// Migration from old weights.json + markdown marker system
//
// Reads:
//   ~/.claude/memory/weights.json  (1,874 entries with metrics)
//   ~/.claude/memory/*.md          (content + mem markers + edges)
//
// Emits:
//   ~/.claude/memory/nodes.capnp   (all nodes with preserved metadata)
//   ~/.claude/memory/relations.capnp (all edges from markers + md links)
//   ~/.claude/memory/state.json    (derived cache)
//
// Old files are preserved as backup. Run once.

use crate::store::{
    self, Store, Node, Category, NodeType, Provenance, RelationType,
    parse_units, new_relation,
};

use serde::Deserialize;
use uuid::Uuid;

use std::collections::HashMap;
use std::env;
use std::fs;
use std::path::{Path, PathBuf};
fn home() -> PathBuf {
    PathBuf::from(env::var("HOME").expect("HOME not set"))
}

// Old system data structures (just enough for deserialization)

#[derive(Deserialize)]
struct OldStore {
    #[serde(default)]
    entries: HashMap<String, OldEntry>,
    #[serde(default)]
    retrieval_log: Vec<OldRetrievalEvent>,
    #[serde(default)]
    params: OldParams,
}

#[derive(Deserialize)]
struct OldEntry {
    weight: f64,
    created: String,
    #[serde(default)]
    last_retrieved: Option<String>,
    #[serde(default)]
    last_used: Option<String>,
    #[serde(default)]
    retrievals: u32,
    #[serde(default)]
    uses: u32,
    #[serde(default)]
    wrongs: u32,
    #[serde(default = "default_category")]
    category: String,
}

fn default_category() -> String { "General".to_string() }

#[derive(Deserialize)]
struct OldRetrievalEvent {
    query: String,
    timestamp: String,
    results: Vec<String>,
    #[serde(default)]
    used: Option<Vec<String>>,
}

#[derive(Deserialize)]
struct OldParams {
    #[serde(default = "default_0_7")]
    default_weight: f64,
    #[serde(default = "default_0_95")]
    decay_factor: f64,
    #[serde(default = "default_0_15")]
    use_boost: f64,
    #[serde(default = "default_0_1")]
    prune_threshold: f64,
    #[serde(default = "default_0_3")]
    edge_decay: f64,
    #[serde(default = "default_3")]
    max_hops: u32,
    #[serde(default = "default_0_05")]
    min_activation: f64,
}

impl Default for OldParams {
    fn default() -> Self {
        OldParams {
            default_weight: 0.7,
            decay_factor: 0.95,
            use_boost: 0.15,
            prune_threshold: 0.1,
            edge_decay: 0.3,
            max_hops: 3,
            min_activation: 0.05,
        }
    }
}

fn default_0_7() -> f64 { 0.7 }
fn default_0_95() -> f64 { 0.95 }
fn default_0_15() -> f64 { 0.15 }
fn default_0_1() -> f64 { 0.1 }
fn default_0_3() -> f64 { 0.3 }
fn default_3() -> u32 { 3 }
fn default_0_05() -> f64 { 0.05 }

fn parse_old_category(s: &str) -> Category {
    match s {
        "Core" | "core" => Category::Core,
        "Technical" | "technical" | "tech" => Category::Technical,
        "Observation" | "observation" | "obs" => Category::Observation,
        "Task" | "task" => Category::Task,
        _ => Category::General,
    }
}

pub fn migrate() -> Result<(), String> {
    let weights_path = home().join(".claude/memory/weights.json");
    let memory_dir = home().join(".claude/memory");
    let nodes_path = memory_dir.join("nodes.capnp");
    let rels_path = memory_dir.join("relations.capnp");

    // Safety check
    if nodes_path.exists() || rels_path.exists() {
        return Err("nodes.capnp or relations.capnp already exist. \
            Remove them first if you want to re-migrate.".into());
    }

    // Load old store
    let old_store: OldStore = if weights_path.exists() {
        let data = fs::read_to_string(&weights_path)
            .map_err(|e| format!("read weights.json: {}", e))?;
        serde_json::from_str(&data)
            .map_err(|e| format!("parse weights.json: {}", e))?
    } else {
        eprintln!("Warning: no weights.json found, migrating markdown only");
        OldStore {
            entries: HashMap::new(),
            retrieval_log: Vec::new(),
            params: OldParams::default(),
        }
    };

    eprintln!("Old store: {} entries, {} retrieval events",
        old_store.entries.len(), old_store.retrieval_log.len());

    // Scan markdown files to get content + edges
    let mut units_by_key: HashMap<String, store::MemoryUnit> = HashMap::new();
    scan_markdown_dir(&memory_dir, &mut units_by_key)?;

    eprintln!("Scanned {} markdown units", units_by_key.len());

    // Create new store
    let mut store = Store::default();

    // Migrate params
    store.params.default_weight = old_store.params.default_weight;
    store.params.decay_factor = old_store.params.decay_factor;
    store.params.use_boost = old_store.params.use_boost;
    store.params.prune_threshold = old_store.params.prune_threshold;
    store.params.edge_decay = old_store.params.edge_decay;
    store.params.max_hops = old_store.params.max_hops;
    store.params.min_activation = old_store.params.min_activation;

    // Migrate retrieval log
    store.retrieval_log = old_store.retrieval_log.iter().map(|e| {
        store::RetrievalEvent {
            query: e.query.clone(),
            timestamp: e.timestamp.clone(),
            results: e.results.clone(),
            used: e.used.clone(),
        }
    }).collect();

    // Phase 1: Create nodes
    // Merge old entries (weight metadata) with markdown units (content)
    let mut all_nodes: Vec<Node> = Vec::new();
    let mut key_to_uuid: HashMap<String, [u8; 16]> = HashMap::new();

    // First, all entries from the old store
    for (key, old_entry) in &old_store.entries {
        let uuid = *Uuid::new_v4().as_bytes();
        key_to_uuid.insert(key.clone(), uuid);

        let content = units_by_key.get(key)
            .map(|u| u.content.clone())
            .unwrap_or_default();

        let state_tag = units_by_key.get(key)
            .and_then(|u| u.state.clone())
            .unwrap_or_default();

        let node = Node {
            uuid,
            version: 1,
            timestamp: store::now_epoch(),
            node_type: if key.contains("journal") {
                NodeType::EpisodicSession
            } else {
                NodeType::Semantic
            },
            provenance: Provenance::Manual,
            key: key.clone(),
            content,
            weight: old_entry.weight as f32,
            category: parse_old_category(&old_entry.category),
            emotion: 0.0,
            deleted: false,
            source_ref: String::new(),
            created: old_entry.created.clone(),
            retrievals: old_entry.retrievals,
            uses: old_entry.uses,
            wrongs: old_entry.wrongs,
            state_tag,
            last_replayed: 0,
            spaced_repetition_interval: 1,
            position: 0,
            created_at: 0,
            community_id: None,
            clustering_coefficient: None,
            degree: None,
        };
        all_nodes.push(node);
    }

    // Then, any markdown units not in the old store
    for (key, unit) in &units_by_key {
        if key_to_uuid.contains_key(key) { continue; }

        let uuid = *Uuid::new_v4().as_bytes();
        key_to_uuid.insert(key.clone(), uuid);

        let node = Node {
            uuid,
            version: 1,
            timestamp: store::now_epoch(),
            node_type: if key.contains("journal") {
                NodeType::EpisodicSession
            } else {
                NodeType::Semantic
            },
            provenance: Provenance::Manual,
            key: key.clone(),
            content: unit.content.clone(),
            weight: 0.7,
            category: Category::General,
            emotion: 0.0,
            deleted: false,
            source_ref: String::new(),
            created: String::new(),
            retrievals: 0,
            uses: 0,
            wrongs: 0,
            state_tag: unit.state.clone().unwrap_or_default(),
            last_replayed: 0,
            spaced_repetition_interval: 1,
            position: 0,
            created_at: 0,
            community_id: None,
            clustering_coefficient: None,
            degree: None,
        };
        all_nodes.push(node);
    }

    // Write nodes to capnp log
    store.append_nodes(&all_nodes)?;
    for node in &all_nodes {
        store.uuid_to_key.insert(node.uuid, node.key.clone());
        store.nodes.insert(node.key.clone(), node.clone());
    }

    eprintln!("Migrated {} nodes", all_nodes.len());

    // Phase 2: Create relations from markdown links + causal edges
    let mut all_relations = Vec::new();

    for (key, unit) in &units_by_key {
        let source_uuid = match key_to_uuid.get(key) {
            Some(u) => *u,
            None => continue,
        };

        // Association links (bidirectional)
        for link in unit.marker_links.iter().chain(unit.md_links.iter()) {
            let target_uuid = match key_to_uuid.get(link) {
                Some(u) => *u,
                None => continue,
            };

            // Avoid duplicate relations
            let exists = all_relations.iter().any(|r: &store::Relation|
                (r.source == source_uuid && r.target == target_uuid) ||
                (r.source == target_uuid && r.target == source_uuid));
            if exists { continue; }

            all_relations.push(new_relation(
                source_uuid, target_uuid,
                RelationType::Link, 1.0,
                key, link,
            ));
        }

        // Causal edges (directed)
        for cause in &unit.causes {
            let cause_uuid = match key_to_uuid.get(cause) {
                Some(u) => *u,
                None => continue,
            };

            all_relations.push(new_relation(
                cause_uuid, source_uuid,
                RelationType::Causal, 1.0,
                cause, key,
            ));
        }
    }

    // Write relations to capnp log
    store.append_relations(&all_relations)?;
    store.relations = all_relations;

    eprintln!("Migrated {} relations", store.relations.len());

    // Phase 3: Compute graph metrics
    store.update_graph_metrics();

    // Save derived cache
    store.save()?;

    eprintln!("Migration complete. Files:");
    eprintln!("  {}", nodes_path.display());
    eprintln!("  {}", rels_path.display());
    eprintln!("  {}", memory_dir.join("state.json").display());

    // Verify
    let g = store.build_graph();
    eprintln!("\nVerification:");
    eprintln!("  Nodes: {}", store.nodes.len());
    eprintln!("  Relations: {}", store.relations.len());
    eprintln!("  Graph edges: {}", g.edge_count());
    eprintln!("  Communities: {}", g.community_count());
    eprintln!("  Avg CC: {:.4}", g.avg_clustering_coefficient());

    Ok(())
}

fn scan_markdown_dir(
    dir: &Path,
    units: &mut HashMap<String, store::MemoryUnit>,
) -> Result<(), String> {
    let entries = fs::read_dir(dir)
        .map_err(|e| format!("read dir {}: {}", dir.display(), e))?;

    for entry in entries.flatten() {
        let path = entry.path();
        if path.is_dir() {
            scan_markdown_dir(&path, units)?;
            continue;
        }
        let Some(ext) = path.extension() else { continue };
        if ext != "md" { continue }

        let filename = path.file_name().unwrap().to_string_lossy().to_string();
        let content = match fs::read_to_string(&path) {
            Ok(c) => c,
            Err(_) => continue,
        };

        for unit in parse_units(&filename, &content) {
            units.insert(unit.key.clone(), unit);
        }
    }
    Ok(())
}