//! The baseline: the fixed prefix of every request in an epoch — the system prompt, core memory
//! and core tool schemas. It is snapshotted per session so an edit to `system.md` changes nothing
//! for a running session, and `messages` turns a session log back into the request's messages.

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

use crate::config::Config;
use crate::llama::{ChatMessage, ToolSchema};
use crate::tools::Registry;
use proto::{Hash32, LogRecord, sha256};

use serde::Deserialize;
use serde::Serialize;

/// The fixed prefix of a request, and the errors assembling or reading it.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct Baseline {
    pub system: String,
    pub tools: Vec<ToolSchema>,
}

#[derive(Debug)]
pub enum BaselineError {
    Read(PathBuf, std::io::Error),
    Parse(PathBuf, serde_json::Error),
    Hash,
}

impl std::fmt::Display for BaselineError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            BaselineError::Read(path, err) => write!(f, "{}: {err}", path.display()),
            BaselineError::Parse(path, err) => write!(f, "{}: {err}", path.display()),
            BaselineError::Hash => write!(f, "hashing the baseline failed"),
        }
    }
}

impl std::error::Error for BaselineError {}

impl Baseline {
    /// The system prompt trimmed, plus core memory if it has content; the core tool schemas.
    pub fn assemble(cfg: &Config, registry: &Registry) -> Result<Baseline, BaselineError> {
        let system = std::fs::read_to_string(&cfg.baseline.system)
            .map_err(|e| BaselineError::Read(cfg.baseline.system.clone(), e))?;
        let mut system = system.trim_end().to_string();

        let core = cfg.paths.home.join("memory/core.md");
        if let Ok(text) = std::fs::read_to_string(&core) {
            let trimmed = text.trim();
            if !trimmed.is_empty() {
                system.push_str("\n\n");
                system.push_str(trimmed);
            }
        }

        Ok(Baseline {
            system,
            tools: registry.core_schemas(),
        })
    }

    /// The canonical JSON: key order is fixed, so the hash is stable.
    pub fn to_json(&self) -> Result<String, serde_json::Error> {
        serde_json::to_string(self)
    }

    pub fn from_json(text: &str) -> Result<Baseline, serde_json::Error> {
        serde_json::from_str(text)
    }

    pub fn load(path: &Path) -> Result<Baseline, BaselineError> {
        let text = std::fs::read_to_string(path)
            .map_err(|e| BaselineError::Read(path.to_path_buf(), e))?;
        serde_json::from_str(&text).map_err(|e| BaselineError::Parse(path.to_path_buf(), e))
    }

    /// The sha256 of the baseline's own JSON, as written.
    pub fn hash(&self) -> Result<Hash32, BaselineError> {
        let json = self.to_json().map_err(|_| BaselineError::Hash)?;
        sha256(json.as_bytes()).map_err(|_| BaselineError::Hash)
    }
}

/// The system message, then each log record replayed in order. Every record variant is named, so a
/// new one is a compile error rather than a silent skip.
pub fn messages(baseline: &Baseline, records: &[LogRecord]) -> Vec<ChatMessage> {
    let mut out = vec![ChatMessage::System {
        content: baseline.system.clone(),
    }];
    for record in records {
        match record {
            LogRecord::SessionStart { .. } => {}
            LogRecord::User { content, .. } => out.push(ChatMessage::User {
                content: content.clone(),
            }),
            LogRecord::Assistant {
                content,
                reasoning_content,
                tool_calls,
                ..
            } => out.push(ChatMessage::Assistant {
                content: content.clone(),
                reasoning_content: reasoning_content.clone(),
                tool_calls: tool_calls.clone(),
            }),
            LogRecord::ToolResult {
                tool_call_id,
                content,
                ..
            } => out.push(ChatMessage::Tool {
                tool_call_id: tool_call_id.clone(),
                content: content.clone(),
            }),
            LogRecord::Usage { .. } => {}
            LogRecord::CacheLoss { .. } => {}
            LogRecord::EpochEnd { .. } => {}
        }
    }
    out
}