// query.rs — peg-based query language for the memory graph
//
// Grammar-driven: the peg definition IS the language spec.
// Evaluates against node properties, graph metrics, and edge attributes.
// Designed for ad-hoc exploration without memorizing 35+ subcommands.
//
// Syntax:
//   expr | stage | stage ...
//
// Stages (piped):
//   sort FIELD          sort descending (default for exploration)
//   sort FIELD asc      sort ascending
//   limit N             cap results
//   select F,F,...      output specific fields as TSV
//   count               just show count
//
// Examples:
//   degree > 15 | sort degree | limit 10
//   category = core | select degree,weight
//   neighbors('identity.md') WHERE strength > 0.5 | sort strength
//   key ~ 'journal.*' AND degree > 10 | count
//   * | sort weight asc | limit 20

use crate::store::{NodeType, Provenance, RelationType, Store};
use crate::graph::Graph;
use regex::Regex;
use std::collections::BTreeMap;

// -- AST types --

#[derive(Debug, Clone)]
pub enum Expr {
    All,
    Comparison { field: String, op: CmpOp, value: Value },
    And(Box<Expr>, Box<Expr>),
    Or(Box<Expr>, Box<Expr>),
    Not(Box<Expr>),
    Neighbors { key: String, filter: Option<Box<Expr>> },
}

#[derive(Debug, Clone)]
pub enum Value {
    Num(f64),
    Str(String),
    Ident(String),
    FnCall(FnCall),
}

#[derive(Debug, Clone)]
pub enum FnCall {
    Community(String),
    Degree(String),
}

#[derive(Debug, Clone, Copy)]
pub enum CmpOp {
    Gt, Lt, Ge, Le, Eq, Ne, Match,
}

#[derive(Debug, Clone)]
pub enum Stage {
    Sort { field: String, ascending: bool },
    Limit(usize),
    Select(Vec<String>),
    Count,
}

#[derive(Debug, Clone)]
pub struct Query {
    pub expr: Expr,
    pub stages: Vec<Stage>,
}

// -- PEG grammar --

peg::parser! {
    pub grammar query_parser() for str {
        rule _() = [' ' | '\t']*

        pub rule query() -> Query
            = e:expr() s:stages() { Query { expr: e, stages: s } }

        rule stages() -> Vec<Stage>
            = s:(_ "|" _ s:stage() { s })* { s }

        rule stage() -> Stage
            = "sort" _ f:field() _ a:asc_desc() { Stage::Sort { field: f, ascending: a } }
            / "limit" _ n:integer() { Stage::Limit(n) }
            / "select" _ f:field_list() { Stage::Select(f) }
            / "count" { Stage::Count }

        rule asc_desc() -> bool
            = "asc" { true }
            / "desc" { false }
            / { false }  // default: descending

        rule field_list() -> Vec<String>
            = f:field() fs:(_ "," _ f:field() { f })* {
                let mut v = vec![f];
                v.extend(fs);
                v
            }

        rule integer() -> usize
            = n:$(['0'..='9']+) { n.parse().unwrap() }

        pub rule expr() -> Expr = precedence! {
            a:(@) _ "OR" _ b:@ { Expr::Or(Box::new(a), Box::new(b)) }
            --
            a:(@) _ "AND" _ b:@ { Expr::And(Box::new(a), Box::new(b)) }
            --
            "NOT" _ e:@ { Expr::Not(Box::new(e)) }
            --
            "neighbors" _ "(" _ k:string() _ ")" _ w:where_clause()? {
                Expr::Neighbors { key: k, filter: w.map(Box::new) }
            }
            f:field() _ op:cmp_op() _ v:value() {
                Expr::Comparison { field: f, op, value: v }
            }
            "*" { Expr::All }
            "(" _ e:expr() _ ")" { e }
        }

        rule where_clause() -> Expr
            = "WHERE" _ e:expr() { e }

        rule field() -> String
            = s:$(['a'..='z' | 'A'..='Z' | '_']['a'..='z' | 'A'..='Z' | '0'..='9' | '_']*) {
                s.to_string()
            }

        rule cmp_op() -> CmpOp
            = ">=" { CmpOp::Ge }
            / "<=" { CmpOp::Le }
            / "!=" { CmpOp::Ne }
            / ">"  { CmpOp::Gt }
            / "<"  { CmpOp::Lt }
            / "="  { CmpOp::Eq }
            / "~"  { CmpOp::Match }

        rule value() -> Value
            = f:fn_call() { Value::FnCall(f) }
            / n:number() { Value::Num(n) }
            / s:string() { Value::Str(s) }
            / i:ident()  { Value::Ident(i) }

        rule fn_call() -> FnCall
            = "community" _ "(" _ k:string() _ ")" { FnCall::Community(k) }
            / "degree" _ "(" _ k:string() _ ")" { FnCall::Degree(k) }

        rule number() -> f64
            = n:$(['0'..='9']+ ("." ['0'..='9']+)?) {
                n.parse().unwrap()
            }

        rule string() -> String
            = "'" s:$([^ '\'']*) "'" { s.to_string() }

        rule ident() -> String
            = s:$(['a'..='z' | 'A'..='Z' | '_']['a'..='z' | 'A'..='Z' | '0'..='9' | '_' | '-' | '.']*) {
                s.to_string()
            }
    }
}

// -- Field resolution --

/// Resolve a field value from a node + graph context, returning a comparable Value.
fn resolve_field(field: &str, key: &str, store: &Store, graph: &Graph) -> Option<Value> {
    let node = store.nodes.get(key)?;
    match field {
        "key"           => Some(Value::Str(key.to_string())),
        "weight"        => Some(Value::Num(node.weight as f64)),
        "category"      => Some(Value::Str(node.category.label().to_string())),
        "node_type"     => Some(Value::Str(node_type_label(node.node_type).to_string())),
        "provenance"    => Some(Value::Str(node.provenance.label().to_string())),
        "emotion"       => Some(Value::Num(node.emotion as f64)),
        "retrievals"    => Some(Value::Num(node.retrievals as f64)),
        "uses"          => Some(Value::Num(node.uses as f64)),
        "wrongs"        => Some(Value::Num(node.wrongs as f64)),
        "created"       => Some(Value::Str(node.created.clone())),
        "content"       => Some(Value::Str(node.content.clone())),
        "degree"        => Some(Value::Num(graph.degree(key) as f64)),
        "community_id"  => {
            graph.communities().get(key).map(|&c| Value::Num(c as f64))
        }
        "clustering_coefficient" | "schema_fit" | "cc" => {
            Some(Value::Num(graph.clustering_coefficient(key) as f64))
        }
        _ => None,
    }
}

fn node_type_label(nt: NodeType) -> &'static str {
    match nt {
        NodeType::EpisodicSession => "episodic_session",
        NodeType::EpisodicDaily   => "episodic_daily",
        NodeType::EpisodicWeekly  => "episodic_weekly",
        NodeType::Semantic        => "semantic",
    }
}


fn rel_type_label(r: RelationType) -> &'static str {
    match r {
        RelationType::Link   => "link",
        RelationType::Causal => "causal",
        RelationType::Auto   => "auto",
    }
}

// -- Comparison logic --

fn as_num(v: &Value) -> Option<f64> {
    match v {
        Value::Num(n) => Some(*n),
        Value::Str(s) => s.parse().ok(),
        Value::Ident(s) => s.parse().ok(),
        Value::FnCall(_) => None,
    }
}

fn as_str(v: &Value) -> String {
    match v {
        Value::Str(s) | Value::Ident(s) => s.clone(),
        Value::Num(n) => format!("{}", n),
        Value::FnCall(_) => String::new(),
    }
}

fn compare(lhs: &Value, op: CmpOp, rhs: &Value) -> bool {
    if let CmpOp::Match = op {
        return Regex::new(&as_str(rhs))
            .map(|re| re.is_match(&as_str(lhs)))
            .unwrap_or(false);
    }

    // Numeric comparison if both parse, otherwise string
    let ord = match (as_num(lhs), as_num(rhs)) {
        (Some(a), Some(b)) => a.total_cmp(&b),
        _ => as_str(lhs).cmp(&as_str(rhs)),
    };

    match op {
        CmpOp::Eq => ord.is_eq(),
        CmpOp::Ne => !ord.is_eq(),
        CmpOp::Gt => ord.is_gt(),
        CmpOp::Lt => ord.is_lt(),
        CmpOp::Ge => !ord.is_lt(),
        CmpOp::Le => !ord.is_gt(),
        CmpOp::Match => unreachable!(),
    }
}

// -- Evaluator --

fn resolve_fn(f: &FnCall, store: &Store, graph: &Graph) -> Value {
    match f {
        FnCall::Community(key) => {
            let resolved = store.resolve_key(key).unwrap_or_else(|_| key.clone());
            graph.communities().get(&resolved)
                .map(|&c| Value::Num(c as f64))
                .unwrap_or(Value::Num(f64::NAN))
        }
        FnCall::Degree(key) => {
            let resolved = store.resolve_key(key).unwrap_or_else(|_| key.clone());
            Value::Num(graph.degree(&resolved) as f64)
        }
    }
}

fn resolve_value(v: &Value, store: &Store, graph: &Graph) -> Value {
    match v {
        Value::FnCall(f) => resolve_fn(f, store, graph),
        other => other.clone(),
    }
}

/// Evaluate an expression against a field resolver.
/// The resolver returns field values — different for nodes vs edges.
fn eval(
    expr: &Expr,
    resolve: &dyn Fn(&str) -> Option<Value>,
    store: &Store,
    graph: &Graph,
) -> bool {
    match expr {
        Expr::All => true,
        Expr::Comparison { field, op, value } => {
            let lhs = match resolve(field) {
                Some(v) => v,
                None => return false,
            };
            let rhs = resolve_value(value, store, graph);
            compare(&lhs, *op, &rhs)
        }
        Expr::And(a, b) => eval(a, resolve, store, graph) && eval(b, resolve, store, graph),
        Expr::Or(a, b) => eval(a, resolve, store, graph) || eval(b, resolve, store, graph),
        Expr::Not(e) => !eval(e, resolve, store, graph),
        Expr::Neighbors { .. } => false,
    }
}

// -- Query result --

pub struct QueryResult {
    pub key: String,
    pub fields: BTreeMap<String, Value>,
}

// -- Query executor --

pub fn execute_query(
    store: &Store,
    graph: &Graph,
    query_str: &str,
) -> Result<Vec<QueryResult>, String> {
    let q = query_parser::query(query_str)
        .map_err(|e| format!("Parse error: {}", e))?;
    execute_parsed(store, graph, &q)
}

fn execute_parsed(
    store: &Store,
    graph: &Graph,
    q: &Query,
) -> Result<Vec<QueryResult>, String> {
    let mut results = match &q.expr {
        Expr::Neighbors { key, filter } => {
            let resolved = store.resolve_key(key).unwrap_or_else(|_| key.clone());
            let edges = graph.edges_of(&resolved);
            let mut out = Vec::new();
            for edge in edges {
                let include = match filter {
                    Some(f) => {
                        let strength = edge.strength;
                        let rt = edge.rel_type;
                        let target = &edge.target;
                        eval(f, &|field| match field {
                            "strength" => Some(Value::Num(strength as f64)),
                            "rel_type" => Some(Value::Str(rel_type_label(rt).to_string())),
                            _ => resolve_field(field, target, store, graph),
                        }, store, graph)
                    }
                    None => true,
                };
                if include {
                    let mut fields = BTreeMap::new();
                    fields.insert("strength".into(), Value::Num(edge.strength as f64));
                    fields.insert("rel_type".into(),
                        Value::Str(rel_type_label(edge.rel_type).to_string()));
                    out.push(QueryResult { key: edge.target.clone(), fields });
                }
            }
            out
        }
        _ => {
            let mut out = Vec::new();
            for key in store.nodes.keys() {
                if store.nodes[key].deleted { continue; }
                if eval(&q.expr, &|f| resolve_field(f, key, store, graph), store, graph) {
                    out.push(QueryResult { key: key.clone(), fields: BTreeMap::new() });
                }
            }
            out
        }
    };

    // Collect fields needed by select/sort stages and resolve them once
    let needed: Vec<String> = {
        let mut set = Vec::new();
        for stage in &q.stages {
            match stage {
                Stage::Select(fields) => {
                    for f in fields {
                        if !set.contains(f) { set.push(f.clone()); }
                    }
                }
                Stage::Sort { field, .. } => {
                    if !set.contains(field) { set.push(field.clone()); }
                }
                _ => {}
            }
        }
        set
    };

    for r in &mut results {
        for f in &needed {
            if !r.fields.contains_key(f) {
                if let Some(v) = resolve_field(f, &r.key, store, graph) {
                    r.fields.insert(f.clone(), v);
                }
            }
        }
    }

    // Apply pipeline stages
    let mut has_sort = false;
    for stage in &q.stages {
        match stage {
            Stage::Sort { field, ascending } => {
                has_sort = true;
                let asc = *ascending;
                results.sort_by(|a, b| {
                    let va = a.fields.get(field).and_then(|v| as_num(v));
                    let vb = b.fields.get(field).and_then(|v| as_num(v));
                    let ord = match (va, vb) {
                        (Some(a), Some(b)) => a.total_cmp(&b),
                        _ => {
                            let sa = a.fields.get(field).map(|v| as_str(v)).unwrap_or_default();
                            let sb = b.fields.get(field).map(|v| as_str(v)).unwrap_or_default();
                            sa.cmp(&sb)
                        }
                    };
                    if asc { ord } else { ord.reverse() }
                });
            }
            Stage::Limit(n) => {
                results.truncate(*n);
            }
            Stage::Select(_) | Stage::Count => {} // handled in output
        }
    }

    // Default sort by degree desc if no explicit sort
    if !has_sort {
        results.sort_by(|a, b| {
            let da = graph.degree(&a.key);
            let db = graph.degree(&b.key);
            db.cmp(&da)
        });
    }

    Ok(results)
}

/// Format a Value for display
pub fn format_value(v: &Value) -> String {
    match v {
        Value::Num(n) => {
            if *n == n.floor() && n.abs() < 1e15 {
                format!("{}", *n as i64)
            } else {
                format!("{:.3}", n)
            }
        }
        Value::Str(s) => s.clone(),
        Value::Ident(s) => s.clone(),
        Value::FnCall(_) => "?".to_string(),
    }
}

/// Execute query and print formatted output.
pub fn run_query(store: &Store, graph: &Graph, query_str: &str) -> Result<(), String> {
    let q = query_parser::query(query_str)
        .map_err(|e| format!("Parse error: {}", e))?;

    let results = execute_parsed(store, graph, &q)?;

    // Count stage
    if q.stages.iter().any(|s| matches!(s, Stage::Count)) {
        println!("{}", results.len());
        return Ok(());
    }

    if results.is_empty() {
        eprintln!("No results");
        return Ok(());
    }

    // Select stage
    let fields: Option<&Vec<String>> = q.stages.iter().find_map(|s| match s {
        Stage::Select(f) => Some(f),
        _ => None,
    });

    if let Some(fields) = fields {
        let mut header = vec!["key".to_string()];
        header.extend(fields.iter().cloned());
        println!("{}", header.join("\t"));

        for r in &results {
            let mut row = vec![r.key.clone()];
            for f in fields {
                row.push(match r.fields.get(f) {
                    Some(v) => format_value(v),
                    None => "-".to_string(),
                });
            }
            println!("{}", row.join("\t"));
        }
    } else {
        for r in &results {
            println!("{}", r.key);
        }
    }

    Ok(())
}