cratefield-cli 0.6.3

//! `fz migrations apply` (issue #18): applies the harness's module
//! migrations directly to a Postgres database — the native counterpart of
//! `wrangler d1 migrations apply`. `--fleet` and `--plan` instead point
//! it at a **control** database and run the boot-time reconciliation the
//! native runtime runs (RECONCILIATION.md, issue #30) by hand.
//!
//! The two are different databases and different work, so neither is the
//! other's default. An earlier cut of #30 made `--url` mean the control
//! database always: against an ordinary venture database that
//! reconciled a registry with no tenants in it, printed nothing, and
//! **exited zero having applied no migrations** — including in
//! ROLLBACK.md's recovery runbook, which runs this command to re-apply
//! what is missing. Silence and success are the two things a migration
//! step must never combine.
//!
//! Requires building `fz` with cratefield-cli's `postgres` feature so
//! sqlx and tokio stay out of the default (wasm-safe) dependency graph.

use cratefield_core::Harness;

#[cfg(feature = "postgres")]
/// Default per-boot fan-out to tenant databases (RECONCILIATION.md §2:
/// "something small like 8"; #30 §10 keeps it a measured question).
#[cfg(feature = "postgres")]
const FLEET_PARALLELISM: usize = 8;

/// Applies the harness's migrations to the database at `url`; with
/// `fleet` or `plan`, reconciles the tenants registered in the control
/// database at `url` instead.
///
/// # Errors
///
/// A human-readable message when the dialect is unsupported, the flags
/// contradict each other, the binary lacks the `postgres` feature, the
/// server is unreachable, or a migration fails. In strict mode any
/// degraded tenant is one.
pub fn apply(
    harness: &Harness,
    dialect: &str,
    url: &str,
    plan: bool,
    fleet: bool,
    tenant: Option<&str>,
    strict: bool,
) -> Result<(), String> {
    if dialect != "postgres" {
        return Err(format!(
            "dialect {dialect:?} is not supported for apply (only postgres, issue #18)"
        ));
    }
    if plan && fleet {
        return Err(
            "--plan and --fleet contradict each other: --plan applies nothing, --fleet \
             applies to every registered tenant"
                .to_owned(),
        );
    }
    if tenant.is_some() && !plan {
        return Err(
            "--tenant only means something with --plan today: fleet apply is the runtime \
             reconciler's job, and one tenant cannot be applied without its neighbours' \
             registry being read anyway"
                .to_owned(),
        );
    }
    if strict && !fleet {
        return Err(
            "--strict says what to do about a degraded tenant, and only --fleet has \
             tenants: a plain apply either applies its migrations or fails"
                .to_owned(),
        );
    }
    #[cfg(not(feature = "postgres"))]
    {
        let _ = (harness, url, plan, fleet, tenant, strict);
        Err(
            "this fz binary was built without cratefield-cli's `postgres` feature — \
             rebuild the fz bin with `--features cratefield-cli/postgres` to apply \
             migrations to Postgres (sqlite/D1 migrations run through \
             `wrangler d1 migrations apply`)"
                .to_owned(),
        )
    }
    #[cfg(feature = "postgres")]
    {
        if plan {
            apply_plan(harness, url, tenant)
        } else if fleet {
            apply_fleet(harness, url, strict)
        } else {
            apply_postgres(harness, url)
        }
    }
}

#[cfg(feature = "postgres")]
fn runtime() -> Result<tokio::runtime::Runtime, String> {
    tokio::runtime::Builder::new_current_thread()
        .enable_all()
        .build()
        .map_err(|err| format!("cannot start the async runtime: {err}"))
}

/// The default, and what issue #18 named: this harness's migrations, on
/// the database `--url` names, tracked in `harness_migrations`.
#[cfg(feature = "postgres")]
fn apply_postgres(harness: &Harness, url: &str) -> Result<(), String> {
    runtime()?.block_on(async {
        // The URL is never echoed: connection strings carry credentials.
        let db = cratefield_adapter_postgres::Postgres::connect(url)
            .await
            .map_err(|err| format!("cannot connect (check --url): {err}"))?;
        db.apply_harness_migrations(harness)
            .await
            .map_err(|err| format!("migrations failed: {err}"))
    })
}

/// `--fleet`: `url` names the **control** database, and every
/// non-degraded tenant in its registry is reconciled against its own
/// database (RECONCILIATION.md §2).
#[cfg(feature = "postgres")]
fn apply_fleet(harness: &Harness, url: &str, strict: bool) -> Result<(), String> {
    runtime()?.block_on(async {
        let db = cratefield_adapter_postgres::Postgres::connect(url)
            .await
            .map_err(|err| {
                format!("cannot connect to the control database (check --url): {err}")
            })?;
        let reports = db
            .reconcile_fleet(harness, FLEET_PARALLELISM)
            .await
            .map_err(|err| format!("reconciliation failed: {err}"))?;
        // An empty registry is the shape that made the old default a
        // silent no-op. Say so rather than print nothing and exit zero.
        if reports.is_empty() {
            println!(
                "no tenants registered in the control database — nothing to reconcile \
                 (a venture database is applied without --fleet)"
            );
            return Ok(());
        }
        let degraded: Vec<&cratefield_adapter_postgres::TenantReport> = reports
            .iter()
            .filter(|report| report.status == cratefield_adapter_postgres::TenantStatus::Degraded)
            .collect();
        for report in &reports {
            println!(
                "tenant {}: {} applied, {} skipped, {}{}",
                report.tenant,
                report.applied,
                report.skipped,
                report.status,
                report
                    .error
                    .as_deref()
                    .map(|err| format!(" — {err}"))
                    .unwrap_or_default()
            );
        }
        if degraded.is_empty() {
            Ok(())
        } else if strict {
            Err(format!(
                "{} tenant(s) degraded ({}): boot would abort in strict mode",
                degraded.len(),
                degraded
                    .iter()
                    .map(|report| report.tenant.as_str())
                    .collect::<Vec<_>>()
                    .join(", ")
            ))
        } else {
            println!(
                "{} tenant(s) degraded; every other tenant serves (re-run with --strict \
                 to make this a failure)",
                degraded.len()
            );
            Ok(())
        }
    })
}

/// `--plan`: what would be applied, per tenant and per module, applied
/// nowhere. Locks are taken so the answer is not a guess about a moving
/// target (RECONCILIATION.md §8).
#[cfg(feature = "postgres")]
fn apply_plan(harness: &Harness, url: &str, tenant: Option<&str>) -> Result<(), String> {
    runtime()?.block_on(async {
        let control = cratefield_adapter_postgres::Postgres::connect(url)
            .await
            .map_err(|err| {
                format!("cannot connect to the control database (check --url): {err}")
            })?;
        control
            .bootstrap_registry()
            .await
            .map_err(|err| format!("cannot bootstrap the registry: {err}"))?;
        let records = control
            .tenants()
            .await
            .map_err(|err| format!("cannot read the tenant registry: {err}"))?;
        let records: Vec<_> = match tenant {
            Some(name) => {
                let found: Vec<_> = records
                    .iter()
                    .filter(|record| record.tenant == name)
                    .collect();
                if found.is_empty() {
                    return Err(format!("tenant {name:?} is not in the registry"));
                }
                found
            }
            None => records.iter().collect(),
        };
        if records.is_empty() {
            println!("no tenants registered");
            return Ok(());
        }
        for record in records {
            match control.reconcile_plan(record, harness).await {
                Ok(plan) => {
                    if plan.modules.is_empty() {
                        println!("tenant {}: nothing to apply", plan.tenant);
                    } else {
                        println!("tenant {}:", plan.tenant);
                        for module in &plan.modules {
                            println!("  {}: {}", module.module, module.migrations.join(", "));
                        }
                    }
                }
                Err(err) => println!("tenant {}: unreachable — {err}", record.tenant),
            }
        }
        Ok(())
    })
}