rdbms-playground/docs/requirements.md

RDBMS Playground — Requirements (Phase 1)

This document is the consolidated Phase 1 requirements checklist for RDBMS Playground. It captures everything the project has committed to so far, derived from the design conversation and the ADRs in docs/adr/.

Purpose. Phase 5 verification at every milestone measures delivered work against this checklist. An item not on this list was not promised; an item silently dropped without confirmation is a process failure.

Scope. The list is intentionally coarse — each item is a unit of "satisfied / not satisfied" judgement. When an item is taken up for implementation, it is decomposed further in a backlog (initially in this repo, later in GitHub issues once the repo is pushed).

Status legend

• [ ] — open, not yet implemented
• [x] — satisfied (implemented + tested)
• [~] — deferred, awaiting an ADR or further design before any implementation
• [-] — explicitly out of scope (rationale at the bottom)

Test baseline

After the ADR-0027 highlight / hint follow-up (precise WARNING spans, the diagnostic overlay + hint wiring, the LIKE-on-numeric WARNING, the debounce state machine) plus two manual-testing bug fixes (optional trailing-flag completion; the --resume temp-project pointer): 1131 passing, 0 failing, 1 ignored (cargo test — the one ignored test is a long-standing ```ignore doc-test in src/friendly/mod.rs). Clippy clean with the nursery lint group enabled. (Earlier reference points: 1100 after ADR-0027's initial ship; 1079 after ADR-0026 (complex WHERE expressions); 1039 after ADR-0025 (indexes); 1006 after ADR-0024 + the handoff-14 cleanup; 449 after B2/C2.)

---

Distribution and install

• D1 Cross-platform binaries: Linux, macOS, Windows on x86_64 and aarch64.
• D2 Single static binary, no runtime dependencies.
• D3 Released via prebuilt binaries plus Homebrew, Scoop, winget, and cargo binstall.

TUI shell

• S1 Three-region layout: items list (left), output panel (right), input field (bottom).
• S2 Items list shows tables and per-table indexes; designed to extend to additional element kinds (relations, views, etc.) without restructuring. (ADR-0025: the items panel renders a nested list — each table with its index names indented beneath it. The nested model is the extension point for future element kinds.)
• S3 Output panel renders a visualization of the currently selected item and supports multiple tabs.
• S4 Hint area below the input field; keyboard-toggleable for inspecting hints about the current input or last error.
• S5 Mode label and distinct border style on the input field communicate the current input mode at all times.
• S6 Input-field validity indicator: a debounced [ERR] / [WRN] marker at the right edge of the input row, summarising — before submit — whether the current command would run. Backed by a walker diagnostics-severity model (ERROR / WARNING). Advisory only — never blocks submission. (ADR-0027: Severity / Diagnostic on WalkResult; input_verdict combines the parse outcome, schema-existence ERRORs — unknown table / column — and the ADR-0026 §7 expression WARNINGs — type mismatch, = NULL. The runtime debounces the indicator's display ~1 s; the rightmost six columns of the input row are reserved unconditionally. New warning theme colour. A follow-up pass completed §2's highlight + hint wiring — diagnostics overlaid on the input field and surfaced in the hint panel, with precise per-literal WARNING spans — and Amendment 1 adds a LIKE-on-numeric-column WARNING.)

Input field

• I1 Multi-line entry that auto-expands; Ctrl-Enter (or equivalent) submits, plain Enter inserts a newline.
• I1a In-line cursor editing in the input field: Left / Right arrows move the cursor by character (UTF-8 boundaries honoured), Home / End jump to the extremes, Delete removes the character at the cursor, Backspace removes the character before. Insertion happens at the cursor position. (Implemented; multi-line editing per I1 still pending.)
• I1b Readline-style cursor shortcuts: Ctrl-A / Ctrl-E as aliases for Home / End for users on keyboards without those keys (and for ergonomics in command-driven workflows). Likely followed by Ctrl-W (delete previous word), Ctrl-K (delete to end), Ctrl-U (delete to start). Pending.
• I2 Persistent navigable input history (project-scoped). (Implemented across Iterations 2 + 6: per-command append to history.log (Iter 2); on project open, the in-memory navigable history is hydrated from the tail of history.log up to the same in-memory cap (Iter 6). Global rolling history is out of scope per OOS-6 / N4.)
• I3 Tab completion for app commands, DSL keywords, table names, column names, and SQL keywords.
• I4 Syntax highlighting for both the DSL and SQL.
• I5 In-flight query/command cancellation (Ctrl-C in the output area or input field).

Input modes (per ADR-0003)

• M1 Simple mode is the default. It accepts DSL data commands and the canonical app-level commands; raw SQL is rejected with a friendly hint.
• M2 Advanced mode accepts SQL plus the canonical app-level commands without any sigil.
• M3 Prefixing a single line with : in simple mode is a one-shot advanced escape (with the prompt label updated). The mode simple / mode advanced command switches modes persistently.
• [~] M4 Execution-time mode side-channel — deferred, awaiting its own ADR (ADR-0033 Amendment 3). Every command should know, at execution time, which of three modes it ran under — simple, advanced, or advanced-one-shot (the : escape) — so execution can adjust output without changing command identity (e.g. a simple-mode create table echoing the generated SQL when run in advanced mode, silent in simple). Today only the rendering side-channel exists (OutputLine.mode_at_submission); the Mode enum is two-way, the one-shot distinction is collapsed at submission, and neither Action::ExecuteDsl nor the worker carries any mode. The work widens Mode to three-way and threads it through the Action → worker interface. Not required for Phase 3 dispatch correctness; tracked here so it is not lost.

App-level commands (per ADR-0003)

• A1 All canonical app-level commands implemented and available in both modes: save, save as, load, new, rebuild, export, import, seed, replay, undo, redo, mode, help, hint, quit. (Progress: quit/q, mode simple|advanced, help, save, save as, load, new, rebuild, export, import, replay all implemented (Iterations 4 + 5; replay via ADR-0024 Phase E — see U4). seed in the seeding iteration; undo / redo in the U-series; hint with H2.)

DSL data commands

• C1 Table operations: create / drop / rename. (Progress: create + drop done; rename pending.)
• C2 Column operations: add / drop / rename / change type. drop column and rename column use SQLite native ALTER TABLE (3.35+ / 3.25+); change column routes through the rebuild-table primitive since ALTER doesn't support type changes. PK and relationship-involved columns are refused with friendly messages (drop the relationship first); SQLite STRICT enforces type compatibility on the data copy during a type change.
• C3 Schema constraints: primary key (single and compound), foreign key with ON DELETE / ON UPDATE referential actions, indexes, NOT NULL, UNIQUE, CHECK, DEFAULT. (PK including compound done at create-table time; FK with ON DELETE / ON UPDATE actions done (ADR-0013) — declared via add 1:n relationship; symmetric outbound + inbound view in the structure renderer; type compatibility validated at declaration via Type::fk_target_type(). Indexes done (ADR-0025) — add index / drop index, rebuild-preserving, persisted in project.yaml. NOT NULL / UNIQUE / CHECK / DEFAULT done (ADR-0029) — a constraint suffix on create table / add column, plus add constraint / drop constraint on existing columns; populated-column additions are guarded by a pre-flight dry-run that refuses with a table of offending rows.)
• [~] C3a Modify relationship: modify relationship <name> [on delete <action>] [on update <action>]. Users can achieve the same via drop + add today; one-step modify is a small follow-up using the existing rebuild-table machinery. ADR pending.
• C4 Convenience: create m:n relationship from <T1> to <T2> produces an auto-named junction table the user can rename; pulls primary keys and FK definitions automatically.
• C5 Data operations: insert / update / delete via DSL. (ADR-0014. INSERT short and long forms, UPDATE/DELETE with required WHERE plus --all-rows opt-in, show data <T>, per-column-type value-literal validation, FK enforcement with metadata-driven error enrichment, auto-show after writes. Bulk insert, complex WHERE expressions, and SELECT in advanced mode are explicitly tracked separately — see C5a below.)
• C5a Complex WHERE expressions (AND/OR, comparison operators, LIKE, IS NULL, IN, BETWEEN) for UPDATE/DELETE/ show-data filtering; show data also gains where and limit. (ADR-0026 steps 1–4: the stratified expression grammar reached through a new Subgrammar node, the recursive Expr AST + build_expr, wiring into update / delete / show data, and Expr → parameterised SQL with an implicit primary-key ORDER BY for limit. Type-mismatched WHERE comparisons are permissive — they run rather than being rejected (§7). The §7 advisory flagging of type mismatches / = NULL is the seam with ADR-0027's diagnostics-severity model and is tracked there — see ADR-0026 "As-built notes".)

SQL handling

• Q1 SQL parsed via sqlparser-rs; supported subset is defined (specifics deferred to a future ADR). (Progress: SQL handling in advanced mode is still a placeholder echo. The architecture is now decided — ADR-0030: SQL is authored as grammar within the unified grammar tree (ADR-0024) and parsed by the existing walker, not a separate batch parser — so SQL gets the same completion / highlighting / hints as the DSL. ADR-0001's sqlparser-rs reservation is superseded. Implementation is phased and pending.)
• Q2 Non-standard syntax rejected with a clear message pointing at the supported subset. (Design done — ADR-0030 §8: out-of-subset statements are refused with an engine-neutral message naming the construct. Implementation pending.)
• Q3 User-facing simplified types map transparently to SQLite STRICT types in generated DDL. (All ten types implemented and tested.)
• Q4 Supported SQL subset specification — ADR-0030. Advanced mode is a standard-SQL surface, engine-neutral; the supported surface — SELECT (full query surface), INSERT / UPDATE / DELETE, CREATE / DROP / ALTER TABLE, CREATE / DROP INDEX — is authored as grammar in the unified tree. DDL routes through the typed Command executor (metadata + the playground type vocabulary preserved); DML and SELECT execute as validated SQL. Q1's implementation is now unblocked.

Database backend (per ADR-0002)

• B1 SQLite via rusqlite; all tables created STRICT; PRAGMA foreign_keys = ON per connection. (Database accessed through a dedicated worker thread per ADR-0010.)
• B2 Schema evolution uses the rebuild-table technique internally where SQLite ALTER TABLE cannot — currently the change-column-type code path. Add-column, drop-column, and rename-column take the simpler ALTER TABLE route since modern SQLite supports them natively; metadata sync into __rdbms_playground_columns and __rdbms_playground_relationships happens in the same transaction either way.
• B3 Query timeout and cancellation supported (no cartesian-join-of-doom can hang the app). (Progress: the worker-thread architecture is in place; the cancellation/timeout protocol on top of it is pending.)

Type system (per ADR-0005)

• T1 All ten user-facing types implemented: text, int, real, decimal, bool, date, datetime, blob, serial, shortid. (Mapping to SQLite STRICT covered by ADR-0005; FK target type rule by ADR-0011.)
• T2 shortid generation: base58, 10–12 characters, omits ambiguous characters; generated client-side at insert. (Implemented per ADR-0014; auto-fills omitted shortid columns and validates user-supplied values against the same alphabet and length range.)
• T3 Compound primary keys handled end-to-end (DSL, storage, display, FK reference). (Progress: DSL grammar (with pk a(int),b(int)), storage, and table-info description are all present; the FK iteration references single-column PKs only — compound-key FK references remain pending.)

Visualizations

• V1 Single-element views render in the output pane: a selected table as its structure (columns, types, keys, constraints); a selected relationship as two tables joined by a line. (Progress: a basic structure view (column rows with SQLite type names) is rendered after each successful DDL; pretty rendering, selection nav, and relationship line-art pending — see V4 for the broader direction.)
• V2 SQL query results render as a dynamic table view in the output pane, with multiple result tabs supported. (Progress: a basic aligned-column data view is rendered for show data and after every write (ADR-0014). Pretty box-drawing tables with truncation/scroll handling, plus multi-tab support, remain in V4 territory.)
• [~] V3 Full ER-diagram export (whole-database graph, viewed outside the TUI) — low priority; design and ADR pending.
• [~] V4 Output panel as a scrollable per-session log with inline rich rendering. Direction agreed in conversation: the output area is a chronological journal of operations and selections (e.g. a "selected table X" entry with the rendered structure underneath); structure renderings choose between a compact ASCII-table form and a vertical line-per-column form based on dimensions; the log is exportable to Markdown so learners can keep a record of their session. Design and ADR pending before any implementation. (Partial: PageUp / PageDown scrolling of the existing line buffer is in, with new output snapping the view to the most recent. The full V4 scope — smart structure rendering, log styling, Markdown export, scroll indicator — remains pending.)
• V5 show <kind> [<name>] family of commands for redisplaying schema info on demand. (Progress: show table <name> and show data <Table> implemented; show tables, show relationships, etc. pending.)

Project lifecycle (per ADR-0004)

• P1 Auto-named temp project on startup under <data-root>/projects/. OS-standard data root via directories crate; --data-dir overrides (Iteration 1).
• P2 save / save as elevate / copy + switch (Iteration 4b). save on a named project reports "already auto-saved".
• P3 Auto-save: per-command write-through to YAML + CSV + history.log inside the SQLite tx with commit-db-last ordering (Iteration 2). No dirty state.
• P4 load opens an in-TUI picker, sorted newest first, with [TEMP] markers and a b-to-browse path-entry sub-mode (Iteration 4b).
• P5 Existence-only load + explicit rebuild command with confirmation modal (Iterations 3 + 4a).
• P-NAME-1 Temp project directory naming pattern: <YYYYMMDD>-[temp]-<word>-<word>-<word> from a 161-word built-in list (Iterations 1 + 4b). Bracketed [temp] marker is unambiguous against user-named projects because validate_user_name rejects brackets.
• P-NAME-2 Display-name prettifier strips YYYYMMDD- AND [temp]-; splits kebab / snake / camel; title-cases each word.
• P-NAME-3 Status bar shows Project: [TEMP] <name> for temp projects, Project: <name> for named.
• P-CLEAN-1 Unmodified empty temp projects are auto-deleted on switch and quit, gated by safely_delete_temp_project's stacked guards (containment, symlink rejection, [temp] marker, contents allowlist).

Project file format (per ADR-0004)

• F1 project.yaml with version: 1 field carries schema (ordered tables + columns), relationships, and created_at. data/<table>.csv carries table data (UTF-8, header row, RFC 4180; NULL distinct from empty string) (Iteration 2). Empty tables produce no CSV.
• F2 .gitignore template (/playground.db, /.rdbms-playground.lock, /project.yaml.v*.bak) created in each new project (Iteration 1). Per ADR-0007 amendment 1, history.log is NOT in the template — user decides whether to commit it.
• F3 Migration framework scaffold (Iteration 6). MigratorRegistry + migrate_to_latest + ensure_project_yaml_migrated are wired into every project open; no migrators registered in v1 (the production registry is empty). The framework is exercised by tests that inject a fake v1→v2 migrator: registry plumbing, .v<N>.bak backup, version-bump sanity check, and newer-than-supported / malformed-version errors are all covered. The first real migrator (when v2 ships) is a one-file change.

Undo and replay (per ADR-0006)

• U1 Auto-snapshot before every data/schema mutation (DSL + SQL) into a persisted ring buffer (size N=50, tunable), per ADR-0006 Amendment 1 (single-step undo, superseding the original destructive-only model). Snapshot is a hybrid whole-project copy (database via online backup API + project.yaml / data/*.csv as files); staged before the mutation's transaction, finalised after the db commit (preserves ADR-0015 §6). A batch command (replay / future batch ops) records one boundary snapshot; import takes none. A --no-undo CLI flag disables snapshotting. (Designed + amended + planned in docs/plans/20260524-adr-0006-undo-snapshots.md; not yet implemented.)
• U2 undo restores the most recent snapshot (database + text, directly); redo re-applies (redo stack discarded on new work); both prompt for confirmation naming the command being undone / re-applied (Y confirms). (Designed + amended; not yet implemented — see U1's plan.)
• U3 history.log records every submitted command in append-only form, tagged with its outcome (Iteration 2; broadened by ADR-0034). Format: <ISO-8601 Z>|<status>|<source> per ADR-0015 §5 / ADR-0034 §1 — status is ok for a successful command and err for one that failed to parse or execute. Hydration (cross-session recall) reads all records; replay reads ok only.
• U4 replay runs commands from a history.log or .commands file. (Implemented via ADR-0024 Phase E: runtime::run_replay parses each non-blank, non-#-comment line in advanced mode and dispatches it through the normal pipeline; stops at the first genuine error, no rollback. ADR-0034 §3: replay reads journal records (<ts>|<status>| <source>), running ok records and skipping non-ok, while still accepting bare-command scripts. ADR-0034 Amendment 1: replay re-applies only schema/data write commands and skips every app-lifecycle command + nested replay — all skips continue (a nested replay is now skipped, not refused), with a [skip] warning on import / nested-replay. Covered by tests/replay_command.rs.)

Sharing and export (per ADR-0007)

• E1 export produces a zip excluding playground.db AND history.log (per ADR-0007 amendment 1); default filename YYYYMMDD-<projectname>-export-NN.zip with a non-clobbering two-digit sequence under the active data root (Iteration 5). The zip preserves the project's directory name as a single top-level folder. import <zip> [as <t>] is the inverse: derive target name from the zip's top folder, auto-suffix -NN on collision (ADR-0015 §11 amendment), rebuild from text on open.
• E2 User documentation includes sharing recipes for git, email, and direct file transfer.

Sample data / seeding

• SD1 seed <table> [count] generates plausible fake data; junction tables are seeded with valid foreign-key references drawn from existing parent rows.
• [~] SD2 Detailed seeding rules (per-type generators, locale, determinism, override hooks) — design and ADR pending.

Query analysis

• QA1 EXPLAIN QUERY PLAN is run on demand for queries; output is rendered as an annotated tree highlighting full scans, index use, and join order. (Implemented per ADR-0028: the explain prefix over show data / update / delete, with a span-styled plan tree. EXPLAIN QUERY PLAN never executes, so explaining a destructive update / delete is safe.)
• QA2 Plan rendering specifics — tree layout, annotation taxonomy, colour scheme. Implemented per ADR-0028 (§3–§6): a box-drawing tree, the substring-pattern taxonomy, and the OutputLine styled-runs mechanism.

Hints, help, errors

• H1 Friendly error-rewriting layer translates SQLite error messages into learner-friendly equivalents. (Progress: foreign-key constraint failures are enriched with both inbound and outbound relationship listings (so RESTRICT errors point at the children that still reference this table); full SQL → English translation pending.)
• H1a Strong syntax-help in parse errors. When the user types something near-correct (e.g. insert into T ('Oli') — forgotten values; or update T set x=1 — missing WHERE), the error should name the missing keyword or clause rather than just point at the unexpected character. This is a separate effort from H1 (which targets database errors); it targets parser errors. Pending — multiple targeted fixes shipping piecemeal so far (e.g. values becoming optional in INSERT removes one such case; ADR-0024's typed value slots give per-column-type rejection wording; insert into T (col) with no values clause now flags "looks like Form A — add values (...)"). A systematic pass is still pending.
• H2 hint provides contextual help for the current input or the most recent error.
• H3 help provides general reference and per-command help. (Progress: the help command lists currently-supported commands + DSL grammar reference + types. As of ADR-0024 §help_id it is assembled by iterating the command REGISTRY and translating each CommandNode.help_id, so a new command appears automatically. A general reference and help <command>-style detailed per-command help are still the missing pieces.)

CLI

• L1 Load a project via a positional CLI argument (Iteration 1). Plus --data-dir to override the data root and --help / -h for the usage banner.
• L1a --resume CLI flag opens the most recently used project (path tracked in <data-root>/last_project). Iteration 6: errors cleanly with a stderr banner above the shell prompt if no previous project is recorded or the recorded path is gone — no silent fallback; mutually exclusive with a positional path argument (ADR-0015 §7). last_project is rewritten on every successful project open (startup, load, new, save as, import).
• [~] L2 Submit a command alongside project load — deferred, not v1.

Tutorials and lessons

• [~] TU1 Tutorial / lesson system — design and ADR pending before any implementation. Out of v1 unless an ADR is written.

Documentation

• DOC1 User- and student-facing reference documentation under docs/: the DSL command surface, the type system, and the boundaries of simple mode. docs/simple-mode-limitations.md is the first piece — it doubles as student explanation and as detailed reference. Distinct from in-app help (H3), the interactive tutorial system (TU1), and the sharing recipes under E2.

Testing (per ADR-0008)

• TT1 Tier 1: cargo test + proptest covering pure-logic modules (parser, dispatcher, type mapping, project I/O, snapshot ring buffer, replay log).
• TT2 Tier 2: Ratatui TestBackend + insta snapshots for representative views.
• TT3 Tier 3: synthetic event-loop integration tests covering the user-facing flows in this checklist.
• TT4 Tier 4: PTY-based end-to-end for the four critical flows named in ADR-0008 (cold launch → DDL → quit; save → reopen; export → import → rebuild; undo after DROP).
• TT5 CI runs all tiers on Linux, macOS, and Windows on stable Rust.

Cross-cutting

• X1 Comprehensive logging via the project's logging infrastructure per CLAUDE.md (decision points, parameter values, fallback paths).
• [~] X2 Language: English-only for v1; multi-language is an open question to revisit later.
• [~] X3 Accessibility: TUI screen-reader support is best-effort and not a v1 commitment; revisit if user need emerges.

---

Non-functional requirements

NFRs are quality bars rather than discrete features. Where a target is measurable, it is stated numerically; where it is necessarily qualitative, the criterion is named and the bar is "reviewer judgement against the criterion."

• NFR-1 Performance — startup. Cold launch to first rendered frame under 500ms on commodity hardware (developer laptop, mid-range desktop). Measured in CI on the Linux runner as a regression gate.
• NFR-2 Performance — input latency. Keystroke-to-render latency under 16ms during normal editing; long-running queries must execute off the UI thread so the interface remains responsive (typing, scrolling, mode switching) while a query is running.
• NFR-3 Performance — resource footprint. Idle memory under 50MB on the smallest target platform; no busy-loops; CPU near zero when waiting for input.
• NFR-4 Visual quality — distinctive design. Colour palette and typography are deliberate and consistent across views; layout uses Unicode box-drawing and symbols where they add clarity; rendering avoids the generic flat-default look that ships with most TUI frameworks. Criterion: a reviewer can identify the app from a screenshot of any view.
• NFR-5 Visual quality — colour use. Colour conveys information rather than decoration: mode indication, query result types (numeric vs text vs null), error severity, syntax highlighting categories. Foreground/background combinations meet WCAG-AA contrast (4.5:1 for normal text) even though we have not committed to broader accessibility.
• NFR-6 Cross-platform parity. Behaviour and visual quality are equivalent across Linux, macOS, and Windows on crossterm-supported terminals. Platform-specific divergence (e.g. font fallbacks) is documented, not silently tolerated.
• NFR-7 Light and dark background support. The colour scheme remains legible and visually coherent on both light and dark terminal backgrounds. The mechanism (auto-detect via terminal query, explicit user setting, or both) is an implementation choice, but the outcome is non-negotiable: no dark-on-dark or light-on-light readability failures on either background.

---

Explicitly out of scope

• [-] N1 Hosted publishing platform — per ADR-0007. Sharing is local-artifact based.
• [-] N2 Real UUID column type — per ADR-0005. The shortid type covers the pedagogical need at TUI-friendly width.
• [-] N3 Cross-emulator visual regression coverage — per ADR-0008. Crossterm abstracts terminals adequately; we revisit only if a real regression surfaces.
• [~] N4 Global rolling input history (cross-session, cross-project). Mentioned in I2's wording; deferred per ADR-0015 §12 — project-scoped history (via history.log) is the v1 surface. Revisit if real demand emerges.

---

Maintenance

This document is updated whenever:

• A new requirement is committed to (added as a new item with the next free ID in its section).
• A deferred item is taken up (status moves from [~] to [ ]).
• An item is satisfied (status moves to [x], with a reference to the commit, PR, or test that demonstrates it).
• An item moves out of scope (status moves to [-] with a rationale and a link to the decision).

IDs are stable: once assigned, they are not reused. Removing a requirement leaves a "withdrawn" entry referencing the decision.