mdx_rust_core/

optimizer.rs

//! The core optimization loop (Phase 3).
//!
//! High-level flow (per the approved plan):
//! 1. Run the agent on the dataset while collecting rich traces.
//! 2. Score outputs (mechanical rules + optional LLM-as-Judge).
//! 3. Diagnose failures using a strong model + policy + traces + code bundle.
//! 4. Generate N targeted candidate fixes (different focus areas).
//! 5. Validate candidates safely (cargo check + clippy + smoke tests in worktree).
//! 6. Evaluate survivors on the full dataset.
//! 7. Accept only net-positive changes with regression guards + holdout set.
//!
//! This module is currently a structural skeleton. Real implementations of
//! the individual steps will be filled in as the analysis crate and LLM
//! client mature.

use crate::registry::RegisteredAgent;
use crate::runner::AgentRunResult;
use crate::safety_pipeline::{
    execute_candidate_edit, CandidateExecutionConfig, CandidateExecutionContext,
};
use crate::{
    diagnose_run, split_dataset, EvaluationDataset, ExperimentLedger, FailureKind, HookDecision,
    HookPolicy, OptimizationBudget, PromptVariantRecord, ScorerMetadata, TraceDiagnosis,
};
use mdx_rust_analysis::editing::ProposedEdit;
use mdx_rust_analysis::editing::ValidationCommandRecord;
use mdx_rust_analysis::AgentBundle;
use serde::{Deserialize, Serialize};
use std::path::{Path, PathBuf};
use std::time::Duration;

/// Generate a proper unified diff with surrounding context for a preamble string change.
/// This produces something `git apply` can reliably use.
fn generate_preamble_patch(file_path: &Path, source: &str, old: &str, new: &str) -> String {
    let diff_path = file_path.to_string_lossy();

    if !source.contains(old) {
        // Fallback: still produce something the later fallback in apply_patch can use
        return format!(
            "diff --git a/{diff_path} b/{diff_path}\n--- a/{diff_path}\n+++ b/{diff_path}\n@@ -1,1 +1,1 @@\n-{old}\n+{new}\n"
        );
    }

    let lines: Vec<&str> = source.lines().collect();
    let mut patch_lines = Vec::new();
    patch_lines.push(format!("diff --git a/{diff_path} b/{diff_path}"));
    patch_lines.push(format!("--- a/{diff_path}"));
    patch_lines.push(format!("+++ b/{diff_path}"));

    // Find the line containing the old preamble
    let mut hunk_start = 0usize;
    let mut old_line_idx = None;
    for (i, line) in lines.iter().enumerate() {
        if line.contains(old) {
            old_line_idx = Some(i);
            hunk_start = i.saturating_sub(3);
            break;
        }
    }

    if let Some(idx) = old_line_idx {
        let context_before = &lines[hunk_start..idx];
        let context_after = if idx + 1 < lines.len() {
            &lines[idx + 1..(idx + 1 + 3).min(lines.len())]
        } else {
            &[][..]
        };

        let new_line = lines[idx].replace(old, new);

        let hunk_header = format!(
            "@@ -{},{} +{},{} @@",
            hunk_start + 1,
            context_before.len() + 1 + context_after.len(),
            hunk_start + 1,
            context_before.len() + 1 + context_after.len()
        );
        patch_lines.push(hunk_header);

        for l in context_before {
            patch_lines.push(format!(" {}", l));
        }
        patch_lines.push(format!("-{}", lines[idx]));
        patch_lines.push(format!("+{}", new_line));
        for l in context_after {
            patch_lines.push(format!(" {}", l));
        }
    } else {
        // very minimal fallback
        patch_lines.push("@@ -1,1 +1,1 @@".to_string());
        patch_lines.push(format!("-{}", old));
        patch_lines.push(format!("+{}", new));
    }

    patch_lines.join("\n")
}

/// Configuration for a single optimization run.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct OptimizeConfig {
    pub max_iterations: u32,
    pub candidates_per_iteration: u32,
    pub use_llm_judge: bool,
    #[serde(default)]
    pub budget: OptimizationBudget,
    #[serde(default)]
    pub hook_policy: HookPolicy,
    /// When true, the optimizer will print proposed changes and wait for confirmation before applying (Phase 4 review gate).
    #[serde(default)]
    pub review_before_apply: bool,
    /// When true, suppress all human progress output (used for --json mode).
    #[serde(default)]
    pub quiet: bool,
    #[serde(skip, default = "default_candidate_timeout")]
    pub candidate_timeout: Duration,
}

/// A single optimization experiment / iteration result.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct OptimizationRun {
    pub iteration: u32,
    pub scores: Vec<f32>,
    /// Number of changes that were fully validated in isolation
    pub validated_changes: u32,
    /// Number of changes that were successfully landed on the real agent tree
    pub landed_changes: u32,
    /// Number of changes that were accepted (landed + final validation + net-positive)
    pub accepted_changes: u32,
    pub notes: String,
    pub candidates: Vec<Candidate>,
    /// Optional unified diff of the last accepted change
    #[serde(default)]
    pub diff: Option<String>,
    #[serde(default)]
    pub policy_hash: Option<String>,
    #[serde(default)]
    pub dataset_version: Option<String>,
    #[serde(default)]
    pub dataset_hash: Option<String>,
    // Net-positive evaluation (P1 stabilization)
    #[serde(default)]
    pub baseline_score: Option<f32>,
    #[serde(default)]
    pub patched_score: Option<f32>,
    #[serde(default)]
    pub score_delta: Option<f32>,

    // Real provenance (P1 requirement) — populated when a change is accepted
    #[serde(default)]
    pub git_sha_before: Option<String>,
    #[serde(default)]
    pub git_sha_after: Option<String>,
    #[serde(default)]
    pub diff_hash: Option<String>,
    #[serde(default)]
    pub working_tree_dirty_after: Option<bool>,
    #[serde(default)]
    pub scorer: Option<String>,
    #[serde(default)]
    pub validation_commands: Option<Vec<String>>,
    #[serde(default)]
    pub validation_command_records: Vec<ValidationCommandRecord>,
    #[serde(default)]
    pub final_validation_command_records: Vec<ValidationCommandRecord>,
    #[serde(default)]
    pub trace_diagnosis: Vec<TraceDiagnosis>,
    #[serde(default)]
    pub hook_decisions: Vec<HookDecision>,
    #[serde(default)]
    pub ledger: Option<ExperimentLedger>,
    #[serde(default)]
    pub holdout_score: Option<f32>,
    #[serde(default)]
    pub budget: Option<OptimizationBudget>,
    #[serde(default)]
    pub policy_path: Option<String>,
    #[serde(default)]
    pub model: Option<ModelProvenance>,
    #[serde(default)]
    pub rollback_succeeded: Option<bool>,
    #[serde(default)]
    pub rollback_error: Option<String>,
    #[serde(default)]
    pub candidate_timed_out: bool,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ModelProvenance {
    pub role: String,
    pub provider: String,
    pub model: String,
    pub used: bool,
}

/// A proposed improvement generated during an optimization iteration.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Candidate {
    pub focus: String, // e.g. "system_prompt", "tool_descriptions", "reasoning_step"
    pub description: String,
    pub expected_improvement: String,
    #[serde(default)]
    pub strategy: Option<EditStrategy>,
}

#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
pub enum EditStrategy {
    SystemPrompt,
    ToolDescription,
    FallbackLogic,
    OutputSchema,
    ModelConfig,
}

fn default_candidate_timeout() -> Duration {
    Duration::from_secs(300)
}

/// Placeholder for the full optimization engine.
/// In a real implementation this would orchestrate:
/// - the runner
/// - the analysis crate (for bundling + editing)
/// - an LLM client (for diagnosis + candidate generation)
/// - the safe editing/validation pipeline
pub async fn run_optimization(
    agent: &RegisteredAgent,
    config: &OptimizeConfig,
) -> anyhow::Result<Vec<OptimizationRun>> {
    let mut runs = vec![];

    let dataset = EvaluationDataset::synthetic_v1();
    let split = split_dataset(&dataset, config.budget);
    let mut ledger = ExperimentLedger::new(config.budget, &dataset, &split);
    let dataset_hash = dataset.content_hash();
    let scorer = ScorerMetadata::mechanical_v1();
    let test_inputs: Vec<serde_json::Value> = split
        .train
        .iter()
        .map(|sample| sample.input.clone())
        .collect();
    let holdout_inputs: Vec<serde_json::Value> = split
        .holdout
        .iter()
        .map(|sample| sample.input.clone())
        .collect();

    // Baseline evaluation (computed once for net-positive comparison)
    let baseline_score: f32 = {
        let mut total = 0.0f32;
        for input in &test_inputs {
            if let Ok(res) = crate::runner::run_agent(agent, input.clone()).await {
                total += mechanical_score(&res);
            }
        }
        if test_inputs.is_empty() {
            0.0
        } else {
            total / test_inputs.len() as f32
        }
    };

    // Provenance: git sha before any optimization changes (P1 requirement)
    let git_sha_before: Option<String> = std::process::Command::new("git")
        .current_dir(&agent.path)
        .args(["rev-parse", "--short", "HEAD"])
        .output()
        .ok()
        .and_then(|o| {
            if o.status.success() {
                Some(String::from_utf8_lossy(&o.stdout).trim().to_string())
            } else {
                None
            }
        });
    let policy_info = load_policy_info(&agent.name);

    for iteration in 0..config.max_iterations {
        let mut scores_this_iter = vec![];
        let mut accepted_patched: Option<f32> = None;
        let mut accepted_delta: Option<f32> = None;
        let mut validated = 0;
        let mut landed = 0;
        let mut trace_diagnoses = Vec::new();
        let mut hook_decisions = Vec::new();
        let mut accepted_holdout_score = None;
        let mut accepted_validation_commands = Vec::new();
        let mut accepted_final_validation_commands = Vec::new();
        let mut accepted_rollback_succeeded = None;
        let mut accepted_rollback_error = None;
        let mut any_candidate_timed_out = false;

        for input in &test_inputs {
            let run_result = crate::runner::run_agent(agent, input.clone()).await?;
            trace_diagnoses.push(diagnose_run(&run_result));
            let score = mechanical_score(&run_result);
            scores_this_iter.push(score);
        }

        let avg_score: f32 = if scores_this_iter.is_empty() {
            0.0
        } else {
            scores_this_iter.iter().sum::<f32>() / scores_this_iter.len() as f32
        };

        // Rich analysis: extract real preambles, tools, entrypoints
        let rich_bundle = mdx_rust_analysis::analyze_agent(&agent.path, None).ok();
        let file_count = rich_bundle
            .as_ref()
            .map(|b| b.scope.optimizable_paths.len())
            .unwrap_or(0);

        // Build a high-signal summary for the LLM
        let bundle_summary = if let Some(ref b) = rich_bundle {
            let mut s = format!(
                "{} source files, Rig agent = {}",
                file_count, b.is_rig_agent
            );
            if !b.preambles.is_empty() {
                s.push_str(&format!(
                    ", current preambles: {:?}",
                    b.preambles.iter().map(|p| &p.text).collect::<Vec<_>>()
                ));
            }
            if !b.tools.is_empty() {
                s.push_str(&format!(
                    ", tools: {:?}",
                    b.tools.iter().map(|t| &t.name).collect::<Vec<_>>()
                ));
            }
            s
        } else {
            format!("{} source files (limited analysis)", file_count)
        };

        let llm = crate::llm::LlmClient::default();
        let diag_req = crate::llm::DiagnosisRequest {
            policy: "Improve the agent so it gives high-quality, reasoned answers instead of echoing. Prefer explicit step-by-step reasoning in the system prompt.".to_string(),
            bundle_summary,
            traces_summary: summarize_trace_diagnoses(&trace_diagnoses),
            scores: scores_this_iter.clone(),
        };

        let diagnosis_result = llm.diagnose(diag_req).await;
        let diagnosis_model_used = diagnosis_result.is_ok();
        let diagnosis = diagnosis_result.ok();

        let mut candidates = vec![];
        let mut accepted = 0;
        let mut notes = format!(
            "Avg score this iter: {:.2} ({} files in bundle)",
            avg_score, file_count
        );
        let mut accepted_diff: Option<String> = None;

        if let Some(d) = diagnosis {
            notes.push_str(&format!(" → LLM: {}", d.summary));
            for c in d.candidates {
                let strategy = strategy_for_focus(&c.focus);
                candidates.push(Candidate {
                    focus: c.focus,
                    description: c.description,
                    expected_improvement: c.expected_improvement,
                    strategy: Some(strategy),
                });
            }
        } else {
            candidates = fallback_candidates_from_trace(&trace_diagnoses);
        }

        if !candidates.is_empty() {
            let candidate_limit = config
                .budget
                .candidate_limit(config.candidates_per_iteration);
            for (candidate_index, candidate) in candidates.iter().take(candidate_limit).enumerate()
            {
                if accepted > 0 {
                    break;
                }

                let Some(edit) =
                    build_edit_for_candidate(&agent.path, rich_bundle.as_ref(), candidate)?
                else {
                    notes.push_str(&format!(
                        " (candidate {} skipped: no safe edit plan for {:?})",
                        candidate.focus, candidate.strategy
                    ));
                    continue;
                };

                notes.push_str(&format!(
                    " → Candidate {}: {} ({:?})",
                    candidate_index + 1,
                    candidate.focus,
                    candidate.strategy
                ));

                ledger.record_variant(PromptVariantRecord::from_patch(
                    format!("{:?}", candidate.strategy),
                    edit.file.display().to_string(),
                    edit.description.clone(),
                    &edit.patch,
                ));

                let outcome = execute_candidate_edit(CandidateExecutionContext {
                    agent,
                    config: CandidateExecutionConfig {
                        hook_policy: &config.hook_policy,
                        review_before_apply: config.review_before_apply,
                        quiet: config.quiet,
                        candidate_timeout: config.candidate_timeout,
                    },
                    iteration,
                    candidate_index,
                    edit: &edit,
                    test_inputs: &test_inputs,
                    holdout_inputs: &holdout_inputs,
                    baseline_score,
                    scorer: mechanical_score,
                })
                .await;

                validated += outcome.validated;
                landed += outcome.landed;
                any_candidate_timed_out |= outcome.timed_out;
                hook_decisions.extend(outcome.hook_decisions);

                if outcome.accepted > 0 {
                    accepted = outcome.accepted;
                    accepted_diff = outcome.accepted_diff;
                    accepted_patched = outcome.patched_score;
                    accepted_delta = outcome.delta;
                    accepted_holdout_score = outcome.holdout_score;
                    accepted_validation_commands = outcome.validation_commands;
                    accepted_final_validation_commands = outcome.final_validation_commands;
                    accepted_rollback_succeeded = outcome.rollback_succeeded;
                    accepted_rollback_error = outcome.rollback_error;
                }

                notes.push_str(&outcome.note);
            }
        } else {
            accepted = 0; // No change was proposed or needed
            notes.push_str(" → No new candidates — current behavior is good (no change applied)");
        }

        let (run_baseline, run_patched, run_delta) = if accepted > 0 {
            (Some(baseline_score), accepted_patched, accepted_delta)
        } else {
            (None, None, None)
        };

        // Populate real provenance when we accepted a change (P1)
        let (prov_before, prov_after, prov_diff_hash, prov_dirty, prov_scorer, prov_cmds) =
            if accepted > 0 {
                let after = std::process::Command::new("git")
                    .current_dir(&agent.path)
                    .args(["rev-parse", "--short", "HEAD"])
                    .output()
                    .ok()
                    .and_then(|o| {
                        if o.status.success() {
                            Some(String::from_utf8_lossy(&o.stdout).trim().to_string())
                        } else {
                            None
                        }
                    });
                let dirty_after = std::process::Command::new("git")
                    .current_dir(&agent.path)
                    .args(["status", "--porcelain"])
                    .output()
                    .ok()
                    .filter(|output| output.status.success())
                    .map(|output| !output.stdout.is_empty());

                (
                    git_sha_before.clone(),
                    after,
                    accepted_diff
                        .as_ref()
                        .map(|diff| stable_hash_hex(diff.as_bytes())),
                    dirty_after,
                    Some(scorer.label()),
                    Some(vec![
                        "cargo check (isolated)".to_string(),
                        "cargo clippy -D warnings (isolated)".to_string(),
                        "final validate_build after land (real tree)".to_string(),
                    ]),
                )
            } else {
                (None, None, None, None, None, None)
            };

        runs.push(OptimizationRun {
            iteration,
            scores: scores_this_iter,
            validated_changes: validated,
            landed_changes: landed,
            accepted_changes: accepted,
            notes,
            candidates,
            diff: accepted_diff,
            policy_hash: policy_info.as_ref().map(|policy| policy.hash.clone()),
            dataset_version: Some(dataset.version.clone()),
            dataset_hash: Some(dataset_hash.clone()),
            baseline_score: run_baseline,
            patched_score: run_patched,
            score_delta: run_delta,
            git_sha_before: prov_before,
            git_sha_after: prov_after,
            diff_hash: prov_diff_hash,
            working_tree_dirty_after: prov_dirty,
            scorer: prov_scorer,
            validation_commands: prov_cmds,
            validation_command_records: accepted_validation_commands,
            final_validation_command_records: accepted_final_validation_commands,
            trace_diagnosis: trace_diagnoses,
            hook_decisions,
            ledger: Some(ledger.clone()),
            holdout_score: accepted_holdout_score,
            budget: Some(config.budget),
            policy_path: policy_info
                .as_ref()
                .map(|policy| policy.path.display().to_string()),
            model: Some(llm.provenance(diagnosis_model_used)),
            rollback_succeeded: accepted_rollback_succeeded,
            rollback_error: accepted_rollback_error,
            candidate_timed_out: any_candidate_timed_out,
        });

        if accepted > 0 && iteration > 0 {
            // In real version we'd apply a safe edit here
        }
    }

    // Persist this optimization experiment under the agent's directory
    let experiment_dir = std::env::current_dir()?
        .join(".mdx-rust")
        .join("agents")
        .join(&agent.name)
        .join("experiments");

    std::fs::create_dir_all(&experiment_dir).ok();

    let timestamp = std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map(|d| d.as_secs())
        .unwrap_or(0);

    let experiment_file = experiment_dir.join(format!("run-{}.json", timestamp));
    if let Ok(content) = serde_json::to_string_pretty(&runs) {
        let _ = std::fs::write(experiment_file, content);
    }

    // Also write a rich human-readable report with provenance
    if runs.iter().any(|r| r.accepted_changes > 0) {
        let git_sha = std::process::Command::new("git")
            .args(["rev-parse", "--short", "HEAD"])
            .output()
            .ok()
            .and_then(|o| String::from_utf8(o.stdout).ok())
            .map(|s| s.trim().to_string())
            .unwrap_or_else(|| "unknown".to_string());

        let mut report = format!(
            "# Optimization Report for '{}'\n\nTimestamp: {}\nGit SHA: {}\n\n## Summary\n\n",
            agent.name, timestamp, git_sha
        );

        for run in &runs {
            if run.accepted_changes > 0 {
                report.push_str(&format!(
                    "- Iteration {}: Accepted {} change(s)\n  Notes: {}\n",
                    run.iteration, run.accepted_changes, run.notes
                ));

                if let Some(d) = &run.diff {
                    report.push_str(&format!("\n```diff\n{}\n```\n", d));
                } else {
                    report.push_str("  (Change persisted to src/main.rs)\n");
                }

                if let Some(h) = &run.policy_hash {
                    report.push_str(&format!("  Policy hash: {}\n", h));
                }
                if let Some(v) = &run.dataset_version {
                    report.push_str(&format!("  Dataset version: {}\n", v));
                }
                if let Some(path) = &run.policy_path {
                    report.push_str(&format!("  Policy path: {}\n", path));
                }
                if let Some(model) = &run.model {
                    report.push_str(&format!(
                        "  Diagnosis model: {}:{} (used={})\n",
                        model.provider, model.model, model.used
                    ));
                }
                if !run.validation_command_records.is_empty() {
                    report.push_str("  Isolated validation commands:\n");
                    for command in &run.validation_command_records {
                        report.push_str(&format!(
                            "    - {} | success={} | timeout={} | status={:?} | duration_ms={}\n",
                            command.command,
                            command.success,
                            command.timed_out,
                            command.status_code,
                            command.duration_ms
                        ));
                    }
                }
                if !run.final_validation_command_records.is_empty() {
                    report.push_str("  Final validation commands:\n");
                    for command in &run.final_validation_command_records {
                        report.push_str(&format!(
                            "    - {} | success={} | timeout={} | status={:?} | duration_ms={}\n",
                            command.command,
                            command.success,
                            command.timed_out,
                            command.status_code,
                            command.duration_ms
                        ));
                    }
                }
            }
        }

        report.push_str("\n## Candidates Considered\n\n");
        for run in &runs {
            for (i, c) in run.candidates.iter().enumerate() {
                report.push_str(&format!(
                    "- [{}] {}: {}\n  Expected: {}\n\n",
                    i + 1,
                    c.focus,
                    c.description,
                    c.expected_improvement
                ));
            }
        }

        let _ = std::fs::write(
            experiment_dir.join(format!("report-{}.md", timestamp)),
            report,
        );
    }

    // Final re-evaluation after any accepted changes (shows the win)
    if runs.iter().any(|r| r.accepted_changes > 0) {
        let mut final_scores = vec![];
        for input in &test_inputs {
            if let Ok(res) = crate::runner::run_agent(agent, input.clone()).await {
                final_scores.push(mechanical_score(&res));
            }
        }
        if !final_scores.is_empty() {
            let final_avg = final_scores.iter().sum::<f32>() / final_scores.len() as f32;
            if !config.quiet {
                println!(
                    "   Final re-evaluation after accepted changes: {:.2}",
                    final_avg
                );
            }
        }
    }

    Ok(runs)
}

#[derive(Debug, Clone)]
struct PolicyInfo {
    path: PathBuf,
    hash: String,
}

fn load_policy_info(agent_name: &str) -> Option<PolicyInfo> {
    let cwd = std::env::current_dir().ok()?;
    let candidates = [
        cwd.join(".mdx-rust")
            .join("agents")
            .join(agent_name)
            .join("policies.md"),
        cwd.join(".mdx-rust").join("policies.md"),
    ];

    candidates
        .iter()
        .find_map(|path| std::fs::read(path).ok().map(|content| (path, content)))
        .map(|(path, content)| PolicyInfo {
            path: path.clone(),
            hash: stable_hash_hex(&content),
        })
}

fn stable_hash_hex(bytes: &[u8]) -> String {
    crate::eval::stable_hash_hex(bytes)
}

fn strategy_for_focus(focus: &str) -> EditStrategy {
    let normalized = focus.to_lowercase();

    if normalized.contains("tool") {
        EditStrategy::ToolDescription
    } else if normalized.contains("fallback") || normalized.contains("logic") {
        EditStrategy::FallbackLogic
    } else if normalized.contains("schema") || normalized.contains("output") {
        EditStrategy::OutputSchema
    } else if normalized.contains("model") || normalized.contains("temperature") {
        EditStrategy::ModelConfig
    } else {
        EditStrategy::SystemPrompt
    }
}

fn fallback_candidates_from_trace(diagnoses: &[TraceDiagnosis]) -> Vec<Candidate> {
    let mut candidates = Vec::new();

    if diagnoses.iter().any(|diagnosis| {
        diagnosis
            .signals
            .iter()
            .any(|signal| signal.kind == FailureKind::EchoFallback)
    }) {
        candidates.push(Candidate {
            focus: "fallback_logic".to_string(),
            description: "Prevent echo fallback and require a useful best-effort answer."
                .to_string(),
            expected_improvement: "Reduce low-value echo responses.".to_string(),
            strategy: Some(EditStrategy::FallbackLogic),
        });
    }

    if diagnoses.iter().any(|diagnosis| {
        diagnosis
            .signals
            .iter()
            .any(|signal| signal.kind == FailureKind::InvalidJson)
    }) {
        candidates.push(Candidate {
            focus: "output_schema".to_string(),
            description: "Make the output contract explicit for answer, reasoning, and confidence."
                .to_string(),
            expected_improvement: "Improve parseability for agent callers.".to_string(),
            strategy: Some(EditStrategy::OutputSchema),
        });
    }

    if diagnoses.iter().any(|diagnosis| {
        diagnosis.signals.iter().any(|signal| {
            matches!(
                signal.kind,
                FailureKind::MissingReasoning | FailureKind::LowConfidence
            )
        })
    }) {
        candidates.push(Candidate {
            focus: "system_prompt".to_string(),
            description: "Strengthen the system prompt with explicit reasoning instructions."
                .to_string(),
            expected_improvement: "Increase reasoning quality and confidence.".to_string(),
            strategy: Some(EditStrategy::SystemPrompt),
        });
    }

    if candidates.is_empty() {
        candidates.push(Candidate {
            focus: "system_prompt".to_string(),
            description: "Strengthen the system prompt with explicit reasoning instructions."
                .to_string(),
            expected_improvement: "Improve answer quality.".to_string(),
            strategy: Some(EditStrategy::SystemPrompt),
        });
    }

    candidates
}

fn summarize_trace_diagnoses(diagnoses: &[TraceDiagnosis]) -> String {
    let mut summaries = Vec::new();

    for diagnosis in diagnoses {
        if diagnosis.has_failures() {
            summaries.push(diagnosis.compact_summary());
        }
    }

    if summaries.is_empty() {
        "No obvious trace failures detected.".to_string()
    } else {
        format!("Trace failures: {}", summaries.join(" | "))
    }
}

fn build_edit_for_candidate(
    agent_root: &Path,
    bundle: Option<&AgentBundle>,
    candidate: &Candidate,
) -> anyhow::Result<Option<ProposedEdit>> {
    let strategy = candidate
        .strategy
        .clone()
        .unwrap_or_else(|| strategy_for_focus(&candidate.focus));

    let Some((target_file, old_preamble)) = select_preamble_target(agent_root, bundle) else {
        if strategy == EditStrategy::FallbackLogic {
            return build_echo_fallback_edit(agent_root, bundle, &candidate.description);
        }
        return Ok(None);
    };

    if strategy == EditStrategy::FallbackLogic {
        if let Some(edit) = build_echo_fallback_edit(agent_root, bundle, &candidate.description)? {
            return Ok(Some(edit));
        }
    }

    let Some(new_preamble) = evolved_preamble_for_strategy(&old_preamble, &strategy, bundle) else {
        return Ok(None);
    };

    if normalize_prompt(&new_preamble) == normalize_prompt(&old_preamble) {
        return Ok(None);
    }

    let content = std::fs::read_to_string(&target_file)?;
    let relative_target = target_file
        .strip_prefix(agent_root)
        .unwrap_or(&target_file)
        .to_path_buf();
    let patch = generate_preamble_patch(&relative_target, &content, &old_preamble, &new_preamble);

    Ok(Some(ProposedEdit {
        file: target_file,
        description: format!("{:?}: {}", strategy, candidate.description),
        patch,
    }))
}

fn build_echo_fallback_edit(
    agent_root: &Path,
    bundle: Option<&AgentBundle>,
    description: &str,
) -> anyhow::Result<Option<ProposedEdit>> {
    let mut candidates: Vec<PathBuf> = bundle
        .map(|bundle| {
            bundle
                .scope
                .optimizable_paths
                .iter()
                .filter(|path| path.extension().is_some_and(|extension| extension == "rs"))
                .cloned()
                .collect()
        })
        .unwrap_or_default();

    if candidates.is_empty() {
        candidates.push(agent_root.join("src/main.rs"));
    }

    for target_file in candidates {
        let Ok(content) = std::fs::read_to_string(&target_file) else {
            continue;
        };

        let replacements = [
            (
                "Echo: {}",
                "Best-effort answer after reasoning: {}",
                "replace echo fallback format string",
            ),
            (
                "Echo: ",
                "Best-effort answer after reasoning: ",
                "replace echo fallback prefix",
            ),
        ];

        for (old, new, label) in replacements {
            if !content.contains(old) {
                continue;
            }

            let relative_target = target_file
                .strip_prefix(agent_root)
                .unwrap_or(&target_file)
                .to_path_buf();
            let patch = generate_preamble_patch(&relative_target, &content, old, new);

            return Ok(Some(ProposedEdit {
                file: target_file,
                description: format!("FallbackLogic: {description} ({label})"),
                patch,
            }));
        }
    }

    Ok(None)
}

fn select_preamble_target(
    agent_root: &Path,
    bundle: Option<&AgentBundle>,
) -> Option<(PathBuf, String)> {
    if let Some(prompt) = bundle.and_then(|bundle| bundle.preambles.first()) {
        return Some((PathBuf::from(&prompt.file), prompt.text.clone()));
    }

    let target = bundle
        .and_then(|bundle| {
            bundle.scope.optimizable_paths.iter().find(|path| {
                let name = path.file_name().unwrap_or_default().to_string_lossy();
                name.ends_with(".rs") && (name == "main.rs" || name.contains("agent"))
            })
        })
        .cloned()
        .unwrap_or_else(|| agent_root.join("src/main.rs"));

    let content = std::fs::read_to_string(&target).ok()?;
    extract_first_preamble_literal(&content).map(|prompt| (target, prompt))
}

fn extract_first_preamble_literal(content: &str) -> Option<String> {
    let marker = ".preamble(\"";
    let start = content.find(marker)? + marker.len();
    let rest = &content[start..];
    let end = rest.find('"')?;
    Some(rest[..end].to_string())
}

fn evolved_preamble_for_strategy(
    old: &str,
    strategy: &EditStrategy,
    bundle: Option<&AgentBundle>,
) -> Option<String> {
    let addition = match strategy {
        EditStrategy::SystemPrompt => {
            "Think step-by-step before answering. Always explain your reasoning in one sentence, then give the final answer."
        }
        EditStrategy::FallbackLogic => {
            "Never echo the user input as the final answer. If uncertain, state assumptions, reason briefly, and provide the best useful answer."
        }
        EditStrategy::OutputSchema => {
            "Always produce an answer, reasoning, and confidence from 0 to 1."
        }
        EditStrategy::ToolDescription => {
            let has_tools = bundle.is_some_and(|bundle| !bundle.tools.is_empty());
            if !has_tools {
                return None;
            }
            "Before answering, decide whether available tools improve factuality or completeness, and only use them when they add real value."
        }
        EditStrategy::ModelConfig => return None,
    };

    if normalize_prompt(old).contains(&normalize_prompt(addition)) {
        return Some(old.to_string());
    }

    let mut base = old.trim().trim_end_matches('.').to_string();
    if base.is_empty() {
        base = "You are a concise, helpful assistant".to_string();
    }
    Some(format!("{base}. {addition}"))
}

fn normalize_prompt(value: &str) -> String {
    value
        .split_whitespace()
        .collect::<Vec<_>>()
        .join(" ")
        .to_lowercase()
}

/// Very rough mechanical scorer for the example agent.
/// Gives higher score if the output is not the echo fallback.
pub fn mechanical_score(result: &AgentRunResult) -> f32 {
    let answer = result
        .output
        .get("answer")
        .and_then(|v| v.as_str())
        .unwrap_or("");
    let reasoning = result
        .output
        .get("reasoning")
        .and_then(|v| v.as_str())
        .unwrap_or("");

    if answer.starts_with("Echo:") {
        return 0.4;
    }

    let mut score = 0.75f32;

    // Bonus for explicit reasoning language (the improvement the optimizer tries to install)
    if reasoning.to_lowercase().contains("think")
        || reasoning.to_lowercase().contains("reason")
        || reasoning.to_lowercase().contains("step")
    {
        score += 0.12;
    }

    // Bonus for non-trivial answer length
    if answer.len() > 20 {
        score += 0.08;
    }

    score.min(0.95)
}

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

    #[test]
    fn test_mechanical_score_echo_vs_reasoned() {
        let echo = AgentRunResult {
            output: serde_json::json!({"answer": "Echo: hello", "reasoning": "no key"}),
            duration_ms: 10,
            success: true,
            error: None,
            traces: vec![],
        };
        let good = AgentRunResult {
            output: serde_json::json!({"answer": "The answer is 42 because...", "reasoning": "Think step by step: 6*7"}),
            duration_ms: 120,
            success: true,
            error: None,
            traces: vec![],
        };

        assert!(mechanical_score(&echo) < 0.5);
        assert!(mechanical_score(&good) > 0.8);
    }

    #[test]
    fn test_optimize_config_defaults() {
        let cfg = OptimizeConfig {
            max_iterations: 1,
            candidates_per_iteration: 1,
            use_llm_judge: false,
            budget: OptimizationBudget::Medium,
            hook_policy: HookPolicy::default(),
            review_before_apply: false,
            quiet: false,
            candidate_timeout: default_candidate_timeout(),
        };
        assert_eq!(cfg.max_iterations, 1);
    }

    #[test]
    fn strategy_for_focus_maps_common_candidate_names() {
        assert_eq!(
            strategy_for_focus("improve tool descriptions"),
            EditStrategy::ToolDescription
        );
        assert_eq!(
            strategy_for_focus("fix fallback logic"),
            EditStrategy::FallbackLogic
        );
        assert_eq!(
            strategy_for_focus("tighten output schema"),
            EditStrategy::OutputSchema
        );
        assert_eq!(
            strategy_for_focus("lower model temperature"),
            EditStrategy::ModelConfig
        );
        assert_eq!(strategy_for_focus("reasoning"), EditStrategy::SystemPrompt);
    }

    #[test]
    fn fallback_candidates_follow_trace_failures() {
        let candidates = fallback_candidates_from_trace(&[TraceDiagnosis {
            signals: vec![
                crate::FailureSignal {
                    kind: FailureKind::EchoFallback,
                    severity: 2,
                    evidence: "Echo: hello".to_string(),
                    span_id: None,
                },
                crate::FailureSignal {
                    kind: FailureKind::InvalidJson,
                    severity: 2,
                    evidence: "raw stdout".to_string(),
                    span_id: None,
                },
            ],
            ranked_span_ids: vec![],
        }]);

        assert_eq!(candidates[0].strategy, Some(EditStrategy::FallbackLogic));
        assert!(candidates
            .iter()
            .any(|candidate| candidate.strategy == Some(EditStrategy::OutputSchema)));
    }

    #[test]
    fn build_edit_for_candidate_creates_schema_preamble_patch() {
        let dir = tempdir().unwrap();
        let src = dir.path().join("src");
        std::fs::create_dir_all(&src).unwrap();
        let main = src.join("main.rs");
        std::fs::write(
            &main,
            r#"fn main() { let _agent = client.agent("m").preamble("You are helpful.").build(); }"#,
        )
        .unwrap();

        let candidate = Candidate {
            focus: "output_schema".to_string(),
            description: "make output contract explicit".to_string(),
            expected_improvement: "more parseable output".to_string(),
            strategy: Some(EditStrategy::OutputSchema),
        };

        let edit = build_edit_for_candidate(dir.path(), None, &candidate)
            .unwrap()
            .expect("schema strategy should produce a prompt edit");

        assert_eq!(edit.file, main);
        assert!(edit.patch.contains("answer, reasoning, and confidence"));
    }

    #[test]
    fn tool_strategy_requires_discovered_tools() {
        let dir = tempdir().unwrap();
        let src = dir.path().join("src");
        std::fs::create_dir_all(&src).unwrap();
        let main = src.join("main.rs");
        std::fs::write(
            &main,
            r#"fn main() { let _agent = client.agent("m").preamble("You are helpful.").build(); }"#,
        )
        .unwrap();

        let candidate = Candidate {
            focus: "tool_description".to_string(),
            description: "clarify tool use".to_string(),
            expected_improvement: "better tool calls".to_string(),
            strategy: Some(EditStrategy::ToolDescription),
        };

        let without_tools = build_edit_for_candidate(dir.path(), None, &candidate).unwrap();
        assert!(without_tools.is_none());

        let bundle = AgentBundle {
            scope: mdx_rust_analysis::BundleScope {
                optimizable_paths: vec![main],
                read_only_paths: vec![],
            },
            preambles: vec![],
            tools: vec![mdx_rust_analysis::ExtractedTool {
                file: "src/main.rs".to_string(),
                name: "search".to_string(),
                description: None,
            }],
            is_rig_agent: true,
            key_files: vec![],
        };

        let with_tools = build_edit_for_candidate(dir.path(), Some(&bundle), &candidate)
            .unwrap()
            .expect("tool strategy should produce a prompt edit when tools exist");
        assert!(with_tools
            .patch
            .contains("available tools improve factuality"));
    }

    #[test]
    fn fallback_logic_strategy_can_patch_echo_fallback() {
        let dir = tempdir().unwrap();
        let src = dir.path().join("src");
        std::fs::create_dir_all(&src).unwrap();
        let main = src.join("main.rs");
        std::fs::write(
            &main,
            r#"fn main() { println!("{}", format!("Echo: {}", "hello")); }"#,
        )
        .unwrap();

        let candidate = Candidate {
            focus: "fallback_logic".to_string(),
            description: "avoid echo fallback".to_string(),
            expected_improvement: "more useful fallback".to_string(),
            strategy: Some(EditStrategy::FallbackLogic),
        };

        let edit = build_edit_for_candidate(dir.path(), None, &candidate)
            .unwrap()
            .expect("fallback logic should patch simple echo fallback");

        assert_eq!(edit.file, main);
        assert!(edit.patch.contains("Best-effort answer after reasoning"));
    }
}