use std::collections::{BTreeMap, BTreeSet};
use std::fs::{self, File};
use std::io::{BufRead, BufReader, BufWriter};
use std::path::{Path, PathBuf};
use std::sync::LazyLock;

use anyhow::{Context, Result};
use clap::Parser;
use rayon::prelude::*;
use regex::Regex;
use serde::{Deserialize, Serialize};

const RADIX_VERSION: &str = "prefix-radix-v1";
const DAG_VERSION: &str = "prefix-dag-v1";

static EPISODE_PATTERNS: LazyLock<Vec<Regex>> = LazyLock::new(|| {
    vec![
        Regex::new(r"(?i)\bS\d{1,2}E\d{1,4}\b").unwrap(),
        Regex::new(r"(?i)\bEP?\.?\s*\d{1,4}\b").unwrap(),
        Regex::new(r"第\s*\d{1,4}\s*[話话集回]").unwrap(),
        Regex::new(r"\b\d{1,4}\s*[話话集回]").unwrap(),
        Regex::new(r"[\[(]\s*\d{1,4}\s*[\])]").unwrap(),
    ]
});

static DIGITS: LazyLock<Regex> = LazyLock::new(|| Regex::new(r"\d+").unwrap());

#[derive(Parser)]
#[command(about = "Build a deterministic DMHY episode-prefix trie graph")]
struct Args {
    #[arg(long, default_value = "datasets\\AnimeName\\dmhy_list.jsonl")]
    input: PathBuf,

    #[arg(long, default_value = "datasets\\AnimeName\\dmhy_prefix_graph.json")]
    output: PathBuf,

    #[arg(long, default_value_t = 2)]
    min_count: usize,

    #[arg(long, default_value_t = 5)]
    example_count: usize,

    #[arg(long)]
    from_prefix_graph: Option<PathBuf>,

    #[arg(long)]
    dag_output: Option<PathBuf>,
}

#[derive(Clone, Deserialize)]
struct InputRecord {
    value: String,
    #[serde(default)]
    uses_path: bool,
    #[serde(default)]
    has_trailing_hash: bool,
    #[serde(default, rename = "has_digits")]
    _has_digits: bool,
    #[serde(default)]
    #[serde(rename = "digit_skeleton")]
    _digit_skeleton: String,
    #[serde(default = "default_count")]
    count: usize,
}

#[derive(Clone)]
struct PatternObservation {
    source_index: usize,
    prefix: String,
    digit_skeleton: String,
    suffix: String,
    value: String,
    uses_path: bool,
    has_trailing_hash: bool,
    count: usize,
}

#[derive(Default)]
struct GroupBuilder {
    prefix: String,
    digit_skeleton: String,
    count: usize,
    weight: usize,
    uses_path_count: usize,
    has_trailing_hash_count: usize,
    suffix_examples: Vec<String>,
    value_examples: Vec<String>,
}

struct TrieNode {
    id: usize,
    edge_label: String,
    depth: usize,
    parent: Option<usize>,
    children_by_label: BTreeMap<String, usize>,
    subtree_patterns: usize,
    subtree_weight: usize,
}

#[derive(Serialize)]
struct GraphOutput {
    meta: Meta,
    nodes: Vec<OutputNode>,
    terminals: Vec<OutputTerminal>,
}

#[derive(Serialize)]
struct Meta {
    input: String,
    output: String,
    input_records: usize,
    observations: usize,
    no_episode_prefix: usize,
    groups: usize,
    nodes: usize,
    max_depth: usize,
    grouped_weight: usize,
    min_count: usize,
    example_count: usize,
    tokenizer: TokenizerMeta,
}

#[derive(Serialize)]
struct TokenizerMeta {
    version: &'static str,
    notes: Vec<&'static str>,
}

#[derive(Serialize)]
struct OutputNode {
    id: usize,
    edge_label: String,
    depth: usize,
    children: Vec<usize>,
    subtree_patterns: usize,
    subtree_weight: usize,
}

#[derive(Serialize)]
struct OutputTerminal {
    node_id: usize,
    prefix: String,
    digit_skeleton: String,
    count: usize,
    weight: usize,
    uses_path_count: usize,
    has_trailing_hash_count: usize,
    suffix_examples: Vec<String>,
    value_examples: Vec<String>,
    annotations: TerminalAnnotations,
}

#[derive(Default, Serialize)]
struct TerminalAnnotations {
    episode_title_suffixes: Vec<String>,
    media_suffixes: Vec<String>,
    title_candidates: Vec<String>,
    needs_llm_review: bool,
    llm_label: Option<String>,
    notes: Option<String>,
}

#[derive(Deserialize)]
struct SourceGraph {
    #[allow(dead_code)]
    meta: serde_json::Value,
    nodes: Vec<SourceNode>,
    terminals: Vec<SourceTerminal>,
}

#[derive(Deserialize)]
struct SourceNode {
    id: usize,
    edge_label: String,
    #[allow(dead_code)]
    depth: usize,
    #[serde(default)]
    children: Vec<usize>,
}

#[derive(Clone, Deserialize, Serialize)]
struct SourceTerminal {
    #[serde(default, skip_serializing_if = "Option::is_none")]
    terminal_id: Option<String>,
    node_id: usize,
    prefix: String,
    digit_skeleton: String,
    count: usize,
    weight: usize,
    uses_path_count: usize,
    has_trailing_hash_count: usize,
    suffix_examples: Vec<String>,
    value_examples: Vec<String>,
    #[serde(default = "default_annotations_value")]
    annotations: serde_json::Value,
}

#[derive(Serialize)]
struct DagOutput {
    meta: DagMeta,
    root: usize,
    nodes: Vec<DagNode>,
    terminals: Vec<DagTerminal>,
}

#[derive(Serialize)]
struct DagMeta {
    version: &'static str,
    input: String,
    output: String,
    source_nodes: usize,
    source_terminals: usize,
    dag_nodes: usize,
    dag_edges: usize,
    root: usize,
    max_depth: usize,
    merged_nodes: usize,
    preserves_digits: bool,
    merge_strategy: &'static str,
    notes: Vec<&'static str>,
}

#[derive(Clone, Serialize)]
struct DagNode {
    id: usize,
    terminal: bool,
    children: Vec<DagEdge>,
    incoming_count: usize,
    reachable_terminals: usize,
    reachable_weight: usize,
}

#[derive(Clone, Serialize)]
struct DagEdge {
    label: String,
    target: usize,
}

#[derive(Serialize)]
struct DagTerminal {
    terminal_id: String,
    node_id: usize,
    prefix: String,
    digit_skeleton: String,
    count: usize,
    weight: usize,
    uses_path_count: usize,
    has_trailing_hash_count: usize,
    suffix_examples: Vec<String>,
    value_examples: Vec<String>,
    annotations: serde_json::Value,
}

#[derive(Clone, Eq, Ord, PartialEq, PartialOrd)]
struct NodeSignature {
    terminal: bool,
    children: Vec<(String, usize)>,
}

#[derive(Clone)]
struct TempDagNode {
    terminal: bool,
    children: Vec<DagEdge>,
}

fn main() -> Result<()> {
    let args = Args::parse();
    if args.from_prefix_graph.is_some() || args.dag_output.is_some() {
        let dag = build_dag_from_args(&args)?;
        println!("{}", serde_json::to_string_pretty(&dag.meta)?);
    } else {
        let graph = build_graph(&args)?;
        println!("{}", serde_json::to_string_pretty(&graph.meta)?);
    }
    Ok(())
}

fn build_graph(args: &Args) -> Result<GraphOutput> {
    ensure_output_parent(&args.output)?;

    let records = read_records(&args.input)?;
    let input_records = records.len();

    let mut observations = records
        .par_iter()
        .enumerate()
        .filter_map(|(source_index, record)| build_observation(source_index, record))
        .collect::<Vec<_>>();

    observations.sort_by(|left, right| {
        left.prefix
            .cmp(&right.prefix)
            .then(left.source_index.cmp(&right.source_index))
    });

    let no_episode_prefix = input_records.saturating_sub(observations.len());
    let groups = aggregate_observations(&observations, args.min_count, args.example_count);
    let (nodes, terminals, max_depth, grouped_weight) = build_trie(&groups);

    let graph = GraphOutput {
        meta: Meta {
            input: display_path(&args.input),
            output: display_path(&args.output),
            input_records,
            observations: observations.len(),
            no_episode_prefix,
            groups: terminals.len(),
            nodes: nodes.len(),
            max_depth,
            grouped_weight,
            min_count: args.min_count,
            example_count: args.example_count,
            tokenizer: TokenizerMeta {
                version: RADIX_VERSION,
                notes: vec![
                    "Episode prefixes are detected with the legacy regex/boundary rules.",
                    "Graph insertion preserves original prefix digits; digit_skeleton is secondary metadata only.",
                    "Graph nodes form a compressed radix trie over complete original prefix strings.",
                    "Edge labels split only at actual branch points; punctuation and separators do not force levels.",
                ],
            },
        },
        nodes,
        terminals,
    };

    let output = File::create(&args.output)
        .with_context(|| format!("failed to create {}", args.output.display()))?;
    let writer = BufWriter::new(output);
    serde_json::to_writer_pretty(writer, &graph)
        .with_context(|| format!("failed to write {}", args.output.display()))?;

    Ok(graph)
}

fn build_dag_from_args(args: &Args) -> Result<DagOutput> {
    let input = args
        .from_prefix_graph
        .as_ref()
        .unwrap_or(&args.output)
        .to_path_buf();
    let output = args
        .dag_output
        .as_ref()
        .cloned()
        .unwrap_or_else(|| PathBuf::from("datasets\\AnimeName\\dmhy_prefix_dag.json"));

    build_dag(&input, &output)
}

fn build_dag(input_path: &Path, output_path: &Path) -> Result<DagOutput> {
    ensure_output_parent(output_path)?;

    let input = File::open(input_path)
        .with_context(|| format!("failed to open {}", input_path.display()))?;
    let reader = BufReader::new(input);
    let source: SourceGraph = serde_json::from_reader(reader)
        .with_context(|| format!("failed to parse {}", input_path.display()))?;

    validate_source_graph(&source)?;
    let dag = minimize_source_graph(&source, input_path, output_path)?;

    let output = File::create(output_path)
        .with_context(|| format!("failed to create {}", output_path.display()))?;
    let writer = BufWriter::new(output);
    serde_json::to_writer_pretty(writer, &dag)
        .with_context(|| format!("failed to write {}", output_path.display()))?;

    Ok(dag)
}

fn validate_source_graph(source: &SourceGraph) -> Result<()> {
    for (index, node) in source.nodes.iter().enumerate() {
        anyhow::ensure!(
            node.id == index,
            "source node id {} appears at index {}",
            node.id,
            index
        );
        for &child_id in &node.children {
            anyhow::ensure!(
                child_id < source.nodes.len(),
                "source node {} references missing child {}",
                node.id,
                child_id
            );
        }
    }

    for terminal in &source.terminals {
        anyhow::ensure!(
            terminal.node_id < source.nodes.len(),
            "terminal prefix {:?} references missing node {}",
            terminal.prefix,
            terminal.node_id
        );
    }

    Ok(())
}

fn minimize_source_graph(
    source: &SourceGraph,
    input_path: &Path,
    output_path: &Path,
) -> Result<DagOutput> {
    let terminal_source_nodes = source
        .terminals
        .iter()
        .map(|terminal| terminal.node_id)
        .collect::<BTreeSet<_>>();
    let postorder = source_postorder(source);
    let mut source_to_temp_dag = vec![usize::MAX; source.nodes.len()];
    let mut signatures = BTreeMap::<NodeSignature, usize>::new();
    let mut temp_nodes = Vec::<TempDagNode>::new();

    for source_id in postorder {
        let source_node = &source.nodes[source_id];
        let mut children = source_node
            .children
            .iter()
            .map(|&child_id| {
                let child = &source.nodes[child_id];
                let target = source_to_temp_dag[child_id];
                anyhow::ensure!(
                    target != usize::MAX,
                    "source child {} was not canonicalized before parent {}",
                    child_id,
                    source_id
                );
                Ok((child.edge_label.clone(), target))
            })
            .collect::<Result<Vec<_>>>()?;
        children.sort();

        let signature = NodeSignature {
            terminal: terminal_source_nodes.contains(&source_id),
            children,
        };

        let temp_id = if let Some(&existing) = signatures.get(&signature) {
            existing
        } else {
            let temp_id = temp_nodes.len();
            temp_nodes.push(TempDagNode {
                terminal: signature.terminal,
                children: signature
                    .children
                    .iter()
                    .map(|(label, target)| DagEdge {
                        label: label.clone(),
                        target: *target,
                    })
                    .collect(),
            });
            signatures.insert(signature, temp_id);
            temp_id
        };

        source_to_temp_dag[source_id] = temp_id;
    }

    let root_temp_id = source_to_temp_dag[0];
    let (temp_to_dag, mut dag_nodes) = renumber_dag(root_temp_id, &temp_nodes);
    for node in &mut dag_nodes {
        for edge in &mut node.children {
            edge.target = temp_to_dag[edge.target];
        }
    }

    let terminals = source
        .terminals
        .iter()
        .enumerate()
        .map(|(index, terminal)| {
            let temp_id = source_to_temp_dag[terminal.node_id];
            DagTerminal {
                terminal_id: terminal
                    .terminal_id
                    .clone()
                    .unwrap_or_else(|| format!("t{}", index)),
                node_id: temp_to_dag[temp_id],
                prefix: terminal.prefix.clone(),
                digit_skeleton: terminal.digit_skeleton.clone(),
                count: terminal.count,
                weight: terminal.weight,
                uses_path_count: terminal.uses_path_count,
                has_trailing_hash_count: terminal.has_trailing_hash_count,
                suffix_examples: terminal.suffix_examples.clone(),
                value_examples: terminal.value_examples.clone(),
                annotations: terminal.annotations.clone(),
            }
        })
        .collect::<Vec<_>>();

    fill_dag_counts(&source, &source_to_temp_dag, &temp_to_dag, &mut dag_nodes);
    let dag_edges = dag_nodes.iter().map(|node| node.children.len()).sum();
    let max_depth = dag_max_depth(&dag_nodes);

    Ok(DagOutput {
        meta: DagMeta {
            version: DAG_VERSION,
            input: display_path(input_path),
            output: display_path(output_path),
            source_nodes: source.nodes.len(),
            source_terminals: source.terminals.len(),
            dag_nodes: dag_nodes.len(),
            dag_edges,
            root: 0,
            max_depth,
            merged_nodes: source.nodes.len().saturating_sub(dag_nodes.len()),
            preserves_digits: true,
            merge_strategy:
                "bottom-up suffix equivalence over radix trie nodes; edge labels remain raw substrings",
            notes: vec![
                "Terminal prefixes and digit_skeleton values are copied from the source graph; digits are not normalized for merging.",
                "Node reachable_terminals and reachable_weight count terminal instances mapped onto the shared DAG suffix, so shared nodes report aggregate suffix usage rather than one caller-specific path.",
            ],
        },
        root: 0,
        nodes: dag_nodes,
        terminals,
    })
}

fn source_postorder(source: &SourceGraph) -> Vec<usize> {
    let mut order = Vec::with_capacity(source.nodes.len());
    let mut stack = vec![(0, false)];
    while let Some((node_id, expanded)) = stack.pop() {
        if expanded {
            order.push(node_id);
        } else {
            stack.push((node_id, true));
            for &child_id in source.nodes[node_id].children.iter().rev() {
                stack.push((child_id, false));
            }
        }
    }
    order
}

fn renumber_dag(root_temp_id: usize, temp_nodes: &[TempDagNode]) -> (Vec<usize>, Vec<DagNode>) {
    let mut temp_to_dag = vec![usize::MAX; temp_nodes.len()];
    let mut dag_nodes = Vec::<DagNode>::new();
    let mut stack = vec![root_temp_id];

    while let Some(temp_id) = stack.pop() {
        if temp_to_dag[temp_id] != usize::MAX {
            continue;
        }

        let dag_id = dag_nodes.len();
        temp_to_dag[temp_id] = dag_id;
        dag_nodes.push(DagNode {
            id: dag_id,
            terminal: temp_nodes[temp_id].terminal,
            children: temp_nodes[temp_id].children.clone(),
            incoming_count: 0,
            reachable_terminals: 0,
            reachable_weight: 0,
        });

        for edge in temp_nodes[temp_id].children.iter().rev() {
            stack.push(edge.target);
        }
    }

    (temp_to_dag, dag_nodes)
}

fn fill_dag_counts(
    source: &SourceGraph,
    source_to_temp_dag: &[usize],
    temp_to_dag: &[usize],
    nodes: &mut [DagNode],
) {
    let mut terminal_ids_by_node = vec![BTreeSet::<usize>::new(); nodes.len()];

    let all_edges = nodes
        .iter()
        .flat_map(|node| node.children.iter().map(|edge| edge.target))
        .collect::<Vec<_>>();
    for target in all_edges {
        nodes[target].incoming_count += 1;
    }

    let source_parents = source_parent_map(source);
    for (terminal_index, terminal) in source.terminals.iter().enumerate() {
        let mut source_node_id = Some(terminal.node_id);
        while let Some(node_id) = source_node_id {
            let temp_id = source_to_temp_dag[node_id];
            let dag_id = temp_to_dag[temp_id];
            terminal_ids_by_node[dag_id].insert(terminal_index);
            source_node_id = source_parents[node_id];
        }
    }

    for (node_id, terminal_ids) in terminal_ids_by_node.into_iter().enumerate() {
        nodes[node_id].reachable_terminals = terminal_ids.len();
        nodes[node_id].reachable_weight = terminal_ids
            .into_iter()
            .map(|terminal_id| source.terminals[terminal_id].weight)
            .sum();
    }
}

fn source_parent_map(source: &SourceGraph) -> Vec<Option<usize>> {
    let mut parents = vec![None; source.nodes.len()];
    for node in &source.nodes {
        for &child_id in &node.children {
            parents[child_id] = Some(node.id);
        }
    }
    parents
}

fn dag_max_depth(nodes: &[DagNode]) -> usize {
    let mut max_depth = 0;
    let mut stack = vec![(0, 0)];
    while let Some((node_id, depth)) = stack.pop() {
        max_depth = max_depth.max(depth);
        for edge in &nodes[node_id].children {
            stack.push((edge.target, depth + 1));
        }
    }
    max_depth
}

fn ensure_output_parent(output: &Path) -> Result<()> {
    if let Some(parent) = output.parent() {
        if !parent.as_os_str().is_empty() {
            fs::create_dir_all(parent)
                .with_context(|| format!("failed to create {}", parent.display()))?;
        }
    }
    Ok(())
}

fn read_records(input_path: &Path) -> Result<Vec<InputRecord>> {
    let input = File::open(input_path)
        .with_context(|| format!("failed to open {}", input_path.display()))?;
    let reader = BufReader::new(input);
    let mut records = Vec::new();

    for (line_number, line) in reader.lines().enumerate() {
        let line = line.with_context(|| {
            format!(
                "failed to read line {} from {}",
                line_number + 1,
                input_path.display()
            )
        })?;
        let line = line.trim();
        if line.is_empty() {
            continue;
        }

        let record = serde_json::from_str(line).with_context(|| {
            format!(
                "failed to parse line {} from {}",
                line_number + 1,
                input_path.display()
            )
        })?;
        records.push(record);
    }

    Ok(records)
}

fn build_observation(source_index: usize, record: &InputRecord) -> Option<PatternObservation> {
    let (prefix, suffix) = find_episode_prefix(&record.value)?;
    if prefix.is_empty() {
        return None;
    }
    let digit_skeleton = digit_skeleton(&prefix);

    Some(PatternObservation {
        source_index,
        prefix,
        digit_skeleton,
        suffix,
        value: record.value.clone(),
        uses_path: record.uses_path,
        has_trailing_hash: record.has_trailing_hash,
        count: record.count,
    })
}

fn aggregate_observations(
    observations: &[PatternObservation],
    min_count: usize,
    example_count: usize,
) -> Vec<GroupBuilder> {
    let mut groups = BTreeMap::<String, GroupBuilder>::new();

    for observation in observations {
        let group = groups
            .entry(observation.prefix.clone())
            .or_insert_with(|| GroupBuilder {
                prefix: observation.prefix.clone(),
                digit_skeleton: observation.digit_skeleton.clone(),
                ..GroupBuilder::default()
            });

        group.count += 1;
        group.weight += observation.count;
        group.uses_path_count += observation.count * usize::from(observation.uses_path);
        group.has_trailing_hash_count +=
            observation.count * usize::from(observation.has_trailing_hash);
        if !observation.suffix.is_empty() && group.suffix_examples.len() < example_count {
            group.suffix_examples.push(observation.suffix.clone());
        }
        if group.value_examples.len() < example_count {
            group.value_examples.push(observation.value.clone());
        }
    }

    groups
        .into_values()
        .filter(|group| group.count >= min_count)
        .collect()
}

fn build_trie(groups: &[GroupBuilder]) -> (Vec<OutputNode>, Vec<OutputTerminal>, usize, usize) {
    let mut nodes = vec![TrieNode::root()];
    let mut terminal_node_ids = Vec::with_capacity(groups.len());

    for group in groups {
        let (terminal_node_id, path) = insert_prefix(&mut nodes, &group.prefix);
        terminal_node_ids.push(terminal_node_id);

        for id in path {
            nodes[id].subtree_patterns += group.count;
            nodes[id].subtree_weight += group.weight;
        }
    }

    assign_depths(&mut nodes);

    let terminals = groups
        .iter()
        .zip(terminal_node_ids)
        .map(|(group, node_id)| OutputTerminal {
            node_id,
            prefix: group.prefix.clone(),
            digit_skeleton: group.digit_skeleton.clone(),
            count: group.count,
            weight: group.weight,
            uses_path_count: group.uses_path_count,
            has_trailing_hash_count: group.has_trailing_hash_count,
            suffix_examples: group.suffix_examples.clone(),
            value_examples: group.value_examples.clone(),
            annotations: TerminalAnnotations::default(),
        })
        .collect::<Vec<_>>();

    let max_depth = nodes.iter().map(|node| node.depth).max().unwrap_or(0);
    let grouped_weight = groups.iter().map(|group| group.weight).sum();
    let output_nodes = nodes
        .into_iter()
        .map(|node| OutputNode {
            id: node.id,
            edge_label: node.edge_label,
            depth: node.depth,
            children: node.children_by_label.into_values().collect(),
            subtree_patterns: node.subtree_patterns,
            subtree_weight: node.subtree_weight,
        })
        .collect();

    (output_nodes, terminals, max_depth, grouped_weight)
}

impl TrieNode {
    fn root() -> Self {
        Self {
            id: 0,
            edge_label: String::new(),
            depth: 0,
            parent: None,
            children_by_label: BTreeMap::new(),
            subtree_patterns: 0,
            subtree_weight: 0,
        }
    }
}

fn insert_prefix(nodes: &mut Vec<TrieNode>, prefix: &str) -> (usize, Vec<usize>) {
    let mut current = 0;
    let mut remaining = prefix;
    let mut path = vec![current];

    loop {
        if remaining.is_empty() {
            return (current, path);
        }

        let matching_child =
            nodes[current]
                .children_by_label
                .iter()
                .find_map(|(label, &child_id)| {
                    let common_len = common_prefix_len(remaining, label);
                    (common_len > 0).then(|| (label.clone(), child_id, common_len))
                });

        let Some((child_label, child_id, common_len)) = matching_child else {
            let child_id = push_node(nodes, current, remaining.to_owned());
            nodes[current]
                .children_by_label
                .insert(remaining.to_owned(), child_id);
            path.push(child_id);
            return (child_id, path);
        };

        if common_len == child_label.len() {
            current = child_id;
            remaining = &remaining[common_len..];
            path.push(current);
            continue;
        }

        let shared_label = child_label[..common_len].to_owned();
        let old_suffix = child_label[common_len..].to_owned();
        let new_suffix = remaining[common_len..].to_owned();

        let split_id = push_node(nodes, current, shared_label.clone());
        nodes[current].children_by_label.remove(&child_label);
        nodes[current]
            .children_by_label
            .insert(shared_label, split_id);

        nodes[child_id].edge_label = old_suffix.clone();
        nodes[child_id].parent = Some(split_id);
        nodes[split_id].subtree_patterns = nodes[child_id].subtree_patterns;
        nodes[split_id].subtree_weight = nodes[child_id].subtree_weight;
        nodes[split_id]
            .children_by_label
            .insert(old_suffix, child_id);

        path.push(split_id);
        if new_suffix.is_empty() {
            return (split_id, path);
        }

        let new_child_id = push_node(nodes, split_id, new_suffix.clone());
        nodes[split_id]
            .children_by_label
            .insert(new_suffix, new_child_id);
        path.push(new_child_id);
        return (new_child_id, path);
    }
}

fn push_node(nodes: &mut Vec<TrieNode>, parent_id: usize, edge_label: String) -> usize {
    let child_id = nodes.len();
    nodes.push(TrieNode {
        id: child_id,
        edge_label,
        depth: nodes[parent_id].depth + 1,
        parent: Some(parent_id),
        children_by_label: BTreeMap::new(),
        subtree_patterns: 0,
        subtree_weight: 0,
    });
    child_id
}

fn common_prefix_len(left: &str, right: &str) -> usize {
    let mut len = 0;
    for ((left_index, left_ch), (_, right_ch)) in left.char_indices().zip(right.char_indices()) {
        if left_ch != right_ch {
            break;
        }
        len = left_index + left_ch.len_utf8();
    }
    len
}

fn assign_depths(nodes: &mut [TrieNode]) {
    let mut stack = vec![(0, 0)];
    while let Some((node_id, depth)) = stack.pop() {
        nodes[node_id].depth = depth;
        let child_ids = nodes[node_id]
            .children_by_label
            .values()
            .copied()
            .collect::<Vec<_>>();
        for child_id in child_ids {
            stack.push((child_id, depth + 1));
        }
    }
}

fn find_episode_prefix(value: &str) -> Option<(String, String)> {
    let best_end = EPISODE_PATTERNS
        .iter()
        .filter_map(|pattern| pattern.find(value).map(|matched| matched.end()))
        .chain(find_delimited_number_episode_end(value))
        .max()?;

    let prefix = value[..best_end].trim_end().to_owned();
    let suffix = value[best_end..].trim().to_owned();
    Some((prefix, suffix))
}

fn find_delimited_number_episode_end(value: &str) -> Option<usize> {
    let mut digits_start = None;
    let mut digit_count = 0;

    for (index, ch) in value
        .char_indices()
        .chain(std::iter::once((value.len(), '\0')))
    {
        if ch.is_ascii_digit() {
            if digits_start.is_none() {
                digits_start = Some(index);
            }
            digit_count += 1;
            continue;
        }

        if let Some(start) = digits_start {
            if (1..=4).contains(&digit_count)
                && has_episode_left_boundary(value, start)
                && has_episode_right_boundary(ch)
            {
                return Some(index);
            }
        }

        digits_start = None;
        digit_count = 0;
    }

    None
}

fn has_episode_left_boundary(value: &str, digits_start: usize) -> bool {
    if digits_start == 0 {
        return true;
    }

    value[..digits_start]
        .chars()
        .next_back()
        .is_some_and(|ch| ch.is_whitespace() || matches!(ch, '.' | '_' | '-'))
}

fn has_episode_right_boundary(ch: char) -> bool {
    ch == '\0'
        || ch.is_whitespace()
        || matches!(ch, '.' | '_' | '-' | ']' | ')' | '【' | '】' | '[')
}

fn digit_skeleton(text: &str) -> String {
    DIGITS.replace_all(text, "<NUM>").into_owned()
}

fn display_path(path: &Path) -> String {
    path.display().to_string()
}

fn default_count() -> usize {
    1
}

fn default_annotations_value() -> serde_json::Value {
    serde_json::json!({})
}

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

    #[test]
    fn dag_merges_equal_suffix_nodes_without_normalizing_digits() {
        let source = SourceGraph {
            meta: serde_json::json!({}),
            nodes: vec![
                SourceNode {
                    id: 0,
                    edge_label: String::new(),
                    depth: 0,
                    children: vec![1, 3],
                },
                SourceNode {
                    id: 1,
                    edge_label: "A01".to_owned(),
                    depth: 1,
                    children: vec![2],
                },
                SourceNode {
                    id: 2,
                    edge_label: "X".to_owned(),
                    depth: 2,
                    children: vec![],
                },
                SourceNode {
                    id: 3,
                    edge_label: "B02".to_owned(),
                    depth: 1,
                    children: vec![4],
                },
                SourceNode {
                    id: 4,
                    edge_label: "X".to_owned(),
                    depth: 2,
                    children: vec![],
                },
            ],
            terminals: vec![
                SourceTerminal {
                    terminal_id: None,
                    node_id: 2,
                    prefix: "A01X".to_owned(),
                    digit_skeleton: "A<NUM>X".to_owned(),
                    count: 1,
                    weight: 1,
                    uses_path_count: 0,
                    has_trailing_hash_count: 0,
                    suffix_examples: vec![],
                    value_examples: vec!["A01X".to_owned()],
                    annotations: serde_json::json!({}),
                },
                SourceTerminal {
                    terminal_id: None,
                    node_id: 4,
                    prefix: "B02X".to_owned(),
                    digit_skeleton: "B<NUM>X".to_owned(),
                    count: 1,
                    weight: 1,
                    uses_path_count: 0,
                    has_trailing_hash_count: 0,
                    suffix_examples: vec![],
                    value_examples: vec!["B02X".to_owned()],
                    annotations: serde_json::json!({}),
                },
            ],
        };

        let dag = minimize_source_graph(
            &source,
            Path::new("dmhy_prefix_graph.json"),
            Path::new("dmhy_prefix_dag.json"),
        )
        .unwrap();

        assert!(dag.meta.preserves_digits);
        assert!(dag.meta.merged_nodes >= 2);
        assert_eq!(dag.terminals[0].prefix, "A01X");
        assert_eq!(dag.terminals[1].prefix, "B02X");
        assert_eq!(dag.terminals[0].node_id, dag.terminals[1].node_id);

        let shared_parent_targets = dag.nodes[0]
            .children
            .iter()
            .filter(|edge| edge.label == "A01" || edge.label == "B02")
            .map(|edge| edge.target)
            .collect::<BTreeSet<_>>();
        assert_eq!(shared_parent_targets.len(), 1);

        let shared_parent = shared_parent_targets.into_iter().next().unwrap();
        assert_eq!(dag.nodes[shared_parent].children.len(), 1);
        assert_eq!(dag.nodes[shared_parent].children[0].label, "X");
        assert_eq!(dag.nodes[shared_parent].reachable_terminals, 2);
        assert_eq!(dag.nodes[shared_parent].reachable_weight, 2);
    }
}