//! Agent integrations: hook extensions that let agents report their own
//! state (herdr's integration model), so detection does not rely on screen
//! scraping for the agents that support it.

use std::io::Read;
use std::path::{Path, PathBuf};

use detect_core::Agent;
use serde_json::{json, Value};

/// The embedded pi extension, adapted from herdr's `herdr-agent-state.ts`
/// (Apache-2.0, Copyright herdr contributors).
/// It carries a placeholder for its version, which install fills in.
const PI_EXTENSION: &str = include_str!("../assets/pi/pi-agent-state.ts");
const VERSION_PLACEHOLDER: &str = "__DINGGER_EXTENSION_VERSION__";

/// The extension's version: a fingerprint of its text (FNV-1a, so it does
/// not change with the Rust release). A running pi reports the version it
/// loaded; one that differs from this runs an old extension.
pub fn pi_extension_version() -> String {
    let hash = PI_EXTENSION.bytes().fold(0xcbf2_9ce4_8422_2325_u64, |hash, byte| {
        (hash ^ u64::from(byte)).wrapping_mul(0x0100_0000_01b3)
    });
    format!("{hash:016x}")
}

/// The extension as installed: stamped with its version.
fn pi_extension_text() -> String {
    PI_EXTENSION.replace(VERSION_PLACEHOLDER, &pi_extension_version())
}

fn pi_extension_path() -> Result<PathBuf, String> {
    Ok(pi_extension_dir()?.join("dingger-agent-state.ts"))
}

fn pi_extension_dir() -> Result<PathBuf, String> {
    let base = std::env::var_os("PI_CODING_AGENT_DIR")
        .map(PathBuf::from)
        .or_else(|| std::env::var_os("HOME").map(|home| PathBuf::from(home).join(".pi").join("agent")))
        .ok_or("cannot determine pi agent dir (no HOME)")?;
    Ok(base.join("extensions"))
}

/// zsh hook: records the command line running in each tmux pane exactly as
/// typed (aliases, pipes, quoting), for restore to retype.
const ZSH_HOOK: &str = r#"# installed by dingger; `dingger install zsh` overwrites this file.
#
# Records the command line running in this tmux pane, as typed, in the pane
# option @dingger_cmd, so `dingger restore` can type it again (without
# running it) after a crash or shutdown.
if [[ -n $TMUX_PANE ]]; then
  _dingger_preexec() { command tmux set-option -p -t "$TMUX_PANE" @dingger_cmd "$1" 2>/dev/null &! }
  _dingger_precmd() { command tmux set-option -p -u -t "$TMUX_PANE" @dingger_cmd 2>/dev/null &! }
  autoload -Uz add-zsh-hook
  add-zsh-hook preexec _dingger_preexec
  add-zsh-hook precmd _dingger_precmd
fi
"#;

fn config_dir() -> Result<PathBuf, String> {
    std::env::var_os("DINGGER_CONFIG_DIR")
        .map(PathBuf::from)
        .or_else(|| std::env::var_os("HOME").map(|home| PathBuf::from(home).join(".config").join("dingger")))
        .ok_or_else(|| "cannot determine the config dir (no HOME)".to_string())
}

fn install_zsh() -> Result<(), String> {
    let dir = config_dir()?;
    std::fs::create_dir_all(&dir).map_err(|err| format!("mkdir failed: {err}"))?;
    let path = dir.join("dingger.zsh");
    std::fs::write(&path, ZSH_HOOK).map_err(|err| format!("write failed: {err}"))?;
    println!(
        "installed {}\nadd this line to your .zshrc (dingger does not edit it):\n\n  [[ -r {0} ]] && source {0}\n",
        path.display()
    );
    Ok(())
}

/// Install an integration: an agent's state hooks, or `zsh` for retyping
/// command lines on restore.
pub fn install(agent: &str) -> Result<(), String> {
    if agent == "zsh" {
        return install_zsh();
    }
    let parsed = detect_core::parse_agent_label(agent)
        .ok_or_else(|| format!("unknown agent: {agent}"))?;
    match parsed {
        Agent::Pi => install_pi(),
        Agent::Claude => install_claude(),
        other => Err(format!(
            "no hook integration for {} yet — screen detection is used",
            detect_core::agent_label(other)
        )),
    }
}

fn install_pi() -> Result<(), String> {
    let dir = pi_extension_dir()?;
    std::fs::create_dir_all(&dir).map_err(|err| format!("mkdir failed: {err}"))?;
    let path = pi_extension_path()?;
    std::fs::write(&path, pi_extension_text()).map_err(|err| format!("write failed: {err}"))?;
    tracing::info!(path = %path.display(), "installed pi extension");
    println!(
        "installed {} — new pi sessions report their state directly;\nrunning pi agents pick it up when reloaded (`dingger reload-agents`)",
        path.display()
    );
    Ok(())
}

/// Whether the installed pi extension is this dingger's: only then does a
/// reload bring an agent up to date (otherwise it loads the old one again).
pub fn pi_extension_installed_is_current() -> bool {
    pi_extension_path()
        .and_then(|path| std::fs::read_to_string(path).map_err(|err| err.to_string()))
        .is_ok_and(|installed| installed == pi_extension_text())
}

/// At the daemon's start: if the pi extension is installed and differs
/// from this dingger's, update it, so a dingger update needs no reinstall.
/// Only dingger's own file (it says so on its first line).
pub fn update_pi_extension() {
    let Ok(path) = pi_extension_path() else { return };
    let Ok(installed) = std::fs::read_to_string(&path) else { return };
    let current = pi_extension_text();
    if installed == current || !installed.starts_with("// installed by dingger") {
        return;
    }
    match std::fs::write(&path, current) {
        Ok(()) => tracing::info!(path = %path.display(), version = %pi_extension_version(), "updated pi extension"),
        Err(err) => tracing::warn!(path = %path.display(), %err, "failed to update pi extension"),
    }
}

/// Claude Code's user settings, where its hooks are configured.
fn claude_settings_path() -> Result<PathBuf, String> {
    std::env::var_os("CLAUDE_CONFIG_DIR")
        .map(PathBuf::from)
        .or_else(|| std::env::var_os("HOME").map(|home| PathBuf::from(home).join(".claude")))
        .map(|dir| dir.join("settings.json"))
        .ok_or_else(|| "cannot determine Claude's config dir (no HOME)".to_string())
}

fn is_dingger_claude_hook(hook: &Value) -> bool {
    hook.get("command")
        .and_then(Value::as_str)
        .is_some_and(|command| command.contains("dingger") && command.ends_with(" hook claude"))
}

/// `settings` with dingger's SessionStart hook running `command`, replacing
/// an earlier one; every other key and hook is kept, in order.
pub fn with_claude_hook(mut settings: Value, command: &str) -> Result<Value, String> {
    let root = settings.as_object_mut().ok_or("settings.json is not a JSON object")?;
    let hooks = root.entry("hooks").or_insert_with(|| json!({}));
    let hooks = hooks.as_object_mut().ok_or("settings.json: \"hooks\" is not an object")?;
    let groups = hooks.entry("SessionStart").or_insert_with(|| json!([]));
    let groups = groups.as_array_mut().ok_or("settings.json: \"hooks.SessionStart\" is not a list")?;
    groups.retain_mut(|group| {
        let Some(list) = group.get_mut("hooks").and_then(Value::as_array_mut) else {
            return true;
        };
        let before = list.len();
        list.retain(|hook| !is_dingger_claude_hook(hook));
        // Drop a group only if it held nothing but dingger's hook.
        !(list.is_empty() && before > 0)
    });
    groups.push(json!({"hooks": [{"type": "command", "command": command, "timeout": 10}]}));
    Ok(settings)
}

/// Add the SessionStart hook to Claude's settings: Claude then reports each
/// session's transcript (`dingger hook claude`), for restore to resume with
/// `claude --resume <id>`. Claude's state still comes from its screen.
fn install_claude() -> Result<(), String> {
    let path = claude_settings_path()?;
    // Write through a symlink to the file it points to.
    let path = std::fs::canonicalize(&path).unwrap_or(path);
    let original = match std::fs::read_to_string(&path) {
        Ok(text) => Some(text),
        Err(err) if err.kind() == std::io::ErrorKind::NotFound => None,
        Err(err) => return Err(format!("cannot read {}: {err}", path.display())),
    };
    let settings: Value = match &original {
        Some(text) if !text.trim().is_empty() => serde_json::from_str(text)
            .map_err(|err| format!("{} is not valid JSON ({err}); not changing it", path.display()))?,
        _ => json!({}),
    };
    let exe = std::env::current_exe().map_err(|err| format!("cannot find the dingger binary: {err}"))?;
    let command = format!("{} hook claude", crate::snapshot::shell_quote(&exe.to_string_lossy()));
    let updated = with_claude_hook(settings.clone(), &command)?;
    let mut text = serde_json::to_string_pretty(&updated).map_err(|err| err.to_string())?;
    text.push('\n');
    if original.as_deref() == Some(text.as_str()) {
        println!("already installed in {}", path.display());
        return Ok(());
    }
    if let Some(original) = &original {
        let backup = path.with_extension("json.bak-dingger");
        if !backup.exists() {
            std::fs::write(&backup, original).map_err(|err| format!("backup failed: {err}"))?;
            println!("backed up {} to {}", path.display(), backup.display());
        }
    }
    write_replacing(&path, &text)?;
    tracing::info!(path = %path.display(), "installed claude hook");
    println!(
        "installed in {}: a SessionStart hook running\n  {command}\nnew Claude sessions report their session for restore; running ones report \
         on their next start, /clear, or /resume",
        path.display()
    );
    Ok(())
}

/// Replace `path` with `text` atomically, keeping its permissions.
fn write_replacing(path: &Path, text: &str) -> Result<(), String> {
    if let Some(dir) = path.parent() {
        std::fs::create_dir_all(dir).map_err(|err| format!("mkdir failed: {err}"))?;
    }
    let temporary = path.with_extension(format!("json.dingger-{}", std::process::id()));
    std::fs::write(&temporary, text).map_err(|err| format!("write failed: {err}"))?;
    if let Ok(metadata) = std::fs::metadata(path) {
        let _ = std::fs::set_permissions(&temporary, metadata.permissions());
    }
    std::fs::rename(&temporary, path).map_err(|err| {
        let _ = std::fs::remove_file(&temporary);
        format!("write failed: {err}")
    })
}

/// `dingger hook <agent>`, run by the agent. Never fails it: exits 0 and
/// prints nothing (Claude adds a SessionStart hook's output to the
/// conversation).
pub fn run_hook(agent: &str) {
    if agent != "claude" {
        return;
    }
    let mut input = String::new();
    let _ = std::io::stdin().read_to_string(&mut input);
    let pane = std::env::var("TMUX_PANE").ok();
    if let Some(report) = claude_report(&input, pane.as_deref()) {
        if let Err(err) = crate::hooks::send(&report) {
            tracing::debug!(%err, "claude hook: no report");
        }
    }
}

/// The report for Claude's SessionStart hook input: the pane and the
/// session's transcript, no state. `None` outside tmux, for other events,
/// and for subagents.
pub fn claude_report(input: &str, pane: Option<&str>) -> Option<String> {
    let pane = pane.filter(|pane| pane.starts_with('%'))?;
    let input: Value = serde_json::from_str(input).ok()?;
    if input.get("hook_event_name")?.as_str()? != "SessionStart" || input.get("agent_id").is_some() {
        return None;
    }
    let transcript = input.get("transcript_path")?.as_str().filter(|path| !path.is_empty())?;
    let params = json!({"pane_id": pane, "agent": "claude", "agent_session_path": transcript});
    Some(json!({"method": "pane.report_agent", "params": params}).to_string())
}

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

    #[test]
    fn the_installed_extension_carries_its_version_once() {
        let version = pi_extension_version();
        assert_eq!(version.len(), 16);
        assert_eq!(PI_EXTENSION.matches(VERSION_PLACEHOLDER).count(), 1, "the asset has one placeholder");
        let text = pi_extension_text();
        assert!(!text.contains(VERSION_PLACEHOLDER));
        assert!(text.contains(&format!("\"{version}\"")), "stamped as a string literal");
        assert!(text.starts_with("// installed by dingger"), "update_pi_extension recognizes its own file");
    }

    #[test]
    fn claude_hook_is_added_beside_other_hooks_and_keys_in_order() {
        let settings: Value = serde_json::from_str(
            r#"{"model":"sonnet","hooks":{"SessionStart":[{"matcher":"^startup$","hooks":[{"type":"command","command":"bash herdr.sh session"}]}],"Stop":[]},"theme":"auto"}"#,
        )
        .unwrap();
        let once = with_claude_hook(settings, "/bin/dingger hook claude").unwrap();
        let twice = with_claude_hook(once.clone(), "/new/dingger hook claude").unwrap();
        assert_eq!(
            twice.to_string(),
            r#"{"model":"sonnet","hooks":{"SessionStart":[{"matcher":"^startup$","hooks":[{"type":"command","command":"bash herdr.sh session"}]},{"hooks":[{"type":"command","command":"/new/dingger hook claude","timeout":10}]}],"Stop":[]},"theme":"auto"}"#,
            "replaced, not added again; nothing else changes"
        );
        assert_eq!(with_claude_hook(json!({}), "d hook claude").unwrap()["hooks"]["SessionStart"][0]["hooks"][0]["command"], "d hook claude");
        assert!(with_claude_hook(json!([]), "d hook claude").is_err());
    }

    #[test]
    fn claude_report_is_the_session_start_transcript() {
        let start = r#"{"session_id":"abc","transcript_path":"/p/abc.jsonl","hook_event_name":"SessionStart","source":"startup"}"#;
        assert_eq!(
            claude_report(start, Some("%7")).as_deref(),
            Some(r#"{"method":"pane.report_agent","params":{"pane_id":"%7","agent":"claude","agent_session_path":"/p/abc.jsonl"}}"#)
        );
        assert_eq!(claude_report(start, None), None, "outside tmux");
        assert_eq!(claude_report(&start.replace("SessionStart", "Stop"), Some("%7")), None);
        assert_eq!(claude_report(&start.replace("\"source\"", "\"agent_id\":\"x\",\"source\""), Some("%7")), None, "a subagent");
        assert_eq!(claude_report("not json", Some("%7")), None);
    }
}