//! `mem capture | resolve | lookup | materialize`
//!
//! Storage layout under `$MEM_HOME` (default `~/.mem`):
//!
//! ```text
//!   events.jsonl        authoritative, append-only
//!   lessons.json        projection, rebuilt by `mem resolve`
//!   skills/<tool>-failures/SKILL.md   projection, Claude Code convention
//!   MEMORY.md           projection, CLAUDE.md-style @import target
//! ```
//!
//! Only `events.jsonl` is authoritative. Everything else is regenerable, which
//! is the same invariant the full design applies to pgvector.

use anyhow::{Context, Result};
use mem_core::lesson::{
    derive_lessons, extract, lookup as lookup_lesson, render_injection, render_skill, tool_of_cmd,
    Confidence, Event, Lesson,
};
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use std::collections::BTreeMap;
use std::fs;
use std::io::Write;
use std::path::{Path, PathBuf};
use time::format_description::well_known::Rfc3339;
use time::OffsetDateTime;

pub fn mem_home() -> PathBuf {
    std::env::var("MEM_HOME")
        .map(PathBuf::from)
        .unwrap_or_else(|_| {
            let home = std::env::var("HOME").unwrap_or_else(|_| ".".into());
            PathBuf::from(home).join(".mem")
        })
}

fn events_path() -> PathBuf {
    mem_home().join("events.jsonl")
}
fn lessons_path() -> PathBuf {
    mem_home().join("lessons.json")
}

/// Cap stored output. A 50KB log adds nothing a signature does not already
/// carry, and the log is append-only so it never shrinks.
const OUTPUT_CAP: usize = 4096;

pub fn cmd_capture(cmd: &str, exit: i32, output_file: Option<&Path>, cwd: Option<&str>) -> Result<()> {
    // Successes are recorded too: without them there is no fail -> success pair
    // to learn from.
    let raw = match output_file {
        Some(p) => fs::read_to_string(p).unwrap_or_default(),
        None => {
            use std::io::Read;
            let mut s = String::new();
            let _ = std::io::stdin().read_to_string(&mut s);
            s
        }
    };
    let tail: String = if raw.len() > OUTPUT_CAP {
        raw[raw.len() - OUTPUT_CAP..].to_string()
    } else {
        raw
    };

    let cwd = cwd
        .map(str::to_string)
        .unwrap_or_else(|| std::env::current_dir().map(|p| p.display().to_string()).unwrap_or_default());

    let ev = Event {
        ts: OffsetDateTime::now_utc().format(&Rfc3339)?,
        cwd,
        cmd: cmd.to_string(),
        exit,
        output: tail,
    };

    let p = events_path();
    fs::create_dir_all(p.parent().unwrap())?;
    let mut f = fs::OpenOptions::new().create(true).append(true).open(&p)?;
    writeln!(f, "{}", serde_json::to_string(&ev)?)?;
    Ok(())
}

fn load_events() -> Result<Vec<Event>> {
    let p = events_path();
    if !p.exists() {
        return Ok(vec![]);
    }
    let s = fs::read_to_string(&p)?;
    Ok(s.lines()
        .filter(|l| !l.trim().is_empty())
        .filter_map(|l| serde_json::from_str::<Event>(l).ok())
        .collect())
}

pub fn load_lessons() -> Result<Vec<Lesson>> {
    let p = lessons_path();
    if !p.exists() {
        return Ok(vec![]);
    }
    Ok(serde_json::from_str(&fs::read_to_string(&p)?)?)
}

pub fn cmd_resolve(json: bool) -> Result<()> {
    let events = load_events()?;
    let mut derived = derive_lessons(&events, tool_of_cmd);

    // Preserve human confirmation across rebuilds. The projection is
    // regenerable, but the human's judgement about it is not.
    let previous = load_lessons().unwrap_or_default();
    for l in derived.iter_mut() {
        if let Some(old) = previous.iter().find(|o| o.sig_sha == l.sig_sha) {
            if old.confidence == Confidence::Confirmed {
                l.confidence = Confidence::Confirmed;
            }
        }
    }

    fs::create_dir_all(mem_home())?;
    fs::write(lessons_path(), serde_json::to_string_pretty(&derived)?)?;

    if json {
        println!("{}", serde_json::to_string_pretty(&derived)?);
    } else {
        println!(
            "{} events -> {} lessons ({} recurring)",
            events.len(),
            derived.len(),
            derived.iter().filter(|l| l.seen >= 3).count()
        );
        for l in &derived {
            println!("  [{}] seen {}x  {}", l.tool, l.seen, l.raw.trim());
        }
    }
    Ok(())
}

/// Default similarity floor. Below this we abstain: an agent acts on the top
/// result, so a weak match is worse than nothing.
pub const DEFAULT_FLOOR: f32 = 0.55;

pub fn cmd_lookup(tool: Option<&str>, cmd: Option<&str>, file: Option<&Path>, floor: f32) -> Result<()> {
    let raw = match file {
        Some(p) => fs::read_to_string(p).with_context(|| format!("reading {}", p.display()))?,
        None => {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s)?;
            s
        }
    };
    let tool = tool
        .map(str::to_string)
        .or_else(|| cmd.map(tool_of_cmd))
        .unwrap_or_else(|| "unknown".into());

    let Some(sig) = extract(&tool, &raw) else {
        return Ok(()); // nothing extractable: stay silent
    };
    let lessons = load_lessons()?;
    match lookup_lesson(&sig, &lessons, floor) {
        // Silence is the correct and common answer.
        None => Ok(()),
        Some(hit) => {
            print!("{}", render_injection(&hit, 600));
            Ok(())
        }
    }
}

pub fn cmd_materialize() -> Result<()> {
    let lessons = load_lessons()?;
    if lessons.is_empty() {
        println!("no lessons yet - run `mem resolve` after capturing some failures");
        return Ok(());
    }
    let mut by_tool: BTreeMap<String, Vec<Lesson>> = BTreeMap::new();
    for l in lessons {
        by_tool.entry(l.tool.clone()).or_default().push(l);
    }

    let skills_dir = mem_home().join("skills");
    let mut written = vec![];
    for (tool, ls) in &by_tool {
        let dir = skills_dir.join(format!("{tool}-failures"));
        fs::create_dir_all(&dir)?;
        let path = dir.join("SKILL.md");
        fs::write(&path, render_skill(tool, ls))?;
        written.push(path);
    }

    // A CLAUDE.md-style digest: only the recurring lessons, because this file
    // is loaded eagerly and every byte competes with the task.
    let mut digest = String::from("# Learned failures\n\nGenerated by `mem materialize`. Recurring failures only.\n\n");
    for (tool, ls) in &by_tool {
        let recurring: Vec<&Lesson> = ls.iter().filter(|l| l.seen >= 3).collect();
        if recurring.is_empty() {
            continue;
        }
        digest.push_str(&format!("## {tool}\n\n"));
        for l in recurring {
            digest.push_str(&format!(
                "- `{}` (seen {}x) -> {}\n",
                l.raw.trim(),
                l.seen,
                l.resolution.join(" && ")
            ));
        }
        digest.push('\n');
    }
    let digest_path = mem_home().join("MEMORY.md");
    fs::write(&digest_path, digest)?;

    println!("wrote {} skill(s):", written.len());
    for p in written {
        println!("  {}", p.display());
    }
    println!("  {}", digest_path.display());
    println!("\nWire into Claude Code / pi:");
    println!("  ln -s {} ~/.claude/skills/", skills_dir.display());
    println!("  echo '@{}' >> ~/.claude/CLAUDE.md", digest_path.display());
    Ok(())
}

/// Skill draft frontmatter
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SkillFrontmatter {
    pub name: String,
    pub description: String,
    pub when_to_use: String,
    pub generated_from: String,
    pub generated_at: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub argument_hint: Option<String>,
}

impl SkillFrontmatter {
    /// Render as YAML frontmatter
    pub fn render(&self) -> String {
        let mut yaml = String::from("---\n");
        yaml.push_str(&format!("name: {}\n", quoted(&self.name)));
        yaml.push_str(&format!("description: {}\n", quoted(&self.description)));
        yaml.push_str(&format!("when_to_use: {}\n", quoted(&self.when_to_use)));
        yaml.push_str(&format!("generated_from: {}\n", quoted(&self.generated_from)));
        yaml.push_str(&format!("generated_at: {}\n", quoted(&self.generated_at)));
        if let Some(hint) = &self.argument_hint {
            yaml.push_str(&format!("argument_hint: {}\n", quoted(hint)));
        }
        yaml.push_str("---\n");
        yaml
    }
}

fn quoted(s: &str) -> String {
    format!("'{}'", s.replace("'", "''"))
}

/// Draft a skill from a memory note
pub async fn cmd_skill_draft(project: &str, from: &str, dry_run: bool) -> Result<()> {
    // Generate stable hash of memory note identifier for provenance
    let mut hasher = Sha256::new();
    hasher.update(format!("{}:{}", project, from).as_bytes());
    let hash = format!("{:x}", hasher.finalize())[..16].to_string();

    // Create skill frontmatter (placeholder)
    let frontmatter = SkillFrontmatter {
        name: format!("{}-{}", project, from.replace("/", "-")),
        description: format!("Handle {} in project {}", from, project),
        when_to_use: format!("When dealing with {} in {}", from, project),
        generated_from: hash.clone(),
        generated_at: OffsetDateTime::now_utc().to_string(),
        argument_hint: None,
    };

    // Build output path
    let vault_dir = mem_home().join("vault");
    let skills_drafts = vault_dir.join("skills").join("_drafts").join(format!("{}-{}", project, from));
    let skill_file = skills_drafts.join("SKILL.md");

    // Verify path is inside _drafts/
    if !skill_file
        .components()
        .any(|c| c.as_os_str() == "_drafts")
    {
        anyhow::bail!("Safety check failed: output path must be inside _drafts/");
    }

    let content = format!(
        "{}\n# {}: {}\n\nThis is a draft skill generated from memory note: {}\n\nEdit and refine before promoting to `skills/`.\n",
        frontmatter.render(),
        frontmatter.name,
        frontmatter.description,
        from
    );

    if dry_run {
        println!("[dry-run] Would write {} bytes to {}", content.len(), skill_file.display());
        println!("{}", content);
        return Ok(());
    }

    fs::create_dir_all(&skills_drafts)?;
    fs::write(&skill_file, &content)?;
    println!("Drafted skill: {}", skill_file.display());
    println!("Generated from: {}", hash);
    println!("\nReview and edit, then move to skills/ to promote:");
    println!("  mv {}/SKILL.md {}/SKILL.md", skills_drafts.display(), vault_dir.join("skills").display());
    Ok(())
}