgentSource::Other(source)) => source.starts_with("agent_job:"),
        _ => false,
    }
}

fn should_suppress_agent_job_event(msg: &EventMsg) -> bool {
    !matches!(
        msg,
        EventMsg::ExecApprovalRequest(_)
            | EventMsg::ApplyPatchApprovalRequest(_)
            | EventMsg::RequestUserInput(_)
            | EventMsg::DynamicToolCallRequest(_)
            | EventMsg::DynamicToolCallResponse(_)
            | EventMsg::ElicitationRequest(_)
            | EventMsg::Error(_)
            | EventMsg::Warning(_)
            | EventMsg::DeprecationNotice(_)
            | EventMsg::StreamError(_)
            | EventMsg::ShutdownComplete
    )
}

async fn resolve_resume_path(
    config: &Config,
    args: &crate::cli::ResumeArgs,
) -> anyhow::Result<Option<PathBuf>> {
    if args.last {
        let default_provider_filter = vec![config.model_provider_id.clone()];
        let filter_cwd = if args.all {
            None
        } else {
            Some(config.cwd.as_path())
        };
        match codex_core::RolloutRecorder::find_latest_thread_path(
            config,
            1,
            None,
            codex_core::ThreadSortKey::UpdatedAt,
            &[],
            Some(default_provider_filter.as_slice()),
            &config.model_provider_id,
            filter_cwd,
        )
        .await
        {
            Ok(path) => Ok(path),
            Err(e) => {
                error!("Error listing threads: {e}");
                Ok(None)
            }
        }
    } else if let Some(id_str) = args.session_id.as_deref() {
        if Uuid::parse_str(id_str).is_ok() {
            let path = find_thread_path_by_id_str(&config.codex_home, id_str).await?;
            Ok(path)
        } else {
            let path = find_thread_path_by_name_str(&config.codex_home, id_str).await?;
            Ok(path)
        }
    } else {
        Ok(None)
    }
}

fn load_output_schema(path: Option<PathBuf>) -> Option<Value> {
    let path = path?;

    let schema_str = match std::fs::read_to_string(&path) {
        Ok(contents) => contents,
        Err(err) => {
            eprintln!(
                "Failed to read output schema file {}: {err}",
                path.display()
            );
            std::process::exit(1);
        }
    };

    match serde_json::from_str::<Value>(&schema_str) {
        Ok(value) => Some(value),
        Err(err) => {
            eprintln!(
                "Output schema file {} is not valid JSON: {err}",
                path.display()
            );
            std::process::exit(1);
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
enum PromptDecodeError {
    InvalidUtf8 { valid_up_to: usize },
    InvalidUtf16 { encoding: &'static str },
    UnsupportedBom { encoding: &'static str },
}

impl std::fmt::Display for PromptDecodeError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            PromptDecodeError::InvalidUtf8 { valid_up_to } => write!(
                f,
                "input is not valid UTF-8 (invalid byte at offset {valid_up_to}). Convert it to UTF-8 and retry (e.g., `iconv -f <ENC> -t UTF-8 prompt.txt`)."
            ),
            PromptDecodeError::InvalidUtf16 { encoding } => write!(
                f,
                "input looked like {encoding} but could not be decoded. Convert it to UTF-8 and retry."
            ),
            PromptDecodeError::UnsupportedBom { encoding } => write!(
                f,
                "input appears to be {encoding}. Convert it to UTF-8 and retry."
            ),
        }
    }
}

fn decode_prompt_bytes(input: &[u8]) -> Result<String, PromptDecodeError> {
    let input = input.strip_prefix(&[0xEF, 0xBB, 0xBF]).unwrap_or(input);

    if input.starts_with(&[0xFF, 0xFE, 0x00, 0x00]) {
        return Err(PromptDecodeError::UnsupportedBom {
            encoding: "UTF-32LE",
        });
    }

    if input.starts_with(&[0x00, 0x00, 0xFE, 0xFF]) {
        return Err(PromptDecodeError::UnsupportedBom {
            encoding: "UTF-32BE",
        });
    }

    if let Some(rest) = input.strip_prefix(&[0xFF, 0xFE]) {
        return decode_utf16(rest, "UTF-16LE", u16::from_le_bytes);
    }

    if let Some(rest) = input.strip_prefix(&[0xFE, 0xFF]) {
        return decode_utf16(rest, "UTF-16BE", u16::from_be_bytes);
    }

    std::str::from_utf8(input)
        .map(str::to_string)
        .map_err(|e| PromptDecodeError::InvalidUtf8 {
            valid_up_to: e.valid_up_to(),
        })
}

fn decode_utf16(
    input: &[u8],
    encoding: &'static str,
    decode_unit: fn([u8; 2]) -> u16,
) -> Result<String, PromptDecodeError> {
    if !input.len().is_multiple_of(2) {
        return Err(PromptDecodeError::InvalidUtf16 { encoding });
    }

    let units: Vec<u16> = input
        .chunks_exact(2)
        .map(|chunk| decode_unit([chunk[0], chunk[1]]))
        .collect();

    String::from_utf16(&units).map_err(|_| PromptDecodeError::InvalidUtf16 { encoding })
}

fn resolve_prompt(prompt_arg: Option<String>) -> String {
    match prompt_arg {
        Some(p) if p != "-" => p,
        maybe_dash => {
            let force_stdin = matches!(maybe_dash.as_deref(), Some("-"));

            if std::io::stdin().is_terminal() && !force_stdin {
                eprintln!(
                    "No prompt provided. Either specify one as an argument or pipe the prompt into stdin."
                );
                std::process::exit(1);
            }

            if !force_stdin {
                eprintln!("Reading prompt from stdin...");
            }

            let mut bytes = Vec::new();
            if let Err(e) = std::io::stdin().read_to_end(&mut bytes) {
                eprintln!("Failed to read prompt from stdin: {e}");
                std::process::exit(1);
            }

            let buffer = match decode_prompt_bytes(&bytes) {
                Ok(s) => s,
                Err(e) => {
                    eprintln!("Failed to read prompt from stdin: {e}");
                    std::process::exit(1);
                }
            };

            if buffer.trim().is_empty() {
                eprintln!("No prompt provided via stdin.");
                std::process::exit(1);
            }
            buffer
        }
    }
}

fn build_review_request(args: ReviewArgs) -> anyhow::Result<ReviewRequest> {
    let target = if args.uncommitted {
        ReviewTarget::UncommittedChanges
    } else if let Some(branch) = args.base {
        ReviewTarget::BaseBranch { branch }
    } else if let Some(sha) = args.commit {
        ReviewTarget::Commit {
            sha,
            title: args.commit_title,
        }
    } else if let Some(prompt_arg) = args.prompt {
        let prompt = resolve_prompt(Some(prompt_arg)).trim().to_string();
        if prompt.is_empty() {
            anyhow::bail!("Review prompt cannot be empty");
        }
        ReviewTarget::Custom {
            instructions: prompt,
        }
    } else {
        anyhow::bail!(
            "Specify --uncommitted, --base, --commit, or provide custom review instructions"
        );
    };

    Ok(ReviewRequest {
        target,
        user_facing_hint: None,
    })
}

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

    #[test]
    fn builds_uncommitted_review_request() {
        let request = build_review_request(ReviewArgs {
            uncommitted: true,
            base: None,
            commit: None,
            commit_title: None,
            prompt: None,
        })
        .expect("builds uncommitted review request");

        let expected = ReviewRequest {
            target: ReviewTarget::UncommittedChanges,
            user_facing_hint: None,
        };

        assert_eq!(request, expected);
    }

    #[test]
    fn builds_commit_review_request_with_title() {
        let request = build_review_request(ReviewArgs {
            uncommitted: false,
            base: None,
            commit: Some("123456789".to_string()),
            commit_title: Some("Add review command".to_string()),
            prompt: None,
        })
        .expect("builds commit review request");

        let expected = ReviewRequest {
            target: ReviewTarget::Commit {
                sha: "123456789".to_string(),
                title: Some("Add review command".to_string()),
            },
            user_facing_hint: None,
        };

        assert_eq!(request, expected);
    }

    #[test]
    fn builds_custom_review_request_trims_prompt() {
        let request = build_review_request(ReviewArgs {
            uncommitted: false,
            base: None,
            commit: None,
            commit_title: None,
            prompt: Some("  custom review instructions  ".to_string()),
        })
        .expect("builds custom review request");

        let expected = ReviewRequest {
            target: ReviewTarget::Custom {
                instructions: "custom review instructions".to_string(),
            },
            user_facing_hint: None,
        };

        assert_eq!(request, expected);
    }

    #[test]
    fn decode_prompt_bytes_strips_utf8_bom() {
        let input = [0xEF, 0xBB, 0xBF, b'h', b'i', b'\n'];

        let out = decode_prompt_bytes(&input).expect("decode utf-8 with BOM");

        assert_eq!(out, "hi\n");
    }

    #[test]
    fn decode_prompt_bytes_decodes_utf16le_bom() {
        // UTF-16LE BOM + "hi\n"
        let input = [0xFF, 0xFE, b'h', 0x00, b'i', 0x00, b'\n', 0x00];

        let out = decode_prompt_bytes(&input).expect("decode utf-16le with BOM");

        assert_eq!(out, "hi\n");
    }

    #[test]
    fn decode_prompt_bytes_decodes_utf16be_bom() {
        // UTF-16BE BOM + "hi\n"
        let input = [0xFE, 0xFF, 0x00, b'h', 0x00, b'i', 0x00, b'\n'];

        let out = decode_prompt_bytes(&input).expect("decode utf-16be with BOM");

        assert_eq!(out, "hi\n");
    }

    #[test]
    fn decode_prompt_bytes_rejects_utf32le_bom() {
        // UTF-32LE BOM + "hi\n"
        let input = [
            0xFF, 0xFE, 0x00, 0x00, b'h', 0x00, 0x00, 0x00, b'i', 0x00, 0x00, 0x00, b'\n', 0x00,
            0x00, 0x00,
        ];

        let err = decode_prompt_bytes(&input).expect_err("utf-32le should be rejected");

        assert_eq!(
            err,
            PromptDecodeError::UnsupportedBom {
                encoding: "UTF-32LE"
            }
        );
    }

    #[test]
    fn decode_prompt_bytes_rejects_utf32be_bom() {
        // UTF-32BE BOM + "hi\n"
        let input = [
            0x00, 0x00, 0xFE, 0xFF, 0x00, 0x00, 0x00, b'h', 0x00, 0x00, 0x00, b'i', 0x00, 0x00,
            0x00, b'\n',
        ];

        let err = decode_prompt_bytes(&input).expect_err("utf-32be should be rejected");

        assert_eq!(
            err,
            PromptDecodeError::UnsupportedBom {
                encoding: "UTF-32BE"
            }
        );
    }

    #[test]
    fn decode_prompt_bytes_rejects_invalid_utf8() {
        // Invalid UTF-8 sequence: 0xC3 0x28
        let input = [0xC3, 0x28];

        let err = decode_prompt_bytes(&input).expect_err("invalid utf-8 should fail");

        assert_eq!(err, PromptDecodeError::InvalidUtf8 { valid_up_to: 0 });
    }
}