use serde::Serialize;
use std::collections::HashMap;
use std::io::BufRead;
use std::path::Path;

/// Statistics derived from a Claude Code transcript JSONL file.
#[derive(Debug, Default, Clone, Serialize)]
pub struct TranscriptStats {
    pub total_tool_uses: u64,
    pub total_turns: u64,
    pub last_tool_name: Option<String>,
    /// Per-tool counts sorted by count descending.
    pub tool_counts: Vec<(String, u64)>,
}

/// Cached format: "tools:N,turns:N,last:Name;ToolA=C,ToolB=C,..."
impl TranscriptStats {
    pub fn to_cache_string(&self) -> String {
        let mut s = format!("tools:{},turns:{}", self.total_tool_uses, self.total_turns);
        if let Some(name) = &self.last_tool_name {
            s.push_str(&format!(",last:{name}"));
        }
        if !self.tool_counts.is_empty() {
            s.push(';');
            let parts: Vec<String> = self
                .tool_counts
                .iter()
                .map(|(name, count)| format!("{name}={count}"))
                .collect();
            s.push_str(&parts.join(","));
        }
        s
    }

    pub fn from_cache_string(s: &str) -> Option<Self> {
        let mut stats = Self::default();

        // Split on ';' — first part is summary, second is per-tool counts
        let (summary, breakdown) = s.split_once(';').unwrap_or((s, ""));

        for part in summary.split(',') {
            if let Some((key, val)) = part.split_once(':') {
                match key {
                    "tools" => stats.total_tool_uses = val.parse().unwrap_or(0),
                    "turns" => stats.total_turns = val.parse().unwrap_or(0),
                    "last" => {
                        if !val.is_empty() {
                            stats.last_tool_name = Some(val.to_string());
                        }
                    }
                    _ => {}
                }
            }
        }

        if !breakdown.is_empty() {
            for part in breakdown.split(',') {
                if let Some((name, count_str)) = part.split_once('=') {
                    let count: u64 = count_str.parse().unwrap_or(0);
                    if count > 0 {
                        stats.tool_counts.push((name.to_string(), count));
                    }
                }
            }
        }

        Some(stats)
    }
}

/// Parse a Claude Code transcript JSONL file and extract tool use and turn counts.
/// `skip_lines` skips that many lines from the start (used after /clear to ignore
/// pre-clear entries in the same transcript file).
///
/// Transcript format (one JSON object per line):
/// - `{"type": "user", ...}` — a user turn
/// - `{"type": "assistant", "message": {"content": [{"type": "tool_use", "name": "Read"}, ...]}}` — tool uses
pub fn parse_transcript(path: &Path, skip_lines: usize) -> Option<TranscriptStats> {
    let file = std::fs::File::open(path).ok()?;
    let reader = std::io::BufReader::new(file);

    let mut stats = TranscriptStats::default();
    let mut counts: HashMap<String, u64> = HashMap::new();

    for line in reader.lines().skip(skip_lines) {
        let line = match line {
            Ok(l) => l,
            Err(_) => continue,
        };
        if line.is_empty() {
            continue;
        }

        let v: serde_json::Value = match serde_json::from_str(&line) {
            Ok(v) => v,
            Err(_) => continue,
        };

        let msg_type = v.get("type").and_then(|t| t.as_str()).unwrap_or("");

        match msg_type {
            "user" => {
                stats.total_turns += 1;
            }
            "assistant" => {
                if let Some(content) = v
                    .get("message")
                    .and_then(|m| m.get("content"))
                    .and_then(|c| c.as_array())
                {
                    for block in content {
                        if block.get("type").and_then(|t| t.as_str()) == Some("tool_use") {
                            stats.total_tool_uses += 1;
                            if let Some(name) = block.get("name").and_then(|n| n.as_str()) {
                                stats.last_tool_name = Some(name.to_string());
                                *counts.entry(name.to_string()).or_insert(0) += 1;
                            }
                        }
                    }
                }
            }
            _ => {}
        }
    }

    // Sort by count descending
    let mut sorted: Vec<(String, u64)> = counts.into_iter().collect();
    sorted.sort_by(|a, b| b.1.cmp(&a.1));
    stats.tool_counts = sorted;

    Some(stats)
}