//! Shared client configuration: server URL, API key, polling cadence,
//! oneliner window. Every native client (desktop, watch, phone) reads
//! the same schema — only the on-disk path differs per platform.
//!
//! Path resolution is deliberately **not** part of this module. Callers
//! provide a concrete `&Path` to `load_from` / `save_to`; the
//! per-platform path helper lives in each client crate.

use std::path::{Path, PathBuf};
use std::time::Duration;

use serde::{Deserialize, Serialize};
use thiserror::Error;

/// Fallback polling cadence for `/api/oneliners` in seconds. Chosen to
/// feel real-time without hammering the server.
pub const DEFAULT_POLL_INTERVAL_SECONDS: u64 = 5;

/// Client configuration loaded from a TOML file at a platform-specific
/// path. All fields except the two durations are mandatory.
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
pub struct Config {
    /// Base URL of the doctate server, e.g. `https://doctate.example.org`.
    pub server_url: String,
    /// Per-user API key used in the `X-API-Key` header.
    pub api_key: String,
    /// Polling cadence for `/api/oneliners`. Omit in TOML to use the
    /// built-in default.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub oneliner_poll_interval_seconds: Option<u64>,
}

#[derive(Debug, Error)]
pub enum ConfigError {
    #[error("cannot determine OS config directory (is $HOME set?)")]
    NoConfigDir,
    #[error("I/O error at {path}: {source}")]
    Io {
        path: PathBuf,
        #[source]
        source: std::io::Error,
    },
    #[error("parse error at {path}: {source}")]
    Parse {
        path: PathBuf,
        #[source]
        source: toml::de::Error,
    },
    #[error("serialize error: {0}")]
    Serialize(#[from] toml::ser::Error),
}

impl Config {
    /// Load from `path`. Returns `Ok(None)` if the file does not exist
    /// (first-run case); `Ok(Some(_))` on success; `Err` on I/O or parse
    /// errors — caller should surface these to the user, not swallow.
    pub fn load_from(path: &Path) -> Result<Option<Self>, ConfigError> {
        let text = match std::fs::read_to_string(path) {
            Ok(t) => t,
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(None),
            Err(e) => {
                return Err(ConfigError::Io {
                    path: path.into(),
                    source: e,
                });
            }
        };
        let cfg: Config = toml::from_str(&text).map_err(|e| ConfigError::Parse {
            path: path.into(),
            source: e,
        })?;
        Ok(Some(cfg))
    }

    /// Save to `path`, creating parent directories as needed.
    pub fn save_to(&self, path: &Path) -> Result<(), ConfigError> {
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent).map_err(|e| ConfigError::Io {
                path: parent.into(),
                source: e,
            })?;
        }
        let text = toml::to_string_pretty(self)?;
        std::fs::write(path, text).map_err(|e| ConfigError::Io {
            path: path.into(),
            source: e,
        })?;
        Ok(())
    }

    /// Polling cadence as a [`Duration`], substituting the default if
    /// the field was omitted.
    pub fn poll_interval(&self) -> Duration {
        Duration::from_secs(
            self.oneliner_poll_interval_seconds
                .unwrap_or(DEFAULT_POLL_INTERVAL_SECONDS),
        )
    }
}

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

    fn sample() -> Config {
        Config {
            server_url: "https://doctate.example.org".into(),
            api_key: "sk-test-12345".into(),
            oneliner_poll_interval_seconds: None,
        }
    }

    #[test]
    fn roundtrip_through_file() {
        let tmp = TempDir::new().unwrap();
        let path = tmp.path().join("client.toml");
        let original = sample();
        original.save_to(&path).unwrap();
        let loaded = Config::load_from(&path).unwrap();
        assert_eq!(loaded, Some(original));
    }

    #[test]
    fn load_missing_file_returns_none() {
        let tmp = TempDir::new().unwrap();
        let path = tmp.path().join("nonexistent.toml");
        assert!(Config::load_from(&path).unwrap().is_none());
    }

    #[test]
    fn save_creates_parent_dirs() {
        let tmp = TempDir::new().unwrap();
        let path = tmp.path().join("deep/nested/client.toml");
        sample().save_to(&path).unwrap();
        assert!(path.exists());
    }

    #[test]
    fn load_invalid_toml_returns_parse_error() {
        let tmp = TempDir::new().unwrap();
        let path = tmp.path().join("bad.toml");
        std::fs::write(&path, "this is not [valid toml").unwrap();
        let err = Config::load_from(&path).unwrap_err();
        assert!(matches!(err, ConfigError::Parse { .. }));
    }

    #[test]
    fn defaults_when_fields_omitted() {
        let tmp = TempDir::new().unwrap();
        let path = tmp.path().join("minimal.toml");
        std::fs::write(&path, "server_url = \"http://x\"\napi_key = \"y\"\n").unwrap();
        let cfg = Config::load_from(&path).unwrap().unwrap();
        assert_eq!(cfg.poll_interval(), Duration::from_secs(5));
    }

    #[test]
    fn explicit_values_override_defaults() {
        let cfg = Config {
            server_url: "http://x".into(),
            api_key: "y".into(),
            oneliner_poll_interval_seconds: Some(10),
        };
        assert_eq!(cfg.poll_interval(), Duration::from_secs(10));
    }

    #[test]
    fn roundtrip_preserves_optional_fields() {
        let tmp = TempDir::new().unwrap();
        let path = tmp.path().join("client.toml");
        let original = Config {
            server_url: "http://x".into(),
            api_key: "y".into(),
            oneliner_poll_interval_seconds: Some(3),
        };
        original.save_to(&path).unwrap();
        let loaded = Config::load_from(&path).unwrap().unwrap();
        assert_eq!(loaded.oneliner_poll_interval_seconds, Some(3));
    }
}